A kilohertz repetition rate 1.9 μm H2 Ramanoscillator

Raman conversion of a high-repetition-rate Q-switched Nd:YAG laser using a gaseous H₂ Raman medium is reported. With a H₂ cell placed in a focusing intracavity Raman oscillator, 3 W of average power at 1.9 μm was obtained from a 15-W 1.06-μm laser operating at 2 kHz. Although the pump beam was multimode, the Stokes output was diffraction limited. At kilohertz repetition rates, conversion efficiencies were improved with a flowing gas cell which substantially reduced the thermal lensing effect in the Raman medium. A rate equation approach was used to model the intracavity conversion process     

Intracavity 1.549-μm pumped 1.634-μm Er:YAG lasers at 300 K

A novel method of generating 1.634-μm laser action from Er:YAG crystals pumped intracavity by an Er:glass laser emitting at 1.549 μm is described. Operation of the Er:glass laser at 1.549 μm (red shifted from the standard 1.532 μm, but with comparable output) at 500 K was obtained using mirrors with tailored spectral reflectivities. Several Er:YAG crystals ranging in concentration from 0.3% to 2% and in length from 1 cm to 8 cm were lased in the intracavity pumping arrangement. All the Er:YAG crystals lased in the ⁴I_13/2 :Y1(6544 cm^-1)-⁴I_15/2:Z6(424 cm ^-1) 1.634-μm transition at 300 K     

Transient frequency shift in a single-mode quasi-continuousdiode-pumped Nd:YAG laser

The transient frequency shift of a quasi-continuous single-mode frequency-doubled diode-pumped Nd:YAG ring laser has been measured using a confocal spherical Fabry-Perot. At a rate of 50 Hz, a quasi-linear shift of 5.4 MHz at the fundamental 1.06-μm wavelength has been measured during the 150-μs laser pulse duration. The doubled frequency, which is obtained by an intracavity LBO crystal, shows also a similar but doubled linear shift. This observed frequency shift is interpreted as due to thermal effects in the rod and fits well a modeling of the pulsed laser diode pumping. Introducing intracavity compensation, a piezoceramic transducer mounted cavity mirror, has limited the observed shift to less than ±1 MHz. Such a quasi-continuous Nd:YAG single-mode and frequency stabilized device should be a very suitable single-mode laser source to pump optical parametric oscillator systems     

连续腔内倍频拉曼激光器的归一化理论解析

腔内倍频拉曼激光器是获得黄光激光光源的重要途径,目前尚未有直接的表达式描述连续腔内倍频激光器的功率输出对抽运和激光器参数的赖关系。以速率方程为基础,对腔内倍频连续拉曼激光器的理论模型进行归一化处理,得到平面波近似下连续腔内倍频拉曼激光器的归一化速率方程组。对此方程组进行求解,得到描述激光器输出的表达式各变量以及参量与输出变量之间的归一化表达式,根据表达式获得了描述激光器运行的理论曲线。     

1.54μm腔内喇曼激光器实验研究

喇曼激光器作为一种将基波频率转换成斯托克斯频率的高量子效率转换装置,实现激光频率的扩展,日益受到人们的重视。腔外喇曼频移过程,国内、外都有过充分的研究,而腔内喇曼频移激光器投入实际使用则只是近几年才发展起来。本文报道了脉冲Nd:YAG1.06μm基频经高压甲烷气体在封闭式激光腔内喇曼频移成1.54μm一阶斯托克斯脉冲输出的实验研究结果。     

Intracavity Raman lasers

Experimental and theoretical studies of intracavity Raman lasers are presented. Advantages of intracavity Raman lasers, particularly for low-emission cross section and broadly tunable vibronic gain media, are described. Experimental studies of a hydrogen gas Raman laser pumped inside the cavity of an alexandrite laser are presented. A theoretical model of the dynamics of a unidirectional intracavity Raman ring laser is developed and solved analytically. This model is adapted for simulation experiments     

Influence of carrier nonuniformity on the phase relationshipbetween frequency and intensity modulation in semiconductor lasers

The modulus and phase of the chirp to modulated power ratio (CPR) was measured for a 1.5-μm buried-heterostructure laser and a 0.85-μm channeled-substrate planar (CSP) laser. The results for the phase are inconsistent with previously published expressions including spontaneous emission and spectral hole burning. In particular, the CSP laser exhibits an abrupt phase shift in the CPR. An explanation of this behavior is presented in terms of the influence of a nonuniform carrier density on the phase-amplitude coupling, as expressed by an integral expression for the mode parameter α representing the linewidth enhancement factor. Using a simple model for lateral behavior which analytically incorporates diffusion and a nonuniform material α parameter, qualitative agreement was obtained with the CSO data. The authors demonstrate the importance of the lateral laser structure on the phase-amplitude coupling in index-guided semiconductor lasers, and the usefulness of CPR phase measurements for laser characterization     

