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 [ 1] and a single element high speed detector with integrating sphere, allows one to obtain spectral or temporal information for each individual micro-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 non-collinear optical mixing in a frequency doubling crystal [2], an imaging telescope and again an image dissector system. Here, the imaging telescope relays the image of the region in file nonlinear crystal in which second harmonie light was generated onto the image dissector. The design and implementation of these vi diagnostics for the 1-11 gm on the IR-FEL at Stanford University are discussed.

Use of Fringe-Resolved Autocorrelation for the Diagnosis of the Wavelength Stability of a Free Electron Laser

“…2) Apart from the applications, developing the techniques to characterize the FEL pulses in terms of the pulse duration and the chirp is also an important issue. [3][4][5][6][7][8][9][10] Recall that the FEL pulses originate from the accelerated electron bunches, and their energy and phase are very difficult to maintain constant. Besides the lasing of FEL starts from the spontaneous emissions which may have slightly different photon energies.…”

“…We note that the single-shot measurement of the spectrum of the FEL micropulse with a single photodetector requires lots of efforts. 3,4) We would like to point out that the pulse spectrum averaged over the entire macropulse is not sufficient to monitor the wavelength stability of the FEL, since it does not provide us with the information on the shotto-shot (micropulse-to-micropulse) fluctuation of the central wavelength. Clearly we must seek for a new reliable technique to monitor the wavelength stability of FEL pulses.…”

An infrared free electron laser system for the proposed chemical dynamics research laboratory at LBL based on a 500 MHz superconducting linac

“…These are the LBL-Stanford collaboratiort on development of novel diagnostics for FEL optical pulses [8], the Stanford-LBL-TRW-BNL collaboration on optimization of SC cavities for FEL [9], and experimental study of hole-coupling and resonator modes [ 10].…”