mW Continuous Wave Research Articles

New electroabsorptive device with negative resistance based on a low-responsivity GaAs/AlAs multiple quantum well

We propose and demonstrate a novel electroabsorptive device which possesses N-type negative resistance. The device consists of a low responsivity GaAs/AlAs multiple quantum well modulator on top of a GaAlAs photodetector. The structure has a larger photocurrent contrast ratio in the negative resistance region (∼3:1 as the voltage changes from 0 to 15 V) than conventional self-electro-optic effect devices (SEEDs). The characteristics of the device change only a little up to high illumination levels (2 mW continuous wave in a 2.8 μm/1e2 diameter spot). We discuss the possible applications of this element as an improved bistable reflection-mode SEED and as an optically controlled microwave oscillator.

High single-mode output power from compact external microcavity surface-emitting laser diode

Transverse mode control is demonstrated in an electrically pumped surface-emitting laser diode coupled to an external microcavity with room-temperature single-mode powers reaching 2.0 mW continuous wave and 36.7 mW pulsed. The wavelength chirp is less than 0.044 nm for the pulsed results. The external microcavity is formed with a flat dielectric mirror placed less than 700 μm from the wafer surface. Diffraction and spatial filtering in the external cavity provide high-order mode suppression and produce a large fundamental mode of width 36 μm. This external cavity geometry readily lends itself to integration.

Design of High Power Electron Linac at PNC

Abstract A high power CW (Continuous Wave) test electron linac was designed to develop a higher power linac to transmute radioactive wastes. The test linac is energized by two 1.2 MW CW L-band klystrons to produce an electron beam with the energy of 10 MeV and current of 100 mA. The average beam power is 200kW–1MW for the duty factor 20–100.%. In designing such a high power linac, authors selected a traveling-wave accelerator with TWRR (Traveling Wave Resonant Ring). This is to enhance the threshold current of BBU (Beam Break-Up) and to get high accelerator efficiency that results from the low value of attenuation constant τ and high field multiplication factor M which are permitted only with TWRR. A kind of efficient cooling structure is adopted to an accelerator structure in order to disperse the generated heat by RF (Radio Frequency). The variational method is used to calculate the sizes and parameters of the disk-loaded accelerator structure employed. There is a discrepancy of the order of a few hundredth of one percent between the calculated sizes and the experimental ones. The M determined in the design agreed well with those measured in low and high power tests.

High-power buried InGaAsP/GaAs (λ=0.8 μm) laser diodes

Buried InGaAsP/GaAs (λ=0.78 μm) separate confinement-single quantum well laser diodes have been prepared and studied for the first time. It has been shown that a stable far field pattern can be observed even at 500 mW continuous wave (cw) output power for diodes with active region width of about 7 μm, and single zero-mode operation has been obtained up to 170 mW cw for diodes with a width of 3.8 μm. Mirror facet overheating for the diodes studied was an order of magnitude less than that for similar AlGaAs/GaAs diodes.

Design of High Power Electron Linac at PNC.

Abstract A high power CW (Continuous Wave) test electron linac was designed to develop a higher power linac to transmute radioactive wastes. The test linac is energized by two 1.2 MW CW L-band klystrons to produce an electron beam with the energy of 10 MeV and current of 100 mA. The average beam power is 200kW–1MW for the duty factor 20–100.%. In designing such a high power linac, authors selected a traveling-wave accelerator with TWRR (Traveling Wave Resonant Ring). This is to enhance the threshold current of BBU (Beam Break-Up) and to get high accelerator efficiency that results from the low value of attenuation constant τ and high field multiplication factor M which are permitted only with TWRR. A kind of efficient cooling structure is adopted to an accelerator structure in order to disperse the generated heat by RF (Radio Frequency). The variational method is used to calculate the sizes and parameters of the disk-loaded accelerator structure employed. There is a discrepancy of the order of a few hundr...

