Mark S. Curtin

First demonstration of a free-electron laser driven by electrons from a laser-irradiated photocathode

We report the results from the first operation of a free electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne/Stanford FEL achieved sustained oscillations, lasting in excess of three hours, driven by photoelectrons accelerated by the Stanford Mark III radiofrequency linac. A LaB6 cathode, irradiated by a tripled Nd: Yag mode-locked drive laser was the source of photoelectrons. The drive laser, operating at 95.2 MHz, was phase-locked to the 30th subharmonic of the S-band linac. Peak currents in excess of 125 A were observed and delivered to the Rocketdyne 2 m undulator which was operated as a stand-alone oscillator. Sustainable small-signal gain of 100% per pass was observed over a 2 h time period with periodic observation of small-signal gain as high as 150% per pass. Preliminary estimates of the electron-beam brightness deliverable to the undulator range from 3.5 × 1011 to 5.0 × 1011 A/(rad m)2.

A high quality permanent-magnet wiggler for the Rocketdyne/Stanford infrared free electron laser

Abstract A high quality, variable gap, variable taper, permanent-magnet wiggler has been built for infrared free electron laser (FEL) experiments to be performed at the Stanford Photon Research Laboratory. The design and characterization procedure used to assemble the wiggler is discussed. A simulated annealing code was used to minimize field errors arising from variations in the individual magnets. The computed electron trajectories associated with the measured magnetic fields are presented for a range of different operating points of the wiggler. These plots indicate a very high quality field over a large range of different wiggler operating regimes. Resultant trajectory wander over the 2 m long wiggler for a 40 MeV electron at a wiggler gap corresponding to 3.3 kG was calculated to be less than 25 μm. The ability to control trajectory wander and optical phase slip using the simulated annealing code suggests future extensions to extremely long wigglers.

First operation of the Rocketdyne/Stanford free electron laser

Abstract A near infrared free electron laser (FEL) has been built and installed by Rocketdyne in the Stanford Photon Research Laboratory. The Rocketdyne/Stanford FEL utilizes a very high quality, 2 m long, permanent magnet planar wiggler whose gap may be continuously tuned, and magnetic field axially tapered by varying the gap at one end relative to the other. The laser is operated with an e-beam supplied by the Stanford Mark-III accelerator. A stable resonator with a broadband, dielectric coated element permits transmissive outcoupling over the 2.7–3.7 μm wavelength range. Results from initial operation of this laser are presented.

Initial results of operating the rocketdyne undulator in a tapered configuration

Abstract The near-infrared Rocketdyne/Stanford free electron laser (FEL) uses a very-high-quality precision undulator whose field strength and field taper are adjustable. The Rocketdyne undulator has been operated in both an amplifier configuration, as in the master-oscillator power amplifier (MOPA) experiments, and an oscillator configuration, as in the photocathode and tapered-undulator experiments. The tapered-undulator experiment was performed at the Stanford Photon Research Laboratory (SPRL) using an electron beam supplied by the Mark III rf-linac. During the experiment we observed sustained oscillations as the undulator magnetic-field taper was continuously tuned from 0% to 10%. We observed ∼1.2% extraction efficiency for a magnetic-field taper of 9.6%. During the same experiment we observed sustained oscillations as the undulator gap was continuously varied over 120 mil. Details of the experiment are presented.

Design of a large-useful-bore permanent-magnet helical wiggler

Abstract A permanent-magnet helical wiggler is being developed at KMS Fusion, Inc., for a two-stage FEL experiment. The theoretical analysis of an analytical model describing a Halbach helical wiggler design is presented. The results of this analysis suggest high field quality can be achieved out to approximately 1 cm radius for moderate segmentation of the magnetization distribution.

A demonstration of loss modulation and cavity dumping in a free-electron-laser oscillator

Abstract The performance of an intraactivity cadmium telluride electro-optic cell in a free-electron laser will be described. The cell, installed in the Stanford Mark III IRFEL, was used to either modulate the optical-cavity losses or to dump the stored optical-cavity energy or both. The results of the experiments will be presented.

Initial results from the free-electron-laser master oscillator/power amplifier experiment

Abstract We describe the first master oscillator/power amplifier experiment in which both the master oscillator and power amplifier are free-electron-laser devices driven by time-sharing an electron beam from a single radiofrequency linear accelerator. The optimized, small-signal gain spectrum realized in the untapered power amplifier is presented. Up to 60% gain was observed at 3 μ with an estimated peak current of 35 A. Additional Q -switched experiments are also discussed.

First Demonstration Of A Free-electron Laser Driven By Electrons From A Laser-Irradiated Photocathode

We report the results from the first operation of a free electron laser (FEL) driven by an electron beam from a laser-irradiated photocathode. The Rocketdyne/Stanford FEL achieved sustained oscillations, lasting in excess of three hours, driven by photoelectrons accelerated by the Stanford Mark III radiofrequency linac. A LaB/sub 6/ cathode, irradiated by a tripled Nd: Yag mode-locked drive laser was the source of photoelectrons. The drive laser, operating at 95.2 MHz, was phase-locked to the 30th subharmonic of the S-band linac. Peak currents in excess of 125 A were observed and delivered to the Rocketdyne 2 m undulator which was operated as a stand-alone oscillator. Sustainable small-signal gain of 100% per pass was observed over a 2 h time period with periodic observation of small-signal gain as high as 150% per pass. Preliminary estimates of the electron-beam brightness deliverable to the undulator range from 3.5 X 10/sup 11/ to 5.0 X 10/sup 11/ A/(rad M)/sup 2/ .

Simulations of the Rocketdyne free-electron laser with a 4 m wiggler

Abstract Rocketdyne is assembling a high-brightness 78 MeV FEL. After full development the laser will be capable of an average output of greater than 1 kW. Performance calculations using the Rocketdyne FELOPT code are presented for a 1.06 μm system.

Key issues in the design of a two-stage FEL

Abstract A number of key issues for the design of a two-stage FEL with a cylindrically symmetric quasioptical cavity are investigated. Designs for long- and short-wavelength cavities are presented. Techniques for designing the wiggler injection optics and determining the effect of finite beam size on laser gain and bandwidth are described. An electrostatic accelerator conceptual design that could permit continuous operation of the two-stage system is also presented.