I. V. Sherstov

Tunable TEA CO2 laser for long-range DIAL lidar

Abstract The high-power pulse-periodic TEA CO2 laser intended for use in the structure of mobile ground-based long-range IR DIAL lidar is developed. For achievement of the highest peak power of radiation, the system of laser excitation with a voltage of ±40 kV and effective preionization allowing one to work at high pressure of various gaseous mixtures is created. A study of energetic, temporal and spatial parameters of laser radiation for used gaseous mixtures are executed at a pressure of 0.5–2.4 atm. The pulses of laser emission with an energy more than 10 J and duration on FWHM of ∼30 ns are obtained for the case of heliumless mixtures. The maximal obtained peak power of the laser radiation is 100 MW. The maximal efficiency of the laser including the energy deposited in the glow discharge is 12.6%. At the use of the selective cavity, the laser operation at 85 emission lines of the CO2 molecule is obtained and at 60 lines, the energy of radiation exceeded 4 J.

A TEA CO2 laser with a peak radiation power of 100 MW

A high-power pulse-periodic TEA CO2 laser is used as a component of a long-range mobile differential absorption lidar. In order to reach the ultimate peak generation power, a system for laser excitation with a supply voltage of ±40 kV and efficient preionization was developed, allowing the laser to operate at high pressures of gas mixtures of various compositions. Energy, time, and spatial characteristics of laser radiation were studied. Laser pulses with an energy of >10 J and FWHM duration of ≈30 ns were obtained. The ultimate peak laser radiation power is 100 MW, and the maximum efficiency with respect to the discharge-consumed energy is 12.6%.

Method for measuring the resonant frequency of photoacoustic detector in the real-time mode

A method for measuring the resonant frequency of a photoacoustic detector (PAD) in the realtime mode in a wide temperature and gas-mixture-composition range is proposed. The method is based on measurements of natural frequencies of the resonance PADs, which are excited using an auxiliary acoustic emitter built into the PAD. The measurement procedure takes ≤0.1 s. When the PAD is filled with air or nitrogen, the high accuracy and reproducibility of the measurement results is experimentally shown. The relative measurement error of the PAD resonant frequency (~1700 Hz) is approximately 6 × 10–5.

Development and research of a laser photo-acoustic SF 6 gas analyzer

An analysis of various optical schemes for the development of a laser SF6 gas analyzer based on a CO2 laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO2 laser wavelength near 10.6 μm on measured SF6 concentration is possible. The results of experimental studies of a laser photo-acoustic SF6 gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF6 concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF6.

Reducing the Energy Consumption of a Laser Photo-Acoustic SF6 Gas Analyzer

Experimental studies of the operating modes of a laser photo-acoustic SF6 gas analyzer that were aimed at reducing its energy consumption were carried out. It was shown in the experiments that an average power of CO2 laser radiation of at least 100 mW is required for the assured detection of low SF6 concentrations (less than 100 ppb). To reduce the energy consumption of the gas analyzer, it is proposed to decrease the repetition frequency of CO2 laser pulses by several times and operate on subharmonics of the resonance frequency of the photo-acoustic detector. The experimental results made it possible to reduce the energy consumption of the gas analyzer to ~15 V A and use a Li-ion battery from a laptop to power it. The duration of the continuous operation of the gas analyzer on one battery charge was at least 6 h.

A compact frequency-stabilized pulse-periodic waveguide CO2 laser for calibration of wavelength meters

A compact pulse-periodic waveguide CO2 laser with high-frequency excitation with automatic assignment of the 10P (14) line and stabilization of the emission frequency in the middle of this line using a sealed-off optoacoustic cell, which is filled with a mixture of C2H4 (0.1%) and nitrogen, was developed. It is shown that the laser-frequency instability is within 3 MHz, thus meeting the requirements that are imposed on the calibration tools for high-resolution wavelength meters that are similar to WS-6IR.

