We analyze the influence of optical coatings on the electro-optical characteristics of quantum cascade lasers. We compare light-current characteristics of devices without and with different combinations of optical coatings. The highest output power is achieved with combination of anti- and high-reflection coatings, while the lowest threshold with partial-high- and highreflection coatings.

Quantum-cascade lasers (QCLs) based on InGaAs/AlInAs/InP with reflective and antireflective coatings are fabricated and studied. The manufactured lasers emit in the spectral range from 4 to 5 μm. The effect of variation in the front mirror reflectance on the output power of a QCL with a highly reflective rear mirror is investigated. It is shown that the use of an antireflective coating on the front face leads to a simultaneous increase in both the threshold current of the QCL and the slope of the light–current characteristic. This allows a higher output power to be achieved at high pump currents. In contrast, the use of a partially reflective coating on the front face not only reduces the threshold current of the QCL, but also decreases the slope of the light–current characteristic. Such QCLs may have an advantage over other emitters at low pump currents.

We report the results of a comparison of metal–dielectric mirror coatings for mid-IR quantum-cascade lasers (QCLs). Samples of QCLs with Al2O3/Ti/Au and SiO2/Ti/Au optical coatings are fabricated and their characteristics are studied. It is shown that the use of metal–dielectric mirror coatings allows the output optical power of devices to be increased up to 93

We analyze the characteristics of semiconductor emitters based on separate-confinement double heterostructures with quantum wells with different configurations of waveguide layers. Lasers with narrow and broad waveguides are considered as applied to the problem of increasing the output power. Semiconductor emitters with undoped and doped waveguide layers are compared. We consider lasers with ultranarrow and broad strongly asymmetric waveguides. It is shown that the reduction of series and thermal resistance reduces the self-heating of lasers and increases the output power and efficiency. The prospects of using the epitaxial integration for designing lasers with several tunnel-coupled emitting sections for increasing the output power and luminosity are considered. The possibility of constructing monolith-integrated thyristor lasers combining the emitting section and an electron switch in a single crystal is demonstrated.

Dielectric mirrors for mid-IR quantum cascade lasers are calculated. Optimal dielectric materials are selected to minimize the absorption of laser radiation. Samples of quantum cascade lasers emitting in the spectral range of 4–5 μm and having various dielectric highly reflective mirror coatings are manufactured and their characteristics are studied. It is shown that the deposition of a highly reflective Si–Si3N4 coating on the back face of the laser cavity leads to an increase in the output optical power of the lasers by 71

This work presents the results of numerical calculations of mirror coatings for quantum cascade lasers (QCLs) at wavelengths of 4.5 μm and 8 μm. The advantages and disadvantages of dielectric and metal-dielectric mirrors are analyzed. It was shown that the output optical power increased by 1.5 times after applying a mirror coating on the back facet of the QCL.

A triple laser – thyristor, i. e., a semiconductor laser with three emitting sections monolithically integrated with an electronic switch (thyristor) is experimentally studied. For comparison, the output characteristics of single and double laser – thyristors are presented. It is shown that the functional integration of a laser with a thyristor in one heterostructure allows the laser to efficiently operate in a pulsed regime (output power ∼50 W), the use of vertical integration of two laser sections increases the power to ∼90 W, and the integration of three laser sections makes it possible to increase the output optical power to ∼120 W with all other conditions being the same.

The influence of doping of waveguide layers on the output characteristics of lasers based on AlGaAs/GaAs double separate-confinement heterostructures is analysed. The heterostructures with narrow and broadened waveguides are studied. Samples of laser diode bars with undoped and doped waveguide layers are experimentally fabricated and compared. It is shown that the latter type of structures with a broadened waveguide allows one to increase the output power of the laser diode bars by 10 % – 15 %, all other conditions being equal.

Based on a matched Ga0.47In0.53As/Al0.48In0.52As heteropair, we have developed a quantum cascade laser emitting at a wavelength of 7.4 mu m. The chosen heterostructure with a relatively large number of quantum wells and barriers represents two mini-bands separated by a mini-gap with a localised doublet level near the upper mini-band, which provides a wide emission band (similar to 100 cm(-1)). In a pulse regime, the maximal laser operation temperature is 371 K. Such a high temperature is explained by two factors: a large energy of the transfer from the doublet to the upper mini-band and a large volt defect. The characteristic temperatures T-0 are found, which are equal to 170 K for low (less than 300 K) temperatures and 270 K for the range of 300 - 370 K. In addition, optical cavity losses are determined to be 2.5 and 7.7 cm(-1) at temperatures of 80 and 254 K, respectively. The pulse power is 0.3 W at 80 K and 0.05 W at 293 K.

