We report on the design study of a free-electron-laser experiment designed to produce coherent radiation at the wavelength of 1.5 angstrom and longer. The proposed experiment utilizes 1/3 of the SLAC linac to accelerate electrons to 15 GeV. The high brightness electron beam interacts with the magnetic field of a long undulator and generates coherent radiation by self-amplified spontaneous emission (SASE). The projected output peak power is about 10 GW. The project presents several challenges in the realization of a high brightness electron beam, in the construction and tolerances of the undulator and in the transport of the x-ray radiation. The technical solutions adopted for the design are discussed. Numerical simulations are used to show the performance as a function of system parameters.

The NSLS has a long-standing interest in providing the best possible synchrotron radiation sources for its user community, and hence, has recently established the Source Development Laboratory (SDL) to pursue research into fourth generation synchrotron radiation sources. A major element of the program includes development of a high peak power FEL meant to operate in the vacuum ultraviolet. The objective of the program is to develop the source, and experimental technology together to provide the greatest impact on UV science. The accelerator under construction for the SDL consists of a high brightness rf photocathode electron gun followed by a 230 MeV short pulse linac incorporating a magnetic chicane for pulse compression. The gun drive laser is a wide bandwidth Ti:sapphire regenerative amplifier capable of pulse shaping which will be used to study non-linear emittance compensation. Using the compressor, 1 nC bunches with a length as small as 50 micrometer sigma (2 kA peak current) are available for experiments. In this paper we briefly describe the facility and detail our plans for utilizing the 10 m long NISUS wiggler to carry out single pass FEL experiments. These include a 1 micrometer SASE demonstration, a seeded beam demonstration at 300 nm, and a high gain harmonic generation experiment at 200 nm. The application of chirped pulse amplification to this type of FEL also is discussed.

The injector system of the advanced photon source (APS) consists of a linac capable of producing 450-MeV positrons or greater than 650-MeV electrons, a positron accumulator ring (PAR), and a booster synchrotron designed to accelerate particles to 7 GeV. There are long periods of time when these machines are not required for filling the main storage ring and instead can be used for synchrotron radiation research. We describe here an extension of the linac beam transport called the low-energy undulator test line (LEUTL). The LEUTL will have a twofold purpose. The first is to fully characterize innovative, future generation undulators, some of which may prove difficult or impossible to measure by traditional techniques. Perhaps the most intriguing and exciting use of the LEUTL, however, will be in the planned investigation and generation of coherent radiation at wavelengths below 100 nm. This is due to the use of the high quality electron beam generated from a thermionic microwave gun.

This paper describes the design, construction, and initial operation of an infrared FEL designed for 1 kW average power. The experiment utilizes the existing advanced free-electron laser (AFEL) accelerator. An expected 6% extraction efficiency of electron beam power to optical power gives an overall wall- plug efficiency of approximately 1%. The 10 to 20 MeV electron accelerator is 1.2 m long. This regenerative amplifier FEL (RAFEL) relies on a few (less than ten) passes to reach saturation. The technique is similar to a FEL oscillator through the use of optical feedback to reach saturation. However, in this design the feedback is limited to less than 1% in the large signal regime. The chief advantage to this approach is that no mirror is exposed to a high peak intensity, enabling high-average power in a compact optical configuration. To compensate for the low optical feedback, the single-pass gain must be very high. In our design, the single- pass gain is 10⁵ in the small signal regime. RAFEL is presently configured to operate at a wavelength near 16 microns. However, this system is scaleable to shorter wavelengths by increasing beam energy. Present results indicate that a single pass gain of 60 in the infrared has been observed.

We consider linac-driven SASE (stimulated amplification of spontaneous emission) using the Duke linac and the PALADIN wiggler. SASE design studies using this equipment are described based on the non-wiggler-averaged FEL simulation code MEDUSA. We have identified a new collective Compton regime in which ac space-charge is unimportant but the dc self-fields of the beam are important.

