Green Laser Light Research Articles

Optical activity in the metastable state of Na 2[Fe(CN) 5NO]·2H 2O crystals

The Na 2[Fe(CN) 5NO]·2H 2O crystal is transformed into its metastable state when it is irradiated with blue or green laser light at low temperatures below 160K. This work describes newly found anomalous optical properties in the metastable state. Under the observation with white light illumination and crossed polarizers, a bright color is visible due to the incomplete extinction. The spectrum of this color has a rather narrow band-width of about 15nm. The wavelength of the maximum intensity, λ MAX, shifts with the wavelength of the irradiated laser light, but is not affected by the thickness of the sample. The incomplete extinction at a narrow range of wavelengths can be explained in terms of the optical activity and the accidental coincidence of two principal indices of refraction at λ MAX. This suggests that the optical activity arises in the metastable state.

Optimized reflection imaging in laser confocal microscopy and its application to neurobiology: Modificationsa to the biorad MRC‐500

AbstractReflection images of biological specimens recorded using laser‐scanned confocal microscopes are frequently degraded by low image contrast, poor signal to noise, and the inability to image deeper in the specimen than 10–20 μm. Artifactual internal reflections often are a source of these limitations, but they can be reduced or eliminated by the use of polarization components. Designs for the incorporation and optimum use of these components in the BioRad MRC‐500 are presented. The effect of the internal reflections was reduced by optimum rotational alignment of both a quarterwave plate and an analyzer. Absorption of incident and reflected light by both the stained cells and the background tissue of the specimen also seriously degrades image signal to noise, and is a function of specimen preparation and the wavelength of light used. The red line of a helium‐neon laser was not as readily absorbed as the blue and green lines of an argon‐ion laser when imaging neurobiological specimens contrasted with either peroxidase/diaminobenzidine or Golgi staining. Specimens many times thicker were imaged with red laser light and with superior image quality compared with blue or green laser light.

Plasma evolution from laser-driven gold disks. I. Experiments and results

Gold disk targets were irradiated with green (λ=0.53 μm) laser light at intensities between 0.5 and 5×1014 W/cm2 using shaped laser pulses. Plasma conditions near and below critical density (nc≂4×1021/cm3) were determined from three diagnostics. Streaked one-dimensional images of the M-band emission (2–3.5 keV) along the laser axis yield the peak emission trajectory. Temporally and spatially averaged measurements of the hard x-ray spectrum (4–25 keV) were used to determine the average coronal electron temperature. Holographic interferometry was used to determine the electron density profiles and scale lengths along the laser axis. The peak emission trajectory, electron temperature, and scale lengths are all in good agreement with simulations, but the magnitudes of the electron density profiles are not, as discussed in an accompanying paper [Phys. Fluids B 2, 2448 (1990)].

The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro

The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin either (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50-100 mW/cm2 and exposure times (2-15 s), representing incident pulse energy fluences of 2.5-5 mJ/cm2 and energy densities of 0.1-1.5 J/cm2. The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm2 (LD90 = 0.54 J/cm2). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm2).

Characterization of sub-10-μm 30-ps flash duration point sources for x radiography

Flash x radiography can provide important information about high-density, high-opacity plasmas. Experiments at KMS investigated the characteristics of point x-ray sources produced when coated fibers, wires, and mounted particles were irradiated with high intensity (I>1016 W/cm2) green laser light. The target materials Bi, CsI, Au, and Ag were evaluated in the areas of (1) the spatial and temporal resolutions that can be achieved, (2) the effect of source size and laser pulse duration on x-ray signal strength, and (3) the practical considerations associated with using the technique to actually obtain radiographs of accelerated polyvinyl alcohol shells.

White Light Phase-conjugate Lensless Image Projection

Abstract The lensless projection in white light of images with ∼ 30 µ;m resolution has been demonstrated using phase-conjugate reflections from a self-pumped BaTiO3 crystal which was simultaneously illuminated with red, green and blue laser light. The relative beam incident intensities were crucial in reducing holographic photoerasure and cross-talk effects.

Measurements of laser plasma coronal conditions and thermal transport with time-resolved x-ray spectroscopy.

This paper presents a detailed characterization of the plasma conditions near the critical density of a laser-produced plasma. Solid spherical plastic targets with small aluminum tracer dots buried below overcoated plastic layers have been uniformly illuminated with green laser light at irradiances of ${10}^{14}$--${10}^{15}$ W/${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Time-resolved temperature and density profiles were obtained by using x-ray emission spectroscopy. Detailed comparisons with hydrodynamic simulations show that the thermal transport is well characterized by a flux limit of 0.1.

532-nanometer green laser beam treatment of superficial varicosities of the lower extremities.

Green laser light at 532 nm was utilized in an attempt to thrombose and blanch superficial varicosities of the lower extremity in 14 patients. Selective vascular damage with sparing of overlying skin was the theoretical rationale for use of green light. Seven of the 14 patients achieved satisfactory results (total or near-total obliteration of vessels without scarring) after a 6-month period of observation.

