Green Laser Light Research Articles

LASER-INDUCED AFTERIMAGES IN HUMANS

Afterimages induced by incoherent light sources have been studied as complex visual perceptions for over 200 years; however, individuals who have viewed a coherent source (a laser) on-axis have reported visual experiences unlike those observed for full-field flashes from incoherent sources. In the present study, 10 volunteers viewed all combinations of blue, green, and red laser light and background colors that matched the wavelengths of the laser sources (a total of 9 conditions). The bright focal (50 μm retinal irradiance diameter) 3-sec. exposures (approximately 9 log trolands-40% of the maximum permissible exposure level) given to the volunteers were administered as they performed a simulator tracking task. A 50/50 mirror (a mirror which reflected 50% of the laser beam into the optical pathway while allowing the 50% of the light from the visual scene to pass through the mirror) permitted simultaneous intrabeam viewing of the laser source and the scene. The volunteers were asked to report what they saw immediately after the laser was turned off and 1-min. postexposure. The immediate reports indicated that the image they observed was the same color as the laser source and not the complementary color. Also, the images were often surrounded by well-defined borders and, regardless of laser's or background's color, were generally red. One minute following presentation of the laser light the images seen were predominantly purple, dark or no longer present; however, the edge color when present generally appeared red. The immediate appearance of the images was inferred to be neural in nature and not photochemical. These results suggest the properties of the laser source, i.e., coherency, monochromaticity, and the laser's capacity to place an intense beam of light in a small retinal area, all contributed to the unique appearance of the postflash images.

Red, blue, and green laser-light generation from the NYAB nonlinear crystal

Continuous wave red, green, and blue laser light are gener- ated under IR-pumping crystals of Nd 31 :YAl3(BO3)4 by a Ti:sapphire la- ser. The red (669-nm) and green (532-nm) radiations are obtained by self-frequency doubling of the fundamental laser lines at 1338 nm ( 4 F3/2! 4 I 13/2 channel) and 1062 nm ( 4 F3/2! 4 I 11/2 channel), respec- tively. Blue laser radiation (458 nm) is achieved by self-sum-frequency mixing of the main laser line at 1062 nm and the pumping radiation at 807 nm. The main spectroscopic and nonlinear properties of this crystal are included. In addition, a simple model devoted to optimizing the blue radiation is provided. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00211-1)

Development of holographic methods for investigating a moving free surface, accelerated by laser-induced shock waves

Holographic methods developed to study the behavior of surfaces shocked by high power lasers are reported. Shock waves of the order of hundreds of kilobars are generated in Sn targets 50-μm thick, by a Nd:YAG laser system with a wavelength of 1.06 μm, a pulse duration of 7.5 ns FWHM, and irradiance in the range (1.0–2.6)·1013 W/cm2. Two configurations of off-axis holography were applied: holograms based on forward scattering, and holograms of both backward and forward scattering. The hologram is produced by scattering of a pulse, 6.7 ns (FWHM), of green laser light synchronized with the laser that generates the shock wave. Holograms of the topology of the rear surface of shocked Sn targets moving in vacuum and in air (at atmospheric pressure) are reported.

Red and Green Laser Doppler Compared with Capillary Microscopy to Assess Skin Microcirculation in the Feet of Healthy Subjects

Skin microvasculature consists of nutritive capillaries and subpapillary arteriolar and venular plexus connected by arteriolovenular anastomoses. Capillary perfusion is of paramount importance for skin viability. Recently a new combined laser Doppler instrument has become available, featuring a combination of near-infrared (RL; 780 nm) and green (GL; 543 nm) laser light sources. Theoretically, the red laser will penetrate deeper, whereas the green laser will read fairly superficially. This may enable differentiation between the more superficial, i.e., capillary, and the deeper skin layers. To test this hypothesis, the combined laser Doppler technique was compared with nail fold capillary microscopy in the feet of 10 healthy subjects. Seven males and 3 females with a median age of 26 (range 20–42) years and without arterial pathology were investigated. The laser Doppler (Periflux 4001, Perimed) was equipped with a special dual probe conducting both GL and RL. The probe was attached to the pulp of the big toe (with many AV-shunts) and to the nail fold, at the site where capillary microscopy was performed too. Laser Doppler and capillary perfusion was assessed at rest and during postocclusive reactive hyperemia. These measurements were performed both in the sitting and the supine positions to test the postural vasoconstriction response. Median resting and hyperemic skin perfusion with GL were lower (P < 0.01) than with the RL in both areas and positions, except for the resting value in the sitting position on the dorsum of the toe. Plantar perfusion was found significantly higher than dorsal perfusion only with the RL in the supine position (P < 0.01). GL and RL on the plantar, but not the dorsal, side showed a significantly decreased perfusion upon dependency (P < 0.05), both at rest and during hyperemia. In contrast, resting and peak capillary velocity did show a decrease on dependency (P < 0.05). Although the green laser measures a lower perfusion than does the red laser, which is likely to be derived from more superficial skin layers, it does not show a reactivity similar to that measured with capillary microscopy. Thus, it is questionable whether the green laser exclusively measures capillary perfusion.

