射频激励双通道不等长电极波导CO2激光器的外频率调制研究

报道了采用不等长电极结构的射频激励双通道波导ＣＯ２激光器,通过调节射频电源功率的方法可以调谐双通道输出激光的外差频率,其调谐率约为０．１ＭＨｚ／Ｗ。在未采取任何措施时,其短期外差频率稳定性可达１０＾－１０。还在理论上分析了射频功率调谐外差频率的原理。     

双通道电光调Q射频激励波导CO2激光器研究

报道了双通道可调谐电光调Q射频激励波导CO2激光器,其中一通道是光栅选支电调Q的脉冲激光输出,调Q脉冲重复频率1Hz-10kHz可调,,脉冲峰值功率为150W,脉冲宽度为180ns,另一通道是光栅选支连续激光输出,可用压电陶瓷调节激光频率,同时分析了激光外差频率调谐范围,实验上获得最大脉冲激光外差频率调谐范围为150MHz。     

分离作用射频四极场加速器频率调谐和高功率试验

在分离作用射频四极场(SFRFQ)加速腔中加入频率调谐装置,用步进电机驱动调谐杆运动,改变调谐板在腔中的位置来改变调谐板与支撑环之间的分布电容,从而改变SFRFQ腔的工作频率,使其谐振频率为26.07 MHz,实现了RFQ和SFRFQ组合加速系统频率的匹配。在完成两腔频率调谐的基础上进行了SFRFQ腔体1/6占空比高功率试验,轫致辐射谱的测量表明,SFRFQ极间电压在入射峰值功率为28.8 kW时已达到86.2 kV,超过了设计指标的70.0 kV。     

宽频调谐的光纤耦合声光调制系统

采用双次通过声光调制器和"猫眼"结构,消除频率调制带来的光路偏转并增大激光频率的调谐范围,使用射频驱动功率反馈调节法实现了激光功率的稳定.理论计算和实验验证表明,选择焦距为40mm透镜方案,激光频率调谐在160 MHz时,系统整体光纤耦合效率达到了56.8%.在保证系统光利用率大于15%时,系统的有效频率调谐范围为100 MHz.通过功率稳定系统,在频率调谐60 MHz的变化范围内,输出光功率波动控制在±0.07%以内并能保持长期稳定工作.     

双通道符合计数光子外差探测系统仿真构建与研究

本文提出将符合测量方法用于光子外差测速技术中,将光子符合计数模式应用于光子外差测速系统,能够在一定程度上减少背景噪声、暗噪声和后脉冲带来的光子误计数,提高信噪比等测速性能。基于外差原理与单光子探测的泊松响应,以及光子符合计数原理,本文仿真研究了双通道符合计数光子外差系统的性能,利用1550 nm连续波激光器探测匀速运动目标,结果表明,双通道符合计数模式下中频信号功率谱的信噪比明显高于单通道自由运行模式和一阶滤波下的功率谱信噪比。随着信号光子数增加,两种计数模式的信噪比能够相差2～3 dB。针对该方法,又进一步通过仿真研究了本振光强、背景噪声、中频频率、探测时长四个因素对双通道符合计数光子外差测速系统性能的影响。结果表明,随着本振光强与信号光强的比值逐渐增大,系统信噪比先增大后减小,在kL=3附近时达到最大;背景噪声越大,饱和信号光子数越大,饱和信噪比越低;探测时长越长,饱和信噪比提高幅度越大;而在探测带宽之内,中频频率也即运动目标的速度对结果影响较小。本文从改变前端光子计数模式的角度提高光子外差探测系统的性能,为提高光子外差测速的信噪比拓宽了思路。     

射频电感性耦合等离子体调谐基片自偏压特性

采用调节射频电感性耦合等离子体中基片电极与地之间的外部电路阻抗的方法,控制基片电极的射频自偏压。研究了调谐基片自偏压随外部调谐电容值的变化特征,得到了调谐基片射频自偏压随射频放电功率、气压的变化曲线。在一定放电参数区域内,调谐基片射频自偏压随调谐电容的变化曲线呈现跳变、双稳、迟滞现象。     