X rays can be produced from FELs by either inverse Compton scattering or by self-amplified spontaneous emission (SASE). Very high brightness peak power is extremely important for a number of users with various requirements for energy spread, positional stability and so on.

At ultrahigh intensities, where the normalized vector potential of the laser wave exceeds unity, the electron axial velocity modulation due to radiation pressure yields nonlinear Compton backscattered spectra. For applications requiring a narrow Doppler upshifted linewidth, such as the gamma-gamma collider or focused x-ray generation, this can pose a serious problem. It is shown that temporal laser pulse shaping using spectral filtering at the Fourier plane of a chirped pulse laser amplifier can alleviate this problem, and that this technique can be scaled to the required multi-TW range. Compton backscattered spectra are derived in three cases: hyperbolic secant, hybrid pulses (hyperbolic secant trnasient and flat-top), and square optical pulses similar to those experimentally obtained by Weiner et al. It is found that the optimum laser pulse shapes correspond to square pulses, yielding a high contrast ratio between the main spectral line and the transient lines. The corresponding spectral filter function is also determined, and its practical implementation in a chirped pulse laser amplifier is addressed.

The design of the magnetic system for the high gain soft x-ray free electron laser is described.

Designs are being developed to produce diffraction-limited sources based on storage-ring free-electron lasers (FELs) for the VUV and soft x-ray regime and linac-driven FELs in the few angstrom regime. The requirements on the beam quality in transverse emittance (rms, normalized) of 1 - 2 pi mm mrad, bunch length (1 ps to 100 fs), and peak current (1 to 5 kA) result in new demands on the diagnostics. The diagnostics challenges include spatial resolution (1 - 10 micrometer), temporal resolution (less than 100 fs), and single-pulse position measurements (approximately 1 micrometer). Examples of recent submicropulse (slice) work are cited as well as concepts based on spontaneous emission radiation (SER). The nonintercepting aspects of some of these diagnostics should also be applicable to high-power FELs.

The BNL/SLAC/UCLA symmetrized 1.6 cell S-band emittance- compensated photoinjector has been installed at the Brookhaven Accelerator Test Facility (ATF). The commissioning results and performance of the photocathode injector are presented. This photoinjector consists of the symmetrized BNL/SLAC/UCLA 1.6 cell S-band photocathode radio frequency gun and a single solenoidal magnet for transverse emittance compensation. The highest acceleration field achieved on the cathode is 150 MV/m, and the normal operating field is 125 MV/m. The quantum efficiency of the copper cathode was measured to be 4.5 multiplied by 10^-5. The measured quantum efficiency of the magnesium cathode is a factor of ten greater than that of copper after using both laser and laser assisted explosive electron emission cleaning. The transverse emittance and bunch length of the photoelectron beam were measured. The optimized rms normalized emittance for a charge of 329 plus or minus 12 pC is 2.0 plus or minus 0.3 pi mm-mrad. The bunch length dependency of photoelectron beam on the rf gun phase and acceleration fields were experimentally investigated. Electric and magnetic field asymmetries studies are presented.

A high brightness electron injector is a necessary component for x-ray FELs. A dedicated rf gun test facility is being developed at SLAC to measure the phase space distribution from a photocathode rf gun generated electron beam. This Gun Test Facility will allow optimization of the beam brightness by independently adjusting parameters such as accelerating field, laser pulse shape and total charge. The test facility is comprised of a single S-band klystron, 3 m SLAC linac section, analyzing magnet, diagnostic section, a cathode drive laser and the gun under test. The laser is comprised of a Nd:YLF oscillator and a Nd:glass regenerative amplifier. The light incident on the cathode is capable of both normal and near grazing incidence and is currently frequency quadrupled into the UV. In the near future a Nd:glass oscillator will be installed which will be capable of generating pulses as short as 200 fs. This oscillator will be used to make emittance measurements as a function of the laser pulse width and shape. Both oscillators will be phase-locked to the 24th sub-harmonic of the linac frequency. Emittance measurements will be made downstream of the linac at an electron beam energy of approximately 30 - 50 MeV using a quad scan with a beam profile screen and/or a wire scanner to measure the spot size. A current transformer and a Faraday cup will be used to measure the charge while a streak camera or a transition radiator can be used to measure the micropulse width. The first gun to undergo testing will be the BNL/SLAC/UCLA 1.6 cell symmetrized cavity gun with a copper cathode. With field gradients in the gun as high as 150 MV/m, using solenoidal emittance compensation and spatial and temporal flat top laser pulses, PARMELA simulations predict normalized emittances of less than 1.5 pi mm-mrad with 10 ps long pulses and 1 nC of charge after acceleration in a 3 meter linac section to about 30 MeV. Appropriate additional acceleration can further reduce the emittance below 1 pi mm-mrad.

