Showing papers on "Laser power scaling published in 1997"

Nonlinear dynamics induced by external optical injection in semiconductor lasers

Abstract: External optical injection of semiconductor lasers changes the resonant coupling characteristics between the circulating optical field in the laser cavity and the free carriers (gain medium). Changes in the characteristic resonance frequency and damping of the system can lead to dynamic instabilities and deterministic chaos and to enhancement of the modulation bandwidth. The changes induced depend on key dynamic parameters of the semiconductor laser such as the photon and carrier decay rates, gain characteristics and the linewidth enhancement factor, and the operating point of the laser determined by the injection current (pump) level, circulating optical power, the amplitude of the external optical injection and the frequency offset between the master and injected lasers. Here, we describe a mapping of the typical dynamics induced in a nearly single-mode semiconductor laser biased well above the threshold for laser oscillation as the amplitude and frequency offset of the master laser are changed. We also present results on a laser initially biased near threshold in a free-running condition where it displays a near-Gaussian optical lineshape. The external optical injection induces spectral holes and spikes, as well as spectral shifts. All features that we observe can be recovered in a standard coupled equation model of semiconductor laser operation.

Modeling of quasi-three-level lasers and operation of cw Yb:YAG lasers

Abstract: We present modeling studies of quasi-three-level laser oscillators, the validity of which was revealed by Ti:Al2O3-pumped Yb:YAG laser experiments, and these results are shown to be in excellent agreement with the theory. As much as 75% slope efficiency was obtained with a hemispherical laser cavity. Previous modeling calculations of laser performance have been valid only for certain special cases, restricting application to TEM00 Gaussian beam pumping and lasing profiles. This analysis may be applied to other longitudinally pumped quasi-three-level laser media in which the modes are not only TEM00 Gaussian beams but also other higher-order transverse modes, including the top-hat pumping profile that can be used to model transverse pumping schemes.

Low-heat high-power scaling using InGaAs-diode-pumped Yb:YAG lasers

Abstract: We report to our knowledge the highest to date quasi-CW output power, 600 W and pulse energy, >1 J, for an InGaAs diode-pumped Yb:YAG laser. In separate preliminary results, we have also obtained 225 W of average output power under true CW diode pumping. This performance was obtained using a laser head designed to be part of a master oscillator power amplifier (MOPA) operating at 3 kW. We summarize why the diode-pumped Yb:YAG crystal laser is ideal for scaling to high average powers and the different approaches being pursued. We also report our latest results for side-pumped rod devices.

High-power continuous-wave upconversion fiber laser at room temperature

Abstract: We report cw laser emission of a Pr, Yb-doped ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF fiber in the red spectral region. Laser emission was achieved on the transition P(0)(3)?F(2)(3)(lambda(L)=635 nm) with a Ti:sapphire pump laser tuned to lambda(p)=850 nm . A maximum output power of P(out)=675 mW was obtained at an incident pump power of P(in)=3.37 W . The output power was increased to P(out)=1020 mW when pumping with P(in)=5.51 W was provided by two Ti:sapphire lasers. A photon avalanche process was found to contribute strongly to the population of the upper laser level.

Observation of a single-beam gradient-force optical trap for dielectric particles in air

Abstract: A single-beam gradient-force optical trap for dielectric particles, which relies solely on the radiation pressure force of a TEM(00)-mode laser light, is demonstrated in air for what is believed to be the first time. It was observed that micrometer-sized glass spheres with a refractive index of n=1.45 remained trapped in the focus region for more than 30 min, and we could transfer them three dimensionally by moving the beam focus and the microscope stage. A laser power of ~40 mW was sufficient to trap a 5- microm -diameter glass sphere. The present method has several distinct advantages over the conventional optical levitation method.

Characterization of a Ho(3+)-doped fluoride fiber laser with a 3.9-mum emission wavelength.

