Showing papers on "Laser published in 1980"
NEC1
TL;DR: In this paper, the effects of external optical feedback on the semiconductor laser properties have been examined, i.e., return of a portion of the laser output from a reflector external to the laser cavity.
Abstract: Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.
2,462 citations
TL;DR: In this paper, a linear polarizer or Brewster plate is placed inside the reference cavity, so that the reflected light acquires a frequency-dependent elliptical polarization, which can provide the error signal for electronic frequency stabilization without any need for modulation techniques.
941 citations
TL;DR: In this paper, the authors proposed a method by which 50 kHz resolution can be obtained for measuring the spectrum of stabilised semiconductor laser with high spectral spread, and the principle, experimental set up and results are described.
Abstract: The spectral spread of the best stabilised semiconductor lasers has been reduced to several megahertz. Conventional spectroscopy techniques cannot offer a spectral resolution fine enough for measuring such a sharp spectrum. The letter proposes a novel method by which 50 kHz resolution can be obtained. The principle, experimental set-up and results are described.
917 citations
TL;DR: Use of lasers has revolutionized the study and applications of radiation pressure, and it is now possible to optically accelerate, slow, stably trap, and manipulate micrometer-sized dielectric particles and atoms.
Abstract: Use of lasers has revolutionized the study and applications of radiation pressure. Light forces have been achieved which strongly affect the dynamics of individual small particles. It is now possible to optically accelerate, slow, stably trap, and manipulate micrometer-sized dielectric particles and atoms. This leads to a diversity of new scientific and practical applications in fields where small particles play a role, such as light scattering, cloud physics, aerosol science, atomic physics, quantum optics, and high-resolution spectroscopy.
559 citations
TL;DR: In this paper, the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser, which is explained in terms of the step-like density of states and the disturbed electron and phonon distributions in the quantumwell active regions.
Abstract: The various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well Al x Ga 1-x As-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high as \sim437\deg C have been obtained for T 0 in the usual expression J_{th}(T) = J_{th}(0) \exp (T/T_{0}) . Since photopumped multiple-quantum-well MO-CVD Al x Ga 1-x As-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses, \lambda \sim 5145 A), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.
487 citations
TL;DR: In this article, a tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl 2 O 4 :Cr3+) over the continuous range from 701 to 818 nm.
Abstract: Wavelength tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl 2 O 4 :Cr3+) over the continuous range from 701 to 818 nm. The tunable emission was observed at room temperature and above in a homogeneously broadened, vibronic, four-level mode of laser action. In this mode the laser gain cross section increases from 7 \times 10^{-21} cm2at 300K to 2 \times 10^{-20} cm2at 475K, which results in improved laser performance at elevated temperatures. Efficient 2.5 percent, low-threshold (10 J) operation has been obtained with xenon-flashlamp excitation of the 6 mm diameter × 76 mm length laser rods. Output pulses of greater than 5 J and average power outputs of 35 W have been demonstrated, limited by the available power supply. The emission is strongly polarized E\parallelb , with a gain that is 10 times that in the alternate polarization. The 262 μs, room-temperature fluorescence lifetime permits effective energy storage and Q -switched operation. Tunable Q -switched pulses as large as 500 mJ have been obtained with pulsewidths ranging between 33 and 200 ns depending on the laser gain. Laser action has also been demonstrated on the high-gain ( 3 \times 10^{-19} cm2emission cross section) R line at 680.4 nm and is also polarized E\parallelb . This three-level mode is analogous to the lasing in ruby except that the stimulated emission cross section in alexandrite is ten times larger than for ruby.
398 citations
TL;DR: In this paper, the transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material, and the thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.
Abstract: Quantitative experimental measurements have been made in the study of thermoelastic generation of elastic waves in a metal by unfocused laser radiation. A calibrated wide‐band detection system, incorporating a capacitance transducer, has enabled acoustic waveforms to be recorded with a minimum of distortion. From these measurements, a theoretical model has been developed. The transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material. The thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.
261 citations
TL;DR: The degree of aiming accuracy, the very small diameter of the laser beam (50 microns) and the use of selector pulses make the laser so precise that it virtually eliminates the risk of damage to the eye or the intraocular lens.
