According to a generally known rule of thumb, a stable single-fundamental-mode operation is achieved in standard
VCSELs with relatively uniform radial active-region gain profiles. However, in analogous detuned oxide-confined
VCSELs, lasing thresholds of higher-order modes may surprisingly be lower than that of the fundamental one. The
above unusual VCSEL behavior is explained with the aid of the comprehensive self-consistent simulation. It has
happened to be a result of a strong wavelength dependence of the active-region optical gain in highly detuned oxide-confined
VCSELs, because of which longer-wavelength higher-order cavity modes may exhibit much higher modal gain
values than that of the fundamental one. For the 10-μm-diameter mesa top-emitting 1.3-μm GaInNAs/GaAs QW VCSEL
design, the optical active region gain spectrum exhibits its maximum for the wavelength distinctly lower than that, for
which the VCSEL cavity and the DBR mirrors have been designed. As a result, the transverse LP<sub>71</sub> mode, whose
wavelength (1291.1 nm) is close enough to the maximal optical gain, has happened to be the lowest-threshold mode
(2221 cm<sup>-1</sup>). For the LP<sub>71</sub> threshold voltage, the fundamental LP<sub>01</sub> mode (1300.7 nm) manifests lower threshold (1432
cm<sup>-1</sup>), as expected, but it is still considerably higher than its available modal gain (958 cm<sup>-1</sup>).
High brightness, high power, semiconductor lasers have many potential applications such as: free space communications,
printing, material processing, pumping etc . Such applications require lasers, which are characterized by reliability
and long lifetime.
Catastrophic optical mirror damage (COMD) process is one of the major mechanisms, which drastically limits laser
lifetime and emitted optical power . Mirror degradation and eventually destruction of lasers is caused by facet heating
due to nonradiative surface recombination of carriers. Facet heating reduces the band gap energy, consequently
increasing the absorption coefficient at the facet. The absorbed light and photo-induced electron-hole pair are increased
by the increase in the absorption coefficient. Both effects lead to further nonradiative recombination of carriers which
induces heating and so on, up to degradation of mirror or even destruction of laser. We see that this effect is very
undesirable and knowledge of the temperature dissipation on the surface is very important for improving
semiconductor lasers design. In this work we present the analysis of temperature distribution at the front facet of the
broad area GaAsP/AlGaAs lasers by means of micro-Thermoreflectance (μTR) Spectroscopy.
Several methods proved to be useful in determining the temperature of the laser surface. These are micro-probe band-to-band
photoluminescence, thermoreflectance spectroscopy and Raman spectroscopy [2, 3, 4, 5]. We have used μTR
because it is contactless, non-destructive technique which enables us to obtain temperature distribution in real time.