James W. Early

Demonstration of ultraviolet lasing with a low energy electron beam

Abstract We report on the design details of the first ultraviolet (UV) free-electron laser (FEL) oscillator driven by low-energy electrons from a radio-frequency linear accelerator. In our experiment we used a high-current, high brightness electron beam in combination with a wiggler of novel design to produce an FEL that lased at wavelengths from 369 to 380 nm using 45.9–45.2 MeV electrons. In addition we performed a proof-of-principle experiment that demonstrated the first ever photolithography on a photoresist-coated silicon wafer using an FEL light source.

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

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.

Performance of the Los Alamos HIBAF accelerator at 17 MeV

Abstract The Los Alamos free electron laser (FEL) is being rebuilt with a photoelectric injector and 40 MeV beam energy for a lower emittance, brighter beam. Tests of the Los Alamos high-brightness accelerator FEL (HIBAF) system have been conducted including the photoinjector and first 17 MeV of acceleration. The photoinjector is designed to operate with a micropulse charge of 5 nC, peak current of 300 A. energy spread of 0.3%, and emittance of 50π mm mrad. Measurements of temporal and spatial beam characteristics have been made up to 10 nC per micropulse for both single micropulses and macropulses. The operational characteristics of the system components, e.g., drive laser and photoinjector are described. The results of beam and rf measurements are briefly presented and compared to simulation. The effects of nonaxially symmetric rf fields in the on axis coupled accelerator structure were observed and are discussed.

Performance of the photoinjector accelerator for the Los Alamos free-electron laser

The Los Alamos free-electron laser (FEL) facility has been modified by the replacement of the thermionic electron gun and bunchers with a 1300-MHz RF photoinjector. Two more accelerator tanks have been added to increase the beam energy to 40 MeV. Preliminary studies at 15 MeV have demonstrated excellent beam quality with a normalized emittance of 40 pi mm-mrad. The beam quality is sufficient to allow harmonic lasing in the visible. FEL experiments have been begun at a wavelength near 3 mu m. A report is presented of the performance of the photoinjector accelerator.<<ETX>>

First dual-sweep streak camera measurements of a photoelectric injector drive laser

Abstract We have performed the first dual-sweep streak camera measurements of a photoelectric injector (PEI) drive laser in regard to micropulse duration, phase jitter, and phase slew. As the drive laser features are directly coupled to the eventual electron-beam properties, the characterization of these features is critical to optimizing free-electron laser (FEL) performance. The features have been investigated on both the intermacropulse and intramacropulse regimes at the Los Alamos FEL facility. In this initial phase we measured the doubled frequency component from the Nd:YLF-based laser system using a Hamamatsu C1587 universal streak camera with a synchroscan plug-in and the dual-sweep upgrade unit. We demonstrated that the macropulse-to-macropulse jitter was about 8 ps (rms) without laser phase stabilization and less than or equal to 2 ps (rms) with laser optimization and phase stabilization. Additionally, for the 100 μs long macropulse the phase slew within the macropulse was reduced with phase feedback from about 5 ps to near the resolution limit ( ps ).

HIGH ENERGY DIODE SIDE-PUMPED Cr:LiSAF LASER

A diode side-pumped Cr:LiSAF laser has been demonstrated with a 30 mJ normal mode output energy, and an optical to optical eficiency of 17%. Improved optical quality laser material has been grown with several Cr concentrations. Optimum Cr concentration has been calculated and experimentally confirmed.

Dual-rod Cr: LiSAF oscillator/amplifier for remote sensing applications

A dual rod configuration is used to achieve 16W average power operation from a flashlamp-pumped Cr:LiSAF laser oscillator. A double-pass dual-rod amplifier configuration was used to amplify 141{mu}J pulses from a Q-switched diode-pumped LiSAF oscillator by a factor of {approximately}120. This experiment established a small signal gain of 13.4% per cm at 820 nm. Improved slope efficiency (7.4% electrical-to-light) and pulse repetition frequency (40Hz) were achieved with a single-rod oscillator using improved Cr:LiSAF material.

Lasing attempt with a microwiggler on the Los Alamos FEL

Abstract The APEX FEL normally lases near a wavelength of 3 μm using a permanent magnet wiggler with a 2.7-cm period and a linear accelerator of 40-MeV energy. Los Alamos National Laboratory is conducting a series of experiments with the goal of lasing at significantly shorter wavelengths with the same accelerator and the same kind of near-concentric resonator, but using a novel pulsed microwiggler of 0.5-cm period capable of generating a peak field of several tesla. We plan to lase on a fundamental wavelength of ∼ 0.8 μm and on the third harmonic at 0.25 μm.

The Los Alamos FEL photoinjector drive laser

Abstract The drive-laser system of the photoelectric injector for the Los Alamos free-electron laser (FEL) is described. The bright electron beams required for high-performance FELs demand stringent specifications on the drive-laser output levels, beam quality, and stability. The laser system generates 7–15 ps (FWHM) Gaussian pulses of 527 nm light at a repetition rate of 21.67 MHz. These “micropulses” are contained within a “macropulse” envelope less than 200 μs long, which is emitted from the drive laser at a rate of 1 Hz. Micropulse energies as large as 12 μJ are obtained. The design specification, laser architecture, and operating performance following the most recent round of upgrades are presented.

Performance of the APEX 40‐MeV photoinjector‐driven linear accelerator

Since the mid‐1980s, Scientists at Los Alamos National Laboratory have been developing photocathode rf guns for high‐brightness electron‐beam applications, such as free‐electron lasers (FELs). The technology has matured to the point where we now have a routinely operating 40‐MeV linac and FEL that uses a a photocathode as its electron source. In this paper, we describe the APEX accelerator’s performance, with an emphasis on the photocathode’s unique features.