259 citations
TL;DR: In this paper, it has been shown that an electric arc can be added to the interaction between a laser beam and a material surface in such a way that in welding and cutting it produces an effect similar to that from a more powerful laser.
Abstract: It has recently been found that an electric arc can be added to the interaction between a laser beam and a material surface in such a way that in welding and cutting it produces an effect similar to that from a more powerful laser. The experimental results are discussed together with an analysis of the process mechanism. In particular it appears that the arc strikes the work piece at the same interaction zone as the laser, and in so doing undergoes a contraction in width to near the same size as the laser beam. It also seems probable that some of the arc energy penetrates the laser generated keyhole. So far the experimental results have shown that arc augmentation of the laser by some 2 kW of arc power in the work piece can be achieved without unduly spoiling the high quality of the cut or weld that would be made by a laser alone of similar total power.
TL;DR: In this article, a new method for measuring absorption and gain spectra of lasers is presented, which is based on the application of general relations between the rates of spontaneous emission, stimulated emission, and optical absorption.
Abstract: A new method for measuring absorption and gain spectra of lasers is presented. These spectra are deduced from measurements of spontaneous emission spectra at different laser currents supplemented by measurements of the laser line energy and the differential quantum efficiency. The spontaneous emission emerged from the side of the laser after traveling through a transparent cladding layer. At each current, the bias energy eV is determined. A simple theoretical model is used to convert eV to minority carrier density. The method is based on the application of general relations between the rates of spontaneous emission, stimulated emission, and optical absorption. A new general proof of these relations is presented. The gain versus carrier density relation at the laser line energy is measured for four samples having different active layer doping or Al composition. Gain increased superlinearly with carrier density in undoped and n‐type samples and increased slightly sublinearly in a p‐type sample. The losses a...
TL;DR: In this article, it was shown that an exact realization of a Collett-Wolf source is given by a laser oscillating on a suitable superposition of (infinitely many) transverse modes.
TL;DR: In this article, a simplified method for measuring the effective photon lifetime in an optical resonator was developed, which requires the passage of a modulated cw laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity.
Abstract: A simplified method for measuring the effective photon lifetime in an optical resonator was developed. The technique requires the passage of a modulated cw laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity. The method not only permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ. Such an on-the-spot evaluation capability should be extremely useful in applications ranging from the investigation of new laser systems to the development of improved optical coatings. The method is also sensitive to the effects of absorption, scattering, and transmission from elements in the cavity. Cavity losses <100 ppm were detected.
10 Jul 1980
TL;DR: A simplified method for measuring the effective photon lifetime in an optical resonator was developed and permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ.
Abstract: A simplified method for measuring the effective photon lifetime in an optical resonator was developed. The technique requires the passage of a modulated continuous-wave laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity. The method not only permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ. Such an 'on the spot' evaluation capability should be extremely useful in applications ranging from the investigation of new laser systems to the development of improved optical coatings. The method is also sensitive to the effects of absorption, scattering, and transmission from elements in the cavity. Cavity losses smaller than 100 ppm were detected.
TL;DR: In this paper, a comprehensive theory developed previously for optical heating in semiconductors is applied to the calculation of laser damage thresholds in Ge, Si, InSb, and GaAs.
Abstract: A comprehensive theory developed previously for optical heating in semiconductors is applied to the calculation of laser damage thresholds in Ge, Si, InSb, and GaAs. The calculated thresholds agree well with the experimental values over a broad range of laser wavelengths and pulse durations. The results demonstrate that the dynamic nature of the material’s optical and transport properties with changing temperature and laser‐generated carrier density has a significant effect on the heating process, particularly at short pulse durations.
TL;DR: In this article, the photofragmentation dynamics of CH2I2 and CH3I at the excimer laser wavelengths of 248 and 308 nm were studied using time and wavelength-resolved infrared fluorescence techniques.
