Proceedings Volume 7582

Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IX

Peter E. Powers
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Proceedings Volume 7582

Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications IX

Peter E. Powers
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 17 February 2010
Contents: 12 Sessions, 49 Papers, 0 Presentations
Conference: SPIE LASE 2010
Volume Number: 7582

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7582
  • Visible and UV Lasers: Joint Session with Conferences 7578 and 7580
  • Visible Sources
  • Ultrafast Nonlinear Devices and Applications I
  • Optical Parametric Devices
  • Nonlinear Optics for Spectroscopic Applications
  • Nonlinear Fiber Devices and Applications
  • Terahertz Generation
  • Engineered Nonlinear Optics
  • Ultrafast Nonlinear Devices and Applications II
  • Nonlinear Materials and Characterization
  • Poster Session
Front Matter: Volume 7582
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Front Matter: Volume 7582
This PDF file contains the front matter associated with SPIE Proceedings Volume 7582, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Visible and UV Lasers: Joint Session with Conferences 7578 and 7580
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Highly efficient and compact microchip green laser source for mobile projectors
John Khaydarov, Stepan Essaian, Greg Nemet, et al.
Recent developments in compact projectors sparked interest in light sources for these applications. While RGB lasers offer advantages, a viable green laser platform has been difficult to realize. In this work, we demonstrate a novel green laser source, based on a monolithic cavity microchip laser platform. The use of highly efficient, periodically poled MgOdoped Lithium Niobate (PPMgOLN) as the nonlinear frequency doubler allows obtaining a significant increase in the overall efficiency of the green microchip laser. Specifically, we demonstrate 50-150mW green output with wall-plug efficiency exceeding 10% in the temperature range over 40°C. We discuss a compact package for this laser source with volume less than 0.4cm3.
High-power green light generation by second harmonic generation of single-frequency tapered diode lasers
We demonstrate the generation of high power (>1.5W) and single-frequency green light by single-pass second harmonic generation of a high power tapered diode laser. The tapered diode laser consists of a DBR grating for wavelength selectivity, a ridge section and a tapered section. The DBR tapered laser emits in excess of 9 W single-frequency output power with a good beam quality. The output from the tapered diode laser is frequency doubled using periodically poled MgO:LiNbO3. We investigate the modulation potential of the green light and improve the modulation depth from 1:4 to 1:50.
Visible Sources
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Compact module of a frequency-doubled, CW diode laser with an output power of more than 500 mW at 531 nm and a beam quality of less than 1.3
J. Wueppen, E. Pawlowski, M. Traub, et al.
We present a compact module, emitting nearly diffraction limited green laser light at 531 nm at an average output power of more than 500 mW. As pump source for the second harmonic generation a DBR tapered laser with a total length of 6 mm was used. The RW section had a length of 2 mm including a 1 mm long passive DBR section. The devices were mounted p-side up on a copper block. For this mounting scheme, the device reaches up to 7 W maximal output power. At the power level of about 3.8 W used in the presented experiment, a wavelength of 1062.6 nm with a line-width below 0.02 nm (FWHM) was determined. More than 80% of the emitted power is originated within the central lobe of the beam waist profile illustrating the nearly diffraction limited beam quality. Using a 30mm long MgO-doped periodically poled LiNbO3 bulk crystal, the second harmonic wave is generated in a single-pass setup. Due to precise alignment and beam shaping based on the results of numerical simulations and a properly temperature control of the PPLN crystal, a maximum optical conversion efficiency of more than 14% (3.7%/W) was achieved. The fluctuation of the output power is far below 1%.
Efficient green lasers for high-resolution scanning micro-projector displays
Vikram Bhatia, Anthony S. Bauco, Hassan M. Oubei, et al.
Laser-based projectors are gaining increased acceptance in mobile device market due to their low power consumption, superior image quality and small size. The basic configuration of such micro-projectors is a miniature mirror that creates an image by raster scanning the collinear red, blue and green laser beams that are individually modulated on a pixel-bypixel basis. The image resolution of these displays can be limited by the modulation bandwidth of the laser sources, and the modulation speed of the green laser has been one of the key limitations in the development of these displays. We will discuss how this limitation is fundamental to the architecture of many laser designs and then present a green laser configuration which overcomes these difficulties. In this green laser architecture infra-red light from a distributed Bragg-reflector (DBR) laser diode undergoes conversion to green light in a waveguided second harmonic generator (SHG) crystal. The direct doubling in a single pass through the SHG crystal allows the device to operate at the large modulation bandwidth of the DBR laser. We demonstrate that the resultant product has a small footprint (<0.7 cc envelope volume), high efficiency (>9% electrical-to-optical conversion) and large modulation bandwidth (>100 MHz).
Simultaneous blue and red light generation with birefringent phase matching
Kentaro Miyata, Nobuhiro Umemura, Kiyoshi Kato
Several nonlinear crystals have been found to be simultaneously birefringent phase-matchable for two different upconversions in the blue and red ranges by using a Nd:YAG laser at 1.0642 μm and a parametric oscillator pumped by its second harmonic. The simultaneous phase-matching configurations and the corresponding tuning characteristics with some currently available nonlinear materials are discussed in detail.
