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- Photonics and Optoelectronics Meetings (POEM) 2008: Laser Technology and Applications
Photonics and Optoelectronics Meetings (POEM) 2008: Laser Technology and Applications
Investigation of chaotic synchronization of VCSELs subjected to anisotropic optical injection
Show abstract
Chaotic synchronization characteristics of the vertical-cavity surface-emitting lasers subjected by
anisotropic optical injection are numerically investigated. First of all, the synchronization quality of the
x-linear polarization (LP) mode and the y-LP mode are both periodically changed with the angle θ
between the polarizer and the light axes. Second, in a enough large scale region of the feedback
coefficient and the injection current, each LP mode can be obtained good synchronization quality when
the angle θ exists in the former half periods region., in the case that their synchronization quality are
independent of the polarization states of the lasers output. However, each LP mode can be achieved very instable and inferior synchronized quality, which is caused by the angle θ in latter half periods range.
Variable pulse duration Nd:YAG laser with two-cell SBS system
Show abstract
A compact laser model featuring adjustable pulse duration is built and tested. The model contains a Q-switch Nd:YAG
oscillator and a two-cell stimulated Brillouin scattering phase conjugation mirror (SBS PCM). The duration and the
energy of output pulses are investigated as a function of the distance between two cells. The oscillator generates pulses
of duration ~9ns and energy ~25mJ. When these pulses are focused into the two-cell SBS system, an output pulse duration variable in 1~5ns range is achieved by adjusting the distance between two cells. When the distance is 15cm, the minimum pulse width (1.0ns) and maximum energy (10.3mJ) of output pulse is obtained with significant improvement of beam quality in contrast to the pump beam.
High-energy pulsed eye-safe intracavity optical parametric oscillator at 1.57 um
Show abstract
We have demonstrated a high-energy, eye-safe, KTP-based intracavity optical parametric oscillator
(IOPO) pumped by a QCW diode-pumped electric-optical Q-switched Nd:YAG. A signal pulse of
31.5mJ energy at 1572nm wavelength was demonstrated at 10Hz with 3.48ns pulse duration. The peak
power of the pulses amounted to 9.1MW. The average conversion efficiency from Q-switched 1.064μm wavelength input power to OPO signal output power was up to 10.5%.
Investigation of thermally determined near hemispherical resonator design for diode-pumped solid state laser
Show abstract
The performance of the side-pumped plane-plane asymmetric resonator, which comprises two identical diode side-pumped Nd:YAG laser heads arranged near the full reflector mirror, is theoretically and experimentally investigated. Theory analysis shows that, when the resonator operates at the boundary of the stable region, the fundamental mode diameter in the rods quickly increases, which leads to the laser beam quality quickly improving while maintaining a higher output from the resonator. Because the performance of this plane-plane asymmetric resonator operating at the boundary of the stable region is similar to a near hemispherical resonator design, we name such resonator design as thermally determined near hemispherical resonator. Comparing with the design of a symmetric plane-plane resonator operating at the boundary of stable region, thermally determined near hemispherical resonator design can shorten the cavity length and is suitable to low and middle power diode side-pumped laser. The performances of thermally determined near hemispherical resonator for cavity length of 970 mm, 820 mm and 770 mm, at a repetition rate of 100 Hz, are experimentally investigated. As expected, for above three cavity length, the beam quality all improves quickly and the output power saturates, once the pump power exceed certain value. For the 970 mm cavity length, under the total pump energy of 1.35 J, laser output with a pulse energy of 220 mJ and a beam quality of M2=1.28 is obtained.
Tunable phase-stabilized infrared parametric laser source
Show abstract
Tunable self-phase-stabilized infrared laser pulses have been generated from a two-stage optical parametric amplifier. With an 800nm pump source, the output idler pulses are tunable from 1.3μm to 2.3μm, and the maximum output energy of the idler pulses is higher than 1mJ at 1.6μm by using 6mJ pump laser. A carrier-envelope phase fluctuation of ~0.15 rad (rms) for the idler pulses is measured for longer than one hour by using a home build f-to-2f interferometer.
Polycrystalline silicon thin films crystallized by green laser
Show abstract
A top hat beam of frequency-doubled Nd: YAG laser is obtained from our beam shaping optical system. With this beam,
amorphous silicon thin films deposited on glass by plasma-enhanced chemical vapor deposition (PECVD) are
successfully crystallized. The surface morphology of the laser-crystallized materials is studied by atomic force
microscopy (AFM). Pronounced increase in surface roughness after the laser treatment could be observed from the
Microscope Photos. Raman spectra of the Si films are measured to confirm the phase transition from amorphous to
polycrystalline and to investigate the silicon structural properties. Crystalline fraction evaluated from the Raman spectra
are found to increase almost linearly with the laser fluence. There exists the optimized laser fluence to produce the best
crystallization in the range of 400 ~1000mJ/cm2.
Theoretical investigation of laser beams with radial polarization
Show abstract
Laser resonator for generating radially polarized beams is designed with aid of a special wire grid polarizer which is used
as the rear mirror in CO2 lasers. A theoretical model for this resonator with polarization selectivity is established, and the
simulation results show that not only radially polarized modes but also azimuthally polarized modes exist in the laser resonator. In order to guarantee pure radial polarization, the purity of radial polarization needs to be improved by suppressing azimuthal polarization. The purity of radial polarization depends on refractive index of the substrate and grating period of the wire grid polarizer. If the substrate of the wire grid polarizer is ZnSe, the purity of radial polarization can arrive at 85%. When the wire grid polarizer has low refractive index and high ratio of laser wavelength to grating period, pure radial polarization can be obtained.
Study of high precision laser collimator on position sensitive detector
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In this paper, the peculiarity of He-Ne was presented. The structure, working principle, non-linear factors, non-linear processing technology on the position output signal of PSD were analyzed, based on which according to characteristics of position output signal of PSD, the double light pathways optical system and signal processing circuit fit for PSD were designed. The commutation rule of the Gauss laser beam passing thin lens and the best collimation area were analyzed, and then the high-precision laser collimator was developed. Also the constitutes, working principle and characteristics of instrument were generalized and the main technique parameters were presented. Combining the developed straightness error evaluation software and high-precision laser collimator to achieve dynamic and static measurements of straightness error. The experiment results showed the consistency between the theoretic analyses and experiment after the repetitious testing. At last the application foreground of the instrument was prospected.
