Exploration of rotational and vibrational stimulated Raman scattering in oxygen-filled fiber

Stimulated Raman scattering (SRS) is performed in pressurized oxygen (O2) within a nested antiresonant fiber (NARF) to investigate the interplay between rotational and vibrational SRS. In this work, the O2-filled NARF is pumped by 500 ps pulses at λ = 1.064 μm with peak powers of up to 60 kW. The pump generates cascaded vibrational Stokes lines spaced by ∼1550 cm-1, and each of these generates cascaded Stokes and anti-Stokes rotational SRS. The extremely spectrally broad guidance of the NARF enables, for the first time, the measurement of the third vibrational Stokes order, which is beyond 2.1 μm with our pump wavelength. We report on the threshold energies and conversion efficiencies of each vibrational SRS order. In addition, we observe the pressure-dependent absorption of O2 in the near-infrared and discuss the ramifications. We also collect pump polarization-dependent spectra while varying O2 pressure and pump power to determine the gain competition between rotational and vibrational SRS. This work explores the spectroscopic complexities of O2 and presents a new multispectral fiber laser source.