High-performance at low cost: the challenge manufacturing frequency doubled green semiconductor lasers for mass markets
T. Hoefer, M. Schmitt, T. Schwarz, et al.
Laser projection arising as a new application in the consumer market has been the driving force for OSRAM Opto Semiconductors to develop a frequency doubled semiconductor laser and the production technology necessary to make the complexity of an advanced laser system affordable. Optically pumped frequency doubled semiconductor lasers provide an ideal platform to serve the laser projection application. Based on this scalable technology, we developed a 50 mW green laser comprising all the properties that can be expected from a high performance laser: Excellent beam quality and low noise, high speed modulation, good efficiency and long life time. More than that, the package is very compact (<0.4 cm3) and may be operated passively cooled at up to 60°C. Managing lasing wavelength and controlling phase matching conditions have been major design considerations. We will describe the key characteristics of the green laser, and will also present results from reliability testing and production monitoring.
Ultrafast Nonlinear Devices and Applications I
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Modeling of optical frequency comb generation in whispering gallery mode resonators and limiting effects
Yanne K. Chembo, Nan Yu
We report a detailed study about the various physical mechanisms that may limit the spectral span of optical frequency combs generated with whispering gallery mode resonators. We developed a modal expansion model able to track the individual dynamics of the various modes, and identify the key parameters determining the comb spectral features. We show that, although the walk-off between the dispersive WGM eigenfrequency distribution and the ideal equidistant comb is the main limiting factor, other phenomena such as modal confinement, material absorption, and modal overlap may also play an important role in extending the comb span.
White light generation and pulse compression with a Ti:Sapphire high energy oscillator
220-nJ, 42-fs, 5.25-MHz pulses from a long-cavity Ti:Sapphire chirped pulse oscillator were spectrally broadened by nonlinear propagation in a Sapphire plate. The chirp was subsequently compensated with dispersive mirrors. After farfield spatial filtering the compressor delivered 80-nJ, sub-15-fs pulses at 5.25 MHz. A novel 500-nJ Oscillator has been developed in order to investigate the energy-scaling potential of this compression scheme. 16-fs 130-nJ compressed pulses were obtained with this source. A second compression stage has been calculated and designed in order to reduce the pulse duration down to < 10 fs.
Tunable broadband optical generation via giant Rabi shifting in micro-plasmas
R. Compton, A. Filin, D. A. Romanov, et al.
Broadband, coherent radiation in the optical frequency range is generated using micro-plasma channels in atmospheric gases in a pump-probe experiment. A micro-plasma medium is created in a gas by a focused intense femtosecond pump pulse. A picosecond probe pulse then interacts with this micro-plasma channel, producing broad, coherent sidebands that are associated with luminescence lines and are red- and blue-shifted with respect to the laser carrier frequency. These sidebands originate from the induced Rabi oscillations between pairs of excited states that are coupled by the probe pulse. These excited states become populated in the process of plasma cooling. Thus, the sideband radiation intensity tracks the micro-plasma evolution. The sidebands incorporate Rabi shifts corresponding to varying value of the electric field magnitude in the probe pulse: this makes them broad and malleable to tuning. The intensity of the probe beam ~ 1010 W cm-2, creates a maximum sideband shift of > 90 meV from the carrier frequency, resulting in an effective bandwidth of 200 meV. The sidebands may be effectively controlled by the intensity and temporal profile of the probe pulse. The giant Rabi shift is both tunable and coherent over a wide range of frequencies and over a wide range of atomic transitions. The fact that the coherence is observed in a micro plasma demonstrates that Rabi cycling is possible at high temperature with moderately high laser intensities (1010 W cm-2) as long as transitions close to the driving frequency (▵ ~ 2% ωc) are available.
Optical Parametric Devices
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LiInSe[sub]2[/sub] nanosecond optical parametric oscillator tunable from 4.7 to 8.7 µm
LiInSe2 is one of the few (in the meanwhile 6) non-oxide nonlinear crystals whose band-gap (2.86 eV) and transparency enabled in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump wavelength of 1064 nm. However, the first such demonstration was limited to the 3.34-3.82 μm spectral range with a maximum idler energy of 92 μJ at 3.457 μm for a repetition rate of 10 Hz. Now we achieved broadly tunable operation, from 4.7 to 8.7 μm, reaching maximum idler pulse energy of 282 μJ at 6.514 μm, at a repetition rate of 100 Hz (~28 mW of average power).
6.3 Watt single frequency CW source at 780nm based on frequency conversion of a fiber laser
Angus Henderson, Peter Esquinasi, Mikhail Levin
6.3 Watts of single frequency output has been generated by single-pass frequency-doubling of a fiber-laser-pumped CW OPO. 40% efficient frequency doubling was demonstrated by focusing 15.8 Watts of 1560nm input into an 80mm length MgO:PPLN crystal. The single frequency 1560nm input was generated as the resonant signal wavelength in a CW OPO based on MgO:PPLN. The OPO was pumped by a 30 Watt Ytterbium-doped fiber laser operating at 1064nm, with a spectral bandwidth of ~0.6nm.
Synchronously pumped at 1064 nm OPO based on CdSiP[sub]2[/sub] for generation of high-power picosecond pulses in the mid-infrared near 6.4 µm
Andre Peremans, Dan Lis, Francesca Cecchet, et al.
The recently developed chalcopyrite CdSiP2 is employed in a picosecond, 90°-phase-matched synchronously pumped optical parametric oscillator pumped at 1064 nm, to produce quasi-steady-state idler pulses near 6.4 μm with an energy as high as 2.8 μJ at 100 MHz. The train of 2 μs long macropulses, each consisting of 200 (picosecond) pulses, follows at a repetition rate of 25 Hz. This corresponds to an average power of 14 mW. The pump depletion (conversion efficiency) exceeds 40%. Without intracavity etalon, the 12.6 ps long mid-IR micropulses have a spectral width of 240 GHz.
