Showing papers on "Laser power scaling published in 1994"

Self-mixing interference inside a single-mode diode laser for optical sensing applications

Abstract: This paper presents a theoretical analysis and a comparison with experimental results on self-mixing interference inside a single-longitudinal-mode diode laser. A theoretical model, based on the steady-state equations of the lasing condition in a Fabry-Perot type laser cavity, is described, and through it a satisfactory analysis of self-mixing interference for optical sensing applications is given. In this work, the self-mixing interference produced by an external optical feedback is found to be due to the variations in the threshold gain and in the spectral distribution of the laser output. The gain variation results in an optical intensity modulation, and the spectral variation determines both the modulation waveform and the coherence properties of the interference. The theoretical analysis of the self-mixing interference is seen to yield a simulation of the laser power modulation which is in good agreement with the experiment results reported. >

A Simple but Realistic Model for Laser Cladding

Abstract: A model which takes into account the main phenomena occurring during the laser-cladding process is proposed. For a given laser power, beam radius, powder jet geometry, and clad height, this model evaluates two other processing parameters, namely, the laser-beam velocity and the powder feed rate. It considers the interactions between the powder particles, the laser beam, and the molten pool. The laser power reaching the surface of the workpiece is estimated and, assuming this power is used to remelt the substrate with the clad having been predeposited, the melt-pool shape is computed using a three-dimensional (3-D) analytical model, which produces mmediate results, even on personal computers. The predictions obtained with this numerical model are in good agreement with experimental results. Processing engineers may therefore use this model to choose the correct processing parameters and to establish cladding maps.

Ultrabroadband femtosecond lasers

Abstract: The exploitation of soliton-like pulse shaping mechanisms and the optimization of phase dispersion in broadband self-modelocked solid state laser oscillators have led to unprecedented advances in ultrafast laser technology. This paper reviews the basic physical mechanisms governing pulse formation and addresses the requirements for optimum performance of these novel ultrashort pulse laser sources. These considerations together with the demonstration of /spl ap/10 fs pulse generation from a Ti:sapphire laser suggest that a family of solid-state laser oscillators with comparable performance can be developed. >

Definition of a laser threshold.

Abstract: We propose that the threshold of a laser is more appropriately described by the pump power (or current) needed to bring the mean cavity photon number to unity, rather than the conventional ``definition'' that it is the pump power at which the optical gain equals the cavity loss. In general the two definitions agree to within a factor of 2, but in a class of microcavity lasers with high spontaneous emission coupling efficiency and high absorption loss, the definitions may differ by several orders of magnitude. We show that in this regime the laser undergoes a transition from a linear (amplifier) behavior to a nonlinear (oscillatory) behavior at our proposed threshold pump rate. The photon recycling resulting from the high spontaneous emission coupling efficiency and high absorption may in this case result in lasing without population inversion, and coherent light is generated via ``loss saturation'' instead of gain saturation. This mechanism for lasing without inversion is very different from lasing without inversion using a radiation trapped state.

Optically induced rotation of anisotropic micro‐objects fabricated by surface micromachining

Abstract: Optical trapping and directional high‐speed rotation by radiation pressure are demonstrated for anisotropic micro‐objects fabricated by reactive ion‐beam etching. These micro‐objects, which have shape dissymmetry (not bilateral symmetry but rotational symmetry) in the horizontal cross section, rotate about the laser beam axis in the designed direction in a liquid medium (e.g., water or alcohol). The rotation speed is almost proportional to the input laser power.

Diffractive optical element for mode shaping of a Nd: YAG laser

Abstract: A diffractive laser cavity mirror is described that can customize the amplitude and phase of a laser mode. The design of this diffractive element is shown for a square, flat-topped fundamental mode. The laser cavity has a theoretical fundamental mode loss of only 0.08% and a second-order mode loss of 48.2%, resulting in high modal discrimination. The fabricated mirror is tested in a Nd:YAG laser system. The resulting square flat-topped mode has an rms variation of 1.5% over the two-dimensional flat-topped region and a large discrimination against higher-order modes.

Method and apparatus for real-time control of laser processing of materials

Abstract: There is provided a method and apparatus for controlling, in real-time, processing variables in laser processing of materials using fuzzy logic control procedures by embedding expertise in the form of a rule base within a fuzzy logic controller. The method uses a visible light detector as part of the control loop to detect light from the laser-material interaction zone. The light is processed to extract spatial information on the size of the interaction zone and in one aspect determines the number of bright pixels above a pre-defined number which effectively gives the spatial extent or area of the visible light emitted from the interaction zone. From this elemental processing two system input variables are obtained, namely the current number of bright pixels, #BP, and the change in this court since the last calculation, ΔBP. These input variables are input to the fuzzy logic controller for an inference pass with the output being used to control a laser processing variable such as laser power, laser intensity and process speed. More than two system input variables may be used to provide greater stability. Integrating the fuzzy logic controller with the image processor provides control of penetration welding of steel plate at a rate of 28 Hz.