This paper investigates various properties of the 'microspikes' associated with self-amplified spontaneous emission (SASE) in a short wavelength free-electron laser (FEL). Using results from the 2-D numerical simulation code GINGER, we confirm theoretical predictions such as the convective group velocity in the exponential gain regime. In the saturated gain regime beyond the initial saturation, we find that the average radiation power continues to grow with an approximately linearly dependence upon undulator length. Moreover, the spectrum significantly broadens and shifts in wavelength to the redward direction, with P(omega) approaching a constant, asymptotic value. This is in marked contrast to the exponential gain regime where the spectrum steadily narrows, P(omega) grows, and the central wavelength remains constant with z. Via use of a spectrogram diagnostic S(omega, t), it appears that the radiation pattern in the saturated gain regime is composed of an ensemble of distinct 'sinews' whose widths (Delta) (lambda) remain approximately constant but whose central wavelengths can 'chirp' by varying a small extent with t.

Two distinct types of free-electron laser simulations are in general use. In 'wiggler-averaged' simulation codes such as FRED and TDA, the Lorentz force equations are averaged over a wiggler period. A reduced orbit analysis is obtained requiring integration only of equations for the energy and ponderomotive phase for each electron. In contrast, 'non-wiggler-averaged' codes such as MEDUSA use the complete three-dimensional Lorentz force equations. A direct comparison of the two techniques is discussed in this paper using the MEDUSA and TDA codes.

In recent years, substantial design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long (30 m - 100 m) undulators. Within the context of the technologies considered, the attainment of such parameters involves the development of large, complex, and highly costly technical systems, and the preliminary or concomitant execution of complex demonstration experiments to study self-amplified spontaneous emission (SASE), or other gain mechanisms, on lower-energy linacs at longer wavelengths. In all phases of the FEL gain processes undertaken by such studies, the strength of the FEL radiation field in the electron bunch rest frame is typically no more than a fraction of a percent of the transformed undulator field. In contrast, recently developed terawatt lasers in the IR/visible/UV regimes could be made to match or exceed a transformed undulator's field strength in an electron bunch of suitable energy, enabling high-level control of the FEL gain process, and thereby of the spectral and temporal parameters of the FEL output. Due to the highly non-linear nature of the radiation/electron bunch interaction, control and generation of high-power FEL radiation with such lasers could, in principle, be extended well into the soft x-ray regime. In this presentation we discuss selected schemes for attaining high-power x ray FEL output in radiation pulses of conventional or ultra-short duration, and examine ways in which lower-cost, equivalent studies of SASE gain at lower energies could be achieved. Selected applications to particle beam diagnostics are also examined.

The nonlinear simulation of x ray free-electron lasers is dealt with using the non-wiggler-averaged MEDUSA simulation code and realistic wiggler model built up from the contributions of permanent magnets in a Halbach configuration in conjunction with a model for a FODO lattice for enhanced focusing. The specific parameters of interest are relevant to the linac coherent light source design at SLAC and deals with a 15 GeV/5 kA electron beam, and a wiggler with a 3.0 cm period and an on-axis amplitude of approximately 12.7 kG which results in x ray emission at wavelengths in the vicinity of 1.3 angstrom.