Red, green, and blue laser light from a single Nd:YAl3(BO3)4 crystal based on laser oscillation at 1.3 μm

Laser radiation corresponding to the three fundamental colors (red, green, and blue) has been generated from the same Nd:YAl3(BO3)4 crystal, operating on a fundamental laser wavelength of 1338 nm in an end-pumping configuration. Continuous wave generation was obtained by pumping with a tunable Ti: sapphire laser. Red (669 nm) has been obtained by self-frequency doubling of the fundamental laser line. Green (505 nm) and blue (481 nm) have been obtained by self-sum-frequency mixing of the fundamental laser radiation at 1338 nm and the pump radiation (807 nm for green and 755 nm for blue).

Optical CT reconstruction of 3D dose distributions using the ferrous-benzoic-xylenol (FBX) gel dosimeter.

In recent years, magnetic-resonance imaging of gelatin doped with the Fricke solution has been applied to the direct measurement of three-dimensional (3D) radiation dose distributions. However, the 3D dose distribution can also be imaged more economically and efficiently using the method of optical absorption computed tomography. This is accomplished by first preparing a gelatin matrix containing a radiochromic dye and mapping the radiation-induced local change in the optical absorption coefficient. Ferrous-Benzoic-Xylenol (FBX) was the dye of choice for this investigation. The complex formed by Fe3+ and xylenol orange exhibits a linear change in optical attenuation (cm-1) with radiation dose in the range between 0 and 1000 cGy, and the local concentration of this complex can be probed using a green laser light (lambda = 543.5 nm). An optical computed tomography (CT) scanner was constructed analogous to a first-generation x-ray CT scanner, using a He-Ne laser, photodiodes, and rotation-translation stages controlled by a personal computer. The optical CT scanner itself can reconstruct attenuation coefficients to a baseline accuracy of < 2% while yielding dose images accurate to within 5% when other uncertainties are taken into account. Optical tomography is complicated by the reflection and refraction of light rays in the phantom materials, producing a blind spot in the transmission profiles which, results in a significant dose artifact in the reconstructed images. In this report we develop corrections used to reduce this artifact and yield accurate dosimetric maps. We also report the chemical reaction kinetics, the dose sensitivity and spatial resolution (< 1 mm3) obtained by optical absorption computed tomography. The article concludes with sample dose distributions produced by "cross-field" 6 MV x-ray beams, including a radiosurgery example.

Photodynamic therapy of superficial basal cell carcinomas using exogenous 5‐aminolevulinic acid and 514‐nm light

AbstractObjective The evaluation of the effectiveness of topical photodynamic therapy with 5‐aminolevulinic acid (5‐ALA) and green laser light on superficial basal cell carcinomas.Background Topical photodynamic therapy with exogenous 5‐ALA and visible or red laser light has been used up to now for the treatment of superficial non‐melanoma skin tumors.Patients and methods Four patients with nine superficial carcinomas participated in this study. The tumors were irradiated with green laser light 5 h after the application of cold cream with 20% aminolevulinic acid under occlusive dressing.Results All nine lesions were resolved with a single treatment and clinical evidence of recurrence was observed in one tumor 1 year after the therapy.Conclusion Topical photodynamic therapy with exogenous 5‐ALA and green laser light is very effective for superficial basal cell carcinomas.

Photodynamic therapy of superficial basal cell carcinomas using exogenous 5-aminolevulinic acid and 514-nm light

Objective The evaluation of the effectiveness of topical photodynamic therapy with 5-aminolevulinic acid (5-ALA) and green laser light on superficial basal cell carcinomas.Background Topical photodynamic therapy with exogenous 5-ALA and visible or red laser light has been used up to now for the treatment of superficial non-melanoma skin tumors.Patients and methods Four patients with nine superficial carcinomas participated in this study. The tumors were irradiated with green laser light 5 h after the application of cold cream with 20% aminolevulinic acid under occlusive dressing.Results All nine lesions were resolved with a single treatment and clinical evidence of recurrence was observed in one tumor 1 year after the therapy.Conclusion Topical photodynamic therapy with exogenous 5-ALA and green laser light is very effective for superficial basal cell carcinomas.

