T.I. Smith

Development of the SCA/FEL for use in biomedical and materials science experiments

Abstract The Stanford SCA/FEL system is being modified to be used as a versatile source of photons for a wide range of biomedical and materials science experiments. Characteristics of the FEL beams to be provided are presented, as well as results of recent experiments on energy recovery. A new high brightness injector will be developed and tested, and the possibility of UV operation of an FEL has been assessed, assuming either fundamental or third harmonic output.

Imaging single living cells with a scanning near-field infrared microscope based on a free electron laser

We report the first sub-wavelength mid-infrared images under water, and describe an application to obtaining images of single living cells in water using the Stanford Free Electron Laser (FEL). Spatial resolution is enhanced at the peak of infrared absorption of water. Images were obtained of single motile fibroblasts with the FEL wavelength tuned to absorption peaks of both protein and lipid molecules. Analysis of the unexpectedly strong absorption due to lipid molecules in motile fibroblasts suggests that the concentration of lipid molecules in lamellopodia is consistent with membrane flow. ” 1998 Elsevier Science B.V. All rights reserved.

Coherent spontaneous radiation from highly bunched electron beams

Abstract Coherent spontaneous undulator radiation has now been observed in several FELs, and is a subject of special importance to the design of self-amplified spontaneous emission (SASE) devices. We report observations of coherent spontaneous radiation at the Stanford Picosecond FEL Center at wavelengths as short as 5 microns. Enhancement of spontaneous radiation over predicted incoherent levels by as much as a factor of 6 × 10 4 has been observed at longer wavelengths when the electron bunches are compressed after off-peak acceleration. We discuss the possible structure responsible for these enhancements and present direct measurements of the electron distributions using transition radiation techniques.

The TRW/Stanford tapered wiggler oscillator

Abstract We report the operation of the first tapered wiggler free electron laser oscillator. The laser operated at 1.6 μm output with a peak power of 1.3 MW. With the wiggler taper adjusted to 0, 1 and 2%, extraction efficiencies of 0.4, 1.1 and 1.2%, respectively, were obtained.

First lasing, capabilities, and flexibility of FIREFLY

Abstract FIREFLY is a free electron laser (FEL) designed to produce picosecond pulses of intense light between 10 and 100 μm. It uses an inexpensive electromagnetic wiggler and variable outcoupling to provide maximum flexibility for user experiments. FIREFLY first lased on November 23, 1994, and has now operated successfully from 15 to 65 μm. It has lased in both a traditional undulator configuration and as an optical klystron, and has also operated in the undulator configuration on the third harmonic. During initial tests FIREFLY reached theoretical extraction efficiency for fundamental, third harmonic, and optical klystron operation, and demonstrated wavelength switching between adjacent peaks in the gain spectrum of an optical klystron for the first time.

Facilities for using the FEL as a research tool

Abstract In this decade the FEL will be used as a tool for serious scientific research. Facilities which will exploit the unique capabilities of FELs are beginning to appear. Among the many issues which these facilities must address regarding the optical beam delivered to users are: stability (position, power, wavelength), quality (transverse mode, spectral purity), flexibility of micropulse and macropulse structure, ease of user control of operating parameters, and complementary experimental facilities. These issues will be explored in the context of some operating and some planned FEL facilities.

Status of the SCA-FEL☆

Abstract The SCA-FEL can now provide FEL beams to users in a wavelength range extending from longer than 3.5 to shorter than 0.5 μm. Harmonic generation can extend the short-wavelength range. As an example of the operational characteristics, during a 3 week run in May–June 1989, the SCA-FEL provide 18 days of FEL beam at 16–18 hours/day. The FEL operated at 3.5 μm, and in a 20% band centered at 1.54 μm. 30 W of optical power was extracted in 3 ms macropulses with a 0.08% line width and a 3 ps micropulse.

Cavity beam position monitor system for the Accelerator Test Facility 2

The Accelerator Test Facility 2 (ATF2) is a scaled demonstrator system for final focus beam lines of linear high energy colliders. This paper describes the high resolution cavity beam position monitor (BPM) system, which is a part of the ATF2 diagnostics. Two types of cavity BPMs are used, C-band operating at 6.423 GHz, and S-band at 2.888 GHz with an increased beam aperture. The cavities, electronics, and digital processing are described. The resolution of the C-band system with attenuators was determined to be approximately 250 nm and 1 � m for the S-band system. Without attenuation the best recorded C-band cavity resolution was 27 nm.

Very High Resolution Optical Transition Radiation Beam Profile Monitor

We have constructed and tested a 2 um resolution beam profile monitor based on optical transition radiation (OTR). Theoretical studies of OTR [1] show that extremely high resolution, of the order of the wavelength of the light detected, is possible. Such high‐resolution single pulse profile monitors will be very useful for future free electron laser and linear collider projects. Using the very low emittance 1.3 GeV electron beam at the KEK Accelerator Test Facility (ATF) [2] (1.4nm ex × 15pm ey), we have imaged transition radiation from 5 micron σ beam spots. Our test device consisted of a finely polished target, a thin fused silica window, a 35 mm working distance microscope objective (5x and 10x) and a triggered CCD camera. A wire scanner located near the target is used to verify the profile monitor performance. In this paper we report results of beam tests.

FEL center user diagnostics and control

Abstract In the past year, the Stanford Picosecond FEL Center has produced more than two thousand hours of beam time dedicated to user experiments. To assure reliable beam delivery and to maximize productivity of our users we have developed a sophisticated system of diagnostics and control. An integrated display is now available in all experimental areas which provides continuously updated measurements of beam spectrum, micropulse duration, power, position, and pointing — all of which may be saved to document beam conditions during an experiment. The beam is actively wavelength and amplitude stabilized to better than 0.01% and 2%, respectively. Direct wavelength control is available to users in every experimental area, allowing changes of wavelength as large as a few percent. Larger wavelength shifts, and adjustments in macropulse or micropulse width or timing, are readily available with operator assistance.