Showing papers on "Laser published in 1987"
TL;DR: In this paper, the use of a matrix for pulsed ultraviolet laser desorption mass spectrometry is shown to extend its applicability into the range of larger, thermally labile biomolecules.
1,909 citations
TL;DR: It is demonstrated that a combination of prisms and diffraction gratings can provide not only quadratic but also cubic phase compensation of ultrashort optical pulses.
Abstract: We demonstrate that a combination of prisms and diffraction gratings can provide not only quadratic but also cubic phase compensation of ultrashort optical pulses We obtain compressed pulses as short as 6 fsec
976 citations
TL;DR: In this article, a new technique is presented that makes it possible, with a single laser pulse, to determine the three-dimensional spatial distribution of state-selected photoproducts.
Abstract: A new technique is presented that makes it possible, with a single laser pulse, to determine the three‐dimensional spatial distribution of state‐selected photoproducts. Initially, absorption of a photon from a laser beam causes fragmentation of a molecule. Multiphoton ionization is used to select the internal state of a desired fragment without perturbing its velocity. Following a short delay, the three‐dimensional spatial distribution caused by the fragment velocities is projected onto two dimensions by accelerating the state‐selected fragment ions into the surface of a channel plate particle multiplier. Electrons emerging from the multiplier are imaged onto a phosphorescent screen for analysis by a digital‐image processing device such as a two‐dimensional optical multichannel analyzer. The three‐dimensional spatial distribution is reconstructed by taking the Hankel transform of the Fourier transform of the projection. The technique is illustrated by recording the spatial distribution of methyl fragments produced in their vibrational ground state by the 266 nm photodissociation of CH3I. From this study it is determined that the fraction of CH3(v=0) formed in coincidence with I(2P1/2) is greater than 0.95, the rest being formed in coincidence with I(2P3/2) ground state.
896 citations
TL;DR: In this article, the authors present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility.
Abstract: The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility. After introducing the definition of α and discussing its dependence on carrier concentration, photon energy, and temperature, we give a short historical summary on how the concept of α evolved over the past two decades. This is followed by a discussion of α dependence on device structure in gain-guided and subdimensional lasers (quantum wells and quantum wires). The bulk of the paper is devoted to a detailed review of laser properties influenced by α and of associated methods of estimating the value of α. Results of measurements reported to date are collected and the most reliable methods are indicated.
646 citations
TL;DR: Above-threshold ionization (ATI) is investigated in xenon with pulses of light at 616 nm ranging from 15 to 0.4 psec, apparently due to resonance enhancements in the ionization process produced by ponderomotive shifts of states.
Abstract: Above-threshold ionization (ATI) is investigated in xenon with pulses of light at 616 nm ranging from 15 to 0.4 psec. Significant energy shifts and broadenings of the ATI peaks are observed. For pulse widths less than 1 psec, the individual ATI peaks break up into a narrow fine structure, apparently due to resonance enhancements in the ionization process produced by ponderomotive shifts of states.
548 citations
TL;DR: In this paper, a lambda = 1.53 microm signal with +22 dB gain was achieved at 295 K in an Er(3+)-doped single-mode fiber using a Lambda = 514.5 nm pump source.
Abstract: Traveling-wave amplification of a lambda = 1.53 microm signal with +22-dB gain is achieved at 295 K in an Er(3+)-doped single-mode fiber using a lambda = 514.5 nm pump source. The optimum fiber length for maximum gain is determined experimentally. A limit in signal-to-noise ratio that is due to concurrent amplification of spontaneous emission is observed. By cooling the fiber to 77 K, the amplifier gain is increased to +29 dB as a result of depopulation of the lower laser level.
531 citations
TL;DR: It is concluded that "laser biostimulation" is of aPhotobiological nature, and low-power laser effects can be related to well-known photobiological phenomena.
Abstract: Quantitative studies of the action of low-power visible monochromatic light on various cells (E. coli, yeasts, HeLa) were performed to find irradiation conditions (wavelength, dose, intensity) conducive to vital activity stimulation. The action spectra of visible light on DNA and RNA synthesis in HeLa cells have maxima near 404, 620, 680, 760, and 830 nm. Growth simulation of E. coli is at a maximum when irradiated at 404, 454, 570, 620, and 750 nm, and biomass accumulation stimulation in yeasts has a maxima at 404, 570, 620, 680, and 760 nm. Absorption of quanta is only a trigger for the rearrangement of cellular metabolism, with photosignal transduction being effected by standard cellular means such as changes in the cAMP level. Respiratory chain components are discussed as primary photoacceptors. It is concluded that "laser biostimulation" is of a photobiological nature, and low-power laser effects can be related to well-known photobiological phenomena.
