Diode laser systems for 1.8- to 2.3-μm wavelength range

Abstract

High-power diode lasers in the mid-infrared wavelength range between 1.8μm and 2.3μm have emerged new possibilities either for direct military applications or as efficient pump sources for laser sources in the 2-4μm wavelength range for infrared countermeasures. GaSb based diode lasers are naturally predestinated for this wavelength range and offer clear advantages in comparison to InP based diode lasers in terms of output power and wall-plug efficiency. We will present results on MBE grown (AlGaIn)(AsSb) quantum-well diode laser single emitters with emitter widths between 90μm and 200μm. In addition laser bars with 20% or 30% fill factor have been processed. More than 30% maximum wall-plug efficiency in cw operation for single emitters and laser bars has been reached. Even at 2200nm more than 15W have been demonstrated with a 30% fill factor bar. Due to an increasing interest in pulsed operation modes for these mid-infrared lasers, we have investigated single emitters and laser bars at 1940nm for different pulse times and duty cycles. More than 9W have been measured at 30A with 500ns pulse time and 1% duty cycle without COMD for a single emitter. Most applications mentioned before need fiber coupled output power, therefore fiber coupled modules based on single emitters or laser bars have been developed. Single-emitter based modules show 600mW out of a 200μm core fiber with NA=0.22 at different wavelengths between 1870nm and 1940nm. At 2200nm an output power of 450mW ex fiber impressively demonstrates the potential of GaSb based diode lasers well beyond wavelengths of 2μm. Combining several laser bars, 20W out of a 600μm core fiber have been established at 1870nm. Finally for a 7 bar stack at 1870nm we have demonstrated more than 85W at 50A in qcw mode.