The mid-infrared range holds numerous applications in various fields such as spectroscopy, gas analysis, atmosphere sensing and other. In this spectral domain, organic compounds exhibit single-bond bending modes thereby resulting in their unique spectral absorption patterns. Therefore, lasing in the mid-IR range have attracted significant attention among scientists and researchers.
Among the available mid-infrared sources, a narrow-bandwidth mid-IR laser is capable for use in the remote sensing, especially for the atmospheric gases. Unfortunately, solid-state mid-IR lasers are not widespread yet for outdoor applications due to their complexity, limited power and tunability range. As such, hybrid laser systems have been identified as an alternative for providing high-energy mid-IR pulses. They convert a radiation frequency of high-power mid-IR molecular gas lasers in nonlinear crystals which opens up their new opportunities and applications. For example, robust broadband mid-IR laser system based on a single multiline sub-microsecond carbon monoxide (CO) laser and cascaded frequency conversion in a single ZnGeP2 crystal was developed. The peculiarity of such a laser system is as follows: broadband multiline CO laser radiation experiences several sum- and difference frequency mixing stages both in parallel and simultaneously in a single nonlinear optical crystal with spectral enrichment and expansion at the each stage.
Recently, researchers at the Lebedev Physical Institute of Russian Academy of Sciences Professor Andrey Ionin, Dr. Igor Kinyaevskiy, Dr. Yury Klimachev, and Vera Mozhaeva in collaboration with Professor Yury Andreev of the Tomsk State University are the first to numerically and experimentally presented a three-stage frequency conversion of a multiline sub-microsecond CO laser pulse in a single ZnGeP2 crystal. This was a significant improvement of the initially developed two-stage conversion frequency. They purposed to extend the laser system spectrum range and also improve on their conversion efficiency. Their work is published in the journal, Optics Letters.
The authors observed more than 200 narrow spectral lines within 2.4-6.2 µm spectral range emitted by the hybrid laser system. The first, second and third stages frequency conversion efficiencies were 4.8%, 0.4%, and 0.5 % respectively. However, due to nonlinearity of the frequency conversion process, the stage efficiencies can be significantly enhanced because of a power law with CO laser power increase, and doing so the efficiency of the third stage may become higher than that of second one. Numerical simulation indicated that such kind of a laser system can emit millions narrow spectral lines within very broad part of the mid-IR range from 2 to 10 micron.
The study is the first to successfully investigate the three-stage frequency conversion of a multiline sub-microsecond laser pulse in a single ZnGeP2 crystal. The authors believe that a development of CO lasers with a compact slab RF discharge configuration, operating in mode-locking regime, and intracavity frequency conversion of the radiation in nonlinear crystals will result in a significant improvement of performance and usability of such mid-IR laser system. This study was supported by the RFBR (Project No. 18-32-00209).
Ionin, A., Kinyaevskiy, I., Klimachev, Yu., Mozhaeva, V., & Andreev, Yu. (2018). Three-stage frequency conversion of sub-microsecond multiline CO laser pulse in a single ZnGeP2 crystal. Optics Letters, 43(13), 3184.Go To Optics Letters