Time/frequency-domain characterization of a mid-IR DFG frequency comb via two-photon and heterodyne detection.

Mid-infrared frequency combs are nowadays well-appreciated sources for spectroscopy and frequency metrology. Here, a comprehensive approach for characterizing a difference-frequency-generated mid-infrared frequency comb (DFG-comb) both in the time and in the frequency domain is presented. An autocorrelation scheme exploiting mid-infrared two-photon detection is used for characterizing the pulse width and to verify the optimal compression of the generated pulses reaching a pulse duration (FWHM) as low as 196 fs. A second scheme based on mid-infrared heterodyne detection employing two independent narrow-linewidth quantum cascade lasers (QCLs) is used for frequency-narrowing the modes of the DFG-comb down to 9.4 kHz on a 5-ms timescale.

Precise radiocarbon determination in radioactive waste by a laser-based spectroscopic technique.

The precise and accurate determination of the radionuclide inventory in radioactive waste streams, including those generated during nuclear decommissioning, is a key aspect in establishing the best-suited nuclear waste management and disposal options. Radiocarbon ([Formula: see text]) is playing a crucial role in this scenario because it is one of the so-called difficult to measure isotopes; currently, [Formula: see text] analysis requires complex systems, such as accelerator mass spectrometry (AMS) or liquid scintillation counting (LSC). AMS has an outstanding limit of detection, but only a few facilities are available worldwide; LSC, which can have similar performance, is more widespread, but sample preparation can be nontrivial. In this paper, we demonstrate that the laser-based saturated-absorption cavity ring-down (SCAR) spectroscopic technique has several distinct advantages and represents a mature and accurate alternative for [Formula: see text] content determination in nuclear waste. As a proof-of-principle experiment, we show consistent results of AMS and SCAR for samples of concrete and graphite originating from nuclear installations. In particular, we determined mole fractions of 1.312(9) F[Formula: see text] and 30.951(7) F[Formula: see text] corresponding to ∼1.5 and 36.2 parts per trillion (ppt), respectively, for two different graphite samples originating from different regions of the Adiabatic Resonance Crossing activator prototype installed on one irradiation line of an MC40 Scanditronix cyclotron. Moreover, we measure a mole fraction of 0.593(8) F[Formula: see text] ([Formula: see text] ppt) from a concrete sample originating from an external wall of the Ispra-1 nuclear research reactor currently in the decommissioning phase.

Tunable Microcavity-Stabilized Quantum Cascade Laser for Mid-IR High-Resolution Spectroscopy and Sensing.

The need for highly performing and stable methods for mid-IR molecular sensing and metrology pushes towards the development of more and more compact and robust systems. Among the innovative solutions aimed at answering the need for stable mid-IR references are crystalline microresonators, which have recently shown excellent capabilities for frequency stabilization and linewidth narrowing of quantum cascade lasers with compact setups. In this work, we report on the first system for mid-IR high-resolution spectroscopy based on a quantum cascade laser locked to a CaF2 microresonator. Electronic locking narrows the laser linewidth by one order of magnitude and guarantees good stability over long timescales, allowing, at the same time, an easy way for finely tuning the laser frequency over the molecular absorption line. Improvements in terms of resolution and frequency stability of the source are demonstrated by direct sub-Doppler recording of a molecular line.

High finesse optical cavity coupled with a quartz-enhanced photoacoustic spectroscopic sensor.

An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) combined with a high-finesse cavity sensor platform is proposed as a novel method for trace gas sensing. We call this technique Intra-cavity QEPAS (I-QEPAS). In the proposed scheme, a single-mode continuous wave quantum cascade laser (QCL) is coupled into a bow-tie optical cavity. The cavity is locked to the QCL emission frequency by means of a feedback-locking loop that acts directly on a piezoelectric actuator mounted behind one of the cavity mirrors. A power enhancement factor of ∼240 was achieved, corresponding to an intracavity power of ∼0.72 W. CO2 was selected as the target gas to validate our sensor. For the P(42) CO2 absorption line, located at 2311.105 cm(-1), a minimum detection limit of 300 parts per trillion by volume at a total gas pressure of 50 mbar was achieved with a 20 s integration time. This corresponds to a normalized noise equivalent absorption of 3.2 × 10(-10) W cm(-1) Hz(-1/2), comparable with the best results reported for the QEPAS technique on much faster relaxing gases. A comparison with standard QEPAS performed under the same experimental conditions confirms that the I-QEPAS sensitivity scales with the intracavity laser power enhancement factor.

Radiochemical characterisation, heavy metal determination and morphologic evolution of coastal sediments in the Ravenna area (Italy).

The basic aim of this work was to achieve a preliminary but integrated characterisation of an area of the Ravenna littoral coastline. The use of suitable computerised procedures has allowed the reconstruction of the morphological evolution of this area by means of historical and recent cartography. Coastal sediments were characterised by sampling 3 cores at about 2 km offshore. The following aspects were studied: 1) Mineralogical characterisation of both the total and the fine fraction of sediments by X-ray Diffraction. 2) Characteristion of sedimentary horizons by radiodating. 3)Magnetic susceptibility profiling. 4) Determination of some heavy metals (Cu, Pb, Zn, Cd) by anodic stripping voltammetry.

Visualization of optical deflection and switching operations by a domain engineered-based LiNbO3 electro-optic device.

An electro-optic device applied as an optical beam deflector and switch at different wavelengths has been built and tested. The electro-optic device is based on domain-engineered lithium niobate (LiNbO3). In this paper, for the first time, its operation has been visualized by an imaging camera. The device has been characterized both at the visible wavelength (632.8 nm) and at a typical telecom wavelength (1532 nm). Furthermore, the device has been tested as an amplitude modulator in the mid-infrared region as well, at a wavelength of ~4.3 microm, where no Pockels cells are available. A detailed description of this device is given, and the experimental results are discussed.

Low-power Lamb-dip spectroscopy of very weak CO(2) transitions near 4.25 mum.

We report saturated-absorption spectra recorded by use of 5 muW of infrared radiation coupled into a build-up cavity. Single-pass generation of difference-frequency radiation tunable near 4.25 mum in a periodically poled LiNbO(3) crystal was used. Lamb dips of weak transitions of the fundamental rovibrational band of CO(2) were observed, for what is believed to be the first time, up to the J=82 level. Application of these results to the extension of frequency-comb-based metrology in the infrared is discussed.