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 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: 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.
387 citations
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.
353 citations
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.
323 citations
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.
282 citations
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: 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.
TL;DR: In this paper, thin films of Y•Ba•Cu•O superconductors using a pulsed laser evaporation technique were prepared using a XeCl excimer laser (λ=0.308 μm, τ=45×10−9 s).
Abstract: We have prepared thin films of Y‐Ba‐Cu‐O superconductors using a pulsed laser evaporation technique. Thin films were formed on (100) Si, (100) MgO, (1102) sapphire, (100) SrTiO3, and amorphous SiO2 substrates using a XeCl excimer laser (λ=0.308 μm, τ=45×10−9 s). The depositions were done in an ultrahigh vacuum chamber with pressure of about 10−6 Torr during thin‐film formation. The deposition by pulsed nanosecond laser irradiation results in stoichiometry close to that of the target. The thickness of the film was controlled by varying the pulse energy density and the number of pulses. The substrate temperature was kept at 470 °C during deposition. Subsequent annealing treatments were carried out at 900 and 650 °C in oxygen atmosphere to recover the superconducting properties of these thin films. The resistance of these films was measured as a function of temperature using the four‐point probe method. These thin films were analyzed using cross‐section transmission electron microscopy, Rutherford backscatt...
TL;DR: In this paper, the laser sparks were generated with the use of pulses from a Nd:YAG laser, and the spark light was collected by using a fiber optic cable.
Abstract: Laser-Induced Breakdown Spectroscopy (LIBS) has been used to provide a rapid analysis of metals at distances between 0.5 and 2.4 m from the focusing lens and light-collection optics. The laser sparks were generated with the use of pulses from a Nd:YAG laser, and the spark light was collected by the use of a fiber optic cable. The wide acceptance angle of the cable relaxed the constraint that the spark be formed at a precise location for maximum light-collection efficiency and allowed the detection system to be placed remote from the sample. The identification of the main elemental component of eight metals using lines over a 40-nm spectral region was demonstrated by the use of a single laser pulse to record each spectrum. The accuracy and precision of analysis of the minor constituents of steel were determined, and the effect of surface contamination was examined. The application of LIBS to some industrial monitoring situations is discussed.
TL;DR: In this paper, the authors present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator.
Abstract: We present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator. Chirp reduction and line narrowing are simply related. We show that the reduction in the Lorentzian line width is equal to the square of the reduction in adiabatic chirp. Both are strongly enhanced near resonances of the external cavity.
TL;DR: The values for the maximum coagulation depth (MCD) of various types of lasers which are specified in the literature are not comparable, because often different irradiation times were used.
Abstract: The values for the maximum coagulation depth (MCD) of various types of lasers which are specified in the literature are not comparable, because often different irradiation times were used. MCD depends not only on the wavelength of laser light, but also on the time of action of the laser beam, because of heat transfer. In excised human skin MCD was determined histologically for irradiation with the argon laser, Nd:YAG laser, and CO2 laser. Extending the irradiation time from 0.2 s to 10 s results in a 4-6-fold increase in MCD. Coagulation experiments performed with a soldering iron have shown results similar to those obtained with the CO2 laser. Enlargement of the laser-beam diameter from 1 to 2 mm leads to a 50% increase in MCD. Additional chilling of the skin with water during laser irradiation protects the skin from evaporation, and the values for MCD increase to 3.5 mm for the argon laser and 5.5 mm for Nd:YAG laser. Detailed knowledge of the MCD is necessary to obtain the desired therapeutic effect, and also to avoid unwanted effects.
TL;DR: In this paper, the roles of the imposed modulation waveform and laser design parameters are evaluated from computer generated eye diagrams and simple analytical observations, and device dependent optimum laser extinction ratios are found.
Abstract: Chirp-induced dispersion penalties in high-bit-rate optical fiber transmission are assessed using numerical integration of laser rate equations and a Fourier transform fiber dispersion routine. The roles of the imposed modulation waveform and laser design parameters are evaluated from computer generated eye diagrams and simple analytical observations. Consistent with experiment, we find device dependent optimum laser extinction ratios. In addition, we address the delicate balance between nonlinear chirp-induced dispersion penalties and the speed limitations imposed by linear current filtering on both the laser transmitter and the receiver. These considerations become increasingly important at higher bit rates such as 8 Gbit/s.
TL;DR: In this paper, a dynamic carrier heating model is presented to explain all of the observed gain nonlinearities, and the implications of the results on the dynamic response of laser diodes are discussed.
Abstract: Ultrafast gain dynamics in GaAlAs diode amplifiers have been studied using 100 fs optical pulses. Pulse propagation through the amplifier resulted in temporal broadening and pulse shaping due to both gain saturation and material dispersion. Pump‐probe experiments indicate the presence of two processes contributing to the gain dynamics but give no evidence of spectral hole burning. A dynamic carrier heating model is presented to explain all of the observed gain nonlinearities, and the implications of our results on the dynamic response of laser diodes are discussed.
TL;DR: This modality of treatment utilises less energy than ultrasound or electrohydraulic probes to fragment a stone and the very fine, flexible fiber represents a considerable miniaturization.
Patent•
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16 Oct 1987
TL;DR: In this paper, an argon-flouride excimer laser or other laser source capable of generating far-ultraviolet radiation at 193 nm is pulsed with energy densities of greater than 20 mj per cm2 at a repetition rate up to 25 pulses per second to form a groove therein of predetermined configuration and depth by a process of ablative photodecomposition.
Abstract: An argon-flouride excimer laser or other laser source capable of generating far-ultraviolet radiation at 193 nm is pulsed with energy densities of greater than 20 mj per cm2 at a repetition rate up to 25 pulses per second to direct its radiation through a mask and onto corneal tissue, or other biological matter, to form a groove therein of predetermined configuration and depth by a process of ablative photodecomposition. The masks are formed with a slit, circular, crescent or other openings of widths between 30 and 800 microns, and may even be formed to provide a graded intensity center to edge. The mask is reflective or composed of or faced with an organic polymer to prevent heat build-up. Each micron of the depth of a 200 micron deep groove formed in corneal tissue, for example, resulted from the application of 1 joule per square centimeter of radiation, from a series of pulses delivered at intensities of between 100 mj and 200 mj per square centimeter and at a laser pulse rate of between 1 and 25 Hertz; the entire groove taking 100 seconds.
AT&T1
TL;DR: In this article, the design of semiconductor laser for efficient response to direct current modulation at microwave and millimeter wave frequencies is described and a rate equation analysis is used to relate the effect of current modulation on laser intensity and frequency.
Abstract: The design of semiconductor lasers for efficient response to direct current modulation at microwave and millimeter wave frequencies is described. A rate equation analysis is used to relate the effect of current modulation on laser intensity and frequency. This analysis is also used to relate the 0, 3 and 6 dB frequencies to the peak frequency and to predict the maximum bandwidth obtainable in a single longitudinal mode laser. The design of structures and packaging for millimeter wave bandwidths is also described.