Colson, W. B.
(William B. Colson)

MOPOS65 Short Rayleigh Length Free Electron Laser Simulations in Expanding Coordinates
Robert L. Armstead, Joseph Blau, William B. Colson (NPS, Monterey, CA)

For compact short-Rayleigh length FELs, the area of the optical beam can be thousands of times greater at the mirrors than at the beam waist. A fixed numerical grid of sufficient resolution to represent the narrow mode at the waist and the broad mode at the mirrors would be prohibitively large. To accommodate this extreme change of scale with no loss of information, we employ a coordinate system that expands with the diffracting optical mode. The simulation using the new expanding coordinates has been validated by comparison to analytical cold-cavity theory, and is now used to simulate short-Rayleigh length FELs.

MOPOS66 Optical Mode Distortion in a Short Rayleigh Length Free Electron Laser
Joseph Blau, William B. Colson, Robb P. Mansfield, Sean P. Niles, Brett W. Williams (NPS, Monterey, CA)

A short-Rayleigh length FEL will operate primarily in the fundamental mode with a Gaussian profile that is narrow at the waist and broad at the mirrors. The gain medium will distort the optical mode profile and produce higher-order modes that will expand more rapidly than the fundamental. Wavefront propagation simulations are used to study the higher-order modes, as the cavity length, Rayleigh length, electron beam current and radius, undulator taper, and the focus positions of the optical mode and electron beam are varied.

THPOS59 Stability of a Short Rayleigh Range Laser Resonator with Misaligned or Distorted Mirrors
Peter P. Crooker, Joseph Blau, William B. Colson (NPS, Monterey, CA)

Motivated by the prospect of constructing an FEL with short Rayleigh length in a high-vibration shipboard environment, we have studied the effect of mirror vibration and distortion on the behavior of the fundamental optical mode of a cold-cavity resonator. A tilt or transverse shift of a mirror causes the optical mode to rock sinusoidally about the original resonator axis. A longitudinal mirror shift or a change in the mirror’s radius of curvature causes the beam diameter at a mirror to dilate and contract with successive impacts. Results from both ray-tracing techniques and wavefront propagation simulations are in excellent agreement.