Nonlinear level crossing in the infrared transitions of optically pumped far infrared laser media

In conjunction with the Stark field induced power enhancement in optically pumped far infrared lasers, absorption transitions in a degenerate two level system under the influence of an weak static Stark field have been analyed. A third order theory to the density matrix formalism leads to zero field level crossing signals for absorption in rate equation approximation and in Doppler limit. For fast relaxation among Zeeman sublevels, the zero field level crossing signal arises from population effect. Optoacoustic measurements have been carried out on the ₅,^qQ(16,8) absorption line of CH₃OH which produces the familiar 119-m laser with the CO₂ 9P(36) pump line. The optoacoustic absorption signals observed are well reproduced by the theoretical expression.     

Microcomputer control and data analysis for a far infrared Fourier spectrometer

A commercial general-purpose microcomputer is used to provide real-time experimental control, data acquisition and data analysis for a far infrared Fourier spectrometer. The interfacing and programming procedures are described. The microcomputer gives excellent performance at a low cost.     

Calibration of power and energy meters for the far infrared/near millimeter wave spectral region

Power and energy measurments in the sub-mm/near-mm wave spectral region are assuming greater importance as experimentation and data exchange increases. Much of the information on power and energy measurements of lasers and other sources is derived from common detectors constructed for operation at visible and near infrared wavelengths. This paper reports on recent progress in attempts to provide accurate calibrations for instruments such as pyroelectrics and calorimeters in the 40 m to 3 mm spectral region.This work was supported by the Department of Energy     

High power, long pulse, CH3I far infra-red laser

A high power, far infra-red laser, pumped by a long pulse high energy CO₂ laser, has been developed to produce 8 μs pulses at 447 μm. The influence of the molecular weight of the far infra-red gas on the absorption of the pump energy is discussed. The results show that the heavy molecules are most convenient for long pulse far infra-red lasers.     

用近红外法在线检测高分子材料中水分和乙醇含量

本文探讨了在工业生产中高分子材料的多组分在线成分分析系统。用近红外漫反射法研究了在线无损测定高分子材料中的水分及乙醇含量。对所测成分进行了定性、定量分析。该研究证明了测试系统的可行性     

基于飞秒锁模光纤激光脉冲基频光的差频产生红外光梳

报道了一种基于飞秒锁模光纤激光脉冲基频光的光纤型差频产生(DFG)红外光梳及其研制技术.基于自主研制的重频锁定200 MHz飞秒锁模掺铒光纤激光器,经啁啾脉冲光纤放大与超连续谱产生技术,优化近零色散OFS光纤(型号:OFS-980-20)长度,结合可调延时线,获得了精准同步的基频双色脉冲;以GaSe为非线性晶体,利用光整流技术,产生了可在6—10μm范围内宽带调谐的DFG红外光梳,光梳最大光谱宽度可达1.3μm.这种光纤型远红外光梳可望在分子光谱精密测量等领域发挥重要作用.     

A magneto-optically modulated CH3OH laser for Faraday rotation measurements in Tokamaks

Distortion-free intracavity polarization modulation of an optically pumped CH₃OH laser is shown to be viable. The possible use of this modulation technique to make a multichannel Faraday rotation measurement on a Tokamak device is discussed. In addition, the CdTe Faraday modulator employed in this study is shown to have an anomalously large Verdet constant.     

Circular dichroism in the far infrared and millimetre wavelength regions: Preliminary measurements

Preliminary spectroscopic measurements in the near millimetre wavelength region are presented which demonstrate that the study of circular dichroism at those wavelengths should be readily achieved using existing Fourier transform instrumentation.     

A vibrationally compensated far infrared laser interferometer for plasma density measurements

A modulated far-infrared laser interferometer which is presently operating on the PDX experiment at Princeton is described. The interferometer geometry permits the characterization of inside D, outside D as well as circular discharges. To achieve this versatility, a titanium corner cube reflector, mounted inside the PDX vacuum vessel is used in conjunction with a second visible wavelength interferometer for vibration corrections. In addition, the use of room temperature quasi-optical Schottky diodes in the far-infrared interferometer is reported. The minimum detectable line average density of the system is 5×10¹¹ cm^–3.     

Far infrared fine structure lines in the interstellar medium

Fine structure lines in the far-infrared have many simple properties that make them useful tools for diagnosing astrophysical plasmas. The line ratios are sensitive and accurate probes of density, elemental abundances, and ionization structure. In addition, studies of line shapes and Doppler shifts should prove valuable in studies of the gross dynamics of H II regions and galaxies. We present a review of the theory involved in the interpretation of these lines, and a summary of the observations made so far.Work supported in part by NASA grant NGR 05-003-511.     

A novel type of cell for differential absorption measurements on liquids in the far infrared

A cell is described which features a fixed length, double chamber divided into two compartments by a transparent but movable septum. A suitable reference liquid, which might be the pure solvent in the case of solution spectroscopy, is placed in one compartment and the liquid or solution to be measured is placed in the other. The transmission spectrum of the doubly filled cell is then determined as a function of septum position and the resulting data are processed to give accurate absorption spectra in which the uncertainties due to reflection effects have been reduced to a very low level.     