EFFECT OF LOW LEVEL LASER THERAPY (LLLT) ON INFERIOR ALVEOLAR, MENTAL AND LINGUAL NERVES AFTER TRAUMATIC INJURY IN 15 PATIENTS. A PILOT STUDY

The therapeutic effect of LLLT on the inferior alveolar, mental and lingual nerves was observed in a group of 15 patients with short and long-term neurosensory impairment, In six subjects with clinical symptoms of less than 1 year’s duration, improvement of sensitivity increased from ‘0’ to between 40 and 100% (average 78.3%) as estimated on the visual analogue scale (VAS). In eight patients with clinical symptoms of more than 1 year improvement increased to between 40 and 90% (average 66.9%). Only one patient had no improvement, but remained at 20% level on the VAS. LLLT was applied using an infrared diode laser (GaAlAs 830 nm, 70 mW continuous wave), with a dose of 4.9 J/cm2 at each point three times per week and varied between 2 and 8 weeks, Considerable improvement of sensation was observed after the final treatment session. No side-effects were reported and patients have maintained the effective results for 2 years follow-up. In future studies, methods should be developed to investigate the possible effect of LLLT on peripheral nerve injuries.

LOW REACTIVE-LEVEL 830 NM GaAlAs DIODE LASER THERAPY (LLLT) SUCCESSFULLY ACCELERATES REGENERATION OF PERIPHERAL NERVES IN HUMAN

Forty patients with short and long-term neurosensory impairment following perioral nerve injuries are presented in this study. Assessment of their sensory level was undertaken using a variety of nerve tests, one of them was a visual analogue scale (VAS) for registration of sensitivity level prior to and after 10 treatment sessions and additionally for 21 of the 40 patients after 20 treatment sessions. Low level laser therapy (LLLT) was applied using GaAlAs 830 nm, 70 mW continuous wave, Dose of 6.0 J/cm2 was standardized for all patients. Improvement of the eight patients with clinical symptoms of less than 1 year after 10 treatments, was between 40-90% (average 51.9%) and after 20 treatments between 60-80% (average 66.7%) for the three patients who continued with the treatment. In 32 of the 40 patients with clinical symptoms of more than 1 year duration, their improvement was estimated at between 40 and 80% (average 54.8%), 21 patients completed 20 treatment sessions and the end results were between 60-90% (average 71.1%). This was an uncontrolled clinical study of LLLT on perioral nerve injuries and demonstrated the effectiveness of GaAlAs laser on the nerve involved when applied to the nerve trunk and terminal endings. Although controlled research into actual mechanisms and pathways is needed, the preliminary findings are very promising.

High-power InGaAs/GaAs singlemode laser diodes with reactive-ion-etched ridges

Continuous-wave (CW)output powers in excess of 320 mW with fabrication yields as high as 90% have been realised from strained-layer InGaAs/GaAs ridge waveguide laser diodes fabricated by SiCl4 reactive ion etching. Single longitudinal mode operation to 100 mW and single spatial mode operation up to 200 mW CW at a wavelength of 965 nm wereachieved for 3.5 μm-wide, 650μ-long discrete devices mounted junction-side down. The relative intensity noise at frequencies of 1–2 GHz is ̃140 –150 dB/Hz.

High power InGaAs/AlGaAs singlemode laser diodes suitable for pumping Pr3+-doped fluoride fibre optic amplifiers

Performance characteristics are presented for high-power, singlemode, strained-layer InGaAs/AlGaAs quantum well separate confinement laser diodes. A maximum output power of 460 mW continuous wave with single transverse mode behaviour to 245 mW is achieved in the wavelength range 1020-1030 nm. These singlemode laser diodes have narrow far-field divergence, making them highly attractive as optical pumps for Pr/sup 3+/-doped fluoride fibre optic amplifiers. >

Electrically gain-switched vertical-cavity surface-emitting lasers

The authors report electrical gain-switching of a packaged vertical-cavity surface-emitting laser (VCSEL). Pulse durations as short as 24 ps at repetition rates up to 2 GHz were obtained from a four-quantum-well GaAs/AlGaAs VCSEL, which emits 0.8 mW continuous wave power in a single mode at room temperature and has a current threshold of 5 mA. Simultaneous measurement of the optical spectrum showed an almost transform limited linewidth indicating ultralow chirp. Optical pumping with subpicosecond pulses of the same packaged devices, held at a constant electrical bias, yielded 22 ps pulses, in good agreement with the electrical pumping. Simple calculations show that the pulse duration obtained by gain-switching is limited by the design constraints necessary to operate the VCSEL continuous wave at room temperature with low-threshold current, high-quantum efficiency, and reasonable output power.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Surface emitting InGaAsP/InP distributed feedback laser diode at 1.53 mu m with monolithic integrated microlens

