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This article reports the design, three-dimensional magnetostatic simulation results, coil fabrication, assembly, and low-temperature test results of a C-frame, iron-dominated high-temperature superconductor dipole magnet for ultra high vacuum magnetic-sensitive spectroscopy techniques at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory. The magnet is required to provide fields up to ~1 T along two spatial directions. With an added capability to rotate about its vertical axis of symmetry, the magnet system is capable of delivering field along all three principal axes. The combination of this magnet and fast-switched, elliptically polarized soft X-rays produced by the NSLS elliptically polarized wiggler forms the basis for an excellent tool for polarization-sensitive studies of magnetic materials. The prototype magnet consists of a set of pancake coils fabricated from BSCCO tape reinforced with stainless steel. Those pancake coils are clamped in a low-carbon AISI 1006 grade steel pole and yoke assembly. For testing purposes, a cold He gas environment provided cooling the superconducting magnet to subtransition temperatures; for operation in an ultra high vacuum endstation environment, cooling can be provided by an external cryocooler. The low-temperature tests establish the safe-operating parameters needed to achieve the target magnetic field values. The measured magnetic field values are in close agreement with the magnetic simulation results, thereby confirming that the magnet design fulfills the performance requirements. The final section of this article lists some suggestions to improve the magnet performance.

The DUV-FEL facility has been in operation in the High Gain Harmonic Generation (HGHG) mode producing a 266-nm output from 177-MeV electrons for 1 year. In this paper, we present preliminary results of the Chirped Pulse Amplification (CPA) of the HGHG radiation. In the normal HGHG process, a 1-ps electron beam is seeded by a chirped 9 ps long, 800-nm Ti:Sapphire laser. The electron beam sees only a narrow fraction of the seed laser bandwidth. However, in the CPA case, the seed laser pulse length is reduced to 1 ps, and the electron beam sees the full bandwidth. We introduce an energy chirp on the electron beam to match the chirp of the seed pulse, enabling the resonant condition for the whole beam. We present measurements of the spectrum bandwidth for various chirp conditions.

The Deep Ultra Violet FEL (DUV-FEL) experiment is being commissioned in the Source Development Laboratory at NSLS in Brookhaven National Laboratory. The goal of the project is to produce coherent radiation below 100 nm wavelength using High-Gain Harmonic Generation utilizing a seed laser. As a first step of this experiment, self-amplified spontaneous emission (SASE) has been achieved at 400 and 266 nm with electron beam energies at 140 and 171.7 MeV. As an intermediate stage of the experiment, direct seeding with the 266 nm laser also has been accomplished. We report the measurements of the SASE and direct seeding. We measure the FEL properties for various electron beam conditions and discuss the performance of the FEL.

VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission FEL, which achieved saturation at 840 nm within a single-pass 4-m undulator. A gain length shorter than 18 cm has been obtained, yielding the gain of 2 ×108 at saturation. The FEL performance, including spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. The results are compared to 3-D SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL system. Detailed agreement between simulations and experimental results is obtained over the wide range of the electron beam parameters.© 2003 Elsevier Science B.V. All rights reserved.

The Deep Ultra-Violet Free Electron Laser (DUVFEL) at the National Synchrotron Light Source consists of a 5 MeV photoinjector, a 200 MeV S-band linear accelerator, a four-magnet chicane compressor and a 10 m wiggler with a 3.9 cm period. The commissioning of the SDL accelerator was completed recently and it is routinely producing a high-quality electron beam with a peak current of ∼400 A and a normalised emittance of 3–4 mm mrad. The first SASE lasing of the DUV FEL has been demonstrated at both 266 and 400 nm. The gain length of the SASE experiments was measured to be 66 cm in both cases and up to 20 nJ per pulse was obtained. A laser seeded FEL at 266 nm is in the very early stages of commissioning and amplification of the laser seed has been observed. The goal of the seeded laser FEL is to saturate the FEL and thereby generate sufficient third harmonic at 89 nm for experimental applications. Here we report the observation and measurements of SASE at 400 and 266 nm and the first results of seeded FEL.

Visible to Infrared SASE Amplifier is a free electron laser (FEL) designed to saturate at a radiation wavelength of 800 nm within a 4 m long, strong focusing undulator. Large gain is achieved by driving the FEL with 72 MeV, high brightness beam of BNL's accelerator test facility. We present measurements that demonstrate saturation in addition to the frequency spectrum of the FEL radiation. Energy, gain length and spectral characteristics are compared and shown to agree with simulation and theoretical predictions.