Surf produced aerosol

A unique source of aerosol found in the coastal environment is the action of the breaking waves near the shore. This process is unique among wave generated aerosol processes because these aerosol are produced even when there is no wind at the site of the aerosol production. The major cause of this phenomenon is distant oceanic storms which produce long wavelength oceanic swell which then propagate for long distances and break on various types of shore lines. These shore lines can be gently sloping rocky or sand beaches, cliffs, or off shore reefs. Surf produced aerosol have usually been considered negligible because of the narrow width of the generating area when the effects of marine aerosol are discussed. They nevertheless exist and their effects can be of local importance. On days of heavy surf, a long narrow cloud stretching along the coastline can be seen when conditions are right, and the deposition of salt nuclei from surf produced aerosol are common near a heavy surf line during on shore winds.This paper utilizes the data recently obtained from a series of experiments from the Electro Optical Propagation Assessment in Coastal Environments, (EOPACE) effort, which has as one of its objectives the determination of the impact of surf produced aerosols in the propagation in infrared radiation. These experiments were carried out in both San Diego and in Monterey Bay, California.The experiments discussed here use several techniques to detect and measure the physical aspects of surf produced aerosol. The primary sources of information were obtained from: 1.Aerosol size distribution spectrometers, condensation nuclei counters, particle volume meters, visibility meters and meteorological instruments mounted at various positions and elevations along a pier, on a beach, and on a small boat.2.The photographic results of the scattering of surf aerosol by a visible laser beam spread vertically into a 45 degree sector of a circle but of very thin thickness.3.The infrared transmission along a low altitude 3.5 micron transmissometer path which includes a surf zone.The initial analysis of the EOPACE data indicates that indeed, the surf produced aerosol cloud is not uniform although it might appear so from looking at it from the outside. Videos and still photographs of the surf zone illuminated by the thin wafer of green laser light at night probe into the interior of this cloud and show a dynamic aerosol production process involving upward projecting streams of aerosol and the gravitational separating of various sizes of these aerosol.

Off-axis holography of laser-induced shock wave targets

Shock waves of the order of hundreds of kilobars are produced in a tin foil 50 μm thick by a Nd:YAG laser system with a wavelength of 1.06 μm, pulse width of 7 ns [full width at half-maximum (FWHM)] and irradiance in the range (1.4–2.4)×1013 W/cm2, focused to a spot of 200 μm. Off-axis holographic measurements of the target, after 0.5 and 1 μs from the shock arrival, are reported. The hologram is produced by backscattering of a pulse, 6.5 ns (FWHM) of green laser light, from the ejected material from the target.

A synergy of technologies: Combining laser microsurgery with green fluorescent protein tagging

When focused through an objective lens with a high numerical aperture, nanosecond pulses of high-intensity green (532-nm) laser light can be used to selectively destroy any cellular component whose boundaries can be defined by light microscopy. These components include, for example, chromosomes, spindle fibers, bundles of keratin, or actin filaments, mitochondria, vacuoles, and so forth. In addition, the definition of poorly resolved components can be enhanced for selective destruction by tagging one or more of their constituent proteins with green fluorescence protein (GFP). As a example we show that the centrosome in living PtK1 cells can be clearly defined, and then destroyed by green laser light, after transforming the cells with γ-tubulin/GFP fusion protein. In some transformed cells it is even possible to target and selectively destroy just one of the centrioles. Cell Motil. Cytoskeleton 38:311–317, 1997. © 1997 Wiley-Liss, Inc.

A synergy of technologies: Combining laser microsurgery with green fluorescent protein tagging

When focused through an objective lens with a high numerical aperture, nanosecond pulses of high-intensity green (532-nm) laser light can be used to selectively destroy any cellular component whose boundaries can be defined by light microscopy. These components include, for example, chromosomes, spindle fibers, bundles of keratin, or actin filaments, mitochondria, vacuoles, and so forth. In addition, the definition of poorly resolved components can be enhanced for selective destruction by tagging one or more of their constituent proteins with green fluorescence protein (GFP). As a example we show that the centrosome in living PtK1 cells can be clearly defined, and then destroyed by green laser light, after transforming the cells with gamma-tubulin/GFP fusion protein. In some transformed cells it is even possible to target and selectively destroy just one of the centrioles.

