Microstructure-fiber sources of mode-separable supercontinuum emission for wave-mixing spectroscopy

Microstructure fibers are shown to provide a high efficiency of generation of mode‐separable and frequency‐convertible supercontinuum of a high spectral and spatial quality, offering much promise as sources of broadband radiation for wave‐mixing spectroscopy and time‐resolved pump–probe measurements, and also for seeding optical parametric amplifiers. The long‐wavelength and visible parts of supercontinuum emission generated by 40 fs pulses of 800 nm Ti : sapphire laser radiation in fused‐silica microstructure fibers are shown to be spatially separated in microstructure‐fiber modes. With an appropriate spectral filtering, bell‐shaped modes of the long‐wavelength section (∼720–900 nm) of the supercontinuum generated in a microstructure fiber with a small core diameter can be separated from either doughnut‐like or bipartite modes of the visible part (∼400–600 nm) of this supercontinuum. This effect can be employed for the spectral slicing of single modes of supercontinuum emission from microstructure fibers. Frequency convertibility of spectrally sliced supercontinuum is demonstrated by experiments on sum‐frequency generation in a non‐linear crystal. Copyright © 2002 John Wiley & Sons, Ltd.