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- Lasers and Laser Technologies
Lasers and Laser Technologies
High power cladding-pumped fiber lasers and their applications
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In this paper, we review the recent works on high power cladding-pumped fiber lasers and amplifiers. And we will present some recent results on their applications such as Raman fiber laser and supercontinuum generation.
Recent specialty fiber research at Corning towards high-power and high-brightness fiber lasers
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This paper reviews and presents the recent specialty fiber research and development conducted at Corning Incorporated
towards high-power and high-brightness fiber lasers. These include the fabrication of all glass-composition, high-NA,
Yb-doped double-clad laser fibers, and also of double-clad single-polarization laser fibers for further improved
brightness in laser beam quality through innovative fiber designs. These have led to the 1st all-glass, high NA, Yb-doped
high-power double-clad fiber made by an all-vapor-phase fiber-preform process in the world, and also the highbrightness,
single-polarization double-clad high power laser fiber.
Phase locking of laser array
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In this paper, we discussed different mechanisms which are proved to ensure phase locking in a laser array. We also reported the phase locking in solid-state (crystal) laser array and fiber laser array by using the self-imaging confocal resonator which provides high feedback efficiency, quite insensitive to power variations among the pump beams, simply modal profile and also can achieve phase locking passively. A passive approach is to utilize the process of self-adjustment in lasing frequency to adapt to changes in the optical path lengths. The phase-locked mode is highly stable despite the phase variations in the individual elements caused by thermal and mechanical effects.
Stable operation of a 532 nm microchip laser with a temperature controller
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A stable 532-nm green-microchip laser with a single-longitudinal operation is achieved by use of a temperature controller. The output power of as much as 17.2 mW is obtained at a 121 mW pumping power. The long-term power stability of the green laser is better than 0.3% for the measuring time of 4 hours and can be further improved by increasing the control accurate for the temperature.
Effect of facet reflectivities on high-power highly strained InGaAs quantum-well diode lasers operating at 1.2μm
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The power enhancement of laser diodes is achieved by single and multilayer facet coatings such as antireflection and high reflection respectively at the front facet and the back facet of the laser diode. In this work, we have experimented with single layer λ/4 thick Al2O3 film for the Anti Reflection (AR) coating and stack of λ/4 thick Al2O3/ λ/4 thick Si bi-layers for the High Reflection (HR) coating. The AR/HR coatings were deposited in an electron beam evaporation system. The effect of front and back facet reflectivities on the output power of diode laser has been studied. The highly strained MOVPE grown InGaAs quantum-well edge emitting broad area (BA) diode lasers have been used for this experiments. The light output versus current (L-I) measurements were made on selected devices before and after the coatings. The devices were tested under pulsed operation with a pulse width of 400 ns and a duty cycle of 1:400. We have also carried out the theoretical analysis and simulation of L-I characteristics for this particular diode structure using LabVIEW. The experimental results were compared with simulated results. The effect of facet coating on external differential efficiency of diode laser has also been studied.
Dependence of harmonic generation efficiency on absolute phase of femtosecond pulse
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Using the computer simulation in the framework of optical thin layer with cubic nonlinearity a dependence of dynamic of third harmonic generation on absolute phase of light few-cycle pulse is shown for small deference between optical carrying frequency and frequency of linear medium oscillator. In particular, the relative small variation of the absolute phase leads to double increasing in third harmonic amplitude of the medium response.
Upconversion fluorescence in LiKGdF5 single crystal co- doped with Er3+, Tb3+
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The upconversion fluorescence was recorded at room temperature and investigated in LiKGdF5: 2%Er3+, 0.4%Tb3+ single crystal grown by the hydrothermal synthesis technique under 514.5 nm and 785 nm laser excitation, respectively. Under 514.5 nm laser excitation, four strong upconverted emission bands with peaks at 410 nm (violet), 470 nm, 486 nm and 492 nm (blue) were obtained. The former two emission bands were assigned to be corresponding to 2H9/2 -> 4I15/2 and 2P3/2 -> 4I11/2 transitions of Er3+ ions, and the latter two are possibly corresponding to 5D4 -> 7F6 of Tb3+ and 4F7/2 -> 4I15/2 of Er3+. The power dependence for 410 nm and 470 nm indicates that they arose from two-photon upconversion processes. While for 486 nm and 492 nm emission, the logarithmic slope is 0.98, which was explained by mutiphonon assisted upconversion process and energy transfer from 4F7/2 (Er3+) to 5D4 (Tb3+). Under 785 nm laser excitation, besides four weak upconverted emissions mentioned above, three strong emissions with peaks at 523 nm (2H11/2 -> 4I15/2), 550 nm ( 4S3/2 -> 4I15/2) and 660 nm (4F9/2 -> 4I15/2) were also observed. The possible upconversion mechanism for these seven emissions was all given with the help of the power dependence of upconversion emission intensity and the energy level diagram of Er3+ ions.
Growth and Q-switching performance on mixed laser crystal Nd0.0053(Gd0.42Y0.58)0.9947VO4
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A mixed laser crystal of Nd0.0053(Gd0.42Y0.58)0.9947VO4 has been successfully grown by the Czochralski method. The special properties of this crystal have also been measured. Formed with a simple concave-plano resonator, passive Q-switching operation of a diode-pumped Nd0.0053(Gd0.42Y0.58)0.9947VO4 laser with Cr4+:YAG has been demonstrated. For Q-switched operation, the maximum average power was measured to be 1.11W with the corresponding repetition rate of 10 kHz, the pulse width of 10 ns when the initial transmission of Cr4+:YAG crystal was 60%. Meanwhile, the largest pulse energy of 111 μJ and the highest peak power of 14.61 kW were obtained.
1.41 W Nd: YAG laser at 556 nm end-pumped by laser diode arrays
Fu-qiang Jia,
Quan Zheng,
Qing-hua Xue,
et al.
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A Nd: YAG laser has longitudinally pumped by a fiber coupling 20 W laser diode array with emission wavelength at 808nm in a three folded cavity configuration. After a 150 μm thickness etalon was inserted into the cavity, the 1112nm fundamental laser operation was obtained, and then intracavity-frequency-doubling with a LBO crystal produced 1.41W of stable output at 556nm.
Angle tuned mid-infrared optical parametric oscillator based on Nd:YAG pumped MgO:LiNbO3
Yong Wan,
Qinyong Zeng,
Kai Han,
et al.
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Some basic principles of angle-tuned magnesium oxide doped lithium niobate (MgO:LiNbO3) critically phase-matched optical parametric oscillators pumped by Q-switched Nd:YAG 1.064μm pulsed lasers have been analyzed theoretically. The permissibility of parametric spectral tuning based on angle tuning the nonlinear MgO:LiNbO3 crystal has been derived algebraically and discussed systematically. Based on these theories, the phase matching type and crystal orientation were chosen. The experimental achievements of 3 to 5μm angle-tuned MgO:LiNbO3 critically phase-matched optical parametric oscillators pumped by Q-switched Nd:YAG 1.064μm pulsed lasers were demonstrated and the experiment results matched well with the theories.
High power planar waveguide solid-state lasers with gain control
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High power diode-pumped planar waveguide Nd:YAG lasers with good output beam qualities are demonstrated with gain control technique. Around 100 W output power with nearly diffraction-limited beam quality is achieved by asymmetric edge-pumping and negative branch confocal unstable resonator. A miniature Nd:glass slab laser and a Nd-glass belt laser are also demonstrated. The beam quality in the Nd-glass belt laser is improved by V-groove pairs scribed on the edges of the Nd:glass belt.
Continuous tuning high power blue light by frequency doubling in BiB3O6 crystals
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We report a high power continuous tunable blue light generation by frequency doubling of signal wave from a nanosecond 532-nm-pumped optical parametric oscillator (OPO) in LiB3O5 (LBO). The nonlinear crystal BiB3O6 (BiBO) is used for the second harmonic generation (SHG). Three BiBO crystals have been arranged for the walkoff compensation SHG. The large blue tuning range from 450 to 495 nm with average output powers around 1 W have been achieved. The maximum output power is up to 1.3 W at 470 nm.
High-power diode-end-pumped intracavity frequency-doubled Nd:GdVO4/LBO red laser
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We report a high-power diode-single-end-pumped continuous-wave and Q-switched Nd:GdVO4 red laser through intracavity frequency-doubling with a type-I critical phase-matched LBO crystal. The maximum CW output power at 671 nm was measured to be 2.1 W at the incident pump power of 30 W, with the corresponding optical conversion efficiency of 7%. At the repetition frequency of 47 kHz, the maximum average output power of quasi-CW red light was obtained to be 6 W, with the corresponding optical conversion efficiency of 12.8% and the pulse width of about 97 ns. At the average output power around 5 W, the power stability was better than 5.8% for one hour. The M2 factor increased from 1.33 to 2.47 when the output power was increased from 1 W to 6 W. At the repetition rate of 25 kHz, the maximum pulse energy of 212 μJ was obtained with the corresponding peak power of 3.98 kW.