A high peak power, compact, eye-safe optical parametric oscillator system
We report the operation of an optical parametric oscillator (OPO) at 1574 nm using KTP, with output peak power of more than 5 megawatts, output pulse energy of up to 30 mJ per pulse, pulse width of less than 6 nanoseconds at full width half maximum (FWHM) and operating frequency of 30 Hz. The OPO was pumped by a diode pumped Nd:YAG Q-switched laser, with pump energy of about 95 mJ and pulse width of approximately 7 ns. The conversion efficiency from 1064 nm Nd:YAG laser to OPO output at 1574 nm is more than 30%. The whole system including the Nd:YAG laser was compactly packed inside a case measuring 15" x 9" x 5.3". The complete OPO system was tested over an operating temperature range of -20 °C to +35 °C and a storage temperature range of -40 °C to +50 °C without significant power or performance variations, which makes it suitable for field operation.
Excitation of individual Raman Stokes lines of up-to ninth order using rectangular shaped optical pulses at 530 nm
Kang Kang Chen, Shaif-ul Alam, Christophe A. Codemard, et al.
We demonstrate the selective excitation of Raman Stokes lines of up-to 9th order with relatively high extinction ratio pumped by rectangular shaped optical pulses at 530 nm of 100 ns duration. The rectangular shaped optical pulses at 530 nm were generated by frequency doubling of an adaptively pulse shaped fiber MOPA operating at 1060 nm. This kind of pulse shape is optimal for frequency conversion since all parts of the pulse experiences the same Raman gain. Therefore, it is possible for a pulse to transfer all of its energy through sequential frequency Raman shifts to successive order Stokes components. Consequently, by adjusting the pump power it is possible to achieve selective excitation of the Raman shift with little residual pump powers. Here, we have achieved extinction ratio as much as 15 dB from successive Stokes lines by coupling 530 nm light in a 1 km long Pirelli Freelight fiber. In addition, we were able to obtain up-to 9th order Stokes shift by launching 5 W of average pump power to the Raman gain medium. Maximum Stokes shifted power of 54 mW was recorded for a launched pump power of 5W. We attribute this to the large background loss of silica fibre in the visible region.
Nonlinear Optics for Spectroscopic Applications
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Tunable nonlinear-optical devices for laser-spectroscopic sensing
Brian J. Orr, Yabai He
Generating coherent light via nonlinear optics drives many of our laser-spectroscopic sensing applications. For instance, narrowband tunable pulsed optical parametric oscillators (OPOs) controlled by injection seeding are used extensively for cavity-ringdown and coherent-Raman spectroscopies. In a high-precision OPO-based spectroscopic system, we employ a long-pulse (>25 ns) pump laser with optical-heterodyne diagnostics to log instantaneous frequency and chirp on a pulseby- pulse basis. In other work, we use photorefractive media for narrowband wavelength control of tunable diode lasers and pulsed OPOs. Additional prospective spectroscopic applications of tunable pulsed OPOs are also considered.
Seeded nanosecond optical parametric generator for trace gas measurements
Kenji Numata, Steve Li, Haris Riris, et al.
We report on the development effort of a nanosecond-pulsed seeded optical parametric generator (OPG) for remote trace gas measurements. The seeded OPG output light is single frequency with high spectral purity and is widely tunable both at 1600nm and 3300nm with an optical-optical conversion efficiency of ~40%. We demonstrated simultaneous tuning over the methane (CH4) absorption line at idler wavelength, 3270.4nm, and carbon dioxide (CO2) absorption line at signal wavelength, 1578.2nm. In this paper, we will also discuss open-path atmospheric measurements with this newly developed laser source.
Filament-based stimulated Raman spectroscopy
J. H. Odhner, D. A. Romanov, R. J. Levis
A new multiplexed stimulated Raman spectroscopic technique encompassing a single-shot spectral measurement range of over 3900 cm-1 is presented. Impulsive excitation of all Raman active vibrational modes present in a medium is achieved by self-compression of a laser pulse undergoing filamentation in air, creating coherent vibrational wave-packets. These wave-packets create a macroscopic polarization of the medium that imparts sidebands on a delayed narrowband probe pulse. The background-free measurement of impulsively excited Raman modes in gas-phase N2, O2, H2, CO2, toluene, ammonia, and chloroform with a spectral resolution of 25 cm-1 is presented.
Generation of quasi-continuous wave 389-nm coherent light by frequency doubling of a Ti:sapphire laser for nuclear spin polarization of [sup]3[/sup]He atoms
Shingo Maeda, Hiroshi Morioka, Tatsuya Ohira, et al.
Magnetic Resonance Imaging based on the hyperpolarized helium-3 (3He) gas has been attracted as a non-destructive testing technique for the porous media and the medical imaging. In order to produce nuclear spin polarization of 3He, optical pumping is the efficient way using a resonant line. However, there is no resonant light source to the line from the ground state of 3He. Then, we have been focusing on the nuclear spin polarization in a discharge cell using the metastability exchange optical pumping (MEOP) technique. We aim at the optical transition 23S1→23P0 at λ=389nm that has never been investigated for the polarization. Therefore, at first, we developed a single-frequency 389-nm coherent light source based on the second harmonic generation of a single-frequency 778-nm continuous-wave Ti:sapphire laser light with a BiB3O6 (BiBO) nonlinear crystal in an external cavity for the enhancement. As a result, we obtained the 389- nm output radiation with the high conversion efficiency of 56%. Additionally, we also demonstrated the frequency doubling of a quasi-continuous wave Ti:sapphire laser for the optical pumping of multiple optical transitions.
