Comment on "Repulsive Casimir forces".
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Comment↗
Biomedical subjects
Federico Capasso
Publications and source records attributed to Federico Capasso.
Resonant second-order nonlinear optical processes in quantum cascade lasers.
We demonstrate an efficient intracavity nonlinear interaction of laser modes in a specially adapted quantum cascade laser. A two-wavelength quantum cascade laser structure emitting at wavelengths of 7.1 and 9.5 micrometer included cascaded resonant optical intersubband transitions in an intracavity configuration leading to resonantly enhanced sum-frequency and second-harmonic generation at wavelengths of 4.1, 3.6, and 4.7 micrometer respectively. Laser peak optical powers of 60 and 80 mW resulted in 30 nW of sum-frequency signal and 10-15 nW of second-harmonic signal, both in good agreement with theoretical calculations.
Journal Article↗
Ultra-broadband semiconductor laser.
The fundamental mechanism behind laser action leads in general only to narrowband, single-wavelength emission. Several approaches for achieving spectrally broadband laser action have been put forward, such as enhancing the optical feedback in the wings of the gain spectrum, multi-peaked gain spectra, and the most favoured technique at present, ultrashort pulse excitation. Each of these approaches has drawbacks, such as a complex external laser cavity configuration, a non-flat optical gain envelope function, or an inability to operate in continuous mode, respectively. Here we present a monolithic, mid-infrared 'supercontinuum' semiconductor laser that has none of these drawbacks. We adopt a quantum cascade configuration, where a number of dissimilar intersubband optical transitions are made to cooperate in order to provide broadband optical gain from 5 to 8 microm wavelength. Laser action with a Fabry-Pérot spectrum covering all wavelengths from 6 to 8 microm simultaneously is demonstrated with this approach. Lasers that emit light over such an extremely wide wavelength range are of interest for applications as varied as terabit optical data communications or ultra-precision metrology and spectroscopy.
Journal Article↗
Thermoelectrically cooled quantum-cascade-laser-based sensor for the continuous monitoring of ambient atmospheric carbon monoxide.
We report the first application of a thermoelectrically cooled, distributed-feedback quantum-cascade laser for continuous spectroscopic monitoring of CO in ambient air at a wavelength of 4.6 microm. A noise-equivalent detection limit of 12 parts per billion was demonstrated experimentally with a 102-cm optical pathlength and a 2.5-min data acquisition time at a 10-kHz pulsed-laser repetition rate. This sensitivity corresponds to a standard error in fractional absorbance of 3 x 10(-5).
Atmosphere↗
Coherent radiation from neutral molecules moving above a grating.
We predict and study the effect of parametric self-induced excitation of a molecule moving above the dielectric or conducting medium with periodic grating. In this case the radiation reaction force modulates the molecular transition frequency which results in a parametric instability of dipole oscillations even from the level of quantum or thermal fluctuations. The present mechanism of instability of electrically neutral molecules is different from that of the well-known Smith-Purcell and transition radiation in which a moving charge and its oscillating image create an oscillating dipole. We show that parametrically excited molecular bunches can produce an easily detectable coherent radiation flux of up to a microwatt.
Journal Article↗
Transportable automated ammonia sensor based on a pulsed thermoelectrically cooled quantum-cascade distributed feedback laser.
A compact ammonia sensor based on a 10-microm single-frequency, thermoelectrically cooled, pulsed quantum-cascade laser with an embedded distributed feedback structure has been developed. To measure NH3 concentrations, we scanned the laser over two absorption lines of its fundamental v2 band. A sensitivity of better than 0.3 parts per million was achieved with just a 1-m optical path length. The sensor is computer controlled and automated to monitor NH3 concentrations continuously for extended periods of time and to store data in the computer memory.
Ammonia↗