Monochromatic x-rays were produced by inverse Compton scattering resolution from counter-propagation of a tunable free electron laser electron beam and its own infrared photon beam. In a manner analogous to electron beam CT, a mechanism was developed here for obtaining multiple projection views with monochromatic x-rays by deflecting x- rays off of mosaic crystals mounted on rotating stages. These crystals are both energy and angle selective. X-rays are detected digitally when they strike a phosphorescent screen mounted in front of a CCD camera. Using this system, multiple projection images of a 3D phantom and of rat lungs ex vivo were obtained. In an alternate micro-CT arrangement, rat lungs in situ were imaged by rotating the rat in front of both a polychromatic beam from a molybdenum target x-ray tube and the same beam monochromatized with a mosaic crystal. In the first arrangement, depth information was revealed by relative position changes of features seen in each projection and the approximately 0.16 mm thick walls of a catheter were visible in the images. Using conventional tomography, the projections were reconstructed into slice images. Overall, these monochromatic x-ray imaging methods offer reduced x-ray dose, the potential for improved contrast resolution, and now 3D information.

In this paper we describe the plans at Stanford University for an x-ray (1.5 - 15 angstroms) free-electron laser based on the last kilometer, 15 - 5 GeV, of the SLAC linear accelerator. The technical requirements are summarized as well as the novel scientific opportunities with this fourth generation source. It is concluded that with the present research and development efforts under way it should be possible to start the construction of such a facility as early as 2002 with a completion date in 2005.

X-ray microscopy is often discussed as one of the experiments that would benefit from the development of x-ray free-electron lasers. We outline the source characteristics required for several different x-ray microscopy experiments, including possible approaches towards atomic resolution imaging. X-ray FELs would help many but not all of these experiments; those that would benefit the most include experiments that are extremely demanding of a high total flux of coherent x rays; experiments that require snapshot imaging at nanosecond or faster timescales; and pump-probe experiments that require synchronization of an x-ray and a UV laser pulse. In all of these experiments, caution must be taken with regard to radiation and thermal damage.

Brookhaven National Laboratory has established an initiative in FEL science and technology development which includes the Deep Ultra-Violet Free Electron Laser (DUV-FEL) experiment. It is configured as a sub-harmonically seeded High Gain Harmonic Generator to improve coherence and pulse control as contrasted with other schemes that start up from noise. In its initial configuration the DUV-FEL will allow operation at wavelengths down to 200 nm at pulse lengths below a picosecond. The DUV-FEL will be used as a test-bed for experiments to utilize the UV radiation it produces, and serve as model for extending its principles to much shorter wavelengths (x-rays).

The Super-ACO storage ring FEL is operating with a high average power in the UV range (300 mW at 350 nm), and recently at wavelengths down to 300 nm. In addition this source exhibits high stability and long lifetime which makes it a unique tool for user applications. The coupling of the FEL with other synchrotron based sources (bending magnet and undulator) opens many unexplored possibilities for various types of two-color time-resolved spectroscopies. Presently, we are developing a two-color experiment where we study the sub-nanosecond time-resolved absorption of different chromophoric compounds. In this type of pump-probe experiments, the intense UV pulse of the Super-ACO FEL is used to prepare a high initial concentration of chromophores in their first singlet electronic excited state. The nearby bending magnet synchrotron radiation provides on the other hand a pulsed, white light continuum ranging from UV to IR, which is naturally synchronized with the FEL pulses and can be used to probe the photochemical subsequent events and the transient species. With a dye molecule (POPOP), we have obtained a two-color effect which demonstrates the feasibility of the experiment in terms of flux. Applications on various chromophores of biological interest are planned.

A versatile free electron laser (FEL) user facility has recently come on line at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) providing high average (kilowatt-level) power laser light in the infrared. A planned upgrade of the FEL in this facility will extend the wavelength range through the visible to the deep UV and provide the photobiology community with a unique light source for a variety of studies. Planned and potential applications of this FEL include: IR studies of energy flow in biomolecules, IR and visible imaging of biomedical systems, IR and visible studies of photodynamic effects and UV and near visible studies of DNA photodamage.

