CC BY
19LS-I-16
Multiband Supercontinuum Generation in the Mid-infrared Gas Fiber Raman Laser
A.V. Gladyshev*, I.G. Pritulenko, Yu.P. Yatsenko, A.N. Kolyadin, I.A. Bufetov
Prokhorov General Physics Institute of the Russian Academy of Sciences, Dianov Fiber Optics Research
Center, 38 Vavilov st., Moscow, Russia, 119333.
*Corresponding author: alexglad@fo.gpi.ru
Mid-infrared (mid-IR) laser sources are required for many applications [1]. To reach the mid-IR, stimulated Raman scattering (SRS) of near-infrared radiation inside a gas-filled hollow-core fiber (HCF) can be used [2]. In this way, a sup-picosecond gas fiber Raman laser (GFRL) have been recently realized in the mid-IR via two-cascade SRS 1.03^1.49^2.68 ^m in a D2-filled HCF [3].
Here, we study the influence of the pump pulse duration Tpump on the spectral properties of the GFRL and generate a multiband supercontinuum (SC) with spectral coverage from 0.65 to 3.3 ^m.
Experimental setup and the HCF (Fig. 1a-b) were the same as published in [3]. The HCF was filled with D2 at a pressure of 5 atm. The duration of initially transform-limited 250-fs-long pump pulses was varied by introducing various amount of positive frequency chirp to the pulses.
Wavelength (nm)
Fig. 1. (a) The scheme of the GFRL (See [3] for details). (b) Image of the HCF. (c) The output spectrum of the GFRL for Tpump = 1 ps, Epump = 210 J PD2 = 5 atm, LHCF = 2.9 m. Optical loss spectrum of the HCF is also shown (grey filled curve).
When sufficiently long pump pulses (Tpump ~ 10 ps) were used, vibrational SRS is a dominant nonlinear effect. About 20 % of pump quanta is converted to the second Stokes wavelength of 2.68 ^m, and no spectral broadening is detected even for pump pulse energy as high as 210 J
However, when Tpump was shortened below ~3 ps, a competition between SRS and other nonlinear effects, such as self-phase and cross-phase modulation, comes into play. The output spectrum of the GFRL experiences broadening with simultaneous reduction of SRS conversion efficiency. For Tpump as short as 250 fs, the SRS conversion into mid-IR was not observed.
The most pronounced spectral broadening was observed for the case of Tpump = 1 ps and Epump = 210 J where a multiband supercontinuum with spectral coverage from 0.65 to 3.3 ^m was achieved (Fig. 1c), and about 6 % of pump quanta were converted to wavelengths above 2 ^m. Numerical modeling suggests that optimization of the SC width and efficiency is possible.
This work is supported by Russian Science Foundation (grant №19-12-00361).
[1] K. L. Vodopyanov, Laser-based Mid-infrared Sources and Applications (John Wiley & Sons, Inc.) (2020)
[2] M. Astapovich et al., "Watt-Level Nanosecond 4.42-^m Raman Laser Based on Silica Fiber" IEEE Photon. Techol. Lett. 31, 78 (2019)
[3] A. Gladyshev et al., "Mid-infrared 10-^J-level sub-picosecond pulse generation via stimulated Raman scattering in a gas-filled revolver fiber," Opt. Mater. Express 10, 3081-3089 (2020)
