Mohamed Rahim

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.

Midinfrared lead-chalcogenide vertical external cavity surface emitting laser with 5μm wavelength

Midinfrared vertical external cavity surface emitting lasers for 5μm wavelength have been realized. The active parts consist either of a 2μm thick PbTe gain layer or of two 150nm PbTe layers embedded in Pb1−xEuxTe barriers, and an epitaxial two pair Pb1−yEuyTe∕BaF2 Bragg mirror. They are optically pumped with a 1.5μm laser. No precautions for efficient heat removal were implemented. The two-layer structure emits 1–2mW continuous wave at 95K with threshold pump power as low as ∼300mW. In pulsed mode, peak powers are >50mW, and lasing occurs up to ∼140K.

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.

Mid-infrared PbTe vertical external cavity surface emitting laser on Si-substrate with above 1 W output power

Mid-infrared vertical external cavity surface emitting lasers (VECSELs) emitting above 1 W output power in pulsed mode and up to 17 mW in continuous mode at −172 °C were realized. Emission wavelength changes from 5 μm at −172 °C to 3.6 μm at 20 °C heat sink temperature. The active medium is a one wavelength thick PbTe layer grown by molecular beam epitaxy on a Si-substrate. It is followed by a 2.5 pair Pb1−yEuyTe/EuTe epitaxial Bragg mirror. The cavity is completed with an external curved Pb1−yEuyTe/BaF2 mirror. The VECSEL is optically pumped with 1.55 μm wavelength laser and In-soldered to Cu heat sink. No microstructural processing is needed.

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.

Optically pumped 5 μm IV-VI VECSEL with Al-heat spreader

Mid-infrared vertical external cavity surface emitting lasers (VECSELs) for 5 μm in wavelength have been realized. The active parts are of a simple structure, either a 2 μm thick PbTe gain layer or two 150 nm PbTe layers embedded in Pb1−xEuxTe barriers. Epitaxial 2.5 pair Pb1−yEuyTe/BaF2 Bragg mirrors are employed to form the cavity, and an Al layer is deposited for improved heat dissipation. Emission up to 300 mWp is observed with microsecond pulses or 3 mW cw at 100 K is obtained. Quantum efficiency is up to 14%, and lasing occurs up to 175 K when pumped with a 1.55 μm wavelength pump laser.

Tunable lead-chalcogenide on Si resonant cavity enhanced midinfrared detector

Midinfrared tunable resonant cavity enhanced detectors have been realized. The linewidths of 0.07μm are determined by the finesse of the cavities, while the length of the cavity can be changed with a movable mirror. This allows tuning across the 4–5.5μm midinfrared wavelength range. The thin (0.3μm) photodiodes inside the cavity are based on lead-chalcogenide narrow gap semiconductor layers grown epitaxially onto a Si substrate. Due to the thin active layer, a higher sensitivity at the higher operation temperatures is achieved as compared to conventional thick photodiodes.

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.

Electrical and optical properties of SnEuTe and SnSrTe films

The SnTe, Sn1−xEuxTe and Sn1−xSrxTe (x<0.06) films were prepared by hot wall epitaxy. The ternary alloy films prepared in cation rich condition had hole concentration around 1×1019 cm−3 with high mobility exceeding 2000 cm2/V s at room temperature. Optical transmission spectra were also measured in the temperature range from 100 to 400 K and compared with theoretical calculations. Optical transmission spectra of the SnTe were simulated successfully assuming bumped band edge structures. A band inversion model was proposed for the Sn1−xEuxTe and Sn1−xSrxTe systems, and the optical transmission spectra were also simulated successfully assuming the band inversion model.

Electrostatically actuated micromirror for resonant cavity enhanced detectors

This paper presents the design, fabrication and measurement results of a vertically moving, electrostatically actuated micromirror. The single crystalline silicon substrate allows the design of a symmetrical and mechanically stable mirror suspension while keeping a geometry with high fill factors and maintaining elasticity and thus keeping the actuation voltage below 25 V. The device is being developed for the use in a tunable resonant cavity enhanced detector (RCED) for the mid-infrared (Arnold, 2005). RCEDs make use of a standing wave formed in an optical cavity and are only sensitive at the resonances. The wavelengths of the resonances are hereby depending on the distance of the two cavity mirrors (Unlu, 1995). Such narrowband detector systems are sought- after in multispectral infrared (IR) thermography or infrared spectroscopy (Musca, 2005).