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ALT'23 The 30th International Conference on Advanced Laser Technologies
N-O-5
Broadband conversion of multiline Q-switched CO laser emission under its double-pass through AR-coated ZnGeP2 crystal
I. O. Kinyaevskiy1,2, Yu. M. Klimachev1, M. V. Ionin1, A. M. Sagitova1, M. M. Zinovev2,3, N.N.Yudin2,3,
A. A. Ionin1
1Lebedev Physical Institute of the Russian Academy of Sciences, 53 Leninskiy Ave., 119991 Moscow, Russia 2National Research Tomsk State University, 36 Lenin Ave, 634050 Tomsk, Russia 3LOC LLC, 28 Vysotsky Str., 634040 Tomsk, Russia
Main author email address: maximionin@gmail.com
To solve a number of problems (for example, environmental monitoring and air control of a working area, analysis of processed gases and gas mixtures composition, detection of leaks in main gas and oil pipelines), the development of broadband mid-IR laser sources is required. One of the most efficient amongst such laser sources is a CO laser. One of its advantages, for example, is that many spectral lines of a CO laser are in the spectral ranges of low atmospheric absorption [1]. However, to solve a number of problems, it is necessary to expand the spectral limits of CO laser radiation. One of the methods for expanding and enriching the spectrum of a CO laser is frequency conversion of its emission in nonlinear crystals.
The Gas Laser Laboratory of P.N. Lebedev Physical Institute of RAS has already implemented broadband sum-frequency generation (SFG) in several nonlinear crystals: ZnGeP2 [2], AgGaSe2 [3], BaGa2GeSe6, GaSe [4] with external conversion efficiency of 2.5%, 0.6%, 0.5% and 0.15%, respectively. Therefore, after comparing the obtained results, we can claim that just the ZnGeP2 nonlinear crystal is the most efficient for this type of conversion. The CO laser SFG efficiency enhancement in nonlinear crystals ZnGeP2 is possible by several procedures.
Firstly, an increase of the SFG efficiency is possible due to a sharper focusing. Secondly, it is potentially possible to increase the SFG efficiency by using an intracavity SFG scheme. Thirdly, conversion efficiency can be increased by an application of a double-pass scheme. The fourth option for increasing the conversion efficiency is application of a nonlinear crystal AR-coating which is the objective of the given research. This research became possible due to the development of new broadband multirange AR-coatings [5] for the ZnGeP2 crystal with the high optical damage threshold both in the CO laser spectral range (5-7 ^m) and in the sum-frequencies range (2.5-3.5 ^m).
Broadband sum-frequency conversion of multiline (~60 spectral lines within ~5-6 ^m) Q-switched CO laser emission in an AR-coated ZnGeP2 crystal was experimentally studied by application of both single-pass and double-pass optical schemes. The maximum conversion efficiency in the double-pass scheme reached ~10% that is 2.5 times higher than one obtained in the same optical scheme with an uncoated ZnGeP2 [6]. The spectrum control of frequency converted radiation by changing angles of incident and reversed CO laser beams in the ZnGeP2 crystal was implemented within the wavelength range from 2.52 ^m up to 2.92 ^m. The maximum spectrum width of 0.35 ^m was obtained with the double-pass scheme when the angle of the laser beam incident on the crystal and the angle of the deflected reversed laser beam were 4.0° and 3.0°, respectively, the spectral bandwidth being three times broader than one obtained with the single-pass scheme. The research was supported from the Russian Science Foundation grant № 22-22-20103.
[1] A.A. Ionin, Yu.M. Klimachev, A.Yu. Kozlov, et al., Application of an overtone CO laser for remote gas analysis of the atmosphere, Atmospheric and Oceanic Optics, Volume 26, Issue 1, pp 68-73, (2013)
[2] I. Kinyaevskiy, A. Ionin, Yu. Klimachev, Yu. Andreev, and V. Mozhaeva, Three-stage frequency conversion of sub-microsecond multiline CO laser pulse in a single ZnGeP2 crystal, Optics letters, Vol. 43, No. 13, 3184-3187 (2018).
[3] Budilova O.V., Ionin A.A., Kinyaevskiy I.O., et al., Broadband two-stage frequency conversion of CO laser in AgGaSe2 crystal // Optics Letters, T. 41. C. 777, (2016)
[4] D. V. Badikov, V. V. Badikov, A. A. Ionin, et al., Sum-frequency generation of Q-switched CO laser radiation in BaGa2GeSe6 and GaSe nonlinear crystals, Optical and Quantum Electronics, 50, 243, (2018)
[5] M. Zinovev, N.N. Yudin; I. Kinyaevskiy; et al., Multispectral Anti-Reflection Coatings Based on YbF3/ZnS Materials on ZnGeP2 Substrate by the IBS Method for Mid-IR, Laser Applications, Crystals, 12(10), 1408; (2022)
[6] I.O. Kinyaevskiy, Yu.M. Klimachev, M.V. Ionin, et al., Broadband sum-frequency conversion of multiline Q-switched CO laser emission under its double-pass through uncoated ZnGeP2 crystal, Infrared Physics & Technology, 104740, (2023)