LD-pumped passive Q-switched Nd:LuVO4 laser
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The absorption spectrum from 300 to 1000 nm and emission spectrum from 960 to 1450 nm of Nd:LuVO4 crystal were measured. A LD-end-pumped passive Q-switched Nd:LuVO4 laser was reported. With a Cr4+:YAG crystal as the saturable absorber, the maximum average output power was measured to be 4.58 W, and the corresponding optical conversion efficiency was 24.0 %, with the pulse energy, peak power, and pulse width being 36.6 μJ, 436.2 W, and 84 ns, respectively.
High-power VCSELs single devices and 2-D arrays
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The high power bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) and laser arrays emitting at 980 nm are reported. Extensive investigations on size scaling behavior of thermal properties of single devices show limits of attainable output characteristics. The maximum continuous wave (CW) output power at room temperature of single devices with aperture size up to 500 μm is as high as 1.95 W. The key characteristics such as maximum output power, wavelength and thermal resistance are discussed. The bottom-emitting arrays of 16 elements and 200 μm aperture size of individual elements show output power of CW 1.35 W at room temperature. The far-field angle is below 17° for all driving current, which is very favorable for focusing or collimating optics.
High power output and temperature characteristics of 1.06μm diode array module
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In this paper high power diode array module with an emission wavelength of 1.06μm is presented. The epitaxial structure is an InGaAs/GaAsP strained-compensated single-quantum well structure. Laser bars with a fill factor of 50% are processed and show a good temperature characteristics with a slope efficiency only decreasing from 1.08W/A to 1.06W/A when the temperature of heat sink changes from 20oC to 40o C. The module's CW output power can reach to 68.5W at a current of 80A when the temperature of cooling water is 20o C. The central wavelength is 1059.4nm.
Study on a novel high-pressure micro-discharge configuration for micro-laser
Chao Jiang,
Youqing Wang
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A "plane cathode micro-hollow anode discharge"(PCMAD) device was researched on the base of the configuration of micro-hollow cathode discharge (MHCD). And a new discharge device was designed for forming large-volume plasmas, and its anode is metallic needle, and its cathode is PCMAD. It composed of a "needle-hole" sustained glow discharge. The discharge experiment was carried through with the air, and the stable direct-current glow discharge was formed in single PCMAD at pressure up to 760Torr, and multi-PCMAD can operate stably in parallel at pressure up to 500Torr without individual ballasting resistors. The dc voltage-current characteristics of these discharges showed a positive slope, and it had positive differential resistance coefficient. "Needle-hole" sustained glow discharge could also operate stably at pressure up to 500Torr to form large-volume high-current density glow discharge plasmas, and the electron density was estimated from 1011 cm-3 to 1012 cm-3 in the discharge plasmas. The total discharge current arrived to 300mA for the fifty "needle-hole" discharges operating stably, and the main discharge sustained voltage was approximately 1000V when the distance of between the needle and the hole was 20mm. The high-pressure, large-volume, high-current-density plasmas could be used the media of micro-laser. When the discharges gas was rare gas, the discharge plasmas would be used the media of the excimer laser. In addition, the configuration of the discharge device was simple and made easily. The experiment results show that the designed discharge device is appropriate for the micro-laser.
Observation of soft x-ray amplification in Ne-like Ar by a capillary discharge
Yuanli Cheng,
Wang Qi,
Yongpeng Zhao,
et al.
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Laser spike pulse has been observed in Ne-like Ar plasma by capillary discharge with a short rising time of 30ns in a
3.1mm-diameter channel. The range of Ar pressure for lasing was measured in the range of 14 Pa~26 Pa.
14.7mJ total output from a gain-switched Tm3+-doped double-clad silica fiber laser
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A gain-switched Tm-doped double-clad silica fiber laser operating at a wavelength of approximately 2μm with moderate output energy is realized. A gain-switched Nd:YAG laser is used to pump the 3 5 H energy level of the doped Tm3+ ions at 1.064μm, and a maximum total output energy of 14.7mJ per pulse is produced at a slope efficiency of 39.5% (with respect to launched pump energy). As we know, this is the first time to realize the gain-switched Tm3+-doped double-clad silica fiber laser pumped at 1.064μm, and both the single pulse energy and the slope efficiency exceed the reported results that produced from single-clad Tm3+-doped silica fiber laser in the past. The results of three different length fibers in experiments are present and contrasted. Because the absorption section at 1.064μm is only 2.5% at 0.79 μm in Tm3+-doped silica fiber, we use three relative long fibers (the fiber.1 length 35 m, fiber.2 length 8m, the fiber.3 length 1m.) to increase the absorption ratios. The laser threshold in fiber.1, fiber.2 and fiber.3 is 37.5mJ, 39.4mJ and 48 mJ, and the slope efficiency is 39.5%, 11.6% and 1% respectively. The output peak wavelength from fiber.1 fiber.2 and fiber.3 is 2.04μm, 2.01μm and 1.92μm measured by a monochromator respectively.
High-power Yb-doped double-cladding photonic crystal fiber superfluorescent source
Yi-gang Li,
Sheng-li Liu,
Wei Zhang,
et al.
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An Yb-doped double-cladding photonic crystal fiber (DC-PCF) superfluorescent source (SFS) is presented experimentally for the first time, which is pumped at 976nm by a diode laser (LD) with the end-coupling method. We employ a single-stage SFS in double-pass forward configuration and get the maximum output power of 1.649W with a slope efficiency of 56.7%. The peak wavelength and the 3dB bandwidth are 1067.6nm and 22.4nm, respectively.
Cavity optimization of erbium-ytterbium co-doped fiber ring lasers
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The cavity configurations of erbium-ytterbium co-doped fiber ring lasers (EYDFL) have been experimentally investigated. Additional attention has been paid to the mode competition effect of the laser. It is demonstrated that even in a traveling wave cavity, mode competition occurs when the cavity configuration or the output splitting ratio are incorrectly chosen. By employing the proper cavity configuration and an optimal output splitting ratio, an extremely stable ring cavity EYDFL with fine-shaped laser spectrum is obtained at 1565.8nm. Output power of 1.07 W is achieved under 3.5W 976nm pump power, with an optical conversion efficiency of 30.6%.
2.7mW output of emerald laser pumped by laser diode
Z. Q. Chen,
G. Zhang
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Free-running emerald laser pumped by 660 nm LD was reported. 2.7mW of CW output power has been obtained with overall efficiency of 1% and slope efficiency of 1.33% when the LD incident power was 2.56 W. The laser threshold value of emerald crystal was estimated 0.5W.
Co-doped Tm,Ho:GdVO4 laser end-pumped by 808nm laser diode
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In this paper, we report a diode pumped Tm,Ho:GdVO4 laser operating at cryogenic temperature, which has 3.5W of 2-μm output. Tm,Ho:GdVO4 crystal has very stronger and broader absorption spectrum than Tm-Ho co-doped YLF and YAG, and very favorable for diode pumping. The fiber-coupled laser diode of 808nm (core diameter 0.4mm,N.A 0.22) is a pumping source to end-pumping Tm,Ho:GdVO4 crystal. The optical-optical conversion efficiency of 34% and threshold pump power of 0.79W has been achieved. The laser design and laser performance is described.
Self-starting, widely tunable ps pulses generation from Yb-doped double-clad fiber laser
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In this paper cw (continuous wave) pumped self-started, widely tunable frequency-shifted feedback Yb-doped double-clad fiber laser is experimentally studied. We observed 1GHz repetition rate with an output power 56.3mW ps pulses. The laser was capable of generating as short as 5ps pulses in the range of 1078.7nm -1140.2nm (more than
60nm). The ps pulses were self-started without any other external trigger. We used 77MHz RF signal AOM and a grating which not only forms external cavity to provide feedback, but also make the laser linewidth narrower.
High-power double-clad large-mode-area photonic crystal fibre laser
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A high power double-clad ytterbium-doped large-mode-area photonic crystal fibre (LMA PCF) laser was demonstrated using a unique Fabry-Perot (F-P) configuration. A Continuous-wave output power of 50 W at ~1.04 μm with a slope efficiency of 76.3% was obtained. Single transverse mode operation is achieved without any thermal-optical problems. This laser has the potential for scaling to much higher output power.
Experimental research on femtosecond mode-locked fiber lasers with potential applications to all-optical packet switching networks
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We experimentally demonstrate an Er3+-doped femtosecond mode-locked optical fiber laser which operates at the 1550-nm wavelength and generates ultrashort optical pulses with width of 270 fs, repetition frequency of 20 MHz, and average output power of 146μW. We find that the pulse width keeps stable increasing when the pump source optical power is enhanced in the range from 25 mW to 60 mW. However, if the pump source optical power exceeds 60 mW, the oscillation phenomenon would occur in pulses width. To be used as an optical source in fiber-optic communications system, the output femtosecond pulses from the mode-locked laser are also amplified specially through an Er3+-doped optical fiber amplifier. The relationships between pump optical power and amplified characteristics including amplified optical pulses width, amplified average optical power, amplified single optical pulse energy, amplified gain and spectrum shape are studied experimentally in the amplified experiment.