Quantitative analysis of immunological reactions on silicon surfaces by multiple-angle Brewster angle reflectometry

An optical biosensing instrument has been developed for the quantitative analysis of immunological reactions on biochemically sensitized surfaces. It is based on the measurement of reflectance changes of polarized laser light incident on high refractive index substrates at angles close to the pseudo-Brewster angle. Multiple-angle Brewster angle reflectometry (MABAR) has been used to investigate the binding of anti-human serum albumin (a-HSA) to human serum albumin (HSA) coated silicon surfaces. The concentration dependence and reaction kinetics of antibody-antigen complex formation have been studied using red and green He-Ne laser light. A significant increase in sensitivity has been observed with green light.

Haematoporphyrin photosensitisation treatment of experimental choroidal melanoma.

Greene amelanotic melanoma transplanted to pigmented rabbit choroid provided the experimental model for studying photosensitisation treatment of choroidal melanoma. Administration of haematoporphyrin derivative (HPD) and subsequent photoradiation with green laser light destroyed much of the melanoma with minimal side effects to normal uvea. The results of treatment were documented by fundus photography and fluorescein angiography. By 24 hours, the irradiated melanoma and surrounding retina appeared whitened and necrotic, with complete non-perfusion of the area. Over the course of one week, the clinical appearance did not alter. Histopathology at 24 hours and 8 days confirmed massive central tumour necrosis, but in all cases this was subtotal. Viable cells were evident at the periphery and also along the base of the tumour. Experimental evaluation of treatment parameters is required before this technique can be recommended for human choroidal melanoma.

Observations of the Rayleigh–Taylor instability in laser imploded microballoons

Mass-modulated plastic microballoons have been ablatively imploded by green (0.53 μm) laser light at an absorbed irradiance of 2×1013 W cm−2. Temporally growing spikes are seen on the outside surface of the target; evidence of the occurrence of mass redistribution indicates that the spikes are due to the Rayleigh–Taylor instability. A growth rate of 0.52±0.06 of classical has been inferred.

Laser pulse‐induced transitions on surfaces of bulk material, traced by thermal and secondary electrons

AbstractThermal and electron beam‐released electrons were exploited to probe the dynamics of surface modifications, induced by a Q‐switched frequency‐doubled Nd:YAG laser within areas of 100 μm Φ on bulk silicon and metals. Changes of surface geometry and phase transitions show up as pronounced peaks and steps in the emitted electron currents. They occur within Φ 200 ns after the laser pulse and consume times from less than 5 ns up to 200 ns.Applications of pulsed radiation power for surface machining, recrystallization and vitrification or for production of microstructures on bulk substrates for integrated devices are continually extending (Bäuerle 1984). Laser pulses are most frequently used, in spite of their inhomogeneous absorption, as contrasted to electron and ion beams, because of easy handling of power and no need for vacuum in many cases. The diagnostic methods usually applied to probe the dynamics of pulse‐induced transitions are still those introduced at the beginning of the “laser annealing” technique, exploiting light reflection and transmission, and to a minor extent x‐ray and electron diffraction, mass spectrometry and electrical conductivity (Khaibullin 1984, Larson 1984). Naturally, each diagnostic tool has a restricted range of useful application, so further methods combining high temporal and spatial resolution and equally applicable to semiconductors and metals are highly desirable.Thermal and secondary electrons are expected to be susceptible to changes of temperature and geometry of a surface, occuring during laser pulse machining. In fact, photon‐assisted thermal electron emission was used to probe thermal relaxations in laser‐pulsed semiconductors (Leung and van Driel 1984), however, the thermal electrons were not used to trace geometric modifications. Furthermore, secondary electrons have not yet been tested as a probe for very fast single effects. This report describes first results, demonstrating the usability of emitted electrons as a probe for nanosecond transitions on surfaces of bulk material.An electron optical equipment was built, consisting of electron gun, condensor lens and specimen chamber, allowing synchronized laser and electron beam pulsing of the specimen. Its surface was probed by the photo‐thermally emitted electrons and ions or by the secondary and backscattered electrons, which were generated by the focussed primary electron beam. The latter was pulsed in order to suppress electron radiation damage. For laser treatment a pulse of a Q‐switched frequency‐doubled Nd:YAG laser (FWHM 20 ns) was focussed with a lens and a dielectric mirror onto the specimen, which could be viewed with a microscope for aligning the laser and the primary electron beam. Both beams had a diameter of 100 μm (FWHM) on the specimen. The emitted charges were collected by a shielded scintillator/multiplier detector of the Everhart‐Thornley type, having a rise time of = 3 ns and being protected against excessive green laser light by an edge filter. Despite the simp1e set‐up, rapid changes of the surface by vaporization, melting, solidification could readily be observed within areas down to 30 μm Φ on the nanosecond time scale. Flow and disrupture of liquid layers occur after the laser pulse, delayed by several 10 ns (Figs. 1 and 2). The dispersion of metal liquids by temperature‐induced gradients of the surface tension may consume times from below 5 ns (Fig. 2a) up to 200 ns (Fig. la). It is signalized by a large increase of electron emission, probably due to Schottky effect at charged transient tips within the disintegrating liquid. First order phase transitions involving latent heats are readily indicated by thermal electrons. Solidification of a melt, for instance, shows up in the emission current as a prolonged plateau with an abrupt drop within 20 … 40 ns (Fig. 3). Summarizing, secondary and thermal electrons are well suited to trace single transitions on the surface of bulk material on the nanosecond‐micrometer scale. In contrast to other diagnostic probes the spatial resolution may be increased well below 1 μm by improved focussing of the primary electron beam.