Continuous-wave optical parametric oscillators on their way to the terahertz range
Rosita Sowade, Ingo Breunig, Jens Kiessling, et al.
Continuous-wave optical parametric oscillators (OPOs) are known to be working horses for spectroscopy in the near- and mid-infrared. However, strong absorption in nonlinear media like lithium niobate complicates the generation of far-infrared light. This absorption leads to pump thresholds vastly exceeding the power of standard pump lasers. Our first approach was, therefore, to combine the established technique of photomixing with optical parametric oscillators. Here, two OPOs provide one wave each, with a tunable difference frequency. These waves are combined to a beat signal as a source for photomixers. Terahertz radiation between 0.065 and 1.018 THz is generated with powers in the order of nanowatts. To overcome the upper frequency limit of the opto-electronic photomixers, terahertz generation has to rely entirely on optical methods. Our all-optical approach, getting around the high thresholds for terahertz generation, is based on cascaded nonlinear processes: the resonantly enhanced signal field, generated in the primary parametric process, is intense enough to act as the pump for a secondary process, creating idler waves with frequencies in the terahertz regime. The latter ones are monochromatic and tunable with detected powers of more than 2 μW at 1.35 THz. Thus, continuous-wave optical parametric oscillators have entered the field of terahertz photonics.
Nonlinear Fiber Devices and Applications
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Bound states of dissipative solitons in optical fiber systems
In this paper we investigate the interaction between solitary-plain pulses (SP) of the quintic CGLE modified, which describes the soliton behaviour in the presence of spectral filtering, linear and nonlinear gains, and selffrequency shift (intrapulse Raman scattering). In particular, we look for a clear understanding of fundamental properties of the bound sates, especially as concerns their stability. We use the interaction plane (distancephase difference) to analyze the dynamics of the two soliton system. We have found stable BS's of plain pulses when the phase difference between them is π / 2 + ▵, and ▵ is a quantity that depends on a selffrequency shift coefficient.
Extraction of a single soliton from a bunch of solitons generated by pulse breakup
Pulses propagating in the fiber with anomalous dispersion are broken up to the bunch of soliton. The extraction of an individual soliton from the bunch can be used for soliton generation and also for investigation of the process of the soliton formation. In this work we experimentally demonstrate that the NOLM allows extraction of an individual soliton. Earlier we have shown numerically that the NOLM has high transmission for the solitons with a range of durations while solitons with shorter and longer durations are rejected. The range of the durations with high transmission depends on the NOLM length and also can be moved by amplification of solitons before entering to the NOLM. In the experiment we launched 25-ps pulses with about 10 W of power to the 500-m single mode fiber with dispersion equal to 20 ps/nm-km. As a result of the pulse breakup, a bunch of solitons is formed at the fiber output. The resulting solitons are launched to the EDFA and then to the NOLM made from the 40-m of the same fiber. The NOLM parameters are adjusted to transmit the highest soliton in the bunch (about 50 W of power and 1 ps of duration according to theoretical estimations). In the experiment we detected at the NOLM output a single pulse with duration of 1.46 ps and autocorrelation function similar to that of the soliton. When a 1-km fiber was attached to the NOLM at the fiber output we detected a soliton with duration of 0.9 ps.
Self-focusing in gain-guided optical fibers and pulse propagation characteristics
We simulate the spatio-temporal pulse propagation in gain-guided (GG) optical fibers. As the pulse propagates and has sufficient energy it will focus quickly in the transverse spatial direction, and eventually collapse into a filament. The pulse is coupled into a single mode fiber to investigate its transmission characteristics.
Monolithic high SBS threshold pulsed fiber laser and frequency doubling for LIDAR and remote sensing spectroscopy
Wei Shi, Eliot B. Petersen, Dan T. Nguyen, et al.
We report a monolithic high SBS-threshold pulsed fiber laser in MOPA for longer nanosecond pulses with transformlimited linewidth. By using a single mode polarization-maintaining large core 25 μm highly Er/Yb co-doped phosphate fiber in the power amplifier stage, we have achieved the highest peak power of 1.2 kW at 1530 nm for 105 ns pulses with transform-limited linewidth, and with a corresponding pulse energy of about 0.126 mJ. The achieved high-energy pulses were frequency doubled by using a commercial periodically poled lithium niobate (PPLN) crystal, and the highest SHG peak power of 271 W has been achieved for the SHG pulses at 765 nm.
Experimental demonstration of fiber optical parametric chirped-pulse amplification
Yue Zhou, Kim K. Y. Cheung, P. C. Chui, et al.
A fiber optical parametric chirped-pulse amplifier (FOPCPA) is experimentally demonstrated. A 1.76 ps signal at 1542 nm with a peak power of 20 mW is broadened to 40 ps, and then amplified by a 100-ps pulsed pump at 1560 nm. The corresponding idler at 1578 nm is generated as the FOPCPA output. The same medium used to stretch the signal is deployed to compress the idler to 3.8 ps, and another spool of fiber is deployed to further compress the idler to 1.87 ps. The peak power of the compressed idler is 2 W, which corresponds to a gain of 20 dB.
Far-UV solid state lasers for semiconductor processing
The wavelength region between 190 and 200 nm is especially relevant to semiconductor manufacturing. In contrast to ArF excimer lasers, frequency up-converted solid-state lasers offer tuning, coherence and beam quality characteristics that are essential to high performance semiconductor processing. This paper reviews various methodologies for implementing pulsed non-linear optical interactions in this wavelength region given a wide range of laser operating formats and describes the utilization of these sources for the specific semiconductor applications of interference lithography and photoresist materials studies.
