Third‐order optical nonlinearities and recombination processes of photoexcited electron‐hole plasma in PbSe and PbTe are directly monitored by picosecond pump‐probe experiments in the wavelength range from 3 to 10 μm. After excitation, a strong blue shift of the absorption edge and large changes of the refractive index are found. Time‐resolved studies of the absorption changes at lattice temperatures between 70 and 160 K reveal a fast partial decrease of the carrier density within 100 ps at excitation densities exceeding 7×10¹⁷ cm⁻³. Comparative emission spectra demonstrate that this behavior is due to recombination by stimulated emission. At room temperature the nonradiative Auger recombination dominates on a 0.5–2 ns time scale below the threshold of stimulated emission. The overall Auger coefficients for carrier densities of about 10¹⁸ cm⁻³ are derived from the data and have values of c_A^PbSe=1.1±0.3×10⁻²⁸ cm⁶/s and c_A^PbTe=2.5±1.3×10⁻²⁸ cm⁶/s.

The dielectric function of PbS quantum dots (Qdots) with diameters of 3.5-5.0 nm in glass matrix is determined from transmission measurements by Maxwell-Garnett effective medium theory combined with iterative Kramers-Kronig analysis. The algorithm used provides real and imaginary part of the dielectric function in the 200-1800 nm spectral range, for both Qdot-doped glasses as well as the PbS Qdots alone. The latter data are compared with the results obtained from colloidal PbS quantum dots and, within the limits of the experimental error, agreement is found.

Carrier transfer between quantum dots (QDs) in very dense InAs/GaAs QD arrays is studied by means of steady state and time-resolved photoluminescence spanning a wide range of laser power from ${10}^9$ to ${10}^{13}$ $\mathrm{photons}/(\mathrm{pulse}\times {\mathrm{cm}}^2).\mathrm{}$ Carrier transfer involves transitions from the ground state of small QDs into lower lying states of larger QDs, a relaxation channel that saturates at high excitation densities. The transition from saturation of the interdot carrier transfer to the unsaturated regime is identified by analyzing the temporal shape of the luminescence signal for decreasing excitation densities. The rate equation model is proposed to account the temporal evolution of photoluminescence in dense QD systems. Numerical simulations of the carrier transfer and relaxation including the interdot coupling are in good agreement with the experimental results.

The transient thermal properties of high-power diode laser bars with active and passive cooling are analyzed. Both thermal imaging and the analysis of the thermal wavelength tuning behavior are employed to extract the device temperature as a function of time. A steady-state thermal situation is established with rise times of about 10 and $60\mathrm{ms}$ for active and passive cooling, respectively. The latter number, however, is substantially increased by the particular properties of the external heat sink. Such results are confirmed by model calculations based on the finite element method.

The early stages of catastrophic optical damage (COD) in 808 nm emitting diode lasers are mapped by simultaneously monitoring the optical emission with a 1 ns time resolution and deriving the device temperature from thermal images. COD occurs in highly localized damage regions on a 30 to 400 ns time scale which is determined by the accumulation of excess energy absorbed from the optical output. We identify regimes in which COD is avoided by the proper choice of operation parameters.

Imaging thermography in the $3\text{–}5\mu \mathrm{m}$ wavelength range is applied to the analysis of thermal properties of high-power diode lasers. We investigate these devices by inspecting their front facets as well as their active regions along the resonator. The latter is done through top windows within the substrate. Raw data are found to be mostly interfered by thermal radiation traveling through the substrate, which is transparent for infrared light. Substracting this contribution and recalibration allows for obtaining realistic temperature profiles along laser structures. Facet heating is analyzed complementary by micro-Raman spectroscopy. We show how hot spots at the front facet, in the substrate, or even in the active region within the substrate are discovered. Our approach paves the way for an advanced methodology of device screening.