AlGaAs Laser Diode Research Articles

Low-cost low-threshold diode end-pumped Tm:YAG laser at 2.016 μm

We report a low-threshold continuous-wave Tm:YAG laser that can be excited near 785 nm with low-cost, single-mode AlGaAs laser diodes. Low-threshold operation was achieved using a tightly focused, astigmatically compensated x-cavity containing a 2-mm-thick Tm:YAG crystal with 5 % Tm3+ concentration. Two linearly polarized single-mode diodes operating at 785.8 nm were polarization coupled to end pump the resonator. With a 6 % output coupler, as high as 32 mW of output power could be obtained at 2016 nm with 184 mW of incident pump power. The output could be further tuned in the 1935–2035 nm range. Slope efficiency measurements indicated that cross-relaxation was very effective at this doping level. With a 2 % output coupler, lasing could be obtained with as low as 32.3 mW of pump power. In the limit of vanishing output coupling, the incident threshold pump power could be reduced to as low as 25 mW. To our knowledge, this is among the lowest lasing thresholds reported to date for continuous-wave, room-temperature thulium lasers.

Characterization of analog modulation of AlGaAs lasers and the induced intensity noise

The dynamics of AlGaAs laser diodes under analog intensity modulation are characterized and the associated intensity noise is evaluated. The study is based on numerical solution of the stochastic rate equations of semiconductor lasers. Based on the shape of the modulated laser signal, the modulation dynamics are classified into eight distinct types. Four types are characterized by continuous periodic signals, and three types have periodic pulsing signals. These signals happen to have period doubling or superposed by sub-peaks from the relaxation oscillations of the laser. The last type is chaos, in which the signal is irregular and non-uniform. The noise results show that the relative intensity noise is closest to the quantum level under weak modulation where the laser signal is sinusoidal. LF-RIN is pronounced when the laser emits irregular spike-like pulses under low-frequency strong modulation. The chaotic dynamics dominate the region of strong with modulation frequencies around the relaxation frequency of the laser.

Diode laser hair removal around ileo‐colo ostomys is safe, effective and beneficial: A pilot study

Hair removal around an ileo-colo ostomy can cause a number of problems. We compared laser hair removal with mechanical shaving around the ostomy. Eleven patients were selected with hairy skin around the ostomy for therapy with an AlGaAs diode laser at 800 nm. Three to four treatments were given with an interval of 6 weeks. Ten patients completed laser therapy. The average hair reduction was 60% based on visual inspection. Shaving frequency reduced from once a week to once every 6 weeks. Laser hair removal likely becomes the preferred method in ostomy patients.

Reduced threshold current in (111)B grown InGaAs∕AlGaAs laser diodes: The positive role of piezoelectric effect

The authors demonstrate that (111)B grown InGaAs∕AlGaAs laser diodes outperform their (100) counterparts, in terms of lower threshold currents observed for all temperature and cavity lengths tested. A low temperature threshold current density as low as 15A∕cm2 has been observed in (111)B grown devices, whereas identical (100) laser diodes exhibited threshold in the range of 30–40A∕cm2. The comparison of experimental findings with a Poisson-Schrodinger self-consistent model reveals that the improved performance of the (111)B devices is attributed to the piezoelectric field present in the (111)B In0.1Ga0.9As active quantum well as well as to the different heavy hole effective masses in the (111)B configuration.

Proton radiation effects in nitride lasers and light emitting diodes

AbstractNitride laser diodes and light emitting diodes were irradiated with 200‐, 80‐ and 10‐MeV protons. The threshold current of violet laser diodes increased with increasing proton fluence to 1 × 1014 p/cm2. The increase in threshold current is considerably small compared with that of AlGaAs laser diodes. Proton energy dependence of the change of threshold current was a little bit different from that of GaN NIEL. Oscillation wavelength did not change before and after irradiation. The defect levels made by proton irradiation do not seem to be radiative recombination centers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and characterization of a diode-pumped Nd:YAG retroreflecting slab laser

We describe the design and lasing characteristics of a miniaturized, chip-scale Nd:YAG slab laser. The Nd:YAG laser slab utilizes a retroreflecting corner to achieve a 17-cm optical path length with slab geometry of 10×12×2 mm. The laser is constructed, tested, and shown to successfully lase at 1064 nm under edge pumping with an AlGaAs diode laser at 808 nm. The slab laser is operated in a pulsed-pump excitation mode and shown to support a TEM10 single output mode. The fluence achievable from the edge pumping of this initial cavity geometry results in a 6.0% experimentally measured lasing efficiency.