Terahertz Generation
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Single-frequency pulsed fiber lasers at ~1.5 µm and fiber-based narrow linewidth THz sources
Wei Shi, Eliot B. Petersen, Dan T. Nguyen, et al.
We have implemented monolithic narrow linewidth single-mode single-frequency pulsed fiber lasers in master oscillator and power amplifier (MOPA) configuration based on highly Er/Yb co-doped phosphate fiber with core size of 25 μm. The narrow linewidth pulsed fiber laser seed has been achieved by directly modulating single-frequency CW fiber laser. An arbitrary waveform generator (AWG) was used to pre-shape the pulse shapes in order to avoid the pulse distortion and the dynamic gain saturation in the cascade fiber amplifiers. Based on the newly developed large core single-mode highly Er/Yb co-doped phosphate fiber in the power amplifier stage, the peak power of single-mode pulses can be scaled to more than 100 kW with transform-limited linewidth and diffraction-limited beam quality. These high power narrow linewidth single-mode fiber laser pulses have been successfully used to generate coherent THz waves based on difference-frequency generation (DFG) in GaSe crystal. The single-pass generated THz peak power can reach 0.12 W. Moreover, we have observed the external cavity enhancement of DFG THz generation by using ZnGeP2 for the first time, and implemented a high spectral resolution THz spectrometer based on the developed fiber-based tunable narrow linewidth THz source.
Enhancement of optics-to-THz conversion efficiency by metallic slot waveguides
A metallic slot waveguide, with a dielectric strip embedded within, is investigated for the purpose of enhancing the optics-to-THz conversion efficiency using the difference-frequency generation (DFG) process. To describe the frequency conversion process in such lossy waveguides, a fully-vectorial coupled-mode theory is developed. Using the coupled-mode theory, we outline the basic theoretical requirements for efficient frequency conversion, which include the needs to achieve large coupling coefficients, phase matching, and low propagation loss for both the optical and THz waves. Following these requirements, a metallic waveguide is designed by considering the trade-off between modal confinement and propagation loss. Our numerical calculation shows that the conversion efficiency in these waveguide structures can be more than one order of magnitude larger than what has been achieved using dielectric waveguides. Based on the distinct impact of the slot width on the optical and THz modal dispersion, we propose a two-step method to realize the phase matching for general pump wavelengths.
Terahertz and optical frequency mixing in semiconductor quantum-wells
Yun-Shik Lee, A. D. Jameson, J. L. Tomaino, et al.
The exciton binding energy in GaAs-based quantum-well (QW) structures is in the range of ~10 meV, which falls in the THz regime. We have conducted a time-resolved study to observe the resonant interactions of strong narrowband THz pulses with coherent excitons in QWs, where the THz radiation is tuned near the 1s-2p intraexciton transition and the THz pulse duration (~3 ps) is comparable with the exciton dephasing time. The system of interest contains ten highquality 12-nm-wide GaAs QWs separated by 16-nm-wide Al 0.3Ga 0.7As barriers. The strong and narrowband THz pulses were generated by two linearly-chirped and orthogonally-polarized optical pulses via type-II difference-frequency generation in a 1-mm ZnTe crystal. The peak amplitude of the THz fields reached ~10 kV/cm. The strong THz fields coupled the 1s and 2p exciton states, producing nonstationary dressed states. An ultrafast optical probe was employed to observe the time-evolution of the dressed states of the 1s exciton level. The experimental observations show clear signs of strong coupling between THz light and excitons and subsequent ultrafast dynamics of excitonic quantum coherence. As a consequence, we demonstrate frequency conversion between optical and THz pulses induced by nonlinear interactions of the THz pulses with excitons in semiconductor QWs.
THz-wave generation inside a high-finesse ring-cavity OPO pumped by a fiber laser
Substantial improvement in the efficiency of photonic THz-wave generation via frequency downconversion results from resonant cavity enhancement. Previously, efficient THz wave generation was demonstrated at 2.8 THz by difference frequency mixing between resonating signal and idler waves of the linear-cavity type-II-phase-matched PPLN optical parametric oscillator (OPO). We present a new, simplified approach to resonantly-enhanced THz-wave generation in periodic GaAs, featuring (i) ring, instead of linear, OPO cavity with much higher finesse, (ii) type-0, instead of type-IIphase- matched PPLN crystal as a gain medium, resulting in much lower OPO threshold, (iii) a compact picosecond 1064-nm fiber laser as a pump source, and (iv) the use of a thin intracavity etalon with a free spectral range equal to the desired THz output frequency. 2.1 μm anti-reflection coated stacks of optically contacted GaAs wafers (OC-GaAs) and diffusion bonded GaAs wafers (DB-GaAs) with periodic-inversion were placed in the second OPO focal plane for intracavity THz generation. Narrowband output in the range 1.4 - 3 THz was produced with more than 130 microwatts of average power at 1.5 THz using 6.6 W of average pump power. The demonstrated approach can be extended to generate 1-10 mW of THz output in a compact setup by optimizing the OPO PPLN crystal length and optimizing spectral characteristics of the fiber pump laser and OPO.
