Control of radiation parameters of pulse-periodic tunable diode lasers based on lead salts with double heterostructure

Spectral and power properties of the pulse-periodic tunable diode lasers based on lead salts with double heterostructure grown by MBE are considered. Procedure and criteria of preliminary selection of the laser samples are discussed. Typical characteristics of such lasers are presented. Methods for controlling the spectral and power properties in the pulse mode are considered. General mechanisms of laser wavelength tuning by current and temperature variations are demonstrated on the basis of experimental data. Methods for optimizing these parameters are considered.     

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.     

Detection of moisture content in high-purity ammonia by means of diode-laser spectroscopy

The aim of this work was the development of an as-simple-as-possible instrument for trace moisture concentration measurements in high-purity ammonia. A near-infrared diode-laser-based instrument has been applied to measure the humidity in a process of on-line detection of water in ammonia during industrial purification. The results of water concentration measurements were compared with alternative techniques (primarily dew-point detection) and good agreement was achieved. The long-term sensitivity of such a diode-laser-based instrument was estimated to be 5 ppm. The calculation of the water concentration from measurements of the integrated volume of water contained in the heavy fraction, extracted during the purification process, yields an even lower detection limit of less than 0.1 ppm, depending on the initial ammonia purity. PACS 42.55.Px; 42.62.Cf; 42.62.Fi     

Diode laser measurements of the first overtone HF lineshape broadened by Ar,Xe, Kr and N2

A high-resolution spectroscopy study of the HF first overtone vibrational–rotational 0–2 R(0) line profile was carried out in Ar, Xe, Kr and N₂ gas mixtures using near-IR tunable diode laser. The HF 0–2 R(0) analytical line is known as the most appropriate for laser detection of HF molecules in the atmosphere. Highly accurate collisional broadening, shift and “narrowing” coefficients were determined from the direct spectroscopic fit employing traditional Voigt, Rautian and Galatry symmetric profiles and using an asymmetric speed-dependent Voigt profile. These data make the information of modern spectroscopic databases, e.g., HITRAN2012, much more exact. A noticeable line shape asymmetry was investigated in detail. In this paper, the validity of the use of model profiles in spectroscopic fitting is severely discussed. For the first time, we draw attention to the need for physically realistic line shape models to avoid systematic errors in retrieved gas concentrations. We stress that in the case of HF, all considered model profiles serve only as ad hoc models; they may conceal the true physics of spectral line formation.     

Remote detection of HF molecules in open atmosphere with the use of tunable diode lasers

This paper sets out to present the results of a study of the feasibility of building a prototype device for prompt (on-line mode) remote measurements of HF trace quantities in atmosphere (with the optical length of up to 100 m, and a cat’s eye as a reflector) making use of near-infrared range diode lasers (DLs). The gas analyzer consisted of DLs operating at λ=1.28 μ, a telescopic system and a retro-reflector. The remotely measured HF sensitivity in atmosphere was better than 10 ppb.     

Results of TDLS application for ammonia monitoring in a process of high-purity arsine and phosphine production

Using the TDLS method it has been found that ammonia (NH₃) is the main impurity in arsine (AsH₃) and phosphine (PH₃), produced by hydrolysis of magnesium arsinide and phosphinide, respectively. NH₃ behavior is abnormal in solutions of these hydrides: NH₃ reveals the properties of a more volatile impurity in relation to arsine and phosphine, although its boiling temperature is higher than that of AsH₃ and PH₃. The observable anomaly is connected with the fact that in solutions of arsine and phosphine NH₃ shows properties differing from the properties of pure ammonia. It was supposed that the influence of intermolecular interaction between ammonia molecules, when diluted by arsine or phosphine, decreases. During the purification of arsine or phosphine one must continuously monitor the NH_3.concentration in the extraction of the light fraction in order to define the point at which to terminate the purification process.     

Collision parameters of N2-broadened methane lines in R5 multiplet of 2ν3 band. Multispectrum fitting of overlapping spectral lines

The results of the investigation of absorption spectra of the methane R5 multiplet of 2ν ₃ band, broadened by nitrogen, are presented. The absorption spectra of the methane-nitrogen mixture (CH₄:N₂ = 1:113.36) were recorded, using a two-channel photometric spectrometer, based on a tunable diode laser. The multispectrum least-squares fitting procedure was applied to all experimental spectra, recorded at different pressures, using the program, developed at IAO SB RAS (Protasevich, 2011). The program is based on a relatively simple line-profile model proposed in Pine (J. Quant. Spectrosc. Radiat. Transf. 57:145, 1997) and linear pressure dependence of the line-profile parameters. The line center positions, intensities, broadening, shifting, and mixing coefficients were determined for four lines of the methane R5 multiplet. The results have been compared with other available data.     

High-Precision Spectroscopy with Diode Lasers. Deviation of Gas from Ideal Behavior

High-precision measurements of the spectral-line profile using near-IR diode lasers (DLs) have been performed, and the measurement results have been analyzed. To carry out these measurements, a multichannel DL spectrometer with a high spectral resolution was developed, calibrated, and put into operation. Particular attention has been paid to the deviation of the gases under study from ideal behavior. CO₂ of natural isotopic composition was chosen as a model gas.     

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.     

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.