We report on the experimental investigation of high-gain harmonic generation carried out at the Accelerator Test Facility at Brookhaven National Laboratory. A seed CO 2 laser at a wavelength of 10.6 μm was used to generate FEL output at a 5.3-μm wavelength. The duration of the output pulse was measured using a second-harmonic intensity autocorrelator, and the coherence length was measured using an interferometer. We also measured the energy distribution of the electron beam after it exited the second undulator, observing behavior consistent with that is expected at saturation. The intensity of the harmonic components of the output at 2.65 and 1.77 μm was determined relative to that of the 5.3-μm fundamental. Finally, using a corrector magnet upstream of the radiator, steering effects on the trajectories of the electron and light beams were studied.

The Visible to Infrared SASE Amplifier (VISA) FEL is designed to obtain high gain at a radiation wavelength of 800 nm. The FEL uses the high brightness electron beam of the Accelerator Test Facility (ATF), with energy of 72 MeV. VISA uses a novel, 4 m long, strong focusing undulator with a gap of 6 mm and a period of 1.8 cm. To obtain large gain the beam and undulator axis have to be aligned to better than 5 μm. Results from initial measurements on the alignment, gain, and spectrum will be presented and compared to theoretical calculations and simulations.

We describe the status and initial commissioning of the Visible to Infrared SASE Amplifier (VISA) experiment. VISA uses a strong focusing 4 m undulator, the Brookhaven National Laboratory ATF linac with an energy of 72 MeV, and a photoinjector electron source. The VISA fundamental radiation wavelength is near 800 nm and the power expected at saturation is near 60 MW. Power, angular and spectral measurements are planned for the VISA radiation and these results will be analyzed and compared with SASE FEL theory and computer simulation. In addition, the induced electron beam micro-bunching will be measured using coherent transition radiation.

We report on the first lasing of a high-gain harmonic generation (HGHG) free-electron laser (FEL). The experiment was conducted at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). This is a BNL experiment in collaboration with the Advanced Photon Source (APS) at Argonne National Laboratory. A preliminary measurement gives a high-gain harmonic generation (HGHG) pulse energy that is 2×10 7 times larger than the spontaneous radiation. In a purely self-amplified spontaneous emission (SASE) mode of operation, the signal was measured as 10 times larger than the spontaneous radiation in the same distance (∼2 m) through the same wiggler. This means the HGHG signal is 2×10 6 times larger than the SASE signal. To obtain the same saturated output power by the SASE process, the radiator would have to be 3 times longer (6 m).

National Synchrotron Light Source-II (NSLS-II) will be a medium energy storage ring of 3GeV electron beam energy with sub-nm.rad horizontal emittance and top-off capability at 500mA. Damping wigglers will be used not only to reduce the beam emittance but also used as broadband sources for users. Cryo-Permanent Magnet Undulators (CPMUs) are considered for hard X-ray linear device, and permanent magnet based elliptically polarized undulators (EPUs) for variable polarization devices for soft X-ray. 6T superconducting wiggler with minimal fan angle will be installed in the second phase as well as quasi-periodic EPU for VUV and possibly high-temperature superconducting undulator. R&D plans have been established to pursue the performance enhancement of the baseline devices and to design new types of insertion devices. A new insertion device development laboratory will also be established.

We report the results of experiments carried out in the X13 straight section of the NSLS X-ray Ring, which explore the limits of operation of small-gap undulators. Two major projects are described: the Prototype Small-Gap Undulator (PSGU) and the In-Vacuum UNdulator (IVUN). The PSGU utilized a variable-aperture vacuum chamber and a separate drive for the 16-mm-period undulator magnet arrays, which were situated in air outside the vacuum vessel. For IVUN, the 11-mm-period undulator arrays were placed directly in the accelerator vacuum. For both devices, stored beam lifetimes in the X-ray Ring were unaffected until electron beam apertures were decreased below 5 mm. A 3 mm aperture resulted in only a slight reduction of beam lifetime, which is acceptable for normal user operations. Measurements of the photon spectra radiated by the PSGU and IVUN were in excellent agreement with theory. Our work provides strong evidence that small-gap, short-period undulators will play an important role in the future.