Study of the interactional mechanism between laser and material
Show abstract
In this paper, based on quantum mechanics and photons theory, the characteristics, the light-wave mode, the excitated
radiation and the theory of light amplifying and producing are expatiated. The interactional process of laser and material
and their influences which are complex, fast, and multidimensional and with many parameters in the process are studied
using the model of mathematics-physics-mechanics. First, the calculate cell and calculate area are selected in reason, and
then the calculate areas are dispersed. Using combining steps function with linearity approximation, non-linear equations
are answered with the iterative method, the changing connections of temperature parameters are obtained, and the
surface intensify technique and processes are given which tradition technics cannot solve. It provides theory basic for
laser intelligent machining engineering.
Laser damage performance of large-aperture fused silica optical components at 351 nm
Show abstract
High power laser facility for ICF will routinely operate at high fluence level. The damage on the large-area FOA optics
is a key lifetime limiter. The optics should be checked after each laser shot for damage initiation and growth. On-line
monitoring equipments are installed for this purpose. Damage pictures of a fused silica component are successfully taken
and the luminance of the pictures could reflect the deterioration of the operational environment. Damage initiation and
growth behaviors at 351nm high-fluence laser were observed. Damage density and damage growth are exponential with
the shot number and some conclusions could be drawn. These results bring forward demands for future monitoring
equipments and more experiments to establish a lifetime model.
A study on the mode selection of fiber-laser with a small aperture
Show abstract
In this paper, it is discussed relationship between the beam quality factor and high order mode in fiber laser, and the relationship between the divergence angle and the beam quality factor. An aperture with adapted diameter in cavity could introduce low loss for the fundament mode but high loss for high order modes. In this method, it is easy to realized mode-selection. By using this method, experiment demonstrated that 23.4W output from a single fiber laser with 1.20 of M2 is obtained.
Laser-diode end-pumped Nd:GdVO4 slab laser at 1342 nm
Show abstract
1.3μm all-solid-state lasers have great important applications in the fields of fiber communication, medicine and laser
color display. In this paper, a LD end-pumped Nd:GdVO4 slab laser with a flat-concave stable cavity at 1342nm was
demonstrated. Under the pumping power of 132W, 25W CW laser was obtained with the slope efficiency of 23%.
Interference between surface harmonics of carrier-envelope phase controlled few-cycle laser field
Show abstract
In this paper, we demonstrate an improved way of providing direct access to the carrier-envelope phase (CEP) in low-energy pulses (nearly 1 μJ) by using the interference between the second harmonic (SH) and the third harmonic (TH) from a solid surface at the same time. The important point is that the spectra of these two harmonics overlap in the UV region. So, the interference signals between the SH and TH from the surface of a solid do not include a constant offset phase component due to the linear dispersion in the SHG crystal and can be used to measure the CEP directly. We describe CEP measurement based on the interference between
SH and TH. The result showed that the CEP fluctuation in our system was within ±π/6 even without a slow
feedback loop. A slow feedback loop, which compensates for an additional CEP drift caused in the amplifier and
the compressor, suppressed the CEP fluctuation within ±π/12 for hours.
Spectral characterization of laser-induced air plasma by pulsed CO2 laser
Zhixian Jiu,
Jian Tang,
Chenguang Yang,
et al.
Show abstract
The spectral characterization of laser-induced air plasma by a pulsed TEA CO2 laser with a GaAs lens is reported. The data were collected using an ICCD spectrograph. The spectra of laser-induced plasma in the range of 300-900 nm and their spatial and temporal behaviors were investigated. Emission spectra of the N II lines occurring between 490 and 520nm were analyzed in detail. The intensity peaks during the laser pulse approximately 0.7 μs and the peak emission spectra decay over the first 1.5 μs. The spectra of plasma at different position were measured in the directions both perpendicular and parallel to the laser propagation respectively. And the spectra of laser-induced air plasma produced by different focal length lens were compared. The affection of different focal length lens for the plasma was described. The shapes of horizontal directions were smaller with the shorter focal length and the intensities of the plasma were higher. In addition, the temperature of plasma was evaluated from the emission intensities. The peak temperature was more than 10000K.
Observation of laser-induced air plasma by pulsed CO2 laser with an ICCD camera
Show abstract
In order to know more about the mechanism of laser propulsion, the temporal evolvement and spatial distribution of the
air plasma produced by a Transversely Excited Atmospheric (TEA) pressure CO2 laser were investigated with a image
intensified charged coupled device (ICCD) camera. The energy of the TEA CO2 laser was 5 ~ 6 J, with pulse FWHM of
100 ns at 10.6 μm, trailing approximately 2 μs. The experimental results indicated that the radial evolution was almost
symmetrical but the axial evolution was not. During the development stage of the breakdown, the laser-absorption region
was propagated along the beam axis in the direction opposite beam incidence. The axial length of plasma and the
maximal intensity of the laser-induced plasma were investigated, which could vary with the laser power. The
propagation speed of the laser-induced plasma was about 104 m/s at the initial stage of breakdown, and then the
propagation speed of the laser-induced plasma decreased gradually.
High-power widely tunable singly resonant optical parametric oscillator based on PPLN or MgO-doped PPLN
Show abstract
Tunable near-infrared and mid-infrared radiations have drawn enormous interest and obtained a variety of applications,
such as, molecular analysis, remote sensing, laser radar, material spectroscopy, air pollution detection and so on. The
periodically poled lithium niobate (PPLN) crystal is a suitable material to realize the infrared solid-state lasers. A QPM
singly resonant OPO based on PPLN crystal is experimentally demonstrated and the measured results are reported in this
paper. The OPO system is pumped by a commercial acousto-optically Q-switched Nd:YAG laser. Its output wavelength
is 1.064 μm, pulse duration of 150 ns at a repetition rate of 10 kHz. A maximum laser output power of 1.23W at the idler
wavelength of 3.09 μm has been obtained for the OPO when the pump power is 8.15 W. And now the optic - optic
conversion efficiency is 15.1%. The widely tunable mid-infrared ranges of 2.80-3.17 μm, 3.34-3.60 μm, 3.77-3.97 μm,
4.15-4.32 μm, and 4.48-4.62 μm are obtained by changing both the crystal's temperature from 40 to 200 °C and grating
periods from 26.5 μm to 30.5 μm.
