Temporal Behavior of the Pump Pulses,Residual Pump Pulses,and THz Pulses for D<Subscript>2</Subscript>O Gas Pumped by a TEA CO<Subscript>2</Subscript> Laser

Temporal behavior of the pump pulses, residual pump pulses, and THz pulses for optically pumped D₂O gas molecules was investigated by using a tunable TEA CO₂ laser as the pumping source. The pulse profiles of pump laser pulses, residual pump pulses, and the THz output pulses were measured, simultaneously, at several different gas pressures. For THz pulse, the pulse delay between the THz pulse and the pump pulse was observed and the delay time was observed to increase from 40 to 70 ns with an increase in gas pressure from 500 to 1700 Pa. Both THz pulse broadening and compression were observed, and the pulse broadening effect transformed to the compression effect with increasing the gas pressure. For the residual pump pulse, the full width at half maximum (FWHM) of the main pulse decreased with increasing gas pressure, and the main pulse disappeared at high gas pressures. The secondary pulses were observed at high gas pressure, and the time intervals of about 518 and 435 ns were observed between the THz output pulse and the secondary residual pump pulse at the pressure of 1400 Pa and 1700 Pa, from which the vibrational relaxation time constants of about 5.45 and 5.55 μs Torr were obtained.     

High peak power and high repetition rate characteristics in acurrent-pulsed Q-switched CO2 laser with a mechanical shutter

An electro-mechanical Q-switched (EMQ) CO₂ laser is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (>10 kW) and high repetition rates (>1 kpps). In order to analyze the output characteristics, the peak power and the duration of the output pulses have been measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure (<4 kPa) CO₂ gas system, the standard rate equations adequately explain the experimental results by introducing a new switching function for the form of the cavity loss for the mechanical chopper. In an EMQ-laser with a high initial inversion density (4.5·10¹⁵ /cm³ at 150 mA peak current), multiple peak pulses or pulse distortion have been observed. This is due to the plasma screening effect induced by the burning of the metal shutter blades placed inside the cavity. It is found that tungsten metal shutter blades can be used up to a power density of 259 MW/cm² for a focused beam without this effect occurring, The solutions of the rate equations show that optimum coupling can prevent the plasma screening effect even for a Q-switching time longer than the pulse buildup time. The EMQ-laser configured for optimum coupling has produced a peak output power of 30 kW for the 9P20 transition branch in the CO₂ spectrum without any pulse distortion. This value has been obtained even though the discharge length was only 1.3 meters     

A 170 J electron beam pumped XeF(C→A) laser

A pulse output energy of 170 J has been achieved from an XeF(C→A) laser system, pumped by a pair of counterpropagating, three-meter-long electron beams. This represents a record for all types of pumping, for this excimer system. Energy was extracted from a volume of ~100 L, using a free-running stable oscillator. No evidence of laser oscillations on the competing XeF(B→X) transition was observed. Within the extraction volume the laser gas was pumped at a rate of 140 kW/cm³ (time average value), for a period of 1.7 μs. The optical cavity was folded, giving a gain length of 6 m. The optical pulse duration was 0.8 μs (full width at half maximum), and the observed flux buildup time of ~1 μs was consistent with modeling and a measurement of the net gain. The specific output energy was 1.7 J/L which is comparable to that achieved in previous, small scale experiments at somewhat higher pump rate. The results confirm the volumetric scalability of the electron beam pumped XeF(C→A) laser system to high output energy per pulse, and the feasibility of operating this system at a low electron beam pump rate which relaxes constraints on the design of the electron gun and pulse power subsystems in a high output energy device. Means for extending the laser pulse duration and increasing the output energy of the specific test device are discussed. An output energy of ~1000 J is projected for an optimized gas cell width, for full size resonator mirrors, and with injection     

Pulse buildup dynamics of an actively mode-locked laser diode arrayin the external cavity

