Jerome Faist

Broadly tunable external cavity quantum-cascade lasers

External cavity quantum-cascade lasers (QCLs) emitting in the long-wave infrared (LWIR) around 10 μm and in the mid-wave infrared (MWIR) around 5.2 μm have been realized. The coupling facet of the QC chips was anti-reflection coated and the optical feedback was provided by a diffraction grating arranged in a Littrow configuration. The active regions of the gain elements were based on bound-to-continuum designs having broad gain curves (Approx = to 300 cm-1 full width at half maximum). The LWIR laser was operated in pulsed mode on a thermoelectric (TE) cooler. It could be tuned over a frequency range of 150 cm-1 from 9.1 to 10.55 μm with a peak power ⩾ 30 mW. The MWIR laser was operated in continuous-wave (CW) mode on a TE cooler. It could be tuned over more than 170 cm-1 from 4.95 to 5.4 μm and was single-mode over more than 140 cm-1. Its output power was in excess of 5 mW over 130 cm-1. This broad tunability (10 times more than that of distributed-feedback QCLs) enables new applications of QCLs in high-resolution infrared spectroscopy.

5μm Intersubband Raman Laser from GaInAs/AlInAs double Quantum Wells

We demonstrate an optically‐pumped GaInAs/AlInAs based intersubband laser operating at a wavelength of ∼ 5.7μm applying a simple three‐level design. Using a sub‐nanosecond long pulsed excitation laser tunable over the linewidth of the transition from the first level to the third level E13, Raman shift in the lasing spectra was observed. Analyzing the lasing behavior we obtained the threshold at an absorbed pump power of 166W and an internal conversion efficiency between pump and intersubband laser of 3% at 70K.

Imaging with a terahertz quantum cascade laser for biomedical applications

We investigated and demonstrated bio-medical imaging using a THz quantum cascade laser. With the THz quantum cascade laser (QCL) at 3.8 THz, we obtained large dynamic range and high spatial resolution in the transmission imaging technique. The various tissues images, such as lung, liver, and brain sections from the laboratory mouse were obtained and studied. The most important factor for this imaging scheme is to obtain high contrast with different absorption characteristics in tissues. We explored distinct images from the fat, muscles and tendon from the freshly cut tissues and investigated absorption coefficient and compared with FTIR measurement. We also demonstrated the image of distinct region of tumors progressed and normal tissues using this technique. The comparison of frequency dependent medical imaging with utilizing different wavelength of QCLs has been addressed.

Dual wavelength intersubband emitters

One of the features that makes intersubband transitions fundamentally different from interband ones are the characteristically narrow joint density of states (in principle, delta-like) and the corresponding absorption peak.

Effective cyclotron mass renormalization in ultrastrong coupling (Conference Presentation)

Ultrastrong light matter coupling has raised high interest in recent years for the predicted unusual quantum properties of its ground state, which contains photons. We have investigated such physics in a system based on the cyclotron transition of a 2D confined electrons (or holes) gas in semiconductors coupled to the modes of highly subwavelength metallic resonators in the 200-1000 GHz range. The extreme reduction of the cavity volume and surface (Seff/λ0=3 x 10-7) led to the observation of ultrastrong coupling on a small (<100) number of electrons. Such extreme conditions reveal also a previously unobserved renormalization of the cyclotron effective mass, effectively breaking Kohn’s theorem. Kohns theorem states the independence of the cyclotron resonance frequency from many-body effects in the case of a parabolic and translationally invariant system. For our resonator the translational invariance is clearly broken since the electric field is concentrated on a circular region of around r= 350 nm for a cyclotron radius of the order of 60 nm for a free space wavelength of 1 mm (300 GHz). In our case we can reveal many body effects on the cyclotron mass because we break the translational invariance of the system with the extreme photonic confinement provided by the cavity, observing an increase of the m*/m0 of 6% with respect to the uncoupled cyclotron mass. Experiments conduced on the same 2DEG with a standard split-ring resonator at the same frequency do not show any effective mass shift.

THz Intersubband Polaritons in LC Resonator Structures

Strong light matter coupling in the THz spectral range is demonstrated. A material excitation is coupled to a novel electronic feedback microcavity, which allows strong subwavelength confinement of the cavity mode and tunability via change of the electrical size of the components. Intersubband transitions in conventional square quantum wells as well as parabolically graded quantum wells are used as material excitations. With the square wells, a splitting of 0.94 THz was found at cryogenic temperatures. The parabolic quantum well samples show a splitting of 0.96 THz up to room temperature.

Cyclotron emission in a THz quantum cascade structure

A terahertz quantum cascade structure has been designed to allow population relaxation between crossing Landau levels from different subbands under perpendicular magnetic field. Emission spectra have been performed and show expected intersubband luminescence as well as radiative inter‐Landau level emission (cyclotron emission) through the surface of the sample. Interface roughness is the mechanism responsible for the population relaxation at resonance.

Room-temperature CW operation of (lambda~9 μm) InP-based quantum cascade lasers

Room temperature CW operation of quantum cascade lasers has recently been demonstrated. However, this important performance milestone still remains a technological challenge. QCLs are characterized by high electrical power consumption (3 - 5 W) and low wall plug efficiencies (1 - 4%). This leads to considerable self-heating that can block CW operation. In order to overcome this self-heating device fabrication has to be optimized for high thermal extraction. In this paper we will demonstrate the factors that influence CW operation in quantum cascade lasers (QCLs). We will compare the performance of different device processing design to achieve maximum thermal dissipation and reduced power consumption.

Chaotic whispering gallery lasers with high power and directional emission

We show how a laser resonator design exploiting chaotic ray motion can dramatically increase output power and directionality of whispering gallery lasers. This effect is demonstrated in quantum cascade (QC) lasers, which are based on mid-infrared intersubband transitions.

Strain-compensated In/sub 0.7/Ga/sub 0.3/As-Al/sub 0.6/In/sub 0.4/As quantum cascade lasers for 3-5 /spl mu/m operation

Summary form only given. We report quantum cascade lasers based on strained InGaAs-AlInAs at 3.5 /spl mu/m with optical powers up to 5 mW to T 280 K. Operations of the first buried-heterostructure QC lasers at 5 /spl mu/m also will be discussed.