Multioctave supercontinuum generation and frequency conversion based on rotational nonlinearity

Abstract

The field of attosecond science was first enabled by nonlinear compression of intense laser pulses to a duration below two optical cycles. Twenty years later, creating such short pulses still requires state-of-the-art few-cycle laser amplifiers to most efficiently exploit “instantaneous” optical nonlinearities in noble gases for spectral broadening and parametric frequency conversion. Here, we show that nonlinear compression can be much more efficient when driven in molecular gases by pulses substantially longer than a few cycles because of enhanced optical nonlinearity associated with rotational alignment. We use 80-cycle pulses from an industrial-grade laser amplifier to simultaneously drive molecular alignment and supercontinuum generation in a gas-filled capillary, producing more than two octaves of coherent bandwidth and achieving >45-fold compression to a duration of 1.6 cycles. As the enhanced nonlinearity is linked to rotational motion, the dynamics can be exploited for long-wavelength frequency conversion and compressing picosecond lasers.

Nonlinear Optics in Multipass Cells

“…Most of the reported experiments have been aimed at pulse compression, and have therefore used atomic noble gases such as argon, krypton, or xenon, to avoid the Raman shift toward longer wavelength that is typically induced by molecular gases' nonlinear response. However, as was demonstrated recently in a number of experiments in gas-filled capillaries, [38,39] molecular gases could be used to simultaneously perform spectral broadening and wavelength shifting of the input pulse.…”

Raman Red‐Shift Compressor: A Simple Approach for Scaling the High Harmonic Generation Cut‐Off

“…[ 20,21 ] This effect is a strong motivation for the development of high‐power few‐cycle drivers, for instance, by the incorporation of advanced nonlinear compression techniques with state‐of‐the‐art ytterbium lasers delivering relatively long pulses (subpicosecond). [ 22,23 ] Finally, since the cut‐off energy scales with the square of the driving wavelength, the fourth knob is the central wavelength of the driver. However, in the single‐atom response, the generated photon flux decreases rapidly with increasing wavelength ( λ −(5–6) ).…”

“…Various approaches based on SRS have been reported in gas cells, [ 26,27 ] hollow‐core photonic crystal fibers, [ 28,29 ] and large‐diameter hollow‐core fibers (HCF). [ 22,23,30–32 ] Particularly, in the study by Safaei et al [ 32 ] , we describe a new regime of nonlinear propagation in HCFs that derives from the spatiotemporal nonlinear Raman enhancement observed with subpicosecond driver pulses. This mechanism allows for scaling the peak power by producing broadband, self‐frequency shifted solitons driven by subpicosecond pulses.…”

Efficient soliton self-frequency shift in hydrogen-filled hollow-core fiber

“…Initial observations of the soliton self-frequency shift (SSFS) in gas-filled hollow-core fibers reported small spectral shifts of tens of nanometers [9][10][11]. The SSFS plays a role in several recent studies, especially those of continuum generation and soliton self-compression [12,13]. The interplay of Raman and multimode effects has led to the recent observation of multidimensional solitary states [14].…”

“…To generate a clean Raman soliton with high efficiency, both the soliton number of the launched pulse and the number of participating Raman transitions should be as small as possible. Several studies have obtained wavelength-tunable sources by extracting the reddest lobe from a supercontinuum [12,13,25]; however, they failed to meet the above conditions and had relatively low efficiency. For example, with N 2 , Carpeggiani et al demonstrated 57 fs pulses with 8 % efficiency in the 1450-1650-nm spectral window.…”