Dynamic pulse evolution characteristics of an actively mode-locked laser diode array in the external cavity have been investigated. Numerical calculations based on modified traveling-wave rate equations reproduce experimentally observed pulse and spectral width evolution and show that the buildup time is about 45 round-trips. We have also performed a theoretical analysis to understand which of the laser operating parameters would affect the buildup dynamics. It is shown that either higher dc bias current or larger radiative recombination coefficient (which is inversely proportional to the excited-state lifetime) will render the laser exhibiting shorter steady-state pulse width and faster evolution to the steady state. Other parameters affecting the buildup, but to a lesser extent, include the radio-frequency (RF) modulation current, spontaneous emission coefficient, and gain coefficient. The power reflectivities of the output mirror and the antireflection coated diode facet, on the other hand, have little effect on the pulse width and buildup time for single pulse generation     

波导CO2激光器电光腔倒空特性研究

对影响射频波导激光器电光腔倒空的激光输出脉冲特性的几个主要参数进行了研究。通过改变加在CdTe电光晶体上高压脉冲的不同上升沿时间,以及在不同布氏窗输出反射率等情况下,对腔倒空的脉冲宽度及脉冲峰值功率的变化特性进行了理论分析。在一台用于主动激光成像雷达光源的准折叠高重频腔倒空射频波导CO2激光器上,通过改变CdTe电光晶体的工作参数,获得了20ns到30ns(FWHM)可调输出脉宽。     

Very short far-infrared pulses from optically pumped CH3OH/D, CH3F, and HCOOH lasers using an EQ-switched CO2laser as a pump source

Very short far-infrared (FIR) pulses were generated from optically pumped CH3F, CH3OH/D, and HCOOH lasers using aQ- switched, current pulsed (200 mA, 100 μs), low pressure (20 torr) CO2laser as a pump source. Values of 20 ns for the rise time and 50 ns for the decay time of the FIR pulses have been observed. The dependence of the FIR pulse shape parameters, i.e., rise time, decay time, and pulse buildup time, on the width of the pump pulse and the pressure of the molecular gas have been investigated experimentally. Due to the regular pulse shape, high repetition rate (350 Hz), high peak power (≳1 W), and broad spectral range (lambda = 100-500 mum), the pulses are very useful for purposes of solid-state and molecular time resolved spectroscopy.     

暗脉冲激光器的研究进展

暗脉冲激光在光波导中传输噪声小、损耗低,因此在信号处理方面比传统亮脉冲更有优势。介绍了暗脉冲激光器的国内外研究进展,重点介绍了经后期光学或电学整形产生暗脉冲和激光器直接产生暗脉冲的各种理论方案,最后对暗脉冲激光器的应用和发展前景进行了展望,并指出了目前还存在的问题。     

低能量抽运的增益开关型Cr4+:Mg2SiO4激光器

为了研究低能量的1.06μm调Q激光脉冲抽运的增益开关型Cr4+:Mg2SiO4激光器,对该激光器的速率方程进行数值求解,并选取合适的初始条件,得到输出的1.22μm激光脉冲的时间波形、脉冲的建立时间和脉冲宽度与抽运能量的关系,理论计算与实验研究结果基本符合。当抽运激光脉冲的能量为45mJ、脉冲宽度为30ns时,激光器输出的1.22μm激光脉冲的能量和脉宽分别是7mJ和8.2ns。输出激光的脉冲宽度是抽运激光的脉冲宽度的近1/4,光-光转换效率为15.5%。数值计算和实验研究结果均表明,在低能量抽运情况下,激光脉冲的建立时间和脉冲宽度均随着抽运能量的增加而减小。     

1064nm可编程半导体激光脉冲种子源的研究

为了运用主振功率放大技术获得纳秒量级的高功率密度激光脉冲,设计了一种运用于主振功率放大的半导体激光种子源,通过编程可输出多种形状光脉冲,并采用主动脉冲外形控制技术提高了输出光脉冲的波形质量。实验中研制了高速大电流驱动模块和可编程多种调制波形发生器,并采用了1064nm量子阱分布反馈的大功率半导体激光器。结果表明,该种子源脉冲光功率优于200mW、动态范围优于20dB、脉冲宽度40ns~1μs和重复频率0MHz~5MHz可调,可编程控制输出多种波形。     