Mode-hopping of pi/2 phase-shifted distributed feedback fiber grating laser
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During the operation of pi/2 phase-shifted distributed feedback Yb-doped fiber grating laser (YDFBL), the phenomenon of mode-hopping has been observed. It has been found that the light power incident into the fiber laser and the ambient temperature will affect the generation of mode-hopping. When the pump power changes in a wide range, i.e., from tens of milliwatts to more than one hundred milliwatts, there are only two modes dominating by turns with the consideration of different resolution error. When the ambient temperature around the fiber grating rises a little, the mode-hopping will be observed. An explanation basing on the spatial hole burning and wavelength shift induced by temperature fluctuation for this phenomenon has been given out.
Energy transfer upconversion in Er3+-doped and Er3+, Ho3+ -codoped Cs2NaGdC16 crystals
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Powder samples Cs2NaGdCl6:10%Er3+ and Cs2NaGdCl6:10%Er3+,20%Ho3+ investigated were prepared. Upconversion and down-conversion spectra from both Er3+ and Ho3+ ions was measured and investigated at room temperature under excitation into the 2H11/2 levels of Er3+ ions by using a 514.5 nm Ar+ laser. The observed emissions were all clearly assigned and analyzed according to the energy level diagrams of Ho3+ and Er3+ ions. It was concluded that many emissions with peaks at 423 nm (5G5 -> 5I8), 492 nm (5F3 -> 5I8), 587 nm (5G4 -> 5I6), 657 nm (5F5 -> 5I8) and 760 nm (5I4 -> 5I8) were all from Ho3+ ions, although Ho3+ ions cannot be excited by a ground-state-absorption (GSA). Therefore, all the emissions from Ho3+ ions were caused by multistep energy transfer from Er3+ to Ho3+ ions. And the 388 nm and 410 nm upconversion emissions were assigned to be 4G11/2->4I15/2 and 2H9/2->4I15/2 transitions of Er3+ ions, respectively. The possible upconversion mechanism for them was deduced to be excitation state absorption (ESA) and energy transfer (ET). In addition, the result that the slopes of 388nm and 410nm upconversion emissions of Er3+ ions were smaller in Er3+-doped than Er3+, Ho3+-codoped Cs2NaGdCl6 crystals was explained successfully.
Multi-wavelength generation in periodically poled lithium niobate pumped by a Q-Switched Nd:YVO4 laser
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Seven output wavelengths ranged from violet to mid-infrared have been observed simultaneously from a optical parametric oscillator with a periodically poled lithium niobate crystal. The pump laser is diode-pumped Q-Switched Nd:YVO4 laser with the wavelengths at 1064 nm. The turning output wavelengths can be obtained by changing the periods or temperatures of PPLN. The seven output wavelengths, corresponding to the sum frequency generation of the pump and the doubling signal ( 2ωs+ωp), the third harmonic generation of the signal ( 3ωs ), the second harmonic generation of the pump (2ωp), the sum frequency generation of the pump and the signal (ωs+ωp), the second harmonic generation of the signal (2ωs), the signal (ωs) and the idler (ωi), measured are 433, 488, 532, 616, 731, 1463 and 3902 nm, at the period of 28.7 μm with the temperature of 333 K. These data showed good agreement with those calculated by the Sellmeier equation. This phenomenon may find novel applications in photonic devices.
A novel structure for high peak power semiconductor lasers
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A novel structure for high peak power output of semiconductor lasers has been designed with a weak optical absorption region near cavity facet and a low optical energy density distribution on both front and back cavity facets has been realized simultaneously. The device has been fabricated with a standard MBE grown AlGaAs/GaAs material wafer, and a stack assembly of five laser chips has been finally obtained. The measured stack has a maximum peak power output of 300W with a whole emitting aperture of 2×0.5mm2 and a satisfactory farfield (θ⊥) output property is also achieved with θ⊥ of 31o.
A novel project of amplifying equally the high repetition ultra-short signal optical pulse in semiconductor optical amplifiers
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A novel project of amplifying equally the high repetition ultra-short signal optical pulse is explored in semiconductor optical amplifiers. It is shown that the signal optical pulse can be amplified equally by injecting another copropagating strong assistant optical pulse into semiconductor optical amplifiers. It is asked that the assistant optical pulse lags behind the signal pulse, and has right initial peak power for assistant optical pulse, and the wavelength of signal pulse is locates in the gain bandwidth, and the wavelength of assistant pulse is far from the gain bandwidth.
980 nm QCW high power semiconductor lasers array
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High power laser bars become more and more important for pumping of solid-state lasers, medical applications, optical data storage, display, and material processing such as welding, cutting, or surface treatment. Diode lasers array emitting at 980 nm has excited considerable interest as optical pumping source for the Erbium-doped fiber amplifier (EDFA), cladding pumped fiber amplifiers or fiber lasers. A high power multi-mode 980 nm InGaAs laser arrays grown by MBE are reported. Non-absorbing windows are integrated at the ends of the cavity to decrease the light density on the mirror for high power operation. A QCW output power of 64.8 W for lasers array with coated facets is achieved. The threshold current is 7.5 A. The lasing spectrum is peaked at 978 nm with a FWHM of 2.5 nm.
Theoretical analysis of 980nm high power vertical external-cavity surface-emitting semiconductor laser (VECSEL)
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By using bottom-emitting structure, we will develop laser diode (LD) pumped 980 nm VECSEL with active region of InGaAs/GaAsP/AlGaAs system. Because the thickness of barrier layer and absorption layer exceed that of quantum well, single well approximation model (KP method) can be used to calculate the band structure of VECSEL. The Schrodinger equation of finite deep potential well can be adopted to calculate the energy level structures of electron, heavy and light holes. According to the transition selection rule, we theoretically obtained the emitting wavelength of VECSEL and calculated quasi-Femi energy of valence band and conduction band based on the analysis of energy level structure of electron and holes. By analyzing the gain of strained quantum wells, we calculated the gain of VECSEL using transition matrix elements of electron, heavy and light holes. We give out the threshold gain, output power and other characteristic parameters. We will study the configuration of VECSEL and pumping scheme. We designed external cavity mirror, active region and bottom-emitting structure. A LD-pumped vertical external cavity surface-emitting laser whose output power is greater than 1.0 W can be predicted.
Study on a new type of electro-optical Q-switch of Langasite crystal
Yunfeng Ding,
Liang Qiao,
Zhi Diao,
et al.
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A new type of electro-optical Q-switch of Langasite (La3Ga5SiO14,LGS) single crystal is introduced in this paper. LGS has been used as a type of piezoelectric crystal for a long time. It has attracted much attention due to its low acoustic velocity, zero temperature. We make a kind of electro-optical Q-switch of LGS single crystal by using its typically optical activity. LGS is compared with a common type of electric-optical crystal DKDP and LN. LGS has some characteristics that DKDP and LN don't have. For example, LGS is non-deliquescent and can be exposed in the air. It can be coated on the end faces. This helps to increase the transmissivity obviously. But DKDP is deliquescent. The packaging technologies are more complex. The application of DKDP is inconvenient. The anti-damaged threshold of LGS is about 900 MW/cm2. It is much higher than LN. A new set of experimental system was developed based on the characteristics of LGS, including Pockels' cell for LGS driving circuit, Q-switch circuit, etc. The detailed experimental data and oscillograms with this system is got and practical conclusion is made from the experiment. Due to the particular characters of LGS, it has vast application, especially in military realm.
Study of discharge transverse uniformity for the RF excited diffusively cool all metal slab waveguide CO2 laser
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In this paper, we have investigated the discharge transverse uniformity of an RF excited diffusively cooled all-metal slab waveguide CO2 laser, the discharge characteristic of an RF excited diffusively cooled all-metal slab waveguide CO2 laser was reported, At different input power, the discharge plasma between all metal slab waveguide were clearly recorded with Nikon camera. The striations were distinctly observed on the discharge photographs, the two bright regions on the pictures is proportional to the visible emission intensity.
Full energy conversion without increasing of pulse duration under the SHG of high intensive femtosecond pulses
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We report the possibility of energy conversion with 95% (and higher) efficiency under the SHG of femtosecond pulse without increasing of pulse duration on doubling frequency. The main feature of the discussing regime of doubling frequency is the absence of the inverse energy conversion. This regime is realized due to cascading generation in medium with quadratic and cubic nonlinear responses at big phase mismatching and to using of compound medium. It should be emphasized that the input pulse shape on fundamental frequency is close to the soliton one. After definite section of medium, in which SHG takes place under the condition of phase matching, a medium with big phase mismatching is used.
