摘要 :
We studied RPE cell damage mechanism for laser duration from 100 femtosec to 5 microsec, and we have investigated the dependence of threshold fluence for cell damage on the laser spot size on the RPE. These results will be summari...
展开
We studied RPE cell damage mechanism for laser duration from 100 femtosec to 5 microsec, and we have investigated the dependence of threshold fluence for cell damage on the laser spot size on the RPE. These results will be summarized in the report. Our current method for studying call damage mechanism in the RPE is stroboscopic time resolved microscopy, which allows us to image the transient microscopic bubble formation inside the RPE tissue ex vivo where the cells following pulse laser irradiation. This technique works well in RPE tissue ex vivo where the strobe light transilluminates the specimen. Since our ultimate goal is to detect the existence of these micobubbles in vivo, we have set up a stroboscopic imaging system in epi-illumination geometry. However, the image quality obtained in this way is inferior to that obtained by transillumination, most likely because of the strong angular dependence of the back-scattered light by the spherical bubbles. It is thus difficult to identify the extent of bubble formation at the RPE by this method.
收起
摘要 :
The transport of relativistic electrons1 generated in wire and foil targets by short-pulse lasers is examined with the new e-PLAS simulation code based on implicit-moment/ hybrid2 techniques. In a 50 m diameter Cu wire (Zeff = 15)...
展开
The transport of relativistic electrons1 generated in wire and foil targets by short-pulse lasers is examined with the new e-PLAS simulation code based on implicit-moment/ hybrid2 techniques. In a 50 m diameter Cu wire (Zeff = 15) as recently illuminated on the TITAN LLNL laser, for example, a 1.7x1020 W/cm2 simulated laser beam delivering a flat 30 m spot from the left (with 40 % absorption) generates the hot electron density profile depicted below at 940 fs. The peak hot density in the laser spot is approximately 3x10(21) electrons/cm3. This density drops to 3x10(19) electrons/cm3 200 microns into the wire. A peak temperature of 2 keV is achieved through Joule heating of the background electrons in the wire head near the deposition surface; a significantly lower approximately 0.4 keV is achieved in the wire body. Here, 300 MG thermoelectric B-fields are also calculated. Parameter studies relate the hot electron stopping to the surface B-field, modest drag slowing, and the background cold electron resisitvity, which is bleached by background heating to low values at late times.
收起
摘要 :
The first dissertation investigated the shaping of hot pressed S3N4 with a high power CW C02 laser. The laser was used to heat the surface of a workpiece forming a groove by vaporization. Shaping was accomplished by overlapping th...
展开
The first dissertation investigated the shaping of hot pressed S3N4 with a high power CW C02 laser. The laser was used to heat the surface of a workpiece forming a groove by vaporization. Shaping was accomplished by overlapping the grooves. Results are given showing that groove shapes and material removal rates are independent of irradiation environment. This suggests that decomposition is responsible for the removal of material. An analysis of multiple overlapping grooves indicated, in some cases, that the shape of the overlapped groove differs significantly from that of the single pass groove. To further evaluate the potential of this shaping processs, 4-point bend specimens were tested with laser machined surfaces. In second dissertation, a laser machining proces for shaping non-solid of revolutiuon shapes with a high power carbon dioxide laser operating in pulse mode was studied and developed. Graphite was used as the model material to develop the process and it was demonstrated that the process can successfully be adapted to machine silicon nitride. Materials were removed, a layer at a time and by controlling the boundaries of the layers: a contour shape can be formed. A detail parametric study was conducted to determine the controlling variables in machining grooves and layers. The effects of angle of beam incidence and polarization on groove shape was studied and analysed on the basis of Fresnel's Law of Reflection. Distortion introduced by reflections at the end of a layer was analysed and corrected by reorientation(tilting) of the workpiece with respect to the optical axis of the laser beam. Smoother surface finishes were obtained by defocussing the laser beam so the focal plane was above the workpiece.
收起
摘要 :
This article reports on studies of continuous wave high power CO2 laser beamatmospheric propogation near the surface. Laser powers are 3kW-5kW. Propagation distances are 77m-107m. Patterns of changes associated with laser receptio...
展开
This article reports on studies of continuous wave high power CO2 laser beamatmospheric propogation near the surface. Laser powers are 3kW-5kW. Propagation distances are 77m-107m. Patterns of changes associated with laser reception spots, given rise to by beam distortion and atmospheric influences, were obtained.
收起
摘要 :
This paper was based on the transmission theory of elliptical Gaussian beamfluxes in deriving some transmission equations for the threshold beam spots of laser weapon simulators, in order to revise and expand the expressions for t...
展开
This paper was based on the transmission theory of elliptical Gaussian beamfluxes in deriving some transmission equations for the threshold beam spots of laser weapon simulators, in order to revise and expand the expressions for the threshold beam spots, their maximum range, the extinction function and the irradiance in ADA 102276, and also in this paper, verification tests were carried out.
