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The influence of injector doping concentration Ninj on the performance of InP-based quantum-cascade (QC) lasers is investigated for devices emitting around 9.2-mum wavelength and injector doping concentrations between 1times1017 cm-3 and 3times1017 cm-3. The threshold current density, the dynamic range, the maximum emitted output power as well as the maximum operating temperature are found to increase with increasing N inj. All in all, there exists no optimal value of Ninj per se. In fact, the injector doping concentration has to be adjusted individually depending whether emphasis is placed on obtaining low threshold current densities or on high-power operation

Conventional strain-compensated quantum cascade (QC) lasers are fabricated with both tensile strained AlInAs and compressively strained GaInAs layers. We show that strain compensation can also be achieved using tensile strained AlInAs barrier layers and lattice-matched GaInAs with thin InAs layers inserted. In the present paper, we use Al 0.6 In 0.4 As as barriers. The tensile strain caused by these barriers is compensated by thin InAs layers inserted into the lattice-matched GaInAs wells. The lasers, mounted epilayer up with as-cleaved facets, operate in pulsed mode up to 400 K (127 °C) at a wavelength of λ∼5.3um. For a laser with a ridge size of 18 μm x 3 mm, the maximum output peak power per facet obtained is 1 W at room temperature (27 °C).

We report the improvement of quantum cascade lasers emitting at λ∼5 μm by introducing AlAs blocking barriers together with strain-compensating InAs layers into the active regions. The blocking barriers are designed to selectively prevent electrons in the initial laser state from tunneling out of the active region, while maintaining the high tunneling probabilities of the electrons in the final laser states. Adopting blocking barriers, the maximum peak power per facet at 77 K (300 K) is increased from 285 (30 mW) to 900 mW (240 mW), and the maximum operation temperature in pulsed mode has been improved from 320 to 350 K with respect to a reference sample without blocking barriers.

We report on the development and characteristics of infrared semiconductor lasers as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). The short-wavelength side of the 2-5 μm wavelength band of interest can be covered by GaSb-based optically pumped semiconductor disk lasers (OPSDLs), delivering a continuous-wave (cw) or temporally modulated multiple-Watt output with a high beam quality (M2

The linewidth enhancement factor (or alpha parameter) describes the coupling of amplitude and phase in a semiconductor laser. In quantum cascade lasers, the self-mixing effect necessary for single mode operation, is usually realized by using a distributed feedback grating. Such a grating is optimized to work for a special wavelength at a fixed temperature. If the temperature of the laser device differs from the optimum temperature the grating was designed for, there is a detuning of the grating wavelength from the gain peak. We investigate the effect of this detuning on the value of the linewidth enhancement factor.

We present a study of the spectral characteristics of Fabry-Perot quantum cascade lasers in pulsed mode operation applying a time resolution of 3 ns in combination with a high spectral resolution of 0.02 cm-1. With this technique the laser spectra were investigated applying pulse lengths ranging between 100 ns and 20 μs and duty cycles between 0.01% and 10%. Depending on the current density and operation temperature, the spectra exhibit complex line patterns, which indicate mode competition caused by gain saturation effects.

Short-wavelength (lambda < 4 µm) GaInAs-AlAsSb quantum cascade (QC) lasers have been demonstrated using a "bound-to-continuum" design for the purpose of reducing the electric injection power density. As a result, we have reduced the low-temperature electric injection power density of the lasers by 40%, compared to that of GaInAs-AlAsSb QC lasers emitting at the same wavelength but adopting a triple-quantum-well design. The lasers in the present report can operate up to room temperature (300 K) in pulsed mode, emitting at short-wavelength lambda about 3.7 - 3.9 µm.

We present experimental and theoretical investigations of the linewidth of quantum cascade lasers. We find linewidths in the kilohertz range depending on the injection current due to a non-constant linewidth enhancement factor

This paper presents the operation and fabrication of GaInAs/Al(Ga)AsSb quantum cascade lasers. This article also focuses on the development of processing technology to enhance the heat removal from the active region of the lasers by depositing a thick gold layer on both sides of the laser ridge. Due to the improved heat removal devices emitting at around 4.9 /spl mu/m, the quantum cascade laser can be operated at high duty cycle (/spl ges/ 50%) up to a heat-sink temperature of 130 K.