A QPM singly resonant OPO based on MgO-doped PPLN crystal is experimentally demonstrated and the measured
results are presented in this paper, too. The pump source is also the acousto-optically Q-switched Nd:YAG laser. A
maximum laser output power of 2.17 W at the idler wavelength of 3.33 μm has been obtained for the OPO when the pump power is 8.15 W. And now the optic - optic conversion efficiency is 26.7%. The tunable mid-infrared ranges are 2.83-2.89 μm, 3.10-3.38 μm, 3.57-3.78 μm, 3.95-4.12 μm, 4.28-4.46 μm, and 4.65-4.79 μm. Compared to PPLN crystal, we can obtain higher idler output power and optic - optic conversion efficiency by using MgO-doped PPLN crystal.
A CFD model for fast-axial-flow CO2 lasers
Qing Li,
Youqing Wang,
Hongyan Huang,
et al.
Show abstract
A three-dimensional (3D) computational fluid dynamics (CFD) model has been applied on a fast-axial-flow CO2 laser. Using a control volume method, a set of governing equations of the model is dispersed and numerically solved. These equations describe the flowing and heat-conducting processes in the discharge tube of the laser. A model, method of solution and computational and experimental results are described and presented in this paper. The parameters of gas pressure, velocity, temperature, density and turbulence energy are obtained by theoretical modeling. The computational results are in very good agreement with the experimental data within a broad range of parameters.
The research on discharge tube structure of fast-axial-flow CO2 lasers
Show abstract
In order to make clear the influence of discharge tube structure on the flow field and discharge processes of a fast-axialflow
CO2 laser, three-dimensional modeling have been made on two different structures of tubes under the same boundary conditions. The computational results show the differences of flow field in two different structures of tubes which lead to the different discharging conditions. There is also a good agreement between the computational results and the experimental observations. The results prove that the two tubes have advantages respectively, and it can explain the
instability of discharge which happened in experiments.
The fabrication of thin wall structure with novel laser vaporizing sintering
Show abstract
Selective laser sintering (SLS) technology which is based on additive material shows great advantages for its'
almost no limitation in sintering material. Beside additive fabrication traditional laser processing technologies such
as laser cuttinglaser drillinglaser marking are based on removing material. In this paper laser vaporizing sintering (LVS) fabrication technology has been introduced to fabricate thin wall structure. This technology is based on both material removal by laser vaporizing and material addition by laser sintering. This is a novel technology which combines two different methods to fabricate micro part. This method can sinter several powder particles together to form microstructure. It can be used to fabricate 2.5 dimension thin wall parts and hopefully will be developed to a new material removing-adding technology to produce micro-components.
Measurements of optical parameters of phantom solution and bulk animal tissues ex vivo at 650 nm
Show abstract
Optical parameters of biological tissues, including absorption coefficient (μa), reduced scattering coefficient (μs') or scattering coefficient (μs), anisotropy factor (g) and refractive index (n) are investigated extensively and systemically at
wavelength of 650 nm. Intralipid solution was selected to be the tissue phantom in order to test the validity of
measurements. Considering the factors of fiber orientation and haemoglobin content, we chose some fresh bulk animal
tissues in vitro which were bovine adipose, bovine muscle, porcine adipose, porcine muscle, porcine kidney, porcine liver,
mutton and chicken breast. The basic assumption is that in vitro samples are a reasonable representation of the in vivo
situation. We have gained numbers of experimental data of Intralipid and some tissues. Particularly, we have set up the
close relationships among six optical parameters involving μa, μs', μs, g, n and μt. The experimental results show that for
animal tissues, μa, μs' or μs and n rely deeply on muscle fiber orientations. Both of μs and μt range from 10mm-1 to 20mm-1. μa ranges from 10-2 mm-1 to 10-3 mm-1 and g from 0.95 to 0.99. The results of this study will be helpful in further understanding of optical properties of tissues.
Self-induced pulsing in Tm3+-doped fiber lasers with different output couplings
Show abstract
Under the pump of a diode laser at 790 nm, self-pulsing phenomena of ~2 μm Tm3+-doped fiber lasers are investigated.
Laser cavity configuration is changed by using different output-coupling mirrors. When the polished fiber-end (Fresnel
reflection) is used as the output coupler, the cavity is dubbed as "bad" cavity. With this "bad" cavity, regular laser pulse
trains can be obtained near threshold pump level. The pulse width and repetition rate are several micro seconds and several kilohertz, respectively. At higher pump levels, the regular pulse-train shape is broken, and some random pulses occur. At the same time, similar mode-locking phenomenon can be observed. When the output coupler is changed to a T=10% (at 2μm) mirror, regular laser pulse train still can be observed near threshold pump. However, a slight increase of pump leads to randomization of the pulse train. Similar mode-locking phenomenon was not observed with this kind of cavity. When the output coupling is decreased to T=5%, even near the pump threshold, regular pulse train can not be achieved. With increased pump powers, laser output changes from pulse state to continuous wave. Based on the experimental results, a theoretical model is proposed and the origin of self-pulsing is discussed.
System design and description of infrared simulator system based on the multidimensional flight table
Show abstract
This paper deals with the simulation for the army aviation and missile command at the thermal infrared range scale from
2.0 to 4.9μm. The infrared simulator system based on the multidimensional flight table(ISSBMFT) is the significant part
of hardware - in - the - loop (HWIL) simulation system for controlling and guiding weapon systems with infrared seekers.
It emphasizes on the infrared scene of HWIL simulation experimentation for controlling and guiding weapon and
provides a realistic environment of combat with target/jamming which owns the specific properties of radiant spectrum,
entrance angle and target's relative distance variation. Optical system is the basis of the characteristics of the simulator.
In the system, three-beam structure is put forward which will make the optical path equal. Through settling attenuators,
filters, and polaroids in the beams, which modulates the transmittance, the energy proportion is simulated, so as wave
energy and the entrance angle. So we can simulate one target and two different forms of jamming through various distance and conformations. Radiant system and controlling system is the guarantee of the simulation. Calculation of energy and the method of controlling is depicted in the article.
An integrated thermal and hybrid model for pulsed laser ablation and plasma expansion in vacuum
Show abstract
An integrated thermal and hybrid model is present in this paper to study the relative physical characteristics when target
is irradiated by high-intensity laser beam. The model can describe the thermophysical effect in the initial stage for
plasma formation and the following process for plasma expansion. Take silicon target as an example, the numerical solutions are obtained from the integrated model using a finite difference method. The results from the present model indicate that the plasma dynamic expansion behavior can be evidently influenced by the vaporization and surface temperature of ablated material. Their effects are similar to a dynamic source for plasma expansion and increase the expansion acceleration. The expansion characteristics from our results are found to be consisting with the relative
studies.
