Time-dependent thermal effects in current-modulated semiconductor lasers

The temporal dependence of the frequency shift in a current-modulated single-mode semiconductor laser is measured and compared with calculations based on solutions to the thermal diffusion equation. The effects of carrier density change, thermal diffusion in the semiconductor, and heat sink thermal resistance are identified.     

Development of EM field in lasers with rotating mirrorQ-switch

A fast-Fourier-transform (FFT) computational scheme based on a Fourier expansion technique is developed to calculate the development of an electromagnetic (EM) field from spontaneous noise inside a loaded rotating mirror Q-switched laser. A rate equations analysis is also carried out, using the FFT-calculated dependence of the diffraction loss on the fixed Q-switch mirror tilt angle. The computational results are compared with the output characteristics of an eye-safe (λ=1.54 μm) erbium glass laser. The experiments are in good qualitative and quantitative agreement with the predictions of the FFT mode. The model reveals short-duration intense spatial regions, as well as two types of temporal modulations of the laser output pulses. These modulations are attributed to the inhomogeneous development of the laser field in the longitudinal and transverse laser resonator direction. These irregularities must be taken into account when calculating eye-safety levels of rotating mirror Q-switched lasers     

High-pressure pulsed molecular lasers

A review of recent developments in high-pressure pulsed molecular lasers is presented. Included are some experimental results on TEA lasers, E-beam lasers, and lasers using Blumlein excitation. Discussions of the kinetic modeling, the parametric behavior, and the characteristics of uniform discharges in the high-pressure pulsed CO2laser are given. Recent results on pulse-initiated chemical lasers, extremely high-pressure lasers, and high-repetition-rate TEA lasers are also discussed. Efforts to control and use the output from these devices are described, and an extensive list of references is given.     

Plasma electronics in pulsed nitrogen lasers

A detailed study showing that the electronic impedances of both the spark gap and the laser channel plasmas play an integral part in the overall discharge circuit of a pulsed nitrogen laser is presented. The electronic properties of these plasmas can critically determine the temporal width of the laser pulse     

Microchamber setup characterization for nanosecond pulsed electric field exposure

Intracellular structures of biological cells can be disturbed by exposure to nanosecond pulsed electric field (nsPEF). A microchamber-based delivery system mounted on a microscope setup for real-time exposure to nsPEF is studied in this paper. A numerical and experimental characterization of the delivery system is performed both in frequency and time domains. The microchamber delivery system presents a high impedance compared to classical 50 Ω loads. Its frequency behavior and limits are investigated using an in-house finite-difference time-domain (FDTD) simulator and through experimental measurements. High-voltage measurements for two nsPEF generators are carried out. The applied pulse voltage measured across the microchamber electrodes is ～1 kV, corresponding to ～10 MV/m electric fields in the microchamber. Depending on the nsPEF generator used, the measured pulse durations are equal to 3.0 and 4.2 ns, respectively. The voltage distribution provided by FDTD simulations indicates a good level of homogeneity across the microchamber electrodes. Experimental results include permeabilization of biological cells exposed to 3.0-ns, 10-MV/m PEFs.     

High-power pulsed xenon ion lasers

Output and threshold characteristics of small-bore pulsed xenon ion lasers are presented in detail as a function of current and gas pressure for ranges of these parameters that are consistent with high optical power output in the green-blue spectral region. It has been found that six wavelengths characteristic of xenon exhibit peak output powers greater than 100 watts, from a 5-foot laser tube over a limited (8-24 mtorr) range of xenon tube pressure. Laser action has also been obtained at high peak powers for longer current pulse (5-50 mus) operation of the tube. In addition, observation of three new laser wavelengths 5340, 5501, and 5590 Å is reported. These lines are only observed at very low tube pressures and very high peak currents.     

Repetitively pulsed Nd-glass slab lasers

The possibility of obtaining high laser output energies at a 1.32-μm wavelength using thin LiNdLa phosphate glass slabs with a high Nd³⁺ concentration is discussed. In the experiments, 3×14×125-mm slabs were prepared from LiNdLa phosphate glass with a Nd-concentration of 1.2×10²¹ cm^-3. The facets of the slabs were not antireflection-coated. They were tested in a silver-coated quartz tube reflector of 25-mm diameter and pumped by 450-μs pulses from a flash lamp with a 120-mm arc length. In this construction the light, which passes through the slab, returns to it after reflection from the tube surface. Most of the radiation falls on the wider side of the slab at large angles of incidence, thus maximizing its path inside the slab. The quartz reflector was water cooled. The 150-mm laser resonator was formed by two flat mirrors. At 1.32-μm lasing wavelength an output mirror of r=95% reflectivity was used with less than 10% reflectivity at 1.32 μm     

Time-dependent semiclassical theory of gain-coupled distributed feedback lasers

A semiclassical treatment of the time-dependent behavior of a gain-coupled, distributed feedback laser (DFL) has been developed. This treatment takes into account the field propagation within the DFL, and is therefore capable of predicting its behavior even for extremely short pump pulses. Comparisons are made to existing steady-state and transient theories where they are valid, showing good agreement, and new predictions are made of the behavior in the short pump pulse regime. It is found that the emitted pulse duration is dominated by the transit time through the pumped region. By studying the evolution of the field distribution inside the cavity, insight can be gained into the operation of the DFL. The effect of spatial hole burning in a gain-coupled DFL is treated and found to be small.     