518 citations
TL;DR: This method is used to stabilize laser frequencies and reduce linewidths by a factor of 1000 from 20 MHz to approximately 20 kHz.
Abstract: With simple optical geometries a separate resonant Fabry-Perot cavity can serve as an optical feedback element that forces a semiconductor laser automatically to lock its frequency optically to the cavity resonance. This method is used to stabilize laser frequencies and reduce linewidths by a factor of 1000 from 20 MHz to approximately 20 kHz.
515 citations
TL;DR: In this paper, the process of electron-phonon energy transfer was time resolved and was observed to be 1--4 ps increasing with the laser fluence, and non-equilibrium electron-lattice temperatures were observed.
Abstract: Amplified 150--300-fs laser pulses are applied to monitor the thermal modulation of the transmissivity of thin copper films. Non- equilibrium electron-lattice temperatures are observed. The process of electron-phonon energy transfer was time resolved and was observed to be 1--4 ps increasing with the laser fluence.
510 citations
TL;DR: In this article, a model for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium was developed for transitions to the manifolds4I 9/2 in Nd3+,4I 15/2 and 3H 6 in Tm3+.
Abstract: A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds4I 9/2 in Nd3+,4I 15/2 in Er3+,5I 8 in Ho3+and3H 6 in Tm3+. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the4F 3/2 -4I 9/2 transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.
399 citations
TL;DR: In this paper, the first diode-laser (nominal 200mW 10-stripe laser diode) end-pump lasing of Nd:YVO4 was reported.
Abstract: We report on the first diode‐laser (nominal 200‐mW 10‐stripe laser diode) end‐pump lasing of Nd:YVO4. The lowest threshold (30 mW) and highest output power (120 mW) were observed from the Nd:YVO4 laser as compared to a similar Nd:YAG laser. Over 50% optical slope efficiency was obtained, the highest yet reported for diode pumping. This device performed at a 10% overall efficiency. Measurements over a 21‐nm range show the advantages of the Nd:YVO4 pump absorption band.
TL;DR: In this article, it was found that GeTe-Sb2Te3 pseud-binary amorphous alloy films showed remarkably fast switching properties to laser irradiation, which is applicable to high data rate direct overwritable disk media.
Abstract: It was found that GeTe-Sb2Te3 pseud-binary amorphous alloy films showed remarkably fast switching properties to laser irradiation. By the static laser irradiation test, the film whose composition corresponded to stoichiometric compound of GeSb2Te4 were crystallized within 50ns of pulse duration at power of 8mW, whilst they could be amorphized with the same pulse duration at power of 20mW. Direct overwriting cycle test was performed on the revolving disk system for 105 times using single laser beam. CNR of more than 50dB and erasability of -22dB were obtained for linear velocity of 22m/s and overwriting frequencies of 5 and 7 MHz. The laser powers were 22 mW for recording and 10 mW for erasing. These materials will be applicable to high data rate direct overwritable disk media.
TL;DR: Clouds of two to about fifty simultaneously stored, laser-cooled ions in a Paul trap were observed in two phases, which are clearly distinguishable by their excitation spectra.
Abstract: Clouds of two to about fifty simultaneously stored, laser-cooled ${\mathrm{Mg}}^{+}$ ions in a Paul trap were observed in two phases, which are clearly distinguishable by their excitation spectra. Transitions between these phases can be induced either by a variation of the power of the laser radiation used to cool the ions or by a change of the size of the radio-frequency voltage applied to the trap. Transitions between a "crystalline" phase and a "gaseous" phase can be repeatedly observed by variation of the appropriate parameters. The two phases and the transitions between them have also been recorded by a photon-counting image system.
TL;DR: In this paper, a single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically, and a theory for the two-mode operation with the TE0 mode and the TE + 1 mode was developed.
Abstract: A single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically. As expected, we got a high SLM operation yield of 80 percent in a moderate coupled case up to a light output power of 10 mW. However, in the strongly coupled cases, the two-mode operation with the TE0 mode and the TE + 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, we have developed a theory. Taking the spatial hole burning along the laser axis into account, we succeeded in explaining the longitudinal mode behavior. From our theory, moderate coupling ( kL = 1.25 ) was found to be optimum to maintain the large threshold gain difference above threshold.
TL;DR: A simple instrument is described which allows single cells to be positioned with high accuracy, transported over several millimeters, and automatically sorted on the basis of their optical properties, and potential applications of this technique in experimental cell biology are discussed.