Monolithic integration of a distributed feedback (DFB) surface-emitting laser diode with a microlens is demonstrated. The transverse and longitudinal cross-sectional views of the laser diode are illustrated. The microlens and a DFB laser structure are located on opposite sides of an n-InP substrate. 11 mA minimum continuous wave (CW) threshold current and 5 mW CW emission perpendicular to the InP substrate are achieved at room temperature using a chemically etched 45 degrees mirror. Single mode emission at 1.53 mu m is obtained. The integrated microlens, etched by ion beam and coated with aluminum oxide, provides optical beam collimation and an ultralow laser mode reflectivity of <10/sup -4/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Efficient continuous wave operation of vertical-cavity semiconductor lasers using buried-compensation layers to optimize current flow

The lateral definition of vertical-cavity surface-emitting lasers (VCSELs) using buried ion implantation and the optimization of this process are described. A VCSEL structure was grown, and lasers were laterally defined using deep proton implantation process. The buried implantation process created a funnel shape current path into the laser active region. By optimizing this process, a serial resistance of 50 Ω, 2.1 mW continuous wave output power and a 1 V lower ‘‘turn on’’ voltage were achieved for an optimum dose of 1×1013 ions/cm2 for 10×10 μm2 lasers. These improvements were achieved, while retaining the same low threshold current level of fully confined VCSELs.

Single-mode InGaAs-GaAs laser diodes operating at 980 nm

Data are presented describing the operation of single-transverse, single-longitudinal mode strained-layer InGaAs laser diodes operating at λ = 980 nm. These diodes exhibit single-transverse mode behaviour to beyond 210 mW continuous wave (CW) and single-longitudinal mode behaviour to beyond 150 mW CW. The maximum output power is approximately 350 mW CW. The threshold current of these lasers is ∼ 10 mA, with a differential quantum efficiency of 85%. The total efficiency of these diodes exceeds 50% at an output power of 100 mW.

Upconversion pumped green lasing in erbium doped fluorozirconate fibre

The first demonstration of upconversion pumped lasing at green wavelengths in an Er3+-doped fluorozirconate fibre laser is reported. 15 mW continuous wave emission at a wavelength of 546 nm has been achieved for an absorbed pump power of 300 mW.

Ten-thousand-hours CW operation of 780 nm high-power AlGaAs laser with thin-tapered thickness active layer

It is investigated that the T3 (thin-tapered thickness active layer) structure is effective in reducing the carrier density in the active layer as well as the optical density near the mirror. 780 nm AlGaAs lasers with this structure have been operating under 50°C, 30 mW CW (continuous wave) conditions over 104 h with little degradation. The minimal degradation rate is about 0.45%/103 h.

High-power operation of a transverse-mode stabilised AlGaInp visible light (λL = 683 nm) semiconductor laser

Continuous-wave (CW), stable fundamental-mode operation, up to 20 mW, was achieved with transverse-mode stabilised MOVPE-grown AlGaInP visible-light (λL = 683 nm) lasers. The CW threshold current was 67 mA and the external quantum efficiency was 41%. Up to 27 mW CW power was obtained from this laser diode.

Axisymmetric quasi-optical gyrotron oscillator

An axisymmetric quasi-optical gyrotron (ASQUOTRON) is considered to realize a 10 MW, 150 GHz, CW oscillator required for an electron cyclotron resonance heating of a fusion plasma. The gyrotron has an axisymmetric mirror to be used as its optical cavity. It is shown that the axisymmetric mirror of relatively small radius (∼20 cm) can be used in producing the 10 MW continuous wave with a tolerable mirror heat load (∼0.5 kW/cm2). Considerations are also made on wave transmissions through the mirror and to a target.