Noise characteristics in repetitively pulsed semiconductor lasers

Timing jitter (phase noise) and power fluctuations (intensity noise) in a semiconductor laser driven with a periodic current waveform, in the large signal regime are investigated theoretically. The temporal behavior of the laser output power is calculated numerically from the modified rate equation with Monte Carlo simulation of the random processes, both free-running and active mode-locked configurations are treated. The temporal width and root-mean-square (rms) timing jitter and energy fluctuation of the pulses are calculated, as are the correlation and spectral properties of the noise     

脉冲强预燃及其对激光光泵效率的影响

本文介绍用于重复率固体激光器的脉冲强预燃技术.给出恒定弱预燃和脉冲强预燃的实验结果.经采用脉冲强预燃后,激光器可获得高效率和高功率输出.     

超辐射掺铒光纤脉冲放大器的时间特性分析

为了分析掺铒光纤脉冲超辐射放大器的输出特性,通过对时变激光速率方程求解的方法,进行了理论分析和数值验证,获得了系统对不同调制频率的响应和输出特性.结果表明,在一定频率范围内,将产生高峰值超辐射脉冲序列.用0.1W抽运1m铒光纤放大,种子具有纳秒级调制周期且占空比为1/2时,输出脉冲峰值渐减,约200ns后渐趋稳定.通过调节种子信号的光谱特性、调制特性并选择合适的光纤参数,可以控制放大脉冲性质.这一结果为利用超辐射光纤光源产生高功率、光谱性质可调的脉冲提供了有效途径,在1.5μm大气窗口及远程应用中具有实际价值.     

脉冲氧碘化学激光模型

采用闪光灯光解RI得到碘原子,再与电子激发态氧O_2(~⊿)传能产生脉冲碘激光的模型。此模型包括35个化学动力学过程。采用Runge-Kutta-Gill积分法求解,得到的结果表明脉冲氧碘化学激光器具有高的效率,提高激光器性能的关键在提高O_2(~1⊿)的分压。     

Resonator interferometry of pulsed submillimeter-wave lasers

In this paper laser resonator interferometry for submillimeter-wave lasers is discussed. In particular, the application of laser resonator interferometry to the study of various aspects of laser emission is shown. The basis of this interferometry is an understanding of the resonator mode structure, which is derived from a theory of resonators with low Fresnel numbers and dielectric enclosure. The mode structure is confirmed by experimental results. Interferometric studies reveal a relationship between the mode structure and the shape of the laser output pulses. This allows for some conclusions with respect to the molecular mechanism that is responsible for laser emission. This mechanism is not yet understood for the long wavelength emissions of ICN (+H2?), up to 0.774 mm.     

Parameter studies of pulsed HF lasers

The average output power of pulsed HF chemical lasers is found to depend strongly on the fluorine source used. The best performance was obtained from H2-C2F6-He mixes, which gave average powers of 850 mW and energies of 20 mJ/pulse. Peak gains of at least 0.036 cm^-1are observed. Average powers of 450 mW from DF and 70 mW from HCl are reported.     

脉冲主动锁模和主被动锁模激光器

本文报导了脉冲式主动、主被动锁模磷酸盐玻璃振荡器的特性.主动锁模的脉冲宽度为200微微秒左右,输出性能比较稳定.对于输出脉宽为7微微秒左右的主被动锁模,出现卫星脉冲的几率与调制器的调制系数有关.使用不同的腔内标准具能产生30微微秒和70微微秒的脉冲,没有观察到卫星脉冲.主被动锁模的性能比被动锁模有所提高.     

Spectral properties of pulsed dye lasers

The model of a homogeneously broadened laser with pulsed excitation is considered. We compute solutions of coupled non-linear differential rate equations describing the spectral properties of the emission as a function of time. It is shown that the use of appropriately space averaged quantities allows one to take into account gain saturation effects. Injected, Fabry-Perot etalon tuned and broad-band oscillator emissions are studied. Spectro-temporal evolution of the laser emission which occurs in all cases is the main result of the computations and fully supports, as expected, the previously derived analytical equations. In addition it is shown that the basic phenomenon of spectral evolution implies the existence of an "ultimate wavelength" of the emission. How to predict the optimum and limits of injection locking is discussed in terms of a "delocking time."     

短脉冲注入锁定染料激光器的理论

本文提出了包含主激光器注入光频率与受迫激光器纵模频率之间失谐影响的新的速率方程模型,并给出了数值解. 注入功率、注入波长和频率先谐等因素对短脉冲注入锁定染料激光器的影响也进行了讨论.     

可控硅开关型脉冲激光电源

建立了开关型脉冲激光电源的数学模型并给出了设计方法。采用快速可控硅做为开关元件完成了一台容量为55kW、重复频率可达200Hz的脉冲激光电源,给出了具体的电路并进行了分析。     

Millimetre-wave signal generation using pulsed semiconductor lasers

A novel technique for millimetre-wave signal generation using a pulsed semiconductor laser is proposed and demonstrated. Optical filtering is used to select only two modes and suppress all other modes in the optical spectrum of the laser. The two selected modes beat together in a photodiode to generate a millimetre-wave signal with 100% modulation depth