On the nature of metastable high-spin states formed during spin transitions in iron(II) complexes

The metastable high-spin (HS) state of iron is formed and fixed in iron(II) complexes during irradiation of a low-spin (LS) sample at low temperatures (~15 K) with green laser light at a wavelength of 514.5 nm [1]. This phenomenon was studied further in [2-4] (see also references in the above papers). In particular, it was shown that the metastable HS form is transformed back to the LS form by irradiation of crystals with red laser light at a wavelength of 752.7 nm. This effect may be of interest for molecular electronics, because molecular systems reversibly changing their state during irradiation with laser light may be used as optical keys in devices for processing and storage of optical data. M/Sssbauer spectroscopy is an essential tool for investigating light-induced spin transitions. The main results obtained by this method are the ratios between the LS and HS forms of iron, determined in various experimental conditions. The aim of this work is to draw attention to a new possibility offered by this method in studying the nature of the metastable HS state of Fe(II) formed in light-irradiated samples. Formulation of the problem will ftrst demand several explanations concerning the nature of the HS and LS forms of iron that are simultaneously observed in a particular temperature range during sharp spin transitions (ST) caused by temperature variations. In some papers (e.g., review [5]), it was shown that the HS form, which appears at increased temperatures, as well as the LS form, which appears during cooling, exist in crystals in the form of domains, i.e., certain regions in which all iron atoms are in the same spin state. An alternative form is chaotic distribution of iron atoms, which do not create regular regions. The domain structure of the LS and HS forms during ST is proved by hysteresis on the curves of the temperature dependences of the effective magnetic moment of the complex [5]. Let us consider the crystal in which the HS form appears during irradiation with light. It would be reasonable to ask whether this state exists in the crystal as dom~in~ or individual paramagnetic centers. The idea of using MiSssbauer spectroscopy for solving this problem is based oft the following fact. The HS state appears in the matrix of the LS state, in which iron atoms participate in cooperative interactions; hence the reaction of the atoms of the LS state to an admixture of the metastable HS state will depend on whether the atoms of the HS state form domains or individual paramagnefic centers in the low-spin matrix. We can assume that in the case of domains their influence on the structure of the LS state will be negligible due to the relatively low content of the neighboring pairs of atoms with different values of spins. The case is different when the HS centers are chaotically distribfited in the LS matrix. The changes in the spin states of iron atoms as a result of irradiation with light can lead to changes in the electronic states of the neighboring iron atoms of the LS matrix because of considerable differences in the metal-ligand distances of the LS and HS forms [7] and due to cooperative interactions in the LS matrix. The effect of the "large" paramagnetic admixture on the structure of the LS matrix will be more simaiflcant for crystals with strong cooperative interactions and for crystals with higher concentrations of admixtures. The "large" paramagnetic admixture loosens the structure of the LS matrix and decreases the covalence of the metal-ligand bond of the LS form, thus increasing the chemical shift c3LS of the M/Sssbauer line for the I~ form. Recently, we reported on a similar effect in [6], in which we studied the influence of iron substitution by zinc on the ST in the polynuclear Fe(ATr)3(NO3) 2 complex (ATr = 4-amino-l,2,4triazole). We found that the chemical shift of the LS form of the complex measured at 78 K monotonically increases with the concentration of zinc atoms. Tiffs effect was explained in terms of the model of steric strai-~ arising in crystals

Spray Visualization by Laser Sheet Tomography.

Laser sheet tomography was applied to the visualization of the cross section of a spray. In this method, fluorescent dye, eosine-Y(C20H6Br4Na2O), was used at a concentration of 10 g/1 of the injectant, water, and the light source which illuminated the spray was a Nd : YAG laser (532wavelength, 20ns pulse width) in laser sheet tomography. The thickness of the laser sheet which was scattered by the spray was measured to elucidate the effect of the concentration of fluorescent dye in the injected liquid. In the case of water without eosine-Y, multiscattered light-illuminated drops were observed outside of the laser sheet ; therefore the thickness of the laser sheet increased. However, in the case of water with eosine-Y, there were few drops which were illuminated by the multiscattered light, and only drops which existed within the laser sheet scattered green laser light and emitted the yellow fluorescent light of eosine-Y.

In vivo fluorescence kinetics and photodynamic therapy using 5-aminolaevulinic acid-induced porphyrin: increased damage after multiple irradiations

The kinetics of fluorescence in tumour (TT) and subcutaneous tissue (ST) and the vascular effects of photodynamic therapy (PDT) were studied using protoporphyrin IX (PpIX), endogenously generated after i.v. administration of 100 and 200 mg kg-1 5-aminolaevulinic acid (ALA). The experimental model was a rat skinfold observation chamber containing a thin layer of ST in which a small syngeneic mammary tumour grows in a sheet-like fashion. Maximum TT and ST fluorescence following 200 mg kg-1 ALA was twice the value after 100 mg kg-1 ALA, but the initial increase with time was the same for the two doses in both TT and ST. The fluorescence increase in ST was slower and the maximum fluorescence was less and appeared later than in TT. Photodynamic therapy was applied using green argon laser light (514.5 nm, 100 J cm-2). Three groups received a single light treatment at different intervals after administration of 100 or 200 mg kg-1 ALA. In these groups no correlation was found between the fluorescence intensities and the vascular damage following PDT. A fourth group was treated twice and before the second light treatment some fluorescence had reappeared after photobleaching due to the first treatment. Only with the double light treatment was lasting TT necrosis achieved, and for the first time with any photosensitiser in this model this was accomplished without complete ST necrosis.