Abstract: Time and wavelength‐resolved infrared fluorescence techniques are used to study the photofragmentation dynamics of CH2I2 and CH3I at the excimer laser wavelengths of 248 and 308 nm. Emission is detected from vibrationally excited CH2I and CH3 radicals as well as from the excited iodine atoms [I*(2P1/2→2P3/2)] produced in the photolysis. A complete infrared fluorescence spectrum of the highly excited CH2I radical is obtained as a function of time after the 248 nm dissociating laser pulse, providing both spectroscopic and vibrational deactivation data for the radical. Significant CH2I emission is observed at all wavelengths, indicating that excitation occurs into a very high density of states, nearing the vibrational quasicontinuum. Stronger emission features are observed in the region of the C–H stretching vibrations, the CH2 bending motion, and a combination band of these two modes. Deactivation rates for various spectral features of the highly excited CH2I radical with CH2I2 and argon are presented, alon...
TL;DR: In this article, small-angle CO2 laser scattering techniques are described which provide detailed information about density fluctuations in plasmas, and the theories of the scattering and the heterodyne and homodyne detection processes are described in detail for the case of smallangle scattering.
Abstract: Small‐angle CO2 laser scattering techniques are described which provide detailed information about density fluctuations in plasmas. These techniques are nonperturbative and measure the frequencies, wave vectors, and amplitudes of the density fluctuations. The theories of the scattering and the heterodyne and homodyne detection processes are described in detail for the case of small‐angle scattering. Several models are developed to describe recent experiments involving both coherent and stochastic fluctuations. The laser, detector, and physical arrangement used in the experiments are described in detail. Experimental studies of driven Bernstein waves, ion acoustic turbulence in a positive column discharge, and fluctuations in tokamaks are described to illustrate these techniques. It is demonstrated that CO2 laser scattering is useful in studying fluctuations with wavelengths between 0.01 and 1 cm and frequencies from 1 kHz to tens of giga‐Hertz in plasmas with mean densities ranging from 1010 to 1017 cm−3.
Patent•
04 Sep 1980TL;DR: In this paper, an optical device coupling light between a first-light waveguide and either a second light waveguide or a radiation source characterized by the first waveguide having a core of a predetermined cross-sectional area, a reflective layer or mirror of a high reflectance being disposed on an angle to the axis of the waveguide, so that only a small portion of the light traveling in the core will be blocked by the presence of the mirror.
Abstract: An optical device coupling light between a first light waveguide and either a second light waveguide or a radiation source characterized by the first light waveguide having a core of a predetermined cross-sectional area, a reflective layer or mirror of a high reflectance being disposed on an angle to the axis of the waveguide and occupying only a small portion of the total cross-sectional area of the core so that only a small portion of the light traveling in the core of the first waveguide will be blocked by the presence of the mirror. The second waveguide will have a core diameter substantially smaller than that of the first waveguide and the mirror is mounted in the first core adjacent to the connection with the second core. The radiation source may be either a laser diode, semi-conductor laser or a light emitting diode.
TL;DR: A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO(2) in air with a sensitivity of better than 100 ppt.
Abstract: A laser absorption spectrometer is described which uses a tunable diode laser and a 1-m multipass White cell to detect NO(2) in air with a sensitivity of better than 100 ppt. The modulation techniques employed to achieve this sensitivity are described in detail, and the noise mechanisms, which currently limit the detectable absorption coefficients to greater, similar 10(-7) m(-1), are examined.
TL;DR: In this article, the magnitude and sign of laser saturation resonances induced in atomic transitions with level degeneracy can be dramatically altered by the presence of optical pumping, and the physical principles underlying the laser optical-pumping saturation effect are discussed.
Abstract: The magnitude and sign of laser saturation resonances induced in atomic transitions with level degeneracy can be dramatically altered by the presence of optical pumping. This paper presents a detailed theoretical treatment of optical-pumping Lamb dips and crossover resonances, and their experimental observation in the 553-nm barium resonance transition. The physical principles underlying the laser optical-pumping saturation effect are also discussed.
TL;DR: A focused, 3 mW UV laser beam has been used to produce micrometer-sized chemical processes on solid surfaces as discussed by the authors, which are initiated by the photodissociatlon of a molecular gas in the vicinity of the gas-solid interface.
