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The possibility of fabrication of 4.6 μm spectral range quantum-cascade laser heterostructures by molecular-beam epitaxy technique with non-selective overgrowth by the metalorganic vapour-phase epitaxy is shown. The active region of the laser was formed on the basis of a heteropair of In0.67Ga0.33As/In0.36Al0.64As solid alloys. The waveguide claddings are formed by indium phosphide. The results of surface defects inspection and X-ray diffraction analysis of quantum-cascade laser heterostructures allow to conclude that the structural quality of the heterostructures is high and the estimated value of the root mean square surface roughness does not exceed 0.7 nm. Lasers with four cleaved facets exhibit lasing at room temperature with a relatively low threshold current density of the order of 1 kA/cm2. [ABSTRACT FROM AUTHOR]

Mid IR Quantum cascade lasers are of high interest for the scientific community due to their unique applications. However, the QCL designs require careful engineering to overcome some crucial disadvantages. One of them is active region (ARn) overheating, which significantly affects laser characteristics, even in the pulsed mode. In this work, we consider the effects related to the nonequilibrium temperature distribution when thermal resistance formalism is irrelevant. We employ the heat equation and discuss the possible limitations and structural features stemming from the chemical composition of the ARn. We show that the presence of solid solutions in the ARn structure fundamentally limits the heat dissipation in pulsed and CW regimes due to their low thermal conductivity compared with binary compounds. Also, the QCL postgrowths affect the thermal properties of a device closer to CW mode, while it is by far less important in the short-pulsed mode. [ABSTRACT FROM AUTHOR]

The results of studies of ring quantum-cascade lasers with surface emission due to a second-order grating formed in the top cladding layers are presented. Surface emission near 7.85 μm with a low threshold current density (3.8 kA/cm2), in comparison with ridge quantum-cascade lasers of the same cavity length is demonstrated. The results of measurements of the intensity distribution of the near and far fields at different pumping levels are presented. The estimated value of the angle of beam extraction relative to the surface normal is in the range 5.7°–6.7°. [ABSTRACT FROM AUTHOR]

The results of studying a ring surface-emitting quantum-cascade laser with radiation emission through a textured layer formed in the layers of the upper cladding of the waveguide by ultrahigh-vacuum ion-beam milling are presented. The far-field profile shows that the radiation is emitted through windows with a textured layer in the range of angles ~63°–75° to the surface normal. [ABSTRACT FROM AUTHOR]

Near- and far-fields of quantum-cascade lasers emitting in the spectral range near 8 μm have been studied. For all laser samples with a ridge width of 20 and 50 μm, lasing on the fundamental waveguide mode with a divergence of ~50° was observed for all laser samples with a ridge width of 20 and 50 μm along the "fast" axis. Along the "slow" axis, a multimode lasing and a competition between the fundamental and higher waveguide modes, which is manifested for lasers with a ridge width of 50 μm in an increase in the emission divergence from ~10° near the threshold to >50° when the lasing threshold is exceeded by a factor of 2–3. The divergence along the "slow" axis for lasers with ridge width of 22 μm remained invariable in the whole range of pumping currents and equaled ~50°. That there is a substantial contribution from the fundamental mode to the total emission intensity of quantum-cascade lasers, which is apparent from the far-field intensity distribution pattern, cannot be established exclusively on the basis of results obtained in near-field measurements. [ABSTRACT FROM AUTHOR]

A cavity scheme based on a half-ring with different radii is proposed and fabricated for 7–8 μm quantum-cascade lasers. A quantum-cascade laser with a half-ring cavity radius of 191 μm demonstrated lasing with a spectral width of 474 nm (82 cm–1) at low temperatures. The free spectral range in these lasers was determined by the whispering gallery modes typical for ring cavities. The laser bandwidth at room temperature was 190 nm (31 cm–1), which may be related to an increase in the internal losses with increasing temperature. An increase in the cavity radius to 291 μm made it possible to achieve room-temperature lasing with whispering gallery modes and a bandwidth of 249 nm (40 cm–1) by reducing losses on the mirrors. [ABSTRACT FROM AUTHOR]

We have studied the spectral and dynamic characteristics of quantum cascade lasers emitting in the long-wavelength infrared range. It is shown that lasers with a short cavity (~1 mm) make it possible to obtain frequency combs in a very wide spectral range. We have investigated the spectral dynamics in the frequency comb generation regime. It is demonstrated that the intensity of longitudinal laser modes varies during a pump pulse propagation. We have observed simultaneous generation of all longitudinal modes of a frequency comb over a pump pulse segment with a constant amplitude. [ABSTRACT FROM AUTHOR]