Diode Laser Arrays

Abstract: Contributors 1. Monolithic phase-locked semiconductor laser arrays D. Botez 2. High power coherent, semiconductor laser master oscillator power amplifiers and amplifier arrays D. F. Welch and D. G. Mehuys 3. Microoptical components applied to incoherent and coherent laser arrays J. R. Leger 4. Modeling of diode laser arrays G. R. Hadley 5. Dynamics of coherent semiconductor laser arrays H. G. Winfuland and R. K. Defreez 6. High average power semiconductor laser arrays and laser array packaging with an emphasis for pumping solid state lasers R. Solarz 7. High power diode laser arrays and their reliability D. R. Scifres and H. H. Kung 8. Strained layer quantum well heterostructure laser arrays J. J. Coleman 9. Vertical cavity surface emitting laser arrays C. J. Chang-Hasnain 10. Individually addressed arrays of diode lasers D. Carlin.

Four-wave mixing and optical modulation in a semiconductor laser

Abstract: There is a direct connection between nearly degenerate four-wave mixing in a semiconductor laser and optical modulation in the laser field. It can be understood using a model of an unlocked, optically injected laser, which emphasizes the effect of the laser resonator on the optical interactions. This model correctly describes the observed spectral characteristics and their dependence on the intrinsic parameters of the semiconductor laser. This is used to develop a simple and accurate technique using a single experimental setup for the parasitic-free characterization of the intrinsic laser parameters, including the relaxation resonance frequency, the total relaxation rate, the nonlinear relaxation rate, and the linewidth enhancement factor. Other parameters, such as the spontaneous carrier lifetime, the photon lifetime, the differential and nonlinear gain parameters, and the K factor, are determined from the power dependencies of these parameters. This technique requires only two CW lasers closely matched in wavelength and is applicable to semiconductor lasers of any wavelength and any dynamic bandwidth. >

The laser welding of thin metal sheets: an integrated keyhole and weld pool model with supporting experiments

Abstract: An integrated mathematical model for laser welding of thin metal sheets under a variety of laser material processing conditions has been developed and tested against the results of experiments. Full account is taken in the model of the interaction of the laser-generated keyhole with the weld pool. Results calculated from the model are found to agree well with experiment for appropriate values of the keyhole radius. The analysis yields values for power absorption in the metal. In a complementary calculation the total absorption of the laser energy is determined from detailed consideration of the inverse Bremsstrahlung absorption in the plasma and Fresnel absorption at the keyhole walls. To test these results, experiments were performed on 1 mm mild steel using a high-speed video camera, which measured the surface dimensions of the melt pool. Processing parameters were varied to study the effect on the melt pool; parameters considered included traverse speed, laser power and shroud gas species. The general shape of the weld pool was found to depend on whether penetration was full, partial or blind; only the results for full penetration were compared with the theory, which is for complete penetration only.

Mars Observer Laser Altimeter: laser transmitter.

Abstract: The Mars Observer Laser Altimeter utilizes a space-qualified diode-laser-pumped Q-switched Nd:YAG laser transmitter A simple numerical model of the laser energetics is presented, which predicts the pulse energy and pulse width Comparisons with the measured data available are made The temperature dependence of the laser transmitter is also predicted This dependence prediction is particularly important in determining the operational temperature range of the transmitter Knowing the operational temperature range is especially important for a passive, thermally controlled laser operating in space

Hollow glass waveguides for broadband infrared transmission

Abstract: Broadband hollow glass waveguides have been fabricated with losses as low as 0.15 dB/m at 10.6 μm. We make these hollow glass waveguides by coating the inside of polyimide-coated silica-glass tubing with a metallic layer followed by a thin dielectric coating of a metal halide. The bore sizes of the guides range from 320 to 700 μm, and we have made lengths as long as 3 m. The bending radii of the waveguides are less than 5 cm for bore sizes less than 500 μm. We have used these waveguides to deliver greater than 80 W of CO2 laser power and 5 W of Er:YAG laser power. The hollow glass guides are inexpensive, robust, and quite flexible and therefore a good infrared fiber for power and sensor applications.

