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At least 919 records · Page 51Linked to original sources
PubMed2003

Optimum holographic optical element lens recorded by visible laser beams for an infrared two-dimensional vertical-cavity surface-emitting laser array.

We have designed an optimum holographic optical element (HOE) lens recorded by visible laser beams for an infrared two-dimensional vertical-cavity surface-emitting laser (VCSEL) array. The hologram computer-aided design tool that we have developed is used for the optimum design. The optimum HOE has both high light efficiency and a small amount of aberration. An Nd:YAG laser operated at 532 nm and an 8 x 8 VCSEL array operated at 850 nm are used for HOE recording and reconstruction, respectively. The designed lens is experimentally demonstrated, and the experimental results of the lens almost agree with the numerical results.

Journal Article↗
PubMed2004

Transverse spatial coherence of a transient nickellike silver soft-x-ray laser pumped by a single picosecond laser pulse.

The degree of spatial coherence in the direction perpendicular to the target surface is reported for a transient nickellike silver x-ray laser at 13.9 nm. An x-ray laser plasma column was produced by irradiating a slab silver target with a single shaped picosecond laser pulse with energy less than 3 J. Young's double-slit method was applied to measure the fringe visibility as a function of the slit separation for different target lengths. The diameter of the equivalent incoherent source and the coherence radius of the output radiation were determined as well.

Journal Article↗
PubMed2004

Er:Yb-doped waveguide laser fabricated by femtosecond laser pulses.

Laser action is demonstrated in a 20-mm-long waveguide fabricated on an Er:Yb-doped phosphate glass by femtosecond laser pulses. An output power of 1.7 mW with approximately 300 mW of pump power coupled into the waveguide is obtained at 1533.5 nm. Waveguides are manufactured with the 520-nm radiation from a frequency-doubled, diode-pumped, cavity-dumped Yb:glass laser operating at a 166-KHz repetition rate, with a 300-fs pulse duration.

Journal Article↗
PubMed2005

Compact continuous-wave blue lasers by direct frequency doubling of laser diodes with periodically poled lithium niobate waveguide crystals.

A compact continuous-wave blue laser has been demonstrated by direct frequency doubling of a laser diode with a periodically poled lithium niobate (PPLN) waveguide crystal. The optimum PPLN temperature is near 28 degrees C, and the dependence of waveguide crystals on crystal temperature is less sensitive than that of bulk crystals. A total of 14.8 mW of 488-nm laser power has been achieved.

Journal Article↗
PubMed2005

Single polarization, single transverse mode, and widely tunable narrow-linewidth laser from a multimode vertical cavity surface-emitting laser by use of a coupled cavity.

A simple method for achieving a widely tunable narrow-linewidth, single polarization state and single transverse mode lasing oscillation from a commercially available multimode vertical cavity surface-emitting laser by use of a coupled cavity is reported. The laser has a wavelength tuning range of more than 5 nm along 850 nm, a side-mode suppression ratio of approximately 15 dB, and an output power of approximately 0.3 mW from a 50-microm multimode optical fiber at a bias current of 15 mA. The laser was operated in a single state of polarization lasing oscillation without any polarization switching.

Journal Article↗
PubMed2006

Laser cooling of trapped ytterbium ions with an ultraviolet diode laser.

We demonstrate an ultraviolet diode laser system for cooling of trapped ytterbium ions. The laser power and linewidth are comparable to those of previous systems based on resonant frequency doubling, but the system is simpler, more robust, and less expensive. We use the laser system to cool small numbers of ytterbium ions confined in a linear Paul trap. From the observed spectra, we deduce final temperatures of < 270 mK.

Journal Article↗
PubMed2006

Ultraviolet laser filaments for remote laser-induced breakdown spectroscopy (LIBS) analysis: applications in cultural heritage monitoring.

We report experiments with subpicosecond UV laser filaments for the remote analysis of samples related to objects of cultural heritage. The classic laser-induced breakdown spectroscopy (LIBS) technique finds new avenues through femtosecond filamentation, and dynamic remote LIBS becomes possible. Advantages such as self-regulated laser intensity deposition on the target suggest that there is significant potential for using UV femtosecond filaments for the remote analysis of sculpture and large monuments.

