Mid-infrared pulsed nanosecond difference frequency generation of oxide LGN crystal up to 5.7 µm

Mid-infrared electronic wavelength tuning through intracavity difference-frequency mixing in Cr:ZnSe lasers

Mid-infrared tunable coherent light sources are used in various laser applications, such as trace gas detection, laser processing, and biomedical diagnostics. This study demonstrates mid-infrared generation in the 8.3-11 µm (i.e., 900-1200 cm^-1) spectral range by configuring intracavity difference-frequency generation (DFG) using ZnGeP₂ (ZGP) in an electronically tuned Cr:ZnSe laser. The broad tunability is achieved with the maximum pulse energies exceeding 100 μJ by combining the electronic wavelength tuning with sligh angle adjustments (Δθ < 0.5°) of ZGP under the spectral noncritical phase-matching condition of the nonlinear material. The proposed DFG method is generalized to give access to a significant fraction of the molecular fingerprint region by utilizing selenide compounds (e.g., AgGaSe₂, CdSe) in addition to ZGP, revealing the remarkable potential of ultrabroadband electronic mid-infrared scanning for numerous spectroscopic applications.

Frequency Down-Conversion of Optical Pulse to the Far Infrared and THz Frequency Ranges Due to the Cascading Process in a Medium with a Quadratic Nonlinear Response

Difference-frequency generation is a well-known method of obtaining IR and THz radiation. It has many practical applications, such as sensing, optical metrology, diagnostics, detection and identification of substances, etc. One of the generation methods is based on the three-wave interaction in a medium with second-order nonlinear susceptibility. In this study, we investigated a special case of the frequency down-conversion into IR and THz ranges of the frequencies: the frequencies of interacting waves were multiple. We analyzed theoretically two cases of three-wave interactions: amplification of the infrared (or THz) radiation (incident weak intensity of a wave at this frequency) and a wave generation with the difference-frequency (incident zero-value intensity at this frequency). The amplification efficiency could achieve 75% and the maximal frequency conversion efficiency is about 25%. The computer simulation results made for the femtosecond pulse interaction in a crystal with the wavelength 4, 10, and 24 μm demonstrates applicability of such a scheme for the frequency down-conversion. This scheme of the THz radiation generation is a perspective tool for its application in the screening system for the detection and identification of substances.

Growth of a large-aperture mid-infrared nonlinear optical La3Nb0.5Ga5.5O14 crystal for optical parametric chirped-pulse amplification

A high optical quality 60 mm-diameter LGN crystal with wide transparency was grown by the Czochralski method. The origin of the wide transparency as for a traditional oxide crystal was investigated from the viewpoint of crystal symmetry.