R. Staske

12 W continuous-wave diode lasers at 1120 nm with InGaAs quantum wells

Highly strained InGaAs quantum wells were grown by metalorganic vapor-phase epitaxy. By lowering the growth temperature to 530 °C, a maximum photoluminescence wavelength of 1192 nm was achieved. High-power diode lasers with a maximum lasing wavelength of 1175 nm were fabricated. A continuous-wave output power of 12 W at a heat-sink temperature of 25 °C was obtained at a lasing wavelength of 1120 nm.

Mounting of high power laser diodes on boron nitride heat sinks using an optimized Au/Sn metallurgy

High power diode lasers have become more and more important to industrial and medical applications. In contrast to low power applications, long cavity lasers or laser bars are used in this field and mounting quality influences considerably laser performance and life time. In this paper we focus on the solder metallurgy and stress-induced laser behavior after mounting. The laser chips have been bonded fluxless epi-side down on translucent cubic boron nitride (T-cBN) using Au/Sn solder. The laser behavior has been tested with different chip metallizations preserving the eutectic solder composition or forming the Au rich /spl zeta/-phase during reflow. The resulting additional stress in the lasing region has been independently indicated by polarization measurements of the emitted light. A metallization scheme has been developed which forms the highly melting /spl zeta/-phase during soldering within a wide process window. This procedure yields better results then using eutectic Au/Sn which has a higher hardness than the /spl zeta/-phase. Laser diodes up to a cavity length of 2000 /spl mu/m and an aperture of 200 /spl mu/m have successfully been mounted on T-cBN. State of the art laser data, excellent thermal stability, high yield and reliability have been obtained.

20W continuous wave reliable operation of 980nm broad-area single emitter diode lasers with an aperture of 96μm

High power broad area diode lasers provide the optical energy for all high performance solid state and fiber laser systems. The maximum achievable power density from such systems is limited at source by the performance of the diode lasers. A crucial metric is the reliable continuous wave optical output power from a single broad area laser diode, typically for stripe widths in the 90-100 μm range, which is especially important for users relying on fibered multi-mode pumps. We present the results of a study investigating the reliable power limits of such 980nm sources. We find that 96μm stripe single emitters lasers at 20°C operate under continuous wave power of 20W per emitter for over 4000 hours (to date) without failure, with 60μm stripe devices operating reliably at 10W per stripe. Maximum power testing under 10Hz, 200μs QCW drive conditions shows that 96μm stripes reach 30W and 60μm stripes 21W per emitter, significantly above the reliable operation point. Results are also presented on step-stress-studies, where the current is step-wise increased until failure is observed, in order to clarify the remaining reliability limits. Finally, we detail the barriers to increased peak power and discuss how these can be overcome.

High-power, high-efficiency 1150 nm quantum well laser

Edge emitting diode lasers with highly strained InGaAs quantum wells and GaAs waveguide layers emitting at 1150 nm were investigated focusing on the impact of the waveguide design on the laser performance. Using a thick GaAs waveguide layer broad area devices with low vertical divergence of 20/spl deg/ FWHM and reliable operation at a power level of 80-mW//spl mu/m stripe width were demonstrated.

Comparative theoretical and experimental studies of two designs of high-power diode lasers

Design and technology developments targeted at increasing both power conversion efficiency and optical output power of GaAs-based diode lasers are under intense study worldwide, driven by the demands of commercial laser systems. The conversion efficiency at the operation point is known to be limited by electrical and optical losses in the p-side waveguide. In this paper an ‘extreme, double asymmetric’ design to mitigate the impact of the p-side waveguide is studied and compared with a more conventional design. An increase of the efficiency at the highest power is demonstrated, but it is less than expected from simulations.

5.6-W Broad-Area Lasers With a Vertical Far-Field Angle of 31

Highly efficient 670-nm high-power broad-area laser diodes with a single InGaP quantum-well embedded in AlGaInP waveguide layers and n-AlInP and p-AlGaAs cladding layers are presented. The developed vertical layer structure leads to a vertical far-field angle of 31deg. At 15degC, 100 mu-m-wide broad-area lasers reach an output power of 5.6 W limited by thermal rollover. The conversion efficiency was 41% at 1.5 W. A 7600-h reliable operation at 1.5 W and a mean time to failure of about 37550 h will be reported.

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Optical power from 1100 nm broad-area laser diodes is found to be limited by the accumulation of minority carriers in the waveguide layer, caused by a small effective barrier between the quantum wells and the GaAs waveguide. This effect is visible as enhanced spontaneous emission at high currents. We show that increasing the number of QWs mitigates this effect and leads to higher emitted powers. Optimized devices deliver more than 55 W per 60 µm stripe width under 300 ns pulse operation. In this paper we present the experimental results of our study.

Emitting at 670 nm

In this paper, we present results on diode lasers in the wavelength range between 715 nm and 840 nm with Al-free QWs which are embedded in a high-quality AlGaAs LOC broadened waveguide structure with low optical loss and a small vertical far field divergence. The laser structures were grown by LP- MOVPE. We studied tensile-strained GaAsP-QWs as well as compressively strained InGaAsP-QWs with strain compensating barriers. For lasers with GaAsP QWs, the lowest transparency current densities of about 130 A/cm2 were obtained in the wavelength range between 750 nm and 800 nm. Very low transparency current densities were achieved with InGaAsP-QWs at wavelengths above 800 nm. At 810 nm, high output powers (100 micrometer aperture) of about 7 W was achieved with both types of QWs from devices mounted epi up. However, with respect to high temperature operation and reliability tensile- strained GaAsP QWs seem to be the better choice, especially for the wavelength range below 760 nm.

55 W peak power from 1100 nm wavelength 60 µm broad-area laser diodes enabled by reduced carrier accumulation in the waveguide

In this paper, results for 650 nm high-power broad area lasers and bars will be presented. The optimized layer structure consists of GaInP quantum wells embedded in AlGaInP waveguide layers. The n-cladding layer consists of AlInP, the p-cladding layer of AlGaAs. The vertical far field of this structure has a width below 32° (FWHM). Devices were fabricated and mounted p-side down on CuW heat spreader using AuSn solder. Broad area lasers reach a maximum output power of 0.94 W at 15°C limited only by thermal rollover. Up to now reliable operation at 500 mW over 6300 h was achieved. The spectral width of the emission is below 1 nm (FWHM). Bars consisting of 19 emitters with 30 μm x 750 μm reached a maximum output power of 9.6 W and a wall-plug efficiency of 30%. Reliable operation from a 5 mm bar at 5 W and 15°C over 1500 h was shown.

Diode lasers with Al-free quantum wells embedded in LOC AlGaAs waveguides between 715 nm and 840 nm

Many solid state laser systems rely on transverse- magnetic polarized 808-nm diode lasers, whose efficiency is limited by the transparency current of the quantum well and whose peak power is limited by facet failure. Using optimized epitaxial growth, low voltage designs, and optimized facet reflectivity, we demonstrate 70% power conversion efficiency at 80 W in 1-cm laser bars under continuous-wave (CW) test conditions. We assess peak power limits in single emitters and find that 100-mum stripe lasers roll thermally under the CW condition at 13 W without failure, then reach >50 W under 300-ns pulse condition, where they fail at internal defects.