Optically pumped submillimeter gas lasers and the prospects for constructing space-qualifiable LO systems

An optically pumped submillimeter laser operating in the 500 μm (600 GHz) to 100 μm (3 THz) spectral range is the primary and, at present, the only available local oscillator (LO) source for laboratory and astronomical heterodyne applications for this wavelength region. A short review of the state-of-the-art of submillimeter lasers as LO sources, with an emphasis given to receiver systems designed for airborne heterodyne observations, will be presented. The characteristics and prospects for constructing a spacequalifiable laser LO system will also be given.     

Determination of laser frequencies by mixing experiments between two submillimeter lasers

The radiation of optically pumped submillimeter lasers has been investigated using a heterodyne system with a Schottky barrier diode in a quasi optical mixer. The laser frequency, the mode purity and the total linewidth was determined by mixing experiments between two submillimeter lasers. The uncertainty of the measured laser frequency is about 200 kHz.     

外差锁定式相干光通信

提出并研制了一种新的外差锁定激光频率调制系统,可用于相干光通信,并进行了闭环调频、调幅实验。对实用的外差锁定式半导体激光器光纤通信系统的技术条件作了讨论。     

Submillimeter astronomy [heterodyne spectroscopy]

Some of the aspects of submillimeter-wave astronomy which are relevant to the field of heterodyne spectroscopy are reviewed. Most of the discussion concerns the dense interstellar medium where stars are forming, with some work presented on nearby galaxies. Extremely sensitive receivers, large accurate telescopes, and high-mountain, airborne, or space platforms are gradually being developed, so that information is steadily improving in quality and scope. Examples are given of line surveys of heavy molecule spectra, extending from millimeter wavelengths well into the submillimeter, of light molecule spectroscopy, and of atomic fine-structure spectroscopy. The importance of the spatial information on atomic and ionized carbon is discussed. The gas cooling process which allows clouds to collapse to form stars by means of the submillimeter line emission is discussed. Also covered are regions suffering shocks, photodissociation regions, and stellar outflow regions. Work on the submillimeter spectrum of nearby galaxies is briefly described     

Submillimeter-wave emission assignments for 1,1-difluoroethylene

Many of the known submillimeter wave emissions of 1,1-difluoroethylene are assigned by using new data from infrared diode laser heterodyne spectroscopy. Six new submillimeter lines are also reported and assigned.     

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.     

Far infrared heterodyne detectors

The characteristics of far infrared detectors are reviewed. Three detectors, the InSb hot electron bolometer, the GaAs Schottky diode and the Josephson point contact junction, have been incorporated as mixers into sensitive heterodyne systems. The performances of existing heterodyne receivers/radiometers are described and compared. Other applications of submillimeter heterodyne techniques are discussed.     

战术机载激光武器

固体激光器的快速发展,现已能在空中平台的紧凑系统中提供武器级的功率,美国空军正在加速发展战术机载激光武器。首先总结了空军先进战术激光计划的经验教训,评述了战术机载激光武器的发展目标、要求和挑战。然后评述和讨论了激光武装直升机和激光战斗机的发展计划、作战目标、组成和技术特点。最后讨论和分析了高能液体激光器、光谱合成光纤激光器和平面波导激光器的特点、关键技术、最新进展和面临的挑战。     

Microwave signals generated by optical heterodyne betweeninjection-locked semiconductor lasers

Single-mode-laser rate equations with added Langevin noise sources are used to study injection-locked semiconductor lasers. Two slave lasers are frequency-locked on the same or different sidebands of a current-modulated master laser. The optical heterodyne between the two secondary lasers is characterized. It is demonstrated that the frequency stability of the source modulating the master laser is preserved on the sidebands and partially transferred to the slaves. A linear model is first investigated. Static operation conditions and small-signal behavior are then calculated. Direct simulation of the rate equations for each laser is next achieved. This highlights the validity domain and limitations of the linear model. A more complete set of results-such as laser and heterodyne spectra-is also obtained. It is moreover shown that synchronization of the slave laser diodes by optical injection-locking leads to strongly correlated, while not identical, laser fields. Finally, simulation results are compared to experimental data     

窄线宽激光器线宽测量方法

回顾了窄线宽激光器线宽测量的各种方法和发展过程,介绍了利用光外差法测量窄线宽激光器线宽的基本原理,描述了双光束外差法和延时自外差法的不同测试机理。针对延时零拍自外差法容易引起的系统误差,说明了光源调制和光路调制移频非零拍自外差法不同改进方案的优缺点。综述了窄线宽激光器测量线宽的新方法。对窄线宽激光器线宽测量方法进行了较全面的梳理,从发展过程看双光束外差法和延时自外差法有着各自的测量优势。     

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.     

The effect of spurious intensity modulation in semiconductor diode lasers on the performance of optical heterodyne frequency shift-keyed communications systems

Analytical expressions are derived for the bit-error rate (BER) of anM-ary frequency shift-keyed (FSK), heterodyne, optical communication system with noncoherent demodulation in the presence of spurious intensity modulation (SIM) and frequency noise. The SIM degradation of an FSK system, implemented with semiconductor diode lasers, is estimated for lasers with zero and nonzero linewidths and will be discussed for a distributed feedback laser operating at 1.5μm and a channeled substrate planer laser operating at 0.83 μm. The SIM power penalty is typically less than 1 dB, but can exceed 1 dB for 2-, 4-, and 8-ary FSK at data rates above 1 Gbit/s.     

