New data processing for multichannel FIR laser interferometer

Usually, both the probing and reference signals received by LATGS detectors of FIR interferometer pass through hardware phase discriminator and the output phase difference--hence the electron line densities is collected for analysis and display with a computerized data acquisition system(DAS). In this paper, a new numerical method for computing the phase difference in software has been developed instead of hardware phase discriminator, the temporal resolution and stability is improved. An asymmetrical Abel inversion is applied to processing the data from a seven-channel FIR HCN laser interferometer and the space-time distributions of plasma electron density in the HT-6M tokamak are derived.     

Density Profile and Diffusion Coefficient During IBW Heating in the HT-7 Superconducting Tokamak

The electron density coefficient was studied during IBW heating in the HT-7 tokamak. The frequency of IBW was 30 MHz, and the injected power was 130 kW. An improved confinement mode was induced by IBW heating in the HT-7. The peaked density profile was formed gradually, and the Ha radiation intensity was decreased abruptly. A five-channel far-infared (FIR) hydrogen cyanide (HCN) laser interferometer was used to measure the electron density profile. The evolution of the density profile and the soft X ray intensity profile were studied during the improved confinement phase. The electron density diffusion coefficient was studied carefully for IBW heating discharges. The results were compared with Ohmic heating plasma and with different toroidal field Bt (2.0 T and 1.8 T). For 30MHz frequency of IBW heating, the higher Bt leads the lower electron density diffusion coefficient at the region of r/a > 0.6 in the HT-7.     

Study of Electron Heat Pulse Propagation and Particle Diffusion During the Synergy of LHW and IBW Heating in the HT-7

A successful experiment on lower hybrid wave (LHW) and ion Bernstein wave (IBW) synergy has been carried out in the HT-7 superconducting tokamak. With 560KW of LHW heating power and 160 KW of IBW heating power, during the synergy of the LHW and IBW experiment we achieved an improved plasma: the electron density increased and peaked, the soft X intensity increased too. A five-channel far-infrared (FIR) hydrogen cyanide (HCN) laser interferometer was used to measure the electron density profile. The particle diffusion coefficient was studied for the experiment, and the result compared with the heat diffusion coefficient. With the same injected LHW and IBW power, high electron density n_e can deduce the electron pulse propagation and the particle diffusion.     

Measurement of electron density profiles on HT-6M tokamak by 7-channel FIR HCN laser interferometer

Electron density measurements are periormed on HT-6M tokamak using a 7 channel Far-Infrared HCN laser interferometer. From the measured line integrals--7 channel phase shifts the electron density profile is reconstructed by a fit procedure. Results were tested by comparison to Abel inverted. Some recent interesting experimental results were reported.     

Plasma diagnostic applications on the TEXT tokamak using a high power,twin frequency optically pumped far-infrared laser

A high-power, twin-frequency, optically-pumped, far-infrared (FIR) laser has been developed at UCLA for diagnostic application on the TEXT tokamak. The source is operated at 245 GHz (λ=1.22 mm) for heterodyne scattering measurements and 694 GHz (λ=432 μm) for high resolution interferometry. Future plans include a 30 channel interferometer/polarimeter operating at 694 GHz to accurately determine current profiles.     

A 337μm density interferometer for the LT-4 tokamak

A 337 μm HCN laser and a single channel interferometer have been built for measurements of the line-average electron density in the LT-4 tokamak. The design of the system is conventional, using a rotating grating to produce continuous beat notes which are detected by pyroelectric detectors, but with considerable simplifications to reduce cost and complexity. With a beat frequency of 1 kHz the system has a response time of 0.5 ms and a detector-noise limited phase sensitivity of about π/20 (1/40th fringe). The resulting density sensitivity is 8×10¹¹ cm^?3 average, for a 20 cm pathlength, but is limited in practice by vibrations to 3×10¹² cm^?3 for the same pathlength. The system has operated reliably since May 1981.     