Defect engineering for high-power 780 nm AlGaAs laser diodes

Defect engineering is carried out to determine optimum growth conditions for highly reliable high-power 780 nm AlGaAs laser diodes (LDs) using deep level transient spectroscopy (DLTS). The DLTS results reveal that the defect density of the Al0.48Ga0.52As cladding layer depended heavily on growth temperature and AsH3 flow but that of the Al0.1Ga0.9As active layer depended mostly on the growth rates of the active layer. As a result of layer optimization at growth condition by DLTS, a record high output power of 250 mW was obtained at an operating current as low as 129.6 mA under room temperature continuous wave (CW) operation.

Continuous wave operation of a 250 mW AlGaAs laser diode

We report a record high continuous wave (CW) output power of 250 mW for the 780 nm band AlGaAs laser. The selectively buried ridge (SBR) structure was used and each layer of the laser was designed to have the lowest defect density by using the deep level transient spectroscopy (DLTS) analyses. The laser operated at a peak wavelength of 783 nm with a threshold current of 38 mA. The stable fundamental transverse mode was observed at 100 mW, 70 °C for more than 3000 h. The far-field aspect ratio, a ratio of far-field vertical angle over far-field parallel angle to the junction plane, was measured to be 1.8, which is small enough for the high density CD-R system.

Spectroscopic and laser properties of Nd3+:Gd0.2Y0.766Al3(BO3)4 laser crystal

Abstract The absorption and fluorescence spectra of Nd3+:Gd0.2Y0.766Al3(BO3)4 crystal have been measured. Basing on Judd–Ofelt and TPM theory, intensity parameters Ω t (t=2,4,6), radiative lifetime, experimental and theory oscillation strength, fluorescence branching ratios and stimulated emission cross-sections were obtained and related to the laser action of this crystal. A laser output of 48 mW at 1060 nm and of 78 mW at 1300 nm with the optical to optical efficiency of 20% and of 9.75% respectively were obtained under a Ti–sapphire laser pumping. Meanwhile, a laser output of 26.7 mW at 532 nm with an optical to optical efficiency of 10.68% was obtained when it was pumped by a AlGaAs diode laser.

The Effect of Pressure and Temperature on AlGaInP and AlGaAs Laser Diodes

InGaP/AlGaInP lasers (emitting from 630 to 690 nm) and GaAs/ AlGaAs lasers (emitting at 780 nm) were studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 to 300 K. The electrical characteristics, the power-current dependencies and the emission spectra were measured. The emission spectra shifted in agreement with the pressure/temperature variation of the band gaps in active layers of the laser. Since at high pressure the Γ-X separation in the conduction band is strongly reduced (both in AlGaInP and AlGaAs), the dominant loss mechanism of the lasers is the electron leakage to X minima in the p-claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple theoretical analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Better agreement between the theory and the experiment is obtained assuming drift rather than diffusion leakage. This indicates that threshold currents could be further reduced if the p-doping is improved in the claddings.

Characterization and Spatial Matching of Laser Diode Beams

It is shown that the type of lateral waveguide of a laser diode cannot be determined uniquely based on just the measured magnitude of astigmatism. For a unique determination, the K-factor of Petermann, which characterizes the wavefront curvature at the laser output facet, must be measured as well. In order to determine the type of lateral waveguide, a setup for measuring astigmatic distances in the range 0–200 μm with an error of ±2 μm and a K-factor with an error of 20% was developed. Operational features of the setup were analyzed, and a technique that allows one to minimize the effect of beam ellipticity on the measurement results was found. Using the technique, the optimization of spatial matching of a laser diode with a ring interferometer of the “butterfly” type was accomplished. For transformation of the astigmatic elliptical beam into the axially symmetric mode of the interferometer, we have used an optical system that consists of two cylindrical and one spherical lenses. The algorithm for designing the matching system was developed, and the 85% injection of radiation of a AlGaAs laser diode into the principal mode of a ring interferometer was experimentally demonstrated.

Damage profile of He implantation in AlGaAs laserdiode material detected by photoluminescence

The extension of the damaged region in a GaAs/AlGaAs layer system after helium isolation implantation was investigated for different energies using the photoluminescence from GaAs quantum wells. It was found that the range of created defects is in good agreement with the results of TRIM simulations for vacancies.

