Conference "Ultrafast Optical Phenomena (Ultra fast Light-2023)" October 2-4, 2023, Lebedev Institute of Physics, Russian Academy of Sciences
Laser physics and laser optics

Second harmonic microscopy from nearsurface plasma ignited by tightly focused femtosecond fiber laser beam

A. A. Garmatina^a, E. I. Mareev^a, A. A. Korshunov^ba, M. D. Mozhaeva^ba, N. V. Minaev^a, A. È. Muslimov^a, D. N. Khmelenin^a, V. E. Asadchikov^a, V. M. Gordienko<sup>ca

a</sup> Kurchatov Complex of Crystallography and Photonics NRC "Kurchatov Institute", 123182 Moscow, Russia
^b National Engineering Physics Institute "MEPhI", 115409 Moscow, Russia
^c Lomonosov Moscow State University, Faculty of Physics, 119992 Moscow, Russia

Abstract: Method measuring in real time the size of the microplasma, which is a source of X-rays, ignited on the target surface by a tightly focused ($NA$ = 0.2) repetition rate femtosecond fiber laser beam (280 fs, 10–25 $\mu$J) has been developed. The technique based on the backreflected second harmonic signal from the microplasma. It has been stated that the size of the microplasma second harmonic beam is $\sim$8.5 $\mu$m at the pulse energy of 10 $\mu$J, pulse repetition rate of 2 MHz, which corresponds to the regime of achieving the maximum X-ray yield and minimum of the microplasma size. The conversion efficiency at laser intensity of $\sim$10$^{14}$ W/cm$^2$ into the second harmonic is about 10$^{-6}$.

Keywords: fiber laser, femtosecond laser pulse, backreflected laser plasma second harmonic.

Received: 11.12.2023
Revised: 09.01.2024
Accepted: 16.01.2024

DOI: 10.61011/EOS.2024.01.58287.11-24

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