Fabricating fluorinated polyimide optical waveguide by CO2 laser direct-writing
Show abstract
Fluorinated polyimide waveguides were fabricated by CO2 laser direct-writing. The poly(amic acid) micro-region
exposed by CO2 laser beam was measured with FT-IR micro-spectroscopy. The FT-IR spectra indicated that the laser
imidized polyimide was semicrystalline, and the imidization degree of scanned micro-region increased with the rising of
output laser power. The increased aspect ratio of waveguide and smoothness of surface can be achieved by increasing the
pre-cured temperature (below 120 °C) and writing rate, and optimizing laser power and the distance between the lens
and the annular aperture. The guided light was clearly confined to the core of the fabricated waveguide, which means this technique can be used for fluorinated polyimide waveguide fabrication.
Spectral properties and laser performance of Tm, Ho: LuLF4 crystal
Haiyan Peng,
Kun Zhang,
Lianhan Zhang,
et al.
Show abstract
LuLiF4 single crystals co-doped with thulium (5%) and holmium (0.5%), which had large size, intact shape and high
optical quality, were successfully grown by the medium frequency induction heating Czochralski Technique. The
absorption spectrum of the crystals showed that the main absorption peak located at 686 nm and 792nm. At room
temperature, LuLiF4 single crystals co-doped with thulium (5%) and holmium (0.5%) were end-pumped by a fiber-coupled laser diode system with pumping wavelength of 795 nm. We achieved power of 50 mw continuous laser output at 2.05 μm wavelength.
The difference analysis of nonlinear absorption coefficient B in the beam sections of plain and Gaussian distribution
Show abstract
The differences of nonlinear absorption coefficient β are theoretically and numerically studied under both of the beam sections of plain and Gaussian distribution. The formula of energy transmission is derived on the base of temporal profile of Gaussian pulse beam. According to the formula, the absolute and relative
differences of β are also estimated in compare with plain beam and the pulse beam that is rectangular in time
but Gaussian in space. The relative differences turn out theoretically to be about 183% and 41.4% respectively.
The further numerical simulation shows that these values are only the least differences. The existed differences mean that, according to the temporal influence of pulse, one should get a lager value of β in past performed routine experiments of nonlinear energy transmission. Our result suggests that, by taking temporal profile of a pulse beam into account, one can obtain more exact value of two-photon absorption cross section of the molecule experimentally.
Application of laser to nondestructive detection of fruit quality
Show abstract
In this study, a hyperspectral imaging system using a laser source was developed and two experiments were carried
out. The first experiment was detection of pesticide residue on navel orange surface. We calculated the mean intensity of
regions of interest to plot the curves between 629nm to 638nm. The analysis of the mean intensity curves showed that
the mean intensity can be described by a characteristic Gaussian curve equation. The coefficients a in characteristic
equations of 0%, 0.1% and 0.5% fenvalerate residue images were more than 2400, 1570-2400 and less than 1570,
respectively. So we suggest using equation coefficient a to detect pesticide residue on navel orange surface. The second
experiment was predicting firmness, sugar content and vitamin C content of kiwi fruit. The optimal wavelength range of
the kiwi fruit firmness, sugar content, vitamin C content line regressing prediction model were 680-711nm, 674-708nm,
669-701nm. The correlation coefficients (R) of prediction models for firmness, sugar content and vitamin C content were
0.898, 0.932 and 0.918. The mean errors of validation results were 0.35×105Pa, 0.32%Brix and 7mg/100g. The experimental results indicate that a hyperspectral imaging system based on a laser source can detect fruit quality effectively.
Character of Nd:GdVO4 laser operating at 1.34 μm with low Nd3+ doped concentrations
Show abstract
Three Nd:GdVO4 crystals with Nd3+doped concentrations of 0.1, 0.2 and 0.3 at% were involved in the experiment. Their laser characteristics at 1.34 μm were experimentally tested with a diode-end-pumped
configuration and a simple plane-parallel cavity. Maximum output powers of 7.3 W, 8.35 and 9.47 W were
achieved, respectively. The thermal stress resistances of these crystals were calculated according to the
experimental data.
Pulse behavior of a short pulse discharged TEA CO2 laser
Show abstract
The studies on a short pulsed TEA (Transversely Excited Atmospheric pressure) CO2 laser pumped by a magnetic pulse
exciter are reported. The exciter includes a magnetic pulse compression circuit, which compresses the pulse duration
below 100 ns. According to our experiments, the maximum output energy of a single pulse can be as high as 2.84 J and
the Full Width at Half Maximum (FWHM) of the laser pulse is 70ns approximately. The pulse shapes and characteristic
times are measured. The results indicate that the single pulse energy keeps a linear relation with the gas pressure and
charge voltage. And there is an optimized composition that the maximum output pulse energy or shortest pulse width can
be obtained. Based on this free oscillation laser, a tunable TEA CO2 laser is developed. Over 62 laser lines from 9.16 to
10.79μm have been obtained and the output pulse energy of 10P(20) line is 0.5 J.
Ytterbium-doped high power fiber lasers with fused fiber bundle combiner
Show abstract
Ytterbium (Yb3+)-doped high power fiber lasers are attractive because of high efficiency, high power and good beam
quality, which have many potential applications in telecommunication, machining and national defense. Most of the high
power Yb3+-doped double-clad (DC) fiber lasers use end pump technology, which is the conventional method to couple
pump lights into the inner cladding. However, this pump method is limited by the single laser diode's power and
brightness. While multimode fused fiber bundle combiner could combine multiplex individual laser diodes and it is
convenient for fabrication compared with side pumped technology. We reported a ytterbium-doped double-clad fiber
laser, one-end pumped by six 915 nm laser diodes combined by a multimode fused fiber bundle combiner. The combiner
fused splicing six fiber pigtails from diodes exhibited low-loss and high efficiency handling of 91%. We demonstrated that the fiber laser generates up to 20.5 W of continuous-wave (CW) output power at 1106 nm with a 22m long D-shape inner cladding ytterbium-doped fiber. The slope efficiency was about 75% and the quantum efficiency was up to 91%. We also demonstrated a high power fiber laser at 300W level pumped by a single 976nm laser diode, and the slope efficiency was nearly 80%.