Short period (14.5mm) hybrid undulator arrays composed of Praseodymium Iron Boron (Pr2Fe14B) magnets (CR53, NEOMAX, Inc.) and vanadium permendur poles have been fabricated at Brookhaven National Laboratory. Unlike Neodymium Iron Boron (Nd2Fe14B) magnets which exhibit spin reorientation at a temperatures below 150 K, PrFeB arrays monotonically increase performance with lower operating temperature. It opens up the possibility for use in operating a cryo‐permanent magnet undulator (CPMU) in the range of 40 K to 60 K where very efficient cryocoolers are available. Magnetic flux density profiles were measured at various temperature ranges from room temperature down to liquid helium (LHe) using the Vertical Testing Facility (VTF) at the National Synchrotron Light Source‐II (NSLS‐II). Temperature variations of phase error have been characterized. In addition, we examined the use of textured Dysprosium (Dy) poles to replace permendur poles to obtain further improvement in performance.

Rocketdyne is assembling a high-brightness 78 MeV FEL. After full development the laser will be capable of an average output of greater than 1 kW. Performance calculations using the Rocketdyne FELOPT code are presented for a 1.06 μm system.

The superconducting wiggler (SCW) with 4.2 Tesla field in 5 main poles has been in operation on the NSLS X-ray storage ring for more than 20 years. The inefficient cryogenic system of this wiggler uses a closed-cycle refrigerator requiring constant maintenance. It is possible to replace this insertion device with a 13-pole SCW originally built by Oxford Instruments. The cryostat of this device could be upgraded to reduce the liquid He consumption using cryocoolers, thereby greatly reducing the refrigerator operating expense. A second option is a new design of a SCW featuring internal chicaning.to serve three user beamlines simultaneously All these upgrade possibilities will be described in the paper.

The experimental observation of FEL efficiency enhancement using a tapered undulator in a single-pass seeded FEL at the NSLS SDL is reported. The last 2.5 m of the 10 m NISUS undulator was linearly tapered so that the magnetic field strength at the end of the undulator was reduced by 5%. The FEL energy gain along the undulator was measured for both the tapered and un-tapered undulators. We observed that the FEL efficiency was more than doubled by applying the taper. The experimental results are compared with the numerical simulation code,GENE- SIS1.3 [1].

NSLS-II is a medium energy storage ring of 3 GeV electron beam energy with sub-nm.rad horizontal emittance and top-off capability at 500 mA. Damping wigglers will be used not only to reduce the beam emittance but also for broadband sources for users. Cryo-permanent magnet undulators (CPMUs) are considered for hard X-ray planar device, and permanent magnet based elliptically polarized undulators (EPUs) are for soft X-ray polarization control. Rigorous R&D plans have been established to pursue the performance enhancement of the above devices as well as building new types of insertion devices such as high temperature superconducting wiggler/undulators. This paper describes the details of these activities and discuss technical issues.

The existing 15‐year‐old hybrid wiggler at the NSLS has been replaced by a state‐of‐the‐art, cryo‐ready in‐vacuum undulator optimized for a dedicated macromolecular crystallography program. The device is a 1m long, 18mm period, hybrid PM‐type with a minimum operating gap of 5.6mm, and has provision for cryo‐cooling to 150K. Unlike the original SPring‐8 cryo‐PM undulator proposal, we use a new high‐remanence, high‐temperature grade of NdFeB (NEOMAX 42AH with Br=1.3T and Hcj=24 kOe) that can be baked to 100°C to be UHV‐ready in case of cooling system failure. A novel optical gap measurement system using a LED‐based product ensures gap accuracy of ±2 micro meter. A friction stir welding technique is used for the first time in an accelerator UHV device to minimize stress and deformation of the magnet arrays due to temperature gradients. This paper describes design issues of the device and other considerations such as magnetic measurement at low temperature.

A short-period in-vacuum undulator for the NSLS X-ray Ring has been developed in a collaboration between SPring-8 and the NSLS, and has achieved its project design goals during commissioning studies. The device is called IVUN (in-vacuum undulator) and employs magnet arrays (31 periods, with an 11 mm period) developed at SPring-8, while the requisite vacuum chamber and mechanical systems were developed at the NSLS. At a magnet gap of 3.3 mm, IVUN produces 4.6 keV radiation in the fundamental, with useful photon fluxes in both the second and third harmonics. The magnet gap is adjustable between 2 and 10 mm. A brief overview of IVUN is presented, together with initial commissioning results: the dependence of electron-beam lifetime and bremsstrahlung on magnet gap, and the output radiation spectrum.

