The APEX (APLE Prototype Experiment) FEL (free-electron laser) is an advanced technology test-bed for the Average Power Laser Experiment (APLE). APEX is a photoinjector-driven FEL that is currently operated as an oscillator with untapered wigglers. Photocathodes are rapidly becoming the source of choice for high-brightness electron beams to drive high-efficiency FELs. The electron accelerator is a 40-MeV L-band rf linac with a 6-MeV photoinjector. Since the commissioning of the FEL in 1991, we have been engaged in accelerator and laser experiments. We have demonstrated that the accelerator is capable of providing a high-brightness electron beam at high current. Initial lasing has been at wavelengths near 3 μm, and our electron-beam brightness is such that harmonic lasing at much shorter wavelengths is possible. We have recently lased on the third harmonic at 0.83 μm. In this paper, we report the results of the accelerator and FEL performance in the oscillator mode. The results show that a photoinjector can be integrated into an FEL system to produce stable and reliable operation.

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.

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.

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.

We report our initial measurements of bright (high-charge, low-emittance) electron beams generated at the Los Alamos high brightness accelerator FEL (HIBAF) facility. Normalized emittance values of less than 50π mm mrad for charges ranging from 0.7 to 8.7 nC were obtained for single micropulses at a y-waist and at an energy of 14.7 MeV. These measurements were part of the commissioning campaign on the HIBAF photoelectric injector. Macropulse measurements have also been performed and are compared with integrated numerical experiment (INEX) calculations.

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.

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.< >

The authors report some initial measurements of electron beam properties from the new photoinjector installed as the front end on the Los Alamos free-electron laser (FEL). The FEL is being rebuilt with the photoinjector, added acceleration to 40 MeV, new diagnostics, and a beam line designed to minimize emittance growth. The authors measured the spatial and temporal properties of the beam at energies of about 15 MeV as a function of several parameters and the results have been compared to simulations. The operational characteristics of the important elements of the system and the theoretical comparisons are described. >

Improving the performance of the Los Alamos free-electron laser (FEL) in 1988 involved the identification and reduction of wake-field effects generated in the wiggler region. The wake-field effect was dramatically reduced by inserting a smooth metal tube into the wiggler gap, and the FEL performance was concomitantly improved.

The Los Alamos free-electron laser has recently lased near 4 μm on the third harmonic of the fundamental frequency of about 12 μm. By a choice of intercavity apertures and cavity length, lasing can be forced to occur on both frequencies simultaneously or on either one alone.

Characterization of the electron beam's properties will be a major task after the upgrade of the Los Alamos Free Electron Laser (FEL) Facility with a photoelectric injector (PEI) and increased acceleration capability to 40 MeV. Adjustments to the previous diagnostics package that address the lower beam emittance, higher energy and wake-field source reduction issues are discussed.

In recent experiments at Los Alamos, we directly observed for the first time free-electron-laser (FEL) fundamental wavelengths from 20 to 45 μm. Our 1988 facility's demonstrated wavelength span now extends from 9 to 45 μm. Upgrades are in progress to increase this span. This wavelength region uniquely complements existing FEL applications facilities.

Fluctuations in the output power and wavelength have been observed in two high-power, rf-driven free-electron lasers (FELs): (1) the 10 μm FEL that has operted at the Los Alamos National Laboratory and (2) the visible FEL at the Boeing Physical Sciences Research Center. The fluctuations have been traced primarily to instabilities in the electron beam. Specifically, these are variations in the electron energy, the charge per micropulse and the time interval between micropulses. The effects of these instabilities on the performance of one of the FELs is demonstrated. Efforts made to minimize these instabilities are discussed and the subsequent improvements in the operation of each of the FELs are presented.

In recent experiments at Los Alamos, we directly observed for the first time free-electron-laser (FEL) fundamental wavelengths from 20 to 45 μm. Our 1988 facility's demonstrated wavelength span now extends from 9 to 45 μm. Upgrades are in progress to increase this span. This wavelength region uniquely complements existing FEL applications facilities.

In recent experiments at Los Alamos, we directly observed for the first time free-electron laser (FEL) fundamental wavelengths from 20 to 45{mu}m. Our 1988 facility's demonstrated wavelength span now extends from 9 to 45{mu}m. Upgrades are in progress to increase this span. This wavelength region uniquely complements existing FEL applications facilities. 5 refs., 6 figs., 1 tab.