Thomas Schwarzl

Vertical-cavity surface-emitting lasers in the 8-/spl mu/m midinfrared spectral range with continuous-wave and pulsed emission

Continuous-wave (CW) as well as pulsed-laser emission from a midinfrared (/spl lambda/=7.92 /spl mu/m) IV-VI vertical-cavity surface-emitting laser at 1.8 K is presented. The high-finesse microcavity, containing PbSe as an active medium, was optically pumped with a carbon monoxide laser at a wavelength of 5.28 /spl mu/m (1894 cm/sup -1/) in either CW or Q-switched mode. The maximum achieved CW power was 4.8 mW and pulsed peak powers were up to 23 W. Linewidths are considerably narrower than 0.10 cm/sup -1/, corresponding to 0.6 nm.

Mid-infrared vertical-cavity surface-emitting lasers based on lead salt/BaF2 Bragg mirrors

We demonstrate mid-infrared continuous-wave vertical-cavity surface-emitting lasers based on Bragg mirrors using IV-VI semiconductors and BaF2. This material combination exhibits a high ratio between the refractive indices of up to 3.5, leading to a broad mirror stop band with a relative width of 75 %. Thus, mirror reflectivities higher than 99.7 % are gained for only three layer pairs. Optical excitation of microcavity laser structures with a PbSe active region results in stimulated emission at various cavity modes between 7.3 μm and 5.9 μm at temperatures between 54 K and 135 K. Laser emission is evidenced by a strong line width narrowing with respect to the line width of the cavity mode and a clear laser threshold at a pump power of 130 mW at 95 K. Furthermore, we study a similar microcavity but without an active region. The resonance of such an empty microcavity has a narrow line width of 5.2 nm corresponding to a very high finesse of 750, in good agreement to transfer matrix simulations and to the expected mirror reflectivities.

Lead-salt-based VCSELs for the 3- to 6-μm range

Operation of IV-VI vertical-cavity surface-emitting lasers emitting in the mid-infrared is reported. The microcavity laser structures were grown by molecular-beam-epitaxy on BaF2(111) substrates. The stimulated emission is generated in PbTe quantum wells embedded in high finesse Pb0.95Eu0.05Te/EuTe microcavity structures by optically pumping with fs and ns laser pulses. Laser samples were designed for operation at 2 K, at 70 K and at room temperature with emission at 6 mm, 4.8 mm and around 3 mm, respectively. At a wavelength of 3.1 mm, laser operation is obtained up to a temperature of 65°C, limited by nonradiative recombination processes. The temperature dependence of the emission is explained in terms of the strong temperature dependence of the energy band gap of the lead salt compounds as compared to the microcavity resonance energy in agreement with envelope function calculations of the quantum well energy levels.