A high-flux insertion device and beamline for macromolecular crystallography has been built at the National Synchrotron Light Source (NSLS) that employs a mini-gap undulator source developed by the NSLS. The mini-gap undulator at beamline X29 is a hybrid-magnet device of period 12.5 mm operating at proven gaps of 3.3-10 mm. The beamline provides hard X-rays for macromolecular crystallography experiments from the second and third harmonics over an energy range of 5-15 keV. The X-ray optics is designed to deliver intense and highly collimated X-rays. Horizontal focusing is achieved by a cryogenically cooled sagittally focusing double-crystal monochromator with approximately 4.1:1 demagnification. A vertical focusing mirror downstream of the monochromator is used for harmonic rejection and vertical focusing. The experimental station hosts an Area Detector Systems Quantum 315 CCD detector with 2.2 s readout time between exposures and Crystal Logic goniostat for crystal rotation and detector positioning. An auto-mounter crystal changer has been installed to facilitate the high-throughput data collection required by the major users, which includes structural genomics projects and the Macromolecular Crystallography Research Resource mail-in program. X29 is 10(3) times brighter than any existing bending-magnet beamline at NSLS with an actual flux of 2.5 x 10(11) photons s(-1) through a 0.12 mm square aperture at 11.271 keV.

One of the challenges of small-gap superconducting undulators is measurement of magnetic fields within the cold bore to characterize the device performance and to determine magnetic field errors for correction or shimming, as is done for room-temperature undulators. Both detailed field maps and integrated field measurements are required. This paper describes a 6-element, cryogenic Hall probe field mapper for the NSLS superconducting undulator Vertical Test Facility (VTF) [1]. The probe is designed to work in an aperture only 3 mm high. A pulsed-wire insert is also being developed, for visualization of the trajectory, for locating steering errors and for determining integrated multi-pole errors. The pulsed-wire insert is interchangeable with the Hall probe mapper. The VTF and the magnetic measurement systems can accommodate undulators up to 0.4 m in length.

The National Synchrotron Light Source at BNL was the first dedicated light source facility and it has now operated for more than 20 years. During this time the user community has grown to more than 2400 users annually. To insure that this vibrant user community has access to the highest quality photon beams, the NSLS is pursuing the design of a new ultra-high brightness (∼1021) electron storage ring, tailored to the 0.3-20 KeV photon energy range. We present our preliminary design and review the critical accelerator physics design issues.

In this paper a new concept for a planar, superconductive, variable polarization undulator (VPU) is presented. Advantage of this design include: (1) electrical tunability for both right and left circular and elliptical, as well as linear vertical or horizontal, (2) it requires no compensation of unwanted vertical field component and (3) used only simple windings of superconductive wire in an interlaced pattern. The construction of the device is described and compared with a permanent magnet VPU with the same gap and period, as well as with previously published concepts.

Saturation of a high-gain harmonic-generation free-electron laser (HGHG-FEL) at 266 nm has been accomplished at the Brookhaven National Laboratory/Deep Ultra Violet Free Electron Laser Facility (BNL/DUV-FEL) by seeding with an 800 nm Ti:sapphire laser. We describe the diagnostics used to characterize the electron beam and the FEL output. Analytic and simulation calculations of the HGHG output are presented and compared with the experimental data. We also discuss the chirped pulse amplification of a frequency chirped seed by an energy chirped electron beam. The third harmonic at 88 nm accompanying the 266 nm fundamental has been used in an ion pair imaging experiment in chemistry, the first application of the BNL/DUV-FEL.

The Deep Ultra Violet Free Electron Laser (DUV-FEL) experiment has reached a milestone by saturating the Free Electron Laser using High Gain Harmonic Generation (HGHG) method in the Source Development Laboratory (SDL) at NSLS. It utilizes the 10 m long, 3.9 cm period NISUS wiggler. The goal of the project is to produce radiation at a wavelength less than 100 nm, utilizing the HGHG method. HGHG at 266 nm has been accomplished by seeding with the 800 nm Ti:Sapphire laser and observed saturation. The third harmonic at 88 nm accompanying the 266 nm is being used in an ion pair imaging experiment in chemistry. We discuss the measurement of energy, gain, spectrum, and pulse length of the FEL output. We also describe the diagnostics used for operating the FEL.