Two schemes of modulation-free frequency stabilization of grating-external-cavity diode laser via cesium sub-Doppler spectra
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We report two methods of modulation-free frequency stabilization of a laser to sub-Doppler atomic absorption line. The first one employs the magnetically induced sub-Doppler dichroism in cesium vapor cell based on Zeeman effect. The second one utilizes two acousto-optical modulators (AOM) as well as sub-Doppler spectra to generate dispersion-like signal. We compared the residual frequency fluctuation in preliminary stabilization with the case of free running. These two schemes can avoid the additional frequency noise as well as intensity noise due to the direct frequency dither on laser source.
Stable propagation of pulsed beams in Kerr focusing media with modulated dispersion
María I. Rodas-Verde,
Humberto Michinel,
Gaspar D. Montesinos,
et al.
Show abstract
We propose the modulation of dispersion to prevent collapse of planar pulsed beams which propagate in Kerr-type self-focusing optical media. As a result, we find a new type of two-dimensional spatio-temporal solitons stabilized by dispersion management. We have studied the existence and properties of these solitary waves both analytically and
numerically. We show that the adequate choice of the modulation parameters optimizes the stabilization of the pulse.
Controlling the nonlinear refractive index via quantum coherence
María J. Paz-Alonso,
Humberto J. Michinel
Show abstract
We study theoretically how to use a four level atomic system with electromagnetic induced transparency, to achieve a situation with giant χ(3) and χ(5) susceptibilities of opposite signs. We show how to use this configuration to obtain multidimensional optical solitons and light condensates with surface tension properties analogous to those of usual liquids.
Device for performance detection of optical scanner
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In optical remote sensing systems especially the imaging systems the quality of the scanner is the key element for obtaining high quality 2-D image of the target. There must be a detection device to verify the scanning performance of the optical scanner. In this paper such a detection device was developed. It consists of large area CCD camera, specific optical lens, electronics shutter, computer control element and scanning performance analysis software. The core technologies in developing the device are to design the specific optical lens, eliminate the delaying trail in the detecting image and recognize and analyze the spot matrix in the detecting image. The detection field of view can be wider than 10o×10o and resolution better than 0.1mrad. This device can not only perform real time detection on line, displaying dynamic values of all the detecting parameters, but also perform off line, displaying values of various detecting parameters for a given image taken at anytime. To consider the objectivity and creditability of the detecting result, there is an adjusting program to ensure the collimation between the detection device and the given optical scanner.
Detection of weak signal in laser ranging based on the theory of stochastic resonance
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A novel approach based on the theory of stochastic resonance (SR) for detecting weak signals in heavy noise for detecting distance information for laser ranging is presented in this paper. SR in a nonlinear system is a cooperative effect of noise and periodic signal driving in bi-stable systems. Under the proper condition, increasing input noise level results in an increase in the output signal-to-noise ratio (SNR), which means increasing the disorder of the input leads to increasing the order of the output. Driven by a periodic signal and a Gaussian white noise, stochastic resonance exists in the double-well potential system. This stochastic resonance phenomenon can greatly improve the SNR of a periodic signal with additive Gaussian white noise. In this paper the theoretical derivation for bi-stable system at the SR and the computer simulation have been given. Under the generic adiabatic approximation condition, a numerical simulation on such as the out SNR shows that the output SNR in heavy ground noise has been improved evidently. In laser ranging system, the SR theory was applied in electronic circuits and the out SNR improved obviously.
High-power InGaAs/GaAs VCSEL's two-dimension arrays
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Selectively oxidized InGaAs/GaAs vertical-cavity surface-emitting lasers (VCSEL) array at an emission wavelength of 980nm was reported. A 16 elements array with 200μm aperture size (250μm center spacing) of individual elements shows a CW output power of 1.21W at room temperature, resulting in 1KW/cm2 average optical power density. The device threshold current is 1.32A The lasing peak wavelength is 981.9 nm, the full width at half-maximum is 0.7 nm, and the far-field divergence angle is about 17o.The characteristics of a single device with a active region diameter of 800μm is compared with that of a 2-D array with active region diameter of individual element of 200μm. These two kinds of devices have the same total lasing area. At the same current injection, the single device has a higher threshold and a higher output power than the array. The red shift of single device is more obvious than that of the array's.
Noise characteristic of laser diode pumped orange-yellow solid-state laser by intracavity sum-frequency of KTP phase matching II
Huiming Tan,
Lanlan Gao
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The laser diode pumped Nd: YVO4 orange-yellow laser has been presented in this paper. The fundamental wavelengths of 1064nm and 1342nm oscillate simultaneous to generate the 593.5nm wavelength by intracavity sum-frequency of KTP nonlinear crystal phase matching II. The noise characteristic of laser output has been measured and analyzed in different pumping power. The relations between the amplitude noise of sum-frequency output and the longitudinal mode of fundamental frequency have been researched. The results show that the sum-frequency output is low noise if the one of fundamental wavelengths is single longitudinal mode. The experiments show that amplitude noise of intracavity sum-frequency laser is lower than that of intracavity doubled frequency laser with the same structure.
Design and characterization of a 300-TW Ti:sapphire laser
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A Ti:sapphire laser system referred to as SILEX-I with the chirped pulse amplification technology has been built at CAEP which consists of three stages operating at 5TW, 30TW, and 300TW, each having a compressor and target chamber to meet different needs from diverse applications. The first and the second stages work at 10Hz, while the third at single shot. Pulse durations of 26fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) before the stretcher to compensate for the spectral gain narrowing in the regen. By taking a number of advanced measures for spatial beam control, such as spatial beam-shaping, relay-imaged propagation, precise alignment of compressor gratings and OAP, near-diffraction limited focal spots (FWHM) have been obtained. Focused intensities
are measured in the range of (1-5) x 1020W/cm2 with an f/2.2 OAP. The laser system will be able to operate at 500TW and even higher soon. The SILEX-I has been operated for experiments since its completion early in 2004, covering electron and proton acceleration, hot electron production, transport and deposition, neutron production, x-ray radiation, femtosecond laser pulse propagation in air, warm matter, and other strong-field studies. The laser system has shown an excellent stability and reliability and has been the most powerful femtosecond Ti:sapphire laser facility to operate for experiments in recent years.
Preparation and optical properties of reverse saturable absorption polymer with alkoxy phthalocyanine Pb
Qian Duan,
Hui Xia,
Da-jun Liu,
et al.
Show abstract
In order to obtain the optical limiting materials with broad protective wavelength and high optical transmission as well as quick response, we synthesize three derivatives of alkoxy phthalocyanine Pb. The structures of these derivatives were characterized by means of IR, 1HNMR spectra and elementary analysis. Mix the three derivatives of alkoxy phthalocyanine Pb into the Monomer of MMA respectively; the phthalocyanine Pb / polymethy methacrylate (PMMA)
that are polymers with non-linear optical properties are prepared. The absorption spectra of the polymers in the visible range (200~800nm) are measured to determine their Q-bands. It is found that there is high possibility having the third-nonlinear optical limiting effect for the polymers. The non-linear reverse saturable absorption and optical limiting measurements of the polymers were performed with a frequency-doubled Q switched Nd:YAG laser with 8ns laser pulse
at wavelength 532nm. The factors that affect the performance of reverse saturable absorption and optical limiting of the polymers were discussed. A phenomenological model is used to describe the optical limiting phenomena.
Research on the application of laser ultrasonic technique in weaponry
Show abstract
Laser Ultrasonics is a new branch in Ultrasonics, which is based on the generation of ultrasonic by a laser and the detection of stress wave with laser interferometer, and is an ideal combination of laser and ultrasonic for non-destructive testing. It is a noncontact, remote and precise technique for nondestructive testing of materials and products. Firstly, this paper introduces the principles of laser ultrasonic generation, and the ablation excitation theory. And then optical detection method of laser-induced ultrasonic with the confocal Fabry-Perot interferometer is introduced. Based on the principles of laser-induced ultrasonic generation and detection, the integrated structure of the laser ultrasonic induced by laser line source and detected by a confocal Fabry-Perot interferometer is presented to detect multilayer structure such as solid propellant rocket motor structures in weaponry. Considering how laser ultrasonics would be used in the field and some mostly effects to the results. The laser system, accepting its present limitations, was optimized and developed for the inspection of the multilayer structure of solid propellant rocket motor as the experimental program progressed.
Spatial alignment and orientation of molecules in intense laser fields of femtosecond duration
Jianxin Chen,
Xingshan Jiang,
Xiangxin Chen
Show abstract
The rotation equation for angle θ between molecular axis and laser polarization direction that described spatial alignment and orientation of molecules in intense femtosecond laser fields has been deduced. A Gaussian laser pulse and the increasing of internuclear distance during the process of molecular muti-electron dissociative ionization and Coulomb explosion are considered. The orientating process of molecules N2, H2, CO, Br2, I2, CO2, and CS2 is investigated by solving numerically the deduced rotation equation for angle. Calculating results show that the linear polarizability and the damping force play an important role in the angular rotation of molecules in conditions of 800nm laser wavelength and 1015W/cm2 laser intensity. Calculating results also indicate that the majority of dynamic alignment for the light molecule N2, H2, CO and CO2 takes place before the molecule ionizes and begins to dissociate. However for the heavy molecule Br2, I2 and CS2, most dynamic alignment occurs during the process of molecular dissociation. The extent of molecular alignment are extensively calculated and discussed.