Investigation of the dynamic process of high fluence femtosecond laser ablation of aluminum by ultrafast time-resolved shadowgraphy
Show abstract
The dynamic process of 800 nm high fluence femtosecond laser ablation of aluminum is revealed by ultrafast time-resolved shadowgraphs. Both single and multiple laser pulses at perpendicular or oblique incidence are employed in the experiment. It is demonstrated that femtosecond laser ablation of aluminum with a fluence of 40 J/cm2 is a complex process involving both photothermal and photomechanical mechanisms. For a single ablation pulse, the propagation direction of the ejected material remains normal to the target surface regardless of the incidence angle of the laser. For
the multiple pulses ablation with an oblique incidence angle, the propagation direction of the ejected material deviates
from the normal of the target surface gradually as the number of ablation pulses increases due to the topographic change
of the ablated region.
Ultrashort pulse laser ionization microscopy
Show abstract
Fundamental principles and advantages of the laser induced air ionization microcopy (LIAIM) and laser induced breakdown microscopy (LIBM) are introduced. Potential applications of these two new types of nonlinear imaging methods using ultrashort laser pulses in imaging both dielectric materials and bio-samples are demonstrated with some representative experimental results. Effects of different laser pulse widths on the discrimination power for laser-written microstructures inside transparent materials and the elemental composition are also investigated. It is shown that femtosecond laser induced ionization probe detects the variation of elemental composition of the sample materials with relatively higher contrast ratio, whereas the ionization probe generated by picosecond laser pulses is more sensitive to the material density or structural change. These observations can be well explained by the different roles of multi-photon ionization and avalanche ionization involved in material breakdown.
Highly efficient light trapping of metallic microstructures induced by femtosecond lasers
Jianjun Yang,
Yang Yang,
Xiaonong Zhu,
et al.
Show abstract
Microstructuring of NiTi alloy plates by 800 nm femtosecond lasers is investigated through the line-scribing experiment
in ambient air. It is found that some distinct surface structures can be generated by varying laser pulse energies and the
scan speeds of the samples. Very weak stray light is detected when
He-Ne laser beam is directed on the micro-structured
targets. The integrated reflectance measurements reveal that the light trapping of these structured metal surfaces can be
improved greatly, even up to 90%, within a large spectral range covering the ultraviolet, the visible and the mid-infrared.
It is expected that this result could have great potential applications in the designing of efficient energy transfer devices.
Filamentation and self-compression of femtosecond laser pulses in optical media
Show abstract
We have investigated the filamentation and self-compression of femtosecond laser pulses in different optical media such as argon gas and fused silica by employing a model developed in the frequency domain. In the case of fused silica, we investigate the nonlinear propagation of femtosecond laser pulses with central wavelengths of 800 nm and 1550 nm, which correspond to the normal group velocity dispersion (GVD) and anomalous GVD regimes, respectively. We have found that the duration of the laser pulse can be self-compressed into less than 10fs from 50 fs for a 1550 nm laser pulse. However, for an 800 nm laser pulse, the self-compressed pulse can only have a duration of about 26 fs. Nevertheless, in the case of 800 nm, by spectral analysis and control, we can obtain sub-5 fs pulses based on the self-guided filaments of femtosecond laser beams. This method avoids the difficulty of complete spectral phase compensation due to the considerable high-order chromatic dispersion.
Nano-aquarium with microfluidic structures fabricated by femtosecond laser direct writing for dynamic microorganism analysis
Show abstract
We demonstrate the fabrication of three-dimensional (3D) hollow microstructures embedded in photostructurable glass by a nonlinear multiphoton absorption process using a femtosecond (fs) laser. Fs laser direct writing followed by annealing and successive wet etching in dilute hydrofluoric (HF) acid solution resulted in the rapid manufacturing of microchips with 3-D hollow microstructures for the dynamic observation of living microorganisms in fresh water. The embedded microchannel structure enables us to analyze the continuous motion of Euglena gracilis and Cryptomonas. Such microchips, referred to as nano-aquariums realize the efficient and highly functional observation of microorganisms.
Study on the interaction between high power fiber laser and matter
Wei Li,
Yong Zhao,
Xi Chen,
et al.
Show abstract
With achievements in scientific fiber laser research, the experiment of fiber laser technology and interaction between high power fiber laser and matter was done. Through the experiment, many effects of it ware analyzed, the experimental of destroy landmine by the fiber laser was researched.
Laser acoustics in water induced by high power CO2 pulsed laser
Show abstract
Experimental study on laser generating acoustics in water has been performed using high power pulsed CO2 laser.
The influences of the laser parameters on the characteristics of the sound pulse, such as amplitude, spectra and peak
frequency of the sound pulse, efficiency of the energy conversion were investigated in detail. The results show that the
amplitude of the sound pulse increases with the energy exposed to water surface. The efficiency of the optoacoustic
energy conversion η is in the range of 0.31×10-6 to 1.65×10-6, and it increases with the laser energy. The spectra have two peaks which are 15.07 kHz and 53.40 kHz, and the sound energy is distributed mainly around 53.40 kHz. The shape of
the spectra is not variable with the laser energy, but the pressure of the peaks increases with deposited laser energy. The
exciting mechanism of laser acoustic in this experiment is the combination of thermoelastic and vaporization.
Thermodynamic analysis of the Nd:YAG disk laser with multiform pumping
Show abstract
In this paper, we demonstrate the thermodynamic effects of the Nd:YAG Disk laser by pumping and cooling approaches,
which is based on the theory of analytical thermal analysis. The thermal models are established to analyze the working
characteristics of the Nd:YAG disk crystal, and they match the actual working state of the disk laser crystal. The
analytical expressions for temperature field within Nd:YAG disk crystal are yielded by using a new approach to solve the
heat conduction equation of isotropic material. The analytical expression of thermal distribution of the Nd:YAG disk
crystal is obtained to analyze the thermal distortion field and additional optical path differences caused by heat in the
Nd:YAG disk crystal. In the end of this paper, a series of the numerical simulations are performed to demonstrate the
thermodynamic analysis of the Nd:YAG disk crystal in different methods of pumping and cooling. The numerical
simulation results match well with the academic outcomes on the whole.