宽带可调谐单频窄线宽光纤激光器

设计出一种集可调谐带通滤波器、高精度环形滤波器和光纤环形镜于一体的全光纤复合腔结构可调谐单频窄线宽光纤激光器。采用980 nm半导体激光器作为抽运源,掺镱光纤在谐振腔内分别作为增益介质和可饱和吸收体,成功实现波长为1030～1090 nm稳定的宽谱可调谐单频窄线宽激光输出。当抽运光的抽运功率为300 mW时,在波长为1070 nm处得到的输出功率最大,为18.5 mW,斜率效率达到7.95%,持续1 h内没有出现跳模现象,功率不稳定性小于1%;当抽运功率为200 mW时,利用延迟自外差法测量线宽,得到波长调谐范围内的平均线宽为8.7 kHz,弛豫振荡频率为64 kHz。     

双驱动射频负氢离子源匹配网络设计与实验研究

随着磁约束聚变实验装置对中性束注入器的输出束流强度与脉冲时间的要求越来越高,开展高功率大面积射频离子源的研究迫在眉睫。为了实现大面积、高密度均匀等离子体放电,基于多驱动射频离子源的设计是当前的发展趋势,而阻抗匹配网络是射频功率源将最大功率输送至线圈并耦合至等离子体的关键,故对其结构设计和调谐特性的研究是不可或缺的。基于前期在单驱动射频离子源的研究基础上,结合双驱动射频离子源的放电需求,开展了双驱动阻抗匹配网络优化结构的设计与分析,通过实验中对匹配网络的调谐,成功实现了140 kW高功率和25 kW/1 000 s长脉冲的稳定运行。随后在等离子体稳定放电的基础上研究了两个驱动器之间的功率分配均匀性问题,实验结果表明了该匹配网络的优化设计合理可行,上下驱动器的射频功率分配基本均匀。     

基于中频相位锁定技术的宽带调谐光电振荡器稳定性研究

提出了一种基于中频相位锁定技术提升宽带调谐光电振荡器长期稳定性的方法.该方法通过外部可调本振源对光电振荡器射频信号进行下变频操作,产生中频信号,该中频信号与光电振荡器的起振频率无关.将该中频信号锁相在稳定的参考源上,能够提升宽带调谐光电振荡器的长期稳定性,同时分析了锁相环对光电振荡器相位噪声性能的影响.实验结果显示,光电振荡器的频率调谐范围可达5~15GHz,10kHz频偏处的相位噪声为-121.2dBc/Hz,频率稳定性达到6.9×10-11/103 s,表明该方法能够显著提升宽带调谐光电振荡器的稳定性.     

基于时变功率谱的激光器调谐瞬时线宽测量方法研究

半导体激光器的线宽通常采用激光外差测量技术,通过差拍信号的功率谱密度函数来确定,受傅里叶变换方法的限制,得到的均是在一定时间段内的静态平均线宽。为了获得半导体激光器在电流调谐过程中的瞬时线宽特性,提出了利用时变功率谱获知调谐瞬时线宽的相干和非相干测量方法,并分别进行了理论分析和实验验证。首先对半导体激光器输出光信号及差拍信号进行了时间-频率域下的数学描述,确定了时变功率谱与调谐瞬时线宽的关系;其次,针对差拍信号的趋向性特征,提出了趋势局部均值分解方法,并研究了利用分解出的乘积函数建立差拍信号及激光器输出光信号的时变功率谱的方法;最后利用非相干和相干测量法分别获得了分布反馈式半导体激光器在50~51及50~100 mA锯齿波电流调谐过程中的瞬时线宽。     

纳秒激光诱导空气等离子体射频辐射特性研究

开展了波长为532 nm、脉宽为8 ns的纳秒激光诱导空气等离子体射频电磁辐射特性实验研究,基于锥形天线探测空气等离子体在30-800 MHz频谱范围有较强的射频电磁辐射,是等离子体内电偶极子振荡变速运动造成的.实验结果表明:随激光能量增加,30-200 MHz范围内射频辐射强度逐渐变强,但360-600 MHz频率范围射频辐射强度逐渐变弱.等离子体射频辐射的空间分布依赖于入射激光的偏振方向,当激光偏振方向与天线放置方向一致时,该方向上空气等离子体的射频辐射强度高,谱线较丰富.射频辐射总功率随激光能量先增加后降低,采用等离子体电子密度变化对等离子体频率及等离子体衰减系数影响(制约)关系,对射频辐射总功率随激光能量的变化规律进行了解释.     