A new design for a single pass X-ray SASE FEL is proposed. The scheme consists of two undulators and an X-ray monochromator located between them. The first stage of the FEL amplifier operates in the SASE linear regime. After the exit of the first undulator, the electron bunch is guided through a non-isochronous bypass and the X-ray beam enters the monchromator. The mail function of the bypass is to suppress the modulation of the electron beam induced in the first undulator. This is possible because of the finite value of the natural energy spread in the bem. At the entrance to the second undulator, the radiation power from the monochromator dominates significantly over the shot noise and the residual electron bunching. As a result, the second stage of the FEL amplifier operates in the steady-state regime. The proposed scheme is illustrated for the example of the 6nm option SASE FEL at the TESLA TEst Facility under construction at DESY. The spectral bandwidth of such a two-stage SASE FEL (Δλ/λ≈ 5 x 10^-5) is close to the limit defined by the finite duration of the radiation pulse. The average spectral brilliance is equal to 7 x 10²⁴ photons/(secxmrad2 x mm2 x 0.1 % bandw.) which is by two orders of magnitude higher than the value which could be reached by the conventional SASE FEL.

This paper reports progress on the commissioning of the photocathode injector and the construction of the one kilowatt visible free electron laser (FEL) at Boeing. This FEL is being built using the equipment and experience acquired during previous Boeing FEL experiments. The injector consists of a 2 MV rf photocathode gun followed by four accelerator sections, all operating at 433 MHz. An additional 1300 MHz section is used to linearize the longitudinal phase space before compressing the electron pulse in a three-dipole chicane. The commissioning of this 18 MeV injector system is finished, and the injector performance results are described. Currently in progress is the construction of the remaining FEL system which includes the installation of six additional 1300 MHz accelerator sections and rf power to boost the beam energy to 100 MeV, installation of the electron beam transport to the wiggler, the instrumentation of the five meter wiggler and the implementation of the concentric resonator cavity. The status of the one kilowatt FEL will be reviewed. Also, the experimental data obtained during the past year's injector tests are summarized and their relevance to the one kilowatt FEL are discussed.

The Thomas Jefferson National Accelerator Facility (formerly known as CEBAF) has embarked on the construction of a 1 kW free-electron laser operating initially at 5 microns that is designed for laser-material interaction experiments and to explore the feasibility of scaling the system in power for Navy defense and industrial applications. The accelerator system for this IR demo includes a 10 MeV photocathode-based injector, a 32 MeV CEBAF-style superconducting radio-frequency linac, and single-pass transport that accelerates the beam from injector to wiggler, followed by energy-recovery deceleration to a dump. The initial optical configuration is a conventional near-concentric resonator with transmissive outcoupling. Following commissioning, the laser output will be extended to an operating range of 3-to-6.6 microns, and distributed to six labs in a user facility built with funds from the Commonwealth of Virginia. A description of the machine and facility and the project status are presented.

An efficient MW-class free electron laser (FEL) directed energy weapon (DEW) system holds promise for satisfying shipboard self-defense (SSD) requirements on future generations of Navy vessels because of the potential for high- power operation and the accessibility to all IR wavelengths. In order to meet shipboard packaging and prime power constraints, the power efficiency and high real-estate gradient achievable in a FEL driven by a superconducting rf accelerator is attractive. Configuration options and the key development issues for such a system are described.

A free electron laser with high average power is under construction in the Siberian Scientific Center. The purpose of this project is to provide the Siberian Center of Photochemical Research with a user facility. The project status and features are described in this paper.

First steps are now being taken to install a prototype laser power-beaming facility in the mountains near China Lake, California. A matching grant has been received from the State of California to establish the infrastructure necessary to fund the construction of a prototype laser power-beaming facility by private capital. The U.S. Navy and several major national laboratories have joined with the city of Ridgecrest, California and its citizens to contribute matching in-kind funding and to participate in the preparations needed for construction of such a facility. An environmental study is required before site approval can be obtained from the Navy at the highest levels. That process has begun and the requirements needed to create this new type of space utility industry in California are being addressed.

