Remote helicopter-borne detector for searching of methane leaks.

Measurements of the content of various molecular impurities in the ambient air using helicopter- and aircraft-borne systems represent an extremely urgent challenge. In this respect, of special interest are the devices that that provide leakage monitoring in gas lines in order to prevent emergencies. In the paper results of the tunable diode laser-based instrument development and testing are presented.

UF6 enrichment measurements using TDLS techniques.

The objective of this work was investigation of possibility of tunable diode laser spectroscopy (TDLS) technique application for gaseous uranium hexafluoride (UF6) isotope measurement. Spectra of uranium hexafluoride gas mixture were investigated using two different Fourier Transform Spectrometers Vector 22 and Bruker 66v. Observed spectral features were identified and model spectra of different gas mixture components were developed. Optimal spectral range for measurements was determined near maximum of UF6 combination band nu1+nu3. Laboratory prototype of multi-channel instrument under consideration based on tunable diode lasers was built and algorithms were developed to measure gaseous UF6 isotopic ratios. Diode laser used operated at the wavelengths near lambda=7.68 microm. It was placed in a liquid nitrogen cooled cryostat. Three instrument channels were used for laser frequency calibration and spectra recording. Instrument was tested in measurements of real UF6 gas mixtures. Measurement accuracy was analyzed and error sources were identified. The root-mean-square random error in the 235U isotopic content is characterized by a spread of about 0.27% for quick measurements (at times less than 1 min) and 1% for periods of more than an hour. It was estimated that the measurement accuracy could be improved by at least an order of magnitude by minimizing the error sources.

Pressure-induced shift and broadening of acetylene lines in the region 6580-6600 cm-1.

Highly accurate measurements of pressure shift and broadening parameters of acetylene absorption lines in the region 6580-6600 cm-1 have been performed by tunable diode laser spectroscopy (TDLS). For these purposes the three channel spectrometer with distributed-feedback diode laser, operated at 1.53 microm was used. The laser is generating pulses of 4-10 ms duration at a repetition frequency of 40 Hz. A temperature-stabilization system, using a thermoelectric cooling unit affords a temperature stability of the order of 10(-4)K in the temperature range from -15 to +50 degrees C. A three channels acquisition system ensured simultaneous real time recording of the sample gas absorption spectrum and of two spectral calibration signals (Fabry-Perot fringes and low-pressure reference lines). We have measured the pressure-induced self-shift and broadening coefficients for six lines of the R-branch in the nu1+nu3 rotation-vibration band of acetylene 12C2H2. The self-shift coefficients have been determined for these lines in the wide pressure region. A non-linear behavior of the pressure dependence of the shift was observed. The temperature exponent n of pressure-induced broadening and shift are reported.

Tunable single-frequency diode laser at wavelength lambda = 1.645 microm for methane concentration measurements.

This paper deals with the development of a novel single-frequency tunable diode laser with fiber-optic output for gas-analysis applications. The approach we propose is a convenient, simple and cheap solution for spectroscopy of single absorption lines of any gases having absorption bands in the optical fiber transparency window (0.7 microm/1.7 microm). The presence of fiber-optic output is an additional advantage for remote sensing applications. The laser operation is demonstrated as applied to R7 line of 2 nu(3) methane absorption band at lambda = 1.645 microm. The mode-hop-free tuning range of 35 GHz (1.2 cm(-1)) has been achieved.