1064nm激光诱导等离子体开关控制355nm脉宽可调输出

为得到脉宽可控的355nm紫外脉冲激光输出,采用1064nm脉冲激光诱导等离子体开关技术,控制355nm激光脉冲宽度,在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了2.8ns～10ns的脉宽可调输出。讨论了1064nm单脉冲输出能量对脉宽压缩的影响,在无延时情况下得到了脉宽最短达2.8ns的脉冲激光输出。在此基础上,保持1064nm单脉冲输出能量不变,采用延时装置改变两光路间的光程差,以控制等离子体开关相对于355nm激光脉冲的形成时间,最终得到脉宽可调的脉冲激光输出。结果表明,等离子体开关结构简单、操作方便、适用范围广,是一种较好的脉冲整形手段。     

High-peak-power picosecond optical pulse generation from highly RF-modulated InGaAsP DH diode laser

The feasibility for generating high-peak-power ultrashort optical pulses was demonstrated from a highly RF-modulated InGaAsP DC-PBH laser diode at 1.3 ?m for the first time. Measured pulse width is found to be approximately 28 ps at 7 mW averaged output power, and peak output power reached about 1.2 W at 210 MHz repetition frequency. Higher peak output and shorter optical pulses could be expected with this type of semiconductor diode laser in the near-infra-red region.     

高重复频率的增益开关Nd3+:YVO4+KTP绿光激光器

摘要：介绍了可连续和脉冲双模式输出的绿光激光器。用一只半导体激光器端面抽运Nd3+:YVO4+KTP胶合晶体,通过腔内倍频,获得光-光转换效率为19%的连续绿光激光输出。利用增益开关技术,改变注入激光器的电脉冲波形,可以得到方波、正弦波或三角波的绿光激光脉冲输出;调节激光器驱动电流的幅度和占空比可改变输出激光脉冲的强度和脉宽;改变驱动电源的重复频率可以使输出绿光激光脉冲的重复频率连续可调,最大重复频率可达2MHz。在重复频率为560kHz时,获得了输出绿光激光脉冲宽度为74ns、峰值功率为285mW、振幅噪声小于3%。     

Investigation of the characterstics of a mode-locked Nd:Glass laser with the aid of a picosecond streak camera

An infrared-sensitive streak camera, capable of resolving optical pulses of durations of ∼3 ps, has been used to analyze the temporal development of the individual picosecond pulses in a mode-locked pulse train. A progressive increase in the duration of the individual pulses throughout the pulse train is observed, the rate of increase in the pulse duration being an approximate quadratic function of the optical field. In addition, temporal analysis of the laser output signal, dispersively delayed with the aid of a grating pair, confirms the existence of phase-modulation effects during the development of the mode-locked pulse train.     

高重复频率的增益开关Nd3+:YVO4+KTP绿光激光器

为了设计一种可连续和脉冲双模式输出的绿光激光器,采用一只半导体激光器端面抽运Nd3+:YVO4+KTP胶合晶体,通过腔内倍频,获得光-光转换效率为19%的连续绿光激光输出.利用增益开关技术,改变注入激光器的电脉冲波形,可得到方波、正弦波或三角波的绿光激光脉冲输出;调节激光器驱动电流的幅度和占空比可改变输出激光脉冲的强度和脉宽;改变驱动电源的重复频率可以使输出绿光激光脉冲的重复频率连续可调,最大重复频率可达2MHz.在重复频率为560kHz时,获得了输出绿光激光脉冲宽度为74ns、峰值功率为285mW、振幅噪声小于%.研究表明,利用增益开关技术可以获得重复频率和窄脉冲宽度的绿光激光脉冲.     

