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Papers by Mariano Troccoli

Chemical Physics Letters, 2010

Quantum cascade lasers absorption spectroscopy in the mid IR can measure absolute concentrations ... more Quantum cascade lasers absorption spectroscopy in the mid IR can measure absolute concentrations of plasma or gas species for a large variety of applications. Recently, a compact quantum cascade laser measurement and control system (Q-MACS) has been developed for timeresolved plasma diagnostics, process control and trace gas monitoring. The Q-MAC System contains a tuneable quantum cascade laser which can be directed through a plasma or into a multi path cell for exhaust or trace gas detection.

The ν1+ν3 combination band of uranium hexafluoride (UF6) is targeted to perform analytical enrich... more The ν1+ν3 combination band of uranium hexafluoride (UF6) is targeted to perform analytical enrichment measurements using laser absorption spectroscopy. A high performance widely tunable EC-QCL sources emitting radiation at 7.74 μm (1291 cm-1) is employed as an UF6-LAS optical source to measure the unresolved rotational-vibrational spectral structure of several tens of wavenumbers (cm-1). A preliminary spectroscopic measurement based on a direct laser absorption spectroscopy of methane (CH4) as an appropriate UF6 analyte simulant, was demonstrated.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

Quantum cascade (QC) lasers with a dual-wavelength interdigitated cascade are presented. Their ac... more Quantum cascade (QC) lasers with a dual-wavelength interdigitated cascade are presented. Their active core consists of a stack of active regions and injectors emitting at 8.0 μm interleaved with a second stack emitting at 9.5 μm. Laser action at two substantially different wavelengths is observed, demonstrating the viability of the "interdigitated cascade" approach for multi-wavelength laser emission in the mid-infrared. This laser was also used to investigate the influence of the injector-doping on the device performance. Two QC lasers with different injector-doping levels were measured, in particular one only doped in the injectors bridging the 8.0 μm active region to the 9.5 μm active region and the remaining injectors undoped. A substantial reduction in threshold was observed for the laser wavelength with the undoped injector, confirming the significance of impurity scattering for the laser threshold in QC-lasers. Dual single-mode and tunable emission at two substantially different wavelength could be demonstrated with a QC laser emitting at 5.0 μm and 7.5 μm simultaneously. These lasers may be of interest for trace gas sensing, as the second wavelength could be used as in-built reference channel.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade las... more We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade lasers with integrated resonant nonlinearity. Modulation of the nonlinear susceptibility is achieved by the periodic modulation of the bias voltage along the ridge waveguide leading to a periodic shift of electronic resonances and a change in the electron population in different energy levels. An up to tenfold enhancement of the conversion efficiency is observed. This technique is applicable to any resonant nonlinear optical process in quantum wells.

The key physical phenomena associated with long-wavelength infrared emission and laser action in ... more The key physical phenomena associated with long-wavelength infrared emission and laser action in quantum cascade lasers based on InP/GaInAs/AlInAs and GaAs/AlGaAs heterostructures are reviewed. The effect of different tunnel injection schemes on the hot-electron energy distributions is compared. High-power superlattice lasers with improved high-energy injection schemes are described. The local temperature distribution, the thermal resistance and the hot-phonon effects are monitored in operating devices by micro-probe Raman and luminescence measurements.

Physical Review A, 2008

A theoretical and experimental study of multimode operation regimes in quantum cascade lasers ͑QC... more A theoretical and experimental study of multimode operation regimes in quantum cascade lasers ͑QCLs͒ is presented. It is shown that the fast gain recovery of QCLs promotes two multimode regimes: One is spatial hole burning ͑SHB͒ and the other one is related to the Risken-Nummedal-Graham-Haken instability predicted in the 1960s. A model that can account for coherent phenomena, a saturable absorber, and SHB is developed and studied in detail both analytically and numerically. A wide variety of experimental data on multimode regimes is presented. Lasers with a narrow active region and/or with metal coating on the sides tend to develop a splitting in the spectrum, approximately equal to twice the Rabi frequency. It is proposed that this behavior stems from the presence of a saturable absorber, which can result from a Kerr lensing effect in the cavity. Lasers with a wide active region, which have a weaker saturable absorber, do not exhibit a Rabi splitting and their multimode regime is governed by SHB. This experimental phenomenology is well-explained by our theoretical model. The temperature dependence of the multimode regime is also presented.