Research on the smokes screening laser
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Smoke interference is an economy and practical way of electro-optical countermeasure. In this paper, the mechanism, characteristic, technology and result evaluation of smokes screening laser is discussed to find more effect way of smoke interference. Smoke screen mechanism, characteristic, experiment device and method are discussed experimentally. Especially the smoke screening laser of 0.53μm, 1.06μm and 1.54μm is discussed in detail. On this foundation, an experiment with titanium tetrachloride is designed to detect the effect of smoke screening. Experiment show that titanium tetrachloride and water reaction can generate a great deal of smoke. The smoke is very thick and last out long time. It has good interference effect of laser of 0.53μm, 1.06μm, 1.54μm. But the smoke presents acidic, strong causticity and stimulative. So ammonia was added. In order to improve the interference effect with the parameter change, a great deal experiments were been done at different concentration of ammonia and different dosage of ammonia. The attenuation performance tables of same concentration different dosage and same dosage different concentration were painted. Analyzing these tables, we can get a series of conclusion for smoke screening laser of 0.53μm, 1.06μm, 1.54μm. And also the best parameters are presented for smoke screening.
Femtosecond laser pulse induced damage in thin films
Show abstract
We have investigated the damage for ZrO2/SiO2 800 nm 45° high-reflection mirror and MgF2/ZnS 800 nm interference filter with femtosecond pulses. The damage morphologies and evolution of ablation crater depths with laser fluences are dramatically different from that with pulse longer than a few tens of picoseconds. We also report their single-short damage thresholds for pulse durations ranging from 50 fs to 900 fs, which depart from the diffusion-dominated τ1/2 scaling. A developed avalanche model, including the production of conduction band electrons (CBE) and laser energy deposition, is applied to study the damage mechanisms. The theoretical results agree well with our measurements.
Pondermotive acceleration of electrons to GeV energies by a tightly focused ultra-short ultra-intense laser pulse
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Laser-driven pondermotive acceleration of electrons in vacuum has been considered using computer simulations. It is demonstrated that a low-energy free electron can be violently accelerated to final kinetic energy of GeV by a tightly focused ultra-short ultra-intense laser pulse. Suitable conditions that are crucial for this phenomenon to occur have been investigated. It is shown that selection of appropriate initial conditions like relative time delay between electron and the laser pulse, electron's incident angle and momentum, laser pulse duration and its focal spot size play important roles in the efficient acceleration scheme.
Coherence measurements of a Nd-YAG laser by image processing of Michelson interferometer fringe patterns
Show abstract
To determine the coherence of a laser device, the concept of visibility is used and applied to the measured interference patterns produced by this laser light in a specific interferometer. In this case, to determine the coherence of a Diode Pumped Solid State Nd -YAG Laser, a digital image processing procedure was developed and applied to the fringe patterns obtained with a rigid arm Michelson interferometer array in order to obtain the coherence function. A spatial filtered laser beam was used to illuminate the interferometer and to produce a circular fringe pattern. The interference pattern was captured on a spatial calibrated translucent screen and photographed by a digital camera. Afterwards, the images were digitally processed to calibrate the pixel distribution and to produce an intensity function from this calibrated image. Data processing of the intensity function values allows to produce the coherence function and to evaluate the coherence degree of the radiation. The interference patterns, intensity distributions and the coherence calculations of the Nd - YAG laser are presented.
Study on the residual stress state of TA2 titanium sheet metal formed perpendicularly with single pulsed laser
A. X. Feng,
Y. K. Zhang,
D. W. Zuo,
et al.
Show abstract
Laser shock forming(LSF) is a new forming technique of sheet metal by applying a compressive shock wave on the surface of metal sheet. The plastic deformation of TA2 titanium metal sheet is performed under single laser shocking perpendicularly with Nd:Glass laser developed in Jiangsu University. The residual stress state in the horizontal and diagonal direction of the foursquare specimen, as well as the residual stress state in the radial direction of the circular specimen, was investigated with X-ray stress analyzer. The residual stress state of laser shock forming specimen is unique to some extent by contrast with traditional punch forming, which is influenced by the specimen shape and the deformation rate. The experiment results show that residual stresses value of TA2 Titanium Sheet Metal in laser shock area are up to 100MPa.Square specimen is more difficult to be formed than circular specimen, and the press value of cave is the larger than the one of convex.
3-D laser Newton-ring device and its application in the checking of elevator tracks
Lixing Jiang,
Yuxiao Peng,
Huihua Xie,
et al.
Show abstract
In this paper, the 3-D laser Newton-ring device and its application system are introduced. In order to keep the elevator works safely and placidly, One of the key factors is the track of elevator should keep linearity and identical to plumb line. In this paper, a new auto-checking system for the track of elevator that is based on the 3-D Laser Newton-ring device and CCD video is introduced. By using of this system, we can guide the installation or check the track of elevator quickly, automatically and high accurately. Otherwise, the detecting method of 3-D Laser Newton-ring's center is mainly introduced. It is tested that the collimation accuracy is higher than 0.1mm.
Design of a novel laser tracking measuring system
G. X. Zhang,
X. W. Sui,
S. Z. Zhao,
et al.
Show abstract
A novel laser tracking measuring system based on the principle of multi-lateration is developed. The system consists of a four-quadrant silicon photoelectric cell measuring the position of reflected beam from the target with sensitivity of 200mv/mm, a rotational tracking mirrror with a solid angle of 35 degrees driven by two motors and a new type of closed-loop control with digital PID and analog PID. The experiment shows that it works reliably with tracking speed 0.7m/s, and the standard deviation of measurement is 1.2μm.
Real-time detecting of Brillouin scattering in water with ICCD
Shujing Li,
Jinwei Shi,
Wenping Gong,
et al.
Show abstract
Brillouin scattering is a way non-touching detection by measuring frequency shift and line width of Brillouin lines. In 1980, Guagliardo got Brillouin spectrum in water using Lidar of wide band pulsed laser. But resolution was low and didn't satisfy detection requirement. Later, Dr. Dahe Liu suggested that Brillouin scattering in water with high resolution and accuracy can be achieved by using edge technique. In this paper, we put forward a new method to do real time detection Brillouin backscattering in water. An intensity CCD (ICCD) was used in our experiment. As we known, when a laser fires a pulsed into the water, the backscattering includes Rayleigh lines and Brillouin lines. The former frequency is equal to original frequency of the incoming light. The later has the different frequency with the former, it is called as Brillouin shift. The signals out from water entered our system and passed through a F-P etalon, then interference rings were imaged by ICCD. It can be seen clearly that Brillouin lines were appeared at the same side of every Rayleigh lines. From the images recorded by ICCD, the Brillouin shift, the Brillouin line width and the signal intensity of Brillouin scattering can be determined. These informations can be used further to determine some parameters of the ocean. Our investigation shows that the instrumentation with ICCD may be used in the real time remote sensing of the ocean.
Experiment study on CO2 laser cleaning rubber sulfuring mould
Show abstract
Parameters and mechanisms of cleaning rubber layer from a rubber sulfuring mould with CO2 laser are analyzed. Laser cleaning is a non-abrasion way, and it can improve mould service life. There are cleaning threshold and damage threshold in laser cleaning, and cleaning percentage of the surface increases with laser power density. The effects of laser parameters on cleaning and performance of the cleaned surfaces are studied. The results show that pulse laser can remove rubber layer completely under proper parameters when the value of laser cleaning threshold is 5~35J/cm2, and no damages are found on substrate surface, mould abrasion that is cleaned by laser decreased.
Theoretical and experimental study on femtosecond laser-induced damage in MgF2 crystals
C. B. Li,
T. Q. Jia,
H. Y. Sun,
et al.
Show abstract
We study single-shot damage morphology of MgF2 irradiated under 800 nm laser using scanning electronic microscope (SEM). The dependence of damage threshold on laser pulse width is measured by the linear relationship between the area of damage spot and the logarithm of laser energy. The pulse duration ranges from 55 fs to 750 fs. We develop the multiple-equation model (Phys. Rev. Lett. Vol.92, pp.187401, 2004), in which two-photon absorption in the conduction band is considered. The experimental results agree well with our model.
Study on improving the surface hardness of TiAl alloy by laser nitriding in an atmospheric ambient
Yuling Yang,
Changsheng Liu,
Wei Yan,
et al.
Show abstract
Laser nitridation in an atmospheric ambient was applied to improve the surface hardness of Titanium alloy. The samples were nitrided with laser power density of 6.5×105 w.cm-2, the scanning speed of 100mm.min-1. The nitrogen gas was pre-heated to 300oC to accelerate the nitriding process. Some interested samples were tested with XRD method to analyze the composition of nitrides, and the surface hardness of HV was measured. The results show that TiN and Ti2N were formed on the surface of Ti alloy with proper nitriding parameters, but TiN is the main composition. The surface hardness increased by three times, that is from the original value of 269 Kg.mm-2 to 794Kg.mm-2.
