A technique for single-pulse spectrum and pulse width measurements for an IR-FEL

Abstract

A diagnostic system has been designed to measure the spectrum and pulse width of infrared FEL pulses. Use of an image dissector [H.A. Baldis et al., Rev. Sci. Instr. 48 (1977) 173] and a single element high speed detector with integrating sphere, allows one to obtain spectral or temporal information for each individual mu-pulse inside the pulse train. The spectral diagnostic consists of a mode matching telescope, a high resolution spectrometer, an imaging telescope and an image dissector system. The imaging telescope between the spectrograph and the image dissector provides for variable magnification (and hence resolution) of the spectrum onto the image dissector. The pulse width measurement uses single pulse autocorrelation through noncollinear optical mixing in a frequency doubling crystal [S.A. Arakelian et al., Opt. Commun. 44 (1982) 67], an imaging telescope and again an image dissector system. Here, the imaging telescope relays the image of the region in the nonlinear crystal in which second harmonic light was generated onto the image dissector. The design and implementation of these diagnostics for the 1–11 μm on the IR-FEL at Stanford University are discussed.