Abstract: The fluoride fiber laser with the longest emission wavelength, the Ho(3+)-transition at 3.9 mum in the attenuation minimum of the 3-5-mum atmospheric window, is characterized. After reviewing the importance of fluoride fibers due to their low phonon energies, we describe room-temperature fluorescence and laser action with liquid-nitrogen cooling. Continuous-wave laser action at 3.9 mum is presented for the 640- and the 890-nm pump ranges. A shift of the emission wavelength is achieved by varying the resonator mirrors. Laser characteristics and temperature dependence are discussed.

Analytical and experimental studies on the characteristics of composite solid-state laser rods in diode-end-pumped geometry

Abstract: In this paper, we report analytical and experimental studies on the characteristics of end-pumped composite laser rods with undoped end, using mainly Nd:YAG rods as an example. It is found that the peak temperature rise in a composite rod decreases to <70% of that in a noncomposite crystal. Thermal stress is dramatically reduced to <60% by employing the composite rod structure, We also demonstrate high-power operation of the diode-end-pumped composite Nd:YVO/sub 4/ rod and a maximum CW output power of 9.3 W was achieved, which is about 1.5 times higher than that in the noncomposite rod. This high-power performance of the composite rod is primarily attributed to the reduction of thermal stress inside the rod.

Long-wavelength (≈15.5 μm) unipolar semiconductor laser in GaAs quantum wells

Abstract: A unipolar semiconductor laser emitting in the mid-infrared spectral region is demonstrated. The laser scheme relies on a simple three-level system in GaAs/AlGaAs asymmetric coupled quantum wells. Population inversion between excited states is achieved by optical pumping of electrons from the ground state with a CO2 laser. Long-wavelength (≈15.5 μm) laser emission is demonstrated. The laser is operated in the pulsed regime up to a temperature of 110 K and with an output peak power ≈0.4 W at 77 K. Unipolar quantum well semiconductor lasers based on this principle are capable of covering the long wavelength mid-infrared spectral region above 12 μm.

Grating coupled vertical cavity optoelectronic devices

Abstract: A edge emitting waveguide laser is obtained that derives its optical power from a vertical cavity laser structure. The vertical cavity laser with top and bottom Distributed Bragg Reflectors produces stimulated emission by resonance in the vertical direction but the optical power so generated is diffracted by a second order grating into an optical mode propagating in the optical waveguide formed by the upper and lower mirrors as cladding layers. The efficiency of the diffraction grating and the reflectivity of the mirrors are maximized so that essentially all of the light is coupled into the guide and the loss through the mirrors can be neglected. The same structure can be utilized as a detector, a modulator or an amplifier. The designated laser structure to achieve this form of operation is the inversion channel laser which is a laterally injected laser having both contacts on the top side of the device. Then the anode and cathode of the laser are essentially coplanar electrodes and the device is implemented in the form of a traveling wave laser, detector, modulator or amplifier which forms the basis for very high frequency performance.

The differential efficiency of quantum-well lasers

Abstract: We have analyzed the internal differential efficiency of quantum-well lasers in terms of current spreading, carrier injection into the well, and the radiative efficiency within the well. We quantify the first two of these processes by extracting information from spontaneous emission measurements as a function of device length, current, and temperature. We show that the carrier injection efficiency is responsible for the temperature dependence of the external differential efficiency of GaInP quantum-well (QW) lasers by comparing values from the slope of the laser power output versus current characteristic with our experimental values for current spreading and injection efficiency.

Dual-wavelength laser emission from a coupled semiconductor microcavity

Abstract: We report photopumped operation of a monolithic coupled semiconductor microcavity laser. The structure consists of two λ-sized GaAs vertical cavities, one on top of the other, coupled together through a common mirror. Due to a wedge induced into each cavity, the detuning between the cavities can be continuously varied when moving across the sample. Depending on the detuning, laser action is simultaneously achieved at two different wavelengths or occurs only at one wavelength. At resonance, we observe coupled dual-wavelength laser emission at two widely spaced wavelengths (13 nm) with the same threshold and same dependence on pump power.

