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With their large mid-infrared spectral coverage, Quantum Cascade Lasers (QCL) are very promising for probing the molecular fingerprint region. Current applications to high-resolution spectroscopy are mainly limited by their large freerunning frequency instability. A lot of efforts have thus been made recently to characterize and improve their spectral properties, especially the emission line width and the traceability to frequency standards. Here we demonstrate the frequency stabilization of a QCL emitting at 10 μm onto an optical frequency comb (OFC), itself controlled with a remote near-infrared ultra-stable laser. The latter frequency is transferred with an optical fiber link of 43 km from a metrological institute, where its frequency is monitored against frequency standards. From the reference ultra-stable laser stability, one can infer a QCL line width below 1 Hz and a relative frequency stability of 2x10 -15 for an averaging time of 1 s. Moreover the QCL frequency is known with an uncertainty of at most 10 -14 after 100 s averaging time, thanks to the traceability to primary standards. This performance overcome by at least two orders of magnitude what has been demonstrated up to now with a QCL. We further demonstrate the continuous tuning of this stabilized QCL and recorded a few OsO4 molecular absorption lines, some of them being unreported so far to our knowledge. The saturated absorption line width is 25 kHz, well below what has ever been recorded with a QCL. These results open the way to ultra-high precision measurements with molecules with the same performance than currently achieved with atoms.

Optical transmission data can aid in the analysis of nonabsorbing inclusions in crystals. For illustration, the inclusions in a AgGaSe(2) sample are analyzed.

A case is reported, the sixth in the literature, in which permanent anterograde block occurred in the accessory pathway of a patient with Wolff-Parkinson-White syndrome, so that pre-excitation no longer occurred. Retrograde conduction remained intact and the patient developed incessant tachycardia with ventriculo-atrial conduction occurring over the accessory pathway. Retrogradely conducting pathways are a common cause of supraventricular tachycardia and this case raises the possibility that many of them may previously have had overt pre-excitation.

International audience; Recently we have improved the efficiency and the output power of our optically pumped continuous-wave THz sources. These sources are based on the beating of two laser lines in a wide bandwidth photodetector. Its intrinsic nonlinear behaviour is used to produce a beatnote at the frequency difference between the two laser lines (photomixing). These photomixers are continuously tunable THz sources working at room temperature. We have developed two kinds of photomixers: GaAs-based for 0.8 mu m pumping and InP-based for 1.5 mu m pumping. On GaAs the best results has been obtained thanks to low-temperature-grown GaAs (LTG-GaAs) photoconductors (PC). Efficiency and power were optimized by designing a new type of thin PC placed in a Fabry-Perot resonator. The high impedance of the PC is a well-known limitation of this device but with our approach it was possible to reduce its impedance by a factor 100. Moreover by designing an impedance matching network it was possible to obtain 1.8 mW at 252 GHz with a total efficiency of 0.5 %. On InP the best results are obtained with uni-travelling-carrier photodiodes (UTC-PD). The device was improved by designing a new heterostructure and new semi-transparent contacts with sub-wavelength apertures. The active layer was also bonded to a silicon substrate thanks to metal thermocompression. It is demonstrated that with this approach it is possible to obtain a power of 0.7 mW at 300 GHz with a total efficiency of 0.7 %. More generally the efficiency of optically pumped terahertz sources will be discussed.

ADF acknowledges support from EPSRC (EP/I004602/1 and EP/J004200/1). In this paper we present the design and applications of flexible photonic membranes. We discuss their use as versatile photonic layers in the framework of lab-on-fibre applications, specifically focusing on the design of angular robust spectral filters. We also show alternative routes to their fabrication, highlighting the opportunities and limitations associated to each approach. Finally we present our preliminary results on the all-optical control over flexible membranes, as a potential method to fine-tune their opto-mechanical properties to the required application. Publisher PDF

In this paper we present our recent work on mid-infrared photonic integrated circuits for spectroscopic sensing applications. We discuss the use of silicon-based photonic integrated circuits (either based on silicon-on-insulator or germanium-on-silicon waveguide circuits) for this purpose and detail how a variety of optical functions in the mid-infrared besides passive waveguiding and filtering can be realized, either relying on nonlinear optics or on the integration of other materials such as GaSb-based compound semiconductors, GeSn epitaxy and PbS colloidal nanoparticles. The integration of photodetectors resulting in fully integrated mid-IR spectrometers, semiconductor laser sources and nonlinear optics based spectral translators between the telecommunication wavelength range and the mid-infrared are discussed.

In this paper, two kinds of colloidal quantum dots, PbS and HgTe, are explored for SWIR photodetectors application. The colloidal dots are prepared by hot injection chemical synthesis, with organic ligands around the dots keeping them stable in solution. For the purpose of achieving efficient carrier transport between the dots in a film, these long organic ligands are replaced by shorter, inorganic ligands. We report uniform, ultra-smooth colloidal QD films without cracks realized by dip-coating and corresponding ligand exchange on a silicon substrate. Metal-free inorganic ligands, such as OH- and S2-, are investigated to facilitate the charge carrier transport in the film. Both PbS and HgTe-based quantum dot photoconductors were fabricated on interdigitated gold electrodes. For PbS-based detectors a responsivity of 200A/W is measured at 1.5μm, due to the large internal photoconductive gain. A 2.2μm cut-off wavelength for PbS photodetectors and 2.8μm for HgTe quantum dot photodetectors are obtained.

International audience; Several molecules of interest have their absorption signature in the mid-infrared. Spectroscopy is commonly used for the detection of these molecules, especially in the short-wave infrared (SWIR) region due to the low water absorption. Conventional spectroscopic systems consist of a broadband source, detector and dispersive components, making them bulky and difficult to handle. Such systems cannot be used in applications where small footprint and low power consumption is critical, such as portable gas sensors and implantable blood glucose monitors. Silicon-On-Insulator (SOI) offers a compact, low-cost photonic integrated circuit platform realized using CMOS fabrication technology. On the other hand, the GaSb material system allows the realization of high performance SWIR lasers and detectors. Integration of GaSb active components on SOI could therefore result in a compact and low power consumption integrated spectroscopic system. In this paper, we report the study on thin-film GaSb Fabry-Perot lasers integrated on a carrier substrate. The integration is achieved by using an adhesive polymer (DVS-BCB) as the bonding agent. The lasers operate at room temperature at 2.02μm. We obtain a minimum threshold current of 48.9mA in the continuous wave regime and 27.7mA in pulsed regime. This yields a threshold current density of 680A/cm2 and 385A/cm2, respectively. The thermal behaviour of the device is also studied. The lasers operate up to 35 °C, due to a 323 K/W thermal resistance