Packaging-induced stress distribution in high power AlGaAs laser diodes by photoluminescence mapping

The microphotoluminescence (μ-PL) technique is proposed for mapping local stress distribution in GaAs/AlGaAs high power laser diode arrays (LDAs). This technique will be used to monitor the stresses that can be induced on the bars during the packaging process. We show herein that also a detailed study of the stress profiles that could exist in the bars before mounting and after aging can be achieved with this technique.

High-power and highly reliable 780 nm band AlGaAslaser diodes with rectangular ridge structure

A record light output power of 240 mW has been achieved for the 780 nm band AlGaAs laser diodes by using a rectangular ridge structure. The laser diodes have been operated for >1000 h at 60/spl deg/C under 150 mW pulsed operation.

Over 200-mW operation of single-lateral mode 780-nm laser diodes with window-mirror structure

The high-power operation of the lateral mode stabilized 780-nm AlGaAs laser diode (LD) with the window-mirror structure has been achieved. The stable lateral mode operation up to 250 mW is realized. This is the highest power record among the narrow stripe LDs with the wavelength of 780 nm. This LD is suitable for the next generation high-speed (16-24/spl times/) CD-R/RW drives needing 200 mW class LDs.

Fabrication of a Highly Efficient Quasi-phase-match Device for Blue-Violet Second-Harmonic Generation.

We present a method for controlling the shape of the domain-inverted structure in an off-cut MgO: LiNbO3 crystal utilizing two-dimensional high-voltage application. Using this technique, a periodically domain-inverted structure with a period of 3.2 Jim and thickness of 2.0 μm was fabricated over a 10-mminteraction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated a cw blue-violet second-harmonic generation of 17.3 mW at the wavelength of 426 nm with a single pass of 55 mW of cw AlGaAs laser diode input, which corresponded to a 31 % power conversion efficiency.

31%-efficient blue second-harmonic generation in a periodically poled MgO:LiNbO_3 waveguide by frequency doubling of an AlGaAs laser diode

We present a method of controlling the shape of the domain-inverted structure in an off-cut MgO:LiNbO(3) crystal by utilizing a two-dimensional high-voltage application. With this technique a periodically domain-inverted structure with a period of 3.2 microm and a thickness of 2.0 microm was fabricated over a 10-mm interaction length. This structure has made possible sufficient overlaps between propagation modes and domain inversion in the waveguide. Using this structure, we demonstrated cw blue second-harmonic generation of 17.3 mW of power at a wavelength of 426 nm with single-pass 55-mW cw AlGaAs laser diode input, which corresponded to 31% power-conversion efficiency.

Microphotoluminescence mapping of packaging-induced stress distribution in high-power AlGaAs laser diodes

Spatially resolved photoluminescence line scans were performed to determine the local stresses in AlGaAs laser diodes designed for high-power operation at 808 nm. In this approach, the sign and magnitude of the local stress are deduced from the spectral shift of the peak associated with band-to-band transitions in the n-type GaAs substrate. The sensitivity of the technique (minimal equivalent hydrostatic stress that can be detected) can reach 10 MPa or better. Correlations between solder-induced stress distribution in the devices and estimated lifetimes are demonstrated.

High-power, reliable operation of 730 nm AlGaAs laser diodes

High-power operation of AlGaAs multi-quantum-well laser diodes emitting near 730 nm is reported. 1000 h, reliable operation at a power of 1.0 W for 100 μm emission aperture and 500 μm cavity length devices has been demonstrated at room temperature. These devices have threshold current densities of 770 A/cm2 with the characteristic temperature coefficients of threshold current, T0, and external differential quantum efficiency, T1, of 152 and 167 K, respectively.

Emission properties of a Tm 3 0 .1mm+ :GdVO 4 microchip laser at 1.9 μm

as a host for thulium has several advantages for diode pumping in comparison with other crystals. The absorption cross section of thulium in GdVO4 is considerably stronger and broader than in YAG and YLF and the spectrum is shifted closer to the emission wavelength of commercially available AlGaAs laser diodes. In our paper, we report on the temporal and spectral emission properties of a monolithical Tm30.01mm+([%at.]6.9):GdVO4 microchip laser at 1.9 μm. The laser can be adjusted to emit either cw or in an oscillating regime. Slope efficiencies up to 47% are achieved. This value exceeds the Stokes limit of 42%.