Brillouin/erbium fiber lasers

Abstract: Brillouin/erbium fiber lasers (BEFLs) have been recently demonstrated as a novel mode of operation of a fiber laser. In a hybrid Brillouin/erbium fiber laser, the combination of two gain media, the gain from the erbium-doped fiber (EDF) and Brillouin gain in single-mode optical fibers allows a resonator to be constructed which supports a laser comb with /spl sim/10 GHz or /spl sim/0.1 nm line spacing at room temperature. In this paper, we present a detailed discussion of the operation of BEFLs. Single and multiple wavelength generation is discussed, and modeling of single wavelength operation is described.

Monolithic integration in InGaAs-InGaAsP multiple-quantum-well structures using laser intermixing

Abstract: The bandgap of InGaAs-InGaAsP multiple-quantum-well (MQW) material can be accurately tuned by photoabsorption-induced disordering (PAID), using a Nd:YAG laser, to allow lasers, modulators, and passive waveguides to be fabricated from a standard MQW structure. The process relies on optical absorption in the active region of the MQW to produce sufficient heat to cause interdiffusion between the wells and barriers. Bandgap shifts larger than 100 meV are obtainable using laser power densities of around 5 W/spl middot/mm/sup -2/ and periods of illumination of a few minutes to tens of minutes. This process provides an effective way of altering the emission wavelengths of lasers fabricated from a single epitaxial wafer. Blue shifts of up to 160 nm in the lasing spectra of both broad-area and ridge waveguide lasers are reported. The bandgap-tuned lasers are assessed in terms of threshold current density, internal quantum efficiency, and internal losses. The ON/OFF ratios of bandgap-tuned electroabsorption modulators were tested over a range of wavelengths, with modulation depths of 20 dB obtained from material which has been bandgap-shifted by 120 nm, while samples shifted by 80 nm gave modulation depths as high as 27 dB. Single-mode waveguide losses are as low as 5 dB/spl middot/cm/sup -1/ at 1550 mm. Selective-area disordering has been used in the fabrication of extended cavity lasers. The retention of good electrical and optical properties in intermixed material demonstrates that PAID is a promising technique for the integration of devices to produce photonic integrated circuits. A quantum-well intermixing technique using a pulsed laser is also demonstrated.

Passively Q-switched Nd:YVO(4) laser with a Cr(4+):YAG crystal saturable absorber.

Abstract: We demonstrate, for the first time as far as we know, a passively Q-switched operation of a Nd:YVO4 laser in which a Cr4+:YAG crystal and a laser-diode bar are used as the saturable absorber and the pump source, respectively. Stable laser pulses as short as 28 ns with 20-µJ energy can be generated with this laser, which has the advantages of simplicity, high efficiency, and good long-term stability.

Ultrafast Photoconductive Detectors Based on Semi-Insulating GaAs and InP

Abstract: Photoconductive dipole antennas fabricated on semi-insulating (SI) GaAs and SI-InP were used to detect terahertz (THz) pulses. The responses of these long-carrier-lifetime photoconductive detectors were compared to that of the photoconductive antenna fabricated on a low-temperature grown GaAs (LT-GaAs) with a subpicosecond carrier lifetime. The SI-InP-based photoconductive detector showed a higher responsivity and a better signal-to-noise ratio (SNR) than the LT-GaAs-based photoconductive detector at low gating laser powers. The SI-GaAs-based detector, however, showed a responsivity comparable to that of the LT-GaAs photoconductive detector only at very weak gating laser power, and the SNR of the SI-GaAs-based detector was poor for overall gating laser powers due to the high background noise originating from a large amount of stray photocurrent.

230 mW of blue light from a thulium-doped upconversion fiber laser

Abstract: We demonstrate a powerful diode-pumped blue laser source, consisting of a 7-W diode at 807 nm that pumps a Nd:YAG laser giving 1.6 W with good beam quality at 1123 nm, and a thulium-doped upconversion fiber laser. The maximum output power achieved at 481 nm is 230 mW. We also describe the behavior of a reversible loss which is generated in the fluoride fiber during high power operation.

