The favorable downscaling behavior of photoacoustic spectroscopy has provoked in recent years a growing interest in the miniaturization of photoacoustic sensors. The individual components of the sensor, namely widely tunable quantum cascade lasers, low loss mid infrared (mid-IR) waveguides, and efficient microelectromechanical systems (MEMS) microphones are becoming available in complementary metal–oxide–semiconductor (CMOS) compatible technologies. This paves the way for the joint processes of miniaturization and full integration. Recently, a prototype microsensor has been designed by the means of a specifically designed coupled optical-acoustic model. This paper discusses the new, or more intense, challenges faced if downscaling is continued. The first limitation in miniaturization is physical: the light source modulation, which matches the increasing cell acoustic resonance frequency, must be kept much slower than the collisional relaxation process. Secondly, from the acoustic modeling point of view, one faces the limit of validity of the continuum hypothesis. Namely, at some point, velocity slip and temperature jump boundary conditions must be used, instead of the continuous boundary conditions, which are valid at the macro-scale. Finally, on the technological side, solutions exist to realize a complete lab-on-a-chip, even if it remains a demanding integration problem.

SiGe alloys present a large Infra-Red transparency window and a full compatibility with the standard Complementary Metal Oxide Semiconductor processing making them suitable for applications in integrated optics. In this paper we report on Mlines characterization of Si(1-x)Ge(x) graded index waveguides at 2.15 µm. First, a law giving the refractive index of a Si(1-x)Ge(x) alloy as a function of the Ge content x: n = 1.342x(2) + 0.295x + 3.451, has been experimentally established in the 0 < x < 0.4 range. Then, we have demonstrated that our methodology based on Mlines measurements can be used as short-loop non-destructive technique to provide feedback for sample growth.

La gestion des émissions industrielles et le contrôle de la pollution de l'air sont aujourd'hui des « impératifs » visant à augmenter la qualité de vie aussi bien du point de vue de la santé publique que du confort. Des moyens importants ont été déployés pour y parvenir avec une volonté forte des pouvoirs publics de s'attaquer aux problèmes de santé environnementale et, pour l'habitat résidentiel, de la consommation énergétique. Les principales avancées technologiques visent aujourd'hui la réalisation d'appareils de mesure permettant de détecter les principaux polluants efficacement et à moindre coût.

We report on the advanced optical characterizations of microfabricated solid immersion lenses with 2-μm diameter, operating at λ= 642 nm. The main feature, the spot size reduction, has been investigated by applying a focused Gaussian beam of NA = 0.9. Particular illuminating beams, e.g., Bessel-Gauss beams of the zeroth and the first order, a doughnutshape beam and its decompositions, i.e. two-half-lobes beams, have also been used to influence the shape of the immersed focal spot. Detailed optical characterizations have been conducted by measuring the amplitude and phase distributions with a high-resolution interference microscope (HRIM) in volume around the focal spot. The immersion effect of the SiO₂ solid immersion lens leads to a spot-size reduction of approximately 1.5 which agrees well with theory. Particularly shaped incident beams exhibit a comparable size reduction of the immersed spots. Such structured focal spots are of significant interest in optical trapping, lithography, and optical data storage systems.