Evidence of nonuniform phase-diffusion in a bad-cavity laser

The quantum-limited linewidth of a short HeNe 3.39-μm laser was measured and seen to increase with increasing nonuniformity of the intracavity intensity distribution. Experiments were done inside as well as outside the bad-cavity regime; in this regime the polarization of the gain medium cannot be adiabatically eliminated but acts as a memory. Good quantitative agreement with theory is obtained inside as well as outside the bad-cavity regime. The effect of nonuniformity is well described by the longitudinal Petermann K-factor. The bad-cavity and nonuniformity effects can be separated from each other as predicted by theory     

Properties of fiber Raman amplifiers and their applicability todigital optical communication systems

Bit error rate performances of fiber Raman amplifiers both as booster amplifiers and as detection preamplifiers are studied in intensity modulation/direct detection optical communication systems. It is theoretically shown that, in the booster amplifier application, receiver sensitivity degradation due to amplification can be made less than 0.2 dB for signal-to-noise power ratio larger than 20 dB, and thus an allowable transmission line loss can be increased approximately by the value of Raman gain. For detection preamplifier use, receiver sensitivities in the Raman preamplifier system are numerically calculated in terms of minimum detectable signal power at 100-Mbit/s and 2-Gbit/s bit rates. In both bit rates, it is shown that, for a Raman gain greater than 20 dB, minimum detectable signal power can be improved by more than 15 dB over the conventional detection level without Raman amplification. Preliminary experiments are carried out using a 1.32-μm Nd:YAG laser and a 1.4-μm laser diode as pump and signal light sources, respectively. The experimental results are in good agreement with theoretical estimations     

Spectroscopy, modeling, and laser operation of thulium-dopedcrystals at 2.3 μm

Pulsed room-temperature lasers based on the thulium 2.3-μm ³H₄-³H₅ transition have been achieved in 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF crystals using a pulsed alexandrite laser at 785 nm as the pump source in a collinear geometry. The absorbed energy thresholds (slope efficiencies) for 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF lasers are measured to be 1.2 mJ (14%), 1.8 mJ (13%), and 1.0 mJ (18%), respectively, which are in good agreement with the theoretically predicted results. The experimental results indicate 1.0 mJ thulium to be the most optimum concentration for 2.3-μm laser action. The thulium lasers are tuned around 2.3 μm using an intracavity single birefringent plate of quartz     

Chirp control of a single-mode, good beam quality, zigzag dye laser

We report a substantial reduction of frequency chirp of a single-mode laser-pumped zigzag dye laser. A linear optical cavity using counterpropagating orthogonally polarized waves was injection-seeded at 568 mn and operated with a laser output of about 1 J. The chirp was controlled by an intracavity Pockels cell that was configured to add optical density at a rate which counterbalanced the decrease in optical density due to dye-solvent heating during the ~1-μs laser pulse. Heterodyne measurements were used to determine that the bandwidth was near the transform limit and chirp rate of ~1 MHz/μs. The beam quality of the laser was measured at 10 Hz as 1.7 XDL     

Raman shifting in the absence of multiple Stokes orders with aNd:YAG laser in hydrogen: evidence of coupling between the forward andbackward Stokes processes

By Raman shifting the output of a 1.319-μm Nd:YAG laser in hydrogen, up to 24.5 mJ of Stokes light at 2.918 μm has been generated. Due to the low energy of the 2.918-μm Stokes photons, the first Stokes is the only Stokes line for this system. The effect of pressure on the conversion is notably simpler in this regime, but the gain saturates unusually slowly. An unexpected pump linewidth sensitivity in the forward Stokes conversion is observed. Coupling of the forward and backward Stokes processes is suggested as an explanation for these effects and is supported by a simple model     

Theoretical and experimental study on the self-Raman laser with Nd:YVO/sub 4/ crystal

The intracavity photon densities and the initial population inversion density were assumed to be Gaussian distributions in the rate equations of the laser diode end-pumped actively Q-switched intracavity Raman laser. These space-dependent rate equations were solved numerically. In the experiment, an efficient self-Raman laser was realized based on the multifunctional Nd:YVO/sub 4/ laser crystal with the acoustooptic Q-switch. The output, temporal, and spectral characteristics of the self-Raman laser were investigated experimentally in detail. The performance of the self-Raman laser was studied numerically, and the theoretical results showed the main trends of the intracavity Raman laser, which are in agreement with the experimental ones.     