This paper will evaluate the potential of ultraviolet free electron lasers, and particularly the soon to be available UV-FEL at the Thomas Jefferson National Accelerator Facility for such experiments.

The objectives of this study were to determine if the optical absorption properties of urinary calculi affect the threshold fluence for ablation or fragmentation and the ablation efficiency due to laser irradiation. The Vanderbilt free electron laser was tuned to selected wavelengths based on the absorption spectrum of various types of urinary calculi. The threshold fluences for ablation of the calculi were measured at different wavelengths. A preliminary study of the ablation efficiency (ablation depth per unit incidence fluence) was performed. The results were fond to be in agreement with a thermal ablation model for which the threshold fluences were proportional to l/(mu) _a. The ablation efficiencies were higher in regions of the infrared spectra in which absorption was higher. For a fixed laser irradiation, the lower threshold fluences within regions of high optical absorption allowed more energy to enhance calculus ablation. This study provided insight into determining the optimum wavelengths for ablation and laser lithotripsy.

We show that myoglobin, which is almost entirely α helix in secondary structure, has an unusually long-lived 12 ps vibrational excited state lifetime generated by optically pumping at the blue side 5.85 microns of the amide I band, indicating the generation of a long-lived trapped soliton- antisoliton breather mode.

The effect of temperature dependent shift of water absorption band, known for pure water, has been examined, for the first time, for tissue water, using the IR Free Electron Laser radiation. Cooling kinetics of cartilage and cornea irradiated was measured with a fluorimeter. We have modified the computation algorithm to calculate the optical properties from these measurements more precisely. Temperature dependence of the absorption coefficient of tissue water is studied, for both sides of water absorption bands at 3.0 and 6.1 micrometers . It is shown that cooling kinetics for samples irradiated with small laser intensity is the same, for both wavelengths of each pair: 6.2 and 6.0; 6.35 and 5.92; 3.22 and 2.81; 3.15 and 2.87 micrometers .

Successful removal of cholesterol ester which is specifically accumulated in the arteriosclerotic region on the arterial walls was achieved by the exposure of 5.75 micrometers -infrared free-electron-lasers (FEL) which is absorbed by C equals O stretching vibrations of ester. Short pulse duration and high power density of FEL-micropulse and suitable wavelength absorbed by specific molecular vibrations may induced these non-thermal effects. However, details of interaction mechanism have not yet been clarified. In this paper, we discussed interaction mechanisms of biomolecules and IR lasers which excited molecular vibrations. Cholesteryl oleate were exposed to FELs and temperature increase was estimated for heating experiments which induce static thermal effects. Changes of the samples were examined with FT-IR. As results, it was found that FEL induces not only thermal effect by macropulse as observations of temperature increase, but also microscopic thermal effect by micropulse as observations of vaporization and IRMPD by wavelength of micropulse of 5.75 micrometers -FEL as observations of ester hydrolysis.

The purpose of this study was to explore the feasibility of using a free-electron laser (FEL) to photothermally coagulate an albumin solder for laser-assisted incision closure. A 50%(w/v) bovine serum albumin solder was used to repair an incision in bovine aorta. The solder was coagulated by targeting absorption peaks in the solder infrared absorption spectrum using the FEL. Acute breaking strengths of repaired incisions were measured and the data analyzed by one-way ANOVA (P < 0.05). Multiple comparisons of means were performed using the Newman-Keuls test. The solder absorption spectrum from 2 - 10 microns was similar to water with an additional peak at 6.45 microns (amide II) due to the albumin. Preliminary results indicated that wavelengths at or very close to the absorption peaks were excessively absorbed, resulting in only the top surface of the solder being coagulated. Using wavelengths at points of weak absorption on the water absorption curve yielded better results.

The Duke FEL Laboratory is a national and international users facility. We describe the current light source capabilities in the infrared, visible, ultraviolet, and Gamma rays. Plans are summarized for the development of two novel beamlines, one for UV-resonant Raman spectroscopy and the other an essentially jitter-free UV-pump, IR-probe `two- color' source with rapid-scan FTIR time-resolved detection of the broadband infrared. Current applications research is summarized, with a more detailed description of research in corneal wound healing.