Theory of laser action in scattering gain media.

Abstract: A laser model based on feedback produced by scattering has been developed to explain the narrow linewidth emission and input–output behavior observed in scattering gain media. The model is based on the transient two-level laser equations and includes the detailed spectral properties of the dye gain system. Monte Carlo methods were employed to calculate the threshold gain required for modeling the input–output and linewidth emission characteristics.

Properties of Brillouin/erbium fiber lasers

Abstract: The unique combination of two gain media in Brillouin/erbium fiber lasers results in distinctive properties of such sources. The paper describes in detail the output and efficiency properties of Brillouin/erbium fiber lasers, from experimental results and a theoretical model. Single longitudinal mode output with linewidth <10 kHz was measured, with a 4-nm tuning range with the Brillouin pump wavelength. Frequency pulling associated with the Brillouin gain was investigated and observed to increase linearly with the Brillouin pump power.

Passive frequency and intensity stabilization of extended-cavity diode lasers

Abstract: Studies are reported on frequency drifts in extended-cavity diode lasers caused by external effects, such as changes in temperature and air pressure. A laser system operating at 780 nm has been constructed utilizing low expansion materials and such mechanical structures that compensate for the external effects. By placing the laser system in a pressure-proof and temperature-controlled housing, a relative frequency stability of better than 10−10 (40 kHz) is obtained for integration times of 10 μs to 10 s. The drift of the laser frequency caused by spectral aging of the diode laser is about 3 MHz/h. As a consequence of high passive stability, the variations of the laser intensity are also greatly reduced to a relative drift value of 4×10−5/h.

Ion-trap laser

Abstract: Laser operation with a single trapped Ca+ ion in a high-finesse optical cavity is predicted at a wavelength of 866 nm. Different from a conventional laser, the formation of two thresholds can be observed. For both small and large pump strengths the field is quasi-thermal, in an intermediate region laser light with Poissonian and even sub-Poissonian statistics is produced. Atomic coherence effects play an important role. The multi-level system is treated by generalizing the pump-operator approach (Europhys. Lett., 33 (1996) 515).

High power laser optical amplifier system

Abstract: A high power laser optical amplifier system for material processing comprises multiple stage fiber amplifiers with rejection of propagating ASE buildup in and between the amplifier stages as well as elimination of SBS noise providing output powers in the range of about 10 μJ to about 100 μJ or more. The system is driven with a time varying drive signal from a modulated semiconductor laser signal source to produce an optical output allowing modification of the material while controlling its thermal sensitivity by varying pulse shapes or pulse widths supplied at a desire repetition rate via modulation of a semiconductor laser signal source to the system to precisely control the applied power application of the beam relative to the thermal sensitivity of the material to be processed. The high power fiber amplifier system has particular utility in high power applications requiring process treatment of surfaces, such as polymeric, organic, ceramic and metal surfaces, e.g., material processing, surface texturing, heat treatment, surface engraving, fine micro-machining, surface ablation, cutting, grooving, bump forming, coating, soldering, sealing, surface diffusion and surface conversion to a compound. A particular example is given for texturing of disk surfaces of magnetic disk media prior to the deposition or coating of a thin magnetic film on the textured surfaces to prevent slider stiction.

Formation of a crack-free joint between Ti alloyand Al alloy by using a high-power CO2 laser

Abstract: The present paper aims at producing a crack-free weld between a commercially available Ti alloy (Ti-6 wt% Al-4 wt% V) and a wrought Al alloy (Al-1 wt% Mg-0.9 wt% Si). Ti alloy and Al alloy with a plate thickness of 3 mm are butt welded using a 2.5 kW continuous CO2 laser. The laser power, welding speeds and offset of the laser with respect to the joint are considered as the variable parameters. It is observed that intermetallic compounds (mainly TiAl and Ti3Al) are formed in the fusion zone depending on the amount of Al and Ti melted by the laser. These intermetallic phases are very brittle and the solid-state cracks are formed near the Al side of the interface because of the stress developed after the solidification.