Broadly tunable terahertz source
Peter E. Powers, Kevan Kramb, Joseph W. Haus
We present the results of a terahertz (THz) source based on difference frequency generation (DFG) that tunes seamlessly from 1.4 to 13.3 THz. The outputs from two seeded periodically poled lithium niobate (PPLN) optical parametric generators (OPGs) are mixed in a DAST crystal to generate the THz frequencies. The OPG's have ~1 nsec pulse duration and an output energy of approximately 200 μJ. The corresponding high peak intensities in the DAST crystal leads to appreciable conversion efficiency such that a room temperature pyro-electric detector is used to measure the THz signal. In one of the OPGs a continuously varying periodicity PPLN crystal is used to tune the output wavelength by translating the crystal. The crystal position and seed laser are computer-controlled and synchronized such that any wavelength within the seed laser's tuning range is randomly accessible, and hence any THz difference frequency between the two seed lasers is also randomly accessible. Phase matching in DAST requires the DFG inputs to have the same polarization. We demonstrate a scheme where the output of one of the OPGs is sent through the second OPG such that the two beams are collinear with the same polarization without using a beam splitter.
Engineered Nonlinear Optics
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Periodically poled silicon
Nick K. Hon, Kevin K. Tsia, Daniel R. Solli, et al.
Bulk centrosymmetric silicon lacks second-order optical nonlinearity χ(2) - a foundational component of nonlinear optics. Here, we propose a new class of photonic device which enables χ(2) as well as quasi-phase matching based on periodic stress fields in silicon - periodically-poled silicon (PePSi). This concept adds the periodic poling capability to silicon photonics, and allows the excellent crystal quality and advanced manufacturing capabilities of silicon to be harnessed for devices based on χ(2)) effects. The concept can also be simply achieved by having periodic arrangement of stressed thin films along a silicon waveguide. As an example of the utility, we present simulations showing that mid-wave infrared radiation can be efficiently generated through difference frequency generation from near-infrared with a conversion efficiency of 50% based on χ(2) values measurements for strained silicon reported in the literature [Jacobson et al. Nature 441, 199 (2006)]. The use of PePSi for frequency conversion can also be extended to terahertz generation. With integrated piezoelectric material, dynamically control of χ(2)nonlinearity in PePSi waveguide may also be achieved. The successful realization of PePSi based devices depends on the strength of the stress induced χ(2) in silicon. Presently, there exists a significant discrepancy in the literature between the theoretical and experimentally measured values. We present a simple theoretical model that produces result consistent with prior theoretical works and use this model to identify possible reasons for this discrepancy.
Polarization effects and fiber-laser-pumping of a 2-µm-pumped OP-GaAs OPO
Gallium arsenide combines a large nonlinear coefficient, a good thermal conductivity, excellent mechanical properties, and a wide transparency range (0.9-17μm). Improvement in hybrid vapour phase epitaxy growing techniques of quasiphase- matched orientation-patterned GaAs (OP-GaAs) allows larger sample thickness and permits efficient operation as a mid-infrared optical parametric oscillator at Watt-level average output powers. Especially its low absorption loss (~; 0.01 cm-1), its laser damage threshold comparable to ZGP (~ 2 J/cm2) are suitable properties for efficient non-critical phase matched OPOs. As there is no natural birefringence in GaAs, phase matching is independent of polarization and propagation direction, offering the ability to pump OP-GaAs with a variety of polarization states. Thus, even unpolarized or poorly polarized sources like simple fiber lasers have been efficiently used as pump sources. The paper will discuss recent results obtained with an OP-GaAs OPO directly pumped by a 2.09 μm Q-switched Tm,Ho:silica fiber laser and a study on polarization effects using a Q-switched 2.09 μm Ho:YAG laser as the pump. With a 2.09 μm Q-switched Tm,Ho:silica fiber laser pump source, up to 2.2 W of average output power was achieved at 40 kHz repetition rate, 1.9 W at 60 kHz and 1.3 W at 75 kHz in the mid-infrared range.
Adhesive-free bond quasi-noncritical phase-matched and quasi-phase-matched optical parametric oscillations
Xiaodong Mu, Helmuth Meissner, Huai-Chuan Lee
With adhesive-free bond (AFB) technology, two walk-off compensated (WOC) KTP composites that consist of 16 layers of 2-mm thick single KTP crystals in each have been designed and prepared for 1.064-μm pumped 2-μm OPO's by means of quasi-noncritical phase-matching (QNCPM) and quasi-phase-matching (QPM). Output pulse energies of 49 μJ and 35 μJ have been achieved for QNCPM and OPM OPO's at pump energy of 523 μJ with pulse duration of 15 ns and repetition rate of 1 KHz, respectively. The OPO pump thresholds were measured as low as 254 μJ (44.6 MW/cm2) for the both types of OPO's. The wavelength shifts were measured to be around 11 nm for both the signal and idler beams when KTP temperature was raised from room temperature to 220°C.
Ultrafast Nonlinear Devices and Applications II
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Mode-locking with phase-sensitive (parametric) amplification
Simon Hachey, Christopher R. Jones, J. Nathan Kutz
A new method is proposed and considered theoretically for using phase-sensitive amplification as the intensitydiscrimination (saturable absorption) element in a laser cavity to generate stable and robust mode-locking. The phase-sensitive amplifier acts as a phase-filter for selecting the specific intensity dependent phase-rotation of the mode-locked pulse that locks the phase to the amplifier pump phase. The nonlinear phase-rotation is analogous to the nonlinear polarization rotation which is used with passive polarizers for mode-locking. It is demonstrated that the phase-sensitive amplification mechanism can indeed result in stable mode-locking. An average cavity model explicitly calculates the stability of the mode-locked pulses.