We discuss the design and performance of quantum cascade laser sources based on intra-cavity seco... more We discuss the design and performance of quantum cascade laser sources based on intra-cavity second harmonic generation operating in at wavelengths shorter than 3.7μm. A passive heterostructure tailored for giant optical nonlinearity is integrated on top of an active region and patterned for quasi-phasematching. We demonstrate operation of λ~3.6μm, λ~3.0μm, and λ~2.6m devices based on lattice-matched and strain-compensated InGaAs/AlInAs/InP materials. Threshold current densities of typical devices with nonlinear sections are only 10-20% higher than that of the reference lasers without the nonlinear section. Our best devices have threshold current density of 2.2kA/cm2 and provide approximately 35μW of second-harmonic output at 2.95μm at room temperature. The second-harmonic conversion efficiency is approximately 100μW/W2. Up to two orders of magnitude higher conversion efficiencies are expected in fully-optimized devices.

Quantum cascade lasers grown by metal organic vapuor phase epitaxy are demonstrated to work in co... more Quantum cascade lasers grown by metal organic vapuor phase epitaxy are demonstrated to work in continuous mode up to room temperature. The lasers have been processed as buried heterostructures with thick gold plating on the top contact. Continuous-wave output powers of 20 mW are obtained at 300 K with threshold current densities of 3.9 kA=cm 2 .

High-power quantum cascade lasers ͑QCLs͒ working in continuous wave ͑cw͒ above 400 K are presente... more High-power quantum cascade lasers ͑QCLs͒ working in continuous wave ͑cw͒ above 400 K are presented. The material was grown by low-pressure metal organic vapor-phase epitaxy and processed into narrow buried heterostructure lasers. A cw output power of 204 mW was obtained at 300 K with an 8.38 m wavelength, 3 mm long and 7.5 m wide coated laser. The device operates in cw mode above 400 K, which exceeds the previous maximum cw temperature operation of QCLs by approximately 60 K. Preliminary reliability data obtained by accelerated aging tests indicate a remarkable robustness of the lasers.

Electronics Letters, 2001

Summary from only given. We present a mid-IR semiconductor optical amplifier based on a quantum c... more Summary from only given. We present a mid-IR semiconductor optical amplifier based on a quantum cascade (QC) active region, which has been used to attain high output powers from distributed-feedback (DFB) QC lasers without affecting their single mode behavior. The device was realized as schematically shown in a master oscillator-power amplifier (MOPA) configuration.

The authors report the fabrication of high-power strained quantum cascade lasers working in conti... more The authors report the fabrication of high-power strained quantum cascade lasers working in continuous mode above 370 K. The devices, processed in narrow buried heterostructures, were grown by low-pressure metal organic vapor-phase epitaxy. Continuous wave output power as high as 312 mW at 300 K was obtained at a wavelength of 5.29 m from a 3.25 mm long, 7.5 m wide laser with a high-reflectivity back facet coating. The slope efficiency was in excess of 1.5 W / A and the power conversion efficiency reached almost 5%.

We combine photonic and electronic band structure engineering to create a surface-emitting quantu... more We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics.