Spectral characteristics of an all solid-state frequency-shifted feedback laser

Abstract: A laser cavity closed via the first-order diffracted light of an acoustooptic modulator is referred to as a frequency-shifted feedback laser (FSF laser). This laser exhibits outstanding features in its oscillation spectrum. We previously demonstrated the first oscillation of an all solid-state FSF laser, and it turned out experimentally that the oscillation spectrum consists of a continuously chirped comb of frequency components. Furthermore, we have been investigating oscillation dynamics both experimentally and analytically for a better understanding of FSF laser. Here experimental results and analyses on the spectral characteristics of the laser are discussed.

All-optical logic NOR gate using a semiconductor laser amplifier

Abstract: The authors report on the realisation of a NOR gate using SLA. The operation is based on the nonlinearity of the SLA gain. The power difference between the output logic level is > 100 µW with a 9 dB contrast.

Phased array Raman laser amplifier and operating method therefor

Abstract: A phased array Raman laser amplifier includes a beam generator for generating a fundamental laser beam and a Raman seed frequency laser beam, and a fiber optic laser amplifier array for forming a diffraction limited output laser beam at the Raman seed frequency by amplifying the fundamental laser beam to a power level corresponding to the Stimulated Raman Scattering (SRS) threshold to thereby pump the SRS process and provide Raman gain to the Raman seed frequency laser beam. The fiber optic laser amplifier includes a beam splitter receiving the fundamental laser beam and the Raman seed frequency laser beam and generating N secondary fundamental and N Raman seed frequency laser beams, N parallel rare earth doped optical fiber sections, each of the optical fiber sections amplifying a respective one of the N secondary fundamental laser beams to thereby produce N tertiary laser beams at the power level corresponding to the Stimulated Raman Scattering (SRS) threshold to thereby pump the SRS process and provide Raman gain to the N Raman seed frequency laser beams to thereby produce N amplified Raman seed frequency laser beams, and an optical combiner for receiving at least the N Raman seed frequency laser beams and for generating the diffraction limited output laser beam at the Raman seed frequency. Preferably, N is an integer greater than or equal to 2. A method for operating the phased array Raman laser amplifier is also described.

Fiber optic micro-doppler ladar system and operating method therefor

Abstract: A micro-doppler ladar system for identifying and analyzing a target of interest includes a transmitter and coherent receiver pair, each of which includes a fiber optic power amplifier, and a controller. Preferably, the transmitter includes a master oscillator for generating a primary laser beam, a voltage controlled oscillator (VCO) for generating a VCO signal having a predetermined, repetitive frequency pattern, a frequency shifting circuit for varying the frequency of the primary laser beam responsive to the VCO signal to thereby produce a frequency-varying primary laser signal, and the optical fiber amplifier, which amplifies the frequency-varying primary laser signal to thereby produce a transmit laser beam. In addition, the coherent receiver, which responds to backscattered light produced by the interaction of the transmit laser beam with the target of interest, includes an optical fiber pre-amplifier for amplifying the backscattered light to thereby produce an amplified return laser beam, and a phase locked loop receiving the primary laser beam and the amplified return laser beam for generating an electrical signal indicative of range, velocity and a characteristic signature of the target of interest. The transmitter and coherent receiver can be operated in a target acquisition mode of operation for determining range and velocity, and a signature acquisition mode of operation for determining a characteristic signature of the target of interest responsive to the electrical signal. A method for operating the micro-doppler ladar system is also described.

Diode-pumped, room-temperature Tm:YAP laser.

Abstract: Room-temperature operation of a continuous-wave Tm:YAP laser is reported. A 3 W laser diode in an end-pumped geometry is used to generate 730 mW of thulium laser output, which represents a conversion efficiency of 42% in terms of absorbed pump power. The laser operates on a number of lines in the wavelength range 1.965 to 2.020 μm.