Generation of superposed orbital angular momentum beams using a free-electron laser oscillator.

With wavelength tunability, free-electron lasers (FELs) are well-suited for generating orbital angular momentum (OAM) beams in a wide photon energy range. We report here the first experimental demonstration of OAM beam generation using an oscillator FEL with the tens of picosecond pulse duration. Lasing around 458 nm, we have produced the four lowest orders of superposed Laguerre-Gaussian beams using a very long FEL resonator of 53.

Transmission of megawatt relativistic electron beams through millimeter apertures.

High-power, relativistic electron beams from energy-recovering linacs have great potential to realize new experimental paradigms for pioneering innovation in fundamental and applied research. A major design consideration for this new generation of experimental capabilities is the understanding of the halo associated with these bright, intense beams. In this Letter, we report on measurements performed using the 100 MeV, 430 kW cw electron beam from the energy-recovering linac at the Jefferson Laboratory's Free Electron Laser facility as it traversed a set of small apertures in a 127 mm long aluminum block.

Time-dependent, three-dimensional simulation of free-electron-laser oscillators.

We describe a procedure for the simulation of free-electron-laser (FEL) oscillators. The simulation uses a combination of the MEDUSA simulation code for the FEL interaction and the OPC code to model the resonator. The simulations are compared with recent observations of the oscillator at the Thomas Jefferson National Accelerator Facility and are in substantial agreement with the experiment.

Selective photothermolysis of lipid-rich tissues: a free electron laser study.

Background And Objectives: In theory, infrared vibrational bands could be used for selective photothermolysis of lipid-rich tissues such as fat, sebaceous glands, or atherosclerotic plaques.

Study Design/materials And Methods: Absorption spectra of human fat were measured, identifying promising bands near 1,210 and 1,720 nm. Photothermal excitation of porcine fat and dermis were measured with a 3.

Second harmonic FEL oscillation.

We have produced and measured for the first time second harmonic oscillation in the infrared region by a free electron laser. Although such lasing is ideally forbidden, since the gain of a plane wave is zero on axis for an electron beam perfectly aligned with a wiggler, a transverse mode antisymmetry allows sufficient gain in this experiment for lasing to occur. We lased at pulse rates up to 74.

Sustained kilowatt lasing in a free-electron laser with same-cell energy recovery.

Jefferson Laboratory's kW-level infrared free-electron laser utilizes a superconducting accelerator that recovers about 75% of the electron-beam power. In achieving first lasing, the accelerator operated "straight ahead" to deliver 38-MeV, 1.1-mA cw current for lasing near 5 &mgr;m.

Cavity dumping for free electron lasers.

The cavity dumping technique, applied to free electron lasers (FEL), is described. Taking advantage of both numerical simulations and experimental results on the Mark III FEL, a fairly exhaustive analysis is reported. In particular, we show that the output peak power can be increased by a factor even higher than one hundred.

Mode characterization, autocorrelation measurements, and harmonic conversion with pico- and femtosecond pulses delivered by the Mark III free-electron laser.

After briefly reporting on the present status of the infrared free-electron laser now operating at the Stanford Photon Research Laboratory and powered by the linear accelerator Mark III, we discuss the results of using nonlinear optical techniques for both the characterization of its output radiation and the enhancment of its tunability range. In particular, to show the evidence of possible self-guiding effects, a new and reliable technique has been devised and successfully tested for real-time monitoring of the micropulse evolution during the buildup of radiation. Finally, we discuss the main problems connected with the damage threshold of optical materials.

Acoustooptical suppression of sideband instabilities in free electron lasers.

We describe an electronically tunable intracavity filter, based on the acoustooptic effect, that suppresses the sideband instabilities in a free electron laser. Different configurations are analyzed, and the problems encountered in the design and construction of a broadband acoustic transducer are discussed in some detail. In addition, some preliminary experimental results on the construction of broadband acoustic transducers are reported.

Tunable electrooptic intracavity filter for sideband suppression in free electron lasers.

We describe a tunable intracavity filter, which, taking advantage on the electrooptic effect, limits the growth of the sidebands in a free electron laser and even suppresses them in some cases.