Diffraction gratings ablated on lithium niobate single crystal by femtosecond pulses
Show abstract
The surface diffraction gratings on lithium niobate single crystal ablated by a femtosecond laser pulse at a wavelength of
800 nm have been investigated. The diffraction efficiencies of the gratings ablated with various parameters were
measured by He-Ne laser at a wavelength of 632.8 nm. The 1-order diffraction efficiencies of the gratings improve from
1.7% to 2.3% with the increase of ablation speed from 20μm/s to 200μm/s, and decrease from 1.9% to 1.3% with the
increase of pulse energy from 70nJ to 110nJ, respectively. The experimental and theoretical results show that the
diffraction efficiencies of gratings can be improved by increase of ablation speed and grating constant or decrease of pulse energy.
Highly stabilized laser intensity during ultra-short laser filamentation
Show abstract
In this work, we investigate the stability of the nitrogen fluorescence signal emitted by a femtosecond laser filament as
an example of a high order nonlinear optical process. It is found that the root-mean-square fluctuation of the fluorescence
signal emitted from the filament is less than 1 %. The corresponding estimated laser intensity fluctuation is as low as
0.14%, which is at least one order of magnitude lower than the input laser pulse power fluctuation. Further numerical
simulation has confirmed that the intensity clamping phenomenon is responsible for this observation. Since the intensity
clamping is an intrinsic property of filamentation phenomenon, it is expected that any intensity sensitive optical
interaction taking place inside filament could lead to highly stabilized outcome. This conclusion potentially affects
various applications of ultra-short laser filamentation.
The design of a laser beam performance test system
Show abstract
The design of laser beam performance test system is a technique consists of optics, mechanism, electricity, computer and
so on. The design and measure methods of the laser beam performance test system in this paper are according to the
ISO laser and laser-related equipment international standard (ISO 1146). This test system consists of laser energy
meter, oscilloscope, high speed photoelectric detector, CCD, laser attenuator, neutral attenuator, PCI image grabbing
card, focal optical system, beam analysis process software and so on. The laser beam performance parameters tested by
the system include spatial characteristic parameters, temporal characteristic parameters, laser output energy and so on.
Spatial characteristic parameters include beam spot two-dimensional distribution, light-intensity three-dimensional
distribution, beam divergence angle, beam direction stability and so on. Temporal characteristic parameters include
laser pulse width and repetition frequency. At last a laser was tested and the result was satisfied.
Influence of compound laser life-extension treatment on mechanical properties of key parts of pellet traveling grate
Show abstract
An new composite strengthening and prolongation technique was discussed on the key components of pellet traveling
grate, which are prone to thermal vibration fatigue, contact fatigue and wear resistance under the alternating high/low
temperature. CO2 laser remelting was used to subject the key components of pellet traveling grate, improving the
material's surface hardness, and the advanced surface treatment technique by utilizing intense laser shockwave was
adopt. The impact of residual compressive stress generated by laser shock processing on fatigue life of surface cracks was discussed, and laser shock could effectively alleviate the residual stress at the surface and significantly improve the fatigue life and anti-stress corrosion performance. The result shows that composite laser treatment could effectively close up and repair cracks.
Optical properties of morphology-controlled gold nanoparticles
Show abstract
Both linear and nonlinear optical properties of metal nanoparticles strongly depend on their particle sizes. Sizedependent
surface plasmon resonant absorption of gold nanoparticles was theoretically accessed using Mie scattering theory based on empirical optical absorption and TEM measurements, which allows to estimate the average size of gold nanoparticles with simple absorption measurement. The nonlinear optical properties of the gold nanoparticles were studied with Z-scan and forward degenerate four-wave mixing techniques.
Numerical study on mirror of high power laser with heatpipe cooling
Show abstract
Mirror surface of high power laser would be deformed by the pressure of the coolant in a liquid cooling mirror system. In
order to eliminate the impact of pressure and vibration of cooling water to the stability of the output beam, a cooling
mirror with heatpipe is designed. With the same structure and conditions, solid mirror, water cooling mirror and heat
pipe cooling mirror are simulated by ANSYS program. The time-varying thermal deformations of the group mirrors after
60s under the net heat absorption of 12W/cm2 are obtained. The maximal peak and valley difference value of mirror
surface deformation of solid mirror along Z-axis, water cooling mirror and heat pipe cooling mirror after 60s is 1.33μm,
0.845 μm and 0.1094 μm respectively.
Research on heat exchange performance of ultra-high power fast axial flow CO2 laser and design of the heat exchanger
Show abstract
The previous research on ultra-high power laser was mostly focused on discharge tubes and resonator. However,
little attention was focused on the heat exchange performance, which is also an essential technology to ensure the long
time stable work of the CO2 laser. The purpose of this paper is to characterize the heat exchange performance of CO2 laser and to supply the method of heat exchanger design. Considering the inner heat cycle and characteristics of the 10
KW fast axial flow CO2 laser which is under development, various types of heat exchangers were compared, rectangle
finned heat exchanger was chosen as the laser radiator, in light of the prominent heat transfer capacity and compact
structure. Further more, this paper also established the heat balance equation, calculated the heat transfer capacity. The
results indicate that the rectangle finned circle tube heat exchanger which has been chosen is suitable to 10 KW fast axial
flow CO2 laser.
Diode pumped Tm:YAP lasers of different doping concentrations
Show abstract
The experimental investigation on the Tm:YAP lasers with different thulium doped concentrations and specialized
crystal dimensions are concluded. The Tm:YAP samples were pumped by a laser diode array (LDA), with the centre
wavelength of 790 nm, and adopted in the end-pumped configuration. A maximum 5 W CW output of 5% Tm:YAP laser
was reported. Especially, we got a maximum 20 mW output power of 15% Tm:YAP with incident 18.93 W pump power,
which was the first demonstration of laser emission for Tm:YAP crystals with the doping concentration higher than 5
at.%. The influences of doping concentration and crystal dimension, the characteristics of absorption and emission spectrum and polarization were discussed. The optimization of laser structure was also analyzed.
Diode pumped thin slab solid-state lasers
Show abstract
Thermal effect is a serious problem in solid-state lasers. Because of superior thermal property which owed to high aspect ratio of laser crystal, solid-state lasers with thin slab configuration can be scaling to high output power with different laser crystal material and pump structure. In this paper, we present side-pumped passive Q-switched and acousto-optic Q-switched Nd: YAG lasers and end-pumped Tm: YAP lasers. We got a maximum 70W output power of passive Q-switched Nd: YAG laser with 220W pump power, which the pulse duration is around 10ns and the pulse repetition rate is higher than 10kHz. And 73W output power is got while pump power is 200W in acousto-optic Q-switched Nd: YAG lasers. Especially, we also applied the thin slab configuration to end pumped Tm: YAP laser and got a maximum 9.6W output power which the doping concentrations is 4% and cut by c-axis.