电光调Q双脉冲输出Nd:YAG全固态激光器

设计了激光二极管(LD)双端面抽运传导冷却复合Nd:YAG晶体电光调Q激光器,实现脉冲间隔可调的双Q脉冲输出。用两个光纤耦合输出的LD模块作为抽运源,偏硼酸钡(BBO)晶体作为Q开关,在一个抽运周期内两次启动Q开关,获得脉冲能量大于14mJ,脉宽小于等于18ns,脉冲间隔200～230μs可调的双Q脉冲输出,激光器重复频率50Hz,光-光转换效率达到24%。探索了用磷酸二氘钾(KD*P)调Q晶体开关实现稳定双脉冲输出的可行性,通过抑制压电环效应,消除子脉冲现象,最终获得脉冲能量约11mJ,脉宽小于等于18ns。     

Electronically controlled high-speed wavelength-tunable femtosecondsoliton pulse generation using acoustooptic modulator

The compact system of electronically controlled high-speed wavelength-tunable femtosecond (fs) soliton pulse generation is realized for the first time using a passively mode-locked fs fiber laser, a polarization maintaining optical fiber, and an acoustooptic (A-O) modulator. The wavelength of the output pulses can be continuously tuned simply by controlling the input voltage into the A-O modulator. The wavelength of the soliton pulses can be changed at 2.5-μs intervals. Wavelength stabilization, time division wavelength multiplexed soliton pulse generation, and a wavelength scanner have been demonstrated     

Pulse energy gain saturation in subpico- and picosecond pulseamplification by a traveling-wave semiconductor laser amplifier

Optical pulses with durations ranging from 0.49 to 21 ps are amplified by a traveling-wave semiconductor laser amplifier. The pulse energy gain is determined by pulse energy only. The dependence of pulse energy gain on output pulse energy does not change in the pulse duration range. The saturation characteristics are successfully explained by a four-level system model     

A pulse repetition frequency scaling law for the high repetition rate neutral barium laser

The variations in the output energy per pulse and in the average power output of the neutral Ba cyclic metal vapor laser as a function of the pulse repetition rate have been analyzed. At constant input power, the output energy per pulse is found to vary inversely as the two-thirds power of the pulse repetition frequency and so the average output power varies as the pulse repetition frequency to the one-third power up to the point where the Ba metastables do not have sufficient time to relax between pulses. Since the experiments which have been analyzed were conducted with a constant value for the laser discharge capacitance, these results imply that the output energy per pulse of this laser varies as the four-thirds power of the input voltage.     

Actively initiated quasi-passive mode-locking in a CW SELFOC Nd:glass laser

Actively initiated quasi-passive mode-locking has been achieved in a small-power CW SELFOC Nd:glass laser. Three means have been taken to enhance the pulse intensity incident on a saturable dye to a magnitude sufficient for nonlinear absorption initiation: 1) tight focusing, 2) controlled spiking oscillation, and 3) auxiliary active mode-locking. Mode-locked pulses having an 11-12-ps pulsewidth were obtained. Interpretation concerning the observed mode-locked-pulse intensity-correlation curves is presented. To obtain satellite-pulse-free mode-locked pulses, a modified mode-locking process with sufficiently long buildup time is considered.     

1064nm激光诱导等离子体开关控制355nm脉宽可调输出

为得到脉宽可控的355nm紫外脉冲激光输出,采用1064nm脉冲激光诱导等离子体开关技术,控制355nm激光脉冲宽度,在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了2.8ns～10ns的脉宽可调输出.讨论了1064nm单脉冲输出能量对脉宽压缩的影响,在无延时情况下得到了脉宽最短达2.8ns的脉冲激光输出.在此基础上,保持1064nm单脉冲输出能量不变,采用延时装置改变两光路间的光程差,以控制等离子体开关相对于355nm激光脉冲的形成时间,最终得到脉宽可调的脉冲激光输出.结果表明,等离子体开关结构简单、操作方便、适用范围广,是一种较好的脉冲整形手段.