The FEL field has grown enormously over the last years, which is reflected in the number of papers presented at the 1998 conference. A few specific areas in FEL are particularly active. Several groups are investigating self-amplified spontaneous emission (SASE) as a route to 0.1 nm FEL. Although the technical challenges are large, a growing portion of the community believes this is a feasible goal and have begun planning 4th generation light sources based on this technique. Already, demonstrations of SASE by many orders of magnitude in an unguided (by external means) optical mode have been achieved in the IR with extension into the UV soon to follow. Other groups are extending the applications of FELs by evolutionary changes in the capabilities of user facilities around the world. Many of these utilize other sources of radiation synchronously with tunable FEL beams. An emerging trend is th use of Thompson scattered photons from the electron beam. Because of the Doppler shift involved, the photons can be up-scattered into the X-ray (keV) or even gamma ray (MeV) regime forming a useful picosecond probe for analysis of materials or nuclear structure. Other groups continue to extend the range of FEL operation and a new record was set this year for short wavelength lasing (210nm) as well as production of the highest CW average power yet for a FEL (311 W). This exhaustive volume will provide the reader with an appreciation of the state of FEL technology and convey also the sense of excitement and interest that exists in the field. Despite the fact that it has been 22 years since the first demonstration of lasing in a FEL oscillator, the field continues to provide interesting areas for study and application.

A real-time spectrograph with a 1Hz update rate was designed and installed at the JLab FEL facility using a Cal Sensors PbSe array and a Roper Scientific SpectraPro 300 monochrometer. This paper describes the implementation of EPICS channel access on a remote PC running LabView with modification of vendor supplied LabView VI's to allow display of FEL light spectra in real-time on a remote workstation. This allows PC based diagnostics to be used in EPICS.

Several FELs have now demonstrated high power lasing and several projects are under construction to deliver higher power or shorter wavelengths. This presentation will summarize progress in upgrading FEL oscillators towards higher power and will discuss some of the challenges these projects face. The challenges fall into three categories: 1. energy recovery with large exhaust energy spread, 2. output coupling and maintaining mirror figure in the presence of high intracavity power loading, and 3. high current operation in an energy recovery linac (ERL). Progress in all three of these areas has been made in the last year. Energy recovery of over 12% of exhaust energy spread has been demonstrated and designs capable of accepting even larger energy spreads have been proposed. Cryogenic transmissive output couplers for narrow band operation and both hole and scraper output coupling have been developed. Investigation of short Rayleigh range operation has started as well. Energy recovery of over 20 mA CW has been demonstrated and several methods of mitigating transverse beam breakup instabilities were demonstrated. This talk will summarize these achievements and give a roadmap of where the field is headed.

A key technology issue of ERL devices for high-power free-electron laser (FEL) and 4th generation light sources is the demonstration of reliable, high-brightness, high-power injector operation. Ongoing programs that target up to 1 Ampere injector performance at emittance values consistent with the requirements of these applications are described. We consider that there are three possible approaches that could deliver the required performance. The first is a DC photocathode gun and superconducting RF (SRF) booster cryomodule. Such a 750 MHz device is being integrated and will be tested up to 100 mA at the Thomas Jefferson National Accelerator Facility beginning in 2007. The second approach is a high-current normal-conducting RF photoinjector. A 700 MHz gun will undergo thermal test in 2006 at the Los Alamos National Laboratory, which, if successful, when equipped with a suitable cathode, would be capable of 1 Ampere operation. The last option is an SRF gun. A half-cell 703 MHz SRF gun capable of delivering 1.0 Ampere will be tested to 0.5 Ampere at the Brookhaven National Laboratory in 2006. The fabrication status, schedule and projected performance for each of these state-of-the-art injector programs will be presented.

Jefferson Lab is in the process of upgrading the Free-Electron Laser Facility to provide higher output power as well as broader wavelength and timing flexibility. As part of the upgrade, a new optical cavity is being constructed. Using a near-concentric configuration, it will provide high average power (10kW) output using one of three sets of dielectrically coated mirrors. A fourth mirror set will provide broadband tuning throughout the mid-IR, but at a lower average power of 1kW. The new optical cavity offers unique features such as in vacuo active stabilization of the mirror orientation and deformable high-reflector mirrors. The status of the construction of the optical cavity and a review of its capabilities will be presented.

Short bunches of electrons in the Jefferson Lab FEL emit multiparticle coherent edge radiation as they enter the dipole prior to the outcoupler mirror. This light is more collimated than synchrotron light and furthermore is modified by interference from the last chicane magnet after the high reflector. This light provides an additional heat load on the outcoupler in a wavelength range it was not designed to handle. We have performed calculations of this effect using a new extension of the Synchrotron Radiation Workshop code which, importantly, takes into account both acceleration and velocity (or Coulomb) terms of the emitted electric field. We have also measured THz properties of some of the mirrors. We show how the addition of a decompression chicane mitigates these problems.

We have observed damage of gold resonator mirrors in the Mark III FEL with 1.2 microsecond macropulses at a fluence threshold of 21 J/cm2. This number agrees with YAG laser damage measurements scaled by the square root of the ratio of the pulse lengths. Silver coated mirrors have not shown damage up to an equivalent threshold of 40 J/cm2. Work aimed at increasing the pulse energy on the silver mirrors is continuing; we expect to extend these measurements in the near future.

This paper describes the phase noise measurement on several different mode-locked laser systems that have completely different gain media and configurations including a multi-kW free-electron laser. We will focus on the state of the art short pulse lasers, especially the drive lasers for photocathode injectors. A comparison between the phase noise of the drive laser pulses, electron bunches and FEL pulses will also be presented.

The design and construction of an optical transport that brings synchrotron radiation from electron bunches to a fast streak camera in a remote area has become a useful tool for online observation of bunch length and stability. This paper will report on the temporal measurements we have done, comparison with simulations, and the on-going work for another imaging optical transport system that will make possible the direct measurement of the longitudinal phase space by measuring the bunch length as a function of energy.