Single-mode tunable quantum cascade lasers in the spectral range ofthe CO2 laser at λ=9.5-10.5 μm

Widely tunable, single-mode quantum cascade distributed feedback (QC-DFB) lasers based on a complex coupling scheme and operating in the wavelength range of the CO₂ laser (λ≈9.5-10.5 μm) are reported. Dynamic single-mode emission up to high current levels is obtained. The continuous single-mode tuning range is 150 nm, while the tuning range of the equivalent Fabry-Perot laser is ~400 nm. By homogeneously reducing all layer thicknesses by 10%, the wavelength coverage of a single QC-laser design can be extended to cover one entire regular band of the fundamental CO₂ laser spectrum     

Internally excited acoustic resonator for photoacoustic trace detection

The quantum-cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device that we describe uses a quantum-cascade laser without collimating optics mounted inside an acoustic resonator. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation along the length of the resonator exciting an axially symmetric longitudinal acoustic mode of an open-ended cylindrical resonator. Experiments are reported with an 8-microm, quasi-cw-modulated, room-temperature laser used to detect N2O.     

Surface-plasmon quantum cascade microlasers with highly deformed resonators

We report the demonstration of surface-plasmon microcylinder quantum cascade lasers with circular and deformed resonators. An improved self-alignment fabrication technique was developed that allows the use of wet etching, necessary to achieve smooth and clean surfaces, in combination with the deposition of the surface-plasmon-carrying metal layer up to the very edge of the resonator, where the optical mode is mostly located. The diameter of the microcylinders ranges from 75 to 180 /spl mu/m while their deformation coefficient /spl epsiv/ ranges from /spl epsiv/=0 to /spl epsiv/=0.32. Circular microcylinder lasers show a reduction of /spl sim/50% of the threshold current density with respect to devices with standard ridge-waveguide resonators. On the other hand, highly deformed microcylinder lasers exhibit a complex mode structure, suggesting the onset of chaotic behavior.     

Simultaneously at two wavelengths (5.0 and 7.5 μm) singlemodeand tunable quantum cascade distributed feedback lasers

Quantum cascade distributed feedback (QC-DFB) lasers based on a heterogeneous-cascade two-wavelength active waveguide core and a multisectioned cavity featuring two different Bragg gratings are demonstrated. Optimised lasers display singlemode emission at λ~5.0 and 7.5 μm simultaneously and a tunability on both modes equal to single-wavelength QC-DFB lasers     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

Milliwatt second harmonic generation in quantum cascade lasers with modal phase matching

Milliwatt second harmonic power at 4.45 /spl mu/m was achieved in InP lattice-matched quantum cascade lasers with monolithically-integrated resonant nonlinear cascades and modal phase matching. The use of an InP top-cladding layer and high-reflectance coating on the laser back facet enabled high linear laser power and consequently record nonlinear power.     

Thermal and Stark-Effect Roll-Over of Quantum-Cascade Lasers

A computational and experimental analysis of rollover in high-performance lambda ~ 8 mum quantum-cascade (QC) lasers is presented. In addition to conventional, thermal rollover, which is also a common cause of power rollover in diode lasers, ";Stark-effect"; rollover is observed. While both effects can occur in the same QC laser design, thermal and Stark-effect rollover are shown to be the dominating factor for high-temperature continuous wave operated, and pulsed low-temperature operated and low-doped lasers, respectively. Additionally, the role of the continuum above the wells and barriers is discussed for both effects.     

Quantum cascade lasers with low-loss chalcogenide lateralwaveguides

Quantum cascade lasers have been fabricated with chalcogenide lateral waveguide claddings. Several-micrometer thick Ge_0.25Se_0.75 glass has been deposited by pulsed laser ablation onto the sidewalls of narrow, deep etched laser ridges. Due to the intrinsically low mid-infrared attenuation of the chalcogenide material, the waveguide loss of the lasers is significantly reduced, by up to ~50%, depending on the ridge width, when compared to conventional ridge waveguides. This resulted in an improved overall laser performance, such as a reduction of the threshold current density, an increase in slope efficiency, and an improved temperature performance     

Continuous wave operation of λ~19 μm surface-plasmonquantum cascade lasers

Continuous wave laser action has been achieved in a superlattice quantum cascade device operating on surface plasmon waveguide modes. The emission wavelength λ~19 μm is by far the longest ever reported for continuous wave III-V semiconductor lasers. The output power at cryogenic temperature is of the order of the mW     

Reduction of Facet Reflectivity of Quantum-Cascade Lasers With Subwavelength Gratings

We demonstrate the reduction of the facet reflectivity of quantum-cascade lasers (QCLs) by using subwavelength gratings. The gratings were fabricated on lambda=4.9- and 9.8-mum QCLs using focused ion beam milling. Reflectivities as low as 1%-3% for the 4.9-mum QCL and as low as 4%-8% for the 9.8-mum QCL are reported