Nature, 2005

Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials,... more Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials, enables the generation of optical gain at a frequency that is shifted from that of the incident radiation by an amount corresponding to the frequency of an internal oscillation of the material 1,2 . This effect is the basis for a broad class of tunable sources known as Raman lasers 2,3 . In general, these sources have only small gain (,10 29 cm W 21 ) and therefore require external pumping with powerful lasers, which limits their applications. Here we report the realization of a semiconductor injection Raman laser designed to circumvent these limitations. The physics underlying our device differs in a fundamental way from existing Raman lasers 3-8 : it is based on triply resonant stimulated Raman scattering between quantumconfined states within the active region of a quantum cascade laser that serves as an internal optical pump-the device is driven electrically and no external laser pump is required. This leads to an enhancement of orders of magnitude in the Raman gain, high conversion efficiency and low threshold. Our lasers combine the advantages of nonlinear optical devices and of semiconductor injection lasers, and could lead to a new class of compact and wavelength-agile mid-and far-infrared light sources.

Iee Proceedings-optoelectronics, 2003

The facet temperature profile and the thermal resistance of operating quantum-cascade lasers (QCL... more The facet temperature profile and the thermal resistance of operating quantum-cascade lasers (QCLs) have been assessed using a microprobe band-to-band photoluminescence technique. Substrate-side and epilayer-side-mounted QCLs based on GaInAs/AlInAs/InP and GaAs/AlGaAs material systems have been compared. The dependence of the thermal resistance on the CW or pulsed injection conditions and its correlation with the output power have been studied. These results were used as inputs for a two-dimensional heat-diffusion model which gives the heat fluxes and the thermal conductivity of the active regions, in order to design QCLs with improved thermal properties.

Chemical Physics Letters, 2010

Quantum cascade lasers absorption spectroscopy in the mid IR can measure absolute concentrations ... more Quantum cascade lasers absorption spectroscopy in the mid IR can measure absolute concentrations of plasma or gas species for a large variety of applications. Recently, a compact quantum cascade laser measurement and control system (Q-MACS) has been developed for timeresolved plasma diagnostics, process control and trace gas monitoring. The Q-MAC System contains a tuneable quantum cascade laser which can be directed through a plasma or into a multi path cell for exhaust or trace gas detection.

The ν1+ν3 combination band of uranium hexafluoride (UF6) is targeted to perform analytical enrich... more The ν1+ν3 combination band of uranium hexafluoride (UF6) is targeted to perform analytical enrichment measurements using laser absorption spectroscopy. A high performance widely tunable EC-QCL sources emitting radiation at 7.74 μm (1291 cm-1) is employed as an UF6-LAS optical source to measure the unresolved rotational-vibrational spectral structure of several tens of wavenumbers (cm-1). A preliminary spectroscopic measurement based on a direct laser absorption spectroscopy of methane (CH4) as an appropriate UF6 analyte simulant, was demonstrated.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

Quantum cascade (QC) lasers with a dual-wavelength interdigitated cascade are presented. Their ac... more Quantum cascade (QC) lasers with a dual-wavelength interdigitated cascade are presented. Their active core consists of a stack of active regions and injectors emitting at 8.0 μm interleaved with a second stack emitting at 9.5 μm. Laser action at two substantially different wavelengths is observed, demonstrating the viability of the "interdigitated cascade" approach for multi-wavelength laser emission in the mid-infrared. This laser was also used to investigate the influence of the injector-doping on the device performance. Two QC lasers with different injector-doping levels were measured, in particular one only doped in the injectors bridging the 8.0 μm active region to the 9.5 μm active region and the remaining injectors undoped. A substantial reduction in threshold was observed for the laser wavelength with the undoped injector, confirming the significance of impurity scattering for the laser threshold in QC-lasers. Dual single-mode and tunable emission at two substantially different wavelength could be demonstrated with a QC laser emitting at 5.0 μm and 7.5 μm simultaneously. These lasers may be of interest for trace gas sensing, as the second wavelength could be used as in-built reference channel.