This paper presents an experimental study of AlGaInAs/InP semiconductor lasers with different barrier layers. The use of strained layers with an increased band gap as blocking barriers limiting carrier leakage is shown to increase the output power of the lasers at a given pump current.

Comparative experiments are performed on a semiconductor laser with different numbers (one or two) of emitting sections monolithically integrated with an electronic switch (thyristor). It is shown that the functional integration of a laser with a thyristor in one heterostructure makes it possible to achieve efficient operation of the laser in a pulsed regime (up to 50 W), while the use of vertical integration of two laser sections in this device additionally increases the optical output power to 90 W with all other conditions being the same.

A quantum cascade laser based on a strain-compensated Ga0.4In0.6As/Al0.58In0.42As heteropair is developed, which operates in the pulse regime in the wavelength range of 5.5-5.6 mu m at temperatures of up to at least 350 K. It became possible due to an increase in the quantum well depth and to the usage of the two-phonon depopulation mechanism for the lower lasing level. The calculated voltage defect is about 100 meV. The laser epitaxial hetero-structure was grown by the MOVPE method. It was investigated by the high-resolution X-ray diffraction technique. It is shown that the heterostructure has a high quality with bandwidths of main satellite peaks of 55 arcsec. The threshold current density is 1.6 kA cm(-2) at 300 K. The characteristic temperature is T-0 = 161 K for the temperature interval of 200-350 K. For the laser of size 20 mu m x 3 mm with cleaved mirrors, the maximum pulsed power is 1.1 W at 80 K and 130 mW at 300 K.

The main results of the development of compact laser diode mini-arrays operating under 875-non pulsed pumping are presented and the instrumental characteristics of these arrays are studied. Specific features of these sources, in addition to a high output power (similar to 1.5 kW), arc a narrow directional pattern (angular divergence 21 degrees x8 degrees) and a small emitting area (less than 1 mm(2)). The use of serially integrated AlGaAs/GaAs MOCVD heterostructures with three emitting regions to develop laser diode arrays allowed us to improve their working parameters.

Short-period GaAs/AlGaAs superlattices, an active region, and a quantum cascade laser heterostructure have been grown by metalorganic vapor phase epitaxy, and their characteristics have been studied by high-resolution X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The heterostructures have been used to produce quantum cascade lasers emitting near 10 μm. Their output pulse power at 77 K is above 200 mW.

The results of development of quasi-cw laser diode arrays operating at a wavelength of 808 nm with a high efficiency are demonstrated. The laser diodes are based on semiconductor AlGaAs/GaAs quantum-well heterostructures grown by MOCVD. The measured spectral, spatial, electric and power characteristics are presented. The output optical power of the array with an emitting area of 5 × 10 mm is 2.7 kW at a pump current of 100 A, and the maximum efficiency reaches 62%.

The results of the development and fabrication of laser diode bars (λ = 800 – 810 nm) based on AlGaAs/GaAs quantum-well heterostructures with a high efficiency are presented. An increase in the internal quantum and external differential efficiencies together with a decrease in the working voltage and the series resistance allowed us to improve the output parameters of the semiconductor laser under quasi-cw pumping. The output power of the laser diode bars with a 5-mm transverse length reached 210 W, and the efficiency was ~70%.

A quantum cascade laser emitting in the spectral range of 9.7 μm at 77 K has been developed. The laser heterostructure based on GaAs/AlGaAs was grown by the MOCVD technology. In the pulsed operation mode, the threshold current density of ~2 kA/cm 2 and the emission power of above 200 mW have been obtained for the laser of the dimensions of 30 μm × 3 mm.

A pulsed quantum cascade laser emitting in the wavelength range 9.5 - 9.7 mm at 77.4 K is developed based on the GaAs/Al0.45Ga0.55As heteropair. The laser heterostructure was grown by MOCVD. The threshold current density was 1.8 kA cm(-2). The maximum output power of the laser with dimensions of 30 mu m x 3 mm and with cleaved mirrors exceeded 200 mW.