Optically pumped VECSEL (vertical external cavity surface emitting lasers) based on IV-VI semiconductors grown on Si
cover the entire wavelength range between 3.0 and 10 μm. Thanks to their simple structure and large wavelength
coverage they are an interesting alternative laser technology to access the mid-infrared wavelength region. The active
layers consist either of homogeneous "bulk" layers, double heterostructures or quantum well structures of the PbSe, PbTe
or PbS material system. Maximum operation temperatures of 325 K are achieved with output powers above 200 mWp.
Further, continuously tunable VECSEL are presented, emitting between 3.2 and 5.4 μm. The single emission mode is
continuously tunable over 50-100 nm around the center wavelength, yielding an output power > 10 mWp. The axial
symmetric emission beam has a half divergence angle of < 3.3°.
Wavelength tunable emitters and detectors in the mid-IR wavelength region allow applications including thermal
imaging and spectroscopy. Such devices may be realized using a resonant cavity. By mechanically changing the cavity
length with MEMS mirror techniques, the wavelengths may be tuned over a considerable range. Vertical external cavity
surface emitting lasers (VECSEL) may be applied for gas spectroscopy. Resonant cavity enhanced detectors (RCED) are
sensitive at the cavity resonance only. They may be applied for low resolution spectroscopy, and, when arrays of such
detectors are realized, as multicolor IR-FPA or IR-AFPA (IR-adaptive focal plane arrays). We review mid-infrared
RCEDs and VECSELs using narrow gap IV-VI (lead chalcogenide) materials like PbTe and PbSe as the active medium.
IV-VIs are fault tolerant and allow easy wavelength tuning. The VECSELs operate up to above room temperature and
emit in the 4 - 5 μm range with a PbSe active layer. RCEDs with PbTe absorbing layers above 200 K operating
temperature have higher sensitivities than the theoretical limit for a similar broad-band detector coupled with a passive
Optically pumped VECSELs (vertical external cavity surface emitting lasers) with above 5 μm emission wavelength
were fabricated on BaF2 and Si substrates. The active layer is just 1 - 2 μm thick PbTe or PbSe, and epitaxial
PbEuTe/BaF2 or PbSrTe/EuTe Bragg mirrors are employed. On BaF2 substrates, output powers up to 260 mW pulsed
and 3 mW cw at 100 K are obtained. The VECSEL presently operate up to 175 K with PbTe, and up to 215 K with PbSe
active layers. On Si-substrates, maximum output was about 30 mW. There is room for considerable improvement with
better adapted designs including improved heat-removal precautions.
We describe two new optoelectronic mid-IR devices employing narrow gap lead-chalcogenide (IV-VI) layers on Si or
BaF2 substrates: (1) Tunable resonant cavity enhanced detectors (RCED) for the mid-infrared with an epitaxial Bragg
mirror and a thin p-n+ heterojunction as detecting layer have been realized for the first time. They are tunable by moving
the top micro-electro-mechanical micromirror, thus changing the cavity length. (2) Optically pumped vertical external
cavity surface emitting lasers (VECSEL) with an emission wavelength above 5 μm were fabricated, for the first time,
too. Presently they operate with an output power of up to 260 mWp and up to 175 K. With improved appropriate
precautions for efficient heat removal, still much higher operation temperatures are expected. Both resonant cavity
enhanced devices may be used as miniature infrared spectrometers to cover the spectral range from < 3 μm up to > 20