The performance and future upgrade of the XUV at the Brookhaven DUV-FEL facility are presented in this report. The High Gain Harmonic Generation (HGHG) Free Electron Laser (FEL) at the DUV-FEL now routinely produces fully coherent 266 nm radiation with the 800 nm seed, and the output energy of the HGHG is about 100 uJ with 1 ps pulse duration (FWHM) [1], The first three harmonics of the HGHG from the nonlinear harmonic generation process were experimented characterized. The third harmonic (89 nm, 14 eV) of the HGHG has been explored for chemical science applications [2]. To further expand the DUV-FEL user base and explore its unique potential, it is proposed that the DUV-FEL to be upgraded to produce XUV (< 100 nm) at the HGHG fundamental. Several options are now under consideration to upgrade the DUV-FEL for XUV radiation generation; which including the electron beam energy upgrade to 300 MeV and installing the shorter period VISA undulator. PACS: PACS codes: 42.72.Bj, 41.60.Cr, 41.60-m

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

The Visible-Infrared SASE Amplifier (VISA) undulator consists of four 99 cm long segments. Each undulator segment is set up on a pulsed-wire bench, to characterize the magnetic properties and to locate the magnetic axis of the FODO array. Subsequently, the location of the magnetic axis, as defined by the wire, is referenced to tooling balls on each magnet segment by means of a straightness interferometer. After installation in the vacuum chamber, the four magnet segments are aligned with respect to themselves and globally to the beam line reference laser. A specially designed alignment fixture is used to mount one straightness interferometer each in the horizontal and vertical plane of the beam. The goal of these procedures is to keep the combined rms trajectory error, due to magnetic and alignment errors, to 50 /spl mu/m.

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL) is an accelerator and beam physics user facility capable of producing a high-brightness, 70-MeV electron beam. Currently, a high-gain harmonic generation (HGHG) free-electron laser (FEL) experiment is underway at the ATF. This is a collaborative effort between BNL and the Advanced Photon Source (APS). The experiment consists of two phases: 1) self-amplified spontaneous emission (SASE) and 2) HGHG. Here, a brief introduction to the HGHG theory, measurements in the SASE phase, the recent modifications in preparation for the HGHG phase, and future plans will be discussed.

The National Synchrotron Light Source (NSLS) prototype small-gap undulator (PSGU) will serve as a tool for studying some of the effects which degrade storage ring performance as the beam duct aperture is decreased. It consists of a variable-gap vacuum vessel and a permanent-magnet, small-period undulator with independent magnet gap control. The design concept of the vacuum vessel, and some details related to it, are presented, followed by a description of the permanent-magnet undulator, its design parameters, and anticipated performance. >

On the NSLS X-ray storage ring, the X13 straight section and beamline have been used for insertion-device-related R&D since 1990. We will describe three important projects: the Prototype Small-Gap Undulator (PSGU), the In-Vacuum Undulator (IVUN), and the Time Varying Elliptically Polarized Wiggler (EPW). The PSGU has successfully operated with a vertical aperture of only 3 mm, with minimal reduction in electron beam lifetime. The EPW has successfully run during regular user operations while switching at either 2 Hz or 100 Hz, with no adverse effects on other experiments. The IVUN project is a collaboration between NSLS and Spring-8, and installation is scheduled for may 1997.

Magnetic measurements have been performed on the In-Vacuum Undulator (IVUN), built jointly by BNL and SPring-8 for the NSLS X-ray Ring. The IVUN magnet has a Halbach-type, pure-permanent magnet structure with a period of 11 mm and a minimum gap of 2 mm. Results of magnetic measurements utilizing Hall probe, moving wire and pulsed wire techniques are presented and compared.

The elliptical multipole wiggler (EMW) has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magnetic field of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magnetic field of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation trim magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.

We review the work carried out in the X13 RD (2) plans to install hybrid IVUNs in the two RF straights of the X-Ray Ring, increasing the number of insertion devices in the X-Ray Ring to eight; (3) the possibility of reducing the vertical beta function in the X13 straight from 0.33 m down to 0.16 m. This reduction in beta function would allow us to decrease the usable undulator gap from 3 mm down to 2 mm, further increasing the tuning range.