Analysis of blue and red laser performance of the infrared-pumped praseodymium-doped fluoride fiber laser

Abstract: The laser performance at 491 and 635nm of praseodymium-doped fluorozirconate fiber pumped at 1.01µm and 835nm is described and is interpreted with analytical solutions to the rate equations. Spectroscopic measurements of the absorption and the emission cross sections are presented, and the values are shown to be consistent with the observed lasing performance. The analytical model is shown to be a reliable indication of the optimum length of fiber for operation on the three-level 491nm transition.

Quantum-limited linewidth of a bad-cavity laser.

Abstract: We show experimentally that the quantum-limited linewidth of a laser can be smaller than the conventional Schawlow-Townes limit when the gain bandwidth is smaller than the cavity loss rate. Data obtained for a HeNe 3.39 \ensuremath{\mu}m laser confirm the theoretical result derived for the linewidth of a homogeneously broadened laser in the bad-cavity limit. We show how this result can be understood in terms of the group refractive index.

Highly-efficient, low-noise grating-feedback Er3+:Yb3+ codoped fibre laser

Abstract: The authors report a highly-efficient, short, robustly single-frequency and linearly polarised Er3+:Yb3+ codoped fibre laser with fibre-grating Bragg reflectors. An output power of 19mW for 100mW of 980nm diode pump power and a slope efficiency relative to a launched pump power of 55% is demonstrated. The RIN of the laser was < -157 dB/Hz and the laser linewidth was 300 kHz.

980 nm compact optical isolators using Cd1-x-yMnxHgyTe single crystals for high power pumping laser diodes

Abstract: The author have developed compact optical isolators operating at 480 nm wavelength with an insertion loss of 1.0 dB, isolation of 30 dB, size of 4 phi *4.5 mm and endurance against laser power of approximately 500 mW using Cd/sub 1-x-y/Mn/sub x/Hg/sub y/Te single crystals for the first time.

Integrated laser power monitor

Abstract: A vertical cavity surface emitting laser source having an integrated power monitor at the non-emitting end of the source.

Continuous-wave self-mode-locked operation of a femtosecond Cr 4+ :YAG laser

Abstract: Continuous-wave self-mode-locked operation of a chromium-doped YAG laser pumped by a continuous-wave Nd:YAG laser at 20 °C is described. We used both regenerative initiation and continuous-wave self-mode-locking techniques to generate nearly transform-limited pulses of 120-fs (FWHM) duration at 1.52 μm. The TEM00 output power was as high as 360 mW. The output of this femtosecond source was tunable from 1.51 to 1.53 μm.

Mid-infrared quantum cascade lasers

Abstract: The achievement of laser action associated with intersubband transitions opens the door to a new class of infrared sources in a technologically important spectral region. Recently, we have demonstrated low temperature lasing action using a coupled-well structure with a graded-gap electron injector imbedded in a waveguide. In this work, we demonstrate high temperature (125K) operation of a similar GaInAs QW laser device.

Static and dynamic properties of injection-locked semiconductor lasers

Abstract: The static and dynamic properties of injection-locked semiconductor lasers considering the influence of nonlinear gain are presented systematically. Depending on locking conditions, the modulation bandwidth of a semiconductor laser may be increased or decreased by external light injection. However, the relaxation resonance frequency and the damping rate as defined for a solitary Fabry-Perot (FP) laser are always enhanced by injection locking. That is, contrary to that in a solitary FP laser, the modulation bandwidth in an injection-locked laser is not determined solely by the relaxation resonance frequency, because an injection-locked laser is a third-order system. Therefore, a new definition of the modulation bandwidth is presented for such a laser. The performances of injection-locked distributed feedback (DFB) lasers are also discussed. The theory is in good agreement with the experiments. >

Carrier transport in laser heterostructures

Abstract: We present two-dimensional numerical simulation of carrier transport in laser structures, which allows calculation of the efficiency of injected carrier consumption by the active region and the dependence of the laser current on applied voltage. It also allows calculation of the current, carrier, and potential distribution in a laser structure. This was done by use of PADRE, a program developed for the modeling of heterostructure electronic devices, which was supplemented with additional calculations of the laser optical properties. We applied this program to investigate the effect on the laser quantum efficiency of thermionic emission of electrons from the active layer. The temperature and current dependence of the laser internal quantum efficiency has been analyzed. This study allowed us to understand the performance of lasers with nearly ideal current-blocking structures. >

