A. Khiar

4.5 μm wavelength vertical external cavity surface emitting laser operating above room temperature

A midinfrared vertical external cavity surface emitting laser with 4.5 μm emission wavelength and operating above room temperature has been realized. The active part consists of a single 850 nm thick epitaxial PbSe gain layer. It is followed by a 2 1/2 pair Pb1−yEuyTe/BaF2 Bragg mirror. No microstructural processing is needed. Excitation is done optically with a 1.5 μm wavelength laser. The device operates up to 45 °C with 100 ns pulses and delivers 6 mW output power at 27 °C heat-sink temperature.

Continuously tunable monomode mid-infrared vertical external cavity surface emitting laser on Si

A tunable PbTe based mid-infrared vertical external cavity surface emitting laser is described. The active part is a ∼1 μm thick PbTe layer grown epitaxially on a Bragg mirror on the Si-substrate. The cavity is terminated with a curved Si/SiO Bragg top mirror and pumped optically with a 1.55 μm laser. Cavity length is <100 μm in order that only one longitudinal mode is supported. By changing the cavity length, up to 5% wavelength continuous and mode-hop free tuning is achieved at fixed temperature. The total tuning extends from 5.6 to 4.7 μm at 100–170 K operation temperature.

PbSe quantum well mid-infrared vertical external cavity surface emitting laser on Si-substrates

Mid-infrared vertical external cavity surface emitting lasers based on PbSe/PbSrSe multi-quantum-well structures on Si-substrates are realized. A modular design allows growing the active region and the bottom Bragg mirror on two different Si-substrates, thus facilitating comparison between different structures. Lasing is observed from 3.3 to 5.1 μm wavelength and up to 52 °C heat sink temperature with 1.55 μm optical pumping. Simulations show that threshold powers are limited by Shockley-Read recombination with lifetimes as short as 0.1 ns. At higher temperatures, an additional threshold power increase occurs probably due to limited carrier diffusion length and carrier leakage, caused by an unfavorable band alignment.

2 W high efficiency PbS mid-infrared surface emitting laser

High efficiency laser operation with output power exceeding 2 W was obtained for vertical external-cavity PbS based IV-VI compound surface emitting quantum-well structures. The laser showed external quantum efficiency as high as 16%. Generally, mid-infrared III-V or II-VI semiconductor laser operation utilizing interband electron transitions are restricted by Auger recombination and free carrier absorption. Auger recombination is much lower in the IV-VI semiconductors, and the free-carrier absorption is significantly reduced by an optically pumped laser structure including multi-step optical excitation layers.

Modular PbSrS/PbS mid-infrared vertical external cavity surface emitting laser on Si

A mid-infrared vertical external cavity surface emitting laser (VECSEL) based on undoped PbS is described herein. A 200 nm-thick PbS active layer embedded between PbSrS cladding layers forms a double heterostructure. The layers are grown on a lattice and thermal expansion mismatched Si-substrate. The substrate is placed onto a flat bottom Bragg mirror again grown on a Si substrate, and the VECSEL is completed with a curved top mirror. Pumping is done optically with a 1.55 μm laser diode. This leads to an extremely simple modular fabrication process. Lasing wavelengths range from 3–3.8 μm at 100–260 K heat sink temperature. The lowest threshold power is ∼210 mWp and highest output power is ∼250 mWp. The influence of the different recombination mechanism as well as free carrier absorption on the threshold power is modeled.

PbSe Quantum Well VECSEL on Si

Lead-chalcogenide Vertical External Cavity Surface Emitting Lasers (VECSEL) employing PbSe, PbTe and PbSnTe as active layers have recently been described [1–4]. Here we present PbSe quantum well (QW) VECSEL covering a wavelength-range from 3.3 to 5.0 µm. Several PbSe QW structures were made, which differ in: • PbEuSe or PbSrSe host material • λ or λ/2 thick active layer (λ is the optical thickness) • different numbers of QW

Mid infrared resonant cavity detectors and lasers with epitaxial lead-chalcogenides

Wavelength tunable emitters and detectors in the mid-IR wavelength region allow applications including thermal imaging and gas spectroscopy. One way to realize such tunable devices is by using a resonant cavity. By mechanically changing the cavity length with MEMS mirror techniques, the wavelengths may be tuned over a considerable range.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 multicolour IR-FPA or “IR-AFPA”, adaptive focal plane arrays.We report the first room temperature mid-IR VECSEL (vertical external cavity surface emitting laser) with a wavelength above 3 μm. The active region is just 850 nm PbSe, followed by a 2.5 pair Bragg mirror. Output power is > 10 mW at RT.

IV-VI Mid-IR Tunable Lasers and Detectors with External Resonant Cavities

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 tunable band-filter.

Lead-chalcogenide VECSELs on Si and BaF2 for 5 μm emission

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.

Mid-infrared continuously tunable single mode VECSEL

Single mode continuously tunable mid-infrared Vertical External Cavity Surface Emitting Lasers (VECSEL) have been realized [1]. IV–VI semiconductors such as PbTe are used for the active region. Emission wavelength is ∼5 µm with a total tuning range >100 nm. The VECSEL is optically pumped using a 1.55 µm laser diode.