690-nm high-power, high-brightness visible laser diode

With continued improvements in materials growth and device fabrication the output power from visible high power semiconductor lasers has been steadily increasing. This paper presents data on high power semiconductor lasers in the visible wavelength around 690 nm operating at room temperature. This InGaAIP broad area 200 micron by 1 micron stripe diode laser that operates at 750 milliwatts output power, and has a threshold current density of435 Amps/cm2. The laser structure was grown by MOCTD on a gallium arsenide substrate and incorporate a tensile strained single quantum well separate confinement heterostructure, a composition profile ofthe laser structure is shown in Fig 1. A 200 micron stripe was defined by proton bombardment, and the wafer was cleaved into 800 micron long cavities. The laser facets were AR and HR coated. The chips were mounted on a custom manufactured oxygen free high conductivity copper heatsink. The laser heat sinks were designed to be as small as possible while still providing adequate heat sinking for the laser chip, at the rated output power ofthe diode. The lasers were initially tested (power Vs current) and then burned in for 1 00 hours at rated output power and after burn-in the diodes were measured for efficiency, beam divergence, wavelength, and power Vs current. The threshold current is around 700 milliamps, and the lasers have a slope efficiency of 0.7 watt/Amps, Fig 2 is the power Vs current for a typical unit. With a forward voltage of these diodes in the 2.3-2.3 range and the overall efficiency is 20 percent. Several lasers have been operated up to 1 watt power at 2.1 Amps drive current Fig 3 is power Vs current for these lasers. At this level the laser shows signs ofbeginning to roll over because ofthermal dissipation. Far field beam divergences both parallel to the junction and perpendicular to the junction the full width half maximum divergences was 6 degrees and in the plane perpendicular to the junction the full width half maximum divergence was typically 32 Degrees Fig 4. The spectral width of these high power visible lasers is about 1 nanometer, in Fig 5. The horizontal scale is2 cm per division. Commercially available lasers are packaged in a high heat load package with TE cooler, monitor diode, and thermistor for sensing diode temperature. The TE cooler is rated at 40 watts (5 Amps, S Volts) and the monitor sensitivity is around 10 micro/Amps per milliwatts output at 0 Volt bias