August 1, 2012.
The Linac Coherent Light Source (LCLS) at SLAC depends on a photocathode electron gun to provide the linear accelerator with the raw material – electrons – used for making X-ray laser pulses. The photocathode used in the LCLS Injector is a clean copper plate in high vacuum. When the cathode is struck with high energy UV light, electrons are liberated from its surface and then accelerated down the linac with radio-frequency electric fields. These fast-moving bunches of electrons are directed through an undulator magnet to radiate X-ray light.
Although scientists have been using photocathode techniques at SLAC for 25 years, some important aspects of the physics involved are not well understood. The ASTA Laser Lab is a replica of the Injector Laser Lab with photocathode gun at the LCLS. As such, ASTA now provides for experimental photocathode research that will directly affect operations at LCLS.
The laser system in ASTA (and the LCLS Injector) uses a 68 MHz pulsed infrared beam to seed an amplifier, the output of which is then frequency multiplied into 253 nm UV. These UV pulses are the end product of the laser lab, used for photo-emission in the electron guns. An important tool in these laser labs is a Cross Correlator. This optical system uses light – with known characteristics – from the 35fs infrared seed beam to make a cross correlated measurement with the 2-3 ps UV pulses. With this technique, time characterization of the UV beam is achieved.
This work involved the construction of ASTA, the installation of the high powered laser system, and the redesign and implementation of a cross correlator for the new lab. This presentation includes Cross Correlator measurements as well as a larger introduction to the LCLS and Injector Laser Lab.
Electromagnetics and Photonics | Materials Science and Engineering | Optics | Plasma and Beam Physics
SLAC National Accelerator Laboratory (SLAC)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0833353. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).