Experiments on the data recording of optical waveguide multilayer storage devices
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The basic principles of optical waveguide multilayer storage (WMS) device include recording data in the form of waveguide defects, reading data by collecting the scatter light from the waveguide defects, and restraining the cross talk between layers by taking the benefit of the waveguide structure. In this paper, we give some experimental results obtained by three different approaches of data recording. They are laser direct writing, photolithography and hot embossing. In the first method, a laser beam is focused on the top of a polymer film. The thermal effect alters the medium property locally at the focus point, which acts as the defect in the waveguide structure. The second method resorts to the processes of photolithography to record pits on the photoresist layer. The process of hot embossing is similar to the fabrication of CD-ROM, however, the data pits deeper than the wavelength are embossed on the polymer surface to increase the scattering efficiency. WMS devices based on different data writing methods are presented and the data scattering patterns are observed. The comparison between the different data writing approaches is made and discussed as well.
Minimum laser energy computation of sheet metal deformation caused by laser shock peening and its experiment
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Mechanism of laser shock forming(LSF) is introduced, and cause of laser shock wave is explained. As shortage of R. Fabbro's laser shockwave model and of pressure estimate, both a mathematical model and the estimated formula of shockwave pressure are put forward, the formula shows clearly the relation between the peak value of shockwave and the overlay, energy absorbed layer, sheet metal properties and the laser parameters. Based on the formula and the tensile yield strength of sheet metal, minimum laser energy of deformation is estimated. To discuss the relationship between laser energy and sheet metal deformation the experiment is done, the results show that minimum energy computation accords with critical value of deformation, and that the deformation increases with the increase of laser energy in a nonlinear way. These provide a theory foundation to exactly control and predict deformation of sheet metal.
Detection of underwater acoustic signal based on multi-resolution analysis
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With the localizing character of wavelet transform, acoustic signal from water surface using laser light can be decomposed into the detail part of every scale by multi-resolution analysis. The results of experiment show that wavelet analysis has the great ability of noise rejection and is fit for weak signal detection and feature extraction.
Color video display technique based on diode-pumped solid state lasers
Yue Zhang,
Wei-qi Liu,
Yu-si Kang,
et al.
Show abstract
This paper will introduce the principle and techniques to realize laser color video display. The characteristics of techniques and bottleneck of restricting the development are analyzed .A novel technical approach to eliminating the laser interference, improving the uniformity of optical field, transforming the chromaticity and extending the virtual color is proposed. The principle device of laser display system has been produced on the basis of the blue, green and red diode-pumped solid state lasers. The wavelengths of the blue, green and red are respectively 473nm, 532nm and 671nm. The output powers of the lasers are 1.3W, 0.32W and 3.5W respectively.
160GHz to 20GHz variable rate RZ and CS-RZ pulse trains generation based on phase and attenuation tunable high-resolution AWG, and its application to photonic networks
Show abstract
We developed an optical spectrum synthesizer based on high resolution synthesized arrayed wave-guide grating (AWG) which consists of 32 ports AWG with 20GHz spacing, tunable attenuators, optical phase shifters, and mirror. All components are integrated by planer light-wave circuit (PLC) technology. It can tune amplitude and phase of each spectrum mode of pulse train. Tuning time is within 3 ms. Optical signal inputs from an In/Out port and divided into 20GHz spacing spectral components. Amplitude and optical carrier phase are tuned by attenuators and phase shifters, respectively. Optical attenuator is a PLC based Mach-Zehnder interferometer with heater. Optical phase shifter is a wave-guide with heater. In this paper, 160GHz to 20GHz variable rate return to zero (RZ) and carrier suppressed return to zero (CS-RZ) pulse trains generation are experimentally demonstrated. Pulse by pulse optical phase shift either "0" or "π" of generated CS-RZ pulse train is verified by test experiment. All optical pulse reshaping of 20GHz distorted pulse is also shown. Spectrum domain matched filtering for optical code division multiplexing (OCDM) and optical label switching is shown experimentally. Other possibility of PLC based all-optical label processing and their application to ultra-high speed and scalable photonic networks are expressed in detail.
Third-order optical nonlinearities of sol-gel silica coating films containing J-like aggregates of a cyanine dye, NK-1967
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The third-order optical nonlinearities and responses of sol-gel silica coating films containing J-like aggregates of a cyanine dye, NK-1967, were measured by the femtosecond degenerate four-wave mixing (DFWM) technique under resonant conditions. While NK-1967 in aqueous solution showed an absorption maximum at 742 nm, J-like aggregates of NK-1967 in sol-gel silica coating films showed that at 877 nm. Though the sol-gel silica coating films were stable at room temperature, they began to decompose after 10 minute irradiation at a laser power of 5 GW / cm2. The temporal profiles of the DFWM signal were measured with a time resolution of 0.3 ps, and were found to be almost same as that of CCl4, i.e., the coherent instantaneous nonlinear response was dominant. The contribution of slow response with decay time constants of ca. 1 ps was very small. The electronic component of the effective third-order optical nonlinear susceptibility of one of the films had a value of ca. 2.0 x 10-8 esu at 850 nm. The present value for the sol-gel silica coating film containing the J-like aggregates of NK-1967 is four orders of magnitude greater than that of CS2.
Characterization of laser beams by using intensity moments
C. Gao,
H. Weber,
M. Gao
Show abstract
Any coherent and partially coherent laser beams can be characterized by their intensity moments. Generally a laser beam has maximal 4 first order moments and 10 second order moments. The centers of gravity of the beam in the near field and the far field are determined by the first order moments. The beam radii, far field divergences, radii of curvature, beam orientations and M2-factors can be obtained from the second order moments. Beam twist which is related to the orbital angular momentum can be also obtained from the second order moments. The intensity moments and related laser beam parameters obey parabolic propagation laws in the first order optical systems. They are measurable by the caustic method or the Hartmann-Shack wavefront sensor method. The principle and technical problems of these methods were analyzed. As examples the beams emitted from high power diode stack and the astigmatic beam with twist were experimentally investigated.
Generation of picosecond soliton pulses with tunable repetition rate by modulational instability
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Picosecond soliton pulse train has been obtained from a passively mode locked erbium-doped ring fiber laser. The passive mode-locking mechanism that is at play in this laser relies on the modulational instability (MI) theory. By accurately adjusting the polarization setting of the circulating cavity light, the repetition rate can be tuned from 58 to 114GHz. Theoretical explanation is also given.
Reduction of debris and thermal destruction by use of transparent material coating method in femtosecond laser processing
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We investigate the morphology of a glass surface processed by tightly focused femtosecond laser pulse. Processing of a cavity with submicrometer-sized diameter is performed with irradiation laser pulse energy near a destructive threshold in air. In many cases, the cavity is surrounded by a ring-shaped protrusion, debris, and small droplets. In order to reduce the debris and the thermal destruction, we propose to process with coating a transparent material on a target material. PMMA (Poly-methyl methacrylate) is used as the transparent material. A thick PMMA film reduces dissolution and vaporization that is caused by an interaction between a high-density hot vapor plume and the target material. Furthermore, the dissolution is reduced because a low energy part in a laser pulse is reduced by sharpening the beam shape with the self-focusing of the laser pulse in the thick PMMA film. As the results, submicrometer-sized cavity that debris and the thermal destructive area are reduced dramatically is produced.
Photon statistic measurement of down-converted light
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Taking advantage of our previous experimental results and calculations that establish a new approach to the calibration of photo detectors using correlated photon pairs, we developed an experimental setup with a fast electronic control unit for the direct measurement of photon statistics. The most convenient source for generating such correlated photon pairs is a nonlinear optical process of spontaneous parametric down conversion (SPDC). When a photon of the pump beam is incident to a nonlinear crystal with phase matching condition, a pair of photons (signal and idler) is created at the same time. The photons are detected in the signal beam, and a controllable shutter is placed in the idler beam. When a detection event is made in the signal beam the fast optical shutter opens for a certain (pre-programmed) time. While the opening time of the shutter is adjustable with good time resolution, the time interval between the photons in the idler beam can be scanned, so the photon statistics can be determined.
Incoherent and coherent coupling for multi-slab solid laser
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Optic field intensities of double and triple parallel slabs solid laser are numerically calculated. The results show that high beam qualities are difficult to obtain no matter coherent or incoherent output. In order to obtain high beam quality for mult-slab solid laser, we designed a new solid laser construction of radial slabs array according to the present condition for solid and RF excited radial array CO2 gas laser. The numerical calculated results show that this kind of laser can output high beam quality laser both coherent and incoherent cases. It is prospective to be a new research direction for high power, high beam quality, compact and scale solid laser.