Possibilities and experimental investigation of parametric frequency converters with LiInSe/sub 2/, AgGaGeS/sub 4/, HgGa/sub 2/S/sub 4/ and Hg/sub 0.65/Cd/sub 0.35/Ga/sub 2/S/sub 4/ crystals

Second harmonic generation of 9 /spl mu/m emission band of CO/sub 2/ laser is for the first time realized with a number of new nonlinear crystals: biaxial LiInSe/sub 2/, AgGaGeS/sub 4/ (that is solid solution AgGaS/sub 2/:GeS/sub 2/ or Ag/sub x/Ga/sub x/Ge/sub (1-x)/S/sub 2/, or AgGaGe/sub x/S/sub 2(1+x)/ at x=0.5) and uniaxial HgGa/sub 2/S/sub 4/, Cd/sub 0.35/Hg/sub 0.65/Ga/sub 2/S/sub 4/ (solid solution HgGa/sub 2/S/sub 4/:CdGa/sub 2/S/sub 4/ with mixing ratio x=0.35). For LiInSe/sub 2/ and AgGaGeS/sub 4/ it is first type of frequency conversion realized at some time or other. The main feature of these crystals is a wide range transparency from 0.4-0.6 to 12.5-16.2 /spl mu/m. Their damage thresholds for 30 ns TEA CO/sub 2/ laser pulses at 9.55 /spl mu/m is determined as 1.7 to 2.3 times higher than for popular middle IR crystals such as ZnGeP/sub 2/ or AgGaSe/sub 2/. Parameters of second harmonic generation were determined correctly in comparison with ZnGeP/sub 2/ crystals at 33 ns pump pulses and intensities that are about 28.5% (40 MW/cm/sup 2/) of damage thresholds of ZnGeP/sub 2/. As high as 7% external peak power efficiencies (4.7% in energy) is typical for orange and yellow phases of 3.1 mm HgGa/sub 2/S/sub 4/ crystal such pumping that is only 13% of its damage threshold. Efficiencies as high as 0.45% and 0.3% are realized in 2.1 mm AgGaGeS/sub 4/ crystal at pump intensities-that is only 11% of the damage threshold. Phase-matching angles, spectral dependence of second harmonic generation efficiencies, and angular and spectral phase-matching widths are investigated in detail.

Short pulse formation in a TEA CO{sub 2} laser using a CO{sub 2} - N{sub 2} - H{sub 2} gas mixture

The use of an optimal CO{sub 2} - N{sub 2} - H{sub 2} gas mixture with a high concentration of hydrogen (30% - 40%) was shown to allow the formation of high-power TEA CO{sub 2}-laser pulses with a base duration of {approx} 200 ns whose energy and peak power significantly exceed the parameters of pulses obtained in binary CO{sub 2} - H{sub 2} mixtures. Considering all the parameters, the helium-free 56% CO{sub 2} - 14% N{sub 2} - 30% H{sub 2} gas mixture at a pressure of 0.7 atm is optimal for the generation of short high-power pulses in the TEA CO{sub 2} laser. A small addition of nitrogen ([CO{sub 2}]/[N{sub 2}] {approx} 10 - 12) to the binary CO{sub 2} - H{sub 2} mixture not only substantially increases the pulse energy and peak power (by a factor of 3 - 3.5) but also shortens their duration at half-maximum with retention of the total (base) duration. (control of laser radiation parameters)The use of an optimal CO2 — N2 — H2 gas mixture with a high concentration of hydrogen (30% — 40%) was shown to allow the formation of high-power TEA CO2-laser pulses with a base duration of ~ 200 ns whose energy and peak power significantly exceed the parameters of pulses obtained in binary CO2 — H2 mixtures. Considering all the parameters, the helium-free 56% CO2 — 14% N2 — 30% H2 gas mixture at a pressure of 0.7 atm is optimal for the generation of short high-power pulses in the TEA CO2 laser. A small addition of nitrogen ([CO2]/[N2] ~ 10 — 12) to the binary CO2 — H2 mixture not only substantially increases the pulse energy and peak power (by a factor of 3 — 3.5) but also shortens their duration at half-maximum with retention of the total (base) duration.