Abstract: Following the recently reported trapping of biological particles by finely focused laser beams, we report on the automated micromanipulation of cells and other microscopic particles by purely optical means as well as on a newly observed interaction between particles in the trapping beam. A simple instrument is described which allows single cells to be positioned with high accuracy, transported over several millimeters, and automatically sorted on the basis of their optical properties. These operations are performed inside a small enclosed chamber without mechanical contact or significant fluid flow. Potential applications of this technique in experimental cell biology are discussed.
TL;DR: In vitro experiments showed that the threshold temperature range for coagulation was 60°–70° C, and the kinetics were first order, with a temperature‐dependent rate constant that obeyed an Arrhenius relation.
Abstract: The propagation of light energy in tissues is an important problem in phototherapy, especially with the increased use of lasers as light sources. Often a slight difference in delivered energy separates a useless, efficacious, or disastrous treatment. Methods are presented for experimental characterization of the optical properties of a tissue and computational prediction of the distribution of light energy within a tissue. A standard integrating sphere spectrophotometer measured the total transmission, Tt, total reflectance, Rt, and the on-axis transmission, Ta, for incident collimated light that propagated through the dermis of albino mouse skin, over the visible spectrum. The diffusion approximation solution to the one-dimensional (1-D) optical transport equation computed the expected Tt and Rt for different combinations of absorbance, k, scattering, s, and anisotropy, g, and by iterative comparison of the measured and computed Tt and Rt values converged to the intrinsic tissue parameters. For example, mouse dermis presented optical parameters of 2.8 cm-1, 239 cm-1, and 0.74 for k, s, and g, respectively, at 488 nm wavelength. These values were used in the model to simulate the optical propagation of the 488-nm line of an argon laser through mouse skin in vivo. A 1-D Green's function thermal diffusion model computed the temperature distribution within the tissue at different times during laser irradiation. In vitro experiments showed that the threshold temperature range for coagulation was 60 degrees-70 degrees C, and the kinetics were first order, with a temperature-dependent rate constant that obeyed an Arrhenius relation (molar entropy 276 cal/mol-degrees K, molar enthalpy 102 kcal/mol). The model simulation agreed with the corresponding in vivo experiment that a 2-s pulse at 55 W/cm2 irradiance will achieve coagulation of the skin.
TL;DR: In this article, the authors report the alteration of spontaneous emission by atoms coupled to the degenerate modes of a confocal resonator, which results in a fractional increase of 1.6% and decrease of 0.5% in the total spontaneous emission rate.
Abstract: We report the alteration of visible spontaneous emission by atoms coupled to the degenerate modes of a confocal resonator. The partial emission rate into the resonator modes is enhanced by a factor of 19 when the resonator is tuned to the atomic transition frequency and inhibited by a factor of 42 when it is detuned. This results in a fractional increase of 1.6% and decrease of 0.5%, respectively, in the total spontaneous emission rate, which we verify by monitoring changes in the intensity of light emitted out the sides of the resonator as it is tuned.
TL;DR: In this paper, a focused Nd:YAG laser is used for direct elemental analysis of solids, which can be used either in singlepulse mode to give a transient signal or at 10 Hz repetition rate, resulting in a continuous signal.
Abstract: A technique for direct elemental analysis of solids is described. A focused Nd:YAG laser efficiently ablates many materials, including ceramics and polymers, that are difficult to prepare for solution analysis. Ablated particulate material is transported by gas flow into an inductively coupled plasma (ICP) and the resulting ions are detected by mass spectrometry. The laser may be used either in single-pulse mode to give a transient signal or at 10 Hz repetition rate, resulting in a continuous signal. The continuous signal may be maintained constant over long periods by translation of the sample, resulting in improved precision and duty cycle for data acquisition. Quantitative analysis is obtained by internal standardization on either a known analyte or the sample matrix signal. Analytical curves obtained for NBS microprobe steel standards are linear over 4 orders of magnitude and estimated detection limits are 0.2-2 ..sigma..=g g/sup -1/ in the solid. Precision and accuracy are approximately +/-5%.
TL;DR: Improved understanding of the scientific rationale for the interaction of CO2 lasers with teeth can lead to several clinical applications, which will depend on the development of a technology to direct a specific frequency laser beam precisely to a desired site.
Abstract: The use of lasers in dentistry has been considered for over 20 years. Higher-energy density lasers were shown to fuse enamel but were potentially unsafe. Subsequently, low-energy density laser radiation was shown to affect artificial caries lesion formation.Recent studies have shown that carbon dioxide lasers can successfully be used at low-energy densities to fuse enamel, dentin, and apatite. Our studies have shown that specific wavelengths are highly efficient. These wavelengths are directly related to the infrared absorption regions of apatite. We have conducted studies with enamel and dentin, using pulsed CO2 laser radiation in the 9.32-μm to 10.49-μm region with energy densities in the 10 to 50 J.cm-2 range. This laser treatment caused surface fusion and inhibition of subsequent lesion progression and markedly improved the bonding strength of a composite resin to dentin. Similar studies have shown no pulpal damage or permanent deleterious effect on soft tissues.This improved understanding of the scie...