Temporal-space transforming pulse-shaping system with knife edge apparatus in Shenguang II upgrade facility
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The temporal pulse shaping was realized by using temporal-space transforming pulse-shaping system with the own-designed "Knife edge" apparatus, for the first time to our best knowledge, in a large energy laser facility with the output energy of 454.37J. A quasi-square laser pulse with the pulse width of 1.16ns, the rising time of 337ps, the falling time of 360ps, and the temporal filling factor of 81.2% was obtained. It is quite satisfied with the requirement of physical experiment. In addition, the further improvements of our system have been suggested in order to enhance the stability and the flexibility as well as the restoring ability of the temporal-space transforming process.
Theory of nonlinear hot-image formation in high-power lasers
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A theoretical approach, based on the paraxial wave equation and the Fresnel integral, are presented to investigate nonlinear hot-image formation of an intense laser beam. Fresnel-zone-plate-like hologram induced by the sum of a wave scattered from a small scatterer and a background wave produces the negative first order diffracted wave (conjugative wave) that is focused to an traditional hot-image, and the negative second order diffracted wave that develops to an intense second-order hot-image. It is seen by the analytical results that the two images may attain a high intensity level enough to damage optical components in high-power lasers, showing that these two images should be equally taken into account for large lasers optimization of system design.
Twisted-free ten-parameter family of partially coherent general anisotropic Gaussian Schell model (TF-AGSM) beams
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We investigate the twist properties of the ten-parameter family of partially coherent general anisotropic Gaussian Schell model (AGSM) beams passing through first-order optical systems. By utilizing the generalized Huygens-Fresnel diffraction integral for asymmetric first-order optical systems, the explicit twist expressions for the principal axes of intensity distribution, transverse coherence distribution and the principal curvatures of phase front in the cross-spectral density function of AGSM beams are obtained. In some special cases when the beams are the twist Gaussian Schell-Model, Gaussian Schell-Model, Li-Wolf and Gori-Guattari beams, our results reduce to well known expressions. It is shown that, under some conditions, although the ten parameters are all not zero and any one of the intensity distributions, transverse coherence distribution and the phase front has its independent principal axis, the beam spot does not twist when the beam passing through free-space. As a result, special partially coherent beams called the twisted-free ten-parameter family of partially coherent general anisotropic Gaussian Schell model (TF-AGSM) beams are introduced and their properties are discussed.
Effect of bandwidth on the intensities of an apertured laser in the near and far fields
Runwu Peng,
Yunxia Ye,
Zhixiang Tang,
et al.
Show abstract
By means of the Huygens-Fresnel diffraction integral, the propagation expression of a laser beam passing through a hard-edged aperture is derived. The effects of the bandwidth on the transverse intensity distributions of the beam in the near and far fields are analyzed. It is found that, in the near field, the beam uniformity is improved with increasing the bandwidth and the broader the spectrum, the smoother the transverse intensity distribution is. Intensity spikes produced by low-frequency diffraction are eliminated in the diffraction patterns and the transverse intensity distribution near axis tends to smooth when the bandwidth increases. The intensity spikes produced by high-frequency diffraction still exist with increasing the bandwidth, but the amplitudes and numbers of them decrease. In the far field, there are only a few differences among the transverse intensity distributions of the beams with different bandwidthes. However, The secondary maximum intensity still presents for the beam with small bandwidth, and it decreases with increasing the bandwidth and is eliminated with large bandwidth.
Dependence of the optical limiting behavior on the medium position and the beam-waist radius in the refractive optical limiters
Show abstract
We study numerically the optical limiting properties of the refractive optical limiting devices based on the self-focusing and defocusing phenomena, and examine the effects of the installation position of the nonlinear media and the waist size of the incident Gaussian beam on the operating performances of the refractive optical limiters. Our results show that the optical limiting curves of the refractive optical limiters assume a vibrating decaying waveform. The optical limiting threshold and the clamped output value of the optical limiters are dependant on the installation position of the sample and the convergence of the incident Gaussian beam to a great extent. When the sample position is given, the smaller the beam-waist radius, the better the optical limiting performance. When the waist radius of the incident light keeps constant, an optimum location of the nonlinear sample can be found in the system. With the fluctuation of the waist size, however, the optimum location changes within a small range. For a self-focusing (self-defocusing) optical limiter, the optimum optical limiting effect can be obtained when the nonlinear medium is positioned at a certain location within half a Rayleigh range in the left (right) side of the focal plane.
Micro-cavity laser of dye molecules loaded in AlPO4-5 crystals
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Micro-cavity laser has attracted extensive attentions due to its potential applications in high-speed integrated opto-electronic device and system. In micro-cavity, spontaneous emission process is enhanced or prohibited, and lasing can occur without a visible threshold. In the past, micro-cavity was realized with semiconductors such as microdisks or vertical cavity surface emitting lasers, with organic dyes embedded in planar resonators as Langmuir-Blodgett films or in spheres, and with gain medium in photonic crystals. In this article, we report a new type of micro-cavity laser based on organic dye molecules incorporated in the channels of AlPO4-5 single crystals by physical diffusion method. The optical measurements reveal that the dipole transition moment of the enclosed organic dye molecules is highly oriented in the channels. Due to size confinement of the AlPO4-5 channels, there is a structure deformation of the dye molecules, which leads to a large blue shift in the absorption spectra for the dye/AlPO4-5 crystal. The micro-sized hexagonal AlPO4-5 single crystal serves as a good natural micro-cavity for the lasing action of the adsorbed dye molecules. The micro-cavity mode of the lasing action is demonstrated.
A new synchronization control circuit based on CPLD for the laser range-gated imaging system
Xiaowen Xu,
Xiaohao Wang,
Fei Tang,
et al.
Show abstract
The synchronization control technique is one of the most key techniques in the laser range gated (LRG) imaging system. Conventional control circuits are composed of discrete components and Medium Scale Integration (MSI) and Small Scale Integration (SSI), which have bad reliability and poor ability of anti-interference.
The idea of using the Complex Programmable Logic Device (CPLD) to realize the monostable trigger circuit is introduced. On the basis of analyzing the performance requirement to the synchronization control of the laser range gated imaging system, a new synchronization control circuit based on CPLD is presented. The circuit based on CPLD is very compact and flexible and has high reliability and strong ability of anti-interference. The synchronization control circuit based on CPLD can provide a wide selection of gate widths, pulse widths and delays. The synchronization control circuit is successfully used in our experiment and the expected result is obtained.
Newton's ring and its new discovery
Huihua Xie,
Yuxiang Peng,
Depu Meng,
et al.
Show abstract
Newton's Ring is a fundamental discovery and is an objective existence, but its distributing mathematic Law has no broad sense. The result come out with by sir Isaac Newton is only a special case. We have done a lot of experiments with laser light and discovered that Laser Newton's Ring possesses many forms. We can not only acquire the image of Newton's ring on the wedge surface, but we can get the image from the space of certain range, and the spatial Laser Newton's Ring possesses some contrary properties compared with traditional Newton's Ring, that is, we have added some new concepts to the knowledge. This new discovery will bring a lot of new applications in many domains.
Enhanced pulse adaptive to PMD by modulating breath-depth
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The enhancement of adaptive abilities of nonlinear optical pulses to polarization mode dispersion (PMD) is obtained by modulating breath-depth of two polarization states of the pulses. The breath-depth modulation is realized based on the interaction among self-phase modulation, cross phase modulation, group velocity dispersion and degenerate four-wave mixing, which results in making two polarization states of the pulses into a tighter state when nonlinear pulses propagate in optical fibers with high birefringence. Numerical results show that the transmission stabilities of modulated breath-depth optical pulses are improved in conventional fibers with random birefringence. The pulse broadening trend of the modulated breath-depth pulses induced by PMD is effectively suppressed by our proposed method. The symmetric output pulse shape is also reshaped in conventional fibers.
Identification of nonlinear optical systems using adaptive kernel methods
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An identification approach of nonlinear optical dynamic systems, based on adaptive kernel methods which are modified version of least squares support vector machine (LS-SVM), is presented in order to obtain the reference dynamic model for solving real time applications such as adaptive signal processing of the optical systems. The feasibility of this approach is demonstrated with the computer simulation through identifying a Bragg acoustic-optical bistable system. Unlike artificial neural networks, the adaptive kernel methods possess prominent advantages: over fitting is unlikely to occur by employing structural risk minimization criterion, the global optimal solution can be uniquely obtained owing to that its training is performed through the solution of a set of linear equations. Also, the adaptive kernel methods are still effective for the nonlinear optical systems with a variation of the system parameter. This method is robust with respect to noise, and it constitutes another powerful tool for the identification of nonlinear optical systems.
Two-mode injection-locking analysis of Fabry-Perot laser for optically generating millimeter wave signal in ROF system
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We report the experimental and theoretical investigation of injection locking technique of the Fabry-Perot laser to generate the two-mode optical millimeter-wave signal. The relation of locking bandwidth, output light power, and the gain of signal-to-noise ratio versus the ratio of injection power and the mode building process of injection locking are measured and theoretically analyzed. The experimental results agree with the input and output power relationship obtained by multi-mode rate equation followed by injection term and the law of conversation of energy.