Journal Article↗
PubMed2006

Pulsed and cw laser oscillations in LiF:F-2 color center crystal under laser diode pumping.

Continuous-wave laser oscillations in LiF:F-2 crystal optically pumped by a laser diode at 970 nm were demonstrated for what is believed to be the first time. The slope efficiency of 14% and conversion efficiency of 5.5% were achieved for 80 micros pump pulse duration and 5 Hz pulse repetition rate. An efficiency twice as low was measured at a 6.25 kHz pulse repetition rate (50% off-duty factor) and in cw mode of laser operation.

Journal Article↗
PubMed2006

Characterization of frequency-tripled nanosecond pulsed Ti:sapphire laser injection seeded by a frequency-scanning cw Ti:sapphire laser by use of optogalvanic spectroscopy of silicon atoms.

The performance of a narrow-linewidth nanosecond pulsed deep-UV coherent light source consisting of a frequency-tripled nanosecond pulsed Ti:sapphire laser injection seeded by a frequency-scanning cw Ti:sapphire laser has been characterized by using optogalvanic spectroscopy of silicon atoms as a diagnostic. The envelope of the optogalvanic spectrum indicates the pure Doppler broadening of silicon atoms, which was estimated to be as broad as 4 GHz, without the broadening effect from the laser linewidth itself.

Journal Article↗
PubMed2006

250 W end-pumped Nd:YAG laser with direct pumping into the upper laser level.

A high-power longitudinally pumped Nd:YAG laser using direct pumping into the upper laser level is demonstrated. With an absorbed pump power of 438 W an output power of 250 W was realized, which results in an optical-to-optical efficiency of 57%. To the best of our knowledge, this is the first demonstration of a high-output power 885 nm pumped laser design.

Journal Article↗
PubMed2006

Remote imaging laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy using nanosecond pulses from a mobile lidar system.

A mobile lidar system was used in remote imaging laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) experiments. Also, computer-controlled remote ablation of a chosen area was demonstrated, relevant to cleaning of cultural heritage items. Nanosecond frequency-tripled Nd:YAG laser pulses at 355 nm were employed in experiments with a stand-off distance of 60 meters using pulse energies of up to 170 mJ. By coaxial transmission and common folding of the transmission and reception optical paths using a large computer-controlled mirror, full elemental imaging capability was achieved on composite targets. Different spectral identification algorithms were compared in producing thematic data based on plasma or fluorescence light.

Journal Article↗
PubMed1998

Laser scanning microscopy in enzyme histochemistry. Visualization of cerium-based and dab-based primary reaction products of phosphatases, oxidases and peroxidases by reflectance and transmission laser scanning microscopy.

The reflectance mode of confocal laser scanning microscopy is suitable to detect cerium-based primary reaction products of oxidases (CeIV-perhydroxide) and phosphatases (CeIII-hydroxy-phosphate converted into CeIV-perhydroxy-phosphate) as well as of DAB-based primary reaction products (Ni-DAB, Ni-FeII-DAB and CeIV-DAB complexes) of cytochrome C oxidase and peroxidases in vibratome, cryotome and semithin plastic sections. In combination with confocal detection 3D images with submicron spatial resolution can be obtained. Moreover, CeIV-perhydroxide, CeIV-perhydroxy-phosphate, CeIV-DAB complexes and catechol-DAB polymers are highly absorptive. Among other additives, especially stable nitroxyl radicals led to a distinct improvement of the DAB staining in terms of sensitivity and proper localization. This was proven in addition by means of blotting a horseradish peroxidase dilution series during several experiments. In sections it was easily possible to record reflectance signals and high transmission contrast at the wavelength of the exciting argon ion laser (preferentially 488 nm). The results of an imbibition study of cerium-containing model precipitates indicate that the cerium generally should be oxidized prior to observation because the index of refraction of CeIV compounds is considerably higher than that of the corresponding CeIII compounds. A comparative numerical assessment of reflection intensities from reflectant parts in morphologically similar sections is possible. Confocal laser scanning microscopy offers a unique way for high resolution detection of primary histochemical reaction products being sufficiently reflective and/or absorptive. The proposed techniques may open new methodological possibilities for basic research and for medical diagnosis.