光泵CH3F和D2O远红外脉冲激光器

本文叙述了无镜远红外激光器的结构及其实验结果。用可调谐TEA CO_2激光器作为泵浦源,其输出能量在9P(20),9R(22)线上均可达1J左右。用CO_29P(20)线泵浦CH_3F分子,获得了能量为0.5mJ,波长为496μm的激光输出;用9R(22)线泵浦D_2O分子,获得了能量为1mJ,波长为385μm的激光输出。输出能量和波长是分别用热电堆和Fabry-Perot干涉仪测量的。     

A compact fir ring laser with open resonator and variable output coupling

We describe the design, construction and first experimental results with an open triangle FIR ring resonator with Michelson interferometer output coupling, which we combined with a Brewster-windowless 10W CO₂ pump laser to a compact laser package of 1m length. The achieved stability of power and frequency of this system is very high, typically on the order of ±0.01% over several hours and <20kHz per hour at 800GHz. For the design, we investigated the balance of all laser processes and determined the optimum dimensions for the open resonator cavity. This analysis is based on a radially homogenous overall laser model, including commonly accepted simplified rate equations together with molecular parameters for weak FIR laser lines. In accordance with the modelling the efficiency on the very most prominent lines is better than with conventional waveguide lasers, giving up to ≈4 times better efficiencies especially on lines with low absorption pump transitions. Several laser lines, however, have substantially enhanced pump thresholds on purely copropagating emission, suppressing laser operation below about 10W pump power threshold. We show that this can not be due to effects from the interferometer.     

A magnetic resonance spectrometer for FIR frequencies; Measurement on LiErF4

A magnetic resonance spectrometer is described with an HCN laser and an optically pumped FIR laser as radiation sources. The latter enables us to measure magnetic resonances at many frequencies throughout the FIR range. High magnetic fields up to 35 T are generated by means of a capacitor discharge with 10 ms pulse duration. The results of our measurments on LiErF₄ are in good agreement with resonance conditions calculated from parameters found by Hansen et al[10]. Different aspects of FIR magnetic resonance spectroscopy are discussed.     

Measurement of far-infrared laser frequencies from optically pumped CHD/sub 2/OH

A three-laser heterodyne system was used to frequency measure 11 previously observed optically pumped far-infrared (FIR) laser emissions of CHD/sub 2/OH. These newly measured frequencies have fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/ and correspond to laser wavelengths ranging from 47.8 to 238.0 /spl mu/m. The pump laser offset frequency was measured for 15 CHD/sub 2/OH FIR laser emissions.     

内壁反射式远红外激光干涉仪的设计和应用

介绍用于HL-2A偏滤器托卡马克装置的远红外（FIR）激光干涉仪及其在等离子体电子密度测量中的应用．一种新的软件比较相位技术被用来计算相移．自恰式光路设计方法用于内壁挂镜光路的设计．防污染装置延长了真空室中反射镜的使用寿命．电子密度测量结果表明偏滤器位形的等离子体放电减小了等离子体与第一壁的相互作用，等离子体密度比孔栏放电位形的略为偏低．     

Multi-channel Heterodyne Radiometer on HT-7 Tokamak

The incoherent radiation emanating out of the tokamak plasmas gives vital information about the electron temperature. Electron cyclotron emission (ECE) is a powerful diagnostic tool for the measurement of electron temperature due to many advantages such as the high spatial and temporal resolutions. This paper presents the sixteen channel superheterodyne radiometer as an electron cyclotron emission diagnostic to measure the electron temperature on HT-7 tokamak.     

Heterodyne frequency measurements of FIR laser lines around 1.2 and1.6 THz

We present the frequency measurements of 14 far-infrared (FIR) laser lines. We use the heterodyne technique of mixing FIR laser transitions and microwave radiation on a MIM point contact diode to determine the FIR frequencies. The main motivation was to measure the frequency of laser lines of metrological interest, around the 1.6 and 1.2 THz regions. We also present 15 new FIR laser lines we found while performing the frequency measurements, with wavelengths ranging from 90 μm to 819.2 μm. All of them are characterized in wavelength, polarization, intensity, working pressure and absorption offset     

Measurement of density fluctuations on the JIPP T-IIU tokamak via an HCN laser scattering

Observation of density fluctuations in tokamak plasmas is important to study the plasma confinement and to perform high power heating of the plasma. We observed the density fluctuations by means of an HCN laser scattering method during rf heating in the ion-cyclotron range of frequency on a tokamak plasma. The density fluctuations at the drift wave frequency are not enhanced so much by the heating, but the frequency spectrum is shifted to higher frequency. The increase of the density fluctuation level during the heating has been observed only in low-frequency region owing to MHD activity.     