TL;DR: Electromagnetic fields with photon-number fluctuation reduced below the standard quantum limit have been generated in a constant-current\char21{}driven semiconductor laser based on a new principle of high impedance suppression for pump-amplitude fluctuation in a highly saturated laser oscillator.
Abstract: Electromagnetic fields with photon-number fluctuation reduced below the standard quantum limit have been generated in a constant-current--driven semiconductor laser. The generation is based on a new principle of high impedance suppression for pump-amplitude fluctuation in a highly saturated laser oscillator. The observed noise level is 7.3% (31% after correction for detection quantum efficiency) in power below the standard quantum limit in the entire frequency range between 350 and 450 MHz.
TL;DR: A beneficial effect of the helium-neon laser on wound healing in vivo and a considerable improvement in the tensile strength of the laser-irradiated wounds at 1 and 2 weeks are suggested.
Abstract: Clinical observations have suggested that low-energy lasers might stimulate wound healing. To understand the mechanism of the biostimulation, we previously examined the effects of low-energy lasers on collagen production by human skin fibroblasts and reported an increase of collagen synthesis in vitro. To examine the effects of low-energy lasers in vivo, hairless mice were experimentally wounded, sutured, and subjected to laser irradiation by a helium-neon laser with a power output of 1.56 mW and an energy fluence of 1.22 Joules/cm2. Experimental wounds were subjected to laser treatment every other day for 2 months; control wounds remained untreated. Specimens from the wounds were then examined for histological findings, tensile strength, and total collagen content. Results demonstrated a considerable improvement in the tensile strength of the laser-irradiated wounds at 1 and 2 weeks. Furthermore, the total collagen content was significantly increased at 2 months when compared with control wounds. These results suggest a beneficial effect of the helium-neon laser on wound healing in vivo.
TL;DR: Measurements of thermal transport in spherical geometry made with 24 uv (351-nm) beams from the OMEGA laser system are presented and it is concluded that the experimental results can be explained by the presence of significant energy at intensities three times the nominal intensity.
Abstract: In this paper we present measurements of thermal transport in spherical geometry made with 24 uv (351-nm) beams from the OMEGA laser system of the Laboratory for Laser Energetics of the University of Rochester. The measurements, using time-resolved x-ray spectroscopy on solid glass targets coated with varying thicknesses of plastic, provide absolute measurements of the onset times of the resonance x-ray lines of silicon. From these measurements, the scaling of the instantaneous mass-ablation rate with absorbed intensity is obtained for times before and after the peak of the laser pulse. The observed large burnthrough depths and early onsets of the x-ray lines are explained by carrying out detailed hydrodynamic-code simulations for the range of the estimated laser-intensity distribution on target which is obtained from the superposition of the equivalent target-plane intensity distribution of a single beam. We find that neglecting the effects of laser illumination nonuniformities can lead to erroneous conclusions about the heat transport. We conclude from the analysis that the experimental results can be explained by the presence of significant energy at intensities three times the nominal intensity, contained in hot spots of size less than 20 ..mu..m. This is almost twice as much as the maximum intensitymore » obtained from the superposition of the single-beam distribution.« less
TL;DR: In this paper, a simple photochemical mechanism in which one photon or less (on average) is absorbed per monomer is shown to be insufficient for significant ablation at 248 nm.
Abstract: Pulsed laser radiation at 193, 248, or 308 nm can etch films of polyimide (DuPont KaptonTM). The mechanism of this process has been examined by the chemical analysis of the condensible products, by laser‐induced fluorescence analysis of the diatomic products, and by the measurement of the etch depth per pulse over a range of fluences of the laser pulse. The most important product as well as the only one condensible at room temperature is carbon. Laser‐induced fluorescence analysis showed that C2 and CN were present in the ablation plume. At 248 nm, even well below the fluence threshold of 0.08 J/cm2 for significant ablation, these diatomic species are readily detected and are measured to leave the polymer surface with translational energy of ∼5 eV. These results, when combined with the photoacoustic studies of Dyer and Srinivasan [Appl. Phys. Lett. 48, 445 (1986)], show that a simple photochemical mechanism in which one photon or less (on average) is absorbed per monomer is inadequate. The ablation proces...