A preparation method of cold atomic beam with fine optical characteristics
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A preparation method of cold atomic beam with fine optical characteristics is presented and discussed in this paper. The method is described as followings: cold atoms in three-dimension magneto-optical trap (3MOT) are pushed out because of the imbalanceable resonance-radiation pressure and form a cold atomic beam, whose propagation is limited in a magnetic guide. And then the atomic beam is further transversely compressed by use of two-dimension magneto-optical trap (2MOT). Finally, a state preparation laser processes the atomic beam. Consequently, the continuous cold atomic beam with lower longitudinal velocity, higher flux, much less transverse velocity and homogenous state is obtained. The simulation results show that the preparation method is feasible, which can be used in the establishment of the high-property atom interferometer.
Influence of third-order nonlinearity on the conversion efficiencies of third harmonics
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A theoretical analysis is presented for third-harmonic generation (THG) in KDP for type I/ type II angle-detuning scheme of high-intensity laser to produce third harmonic radiation near 0.35μm. The effects of the third-order nonlinear susceptibilities (χ(3) ), transverse walk-off and diffraction, especially, the effects of third-order nonlinearity and the phase variations on the frequency conversion have been discussed. A split-step algorithm based on the Fast Fourier Transform and fourth-order Runge-Kutta integrator is used. The results shown that the third-order nonlinear interactions decreases the tripling efficiency, and increases of the modulate strength of the output intensity of 3ω radiation. However, adjusting the angular detuning can compensate effectively the effects of third- order nonlinearity. Furthermore 3ω conversion efficiency will drop with the increase of the degree of phase variations, and the improve 3ω conversion efficiency can suppress the 3ω wave amplitude ripples.
Thermal distortions of optics irradiated by periodically repeated short pulses
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Temperature variation and wave front distortions due to temperature rise and thermal stress, in rotationally symmetric and isotropic optical elements irradiated by periodically repeated short pulses, have been calculated. The analytical expressions of the periodically varying temperature distributions have been obtained by making full use of the periodicity of the pulsed laser system. For the case that the diameter of optical element is considerably larger than the thickness and the temperature variation along the thickness direction is negligibly small, the plain approximation has been used to estimate the phase distortions. The results have shown that the polarization independent phase distributions due to thermal deformations of the optical element may be a problem of concern, especially if one considers the fact that the phase distortions of the light wave may be accumulated after passing through several optics.
Study on the extinction coefficeient of graphite smoke to 10.6 microns laser emission
Xuanyu Wang,
Gongpei Pan
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The transmitting properties of 10.6μm laser emission and the infrared screening performances of graphite smoke are elaborated. The experimental method and steps are detailedly expounded to test the extinction coefficient of graphite smoke to laser emission in a smoke chamber. The test results are listed with a comparison to other smokes. The curves of laser power varied with time in graphite smoke are drawn and the average particle's diameter of graphite smoke is tested. The extinction efficiency factors of a single particle of graphite smoke are calculated according to Mie theory. By the experimental result, the mass extinction coefficient of graphite smoke to 1.032W 10.6μm laser emission is 1.28m2/g and much bigger than other smokes'. By the analysis, the extinction efficiency factor of graphite smoke's particles to 10.6μm laser emission is decided by scattering efficiency factor when the diameter is bigger than 3μm and the optimal scattering diameter is 9.0μm. The graphite smoke has a better extinction ability to ordinary infrared than 10.6μm laser emission.
Water vapor concentration measurement in singlet oxygen generator by using emission spectroscopy method and absorption at 1392nm
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By using emission spectroscopy method and absorption at 1392nm, partial water pressure at the exit of a square pipe-array jet-type singlet oxygen generator (SPJSOG) for chemical oxygen-iodine laser (COIL) was measured. The water vapor fraction was calculated from the partial water pressure in the diagnostic cell when we assumed the water vapor fraction in the diagnostic cell is the same as that in the generator. The results from the two methods showed that the water vapor concentration is less than 0.08 in this SPJSOG during normal operation. The water vapor fraction decreases with the increasing of the pressure in the generator and rises with the increasing of buffer gas flow rate and the basic hydrogen peroxide (BHP) temperature in the case of constant chlorine flow rate. Measurements showed that the change of water vapor fraction due to BHP temperature could be ignored during normal operation. It is indicated that the gas flow velocity is the main reason that affects on the water vapor fraction in COIL. It is proved that the emission spectroscopy method is one of the simple and convenient ways to measure the water vapor concentration in singlet oxygen generator (SOG), especially in real time measurements. But absorption spectroscopy method, as a direct measurement, can give the more factual results of the water concentration.
Time-evolution of a trapped Bose-Einstein condensation in a quantum cavity
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The dynamics in the Bose-Einstein Condensation(BEC) process with interaction between two energy-level Bose atoms and single-mode active cavity field in the quantum cavity is analyzed using the ordinary method suggested by the authors for solving the wave function in the Schrodinger ideal from the Heisenberg idea. A wave function has been established for the atoms under the BEC conditions in the quantum cavity. Then the stability factor determining the BEC and the selection rules of the quantum transition can be solved.
Study on LD-pumped Nd:YAG laser cutter
Jianfeng Cui,
Jing Zhao,
Zhongwei Fan,
et al.
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The theory of laser cutter and the technology neck is analyzed. We can conclude that it is almost impossible to deal with the waste thick silicon wafers which are yielded in producing silicon wafers by conventional eroding or diamond cutting, while it is also unperfected with ecumenical laser cutter without good beam quality or precise laser and optics system. It is represented that high average power and high repetition rate laser with good beam quality and precise laser and optics system are pivotal to obtain excellent cutting effect such as thick groove depth, rapid cutting speed, fine kerf section without considering the effect of technique. Considering laser medium thermal lens effect and thermal focal length changing with pumping power, using plano-convex high reflectivity mirror as the back cavity mirror to compensate the heat lens influence, aλ/4 waveplate to compensate heat-induced birefraction, utilize the Nd:YAG self-aperture effect, more than 50 W average power 1.064 um IR output is obtained with beam quality factor (M2) equals 3.19. Through the LD-Pumped Nd:YAG laser cutter we developed with short focus length negative spherical aberration focusing lens, double axis linear step motor positioning system, suitable beam expander multiplying factor, appropriate diameter of exit beam aperture, proper repetition rate, when the cutting velocity equals 400mm/min, 0.75mm thick silicon wafer can be penetrated; when the cutting velocity equals 100mm/min, double-layer 0.75mm thick silicon wafer can be penetrated. The cross section is fine and the groove is narrow, the cutting quality meets the expecting demand.
Research on LD-pumped dual wavelength Nd:YAG laser with high beam quality for machining
Jianfeng Cui,
Zhongwei Fan,
Chunhua Zhao,
et al.
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Considering laser medium thermal lens effect and thermal focal length changes with pumping power, conventionally, lasers are designed to operate in the middle of thermal stable zones, where the fundamental mode size is insensitive to thermal perturbation, while this method seems impossible when large fundamental mode size is required. Through self-select mode cavity, lasers are designed to work at the border of stable zone instead, where large fundamental mode size in gain media can be reached. With increase of pumping power and self-aperture mode-selective effect, mode size would grow up automatically to a certain value suitable for monomode resonance. With double 180 W pump modules, acoustic Q-switch and LBO external frequency-doubled, over 28 W which M2 equals 4.5 quasi-CW output green laser and 52W 1.064 um IR output is obtained simultaneity. With the insertion or not of the harmonic separator by footswitch high beam quality green IR, and green & IR lasers are obtained conveniently.
Laser feedback interference in gain-coupled DFB lasers
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The laser feedback interference in gain-coupled DFB laser diodes (Distribute Feedback LD) is analyzed. The threshold gain and frequency variation in the DFB laser diode are theoretically deduced. Considering the experiment in practice, we analyze the laser feedback interference at the condition of multiple external cavities. Some parameters have influences on the feedback interference, e.g., the coupling coefficient, the linewidth enhancement factor of gain-coupled DFB laser, the reflection coefficient of external reflector. We discussed these different parameters value in numerical analysis, including the simulation at the condition of multiple external cavities. Compared with the effect of laser feedback interference on F-P and λ/4 phase-shifted DFB lasers, the gain-couple DFB lasers are more sensitive to optical feedback for a specific κL value (coupling coefficient and L cavity length). These results show that the gain-couple DFB lasers can be used as laser feedback sensors with a high accuracy.
LD-pumped double-clad fiber single-frequency power amplifier
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Single frequency, single mode laser output from a monolithic resonator was amplified by a double-clad D-shape fiber of 4.4 meters long. When the signal laser is 200mw, up to 6.65 W single frequency laser output was obtained, slope efficiency is 30.6%. The amplifier is Yb3+ doped glass fiber pumped by a laser diode array at 976nm with signal at 1064nm. Single frequency amplification has been proved by a Fabri-Parrot interferometer. It is shown from the
experiments that the signal input has not been saturated. By increasing the input signal, amplification can be increased further under the same pumping power. Experimental results meet well with theoretical calculation.