Parametric four-wave mixing sidebands in strongly driven Raman molecular D2-filled HC-PCF

Summary form only given. The development of the Raman gas-filled hollow core photonic crystal fibers allow to exacerbate the light-matter interaction with extremely high efficiency. Among the nonlinear optical effect that were extensively explored we count stimulated Raman scattering, with demonstrations like over 5-octaves wide Raman comb using H
₂
-filled inhibited coupling guiding HC-PCF pumped with a picosecond pulsed laser [1]. Furthermore, Raman-active gases are known to exhibit very weak susceptibility outside the Raman frequencies, and thus are considered to be poor media for the generation of new frequencies through parametric four-wave mixing (FWM).Here we demonstrate, for the first time to our knowledge, the generation of pairs of sidebands via parametric FWM in strongly driven Raman molecular gas. The experimental set-up used a 1030 nm Yb-fiber laser with average power of 15 W, a repetition rate of 1 MHz and pulse duration of 27 ps. The light is then coupled into a photonic microcell composed by a D2-filled inhibited coupling tubular-lattice single-ring HC-PCF [2]. The fiber exhibits a low-loss broadband guidance with a minimum of 10 dB/km around the pump wavelength and operates in almost a single mode regime with a mode field diameter of 28 μm. The D2 molecule has a vibrational Raman resonance around 89.8 THz, and rotational resonances of 12.4 THz for the ortho-D2 and 7.1 THz for the para-D2. The pressure of D2 was set at 40 bar to experimentally maximize the Raman lines from ortho-D2. The results are shown in the figure 1. The generated spectrum presents around 100 laser lines over a 200 THz wide spectral span with a dense cluster whose frequency-difference is under 2 THz by a ro-vib SRS/FWM combination. Four FWM sidebands can be identified (plotted in red color), generated in both sides of two para-rotational lines reproduced eight times around the pump radiation and three times around the first vibrational Stokes.