Free-electron-laser electron beam requirements generated by the need for coherent, short pulse radiation at x-ray wavelengths and those generated by the need for high average power, good wavefront quality at infrared wavelengths are compared. Various approaches and the accelerator technologies employed to achieve the required electron beam current, quality and pulse format are discussed and compared for a range of proposed FEL applications. The commonality and synergism between the electron beam generation and measurement technologies required for the two different FEL operating regimes are described.

Free-electron lasers (FELs) capable of operating in vibrational infrared (IR) (3 - 30 micrometer) regime have been developed at a small number of fixed sites around the world. However, there is a need for portable systems capable of operating in the 3 - 5 and 8 - 13 micrometer atmospheric windows for remote sensing applications. Wider use of FELs is inhibited by system size, cost, and the shielding requirements associated with the production of high current 15 - 45 MeV electron beams which are currently needed to lase in the infrared. The concept of an electromagnetic wiggler, in which the magnetostatic wiggler system of fixed transverse magnets is replaced by an intense counter-streaming microwave or optical radiation beam, has been of interest from the early work on FELs as a means of reducing the required electron beam energy. Although there has been little experimental progress to date due to the lack of high power wiggle radiation sources, the recent development of high power millimeter-wave gyrotrons has led to a re-evaluation of the feasibility of electromagnetic wigglers. We have published earlier studies of the possibility of IR FELs using low energy beams (3 - 5 MeV) using a gyrotron-powered millimeter-wave wiggler. Both waveguide cavity and open-mirror resonator (quasioptical) gyrotron (QOG) powered wigglers were considered. In this talk we present a new wiggler design, in which the millimeter-wave power generated by the QOG is coupled into a corrugated waveguide and compressed. This has the possibility of substantially increasing the single-pass FEL gain over previously published design concepts. Designs for proof-of- principle low voltage infrared FEL experiments based on both radio-frequency (rf) linear accelerator and electrostatic accelerator technology are presented together with point designs for portable systems covering the infrared windows in the atmosphere.

The FELs based on the rf accelerator-recuperator and the electron outcoupling is promising for obtaining average output power of hundreds of kilowatts. We present basic considerations for the system stability and performance optimization for this scheme.

Polymers are everywhere in modern life because of their unique combination of end-use functionalities, ease of processing, recycling potential and modest cost. The physical and economic scope of the infrastructure committed to present polymers makes the introduction of entirely new chemistry unlikely. Rather, the breadth of commercial offerings more likely to shrink in the face of the widening mandate for recycling, especially of packaging. Improved performance and new functionality must therefore come by routes such as surface modification. However they must come with little environmental impact and at painfully low cost. Processing with strongly absorbed light offers unique advantages. The journal and patent literatures disclose a number of examples of benefits that can be achieved, principally by use of excimer lasers or special UV lamps. Examples of commercialization are few, however, because of the unit cost and maximum scale of existing light sources. A FEL, however, offers unique advantages: tunability to the optimum wavelength, potential for scale up to high average power, and a path to attractively low unit cost of light. A business analysis of prospective applications defines the technical and economic requirements a FEL for polymer surface processing must meet. These are compared to FEL technology as it now stands and as it is envisioned.

A ground based laser beam transmitted to space can be used as an electric utility for satellites. It can significantly increase the electric power available to operate a satellite or to transport it from low earth orbit (LEO) to mid earth or geosynchronous orbits. The increase in electrical power compared to that obtainable from the sun is as much as 1000% for the same size solar panels. An increase in satellite electric power is needed to meet the increasing demands for power caused by the advent of 'direct to home TV,' for increased telecommunications, or for other demands made by the burgeoning 'space highway.' Monetary savings as compared to putting up multiple satellites in the same 'slot' can be over half a billion dollars. To obtain propulsion, the laser power can be beamed through the atmosphere to an 'orbit transfer vehicle' (OTV) satellite which travels back and forth between LEO and higher earth orbits. The OTV will transport the satellite into orbit as does a rocket but does not require the heavy fuel load needed if rocket propulsion is used. Monetary savings of 300% or more in launch costs are predicted. Key elements in the proposed concept are a 100 to 200 kW free- electron laser operating at 0.84 m in the photographic infrared region of the spectrum and a novel adaptive optic telescope.

