OPTICS AND NUCLEAR PHYSICS

Angular distribution of the intensity of a mid-infrared femtosecond radiation source in a nonlinear crystal with a signal wave formed in a filament in a gas

I. O. Kinyaevskiy^a, M. V. Ionin^a, A. V. Koribut^a, Yu. M. Andreev<sup>b

a</sup> Lebedev Physical Institute, Russian Academy of Sciences, 119991, Moscow, Russia
^b Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, 634055, Tomsk, Russia

Abstract: The divergence of mid-infrared radiation obtained by difference frequency generation of femtosecond titanium–sapphire laser pulses in a 2-mm-thick nonlinear HgGa$_2$S$_4$ crystal has been measured. At a pump radiation aperture of 2.8 mm, the output radiation divergence is 5.2 and 9.2 mrad at wavelengths of 7.2 and 10.5 $\mu$m, respectively. It has been shown experimentally that the angular distribution of the difference frequency radiation intensity differs significantly from the Gaussian one and the divergence of the central maximum is determined as in Fraunhofer diffraction on a circular hole with a radius equal to the radius of the interaction region.

Received: 26.02.2025
Revised: 14.04.2025
Accepted: 16.04.2025

DOI: 10.31857/S0370274X25050161

 English version: Journal of Experimental and Theoretical Physics Letters, 2025, 121:10, 778–782