Generation and Photonic Guidance of Multi-Octave Optical-Frequency Combs

TLDR

Ultrabroad coherent comb-like optical spectra spanning several octaves are a chief ingredient in the emerging field of attoscience. The study demonstrates generation and guidance of a three‑octave optical comb from 325 to 2300 nm in a hydrogen‑filled hollow‑core photonic crystal fiber. Generation occurs by driving the fiber with a 10‑kW infrared laser, producing up to 45 high‑order Stokes and anti‑Stokes lines, while waveguiding is achieved via inhibited coupling between core and cladding modes rather than a photonic band gap. The approach reduces required laser power by six orders of magnitude compared to prior methods and provides a robust, simplified route to synthesizing attosecond pulses.

Abstract

Ultrabroad coherent comb-like optical spectra spanning several octaves are a chief ingredient in the emerging field of attoscience. We demonstrate generation and guidance of a three-octave spectral comb, spanning wavelengths from 325 to 2300 nanometers, in a hydrogen-filled hollow-core photonic crystal fiber. The waveguidance results not from a photonic band gap but from the inhibited coupling between the core and cladding modes. The spectrum consists of up to 45 high-order Stokes and anti-Stokes lines and is generated by driving the confined gas with a single, moderately powerful (10-kilowatt) infrared laser, producing 12-nanosecond-duration pulses. This represents a reduction by six orders of magnitude in the required laser powers over previous equivalent techniques and opens up a robust and much simplified route to synthesizing attosecond pulses.