光泵铯蒸气激光的动力学模型

建立了一个物理模型描述了光泵铯蒸气激光的动力学过程和激光机理.结合实验参量,经数值求解该模型,定量分析了抽运光参量、缓冲气压和输出镜反射率等对激光输出功率和光光效率产生的影响,得到了与实验基本一致的模拟结果.表明该模型较好地反映了光泵銫蒸气激光的动力学机理和发射过程,为该类激光的优化设计提供了借鉴和参考.     

Transmittance investigation on capacitive mesh on thick dielectric substrates as output windows for optically pumped terahertz lasers

This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick).Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation,a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s.A transmittance spectrum of the output window in a certain frequency range (say,from zero to 1 THz) has been obtained by using THz time domain spectroscopy.Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate.The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz.Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.     

The optimum pumping power for optically pumped FIR lasers

The relations between the output power of optically pumped FIR laser and the pumping power were studied theoretically by solving the density matrix equation of four-level system by means of the matrix signal flow graph method. The output power density of FIR laser was calculated by iteration method. A set of curves of output FIR power density against pumping power has been obtained. It has found that every of each curve has a maximum point of which the position is different for different pumping detuning. According the these results we predicted that there would exist an optimum pumping power density for an optically pumped FIR laser with certain pumping detuning. This theoretical results would help us to design the optically pumped FIR lasers.     

Dynamic nuclear spin resonance in n-GaAs

The dynamics of optically detected nuclear magnetic resonance is studied in n-GaAs via time-resolved Kerr rotation using an on-chip microcoil for rf field generation. Both optically allowed and optically forbidden NMR are observed with a dynamics controlled by the interplay between dynamic nuclear polarization via hyperfine interaction with optically generated spin-polarized electrons and nuclear spin depolarization due to magnetic resonance absorption. Comparing the characteristic nuclear spin relaxation rate obtained in experiment with master equation simulations, the underlying nuclear spin depolarization mechanism for each resonance is extracted.     

Photon recyclers

We present a radical approach for improving the efficiency of optically pumped NMMW lasers in which the Manley-Rowe limit is transcended by recycling pump photons. The resulting new class of lasers, called photon recyclers, can be described as heat engines in which heat is converted into coherent NMMW radiation using pump photons as a catalyst. Practical implementation of the proposed schemes by combining features of optically pumped NMMW lasers and gas dynamic expansion is discussed. Such systems may yield high power c.w. NMMW output.Work supported by U.S. Army Research Office, Durham, NC.     

Frequency Stabilization of Waveguide CO2 Laser by a Digital Technique

In this work we present a simple technique for laser frequency stabilization, based on Digital signal processing. The technique is used to stabilize a waveguide CO₂ laser of wide tunability by using three kinds of reference signals: the CO₂ laser ouptut power, an infrared absorption optoacoustic signal and the output power of a Far-Infrared optically pumped molecular laser.     

Continuous-wave all-solid-state 244 nm deep-ultraviolet laser source by fourth-harmonic generation of an optically pumped semiconductor laser using CsLiB6O10 in an external resonator

We report an all-solid-state laser system that generates over 200 mW cw at 244 nm. An optically pumped semiconductor laser is internally frequency doubled to 488 nm. The 488 nm output is coupled to an external resonator, where it is converted to 244 nm using a CsLiB(6)O(10) (CLBO) crystal. The output power is limited by the available power at 488 nm, and no noticeable degradation in output power was observed over a period of several hours.     

On the possibility of compensating for small-scale wave-front distortions using a Zernicke cell and an optically controlled spatial light modulator

The possibility of compensating for small-scale wave-front distortions using a spatial light modulator which is optically controlled by the output beam of a Zernicke interferometer was studied theoretically. The optimal parameters of the system, requirements of its elements, the range of the compensated distortions, and the compensation quality are determined for the case of compensation for sinusoidal distortions. It is shown that this technique allows for the compensation of small-scale sinusoidal phase distortions with a depth of up to 3λ and a 20-fold gain in the Strehl number can be achieved.     

Fine frequency tuning of a high power CO2 laser and its application to optically-pumped molecular lasers

We describe a novel technique for shifting the output frequency of a high power TEA CO₂ laser. The performance of a 16 μm laser is shown to be greatly improved when optically pumped by this tunable source.     

The possibility of compensating small-scale wavefront distortions with a Zernike cell and a spatial light modulator in an optical feedback scheme

The possibility of compensating small-scale wavefront distortions in an optical feedback scheme by using a spatial light modulator optically addressed by the output beam of a Zernike cell is theoretically considered. The optimal parameters of the system for compensating sinusoidal distortions and distortions characteristic of phasing of subapertures, the requirements for the elements of the system, the range of compensated distortions, and the quality of compensation are determined. It is shown that the use of this method makes it possible to compensate small-scale phase distortions with a peak-to-peak amplitude of up to 3λ; in this case, the gain in the Strehl number can be as high as 80.     

Effects of Buffer Gas on the Output of Optically Pumped NH3 Far-Infrared Cavity Laser

By solving the semi-classical density matrix equations and developing a buffer gas mechanism model, the effects of buffer gas on the output power of optically pumped NH₃ far-infrared cavity laser were calculated and verified by experiment. Our results showed that: the output power of NH₃ far-infrared laser could be increased when certain buffer gas was added into the laser medium, and there existed an optimum ratio of gases mixture and an optimum operating gas pressure which could make the output power of far-infrared laser reach maximum.     