High power RF excited diffusively cooled all-metal slab waveguide CO2 laser
Show abstract
The common design of high power CO2 lasers is based on the fast gas flow to remove the heat produced in the
electrically gas discharge plasma, in this paper, we shall discussed the parameter design consideration for the high power
RF excited diffusively cooled slab waveguide laser, which including the RF power deposition density and RF discharge
longitudinal uniformity. Besides, a kilowatts RF excited diffusively cooled all-metal slab waveguide CO2 laser is presented, from this type of structure; a laser power output of 1475w was obtained and a maximum efficiency of over 13% was achieved.
Studies on high energy pulsed CO2 laser
Show abstract
The recent results on pulsed CO2 laser, including the effects of preionization structure, electrode profile, and discharge
circuit are reported. Two sizes of discharge gap, 70 mm and 100 mm were selected. For the 70 mm gap, lateral
preionization was used; for the 100 mm gap, preionization beneath the meshed electrode, and mixed preionization
beneath and beside the electrodes were all tested. Strong lateral discharge was found in the case of near-Rogowski
profile or Stappaerts profile, and strong central discharge was found in the case of Ernst profile. When the near-
Rogowski profiled electrode was paired with an Ernst profiled electrode, better performance was obtained. Discharge
distribution corresponding to the spark pins under the mesh grid was found obviously, which means that the uniformity
of preionization should be further improved. Small signal gain coefficient was measured to evaluate the discharge. For
the experimental setup with 70 mm discharge gap and 4 liters discharge volume, the highest small signal gain coefficient
was 2.94% cm-1. When a laser cavity was installed, the highest pulsed energy obtained from this setup was 169 J. When
the discharge volume was enlarged to 16 liters, pulsed laser energy up to 580 J was obtained.
Numerical analysis of high power ytterbium-doped segmented-cladding fiber amplifier
Show abstract
We analyze numerically an ytterbium-doped segmented-cladding fiber (SCF) for optical amplification. The analysis
combines a full-vector finite-element method with propagation rate equations to calculate mode-field distributions and
longitudinal power distribution. The results show that optimal parameters depend directly on the depletion position of the
pump power. With a typical ytterbium-ion concentration of 4.0×1025 ions/m3, an launched pump power of 5 W, and an input signal power of 1 μW, the maximum achievable gain is around 33 dB with an optimal fiber length of 0.6 m. The threshold pump power is about 500 mW for input signal power below 0.3 mW and the saturation output signal power is about the order of 300 mW at the pump power of 5 W. The results reveal that, by using appropriate pump power, a few meters of ytterbium-doped ultra-large-core SCF can provide much higher gain by its large core than that of a conventional ytterbium-doped fiber while maintaining the flexibility of length and dynamic range.
A novel method for square pulse generation using nonlinear amplifying loop mirror
Show abstract
In this paper, we theoretically present a novel method applying nonlinear amplifying loop mirror to generate
square pulse. From our analysis, the generated square pulse is steady and flat. We give the criteria for steady
power and point out that there would be a stable region around the certain steady power. With the steady power
given, the temporal width and other properties of square pulse will be determined. We also find that due to
the steady power and stable region, the laser could give a multi-square-pulse output by adjusting the controlling
light. An example of initially Gaussian pulse is discussed to support the idea. By adjusting transmission
characteristics of the nonlinear amplifying loop mirror we will get different steady power, and then we can
control power, temporal width and other properties of the generated square pulse by tuning the controlling light
and choosing proper optical components. We also give a restriction for choosing optical components.
The nonlinear dynamics of an FP laser under external optical injection
Show abstract
Multiple nonlinear states of a Fabry-Perot (FP) laser under external optical injection and their applications are
experimentally studied. The intensity noise of the FP laser has been demonstrated to be optimally suppressed under
injection locking state, and the comparison between stable locking range and noise suppression range at different
injection powers has been made. Photonic microwaves can be acquired at both period-one and period-two states. When
an external RF signal is added to the FP laser operated at period-one state, its nonlinear state is switched to period-two
state, which indicates the equivalence between external optical and electrical modulation added to the FP laser. At the
same time, the photonic microwave linewidth can be obviously narrowed as an effect of external RF modulation.
Control of the pulse duration in a diode-pumped doubly passively Q-switched Nd:YVO4 laser with Cr4+:YAG and GaAs saturable absorbers
Show abstract
Using both Cr4+:YAG and GaAs saturable absorbers in the same cavity, a diode-pumped doubly passively Q-switched
Nd:YVO4 laser is realized. Compared with the solely passively Q-switched laser Cr4+:YAG or GaAs, the pulse shape of doubly Q-switched laser is more symmetric and the pulse duration is compressed. The technique to control the pulse
duration has been studied. With different position of the saturable absorber, the pulse duration changes in the range from
41.8ns to 118ns at the pump power of 4.47W, respectively. A rate equation model is introduced to theoretically analyze
the results obtained in the experiment, in which the Gaussian spatial distribution of the intracavity photon density and the
longitudinal variation of the photon density are taken into account. The numerical calculations of the rate equations are
consistent with the experimental results.
Effect of transit time on characteristics of the output pulse in an actively Q-switched Nd:YVO4 laser with acoustic-optic modulator
Show abstract
By considering the AO switch as a low speed switch and the AO turnoff time including the transit time of the acousticwave
and the electronic turnoff time as well as the Gaussian spatial distribution of the intra-cavity photon density, the
coupled equations of a Laser-diode pumped actively Q-switched Nd:YVO4 laser with acoustic-optic modulator are
given. By changing the position of AO in the cavity for changing the transit time of the acoustic-wave, the effect of the
AO transit time on the characteristics of the output Q-switched pulse is obtained. It is show that the longer transit time
leads to the wider pulse duration. In the experiment, a laser-diode-pumped actively Q-switched Nd:YVO4 laser with
acoustic-optic modulator is realized, and the experimental results are in fair agreement with the numerical solutions.
Capillary Z-pinch discharge produced plasma EUV source
Show abstract
Extreme ultraviolet (EUV) radiation is seen as the most promising candidate for the next generation of lithography and semiconductor chip manufacturing for the 32nrn node and below. This paper elaborately describes the EUV source in our lab based on the capillary Z-pinch discharge produced plasma (DPP).
