The optical parametric oscillator based on the first PPKTP crystal produced in Russia was created. This crystal has dimensions of 8×0.5×10 mm and polling period of Λ1=37.9 μm, Λ2=38.7 μm. The conversion efficiency of pump into idler at repetition rate 1 kHz is 7.5%, quantum efficiency 17.8% and slope efficiency 16.3%. The generation threshold was 110 μJ. The optical parametric oscillator based on the first PPKTA crystal was developed. Threshold for parametric generation was 130 μJ (14.4 MW/cm2), the quantum efficiency was 27% and the differential efficiency was 12%. The signal wavelength was 1.54 μm, and the idler wavelength corresponded to 3.31 μm.
Optical parametric oscillator based on Russian domestic PPKTP structure was created. High quality KTP crystals, of resistivity as high as~1013 Ohm*cm and coercive electric field as low as 2,3 kV/mm weregrownat Crystals of Siberia Ltd.,and 1.8 mm-thick substrates were processed at Labfer Ltd.
A singly-resonant OPO (SRO) based on AgGaSe2 (AGSe) intracavity pumped at ~1.85 μm by the signal pulses of a Rb:PPKTP doubly-resonant OPO (DRO) provided extremely broad tuning (5.8 to ~18 μm) for the non-resonated idler. In a similar set-up with the same nonlinear crystals, we studied intracavity difference-frequency generation (DFG). Both AGSe and the new monoclinic crystal BaGa4Se7 (BGSe) generated single pulse energies of ~0.7 mJ near 7 μm at an overall conversion efficiency from the 1.064 μm pump of 1.2%. The main advantage of BGSe is its damage resistivity up to the maximum pump levels applied at 100 Hz.
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.
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.
LiInSe2 is one of the few (in the meanwhile 6) non-oxide nonlinear crystals whose band-gap (2.86 eV) and transparency
enabled in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump
wavelength of 1064 nm. However, the first such demonstration was limited to the 3.34-3.82 μm spectral range with a
maximum idler energy of 92 μJ at 3.457 μm for a repetition rate of 10 Hz. Now we achieved broadly tunable operation,
from 4.7 to 8.7 μm, reaching maximum idler pulse energy of 282 μJ at 6.514 μm, at a repetition rate of 100 Hz
(~28 mW of average power).
LiInSe2 is one of the few (in the meanwhile 6) non-oxide nonlinear crystals whose band-gap (2.86 eV) and transparency
enabled in the past nanosecond optical parametric oscillation in the mid-IR without two-photon absorption for a pump
wavelength of 1064 nm. However, the first such demonstration was limited to the 3.34-3.82 μm spectral range with a
maximum idler energy of 92 μJ at 3.457 μm for a repetition rate of 10 Hz. Now we achieved broadly tunable operation,
from 4.65 to 7.5 μm, with a single crystal, reaching maximum idler pulse energy of 282 μJ at 6.514 μm, at a repetition
rate of 100 Hz (~28 mW of average power).
Sergei Bagayev, S. Chepurov, Vladimir Denisov, V. Klementyev, D. Kolker, Igor Korel, S. Kuznetsov, Yu. Matyugin, V. Pivtsov, V. Zakharyash, Timothy Birks, William Wadsworth, Philip Russell
We propose an experimental results and theoretical description of the ultrashort pulse train spectral broadening in tapered fibers. Multi-peak spectral structure due to the effect of self-phase modulation was obtained. Phase and amplitude fluctuations were investigated. Shown that stability of intermode beats decreased slightly after the propagation through tapered fiber. A technique and results of high precision measurements of the intermode frequency of a femtosecond Ti:sapphire laser for investigation of the influence of a tapered fiber are described. The experiments have shown that the intermode frequency stability does not depend on the broadened spectrum range.
Sergei Bagayev, S. Chepurov, Vladimir Denisov, V. Klementyev, D. Kolker, Igor Korel, S. Kuznetsov, Yu. Matyugin, V. Pivtsov, V. Zakharyash, Timothy Birks, William Wadsworth, Philip Russell
Experimental and theoretical investigations of the Ti:S laser spectrum broadened in tapered fiber are presented. Dependence of broadened spectrum envelope on the waist diameter and coupled laser power was studied.
Sergei Bagayev, S. Chepurov, Vladimir Denisov, Alexander Dmitriyev, A. Dychkov, V. Klementyev, D. Kolker, Igor Korel, S. Kuznetsov, Yu. Matyugin, M. Okhapkin, V. Pivtsov, M. Skvortsov, V. Zakharyash, Timothy Birks, William Wadsworth, Philip Russell
The principles of precision measurement of frequency intervals in optical range with the help of femtosecond lasers are described. An experimental scheme of femtosecond optical clock is described. The characteristics of the basic elements and units of the setup are presented. The results of a broadened spectrum researches with the help of tapered fibers are reported.
Sergei Bagayev, Alexander Dmitriyev, S. Chepurov, A. Dychkov, V. Klementyev, D. Kolker, S. Kuznetsov, Yu. Matyugin, M. Okhapkin, V. Pivtsov, M. Skvortsov, V. Zakharyash, Timothy Birks, William Wadsworth, Philip Russell, Alexei Zheltikov, Valentin Beloglazov
An experimental scheme of femtosecond optical clock is described. The characteristics of the elements and blocks of the setup are given. Possible application areas of the optical clock described are discussed.
The spectral characteristics and stability of a frequency of intermode beats of a femtosecond Ti:S laser are investigated. An active method is used to obtain high stability. The frequency stability of intermode beats not lower than 5.8.10-14 rms in 100s is achieved. Possible applications of the setup, such as measurement of large frequency intervals in the optical range, creation of optical frequency synthesizers, etc. are proposed. The physical principles for the creation of an optical clock of a new type using highly stable femtosecond Ti:S laser are considered.
Frequency standard at 732 nm for absolute measurements of the muonium 1S-2S transition frequency has been developed. A suitable reference line for that standard was found in the absorption spectra of the iodine vapor heated up to 600 degree(s)C. In order to measure the absolute frequency of the developed standard, an optical synthesis chain was built up. The frequencies to be measured were synthesized from two secondary standard frequencies: a frequency of the diode laser stabilized to rubidium absorption line and a frequency of the CO2 laser, locked to CO2 absorption line. An accuracy of the measurements is order 10$min9.
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