3,3'-Diaminobenzidine↗
PubMed2001

The wound healing response after laser in situ keratomileusis and photorefractive keratectomy: elusive control of biological variability and effect on custom laser vision correction.

Biological diversity in the wound healing response is thought to be a major factor limiting the predictability of the outcome of refractive surgical procedures such as laser in situ keratomileusis and photorefractive keratectomy. Corneal wound healing is critical to the success of topography-linked or wave front-linked excimer laser ablation to optimize visual performance. This is because of the importance of retaining subtle features of custom ablation and the tendency of epithelial hyperplasia and stromal remodeling to obscure these features following either procedure. The corneal wound healing response is exceedingly complex. Keratocyte apoptosis, which occurs in response to epithelial injury, is the earliest observable event in the wound healing cascades and is therefore an excellent target for pharmacological intervention. Alterations of surgical technique can be designed to limit keratocyte apoptosis and the subsequent events in corneal wound healing. Abnormalities of the cascades could contribute to the pathogenesis of corneal diseases. For example, recent data have suggested that perturbation of the keratocyte apoptosis/mitosis balance could underlie the development of keratoconus in a proportion of patients.

Animals↗
PubMed1987

Experimental study of CO2-laser-induced histological effects on human fallopian tube: determination of CO2 laser parameters to be used in microsurgery.

This experiment investigates CO2-laser-induced histological effects on fallopian tubes obtained during hysterectomies in women. Tubal transversal sections were performed at isthmic and ampullar sites. Forty strips were available for histological study of the cut section area. The role of different parameters such as radiation power and beam fractionation (continuous versus pulsed) on tissue lesions was assessed. In tubal microsurgery, the CO2 laser can be used as a scalpel with the predominant advantage of minimal tissular alterations. As a result of this study, our recommended parameters are the following: radiation power, 7-10 W; beam focalization zone, 0.2 mm; energy density, 20,000-35,000 W/cm2; continuous operation; moving speed, 1 cm/s.

Carbon Dioxide↗
PubMed1995

Spot size reduction in coupling of laser to micromanipulator in laser microsurgery by fiberoptic link.

BACKGROUND AND OBJECTIVE: In coupling laser with micromanipulator through fiberoptics, the resulting diameter of the spot is limited by the laws of geometrical optics, because of the high numerical aperture (N.A.) of fiberoptic radiation. A new method for the reduction of spot size diameter is suggested. STUDY DESIGN/MATERIALS AND METHODS: The output of a 2 mW He-Ne laser was couped via fiberoptic link, the fiberoptic output light collected by a single lens collimator and directed to the input of the micromanipulator. RESULTS: The spot size can be considerably reduced by the introduction of an aperture which reduces the numerical aperture (N.A.) of the fiberoptic. The resulting reduction in total power has little effect on the power density. CONCLUSION: This approach to the collimator design permits reduction in spot size without any significant changes in power density, thus avoiding damage to the tissue and obtaining optimum performance from the micromanipulator.

Algorithms↗
PubMed2004

Oligomeric carbon and siloxane series observed by matrix-assisted laser desorption/ionisation and laser desorption/ionisation mass spectrometry during the analysis of soot formed in fuel-rich flames.

Oligomeric carbon and siloxane series have been observed by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS), during the analysis of the dichloromethane (DCM)-soluble fractions of condensable material recovered from fuel-rich flames. Laser desorption (LD) spectra showed a pattern of oligomeric dimethyl-siloxane structures with a spacing of 74 u. The siloxane series appears to have originated as contamination of samples by silicone oil used to lubricate connections of polymer tubing. This was confirmed by extracting silicone tubing and silicone grease with DCM followed by MALDI-MS analysis. A series of peaks with a mass spacing of 24 u was also observed, superimposed on the continuum of unresolved organic ions. This oligomeric series appears to correspond to polycyclic aromatics separated by (mainly) ethylene bridges. Thus LD-MS appears to have revealed a series of soot precursors, intermediate between polycyclic aromatics and particulate soot, which was not detected by MALDI-MS. More detailed work is necessary to define these species with precision.

Carbon↗