The method of molecular-beam epitaxy was used to fabricate an elastically balanced heterostructure of a quantum-cascade laser for the spectral range of 4.6 μm based on a heteropair of solid alloys, In0.67Ga0.33As/In0.36Al0.64As, and indium phosphide layers serving as waveguide cladding layers. An X-ray diffraction analysis demonstrated the high uniformity of the composition and thickness of layers in cascades of the heterostructure over the substrate area. Lasers with four cleaved facets show lasing at room temperature at a wavelength close to 4.6 μm with a comparatively low threshold current density of 1.1 kA/cm2. [ABSTRACT FROM AUTHOR]

We have studied the generation of frequency combs by quantum cascade lasers (QCLs) emitting in the 8-μm wavelength range. Results showed the presence of a self-pulsation regime near the lasing threshold. Further increase in the pumping current led to a sharp increase in width of the lasing spectrum, which allowed us to obtain frequency combs with a spectral width exceeding 1.5 THz. This behavior of QCLs can be explained by radiation absorption at the stripe edge that is related to the penetration of waveguide mode into unpumped regions. [ABSTRACT FROM AUTHOR]

Results of studying stripe quantum cascade lasers emitting at room temperature in the spectral range of 4.8 µm are presented. Power characteristics and turn-on dynamics of the lasers upon pulse pumping are studied. The performed investigations demonstrate the presence of a significant heating of the active region during the pump pulse. [ABSTRACT FROM AUTHOR]

Molecular beam epitaxy techniques were used to grow a quantum-cascade laser (QCL) heterostructure based on an In0.53Ga0.47As/Al0.48In0.52As heteropair lattice-matched with an InP substrate. InP layers were used to form an optical waveguide. The obtained QCL heterostructure ensured room-temperature lasing in the 8-μm wavelength range at a maximum output optical power of 0.45 W from one facet in a standard ridge geometry of the Fabry–Pérot cavities formed by cleaved facets. [ABSTRACT FROM AUTHOR]

Abstract: Lasing in MBE-grown impulsively pumped quantum cascade lasers of 9.6 μm at 140 K has been demonstrated. The active area is based on three-phonon resonance scattering of electrons. An In0.53Ga0.47As/Al0.48In0.52As solid alloy heteropair was used to form periods of quantum cascade lasers. The upper In0.52Al0.48As cladding of the waveguide was made thick. Alloyed and unalloyed lower metallization systems were studied. The threshold current density for a ridge laser 1 mm long and 27 μm wide has been found to roughly equal 3 kA/cm2 at 87 K. The optical output power has been estimated at a level of 20-35 mW. [ABSTRACT FROM AUTHOR]

Room-temperature lasing at a wavelength of 8 μm in multistage quantum-cascade lasers pumped by current pulses is demonstrated. A quantum-cascade laser heterostructure based on the In0.53Ga0.47As/Al0.48In0.52As alloy heteropair, matched to an InP substrate, is grown by molecular-beam epitaxy and consists of 50 identical cascades placed in a waveguide with air as the top cladding. A threshold current density of ~5.1 kA/cm2 at a temperature of 300 K is obtained in ridge lasers with a cavity length of 1.4 mm and a ridge width of 24 μm. [ABSTRACT FROM AUTHOR]

Single-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In0.53Ga0.47As/Al0.48In0.52As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings. [ABSTRACT FROM AUTHOR]

Abstract: Lasing of quantum cascade lasers is demonstrated at a radiation wavelength of 8100 nm at room temperature. Analysis of oscillograms of optical pulses is used to determine dependence of mean and peak radiation intensities on current. A delay of turn-on of quantum cascade lasers is experimentally estimated at a level of two times higher than the lasing threshold to be greater than theoretically estimated delay by several orders of magnitude. [ABSTRACT FROM AUTHOR]

Results of an investigation of quantum cascade lasers of the 8-μm spectral range generating dual-frequency radiation at room temperature are presented. The dependences of radiation intensity for two lines of laser generation obtained as a result of investigation of the generation spectra revealed the presence of saturation and decay of the long-wavelength line of generation and linear growth of the intensity of the short-wavelength one. Based on analysis of the obtained data, a mechanism of the dual-frequency generation in the studied QCL samples is proposed Generation. [ABSTRACT FROM AUTHOR]