Mode-locked laser pulse sources for wavelength division multiplexing
Recent theoretical investigations have demonstrated that the stability of mode-locked solution of multiple frequency channels depends on the degree of inhomogeneity in gain saturation. In this paper, these results are generalized to determine conditions on each of the system parameters necessary for both the stability and existence of mode-locked pulse solutions for an arbitrary number of frequency channels. In particular, we find that the parameters governing saturable intensity discrimination and gain inhomogeneity in the laser cavity also determine the position of bifurcations of solution types. These bifurcations are completely characterized in terms of these parameters. In addition to influencing the stability of mode-locked solutions, we determine a balance between cubic gain and quintic loss, which is necessary for existence of solutions as well. Furthermore, we determine the critical degree of inhomogeneous gain broadening required to support pulses in multiple frequency channels.
Dynamics of ultrashort pulse solutions of the complex Ginzburg-Landau equation
We investigate numerically the dynamics of pulsating, erupting and creeping soliton solutions of a generalized complex Ginzburg-Landau equation (CGLE), including the third-order dispersion (TOD), intrapulse Raman scattering (IRS) and self-steepening (SST) effects. We show that these higher-order effects (HOEs) can have a dramatic impact on the dynamics of the above mentioned CGLE solitons. For small values of the HOEs, the periodic behavior of some of these pulses is eliminated and they are transformed into fixed-shape solitons. However, a rather different behaviour is observed by increasing the magnitude of the HOEs. Some particular interesting cases are discussed concerning the combined action of the three HOEs.
Novel high-sensitivity Z-scan technique based on a Hartmann-Shack wavefront sensor
Diego Rativa, Brian Vohnsen, Anderson S. L. Gomes, et al.
Here we report on a new variation of the Z-scan method to characterize the third-order optical nonlinearity of photonic materials. By exploiting a Hartmann-Shack wavefront sensor on a Z-scan set up we demonstrate an improvement in sensitivity of the method. We also show that the method is suitable for the evaluation of samples having strong nonlinear absorption. The nonlinear indices of refraction values have been obtained by analyzing the variation of the fifth-order Zernike coefficients C5 that describe defocus as function of the sample position on the Z-scan setup. Here the method is demonstrated by evaluating the nonlinear optical properties of CS2 and Coumarin as standard materials, using a 1 KHz repetition rate Ti-Sapphire laser delivering 100fs pulses.
Nonlinear Materials and Characterization
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The physical basis and modeling of Cr[sup]4+[/sup]-based saturable absorbers
This paper summarizes the physics and experimental results pertaining saturable absorbers based on Cr4+ doped crystals, in several types of diode-pumped Nd and Yb - doped solid state lasers. The paper focuses on the understanding and on analyzing the saturation curves of several Cr4+ garnets and other crystals (such as forsterite). Several systems of passively Q-switched diode-pumped lasers and microlasers were also described, and their performance in terms of average output power, pulsewidth and repetition rates were described and analyzed. Analytical models which use some measured physical constants were used to predict the Q-switched laser performance.
Comparison of nonlinear absorption and carrier recombination times in GaAs grown by hydride vapor phase epitaxy and Bridgman processes
Leonel P. Gonzalez, Joel Murray, Amelia Carpenter, et al.
μA 760 μm thick GaAs crystal was grown using HVPE. Transmission spectrum of this sample showed minimal absorption for light having photon energy below the bandgap energy, indicating the absence of the EL2 defects commonly found in Bridgman grown samples. Irradiance dependent absorption measured at 1.535 μm using 100 ns duration laser pulses showed increased nonlinear absorption in the HVPE grown GaAs compared to Bridgman grown samples. The dominant nonlinear absorption process in both samples was absorption due to free carriers generated by two-photon absorption. The HVPE grown sample showed higher nonlinear absorption due to longer carrier lifetimes.
Efficiency of a one-phonon Bragg anomalous light scattering in tellurium dioxide single crystal with variously polarized incident light of visible range
Estimating the effective photo-elastic constants peculiar to a set of partial processes inherent in a one-phonon Bragg anomalous light scattering of light in tellurium dioxide crystal is progressed. Really high optic and acoustic anisotropy of this crystal leads to the fact that the efficiency of light scattering is critically conditioned by the ellipticity of the incident light polarization and details in the geometry of acousto-optical interaction. Using a technique of the eigenvectors for elliptical states of light polarization in anisotropic medium, we describe analytically the efficiency of a onephonon Bragg anomalous light scattering in and optimized cell, oriented along the [001] and [110] crystallographic axes with variously polarized incident light modes. Possible interpretation of the results obtained is briefly discussed.
One- and two-photon pumped soft lithographed DFB laser systems based on semiconductor core-shell quantum dots
In the last years inorganic semiconductor (particularly CdSe and CdS) quantum dots (QDs) have received great attention for their important optical properties. The possibility to tune the emission wavelength, together with their high fluorescence quantum efficiency and photostability, can be exploited in photonic and optoelectronic technological applications. The design of DFB devices, based on QDs as active optical material, leads to the realization of compact laser systems. In this work we explore the use of an inorganic/organic hybrid material composed of CdSe-ZnS semiconductor quantum dots doped into a zirconia sol-gel matrix for optical gain applications. Through the use of soft lithography on a sol-gel germania-silica hybrid, large scale distributed feedback gratings can be created. Used in conjunction with the CdSe-ZnS/ZrO2 hybrids, these gratings can act as microcavities and allow for the realization of true lasing action. The lasing properties within these devices are characterized in the femtosecond regime by both one- and two-photon excitation. From experimental data the value of the optical gain of the core-shell quantum dot samples has been estimated. Moreover, one- and two-photon lasing threshold and stability are reported.