Sensor-controlled laser processing of polymers and compound materials
Show abstract
This report discusses the optimisation of laser materials processing of polymers and compound materials by employment
of smart sensors which measure laser parameters as well as processing progress online and deliver signals which are used
for instantaneous laser and motion control. The mutual interdependence between suitable laser parameters and given
mechanical, thermal and optical material properties is considered. Some examples of laser cutting, laser milling of
channels and holes with precisely defined depth as well as laser of welding are treated. Process simulation plays an
important part in finding the right adjustment of laser parameters as function of sample properties and processing aim.
Often laser parameters and sample changes have to be measured and controlled very fast between adjacent irradiations of
the sample by pulse sequences (up to about 100 KHz) or between repetition cycles of scanned cw lasers. The same
sensors measure and store the processing results and decide whether the sample finally fulfils all quality criteria. The
value of such laser processing units strongly depends on the smartness of the applied sensors and their interplay with the
laser as a tool.
Cooling of a pulsed energy-storage rep-rated Yb:YAG laser disk by heat sink
Show abstract
The thermal effect is one of the biggest obstacles that the solid laser heads into high power and high beam quality. The
characteristic of heat-storage mechanism and heat conduct behavior about the phase change material is studied in this
text. Inserting appropriate metal pieces or graphite can elevate the conduct coefficient of phage change material
effectively. Researches are performed on the cooling characteristics of the pulsed energy - storage rep-rated
large-aperture end-pumped Yb:YAG disk laser with non-uniform heat source by forced convection cooling in a narrow
passage and heat sink. Two cooling schemes are selected; they are forced convection cooling with water, heat sink with
phase change material. Numerical simulations are conducted to investigate the temperature and thermal stress
distributions of the laser disk. The calculation results show that the cooling scheme using phase change material heat
sink is the best, which may practicality applied.
Propagation of Gaussian beam in self-defocusing photovoltaic photorefractive nonlinear crystal of LiNbO3:Fe
Show abstract
We investigate experimentally the propagation of Gaussian beam in self-defocusing photovoltaic
photorefractive nonlinear crystal of iron-doped lithium niobate. In steady-state, the propagating beam
in the low-refractive-index optical channel written by the beam itself is affected mostly by linear
diffraction and anisotropic divergence of the saturated negative lenslike effect. And the latter affects the
incident beam with convergent wavefront much more than that with divergent wavefront. In the case of
the incident beam with the convergent wavefront, the angular width of the spatial spectrum of the
output beam decreases along with the size of the output beam. We believe that the phase-type spatial
filtering of the funnel-type low-refractive-index optical channel written by the propagating beam itself
causes the results.
Thermal diffusivity of light-emitting material determination by photoacoustic piezoelectric technique
Show abstract
The theory of Photoacoustic Piezoelectric (PAPE) technique has been developed for two-layered model.
An analytical expression for the phase of output voltage versus modulation frequency has been
obtained. The thermal diffusivity of Phosphor/PVA light-emitting composite material has been studied.
PAPE technique has been employed successfully for investigating the thermal diffusivity of
two-layered materials.
Drastically reducing circular birefringence induced depolarization in pre-temperature compensation design in high power Faraday isolators
Show abstract
A new Pre-Temperature compensation design of Faraday isolators is proposed, for the first time to our knowledge. And
depolarization induced by linear birefringence and circular birefringence in this kind of Faraday Isolator is investigated.
For compare, depolarization in conventional Faraday isolators is also given. The results show that depolarization induced
by linear birefringence has no difference between conventional design and compensation design of isolators, and
depolarization induced by circular birefringence in Pre-Temperature compensation design is greatly reduced, which
becomes beam-radius-independent, and can be neglected when compared to depolarization induced by linear birefringence.
Nonlinear optical semiconductor nanocrystals and their photonic applications
Qiguang Yang,
Jaetae Seo,
William Yu,
et al.
Show abstract
Nonlinear optical materials with large third-order nonlinear susceptibilities and appropriate response time have attracted
great interests recently because of their potential applications of optical computing, ultrafast switching, optical power
limiting, and group velocity manipulation. Among nonlinear optical materials, semiconductor nanocrystals, metal
nanoparticles, and organic materials have been intensively studied since their nonlinear optical properties may be tuned by
varying their sizes and surface/interface environments. Recently, we investigated the third-order nonlinear optical
properties of semiconductor nanocrystals both theoretically and experimentally. The possible physical limitation of the
third-order nonlinear susceptibility of typical semiconductor nanocrystal as well as the ways to optimize its nonlinearity
has been studied. Experimental measurements have been compared with theoretical calculations on linear and nonlinear optical properties of cadmium chalcogenide semiconductor nanocrystals for the photonic applications of optical switching, optical power limiting, and group velocity manipulation.
Diode-side-pumped TEM00 mode Nd:YAG laser with plane-convex resonator
Show abstract
We demonstrate a diode-side-pumped TEM00 mode Nd:YAG laser with plane-convex resonator. The design of plane-convex resonator increases the loss of higher-order mode and the volume of fundamental mode, so the efficient
mode match between the pump light and the oscillating light and good beam quality is obtained. The continuous wave
output power of 13W is generated with M2x=1.33 and M2y=1.31. The 9W average output power of acousto-optically Q-switched laser with M2x=1.29 and M2y=1.27 is also achieved. When the Q-switching repetition rate is 10kHz, pulse width is 240ns with peak power of 3.8kW.
Experimental research of pulsed discharge in oxygen mixtures
Show abstract
The pulsed discharge in oxygen and its mixtures to produce singlet delta oxygen has been studied experimentally at gas
pressure of 30~ 936mBar. As singlet sigma state of oxygen O2(b1Σg+) and atomic oxygen O have great influence on the
yield of singlet delta oxygen O2(a1▵g), the visible spectrum of O2(b1Σg+) at 762nm and O at 778nm have been measured,
and the effects of argon, helium and carbon monoxide have been discussed. The electric stability was better in O2-He
than in O2-Ar mixtures, while it could be increased quickly with a small amount of CO. In O2-He mixtures more oxygen were decomposed than in O2-Ar mixtures, while adding CO the decomposition was reduced, the amount of atomic
oxygen was decreased, and the O2(b1Σg+) was increased comparatively. The time-resolved spectrum of the plasma has also been measured. The life-time of atomic oxygen was longer than O2(b1Σg+)'s, and it could be shorten with argon.