Compact waveguide CO2 laser excited by a RF power supply

The design and performance of radio frequency (RF) excited partial Z-fold waveguide CO2 laser with two channels are exposed. The length of the partial Z-fold channel is 3×460 mm and that of the single channel is 460 mm. The electrodes for the two channels are common and excited by a same RF source. According to our analysis, this kind of structure can greatly improve the laser offset frequency stability. In the experiments, we studied the variation of laser output power with gas pressure for two different channels.The maximum laser output power is about 23 W for the partial Z-fold channel and about 6 W for the single channel.     

Laser capabilities of CuBr mixture excited by RF discharge

Our investigations demonstrated that utilizing copper bromide (CuBr) mixture as a source of Cu atoms in a RF-excited discharge can be a promising alternative to the Cu sputtered system, when the development of Cu ion gas laser is considered. Both spectroscopic and laser investigations showed that the threshold input power for lasing was reduced about 5 times using the CuBr-based system instead of the Cu-sputtered system. Pulsed and CW laser oscillation on Cu⁺ transitions in the near IR spectral region was obtained in RF-excited He-CuBr discharge operated at 13.56 MHz and 27.12 MHz. At input RF power of 800 W, a laser output power of 10 mW at the 780.8 nm Cu ion laser line was achieved. An increase of laser output power by a factor of two, as well as better Cu vapour axial distribution and better discharge stability, was attained when DC discharge was superimposed on the RF discharge. Laser gain on 11 UV Cu ion lines was observed in RF-excited Ne-CuBr discharge. basing on the obtained results, we consider the CuBr laser system excited by RF discharge capable of generating UV laser radiation at relatively low input power. Received 4 January 1999     

Noise properties of an optical frequency comb from a SESAM-mode-locked 1.5-μm solid-state laser stabilized to the 10?13 level

We present a detailed investigation of the noise properties of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser operating in the 1.5-??m spectral region. The stabilization of the passively mode-locked Er:Yb:glass laser oscillator, referred to as ERGO, is achieved using pump power modulation for the control of the carrier envelope offset (CEO) frequency and by adjusting the laser cavity length for the control of the repetition rate. The stability and the noise of the ERGO comb are characterized in free-running and in phase-locked operation by measuring the noise properties of the CEO, of the repetition rate, and of a comb line at 1558?nm. The comb line is analyzed from the heterodyne beat signal with a cavity-stabilized ultra-narrow-linewidth laser using a frequency discriminator. Two different schemes to stabilize the comb to a radio-frequency (RF) reference are compared. The comb properties (phase noise, frequency stability) are limited in both cases by the RF oscillator used to stabilize the repetition rate, while the contribution of the CEO is negligible at all Fourier frequencies, as a consequence of the low-noise characteristics of the CEO-beat. A?linewidth of ??150?kHz and a fractional frequency instability of 4.2×10^?13 at 1?s are obtained for an optical comb line at 1558?nm. Improved performance is obtained by stabilizing the comb to an optical reference, which is a cavity-stabilized ultra-narrow linewidth laser at 1558?nm. The fractional frequency stability of 8×10^?14 at 1?s, measured in preliminary experiments, is limited by the reference oscillator used in the frequency comparison.     