Active energy control for diode pumped laser systems using pulsewidth modulation

Abstract: An active energy control circuit and method employing pulsewidth modulation for use with diode pumped laser systems. The active energy control circuit and method employs optical energy feedback sensing and output control of the electrical pulsewidth to pump diodes of the laser system. This creates an active energy control loop for maintaining diode pumped laser output energy at a desired level over different pulse repetition frequencies, time, and environmental conditions. The diode pumped laser output energy is controlled by varying the pulsewidth of the output energy pulse while maintaining a current amplitude set point. By using a pulsewidth-modulation-based control system, the current applied to the pump diodes is regulated at an efficient set point below their damage level, and the pulsewidth is adjusted to maintain a desired output optical energy of the laser system. The pulse width modulated output energy control scheme provided by the present invention is appropriate for all diode pumped laser applications including laser rangefinders, laser designators, laser radar systems, laser welding systems, and other low and high power laser systems.

Semiconductor laser confocal microscopy

Abstract: A compact scanning microscope that uses a semiconductor laser both to illuminate a specimen and to detect the signal reflected from it is described. It is demonstrated that the spatial filtering performed by the laser detector ensures confocal operation. Two detection regimes, one employing a laser power monitor and the other using the diode junction voltage as a signal, are compared.

Tunable dual-wavelength operation of a diode array with an external grating-loaded cavity

Abstract: A novel grazing‐incidence grating cavity has been developed for simultaneous generation of laser output at two wavelengths. The gain section is a commercial laser diode array. By moving vertically with respect to the optical axis V‐shaped double slit at the end mirror, we demonstrate tuning of the spectral separation of the dual‐wavelength laser output from 3.52 to 11.29 nm. The side‐mode suppression ratio is 10–20 dB. Examination of the far‐field patterns reveal that the laser mode at the two wavelengths corresponds to a different order of the array modes.

Amplitude detection scheme for optical transmitter control

Abstract: An amplitude control scheme for a high bit rate digital optical transmitter is disclosed. The data to be transmitted by the laser is pulse-width modulated by a low frequency signal (MOD). The pulse-width modulated signal is applied to the laser via a laser driver (14) and to a mark density reference generator (15). The magnitude of the low frequency components from the mark density reference generator is a signal (ARS) indicative of the desired amplitude of the laser light pulses. A back-face photodiode (20) converts a portion of the laser light into an electrical signal, the magnitude of the low frequency portion thereof being a signal (ACS) indicative of the actual amplitude of the laser light pulses. The actual amplitude of the laser light pulses is compared to the desired amplitude and the laser driver output amplitude may then adjusted to compensate for variations in the laser performance.

Double-clad upconversion fiber laser

Abstract: An upconversion fiber laser with a double-clad fiber is pumped with a laser-diode-based laser pump source, the inner cladding of the fiber forming a low transmission loss waveguide for the pump light. The central core of the fiber is doped with an active lasing ionic species capable of undergoing upconversion excitation, such as certain rare earth ionic species. The use of a double-clad fiber permits the use of high power, high brightness laser diodes, including those with broad emitting apertures, as well as high power diode laser pumped fiber lasers, as the pump source, thereby achieving higher pump intensities within the upconversion laser fiber and improved upconversion efficiency. Pump brightness can be further increased with multiple pump schemes which use multiple pump wavelengths in different absorption bands, multiple pump wavelengths within the same absorption band, pump light from pairs of cross-polarized sources, and pumping from both ends of the fiber.

Laser pumping of erbium amplifier

Abstract: Stability of a pump laser for activating an erbium amplifier is enhanced by a grating which results in laser operation in the coherence collapse regime.

Characteristics of a semiconductor laser with external feedback

Abstract: The theoretical analysis of the compound cavity of a semiconductor laser with external optical feedback is conducted. For large optical feedback, the output power from the laser and its oscillation frequency differ from those for small optical feedback. From the rate equations of the compound cavity, the conditions of the laser oscillation are derived in the presence of large optical feedback The dependencies of the output power and the laser oscillation frequency on the external-cavity length are investigated. Some new results involving laser oscillation depending on the external-cavity length are presented. The experimental results are compared with theoretical predictions. The dependence of the laser oscillation on the external-cavity length is qualitatively explained in the present model. >

High modal discrimination in a Nd:YAG laser resonator with internal phase gratings

Abstract: A unique laser resonator containing an internal phase grating and a diffractive mode-selecting mirror provides high modal discrimination in a Nd:YAG laser cavity. Single-spatial-mode lasers with high Fresnel numbers are possible, with negligible loss to the fundamental mode.