Design considerations for fiber-coupled streaked optical spectroscopy

Optical fibers are used to couple light into fast time-resolved spectromete rs for many applications. Here several issues arise that can seriously limi t the temporal resolution, such as the wavelength dependent group delay, an d intermodal dispersion. These issues are investigated in 10 m length fiber s using either a 400 mum core step index or graded index fiber. A unique br oadband (400-700 nm) short pulse (similar to1 ps) light source is used to m easure the fiber group delay with a time-resolved spectrometer. Intermodal dispersion is also studied in these fibers using a narrow-band 1 ps pulse t hat is injected into the fiber with various coupling schemes, and a novel t echnique is employed to record the time-dependent angular mode structure. F inally, a conceptual design using similar to 100 mum core graded-index fibe rs is proposed for multichannel streaked optical spectroscopy on the Nation al Ignition Facility. Designs appropriate for a low spectral resolution ins trument (stimulated Raman backscattering) and a high spectral resolution in strument (stimulated Brillouin backscattering) are presented. The fiber dis persion issues are discussed in the design of these diagnostics. (C) 2001 A merican Institute of Physics.