Over the past fifteen years, the mid-infrared advanced chemical laser (MIRACL) and SeaLite beam director (SLBD) have been completed, moved to the High Energy Laser System Test Facility (HELSTF) at White Sands Missile Range, New Mexico, and integrated into the largest and most powerful high energy laser system in the U.S. The high energy laser system was modified, incorporating a shared aperture (pointing and tracking) capability to improve pointing performance. High power propagation, tracking, and beam control experiments over near vertical beam paths have been conducted. The system modifications, instrumentation, and test results are described.

Over the past 25 years, in an attempt to develop a speed-of- light hard-kill weapon system, the U.S. Navy has successfully reduced megawatt-class chemical laser and high power beam control technologies to engineering practice. This Navy program was established during the cold war era when defending naval battle group was the primary concern of the U.S. Navy. Since the collapse of the Soviet Union, however, an urgent and challenging issue facing the U.S. Navy is the self-defense against cruise missile in a littoral battlefield environment against threats originating from shore and/or scattered low- value platforms. This fundamental shift in the battlefield environment and engagement configuration profoundly affected the basic performance requirements placed on potential shipboard high energy laser weapon systems (HELWS). In a littoral maritime environment, thermal blooming limits atmospheric propagation of an HEL beam, and thus limits the weapon's effectiveness. This paper identifies and discusses the technical issues associated with HELWS requirements in this new environment. It also discuses the collateral capabilities that enhance and complement the performance of other weapon and sensor systems onboard ship. This paper concludes that the HELWS using a free electron laser (FEL) offers a unique weapon option for our warships in facing the new defense challenges of the future.

A historical summary review of recent component technology advancements within NASA's program for launch vehicles and space transfer systems utilizing high average power laser beams sets the foundation of this paper. Research into highly speculative propulsion alternatives is being sponsored by the advanced concepts branch of the Advanced Space Transportation Program. Topics include such high payoff technologies as an energy beam fired combined cycle rocket engine for launch of small payloads from the ground to space and high specific impulse upper stage propulsion utilizing energy supplied from photovoltaic arrays illuminated with a ground based laser. The NASA beamed energy transportation (BET) development plan is described.

This paper presents the further development of a concept of a FEL based driver for commercial inertial confinement fusion reactor. We have shown technical feasibility of constructing a laser system with the following parameters: laser light wavelength 0.5 μm, flash energy 4 MJ, repetition rate 10 pps and net efficiency 10%. It becomes possible due to the use of a novel scheme of optical power summation.

The OK-4/Duke storage ring FEL was commissioned in November 1996 and demonstrated lasing in the near UV and visible ranges (345 - 413 nm). The OK-4 is the first storage ring FEL with the shortest wavelength and highest power for UV FELs operating in the United States. During one month of operation we have performed preliminary measurements of the main parameters of the OK-4 FEL: its gain, lasing power and temporal structure. In addition to lasing, the OK-4/Duke FEL generated a nearly monochromatic (1% FWHM) 12.2 MeV gamma-ray beam. In this paper we describe the design and initial performance of the OK-4/Duke storage ring FEL. We compare our predictions with lasing results. Our attempt to lase in the deep UV range (around 193 nm) is discussed. The OK-4 diagnostic systems and performance of its optical cavity are briefly described.

The wavelength from the deep ultraviolet (UV) to x-ray is very attractive for free electron lasers (FELs), because there is no conventional laser which can supply powerful coherent light with a wide wavelength tunability in this range. However, a large-scale accelerator is usually required to obtain FELs in such a wavelength range, because of the necessity of high- energy electron beam with a very good beam quality. In this article we report our attempts to realize FELs in the deep UV and vacuum ultraviolet (VUV) on a small-scale storage ring.