Physical Review A, 2007

We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), w... more We report the observation of a coherent multimode instability in quantum cascade lasers (QCLs), which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago for ring lasers. The threshold of the observed instability is significantly lower than in the original RNGH instability, which we attribute to saturable-absorption nonlinearity in the laser. Coherent effects, which cannot be reproduced by standard laser rate equations, can play therefore a key role in the multimode dynamics of QCLs, and in lasers with fast gain recovery in general.

We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade las... more We demonstrate a quasiphase matching scheme for second-harmonic generation in quantum cascade lasers with integrated resonant nonlinearity. Modulation of the nonlinear susceptibility is achieved by the periodic modulation of the bias voltage along the ridge waveguide leading to a periodic shift of electronic resonances and a change in the electron population in different energy levels. An up to tenfold enhancement of the conversion efficiency is observed. This technique is applicable to any resonant nonlinear optical process in quantum wells.

The key physical phenomena associated with long-wavelength infrared emission and laser action in ... more The key physical phenomena associated with long-wavelength infrared emission and laser action in quantum cascade lasers based on InP/GaInAs/AlInAs and GaAs/AlGaAs heterostructures are reviewed. The effect of different tunnel injection schemes on the hot-electron energy distributions is compared. High-power superlattice lasers with improved high-energy injection schemes are described. The local temperature distribution, the thermal resistance and the hot-phonon effects are monitored in operating devices by micro-probe Raman and luminescence measurements.

Physical Review A, 2008

A theoretical and experimental study of multimode operation regimes in quantum cascade lasers ͑QC... more A theoretical and experimental study of multimode operation regimes in quantum cascade lasers ͑QCLs͒ is presented. It is shown that the fast gain recovery of QCLs promotes two multimode regimes: One is spatial hole burning ͑SHB͒ and the other one is related to the Risken-Nummedal-Graham-Haken instability predicted in the 1960s. A model that can account for coherent phenomena, a saturable absorber, and SHB is developed and studied in detail both analytically and numerically. A wide variety of experimental data on multimode regimes is presented. Lasers with a narrow active region and/or with metal coating on the sides tend to develop a splitting in the spectrum, approximately equal to twice the Rabi frequency. It is proposed that this behavior stems from the presence of a saturable absorber, which can result from a Kerr lensing effect in the cavity. Lasers with a wide active region, which have a weaker saturable absorber, do not exhibit a Rabi splitting and their multimode regime is governed by SHB. This experimental phenomenology is well-explained by our theoretical model. The temperature dependence of the multimode regime is also presented.

We discuss the design and performance of quantum cascade laser sources based on intra-cavity seco... more We discuss the design and performance of quantum cascade laser sources based on intra-cavity second harmonic generation operating in at wavelengths shorter than 3.7μm. A passive heterostructure tailored for giant optical nonlinearity is integrated on top of an active region and patterned for quasi-phasematching. We demonstrate operation of λ~3.6μm, λ~3.0μm, and λ~2.6m devices based on lattice-matched and strain-compensated InGaAs/AlInAs/InP materials. Threshold current densities of typical devices with nonlinear sections are only 10-20% higher than that of the reference lasers without the nonlinear section. Our best devices have threshold current density of 2.2kA/cm2 and provide approximately 35μW of second-harmonic output at 2.95μm at room temperature. The second-harmonic conversion efficiency is approximately 100μW/W2. Up to two orders of magnitude higher conversion efficiencies are expected in fully-optimized devices.

Quantum cascade lasers grown by metal organic vapuor phase epitaxy are demonstrated to work in co... more Quantum cascade lasers grown by metal organic vapuor phase epitaxy are demonstrated to work in continuous mode up to room temperature. The lasers have been processed as buried heterostructures with thick gold plating on the top contact. Continuous-wave output powers of 20 mW are obtained at 300 K with threshold current densities of 3.9 kA=cm 2 .

