About the physical meaning of the critical temperature for catastrophic optical damage in high power quantum well laser diodes

Abstract

Short title: About the physical meaning of the critical temperature for catastrophic optical damage AbstractIt is usually assumed that the catastrophic optical damage of high power laser diodes is launched when a critical local temperature (Tc) is reached; temperatures ranging from 120ºC to 200ºC were experimentally reported. However, the physical meaning of Tc in the degradation process is still unclear. In this work we show that, in the presence of a local heat source in the active region, the temperature of the laser structure, calculated using finite element methods, is very inhomogeneously distributed among the different layers forming the device. This is due to the impact that the low dimensionality and the thermal boundary resistances have on the thermal transport across the laser structure. When these key factors are explicitly considered, the quantum well (QW) temperature can be several hundred degrees higher than the temperature of the guides and cladding layers. Due to the size of the experimental probes, the measured critical temperature is a weighted average over the QW, guides and claddings. We show the existence of a great difference between the calculated average temperature, equivalent to the experimentally measured temperature, and the peak temperature localized in the QW. A parallel study on double heterostructure lasers is also included for comparison.

Nanoscale effects on the thermal and mechanical properties of AlGaAs/GaAs quantum well laser diodes: influence on the catastrophic optical damage

“…In previous works [4,13] we expected the onset of the COD process to occur at the crosshatch of the calculated Tresca stresspeak temperature data and the experimental curve for the yield strength of GaAs. For a facet heat source, this concurrence establishes a critical temperature of about 480 K. In a recent publication [12] we discussed the difference between this estimated local temperature and the commonly reported critical temperatures for COD, as derived from techniques with a micrometric resolution. A distribution with a maximum of 480 K leads to a very low mean temperature compared to the experimental values [12].…”

“…A uniform local heat source, generated by the accumulation of energy in the defect rich region of the active zone, has been assumed [12,13]. The heat transfer equation has been solved using finite element methods (FEM).…”

“…The thermal transport across the laser is limited because of the reduced thicknesses of the central layers and the presence of interfaces [10,11]. This leads to an inhomogeneous temperature distribution and results in a severe peak temperature underestimation [12].…”

“…We discuss the catastrophic degradation using a thermo-mechanical model that takes account of the thermal transport limitations of the multilayer structure, so that it provides a realistic picture of the temperature distribution around the local heat source [12,13]. We analyse the role played by the different physical variables that participate in the COD process, both those that accelerate it, and those responsible for the laser endurance.…”

Catastrophic optical damage of high power InGaAs/AlGaAs laser diodes

“…Our model estimates a very inhomogeneous temperature distribution across the laser structure, Fig. 4, with a peak temperature at the QW substantially higher than the temperature of the surrounding layers [14].…”