Initial results from the Los Alamos photoinjector-driven free-electron laser

Abstract

Abstract We report initial results on the APEX (APLE prototype experiment) photoinjector-driven infrared free-electron laser (FEL). The APEX FEL is operating in support of a Boeing Aerospace and Electronics/Los Alamos National Laboratory collaboration to build the average power laser experiment (APLE). Our system uses a high quantum efficiency (3–7%) multi-alkali photocathode, illuminated with a frequency-doubled Nd:YLF mode locked laser at 21.7 MHz. The photocathode is located in this first cell of a six-cell 1.3 GHz, 6 MeV photoinjector that feeds a linac with a final energy up to 40 MeV. Because the illuminating laser pulse on our photocathode is short (10 ps), no pulse compression is required in the linac. Emittance measurements made after the second linac tank at 15 MeV have shown that a normalized emittance (for 90% of the particles) of less than 50π mm mrad can be achieved at a peak micropulse current of 300 A. Our initial lasing has been at a wavelength of 3.6 μm over a 30 μs macropulse with an electron beam energy of 35 MeV and a 2.7 cm period permanent magnet wiggler. We are continuing to characterize and optimize our system, with particular emphasis on understanding and minimizing electron beam emittance-growth mechanisms, and subsequently improving the quality of the beam delivered to the wiggler.