Poster Session
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Practical aspects of applying triple correlations to the characterization of high-frequency repetition trains of picosecond optical pulses
Alexandre S. Shcherbakov, P. Moreno Zarate, J. Campos Acosta, et al.
Practical feasibility of measuring the train-average parameters of picosecond optical pulses being arranged in highfrequency repetition trains is investigated. For this purpose we consider exploiting the triple auto-correlations, whose Fourier transformations give the bispectrum of a pulse train. The main merit of similar approach consists in the capability of recovering signals and revealing asymmetry of pulse envelopes. The triple auto-correlation can be shaped by a three-beam scanning interferometer with the following one- or two-cascade triple harmonic generation. The efficiencies of these processes depend on the number of cascades and differ in various modern materials. The key features of measuring the train-average parameters of pulses with possible frequency chirp are also discussed.
Upconversion fluorescence spectroscopy in rare earth doped sol-gel nano-glass ceramics
Luciano A. Bueno, Artur S. da Gouveia-Neto, Andréia F. da Silva, et al.
There has recently been a great deal of interest in searching for new materials for application as hosts in infrared-tovisible light upconverters or optical amplifiers based upon rare-earth doped systems. Some of their many applications include: color displays, high density optical recording, biomedical diagnostics, infrared laser viewers and indicators, fiber lasers and amplifiers. Fluorosilicate based sol gel glass ceramics have recently emerged as auspicious candidates for such photonic devices applications. These glasses are advantageous because they present low temperature of preparation, better mechanical strength, chemical durability, and thermal stability than fluoride-based glasses. The present work involves the investigation of optical transitions and upconversion fluorescence spectroscopy of trivalent lanthanide ions Er3+ codoped with Yb3+ in β-PbF2 nanocrystals dispersed in silica glassy matrix, excited with nearinfrared diode lasers. The dependence of the upconversion luminescence upon diode laser power, and the upconversion excitation mechanisms involved are also investigated.
A high Brillouin amplification using liquid fluorocarbon
Although the gain coefficient of the Stimulated Brillouin Scattering (SBS) of the fluorocarbon liquid C8F18 is substantially lower than for other nonlinear media, it is an attractive medium since its highly purified version has a high optical breakdown threshold, and it is stable and very safe to operate. We have utilized it as a phase conjugate mirror (PCM) and the PCM reflectivity better than 90% has been achieved at optimized focusing conditions of an incoming beam. The output energy of the phase conjugated pulse linearly followed the input pulse energy after reaching the threshold level at about 3.3 mJ. The slope efficiency was estimated about 95% without taking into account components' losses. Brillouin amplification through SBS has been realized in highly purified fluorocarbon liquid C8F18. This report discusses the design and results of performed experimental studies of the SBS in C8F18 demonstrating the amplification of a week signal beam (37 nJ) reaching up to 105 or 50 dB.
Sellmeier and thermo-optic dispersion formulas for Beta-BaB[sub]2[/sub]O[sub]4[/sub] (revisited)
K. Kato, N. Umemura, T. Mikami
This paper reports the high-accuracy Sellmeier and thermo-optic dispersion formulas for β-BaB2O4 (β-BBO) that provide the excellent reproduction of our data for second-harmonic generation (SHG) and sum-frequency generation (SFG) down to 0.2048 and 0.1925μm as well as the optical parametric oscillator (OPO) tuning points up to 3.2μm, and the temperature-dependent phase-matching angles for SHG and SFG that we have measured in the 0.193-0.6420μm range as well as the recent data for SFG at 0.1934μm.
UV supercontinuum excitation source generated by SPM and XPM in photonic crystal fibers
R. R. Alfano, V. Kartazaev, I. Zeylikovich, et al.
The supercontinuum spectrum generated by femtosecond Ti:Sapphire laser in photonic crystal fiber (PCF) can be increased into the UV by using small core diameter PCF with zero dispersion wavelength (ZDW) shorter 600nm. SC is generated in the region 350 to 1200nm with modulation less than 10 dB and with maximum spectral intensity near 350- 450nm. It is further shown that spectral intensity in the UV spectral region can be increased by employing dualwavelength pumping using the second harmonic of Ti:Sapphire laser beam as a second pumping wavelength.
Accurate characterization of free carrier refraction in InP
Leonel P. Gonzalez, Srinivasan Krishnamurthy, Shekhar Guha
Using recently published results of intrinsic and free carrier nonlinear absorption coefficients in InP, nonlinear refraction was investigated at 1.064 μm using ns duration lasers to characterize refraction from generated free carriers. A phase retrieval algorithm was implemented to determine the amplitude and phase profiles of the incident beam. Accurate spatial and temporal profiles of the incident field were used to model nonlinear propagation through and beyond the sample. With the sample held fixed at focus and the incident energy increased, images of the transmitted beam a fixed distance away were recorded as a function of irradiance. Excellent agreement was observed between recorded beam images and those generated from the numerical model.
1 W at 490 nm on a compact micro-optical bench by single-pass second harmonic generation
We demonstrate a compact 1 W laser module at 490 nm using a Distributed Bragg Reflector tapered diode laser in single-path second harmonic generation (SHG) configuration. The frequency conversion is performed with a 3 cm periodically poled MgO:LiNbO3 crystal on a micro-optical bench having a footprint of 2.5 cm3. 1 W blue light could be achieved at a pump power of about 9.5 W resulting in an optical conversion efficiency of about 10 %. The output power stability is better than ± 2% and the blue laser beam shows an excellent beam quality of M2σ = 1.2 in vertical and M2σ = 2 in lateral direction, respectively.