Home – Home – Jornals – Atmospheric and Oceanic Optics 2025 number 4

Theoretical studies of the ways of increasing the efficiency of second harmonic generation (SHG) in visible lasers are relevant because of common use of UV radiation in different scientific and engineering problems. The work compares three most common approaches to second harmonic generation: SHG(L), where laser radiation (LR) is guided directly into a crystal (without additional optics); SHG(F), where LR is focused into a crystal by a spherical lens; and SHG(T), where LR is compressed by a lens (or mirror) telescope before entering a crystal. The SHG efficiency is shown to be maximal at optimal transverse size of LR in a crystal, which depends on LR amplitude profile in a cross section. When SHG is implemented under near-optimal conditions, SHG(F) is the most effective. If the transverse size of LR in a crystal is noticeably larger than optimal, SHG(F) is the least effective. It is shown that the gain in SHG efficiency, which is provided by replacing a long-focus lens with a suitable telescope, can exceed 100% with an increase in the transverse size of LR in a crystal and for super-Gaussian beams. In the first part of this paper, all the results are obtained in the preset field approximation. The refined results (with a strict solution of a set of nonlinear wave equations) will be presented in the second part. The results of the study can be useful for developing efficient frequency converters for metal vapor lasers.