S. Gianordoli

GaAs/AlGaAs superlattice quantum cascade lasers at λ≈13 μm

We report the realization of an injection laser based on intraband transitions in a finite AlGaAs/GaAs superlattice. The active material is a 30 period sequence of injectors/active regions made from AlGaAs/GaAs quantum wells. By an applied electric field, electrons are injected into the second miniband of a chirped superlattice and relax radiative to the lowest miniband. At a heat-sink temperature of 10 K, the laser emission wavelength is 12.9 μm with peak optical powers exceeding 100 mW and a threshold current density of 9.8 kA/cm2. The maximum operating temperature is 50 K. For this device, a waveguide consisting of heavily doped GaAs cladding and low doped core layers has been used as a plasma-enhanced confinement.

Continuous-wave operation of distributed feedback AlAs/GaAs superlattice quantum-cascade lasers

We report on continuous-wave operation of first-order distributed feedback quantum-cascade lasers at λ=11.8 μm, based on interminiband transitions in a chirped AlAs/GaAs superlattice. Short devices operate in continuous-wave up to ∼30 K. The single-mode emission wavelength is continuously tunable with the temperature. A metallized surface-relief grating is used for feedback to achieve single-mode emission.

GaAs/AlGaAs distributed feedback quantum cascade lasers

We report on the realization of distributed feedback quantum cascade lasers in the GaAs/AlGaAs material system. A metallized surface relief grating is used for feedback. Both single mode and double mode emission is observed at λ≈10 μm. The coupling coefficient is measured from the mode spacing for double mode emission to be 24 cm−1. The emission wave number can be tuned with the temperature at a rate of dν/dT≈0.048 cm−1/K.

Surface-emitting distributed feedback quantum-cascade lasers

We report on the realization of second-order distributed feedback quantum-cascade lasers at λ=9.35 μm, where the active region consists of GaAs, AlGaAs, and strained InGaAs grown on GaAs. A metal-stripe surface grating structure allows a high surface emission efficiency for the TM-polarized light. The emitted power via the surface is in the range of 100 mW and exceeds the emitted power from one facet. A double-lobed surface-emission far-field pattern is obtained for the lasing mode. The single-mode emission wavelength is continuously tunable by the heat sink temperature.

GaAs/AlGaAs-based microcylinder lasers emitting at 10 μm

The realization of electrically pumped GaAs/AlGaAs quantum cascade microcylinder lasers is reported. Design and fabrication of special resonator shapes (microcylinder and ridge waveguide) are presented. Threshold characteristics and optical output of different resonators of the same quantum cascade laser material emitting at 10 μm are investigated. A low threshold current of 318 mA is obtained for a microcylinder resonator with circular cross section. The maximum working temperature of the microcylinder lasers is 165 K. Single mode emission is detected with a side mode suppression ratio better than 20 dB.

Spectroscopy in the gas phase with GaAs/AlGaAs quantum-cascade lasers.

We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/AlGaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 microm is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup.

Strained InGaAs/AlGaAs/GaAs-quantum cascade lasers

We report on the realization of a quantum cascade laser based on strained In0.04Ga0.96As/Al0.33Ga0.67As/GaAs grown on GaAs substrate using molecular beam epitaxy. Lasing at 10.40 μm and at 9.45 μm was achieved with a good temperature performance showing a T0,2=112 K between 125 and 200 K and a maximum working temperature exceeding T=200 K. Between 78 and 130 K a considerably higher T0,1 of 291 K is found. The decreasing T0 with higher temperatures is due to misalignment of the injector with the upper laser level at elevated temperatures, thermal activation of tunneling of carriers above 130 K, and increasing carrier leakage from the injector into the continuum.

Continuous-wave operation of distributed feedback AlAs/GaAs quantum cascade lasers

Summary form only given. Quantum cascade lasers QCLs are powerful light emitters in the mid infrared. For chemical sensing, single mode emission is advantageous. We fabricated first order distributed feedback lasers to achieve single mode emission. The emission wavelength is continuously tunable according to the temperature dependence of the effective refractive index, which shifts the Bragg wavelength. A rigorously on-resonant Floquet-Bloch analysis of the waveguide grating problem was used to design the grating geometry and the cladding layer thickness. The active material consists of 40 periods of an AlAs/GaAs chirped superlattice, grown by solid source molecular beam epitaxy. A double plasmon enhanced waveguide is used for vertical optical confinement while lateral electrical and optical confinement is achieved by deep etched ridges. The Bragg grating is defined by contact lithography and etched into the surface of the top cladding layer, thus avoiding the need of regrowth. The whole grating region is covered with gold, resulting in a large contact area. The lasers, with as cleaved facets, are soldered with In on Cu-plates (epilayer up) and mounted in a flow cryostat.

Gas absorption spectroscopy using GaAs/AlGaAs quantum cascade lasers and a hollow waveguide absorption cell

In this contribution, the first application of the recently developed GaAs/AlGaAs quantum cascade lasers and hollow waveguides in gas sensing spectroscopy is demonstrated. A multimode GaAs/AlGaAs quantum cascade laser tuned to an emission maximum at 10.009 ?m is used to investigate a mid-infrared absorption of ethene at atmospheric pressure. The laser radiation is focused onto the entrance of a 434 mm long, gas-tight terminated hollow waveguide and it is collected after passing it. Well defined mixtures with ten different concentrations of helium and ethene are flushed through the waveguide. The radiation is analyzed using a Fourier-transform infrared spectrometer (FTIR) equipped with a mercurycadmium- telluride detector. The obtained discrete ethene spectrum is compared to a calculated spectrum finding a good agreement. A detection threshold of 250 ppm and a response time in the range of 100 ms have been obtained with the current setup.

Quantum cascade lasers with monolithic photonic bandgap mirrors

Summary form only. We present an electrically pumped GaAs-AlGaAs ridge waveguide laser using a focused ion beam (FIB) cut photonic band-gap crystal at the end of the cavity. A 1.35 mm long and 29 /spl mu/m broad ridge laser emitting at 9.4 /spl mu/m, has been cut twice, perpendicularly to the axis of the resonator. A one dimensional photonic bandgap crystal, formed of the two free-standing laser material plates and two air gaps is created on one of the ends. The other end of the laser is left unmodified.