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.
We demonstrate an optical parametric oscillator (OPO) based on two HgGa2S4 (HGS) crystals with exceedingly wide tuning range from 4.2 μm to 10.73 μm. The HGS OPO was pumped by Q-switched Nd:YLF laser at 1.053 μm with a 5-7 ns pulse duration. Absorption spectrum of ammonia was presented to demonstrate the feasibility of the OPO system for spectroscopic measurements and gas detection.
A. Boyko, A. Karapuzikov, S. Chernikov, V. Spitcin, Yu. Ponomarev, M. Starikova, M. Yu. Shtyrov, I. Kuznetcova, I. Tikhonyuk, I. Miroshnichenko, M. Miroshnichenko
We report automated waveguide RF excited 13С16О2 - laser based on Z-shaped resonant cavity. The laser possesses possibility of wavelength tuning from 9.5 to 11.5 μm by means of the cavity's diffraction grating position management. The diffraction grating position is driven by precision motorized linear actuator. The lasing lines of P-branch from 11.04 to 11.31 μm were studied in details. Operating mode selection is performed with specially designed PC software "Tunable CO2 – Laser". P-branch 11P(10) – 11P(32) lines' tuning time does not exceed 3 sec.
Pulmonary diseases diagnostics always occupies one of the key positions in medicine practices. A large variety of high
technology methods are used today, but none of them cannot be used for early screening of pulmonary diseases.
We discuss abilities of methods of IR and terahertz laser spectroscopy for noninvasive express diagnostics of pulmonary
diseases on a base of analysis of absorption spectra of patient’s gas emission, in particular, exhaled air.
Experience in the field of approaches to experimental data analysis and hard-ware realization of gas analyzers for
medical applications is also discussed.
We investigated optical damage (surface and bulk) in one of the most promising wide bandgap nonoxide nonlinear crystals, HgGa 2 S 4 , that can be used in ∼1 -μm pumped optical parametric oscillators (OPOs) and synchronously pumped OPOs (SPOPOs) for generation of idler pulses above 4 μm without two-photon absorption losses at the pump wavelength. The optical damage has been characterized at the pump wavelength for different repetition rates using uncoated and antireflection-coated (mainly with a single layer for pump and signal wavelengths) samples. HgGa 2 S 4 is the most successful nonlinear crystal (both in terms of output energy and average power) for such OPOs, but optical damage inside the OPO has a lower threshold and represents at present the principal limitation for the achievable output. It is related to peak pulse and not to average intensity, and bulk damage in the form of scattering centers occurs before surface damage. Such bulk damage formation is faster at higher repetition rates. Lower repetition rates increase the lifetime of the crystal but do not solve the problem. The safe pump fluence in extracavity measurements is <1 J/cm 2 , which corresponds to ∼100 MW/cm 2 for the 8-ns pulse duration (both values peak on-axis). In the OPO, however, peak on-axis fluence should not exceed 0.3 J/cm 2 limited by the formation of bulk scattering centers in orange-phase HgGa 2 S 4 . In the nanosecond OPO regime, the damage resistivity of Cd-doped HgGa 2 S 4 is higher and that of the almost colorless CdGa 2 S 4 is roughly two times higher, but the latter has no sufficient birefringence for phase-matching. In SPOPOs operating in the ∼100 MHz regime, the damage limitations are related both to the peak pulse and the average intensities, but here HgGa 2 S 4 seems the best nonoxide candidate to obtain first steady-state operation with Yb-based mode-locked laser pump sources.
We investigated optical damage (surface and bulk) in wide band-gap (absorption edge below 532 nm) sulphide and
selenide nonlinear crystals that can be used in 1064-nm pumped optical parametric oscillators (OPOs) for generation of
idler pulses above 4 μm without two-photon absorption losses at the pump wavelength. The optical damage has been
characterized at the pump wavelength for different repetition rates. Surface damage has been studied for uncoated and
antireflection-coated (mainly with a single layer for pump and signal wavelengths) samples. Optical damage inside the
OPO has a lower threshold and represents at present the principal limitation for the achievable output. It is related to
peak and not to average intensities and in many of the studied crystals bulk damage in the form of scattering centers
occurs before surface damage. Such bulk damage formation is faster at higher repetition rate. Lower repetition rates
increase the lifetime of the crystal but do not solve the problem. In the most successful nonlinear crystal (both in terms of
output energy and average power), orange-phase HgGa2S4, the safe pump intensity in extracavity measurements is below
100 MW/cm2 which corresponds to less than 1 J/cm2 for the 8 ns pulse duration (both values peak on-axis). In the OPO,
however, peak on-axis fluence should not exceed 0.3 J/cm2 limited by the formation of bulk scattering centers. The
damage resistivity of yellow-phase HgGa2S4 or Cd-doped HgGa2S4 is higher and of the almost colorless CdGa2S4 it is
roughly two times higher but the latter has no sufficient birefringence for phase-matching.
High chalcogen volatility and Li interaction with the container walls result in variation of crystal composition and
presence of both extended and point defects in as-grown LiGaS2 nonlinear crystals. Annealing in appropriate
conditions is used to correct the composition and improve the optical quality. We annealed LiGaS2 in vacuum, in the
presence of Li2S, Ga2S3, and S, and studied changes in transmission, photoluminescence and photo-induced
absorption. OH groups, S-H and S-S complexes, sulfur vacancies and cation antisite defects (GaLi) are most important.
Photo-induced absorption is reversible: It appears after illumination with UV/blue light and disappears after
illumination with IR light or by heating the sample.
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