The primary objective of this effort is to develop a low-cost, self-powered, and compact laser event recorder and warning sensor for the measurement of laser events. Previously we reported on the technology and design of the Laser Event Recorder. In this paper we describe results from a series of ground and airborne tests of the Laser Event Recorder.
Lasers for defense applications continue to grow in power and fill in new portions of the spectrum, expanding the laser eye safety hazard, particularly to aircrew and aviation safety. The Laser Event Recorder Program within Naval Air Systems Command (NAVAIR) seeks to develop a low cost, self-contained laser sensor able to detect, warn and record laser exposures that hazard aircrew vision. The spectral and temporal range of hazardous lasers (400 to 1600 nm and pulsed to continuous) has presented a challenge in the past. However, diffractive optics and imaging technologies have enabled a solution to this growing threat. This paper will describe the technical requirements for the Laser Event Recorder, which are based on ANSI Z136.1 laser safety standards and common to its use on any platform. To support medical and operational laser eye protection, the LER extracts and records laser wavelength, radiant exposure, exposure duration, pulse structure, latitude, longitude, altitude and time of laser exposure. Specific performance and design issues of the LER prototype will be presented in a companion paper. In this paper, fundamental challenges to the requirements encountered during the first two years of research, development and successful outdoor testing will be reviewed. These include discrimination against all outdoor light levels and the impact of atmospheric beam propagation on accuracy of the radiant exposure determination. Required accuracy and response time of the determination of whether a laser exposure exceeds the maximum permissible exposure (MPE) will be described. Ongoing efforts to coordinate laser exposure reporting and medical management will also be discussed.
The confocal principle was applied to double pass method to measure the point spread function (PSF) of the human eye and an artificial eye, and to improve the ratio of signal to noise of retinal images. The double-pass PSFs of four human eyes on and off the optical axis of the eyes were measured. The off-axis double pass PSF in the human eye along vertical and horizontal direction is asymmetrical. When the subject looks left on the horizontal off axis, the PSF appears right of the optical axis of the subject eye. When the subject looks right the PSF is located left of the optical axis. The location of the PSF on the vertical off axis appears above the optical axis when the subject looks up. When the subject looks down the double pass PSF is located below the axis. The PSFs of the human eye recorded at varying off-axis angles are presented. Asymmetrical results suggest a more dynamic process in the optical system of the eye perhaps driven by the complicated outer or inner ocular structure.
Laser-induced thermal-elastic stress waves are of importance both in therapeutic applications and in potential morbidity associated with laser surgical procedures. Recent experiments have shown that drug cytotoxicity can be enhanced with stress waves and that direct cell injury correlates with the stress gradient (stress rate of change). To systematically investigate the biological effects of stress waves, it is essential to vary individually the parameters of the stress wave. The Free Electron Laser (FEL) is the ideal laser for generating controllable stress waves. A unipolar stress wave can be characterized by its rise time, duration, peak pressure, and decay time. For short laser pulses, the rise time and decay time are dependent upon the absorption depth of the tissue and can be varied by changing the wavelength of the FEL. The duration of the stress wave can be changed by selecting a different number of micropulses from the FEL macropulse with Pockels cell. The peak pressure can be altered by varying the laser intensity. Results on water have confirmed that the individual parameters of the stress wave can be varied independently.
A theoretical model is presented to account for the experimental observation that infrared tissue ablation is optimized by the use of wavelengths near the amide II band of proteins. The model recognizes the partitioned absorption of IR photons between protein and water due to overlapping spectral features along with the dynamics of biopolymers, the loss of mechanical integrity in proteins, and the explosive role played by the vaporization of water. The theoretical foundation for this model can be found in previous accounts of thermal confinement, multicomponent models, and selective photothermolysis.
Glenn Edwards, Regan Logan, Michael Copeland, Lou Reinisch, Jeffrey Davidson, J. Johnson, Robert Maciunas, Marcus Mendenhall, Robert Ossoff, Jerri Tribble, Jay Werkhaven, Denis O'Day
The Vanderbilt free-electron laser has been operational for several years. This extended collaboration has been investigating outstanding problems in biological physics and medical physics with several research goals in mind. Our most fundamental goal is to improve the understanding of intermolecular and intramolecular vibrational energy transfer mechanisms in biopolymers. Our approach is to pursue both experimental and theoretical research addressing vibrational energy transfer in biological physics. The remaining goals can be summarized as the application of our fundamental advancements in polymer physics to molecular biology and to clinical and surgical medicine.
Tunable, pulsed radiation sources in the ultraviolet, visible, and infrared wavelength ranges offer novel opportunities for investigating laser-induced biomedical effects. Free-electron lasers (FELs) deliver continuously tunable, pulsed radiation in the infrared, providing the capability to selectively target radiation into the vibrational modes of water or other biopolymers. Experimental techniques for measuring the absorption spectra of biological samples are described. These spectra indicate wavelengths that potentially serve as the basis for laser-induced biomedical effects. Some practical considerations for infrared, visible, and UV spectroscopy of biological samples are summarized, and the connection between biomedical research and more fundamental investigations of vibrational energy transfer are emphasized.
Free-electron lasers (FELs) provide tunable, pulsed radiation in the infrared. Using the FEL as a pump beam, we are investigating the mechanisms for energy transfer between localized vibrational modes and between vibrational modes and lattice or phonon modes. Either a laser-Raman system or a Fourier transform infrared (FTIR) spectrometer will serve as the probe beam, with the attribute of placing the burden of detection on two conventional spectroscopic techniques that circumvent the limited response of infrared detectors. More specifically, the Raman effect inelastically shifts an exciting laser line, typically a visible frequency, by the energy of the vibrational mode; however, the shifted Raman lines also lie in the visible, allowing for detection with highly efficient visible detectors. With regards to FTIR spectroscopy, the multiplex advantage yields a distinct benefit for infrared detector response.
Our group is investigating intramolecular and intermolecular energy transfer processes in both biopolymers and more traditional materials. For example, alkali halides contain a number of defect types that effectively transfer energy in an intermolecular process. Similarly, the functioning of biopolymers depends on efficient intramolecular energy transfer. Understanding these mechanisms will enhance our ability to modify biopolymers and materials with applications to biology, medecine, and materials science.
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