The Vanderbilt Free Electron Laser (FEL) is capable of lasing between 2.0 and 8.0 microns with a high peak intensity pulsed structure. The FEL is used to investigate potential applications in otolaryngology. Charring of temporal bones and thermal stress patterns in Plexiglas indicate thermal buildup at 20 and 10 Hz repetition rates of the laser. Also, transient temperature changes measured with thermocouples in a gelatin model reveal that significant heat production occurs at these laser repetition rates. To utilize the fastest laser repetition rates and maintain minimal lateral thermal damage, a computer-controlled scanning system was devised. The authors have also used the computer control with the carbon dioxide laser and experienced improved ablation.

1197he science of X-ray production and application is now a little more than a century old [1] but is still an active field of research and development [2].Historically, X rays for imaging and crystallography have generally been produced through the use of bremsstrahlung and line X rays from electrons impinging on a metallic anode. Such sources are inexpensive, simple, and robust but provide little control over the X rays produced. More recently, synchrotron sources have been used for both applications, with good results. Unfortunately, synchrotrons are large, expensive facilities with less than ideal beam geometry and are therefore not entirely practical for routine imaging applications.The excellent results of experiments with monochromatic sources [3][4][5] show the desirability of improving on the current broadband X-ray imaging practice. No alternative has existed for experiments that need to operate at various X-ray energies. The availability of such a source may fundamentally change the practice of X-ray imaging and provide much wider availability of tuned X rays to crystallographers.A compact source of pulsed tunable monochromatic X rays has been designed, built, and tested. This device can deliver "hard" X rays from 10-to 50-keV at narrow bandwidths (1-10%), with a flux of 10 10 photons in each 8-psec pulse. These are produced in a cone-beam area geometry useful for human imaging, small animal imaging, protein crystallography, and nondestructive testing in industry. The machine integrates a laser with a linear accelerator (LINAC) and can be used in an unshielded environment.The source described here is a tabletop-terawatt (T 3 ) laser-based Compton backscattering system, which uses few-joule pulses from a 1,052-nm laser to collide with a 20-to 50-MeV electron beam to produce an intense pulse of narrowband X rays. The entire system footprint is 4 m wide by 10 m long, and it requires no shielding vault. It produces X rays in a smallangle cone-beam geometry in the 10-to 50-keV range, with up to 10 10 photons in an 8-psec pulse, which is sufficient flux for medical and industrial imaging to be performed in a single shot. This source is certainly not the first Compton backscattering or laser-synchrotron X-ray source built. Experiments have been carried out at a number of the large accelerator facilities [6, 7] that have produced modest fluxes of photons over a wide range of interesting energies. Also, sources similar in concept to this one have been proposed [8,9] and operated on a small scale. However, none of these sources has been designed and built in a small practical form and with a high enough flux to be deployed as a common laboratory-scale or clinical resource. Further, most of the current generation of sources produce high levels of background radiation from the linear accelerator and require the source to be embedded in a shielding vault.The source at Vanderbilt University has its roots in a project that was built as an add-on to the free-electron laser at Vanderbilt that was proposed in 1987. It p...

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During the second half of 1979, substantial radon anomalies were recorded at two stations of the automated radon-thoron monitoring network operated by

The Vanderbilt Free Electron Laser (FEL) operates between 2.0 and 8.0 p.m with high peak intensities and a pulsed structure. Both the tunability of the EEL and the unique pulse structure make this an attractive tool for surgery. To be used effectively in surgery, one must be concerned with the control and delivery of the laser light from the FEL wiggler to the operating room. Several innovative delivery and monitor systems are being developed in our Computer Assisted Surgical Techniques (CAST) program at the FEL. The union of computer and robotic control to assist the surgeon with surgical laser beams presents many new and exciting applications. For instance, the transient temperature changes in the tissue lateral to an ablation site reveal that significant heat production occurs at the highest pulse repetition rates. To use the fastest pulse repetition rates and maintain minimal lateral thennal damage, a computer controlled scanning system is used. In the surgical applications of lasers, it is often necessary to know when a laser has penetrated a bone. There are many instances when it is critical to avoid damaging tissue beneath the bone. We are developing a method to detect when the bone has been penetrated by measuring the photo acoustic signal generated by a pulsed laser.