Hologram Recording With A New Photopolymer System

Holography with a new photopolymer system, Polaroid DMP-128, is described. Films of DMP-128 from an aqueous solvent are coated on either solid or flexible substrates. The resulting films, when stored dry, have a shelf life that exceeds nine months. The dry films are inactive and must be incubated for a few minutes in an environment of approximately 50% RH before laser expo-sure. Recording is possible with either blue (442 nm, 488 nm), green (514 nm), or red (633 nm, 647 nm) laser light. Exposure of 5 mJ/cm2 is sufficient for high diffraction efficiency (80% to 95%) transmission holograms, while 30 mJ/cm2 is required for bright reflection holograms. It is not necessary to exclude atmospheric oxygen during hologram recording. Refractive index modulation of 0.03 is routinely achieved. After laser exposure a uniform white-light illumination is used to complete the photopolymerization. A single processing bath yields holograms with good environmental stability. An additional processing bath yields images with exceptional resistance to high humidity.

Gain spectra of GaSe

We report on our detailed measurements of the gain spectra in the region just below the transition of the direct free exciton ground state. We use the very sensitive method recently introduced by Hvam. The crystals, immersed in superfluid He, are excited by green laser light (532 nm) the intensity of which is varied from 0.1 to 3 MW cm −2. At excitation intensities above about 0.3 MW cm −2, all samples show a wide band which starts at about 5970 Å and peaks at round 6000 Å. The high energy edge of this well-known emission is independent of excitation intensity; its peak, however, shifts to low energies as the excitation increases. Induced absorption is virtually absent. In addition, our gain spectra show a structure of several weak lines which varies from sample to sample. The measured gain spectra are compared with the predictions of the recently developed theories of stimulated emission of strongly excited semiconductors.

ESR study of the ionic radical species in an irradiated single crystal of isocytosine

The radicals in a single crystal of isocytosine, irradiated with gamma rays at 77 K, were studied with the ESR spectroscopy. Three types of radicals were detected. One of them, whose ESR spectrum exhibits two 14N and two 1H coupling nuclei, is interpreted to be the isocytosine cation radical. The second species, characterized by a doublet structure, is thought to be formed by a proton transfer to the isocytosine anion. The third species could not be analysed in detail. All three species are unstable upon warming or upon illumination with green Ar laser light.

Acousto-optic processing for real-time and adaptive memory applications

Two different types of acousto-optic correlators, a real-time large time-bandwidth (∼3000) device and a memory correlator, have been developed. The real-time correlator utilizes successive interactions of a cw laser sheet beam with two “live” surface acoustic waves (SAW's) propagating in the same direction along long (14 cm) lithium niobate (LiNbO3) and bismuth germanium oxide (BGO) crystals that are placed side-by-side. The almost 2:1 SAW velocity ratio for these crystals permits a signal propagating in the LiNbO3 to pass one propagating in the BGO. Focusing the emerging SAW-modulated laser beam onto a nonlinear photo-diode results in an output proportional to the correlation integral. In the memory correlator, a SAW pattern is stored initially (as changes of the index of refraction in LiNbO3) by illuminating the LiNbO3 with high-intensity, short-duration pulses of green laser light during propagation of the (10 MHz) SAW signal to be stored. Subsequently, a live signal may be correlated with the stored signal by modulating a low-intensity laser sheet beam with both the live and stored signals, and focusing the emerging beam onto a photo-diode. Memory storage times of a few months have been demonstrated. Both device types have successfully correlated complex waveforms, such as FM chirps and Barker codes.

Design and Performance of a 20-Stage Digital Light Beam Deflector

This paper gives optical design considerations and experimental results of a 20-stage digital light beam deflector consisting of a series of nitrobenzene Kerr cells and birefringent calcite prisms. The laser beam is deflected into a two-dimensional raster of 1024 by 1024 positions with a deflection rate of 500 kHz. The optical transmission of the deflector itself is 79% for green laser light. Data about background light and resolution as well as display examples showing alphanumerics and graphics are given.