We describe a major paradygm shift in in the approach to the production of synchrotron radiation This change will considerably improve the scientific capabilities of synchrotron light sources. We introduce plans for an upgrade of the National Synchrotron Light Source (NSLS). This upgrade will be based on the Photoinjected Energy Recovering Linac (PERL). This machine emerges from the union of two technologies, the laser-photocathode RF gun (photoinjector) and superconducting linear accelerators with beam energy recovery (Energy Recovering Linac). The upgrade will bring the NSLS users many new insertion device beam lines, brightness greater than 3rd generation light-source's and ultra-short pulse capabilities, not possible with storage ring light sources.

The DUVFEL electron linac is designed to produce sub-picosecond, high brightness electron bunches to drive an ultraviolet FEL. The accelerator consists of a 1.6 cell S-band photoinjector, variable pulse length Ti:Sapp laser, 4 SLAC-type S-band accelerating sections, and 4-dipole chicane bunch compressor. In preparation for FEL operation, the compressed electron beam has been fully characterized. Measurement of the beam parameters and simulation of the beam are presented.

We discuss the design and output radiation parameters for the Deep Ultra-violet Free Electron Laser at BNL, which will generate coherent output down to 100 nm using high gain harmonic generation. The result of the FEL calculation and the status of the experiment are presented.

We are proposing an Atto-second electron beam generation and diagnostics experiment at the Brookhaven Accelerator Test facility (ATF) using 1 {micro}m Inverse Free Electron Laser (IFEL). The proposed experiment will be carried out by an BNL/LBNL collaboration, and it will be installed at the ATF beam line II. The proposed experiment will employ a one-meter long undulator with 1.8 cm period (VISA undulator). The electron beam energy will be 63 MeV with emittance less than 2 mm-mrad and energy spread less than 0.05%. The ATF photocathode injector driving laser will be used for energy modulation by Inverse Free Electron Laser (IFEL). With 10 MW laser peak power, about 2% total energy modulation is expected. The energy modulated electron beam will be further bunched through either a drift space or a three magnet chicane into atto-second electron bunches. The attosecond electron beam bunches will be analyzed using the coherent transition radiation (CTR).

The visible-infrared self-amplified spontaneous emission amplifier (VISA) free electron laser (FEL) is an experimental device designed to show self-amplified spontaneous emission (SASE) to saturation in the near infrared to visible light energy range. It generates a resonant wavelength output from 800\char21{}600 nm, so that silicon detectors may be used to characterize the optical properties of the FEL radiation. VISA is designed to show how SASE FEL theory corresponds with experiment in this wavelength range, using an electron beam with emittance close to that planned for the future Linear Coherent Light Source at SLAC. VISA comprises a 4 m pure permanent magnet undulator with four 99 cm segments, each of 55 periods, 18 mm long. The undulator has distributed focusing built into it, to reduce the average beta function of the 70\char21{}85 MeV electron beam to about 30 cm. There are four FODO cells per segment. The permanent magnet focusing lattice consists of blocks mounted on either side of the electron beam, in the undulator gap. The most important undulator error parameter for a free electron laser is the trajectory walk-off, or lack of overlap of the photon and electron beams. Using pulsed wire magnet measurements and magnet shimming, we were able to control trajectory walk-off to less than $\ifmmode\pm\else\textpm\fi{}50\ensuremath{\mu}\mathrm{m}$ per field gain length.

We report on an experimental investigation characterizing the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO2 laser at a wavelength of 10.6 microm was used to generate amplified FEL output at 5.3 microm. Measurement of the frequency spectrum, pulse duration, and correlation length of the 5.3 microm output verified that the light is longitudinally coherent. Investigation of the electron energy distribution and output harmonic energies provides evidence for saturated HGHG FEL operation.

We report on observations of the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO/sub 2/ laser at a wavelength of 10.6 /spl mu/m was used to generate amplified FEL output at 5.3 /spl mu/m. Measurement of the frequency spectrum, pulse duration and correlation length of the 5.3-/spl mu/m output verified the longitudinal coherence of the light. At the exit of the device, measurements of the energy distribution of the electron beam indicated that the HGHG process had reached saturation. By comparing the intensities of the higher harmonics (2.65 /spl mu/m and 1.77 /spl mu/m) relative to the 5.3-/spl mu/m fundamental, additional evidence confirming saturated operation was obtained. These results agree with theoretical predictions at saturation. We also briefly describe the status of a new HGHG experiment at the Source Development Laboratory (BNL), aimed at achieving generation of 100-nm radiation.

