A. I. Karapuzikov

High-sensitivity laser photoacoustic leak detector

A photoacoustic (PA) leak detector on the base of a compact CO2 laser is proposed for the detection of hydrogen leaks from cooling systems of electric power generators. Leak detection is based on a trace gas marker SF6 registration, which is added to the gas carrier within the leakage area. Experimental results of SF6 impurity detection in weak gas leakage using a PA detector with a differential ring cavity flow type are sited. The threshold sensitivity of the detector is measured at ~7.5·10−10 cm−1. The effect of gas-flow rate through the detector is studied. The minimum reliably detectable flow is estimated to be ~1·10−10 Pa·m3/s, which exceeds the sensitivity of commercial helium and halogen leak detectors. Description and specifications of the developed model of a portable laser leak detector, designed in accordance with experimental results, are given.

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.

Modeling of helicopter-borne tunable TEA CO2 DIAL system employment for detection of methane and ammonia leakages

Abstract The characteristics of a helicopter-borne lidar based on tunable TEA CO2 laser and its third harmonic designed for remote detection of methane and ammonia leakages from pipelines are analyzed numerically. The spectral range near 3 μm was shown to be most promising for remote sensing of methane emissions. Parameters of radiation of the tunable pulse-periodic mini-TEA CO2 laser and generators of harmonics to be utilized in the helicopter-borne differential absorption lidar are estimated. Emissions of different gas intensities are analyzed for possible detectability at a distance of up to 1 km. The use of the third harmonic of the TEA CO2 laser allows methane emissions from a pipeline to be detected and measured with mean measurement error from 10% to 15% for methane concentrations varying from the background level to the explosion-hazardous one. The optimal pair and possibilities of the ammonia remote sensing on the base of the first harmonic of TEA CO2 laser were determined as well.

Parametric frequency converters with LiInSe2, AgGaGeS4, HgGa2S4 and Hg0.65Cd0.35Ga2S4 crystals

Second harmonic generation of 9 μm emission band of CO2 laser is for the first time realized with a number of new nonlinear crystals: biaxial LiInSe2, AgGaGeS4 and uniaxial HgGa2S4, Cd0.35,Hg0.65Ga2S4. For LiInSe2 and AgGaGeS4 it is first type of frequency conversion realized some time or other. Main feature of this crystals is wide range transparency from 0.4-0.6 to 12.5-16.2 μm. Their damage thresholds for 30 ns TEA CO2 laser pulses at 9.55 μm is determined as 1.7 to 2.3 times higher than for popular middle IR crystals such as ZnGeP2 or AgGaSe2. Parmateters of second harmonic generation were determined correctly in comparison with ZnGeP2 crystals at 33 ns pump pulses and intensities that are about 28.5% of damage thresholds of ZnGeP2. As high as 7% external peak power power efficiencies is typical for orange and yellow phases of 3.1 mm HgGa2S4 crystal at such pump that is only 13% of its damage threshold. Efficiencies as high as 0.45% and 0.3% are realized in 2.1 mm AgGaGeS4 crystal at pump intensities that is only 11% of damage threshold. It was determined phase-matching angles, spectral dependence of second harmonic generation efficiencies, so as angular and spectral phase-matching widths that are investigated in details.

LaserBreeze gas analyzer for noninvasive diagnostics of air exhaled by patients

A laser gas analyzer has been designed for determining the composition of exhaled air by means of photoacoustic spectroscopy. The analyzer, based on a broadband optical parametric oscillator and photoacoustic detector, provides high-precision rapid analysis of the multicomponent composition of human exhaled air for dynamic estimation of the efficiency of treating bronchus and lung diseases.

Wide band frequency converters for Lidar systems

Estimations are carried out on creation possibilities of all solid state laser sources capable significantly or fully to solve the problem of the universal Aerosol-Gas Lidar System design. Best existing Ho2+:ILF and Nd:YAG lasers supplied with LBO, KTA, KTP, BBO, CLBO, DLAP; GaSe, GaSe:In, AgGaxIn1-xSe2, LiInS2, LiInSe2, AgGaS2, AgGaxIn1-xS2, and HgGa2S4 frequency converters are considered. The investigation results show development of UV to FIR laser source is really to carry out with efficiencies from one-two up to several tens of percent in several ways.

Screening of patients with bronchopulmonary diseases using methods of infrared laser photoacoustic spectroscopy and principal component analysis

Abstract. A human exhaled air analysis by means of infrared (IR) laser photoacoustic spectroscopy is presented. Eleven healthy nonsmoking volunteers (control group) and seven patients with chronic obstructive pulmonary disease (COPD, target group) were involved in the study. The principal component analysis method was used to select the most informative ranges of the absorption spectra of patients’ exhaled air in terms of the separation of the studied groups. It is shown that the data of the profiles of exhaled air absorption spectrum in the informative ranges allow identifying COPD patients in comparison to the control group.

A nanosecond optical parametric oscillator in the mid-IR region with double-pass pump

An optical parametric oscillator (OPO) with double-pass pump based on MgO:PPLN and PPLN periodic structures is described. A compact nanosecond Nd:YLF laser has been used as a pump source at 1.053 μm (the pumping pulse duration is 5–7 ns at a maximum pulse energy of 300 μJ at frequencies of 1–7 kHz). The oscillation threshold of the OPO based on MgO:PPLN was varied in a range of 11–28 μJ at wavelength of 2.1–4.3 μm. The conversion efficiency from the pump wave to an idler wave decreased from 8.6 to 2.5% in the range of 2.0–4.3 μm. For PPLN-OPO the measured threshold was 36 μJ at 4.2 μm and 49 μJ at 4.7 μm. The conversion efficiency of the pump energy into the energy of an idler wave was 3.3μ-0.4% at wavelengths of 4.2–4.7 μm.

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%.

Optical parametric oscillator within 2.4–4.3 μm pumped with a nanosecond Nd:YAG Laser

An optical parametric oscillator has been designed on the basis of MgO:PPLN periodic structure. A compact nanosecond Nd:YAG laser has been used as a pump source at 1.053 μm. The pump pulse length is 5–7 ns at a maximum pulse energy of 300 μJ and a frequency of 1000–5000 Hz. The oscillation threshold is 22 μJ at 3 μm and 48 μJ at 4.3 μm. The maximum conversion efficiency from incident pump power to the idler output is 3.9%.