Design considerations and analytical approximations for high continuous-wave power, broad-waveguide diode lasers

Accurate analytical approximations are derived for the equivalent transverse spot size, d/Gamma (<5% error), and the transverse beamwidth theta(1/2) (<2% error), of broad-waveguide-type diode lasers, over a wide range in waveguide width: from the first-order-mode cutoff to the third-order-mode cutoff. The analytical formulas are found to be in good agreement with experimental values. For low-series-resistance and thermal-resistance devices, it is found that the junction-temperature rise Delta T-j in continuous wave (CW) operation is a strong function of both the characteristic temperature T-1 for the external differential quantum efficiency eta(D) as well as of the heatsink thermal resistance. If the device has relatively temperature-insensitive eta(D) (i.e., T1 greater than or similar to 1000 K) the maximum CW power as well as the power density at catastrophic optical mirror damage, (P) over bar(COMD), are limited, for a given active-region material, only by the heatsink heat-removal ability. For large d/Gamma, 0.97 mu m emitting, 100 mu m stripe InGaAs/InGaAs(P)/GaAs devices with T-1 = 1800 K, record-high CW and quasi-CW (100 mu s wide pulses) output powers are obtained. The ratio of quasi-CW to CW (P) over bar(COMD) values is only 1.3, in contrast to devices of poor carrier confinement and subsequent low-T-1 values (similar to 140 K), for which the ratio is 1.9, and whose maximum CW powers are similar to 40% less than those obtainable from high-T-1 devices. (C) 1999 American Institute of Physics. [S0003-6951(99)03421-X].