高功率宽带射频调制连续激光源

射频强度调制激光作为激光雷达系统的载波可以有效提高系统的抗干扰和抗散射能力,高功率宽带射频强度调制光源是实现高分辨率远距离探测的关键.本文采用在Nd:YAG激光器的耦合腔中插入一对四分之一波片的方法实现了频差调谐范围为30 MHz—1.5 GHz的双频激光输出,结合光纤振荡功率放大技术,将双频信号光功率放大为50 W.耦合腔双频种子源具有良好的功率和频率稳定性,输出功率为9.5 mW时,功率标准差为0.145 mW,稳定性为1.52%,输出双频激光的频差为250 MHz时,拍频的标准差为1.6144 MHz.种子光进行三级光纤功率放大,得到50 W双频激光输出.放大后的双频激光功率波动范围小于0.1 W,双频拍频的标准差为1.777 MHz,很好地保持了放大之前的功率稳定性和双频频差稳定性.     

Environmentally-stable all-normal-dispersion picosecond Yb-doped fiber laser with an achromatic quarter-wave-plate

We present an environmentally-stable picosecond Yb-doped fiber laser by employing an achromatic quarter-wave-plate (AQWP) as a pulse stabilizer in the all-normal-dispersion and polarization-maintaining linear laser cavity. It is shown that the AQWP plays a critical role to control both the polarization state and spectral filtering of the proposed mode-locked laser. The demonstrated laser generates 2-ps-long pulses with pulse energies of 1 nJ at a repetition rate of 117 MHz and parabolic spectral width of 26 nm. The fundamental RF carrier frequency exhibits Allan deviation of 3.8 × 10⁻⁸ at 1-s averaging time and phase noise of −95 dBc/Hz at 10-Hz offset frequency.     

Tapered semiconductor amplifiers for optical frequency combs in the near infrared

A tapered semiconductor amplifier is injection seeded by a femtosecond optical frequency comb at 780 nm from a mode-locked Ti:sapphire laser. Energy gains of more than 17 dB(12 dB) are obtained for 1 mW(20 mW) of average input power when the input pulses are stretched into the picosecond range. A spectral window of supercontinuum light generated in a photonic fiber has also been amplified. Interferometric measurements show sub-Hertz linewidths for a heterodyne beat between the input and amplified comb components, yielding no detectable phase-noise degradation under amplification. These amplifiers can be used to boost the infrared power in f-to-2f interferometers used to determine the carrier-to-envelope offset frequency, with clear advantages for stabilization of octave-spanning femtosecond lasers and other supercontinuum light sources.     

Optical and RF stability transfer in a monolithic coupled-cavity colliding pulse mode-locked quantum dot laser

We report a novel quantum dot based laser design where a stable high-Q master laser is used to injection lock a passively mode-locked monolithic colliding pulse slave laser. Coupling between the crossed orthogonal laser cavities is achieved through a common monolithically integrated saturable absorber, which results in the locking and hence reduction of the timing jitter as well as the long-term frequency drift of the slave laser. A stable 30?GHz optical pulse train is generated with more than 10?dB reduction in the RF noise level at 20?MHz offset and close to 3 times reduction in the 10?dB average optical linewidth of the slave laser.     

用于中性束注入的大功率射频离子源激励器研制

建立了一个等离子体射频激励器,工作气体为氢气,工作气压为0.3Pa,激励器陶瓷桶直径300mm,工作频率1MHz。实现了RF等离子体激发放电,在输入射频功率16kW条件下,采用朗缪尔探针测得的等离子体密度>10¹⁸m^-3,初步建立了一个RF等离子体源实验平台。     

高效频率转换下双波长外腔共振和频技术研究

基于外腔的高效频率转换, 尤其是当系统运行在抽运不消耗近似机理下, 信号光可实现大于90%的转换, 因此无法通过信号光直接获得其到腔模频率锁定的误差信号. 本文通过对信号光调制、和频光解调的方法获得了该误差信号, 实现了双波长激光到外腔腔模的级联锁定. 实验中外部环形腔将1.3 W的1064 nm抽运光放大到约14.3 W. 当1583 nm信号光从10 μW变化到50 mW, 其到636 nm和频光的转化效率约为73%; 当从50 mW变化到295 mW时, 转换效率呈线性降低到60%, 最终获得了440 mW的636 nm激光.