Development and application of the Fraunhofer-diffraction method for measurements of plasma density fluctuations using infrared lasers

This paper is concerned with systematic developments of the Fraunhofer-diffraction method for studies of plasma density fluctuations in high-temperature plasmas using infrared lasers, namely (i) development of the general theory of the Fraunhofer-diffraction method, (ii) measurements of fluctuations propagating in an azimuthal direction, (iii) measurements of fluctuation intensities, and (iv) application in measurements on high-temperature plasmas.     

Thermography: Imaging in the far infrared

Thermography, the art of visualizing and interpreting thermal patterns, is a versatile new tool for science, medicine and technology. It is developing rapidly and spreading into widely diverse fields. Although its origins are more than 130 years old, the first practical applications (in military reconnaissance) were achieved only 15 years ago. Today, clinical thermography offers new hope in the fight against cancer, and has many other uses; it is a completely passive diagnostic method and absolutely safe. In industry, thermography has potential value whenever there are problems in measuring temperature over extended areas, where point contact methods are insufficient, tedious, or impossible (e.g. in inaccessible places). Thermographic microscopes and telescopes offer great possibilities which are only just beginning to be explored. The design of thermographic equipment presents problems which do not arise in most electro-optical systems, including television, and which more nearly resemble the design problems of radio telescopes. This article reviews the basic principles and the design optimization of thermographic scanners.     

New far infrared measurements of the rotational spectrum of cyanoacetylene HC3N

Several rotational lines of cyanoacetylene in the ground state and the first excited state v7=1 have been measured between 580 and 1100 GHz with a new FIR laser sidebands spectrometer. A global analysis which takes into account the previous measurements on this molecule is performed.     

Effect of moisture content on ultrasonic velocity and attenuation in woods

Ultrasonic velocity and attenuation are measured at 1 MHz in several kinds of wood as a function of the moisture content U. The results are interpreted in terms of water absorption mechanism of woods. The velocity decreases rapidly with increasing U up to a critical value U₁ at which the curve shows a sharp bend, and the decrease is very slow for U>U₁. This critical point U₁ is in the range 20–50% depending on the species of wood and is regarded as the fibre saturation point of the wood, the moisture content at which the wood substance is saturated with absorbed water. Ultrasonic measurements thus provide us with an accurate way to determine the fibre saturation point. The attenuation curve also shows a critical change at U = U₂, which is slightly lower than U₁. The attenuation shows no change from U = 0 up to U₂, but begins to increase rapidly thereafter. This point U₂ indicates the moisture content at which free water begins to enter the vacant space of wood cells.     

Optical properties of barite in the infrared and far infrared ranges

Far infrared and infrared reflectivity was measured for barite single crystal using polarized light. Twenty six oscillators were observed. The real and imaginary parts of the complex dielectric function were obtained by a fitting procedure for three directions (E a;E b andE c). Group theory analysis has been done in detail and the number and position of experimentally observed infrared active modes were compared with the theoretical predictions.     

Lattice absorption of Ge in the far infrared

The lattice absorption at low frequency (100 cm⁻¹) and low temperature (50 K) of Ge is very small, yet it may influence the performance of the p---Ge hot hole far-infrared laser. We have measured by temperature-tuned laser interferometry.     

Frequency measurements of far infrared laser lines by means of MIM point contact diodes

We present frequency measurements of 85 Far Infrared (FIR) laser lines ranging from 2 748 GHz to 421 GHz. We use the heterodyne technique of mixing FIR laser transitions and microwave radiation on MIM point contact diodes to determine the FIR frequencies.Work supported by Consiglio Nazionale delle Ricerche -Italia and INFM (Consorzio Interuniversitario di Fisica della Materia)     

Frequency measurements of far infrared cw lasing lines in optically pumped CHCl2F

The wavelengths, frequencies, and relative polarizations of 15 FIR cw lasing lines obtained by optically pumping CHCl₂F with a cw CO₂ laser have been measured. The lines are in the wavelength range from 340.3 to 905.4 m and were pumped by P- and R-branch laser lines in the 9 m band of CO₂.Supported in part by a joint grant with the U. S. National Science Foundation grant # INT80-19014 and the Brazilian Consellio Nacional de Pesquisas (CNPq)Contribution of the U. S. Government, not subject to copyright.     

用于定向红外对抗的中波红外激光器技术

针对定向红外对抗系统对中波红外激光器在激光波段、激光功率、激光束散角、激光重复频率以及调制波形等方面的具体要求,通过对光泵半导体激光器、量子级联激光器和基于光学参量振荡的固体以及光纤激光器的技术特点与发展现状的分析比较,和对双折射相位匹配与准相位匹配的特点和最新发展动态的梳理,提出用高功率高光束质量的1 064 nm固体激光器或光纤激光器泵浦基于掺氧化镁的周期极化铌酸锂晶体（PPMgLN）的光学参量振荡器的中波红外激光器方案,其波段转换效率可达到16%以上。