High-power quantum cascade lasers ͑QCLs͒ working in continuous wave ͑cw͒ above 400 K are presente... more High-power quantum cascade lasers ͑QCLs͒ working in continuous wave ͑cw͒ above 400 K are presented. The material was grown by low-pressure metal organic vapor-phase epitaxy and processed into narrow buried heterostructure lasers. A cw output power of 204 mW was obtained at 300 K with an 8.38 m wavelength, 3 mm long and 7.5 m wide coated laser. The device operates in cw mode above 400 K, which exceeds the previous maximum cw temperature operation of QCLs by approximately 60 K. Preliminary reliability data obtained by accelerated aging tests indicate a remarkable robustness of the lasers.

Electronics Letters, 2001

Summary from only given. We present a mid-IR semiconductor optical amplifier based on a quantum c... more Summary from only given. We present a mid-IR semiconductor optical amplifier based on a quantum cascade (QC) active region, which has been used to attain high output powers from distributed-feedback (DFB) QC lasers without affecting their single mode behavior. The device was realized as schematically shown in a master oscillator-power amplifier (MOPA) configuration.

The authors report the fabrication of high-power strained quantum cascade lasers working in conti... more The authors report the fabrication of high-power strained quantum cascade lasers working in continuous mode above 370 K. The devices, processed in narrow buried heterostructures, were grown by low-pressure metal organic vapor-phase epitaxy. Continuous wave output power as high as 312 mW at 300 K was obtained at a wavelength of 5.29 m from a 3.25 mm long, 7.5 m wide laser with a high-reflectivity back facet coating. The slope efficiency was in excess of 1.5 W / A and the power conversion efficiency reached almost 5%.

We combine photonic and electronic band structure engineering to create a surface-emitting quantu... more We combine photonic and electronic band structure engineering to create a surface-emitting quantum cascade microcavity laser. A high-index contrast two-dimensional photonic crystal is used to form a micro-resonator that simultaneously provides feedback for laser action and diffracts light vertically from the surface of the semiconductor surface. A top metallic contact allows electrical current injection and provides vertical optical confinement through a bound surface plasmon wave. The miniaturization and tailorable emission properties of this design are potentially important for sensing applications, while electrical pumping can allow new studies of photonic crystal and surface plasmon structures in nonlinear and near-field optics.

Nature, 2005

Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials,... more Stimulated Raman scattering is a nonlinear optical process that, in a broad variety of materials, enables the generation of optical gain at a frequency that is shifted from that of the incident radiation by an amount corresponding to the frequency of an internal oscillation of the material 1,2 . This effect is the basis for a broad class of tunable sources known as Raman lasers 2,3 . In general, these sources have only small gain (,10 29 cm W 21 ) and therefore require external pumping with powerful lasers, which limits their applications. Here we report the realization of a semiconductor injection Raman laser designed to circumvent these limitations. The physics underlying our device differs in a fundamental way from existing Raman lasers 3-8 : it is based on triply resonant stimulated Raman scattering between quantumconfined states within the active region of a quantum cascade laser that serves as an internal optical pump-the device is driven electrically and no external laser pump is required. This leads to an enhancement of orders of magnitude in the Raman gain, high conversion efficiency and low threshold. Our lasers combine the advantages of nonlinear optical devices and of semiconductor injection lasers, and could lead to a new class of compact and wavelength-agile mid-and far-infrared light sources.

Iee Proceedings-optoelectronics, 2003

The facet temperature profile and the thermal resistance of operating quantum-cascade lasers (QCL... more The facet temperature profile and the thermal resistance of operating quantum-cascade lasers (QCLs) have been assessed using a microprobe band-to-band photoluminescence technique. Substrate-side and epilayer-side-mounted QCLs based on GaInAs/AlInAs/InP and GaAs/AlGaAs material systems have been compared. The dependence of the thermal resistance on the CW or pulsed injection conditions and its correlation with the output power have been studied. These results were used as inputs for a two-dimensional heat-diffusion model which gives the heat fluxes and the thermal conductivity of the active regions, in order to design QCLs with improved thermal properties.