The VISA (Visible to Infrared SASE Amplifier) SASE free electron laser has been successfully operated at the Accelerator Test Facility (ATF) at BNL. High gain and saturation were observed at 840 nm. We describe here the diagnostic system, experimental procedures and data reduction algorithms, as the FEL performance was measured along the length of the undulator. We also discuss selected spectral radiation measurements.

A high-gain harmonic-generation free-electron laser is demonstrated. Our approach uses a laser-seeded free-electron laser to produce amplified, longitudinally coherent, Fourier transform–limited output at a harmonic of the seed laser. A seed carbon dioxide laser at a wavelength of 10.6 micrometers produced saturated, amplified free-electron laser output at the second-harmonic wavelength, 5.3 micrometers. The experiment verifies the theoretical foundation for the technique and prepares the way for the application of this technique in the vacuum ultraviolet region of the spectrum, with the ultimate goal of extending the approach to provide an intense, highly coherent source of hard x-rays.

The Visible-Infrared SASE Amplifier (VISA) undulator is an in-vacuum, 4-meter long, 1.8 cm period, pure-permanent magnet device, with a novel, strong focusing, permanent magnet FODO array included within the fixed, 6 mm undulator gap. The undulator magnet is constructed of 99-cm long segments, joined into a continuous structure. To attain maximum SASE gain requires establishing overlap of electron and photon beams to within 50 microns rms. This imposes challenging tolerances on mechanical fabrication and magnetic field quality, and necessitates use of laser straightness interferometry for calibration and alignment of the magnetic axes of the undulator segments. This paper describes the computerized magnet sorting, pulsed-wire magnetic measurements, trajectory shimming and magnetic axis calibration performed to meet this goal.

As part of the research and development effort for a 4th generation light source, we have designed a 4-meter long free-electron laser (FEL) undulator. The undulator will be installed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory to conduct a self-amplified spontaneous emission (SASE) demonstration. The demonstration is called VISA, which stands for "Visible to Infrared SASE Amplifier." The undulator consists of 440 permanent dipole magnets per meter which are supported and aligned on a precision strongback. Focusing and defocusing permanent quadrupole magnets are also supported by the strongback. Each of the 4 one-meter sections of undulator are kinematically supported and housed within the vacuum vessel. The undulator and the vacuum vessel are supported independently to eliminate undulator misalignment during vacuum pump-down of the vessel. We describe the design requirements and features of the undulator, vacuum vessel and support system.

We propose an approach to the optimization of segmented in-vacuum undulators, in which different segments along an undulator may have different gaps and periods. This enables close matching between the gaps and the vertical "envelope" of electron beam motion in a storage ring straight section (carefully satisfying the associated vertical "stay clear" constraint) and, at the same time, precise tuning of all the segments to the same fundamental photon energy. Placing together undulator segments with different periods may introduce small kicks to electron trajectories at the segment junctions, which can be easily compensated, without introducing any significant radiation phase error, by active correction magnets or by special design of terminating magnets in the segments. Thanks to this, the entire multi-segment structure can operate as one long undulator. On the other hand, since the vertical gaps in segments located close to straight section center can be smaller than at extremities, such structure can offer better magnetic performance, compared to the case of a standard undulator with constant gap (and period) over its length. We present magnetic field, radiation flux and brightness calculation results for such segmented adaptive-gap in-vacuum undulators if used in low-beta straight sections of NSLS-II, and demonstrate their gain in spectral performance, especially in hard X-ray range, over standard room-temperature and even cryo-cooled in- vacuum undulators.

The Rocketdyne free-electron laser (FEL) being presently developed for operation in the visible to one-micron regime is described, with particular attention given to some of the principal optics and atmospheric propagation issues. The paper describes the system assembly and discusses the performance requirements for power beaming, the resonator design, and the basic ideas and calculations involved in the beam propagating through the atmosphere and tilt corrections. This FEL will be capable of an average output of greater than 1 kW in the near infrared. The laser system has an ability of scaling to power levels required for beaming power to space platforms.