Frequency measurements of optically pumped far-infrared laser lines

In this work, we report the frequency measurements of optically pumped far-infrared (FIR) laser lines. We use the heterodyne technique of mixing FIR laser radiation and microwave radiation on a metal-insulator-metal (MIM) point contact tunnel diode, to determine the FIR laser frequencies. The two FIR laser systems, consisting of CO₂ waveguide pump lasers and Fabry-Perot FIR laser cavities, and MIM diode were developed by us. To check the system, we have measured some FIR laser line frequencies previously reported in the literature. An average fractional frequency reproducibility of ±7×10^-7, between our measurements and the previous ones, permit us to use our system to measure five new FIR laser frequencies     

The generation and frequency measurement of short-wavelength far-infrared laser emissions

A significantly improved three-laser heterodyne system has been assembled to generate and measure short-wavelength far-infrared (FIR) laser emissions. Over the past several years, this system has been used to discover fifty-five FIR laser emissions, ranging in wavelength from 26.3 to 185.0 /spl mu/m. These emissions were generated by optically pumping a FIR cavity with a continuous-wave carbon dioxide laser in a X-V geometry when using either hydrazine or a methanol isotopologue as the FIR laser medium. Although heterodyne techniques can be used to measure the frequencies of these FIR laser emissions with fractional uncertainties of /spl plusmn/2/spl times/10/sup -7/, shortcomings in the previous system limited its effectiveness. Improvements made to the three-laser heterodyne system have resulted in an increase in the spectral range used to search for the beat between the known and unknown laser frequencies (an increase of up to 25 GHz) as well as an increase in the system's sensitivity (by up to a factor of 30), all without requiring the use of an additional microwave frequency source. With this improved system, the FIR laser frequencies for the recently discovered 53.9- and 90.0-/spl mu/m laser emissions generated by optically pumped CH/sub 3/OD have been measured.     

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%.     

Spectral characteristic study of Raman transition interaction in optically pumped FIR laser

The spectral characteristic of an optically pumped NH3 molecules FIR laser has been studied by a F-P interferometer and a Michelson interferometer. It was verified that when NH3 molecules were pumped by CO2-9R(16) line, a emission by Raman transitions of two photons was produced. When the gas pressure of NH3 increased, the interaction of the Raman transitions rose, then the emission was enhanced and the width of spectral lines were broadened. The experimental results are in good agreement with the theoretical calculations.     

Measurement of Optical Constants of CVD-Diamond for Short-Wavelength Far-Infrared Lasers

A diagnostic system using short-wavelength far-infrared (FIR) lasers (40–70 μm in wavelength) is now being developed for high density and large volume plasmas. In the wavelength region, a CVD-diamond is the excellent materials for optical windows of the laser and the plasma vessel and beam splitters of a multichannel interferometer. To design these optical elements, the optical constants (refractive index n, absorption coefficient α and transmissivity T) of the CVD-diamond have been measured precisely by using FIR lasers of 48-, 57- and 71-μm in wavelength. As an example, the result for 57.1511 μm light is n = 2.383(1) ± 0.002, α = 0.19 ± 0.05 cm^-1 and T = 97.5 ± 1.5% at 1.023 mm in thickness.     

A variable reflectivity output coupler for optically pumped far infrared lasers

In this paper we describe the design and performance of a variable reflectivity output coupler for optically pumped far infrared (FIR) lasers. The output coupler is a compact, tunable Michelson interferometer. The output coupling ratio (i.e. the Michelson transmission) is adjustable between 0 and ≥60% for laser line wavelengths between 110 and 500 μm. This output coupler provides increased output power and flexibility, since it can be tuned to optimum coupling ratio for different laser lines. Beam profile measurements show that the Michelson output coupler produces a well collimated Gaussian laser beam. Design features are a) the use of 10 μm reflection coated quartz vacuum window which acts as a dichroic mirror for the pump radiation and b) the high mechanical stability obtained by a leaf spring flexure mount of the movable Michelson mirror and by restricted alignment devices.