LD泵浦被动调Q腔内和频拉曼激光器速率方程

运用非线性光学的和频理论推导出被动调Q腔内和频拉曼激光器速率方程理论中的和频项,在被动调Q拉曼激光器速率方程的基础上,推导被动调Q腔内和频拉曼激光器速率方程,再将方程归一化,得到八个综合参量。推导出和频脉冲峰值功率和单脉冲能量的归一化表达式。数值模拟观察各参量对和频脉冲峰值功率、单脉冲能量和脉冲宽度的影响。对各参量影响进行分析,发现和频因子与归一化拉曼增益系数需要相互匹配才能实现高效率的和频光输出。同时,比较了被动调Q腔内和频拉曼激光器与被动调Q腔内倍频拉曼激光器的数值模拟结果。     

Mode-locked operation of a Nd:YLF laser and amplification in aQ-switched Nd:glass slab laser

A Nd:YLF laser pumped with a CW dye laser and acoustooptically mode locked at 38 MHz has an output power of 130 mW and a pulse length of 60 ps. Insertion of intracavity etalons and misaligning the mode locker allows for stable operation with a continuous range of pulse lengths from 60 ps to 4 ns. The 1.053-μm emission permits amplification of these pulses in a Q-switched Nd:phosphate glass slab laser oscillator up to intensities limited by optical damage     

Stimulated Raman scattering in methane-experimental optimizationand numerical model

The stimulated Raman effect in methane was investigated both theoretically and experimentally. An experimental setup was used to optimize the Raman conversion of a 1.06-μ laser source into a wavelength of 1.54 μm in pressurized methane. Efficient conversion (up to 45% efficiency) is accomplished when using a full-resonator configuration for the Stokes wavelength. A numerical model is introduced, describing the Raman conversion process in the backward and the forward directions. Half-resonator and full-resonator configurations are studied. The results of the numerical model are in agreement with the experimental results     

1.5-μm-band optical time domain reflectometer for single-modeoptical fiber using a P2O5-highly-doped fiberRaman laser

A wide-dynamic-range 1.5-μm-band optical time-domain reflectometer (OTDR) for single-mode optical fibers using a P₂O₅-highly-doped fiber Raman laser light source and a cooled Ge-p-i-n photodiode is realized for the first time. The stimulated-Raman-scattering properties of P₂O₅-doped single-mode fiber are investigated. Using this fiber and an Nd:YAG laser operating at 1.32 μm, a high-power light pulse at 1.59 μm is generated with high efficiency. Using the stimulated-Raman-scattering light as the light source and a high-sensitivity optical receiver, a 1.5-μm-band OTDR having a one-way dynamic range of 35 dB is realized     

5 Gb/s optical soliton transmission experiment using Ramanamplification for fiber-loss compensation

Optical soliton transmission of 5 Gb/s over a 23-km amplification spacing using a gain-switched 1.55-μm distributed feedback laser diode and Ti:LiNbO₃ intensity modulator is discussed. An Er ⁺-doped fiber amplifier, pumped by 1.45- and 1.48-μm laser diodes, is employed for achieving intense optical pulses. Transmission fiber-loss is completely compensated for by Raman amplification using by 1.45- and 1.48-μm laser-diode pumping. A bit error rate (BER) of 2×10^-10 has been obtained     

Intracavity contacts for low-threshold oxide-confinedvertical-cavity surface-emitting lasers

Very low threshold vertical-cavity surface-emitting lasers are demonstrated using intracavity contacts, an upper dielectric Bragg reflector, and an undoped lower AlAs-GaAs Bragg reflector. The undoped lower mirror allows the demonstration of the highest differential efficiency yet achieved for sub-100-μA threshold, which is 60% for a 67-μA threshold. Devices with smaller output coupling show threshold current densities as low 98 A/cm², and a minimum threshold current of 23 μA for a small aperture     

3.6 Gb/s all laser-diode optical soliton transmission

3.6-Gb/s optical soliton transmission using a gain-switched 1.55-μm distributed-feedback laser diode and a Ti:LiNbO₃ intensity modulator is demonstrated. An Er³⁺-doped fiber amplifier and a Raman amplifier, both pumped by 1.48-μm laser diodes, are used for achieving intense optical pulses and fiber-loss compensation, respectively. The intensity-modulation direct-detection optical receiver of a commercial F-1.6 G system is used to measure the bit-error rate