Patent•
08 Jan 1987TL;DR: In this paper, a process and apparatus for ablating atherosclerotic or tumorous tissues is described, where a source of high power ultraviolet laser energy directed through an optical fiber at the section of tissue is fired only when the fluorometric analysis indicates that it is directed at abnormal tissue.
Abstract: A process and apparatus for ablating atherosclerotic or tumorous tissues is disclosed. Optical fibers direct low power light energy at a section of tissue to be ablated to cause the section to fluoresce. The fluorescence pattern is analyzed to determine whether the fluorescence frequency spectrum is representative of normal or abnormal tissue. A source of high power ultraviolet laser energy directed through an optical fiber at the section of tissue is fired only when the fluorometric analysis indicates that it is directed at abnormal tissue.
TL;DR: It is shown that optical cavities have been used to enhance the nonlinear interaction for continuous wave CW pumping but this limits the bandwidth and also increases the total linear loss.
Abstract: Generation of squeezed light is at present limited to narrow regions of the optical spectrum.(1–3) For the parametric amplifiers used to generate squeezed light, this limit is imposed by the following properties of the nonlinear material used for the parametric process: 1) small nonlinear response, 2) linear losses, 3) insufficient laser pump power and 4) optical damage at high pump powers. Optical cavities have been used(1,2) to enhance the nonlinear interaction for continuous wave CW pumping but this limits the bandwidth and also increases the total linear loss.
TL;DR: An upconversion pumping scheme was used to produce cw laser action at 0.55 μm in YAlO3:Er3+ at temperatures up to 77 K on the 4S3/2→4I15/2 transition as mentioned in this paper.
Abstract: An upconversion pumping scheme was used to produce cw laser action at 0.55 μm in YAlO3:Er3+ at temperatures up to 77 K on the 4S3/2→4I15/2 transition. Two infrared dye lasers at 792.1 and 839.8 nm were used as the pump sources for stepwise two‐photon excitation of the 4S3/2 upper laser level at 18 406 cm−1. The laser operates in the fundamental TEM00 mode, and a cw output power of ∼1 mW was achieved with ∼200 mW pump power from each infrared dye laser.
TL;DR: The instrument response is shown to be proportional to pump power, probe power, and sample absorptance, and different frequency synthesizers and different modes of triggering are used to study their effect on signal stability.
Abstract: We report the results from a new pump/probe spectrometer for potential use in combustion diagnostics that employs asynchronous optical sampling. The instrument consists of two frequency-doubled mode-locked Nd:YAG lasers operating at slightly different repetition rates, synchronously pumping two dye lasers (rhodamine 6G) to generate the pump and probe beams. The spectral and temporal capabilities of the instrument are examined by obtaining a spectrum and an excited state decay of rhodamine B. The instrument response is shown to be proportional to pump power, probe power, and sample absorptance. Different frequency synthesizers and different modes of triggering are used to study their effect on signal stability.
TL;DR: In this paper, laser-induced breakdown spectroscopy was used to determine uranium in solution for possible application to process control in nuclear fuel reprocessing facilities, and a calibration curve was prepared that spanned uranium concentrations from 0.1 to 300 g/L.
Abstract: Laser-induced breakdown spectroscopy was used to determine uranium in solution for possible application to process control in nuclear fuel reprocessing facilities. Pulses from a Nd: YAG laser were focused on the surfaces of the liquids in order to generate the sparks. The spark light was spectrally resolved and detected with the use of a time-gated photodiode array. The detection limit for uranium in 4 molar nitric acid was 0.1 g/L. Measurement precisions were 1–2% for a 4.2-g/L solution with the use of 1600 laser sparks, corresponding to a measurement time of about three minutes. A calibration curve was prepared that spanned uranium concentrations from 0.1 to 300 g/L. The effects of some experimental parameters on the analysis are discussed.
Patent•
11 Jun 1987
TL;DR: In this paper, a medical laser handpiece comprising a grip body, a semiconductor laser generator disposed in the grip body and an irradiation nozzle which is detachably cross-connected to the head of the gripper at an angle was presented.
Abstract: A medical laser handpiece comprising a grip body, a semiconductor laser generator disposed in the grip body and an irradiation nozzle which is detachably cross-connected to the head of the grip body at an angle and includes a laser light transmitting means from the semiconductor laser generator. With this laser handpiece, an operator can accurately and easily treat even relatively small and complicated shaped teeth and periodontal sections in the mouth. In addition to a structure capable of irradiating laser lioght and a structure capable of cooling the semiconductor generator, this invention also includes a structure capable of jetting air, water and a mist of air and water, and a structure capable of reducing irradiation loss of laser light.