Abstract: A focused, ultraviolet (UV) laser beam has been used to produce micrometer-sized chemical processes on solid surfaces. These processes are initiated by the photodissociatlon of a molecular gas in the vicinity of the gas-solid interface. Depending on whether the active photofragment reacts with or is adsorbed on the solid, microetching or microdeposition occurs. Both the surface properties of the solid and the gas-phase kinetics contribute to the process localization. Metal alkyls and methyl halides have been used as parent molecules for deposition and etching, respectively. A focused, 3 mW UV laser is sufficiently intense to produce satisfactory rates for both processes. Several applications of this small-scale photochemistry to microelectronics have been investigated.
Patent•
23 Jun 1980
TL;DR: In this paper, a fiber optic bundle is used to intercepting radiation reflected from the lesion at an intensity corresponding with the color intensity of the region at which the beam is directed.
Abstract: A laser for directing a nominally 5 micron wavelength beam at a hemangioma or other variegated lesion. A fiber optic bundle for intercepting radiation reflected from the lesion at an intensity corresponding with the color intensity of the region at which the beam is directed. The output beam from the fiber optic bundle modulates a photodetector stage whose amplified output drives a galvanometer. The galvanometer shaft is coupled to the shaft of a potentiometer which is adjustable to regulate the laser power supply and, hence, the laser output energy level so laser beam energy is reduced when high absorption regions in the lesion are being scanned by the beam and increased as low absorption regions are being scanned.
TL;DR: In this paper, a general analysis of free electron lasers in which a static periodic magnetic pump field is scattered from a relativistic electron beam is presented, and scaling laws for the growth rates and efficiencies at a fixed radiation frequency as a function of the magnetic pump amplitude are obtained.
Abstract: Abstract : A general analysis is presented of free electron lasers in which a static periodic magnetic pump field is scattered from a relativistic electron beam. The steady state formulation of the problem is fully relativistic and contains beam thermal effects. Growth rates associated with the radiation field, efficiencies, and saturated field amplitudes are derived for various modes of operation. Effects of space charge on the scattering process are included and shown to play a dominant role in certain situations. Scaling laws for the growth rates and efficiencies at a fixed radiation frequency as a function of the magnetic pump amplitude are obtained. The shear in beam axial velocity due to self fields is discussed and various methods of reducing it are suggested. Finally, a detailed illustration of a far infrared (lambda = 2mu m) two-stage free electron laser using a 3 MeV electron beam and a 2 cm wavelength magnetic pump field is presented.
TL;DR: In this article, an investigation of the relevant parameters for broadly tunable lasers utilizing the efficient, broad-band 5d → 4f emission in a number of Eu2+ doped metal fluorides, chlorides, and fluoro-chlorides has been performed.
TL;DR: A semiclassical theory is proposed that agrees well with experimental results and is presented as a comparison with stimulated-Raman-scattering pulse compression.
Abstract: A 20-nsec Nd:YAG laser pulse is compressed to a 2-nsec phase-conjugated pulse in a tapered glass tube filled with methane at 130 atm. A comparison with stimulated-Raman-scattering pulse compression is made. A semiclassical theory is proposed that agrees well with experimental results.
TL;DR: In this paper, the semiconductor Raman laser has been realized by using a GaP crystal, which was made by a Q-switched YAG laser operating at 1.064 μm.
Abstract: The semiconductor Raman laser has been realized by using a GaP crystal. Pumping is made by a Q‐switched YAG laser operating at 1.064 μm. The round‐trip loss in the Fabry‐Perot resonator is 2% or less. The Raman scattering from LO phonons stimulates in the 〈100〉 direction, while the forward and backward Raman scattering from TO phonons stimulate in the 〈110〉 direction. This semiconductor Raman laser is promising as a semiconductor far‐infrared radiation source.
TL;DR: In this paper, a 5d-4f transition in Ce3+-doped LaF3 was obtained with a 286-nm wavelength, the shortest of any solid-state laser.
Abstract: Ultraviolet laser action has been obtained from a 5d–4f transition in Ce3+-doped LaF3. The 286-nm wavelength obtained is the shortest of any solid-state laser. The approximate potential tuning range is from 275 to 315 nm.
TL;DR: In this article, the authors reported an efficient conversion from 1.054 μm to 0.35 μm by third harmonic generation in two Type II KDP crystals, achieving energy conversion efficiencies of up to 80% under conditions applicable to large glass laser systems.