收起
摘要 :
This report identifies and discusses two distinct dynamic components in a mathematical model of the stochastic motion of a laser spot on a moving target as viewed from the position of the designator. One of these components is con...
展开
This report identifies and discusses two distinct dynamic components in a mathematical model of the stochastic motion of a laser spot on a moving target as viewed from the position of the designator. One of these components is contributed by manual tracking and possesses approximately second-order dynamics. The other component is contributed jointly by laser device and atmospheric propagation effects (scintillation) and exhibits nearly first-order dynamics. Both frequency-domain and time-domain analyses are pursued in comparing the mathematical model with a sample of spot motion test data. Algorithms for digital implementation of the components of the stochastic model are derived. The implementation is conceived as an input generator for a laser target signature model. There is an exposition of certain distortions which are produced in the autospectra of the stochastic components due to the implementation. Additionally,some statistical aspects of parameter estimation are presented. (Author)
收起
摘要 :
We have developed tools for accurately and economically mapping and inspecting damage and artifacts in the bulk as well as on the surface of meter- sized optics intended for use on large-scale lasers such as Beamlet and NIF. Optic...
展开
We have developed tools for accurately and economically mapping and inspecting damage and artifacts in the bulk as well as on the surface of meter- sized optics intended for use on large-scale lasers such as Beamlet and NIF. Optics are illuminated by white light through the optic edge or externally at grazing incidence using linear fiber- optics arrays. The mega-pixel camera records a digital map of the entire optic with precise addresses of highlighted artifacts. From these coordinated, artifacts are located and digitally recorded with resolution of less than 5 microns using a long-working-distance microscope. Total internal reflection of edge illumination efficiency couples light into the entire optic to inspect for bulk artifacts, such as bubbles, inclusions, edge-cladding flaws and laser- induced damage as well as surface scratches and pits which propagate into the substrate. Surface contamination such as dust, fingerprints, coating flaws, and cleaning flaws are highlighted by external grazing illumination. The procedures permit accurate recording of the evolution of damage after many laser shots as well as correlation of damage from one optic to the next in a laser chain.
收起
摘要 :
In the early 1970's the Army Materiel Test and Evaluation Directorate, White Sands Missile Range, undertook a multi-year test methodology development program to perfect techniques and develop hardware required to evaluate an antic...
展开
In the early 1970's the Army Materiel Test and Evaluation Directorate, White Sands Missile Range, undertook a multi-year test methodology development program to perfect techniques and develop hardware required to evaluate an anticipated family of Army Laser Designators. Standard laboratory test instruments and procedures were readily available; however, the more complex problems of energy distribution within the laser beam were not resolved. A concurrent development, at this point, was a shift toward acquiring data, wherever possible, in an image format, and subsequently processing the data on a large-scale digital computer. These two ideas led to the development and subsequent procurement of a data acquisition system known as the Laser Spot Scanning System or LS3. The LS3 is a gated, image-intensified silicon vidicon camera with a standard S-1 response. The camera is equipped with a 1.06 micrometer spike filter mounted on a 15 mm to 150 mm zoom lens. Mounted on top of the camera's environmental container is a YAG 444 series photo-diode with associated optics. The photo-diode controls the gating function of the camera. Control of the camera is remoted, and the output recorded on a standard video tape recorder and/or displayed on a standard closed circuit television monitor.
收起
摘要 :
Large-spot laser damage thresholds were measured for bowl-feed-polished CaF2 and sapphire windows (bare and antireflection-coated) and for highly polished copper mirrors (bare and carbyne-coated) at DF chain-laser wavelengths (3.5...
展开
Large-spot laser damage thresholds were measured for bowl-feed-polished CaF2 and sapphire windows (bare and antireflection-coated) and for highly polished copper mirrors (bare and carbyne-coated) at DF chain-laser wavelengths (3.58-4.78 micrometers). The chain reaction between F2 and D2 was initiated by a magnetically confined electron beam, producing DF-laser outputs of 10 to 20 J in pulses of 0.6 to 0.9 microseconds (FWHM) duration. Energy extracted from a transmission-coupled unstable resonator was focused by means of a CaF2 lens. A soft-aperture technique was employed to suppress effects of Fresnel diffraction so that uniform (top-hat) intensity profiles were obtained along the focusing beam. With this laser system, commercially available antireflection-coated CaF2 and Al2O3 samples were tested and found to have damage thresholds from 17 to 28 J/sq cm 2. Significantly larger damage thresholds were observed for uncoated, polished samples of Al2O3, but damage resistance of uncoated polished CaF2 was found to equal that of the best antireflection-coated CaF2 samples. A highly polished copper mirror had the highest damage threshold of all the materials tested, i.e., 58 J/sq cm 2.
收起
