Design considerations for fiber-coupled streaked optical spectroscopy

Optical fibers are used to couple light into fast time-resolved spectrometers for many applications. Here several issues arise that can seriously limit the temporal resolution, such as the wavelength dependent group delay, and intermodal dispersion. These issues are investigated in 10 m length fibers using either a 400 mum core step index or graded index fiber. A unique broadband (400-700 nm) short pulse (similar to1 ps) light source is used to measure the fiber group delay with a time-resolved spectrometer. Intermodal dispersion is also studied in these fibers using a narrow-band 1 ps pulse that is injected into the fiber with various coupling schemes, and a novel technique is employed to record the time-dependent angular mode structure. Finally, a conceptual design using similar to 100 mum core graded-index fibers is proposed for multichannel streaked optical spectroscopy on the National Ignition Facility. Designs appropriate for a low spectral resolution instrument (stimulated Raman backscattering) and a high spectral resolution instrument (stimulated Brillouin backscattering) are presented. The fiber dispersion issues are discussed in the design of these diagnostics. (C) 2001 American Institute of Physics.