M. Böberl

Midinfrared continuous-wave photoluminescence of lead–salt structures up to temperatures of 190 °C

Continuous-wave photoluminescence in the midinfrared for PbSe/PbEuSe and PbTe/PbEuTe multiquantum well structures as well as for PbSe and PbTe bulklike structures, excited by a semiconductor laser diode, is investigated. All samples are grown by molecular-beam epitaxy on BaF2(111) substrates under the same growth conditions. Both for the Te-based systems and for the Se-based systems, it turns out that bulklike structures show photoluminescence up to higher temperatures than multiquantum well structures. In particular, emission spectra from PbTe/PbEuTe multiquantum wells are obtained up to temperatures of 200 K and from PbSe/PbEuSe multiquantum well structures up to 60u200a°C whereas for bulklike PbSe photoluminescence at temperatures as high as 190u200a°C is demonstrated.

Midinfrared IV–VI vertical-cavity surface-emitting lasers with zero-, two-, and three-dimensional systems in the active regions

A comparison between IV–VI vertical-cavity surface-emitting midinfrared lasers containing active regions of different dimensionality is presented. Optically pumped laser emission is observed at wavelengths between 3.5 and 4.4 μm. The microcavities consist of high-reflectivity EuTe/PbEuTe Bragg mirrors, with active regions consisting either of a self-organized PbSe/PbEuTe quantum-dot superlattice, PbTe/PbEuTe multiquantum wells, or bulk-like PbTe. For the zero dimensional active medium, laser emission is obtained at temperatures up to 150 K. The results for the lasers with two-dimensional active region are similar to those with the three-dimensional bulk-like active region, for which lasing is observed up to 317 K. The threshold pump intensity is only 4 kW/cm2 at 195 K, and 15.6 kW/cm2 at room temperature.

Emission properties of 6.7μm continuous-wave PbSe-based vertical-emitting microcavity lasers operating up to 100K

A detailed analysis of midinfrared cw lasing of IV–VI vertical-cavity surface-emitting devices is presented. The structures, based on high-finesse microcavities containing PbSe as active medium, show optically pumped cw laser emission up to temperatures of 100K at a long wavelength of 6.7μm. Stimulated emission with a very narrow beam divergence below 1° and a large temperature tuning range of 70nm is found. The measured linewidth of the laser emission is only 0.6nm, limited by the spectrometer resolution with a strong narrowing with respect to the linewidth of the subthreshold signal. The observed cw output power amounts up to 1.2mW at 85K.

Room temperature operation of epitaxial lead-telluride detectors monolithically integrated on midinfrared filters

Epitaxial PbTe midinfrared photodetectors are monolithically integrated on optical filter structures, like λ∕4 antireflection layers or λ∕2 microcavities. The antireflection layers result in an increased photoresponsivity of the detectors by a factor of 2.2, measured at the target wavelength of 3.1μm. The microcavities, acting as efficient narrow band filters, consist of two PbEuTe∕EuTe Bragg interference mirrors separated by a PbEuTe cavity layer. The photoresponse spectra of the detectors integrated with the microcavity filters exhibit a single resonance at 3.6μm with a relative line width of 2.7%. The narrow photoresponse peak is in coincidence with a molecular absorption line typical for nonaromatic aldehydes. For all devices room temperature operation is demonstrated either in photoconductive or in photovoltaic operation mode.

Continuous-wave emission from midinfrared IV–VI vertical-cavity surface-emitting lasers

Continuous-wave emission of two midinfrared PbSe vertical-cavity surface-emitting laser structures is presented. For both structures, optically pumped cw laser emission is observed at a wavelength of about 7.9 μm. Stimulated emission is found up to temperatures of 80 K. We achieved internal threshold pump intensities of down to 25u2009W/cm2, which is two orders of magnitude smaller than reported so far. The linewidth of the laser emission is only 18 μeV (0.9 nm) with a strong narrowing as compared to the linewidth of the cavity resonance. Continuous-wave output powers are up to 350 μW.

Magnetic field tunable circularly polarized stimulated emission from midinfrared IV-VI vertical emitting lasers

Optically pumped laser emission from a midinfrared PbSe vertically emitting microcavity structure in a magnetic field applied in Faraday geometry is presented. It is shown that the emission line at a wavelength of about 7.9μm splits into two circularly polarized components with opposite helicity. The splitting of the emission line in the magnetic field is caused by different refractive indices of the material inside the microcavity for left- and right-hand circularly polarized light, yielding two resonator modes. Thereby the emission wavelength can be fine tuned by, e.g., 2cm−1 at 30kG. At higher fields the laser emission is 100% circularly polarized. This indicates that lasing in this case originates from completely spin polarized carriers.Optically pumped laser emission from a midinfrared PbSe vertically emitting microcavity structure in a magnetic field applied in Faraday geometry is presented. It is shown that the emission line at a wavelength of about 7.9μm splits into two circularly polarized components with opposite helicity. The splitting of the emission line in the magnetic field is caused by different refractive indices of the material inside the microcavity for left- and right-hand circularly polarized light, yielding two resonator modes. Thereby the emission wavelength can be fine tuned by, e.g., 2cm−1 at 30kG. At higher fields the laser emission is 100% circularly polarized. This indicates that lasing in this case originates from completely spin polarized carriers.

Comparison of IV-VI semiconductor microcavity lasers for the mid-infrared with active regions of different dimensionality

In this paper, we present a comparison between IV-VI vertical-cavity surface-emitting lasers (VCSELs) containing active regions of different dimensionality but with a nearly identical optical design of the cavity. In addition, the same optical set-up as well as pump source was used for laser excitation and characterization. This allows studying the influence of the dimensionality of the active material on the laser properties.

Femtosecond dynamics of lead-salt vertical-cavity surface-emitting mid-infrared lasers

In this paper we present the fs time resolved two-color pump-probe experiments performed in the mid-infrared region. The pump beam was at a wavelength of 2 /spl mu/m well above the Bragg mirror and the probe beam was at 3.76 /spl mu/m. The transmission spectra measured by the weak probe beam are shown for various delay times in respect to the pump pulse.