Theoretical study of multi-mode optically pumped NH3 FIR laser

The two or multi-mode optically pumped NH₃ FIR laser had been studied theoretically. The NH₃ molecular gas was assumed to be a three-level system and obeyed the time-dependent behavior of the density matrix equations. Considering the situation of playing the two or multi-mode optical pumping and the FIR laser field were same polarized. The gain coefficient and the output FIR power of the system could be calculated by using the iteration method.It had been predicted that the two or multiple longitudinal mode optically pumped NH₃ FIR laser could have a greater output power or higher lasing efficiency than single mode pumped FIR laser under suitable selected operating parameters of laser.Supported by The Education Foundation of PRC.     

Dramatic enhancement of optical-field-ionization collisional-excitation x-ray lasing by an optically preformed plasma waveguide

Dramatic enhancement of optical-field-ionization collisional-excitation x-ray lasing is achieved by using an optically preformed plasma waveguide. With a 9-mm-long pure krypton plasma waveguide prepared by using the axicon-ignitor-heater scheme, lasing at 32.8 nm is enhanced by 400 folds relative to the case without the plasma waveguide. An output level of 8 x 10(10) photon/shot is reached at an energy conversion efficiency of 2 x 10(-6). The same method is used to achieve x-ray lasing in a gas jet for the high-threshold low-gain transition at 46.9 nm in neonlike argon.     

Surface-profile measurement by means of a polarization Sagnac interferometer with parallel optical feedback

We describe a novel feedback interferometer for real-time, unambiguous measurement of surface profiles that consists of a polarization Sagnac interferometer and an optically addressed phase-only spatial light modulator. In this system the output intensity from the Sagnac interferometer is optically fed back to the phase modulator placed in one arm of the interferometer, which produces a sawtooth fringe intensity profile (instead of the conventional cosinusoidal one) that is directly and unambiguously related to the surface profile. Preliminary experimental results demonstrate the feasibility of applying this system to surface-profile measurement.     

The Optimum Coupling Coefficient of Optically Pumped NH3 Far-Infrared Cavity Laser

Based on the semiclassical density matrix theory, the optimum output power reflection coefficient (coupling coefficient) of output coupler for optically pumped NH₃ far-infrared (FIR) cavity laser was calculated by means of iteration method. Experimentally, FIR Fabry-Perot cavity laser was designed and constructed by using inductive metallic meshes as couplers, and the measurement showed that the theoretical calculation were in agreement with experimental results.     

10 J energy-level optically pumped XeF(C-A) laser with repetition mode

An optically pumped XeF(C-A) laser with 0.1-1 Hz pulse-repetition mode is demonstrated. The maximum output energy is up to 18.7 J, which corresponds to the conversion efficiency of the stored electrical energy to laser output energy of 0.25%. The laser active medium is optically excited by vacuum-ultraviolet radiation of two single-channel surface discharges initiated along opposite walls of the laser cell. The laser resonator output coupling is 10%, and the initial XeF2 concentration in the active gas mixture is ~1 x 10(17) cm(-3). The duration of the observed laser pulses is 0.8 to 1.2 micros, and the spectral band is 470-500 nm.     

Hybrid output mirror for optically pumped far infrared lasers

A hybrid metallic mesh multilayer dielectric coating mirror has been developed for use as an output mirror for optically pumped far infrared lasers. The metallic mesh provides a high reflectance in the far infrared while the multilayer dielectric coating is chosen to provide a maximum reflectivity at the pump wavelength (10 μm). This hybrid mirror has increased the output power of a CH₃F waveguide laser at 496 μm by a factor of 350 over that obtained with a hole coupling mirror. In addition, this mirror results in a far infrared output beam which has a minimum angular divergence limited only by the particular oscillating transverse waveguide mode (the EH₁₁ mode for this experiment).     

Mode locking a 1550 nm semiconductor disk laser by using a GaInNAs saturable absorber

Passive mode locking of an optically pumped, InP-based, 1550 nm semiconductor disk laser by using a GaInNAs saturable absorber mirror is demonstrated. To reduce material heating and enable high-power operation, a 50 microm thick diamond heat spreader is bonded to the surface of the gain chip. The laser operates at a repetition frequency of 2.97 GHz and emits near-transform-limited 3.2 ps pulses with an average output power of 120 mW.     

Optical binary logic gate-based modified signed-digit arithmetic

A new design approach for a three-step modified signed-digit (MSD) adder is presented that can be optically implemented using binary logic gates. The proposed scheme depends on encoding each MSD digits into a pair of binary digits using a two-state and multi-position encoding scheme. The proposed design algorithm depends on constructing the addition truth table of binary-coded MSD numbers and then using Karnaugh map to achieve output minimization. The optical binary logic gates are obtained by simply programming the decoding masks of a shadow-casting-based optical logic gate system. The proposed scheme results in a simple, compact, and efficient optical binary gate-based parallel addition system.     

Sudden chaotic transitions in an optically injected semiconductor laser

We study sudden changes in the chaotic output of an optically injected semiconductor laser. For what is believed to be the first time in this system, we identify bifurcations that cause abrupt changes between different chaotic outputs, or even sudden jumps between chaotic and periodic output. These sudden chaotic transitions involve attractors that exist for large regions in parameter space.