We report on the demonstration of continuous-wave (CW) operation of GaInAs-AlGaAsSb quantum cascade (QC) lasers. By placing a 2.5-/spl mu/m-thick gold layer on both sides of the laser ridge to extract heat from the active region in the lateral direction, together with mounting the device epilayer down, we have achieved CW operation of GaInAs-AlGaAsSb QC lasers composed of 25 stages of active/injection regions. The maximum CW operating temperature of the lasers is 94 K, and the emission wavelength is around /spl lambda//spl sim/4.65 /spl mu/m. For a device with the size of 10/spl times/2000 /spl mu/m/sup 2/, the CW optical output power per facet is 13 mW at 42 K and 4 mW at 94 K. The CW threshold current density is 1.99 kA/cm/sup 2/ at 42 K, and 2.08 kA/cm/sup 2/ at 94 K, respectively.

There is an increasing demand for spectrally agile compact solid-state lasers for spectroscopic sensing and diagnostics. This demand can be met by III–V semiconductor-based lasers employing various design concepts for the active region. These concepts include, apart from the classical type-I interband diode laser, the type-II W-laser and the unipolar quantum cascade laser. Representative device data will be presented for these three types of lasers in conjunction with a discussion of the relative merits of the different active-region concepts.

Summary form only given. We report on a new design of GaInAs-AlInAs quantum cascade lasers (QCLs) improving the concept of Bragg reflectors by incorporating "blocking barriers" into the active regions. These barriers significantly enhance the confinement of electrons in the initial state of the laser transition by selectively blocking direct tunneling through the exit barrier (reducing the tunneling probability by a factor of 2). The high tunneling probability of electrons in the final state into the injector's miniband is maintained by reducing the total width of the exit barrier appropriately.

Short-wavelength (λ∼4μm) single-mode distributed-feedback GaInAs∕AlAsSb quantum-cascade lasers operating in pulsed mode up to room temperature (300K) have been demonstrated by etching an index-coupled first-order distributed-feedback grating into the upper GaInAs separate confinement layer. The temperature-dependent wavelength shift of the distributed-feedback lasers is −0.14cm−1∕K (0.238nm∕K). For devices with a size of 18μm×2.9mm mounted epilayer-up with as-cleaved facets, a maximum peak power per facet of 840mW has been achieved at 77K and 4mW at 300K. The characteristic temperature T0 of the threshold current density is 105K.

Above room-temperature (T⩾400K) operation of GaInAs∕AlAsSb-based quantum-cascade lasers has been demonstrated. The lasers are based on vertical-transition active regions and consist of 25 periods of Ga0.47In0.53As∕AlAs0.56Sb0.44 active∕injection regions grown lattice-matched on InP substrates by molecular-beam epitaxy. They emit at a wavelength of λ∼4.5μm. For a device with the size of 18μm×2.8mm mounted substrate-side down with as-cleaved facets, a maximum peak power per facet of 750mW has been achieved at 300K and remains as high as 30mW at 400K. The characteristic temperature T0 of the threshold current density is 171K in the temperature range between 280K and 400K.

A report is presented on the continuous-wave operation of λ≃5 µm GaInAs/AlInAs/InP-based quantum cascade lasers up to a heatsink temperature of 222K (−51°C). The devices are mounted epi-side down with high-reflection coated facets.

Quantum cascade lasers emitting at λ ∼ 5µm based on different ac- tive region designs are investigated. Using lattice-matched GaInAs/AlInAs on InP substrates the maximum peak optical power as well as the maximum pulsed-mode operating temperature is enhanced by incorporating AlAs blocking barriers together with strain-compensating InAs layers into the active regions. Further improvement is achieved by employing strain-compensated GaInAs/AlInAs quantum wells for which maximum pulsed-mode operating temperatures in excess of 350K are ob- served. High-reflectivity coated devices mounted substrate-side down show a maxi- mum continuous-wave operating temperature of 194 K. Also the normalized relative intensity noise is investigated. Finally, a comparison trace-gas sensing experiment employing one of the present quantum cascade lasers and a lead-chalcogenide laser is presented. Detecting the P(25) absorption line of CO, higher stability is obtained using a quantum cascade laser.