Heterodyne measurements of submillimeter laser spectrometer frequencies

The frequencies of 46 CW laser lines commonly used for submillimeter spectroscopy, with wavelengths between 0.1 and 0.7 mm, have been measured by heterodyne methods. All the fines are optically pumped by a CO2laser, with threshold pump powers of 3 W or less. The precision of measurement, limited by the laser linewidth, is typically ± 1 part per million.     

用飞秒锁模激光测量光的频率

介绍了2005年诺贝尔物理学奖的获奖工作-用锁模飞秒激光光梳去测量光的频率.飞秒激光光梳技术大大简化了光频的测量.锁模飞秒激光通过光子晶体光纤时,由于自相位调制,在可见光和近红外区能够产生上百万等间隔的梳状频率,其频率间隔等于锁模脉冲的重复率.利用光频梳和倍频技术,把对光频的测量变为对射频的测量,这样就能够很容易地测出光的频率.使得光频测量精度和原子钟精度达到前所未有的高度,从而对物理学和计量学的发展有重要意义.     

Theory of optically pumped submillimeter lasers

Theoretical models of the operating characteristics of both pulsed and CW optically pumped submillimeter (SMM) lasers are reviewed. The SMM laser gain is discussed for both pressure and Doppler broadened transitions. A review is given of expressions for SMM laser gain based on quantum mechanical calculations in a three-level molecular system.     

Assignment of laser lines in optically pumped submillimeter lasers: HDCO, D2CO

Respectively, three and eight laser lines have been precisely measured and assigned in asymmetric-top molecules HDCO and D2CO. Frequency calculations of rotational transitions use parameters obtained from microwave studies. For frequency calculations of rovibrational transitions, vibrational energies derived from infrared band analysis have been also taken into account. The assignment is confirmed by infrared radio frequency double resonance experiments inside the submillimeter laser cavity.     

不同脉宽激光和频产生蓝色超短激光的模拟研究

为了扩展现有飞秒激光的波段,采用非周期的准位相匹配光学超晶格进行了两束激光的和频研究.光学超晶格的结构由遗传算法根据要求模拟计算得到,在此结构晶体上进行平顶长脉宽激光与飞秒激光和频,可以有效地抑制和频光的脉宽展宽,生成457nm的蓝色飞秒激光.结果表明,该技术提供了一种通过两束不同激光和频产生新波长超短脉冲激光的全新技术方案.     

Application of submillimeter wave lasers to high voltage cable inspection

An experimental device designed for real-time, nondestructive inspection of cross-linked polyethylene insulation during cable manufacture has been built, analyzed, and tested under laboratory conditions. The device detects scattered far-infrared (FIR) laser energy at 118.8 μm from imperfections, such as voids and contaminants, known to have a serious deleterious influence on cable in-service lifetime. As presently configured, the device can readily detect voids as small as 100 μm in diameter in a cable 2.8 cm in diameter moving past the sensor at 5 cm/s. Better performance of the liquid helium cooled Ga-doped Ge detectors could lead to a significant improvement in void detection capability.     

Application of the optoacoustic effect in optically pumped submillimeter lasers

The dependence of the optoacoustic signal generated in an optically pumped submillimetre laser system on gas pressure and modulation frequency has been studied experimentally and the results accounted for theoretically. With care an extracavity optoacoustic cell containing the laser gas diluted with air can be used to stablize the pump laser frequency to maximum absorption but this does not always optimise laser output.     

Wavelength-tunable optical mixing experiments between 208 nm and 259 nm

Sum-frequency generation experiments in which the second harmonics of rhodamine and coumarin dye lasers are upconverted to the 208-234 nm by mixing with 1064 nm are described. The dye lasers were pumped by the second and third harmonics of a repetitively pulsed Nd:YAG laser. Both temperature-tuned and angle-tuned phase matching techniques were used with mixer crystals of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP). Tunable light from 246 nm to 259 nm also was generated by mixing the output of a coumarin laser with the 532-nm harmonic of the Nd:YAG laser. Peak powers between about 500 W and 10 kW were obtained, and both theoretical and experimental tuning curves have been determined for these processes. Limitations imposed by mode beating effects in the Nd:YAG laser and by the relatively broad linewidth of the dye lasers are discussed.     

Electric field effects on the efficiency of optically pumped submillimeter lasers

The FIR power dependence on an applied electric field is carefully investigated for optically pumped lasers. The enhancement effect observed for many laser lines, both "orthogonal" and "parallel," is analyzed as a function of different parameters such as gas pressure, laser threshold, cavity tuning, and transitions selection rules. Measurements of the IR absorption of the gases are also carried out by a Stark optoacoustic technique. Absorption increases are observed at low electric field values. The experimental results disagree with the previously proposed linear Hanle effect explanation. They are explained with the increase in the pump saturation intensity, also detected with the transferred Lamb-dip technique. The combined effects of the absorption increase and of the small-signal gain curve decrease are shown to qualitatively explain the observed FIR enhancement features.     

