Multiplexed direct-frequency-comb Vernier spectroscopy of carbon dioxide 2ν1 + ν3 ro-vibrational combination band.

We investigated a set of nineteen 12C16O2 transitions of the 2ν1 + ν3 ro-vibrational band in the spectral region from 5064 to 5126 cm-1 at different pressures, using frequency-comb Vernier spectroscopy. Our spectrometer enabled the systematic acquisition of molecular absorption profiles with high precision. Spectroscopic parameters, namely, transition frequency, linestrength, and self-pressure broadening coefficient, have been accurately determined by using a global fit procedure. These data are in agreement with theoretical values contained in HITRAN2016 database [I. E. Gordon et al., J. Quant. Spectrosc. Radiat. Transfer 203, 3-69 (2017)] at the same precision level. A moderate improvement of the line intensity determinations, by a factor 1.5 in the best case [P(10) transition at 5091.6 cm-1], should be noticed, projecting direct-comb-Vernier-spectroscopy as an adequate tool for spectral intensity calibration.

Ultimate Limit in the Spectral Resolution of Extreme Ultraviolet Frequency Combs.

We present the results of direct interferometric measurements on the pulse-to-pulse phase jitter of a metrological, fiber-based, infrared (IR) frequency comb. We show that the short-time evolution of such phase fluctuations, which cannot be actively controlled by any feedback system, imposes a stringent limit on the tooth linewidth of extreme ultraviolet (XUV) combs produced by high-order harmonic conversion, thus explaining the difference of 9 orders of magnitude between the coherence times of state-of-the-art IR and XUV frequency combs.

Note: An analyzer for field detection of H2S by using cavity ring-down at 1.57 µm.

A prototype analyzer for the detection of hydrogen sulfide (H2S), based on cavity ring-down spectroscopy, is described. The device exploits, whenever possible, optical fibers, in order to simplify the alignment and to improve the stability. A trade-off between low detection level and simplicity has been pursued. The experimental results obtained during tests on different kinds of H2S samples are shown.

Widely-tunable mid-infrared fiber-coupled quartz-enhanced photoacoustic sensor for environmental monitoring.

A compact widely-tunable fiber-coupled sensor for trace gas detection of hydrogen sulfide (H2S) in the mid infrared is reported. The sensor is based on an external-cavity quantum cascade laser (EC-QCL) tunable between 7.6 and 8.3 µm wavelengths coupled into a single-mode hollow-core waveguide. Quartz-enhanced photoacoustic spectroscopy has been selected as detecting technique. The fiber coupling system converts the astigmatic beam exiting the laser into a TEM(00) mode. During a full laser scan, we observed no misalignment between the optical beam and the tuning fork, thus making our system applicable for multi-gas or broad absorber detections. The sensor has been tested on N2:H2S gas mixtures. The minimum detectable H2S concentration is 450 ppb in ~3 s integration time, which is the best value till now reported in literature for H2S optical sensors.

Direct observation of coherent interorbital spin-exchange dynamics.

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold 173Yb fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of 173Yb atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism.

Mid-infrared digital holography and holographic interferometry with a tunable quantum cascade laser.

Mid-infrared digital holography based on CO2 lasers has proven to be a powerful coherent imaging technique due to reduced sensitivity to mechanical vibrations, increased field of view, high optical power, and possible vision through scattering media, e.g., smoke. Here we demonstrate a similar and more compact holographic system based on an external cavity quantum cascade laser emitting at 8 µm. Such a setup, which includes a highly sensitive microbolometric camera, allows the acquisition of speckle holograms of scattering objects, which can be processed in real time. In addition, by exploiting the broad laser tunability, we can acquire holograms at different wavelengths, from which we extract phase images not subjected to phase wrapping, at synthetic wavelengths ranging from hundreds of micrometers to several millimeters.