Recent topics of optoelectronic materials in Japan: a review

Some recent topics of optoelectronic materials research in Japan are introduced. The topics include materials for blue and green laser light sources, materials for optical switches, and materials for optical fibers of various functions. Emphasis is put on the development of blue and green laser diodes, the third-order non-linear materials to be eventually used in optically controlled optical switches, optical amplifiers and non-oxide glass fibers for the infrared region.

11.7 mW green InGaAs-laser-pumpederbium fibre laser

A room-temperature erbium-doped fluoride glass upconversion fibre laser generated 11.7 mW of 544 nm continuous-wave laser light when pumped by a 150 mW, 971 nm InGaAs semiconductor laser. A similar laser system, enclosed in a compact (432cm3) package produced 4 mW of green laser light. A long time-constant hysteresis effect in the excitation mechanism, as well as active electronic noise reduction are discussed.

Clinical usefulness of the Hexascan. Treatment of cutaneous vascular and melanocytic disorders.

The Hexascan is an automated scanning laser handpiece originally developed to treat port-wine stains. It can be adapted to operate with most continuous wave laser systems delivering a variety of visible wavelengths. To review the use of Hexascan with 585-nm yellow dye laser light for cutaneous vascular disorders and 514-nm green argon light for benign cutaneous melanocytic disorders. The current clinical results, treatment parameters, indications, limitations, and complications of these procedures are discussed in a review format. In addition, a new clinical study of benign lentigines treated with green laser light is presented. Most benign lentigines showed considerable lightening or complete disappearance after one or two treatments. Other melanocytic disorders may also respond. Deep dermal lesions such as Nevus of Ota may be totally unresponsive. Both vascular malformations such as port-wine stains and hemangiomas are also treatable. The Hexascan device attached to a continuous wave tunable dye laser can successfully treat a wide variety of cutaneous vascular and melanocytic disorders in both infants and adults.

Depth of tissue sampling in the optic nerve head using laser Doppler flowmetry

Laser Doppler flowmetry (LDF) was performed on a simulated blood vessel in a model eye through optic nerve tissue sections in order to ascertain the ability to detect flow through them. LDF was performed using either near-infra-red or green laser light. Tissue section thickness ranged from 50 μm to 1000 μm. As expected, we found that our ability to detect flow with LDF decreased as we increased the thickness of optic nerve sections interposed between the LDF apparatus and the simulated blood vessel. We also found that the sampled depth of LDF increased with increasing separation of the optical detection fibre from the centre of the illuminated tissue volume. With adequate separation, we were able to detect flow with LDF through tissue sections of 1000 μm thickness using either near-infra-red or green laser light.

Copper vapor laser machining of polyimide and polymethylmethacrylate in atmospheric pressure air

A repetitively pulsed copper vapor laser (510 and 578 nm) is used to machine an opaque polymer (polyimide-Vespel) and a transparent polymer (polymethylmethacrylate-Lucite). Lucite is machinable by coating the surface with an ink which is semi-opaque to the green and yellow laser light. The repetition rate of the laser was 10 kHz with approximately 0.35 mJ/pulse and 3.5 W average power at the copper vapor laser wavelengths for a pulse width of 40 ns. The copper vapor laser thermally loads the target, generating thermal waves and sound waves in the gas which are investigated using HeNe laser beam deflection. The gas adjacent to the target is heated to steady state on the order of 100–400 s. Above the etching threshold, at approximately 10 mJ/cm2/pulse, the target is rapidly machined: 2-mm-diam, 2-mm-deep holes are drilled in 300 s in Vespel. At higher fluences of 100–150 mJ/cm2/pulse in 760 Torr of air it takes 180 s to bore through a 2-mm-thick disk of Vespel. The machined surfaces of the two polymers are very different. Machined Vespel samples are charred and cratered, whereas the Lucite samples show evidence of melting with little charring. The machining of polymers by visible-light copper vapor lasers is being compared to UV photoablation by KrF excimer laser light in order to study thermal versus nonthermal etching mechanisms.