Investigations of optically pumped submillimeter wave laser modes

A complete theory for waveguide laser modes for oversized metallic and dielectric waveguides with circular cross section has been developed for the submm wavelength region. The experimental investigations have been done by a submm heterodyne technique for the first stage using a Schottky barrier diode in an open structure mixer.     

Frequency pulling in an optically pumped submillimeter laser by Doppler induced dispersion

The dependence of the frequency of a CW optically pumped submillimeter laser on the frequency of its pump laser has been directly measured and shown to result largely from the dispersion produced by the two peaked gain spectrum resulting from pumping in the wings of a Doppler broadened absorption line.     

亚毫米波激光的应用领域及应用前景

阐述了亚毫米波研究、开拓的重大意义,重点介绍和分析了亚毫米波激光在基础学科、天文物理、医学生物学研究以及军事、通信、工程等领域的应用及应用前景。     

Modulation of room-temperature GaAs lasers at X-band frequencies

GaAs lasers operating at room temperature are directly modulated at X-band frequencies. A fast silicon avalanche photodiode is used to demodulate the laser light.     

Visible fiber lasers excited by GaN laser diodes

This paper describes and discusses visible fiber lasers that are excited by GaN laser diodes. One of the attractive points of visible light is that the human eye is sensitive to it between 400 and 700 nm, and therefore we can see applications in display technology. Of course, many other applications exist. First, we briefly review previously developed visible lasers in the gas, liquid, and solid-state phases and describe the history of primary solid-state visible laser research by focusing on rare-earth doped fluoride media, including glasses and crystals, to clarify the differences and the merits of primary solid-state visible lasers. We also demonstrate over 1 W operation of a Pr:WPFG fiber laser due to high-power GaN laser diodes and low-loss optical fibers (0.1 dB/m) made by waterproof fluoride glasses. This new optical fiber glass is based on an AlF₃ system fluoride glass, and its waterproof property is much better than the well known fluoride glass of ZBLAN.     

激光二极管侧面抽运免温控激光器的研究

为了解决激光二极管抽运波长随温度漂移导致激光器输出能量下降的问题，采用激光二极管抽运源波长匹配及凹凸稳定谐振腔技术实现免温控，并进行了理论分析和实验验证。该激光器腔长210mm，电光转换效率5.7%；输出单脉冲能量大于60mJ，在10℃~30℃范围内，能量稳定度优于5%；激光器输出光斑直径4mm、脉冲宽度8ns、激光器10Hz工作时，激光远场束散角为1.1mrad。结果表明，实验与理论分析计算结果符合，该激光二极管侧面抽运免温控激光器可在一定温度范围内保持稳定的能量输出。该理论分析与方案对研究免温控激光器具有重要意义。     

Electronic control of the difference frequency between two semiconductor lasers

A method for controlling the difference frequency between two semiconductor lasers has been developed. The beat frequency is directly measured and current feedback applied to one laser to control this frequency. Stability to plus or minus 10 MHz was achieved. Applications include coherent optical communication systems.     

铜蒸气激光链中激光脉冲的抖动分析

运用概率论方法导出了铜蒸气激光链中激光脉冲抖动量的表达式,结果表明:当铜蒸气激光器并联时,两台激光器输出光脉冲之间的抖动量的平方等于每台激光器输出光脉冲相对于电触发脉冲抖动量的平方和;当多台铜蒸气激光器串联放大时,第m台激光器输出光脉冲相对于振荡器输出光脉冲的抖动量随m的增加而增加,但总是小于每台激光器放电脉冲抖动量的2~(1/2)百倍。实验结果与理论计算基本相符。     

HCN激光器及亚毫米波波长的测量

简要地描述工作在亚毫米波段的连续波HCN(氰化氢)气体激光器的结构及工作特性,并分别应用反射光栅法及法布里-珀罗干涉仪法对HCN激光器的输出波长进行测量.其测量精度反射光栅法达到1%;法布里-珀罗干涉仪法达到0.1%.     

基于双频锁定的谐振式微光陀螺背散噪声抑制

经过十余年的发展,谐振式微光陀螺(RMOG)系统中的光学噪声依旧是制约陀螺输出精度的重要因素,其中背向散射噪声是谐振式微光陀螺系统中的主要光学噪声之一。本文首先分析了背散噪声产生机理,建立了谐振式微光陀螺系统背散噪声数学模型。其次,利用不同频率激光,将CW与CCW光路中的背散噪声与反向光信号的相干噪声信号移频至高频段并滤除,实现背散噪声抑制的方法。并利用双激光器双频锁定的方法进行了验证。实验结果显示,谐振曲线中背散噪声被有效抑制,从而使谐振式微光陀螺系统锁频精度提高了5倍,锁频精度达到6 °/h。