Simulations of the TJNAF FEL with tapered and inversely tapered undulators

Experiments using the TJNAF FEL have explored the operation with both tapered and inversely tapered undulators. We present here numerical simulations using the TJNAF experimental parameters, including the effects of taper. Singlemode simulations show the effect of taper on gain. Multimode simulations describe the evolution of short optical pulses in the far infrared, and show how taper affects single-pass gain and steady-state power as a function of desynchronism. A short optical pulse presents an ever-changing field strength to each section of the electron pulse so that idealized operation is not possible. Yet, advantages for the recirculation of the electron beam can be explored.The authors are grateful for support by the Naval Postgraduate School

TJNAF free electron laser damage studies

Laser material damage experiments were conducted at the Thomas Jefferson National Accelerator Facility (TJNAF) free electron laser (FEL) user laboratory with an average power of 100W and a power density of 104 W/cm2. The FEL beam bombards the target with a steady stream of tens of millions of pulses per second each containing 50MW of power in a short burst of B1 ps. No conventional laser combines these characteristics, and no experiments have previously been done to explore the effects of the FEL pulse. The goal is to develop scaling laws to accurately describe large-scale damage from a MW FEL using small-scale experiments.The authors are grateful for the support by the Naval Postgraduate School

Near-IR absorption of Ga:La:S and Ga:La:S:O glasses by FEL-based laser calorimetry

Optical absorption of Ga:La:S and Ga:La:S:O glasses in the near infrared was investigated by laser calorimetry using the free-electron laser source at the Thomas Jefferson National Accelerator Facility. An absorption coefficient of 1.2 and 2.1 x 10-2cm-1 was measured at 1.55 µm for Ga:La:S and Ga:La:S:O respectively. Comparing this result with conventional transmission measurements, we conclude that absorption is the prevailing loss mechanism in the near-IR region for these materials