Coherent laser radar in Europe

European work in coherent laser radar with 10 μm and shorter wavelength lasers is reviewed. Fundamental aspects include heterodyne studies of signal statistics and fluctuations, and detailed experimental and theoretical work on signal amplification and autodyne arrangements with light reinjected into the laser cavity. Progress with lasers, detectors, and modulators has led to the development of several compact robust field systems both continuous-wave and pulsed. Various ground-based programs are described including local wind field measurement and wake vortex investigation at airfields, and study of range, image, and Doppler shift of hard targets. Airborne systems have investigated avionics problems of true airspeed, pressure error, and wind shear warning. Other airborne studies include ground imaging, obstacle warning, terrain following, and a compendium of atmospheric backscattering over the North and South Atlantic. In recent years, the European Space Energy has supported studies and technology development for a space-borne wind lidar in the Atmospheric Laser Doppler Instrument (ALADIN) program     

Optical FSK signal detection in a heterodyne system using semiconductor lasers

A 10?8 bit error rate is achieved for 100 Mbit/s signals in an FSK heterodyne frequency-discrimination detection system, in which AlGaAs double-heterostructure lasers are used as both the FSK transmitter and the local oscillator. Receiving signal power level to achieve a low bit error rate is experimentally obtained, which confirms the principle of optical heterodyne detection. AM quantum noise in the laser local oscillator and FM quantum noise are important factors which determine the system performance.     

四波混频非线性效应和腔各向异性对横向塞曼激光特性及其应用的影响

讨论了激光腔中四波混频非线性效应和腔各向异性对横向塞曼激光拍频波形畸变和频率锁定的影响,解释了这种现象的物理机制,同时讨论了拍频波形畸变对光拍相位检测技术的影响,这对STZL的应用研究有重要意义.     

M-ary FSK Performance for Coherent Optical Communication Systems Using Semiconductor Lasers

This paper describes the design and performance of anMary frequency shift keyed (FSK) signaling and demodulation scheme for an optical communication system using semiconductor lasers and heterodyne detection. Frequency or phase noise in semiconductor lasers causes spectral spreading, producing a nonzero linewidth laser signal. This degrades communication performance when compared to a system using an ideal laser with zero linewidth. We present estimates of the bit error rate (BER) performance ofM-ary frequency shift keying (FSK) with noncoherent demodulation in the presence of white Gaussian frequency noise and additive channel noise. This is typical of an optical system using semiconductor lasers and heterodyne detection. Estimates use the union-Chernoff bound with a simplified channel model to predict the effects of frequency noise. Two effects of frequency noise are identified: signal attenuation or suppression, and crosstalk. These cause an offset in the BER curve from the BER in the absence of frequency noise, and an error rate floor, respectively. The error rate floor is lower than previously predicted. When performance is not crosstalk limited,M-ary FSK is found to perform better than binary FSK with the same system bandwidth constraints, as would be predicted if ideal lasers are used. Theoretical results are compared with Monte Carlo simulations of the system.     

Design of SMMW Laser Resonators with On-Axis Signal and Pump Beam Guiding in a Mirror Ring

A ring resonator design for optically pumped submillimeter wave (SMMW) lasers using the same set of four mirrors (including one focussing mirror) for pump beam and SMMW beam guiding is introduced. The optimum design is discussed on the example of a 2.523 THz methanol laser. It turns out that the focal length of the focussing mirror has to be adapted to the resonator perimeter. Eleven well suited focal length - resonator perimeter ratios, defining eleven standard resonator configurations, can be distinguished. The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed. This paper is the extended version of the paper presented on the 23rd International Conference in Colchester [1] and continues a former article presented in this journal [2].     

High frequency heterodyne spectroscopy with current-modulated diode lasers

The use of current-modulated semiconductor lasers for optical heterodyne spectroscopy has been investigated at modulation frequencies up to 2.6 GHz. The current modulation produces a simultaneous frequency and amplitude modulation of the laser output. A characteristic heterodyne spectrum occurs when the modulated laser probes a narrow absorption line. In order to analyze the measured spectra, a complete line shape theory has been derived for heterodyne spectroscopy with frequency- and amplitude-modulated laser light. The results show how the obtained signals depend on the modulation frequency and the phase difference between the frequency and the amplitude modulation. The measurement technique permits investigation of the FM-AM phase difference of current-modulated semiconductor lasers.     

New SMMW laser transitions optically pumped by a tunable CO2waveguide laser

Optical pumping of a submillimeter wave (SMMW) laser with a relatively compact RF-excited CW CO2laser is described. The increased frequency tunability of the waveguide pump laser has resulted in new low threshold SMMW emissions in C2H2F2, CDF3, and CD2F2by pumping into absorption lines which are beyond the tuning range of a conventional CO2laser. Frequency offsets and some assignments obtained with the aid of a tunable diode laser heterodyne spectrometer are reported.     

Quantum effects in cyclotron resonance using a CW hydrogen-cyanide laser

A submillimeter resonance spectrometer has been developed, which employs a molecular gas laser as a source of radiation. Cyclotron resonance measurements of the quantum effects in the valence bands in germanium were taken with the use of a CW HCN laser. It is shown that the use of CW instead of pulsed lasers helps to avoid resonance line broadening and permits extensive quantitative results suitable for theoretical analysis to be recorded. The purpose of pursuing these methods to acquire detailed data on quantum transitions in semiconductors is to collect the information needed to design and develop a tunable submillimeter maser based on cyclotron resonance transitions.