Frequency metrology of buffer-gas-cooled molecular spectra
Nowadays, buffer gas cooling (BGC) represents an invaluable option to produce cold stable molecules, both in view of secondary cooling strategies towards the achievement of quantum degeneracy and for fundamental spectroscopic studies. In particular, by reducing both the internal and translational temperature of any species down to a few kelvins, the BGC technique has the potential to dramatically improve the quality of ro-vibrational molecular spectra, thus offering unique opportunities for transition frequency measurements with unprecedented accuracy. By combining saturated cavity ring-down spectroscopy with the buffer-gas-cooling technique, we have demonstrated a general approach to Lamb-dip ro-vibrational measurements on cold molecules. The developed scheme represents the launch pad to high-accuracy molecular tests of fundamental Physics at the electron volt energy scale. Examples include: searching for putative fifth-force interactions and assessing the space-time stability of the proton-to-electron mass ratio. In particular, we aim to set new bounds on hadronic long-range (on the Angstrom scale, typical of intramolecular bonds) forces beyond the Standard Model, by accomplishing sub-kHz-accuracy line-center frequency determinations for selected hydrogen deuteride (HD) ro-vibrational transitions in the (2,0)/(1,0) overtone/fundamental band at 1.4/2.7 micron wavelength. To address this challenge, a second-gneration BGC source will be first realized to create 20-Kelvin HD samples. Then, a metrological-grade infrared laser source will be coupled to a high-finesse cavity with superior mechanical stability surrounding the cold HD sample, to implement either the noise-immune cavity-enhanced optical-heterodyne molecular-spectroscopy (NICE-OHMS) or the saturated-absorption cavity ring-down (SCAR) technique. Ultimately, comparison of the measured transition frequencies with state-of-the-art ab initio calculations will constrain the coupling strength of extra long-range (Angstrom length scales) hadron-hadron interactions below 10-10α (being α the fine-structure constant), one order of magnitude better than the present limit.
C-14 SCAR
The C14-SCAR spectrometer, acquired within the project SHINE (StrengtHening the Italian Nodes of E-RIHS, is based on a 4.5-μm-wavelength quantum cascade laser (QCL) and the SCAR technique, for radiocarbon dating of archaeological finds with performance comparable to those of AMS infrastructures.
Time-domain THz spectroscopy
Terahertz (THz) systems are non-invasive broad-band devices exploiting non-ionizing electromagnetic waves from 0.1 to 10 THz, a frequency region that is nowadays triggering interest in many disciplines, both theoretically and experimentally, and is considered a frontier area for research in the cultural heritage field. THz radiation has long been ignored due to technological difficulties in its generation and detection. In recent years, the THz region has undergone a technological renaissance driven by improvements in sources and detector responses, promoting and accelerating the diffusion of THz technologies in several fields. THz radiation penetrates non-polar, non-metallic optically opaque materials (such as plastics, paper, painting materials and textiles), a characteristic that makes it suited for the stratigraphic survey of objects with a penetration depth depending on the encountered materials and usually less than 1 cm. Therefore, it can be used for subsurface imaging since it penetrates much further into the sample than infrared techniques, commonly used in art examination. Moreover, THz radiation can be used to perform spectroscopy to identify materials according to their spectral fingerprints. Imaging techniques and spectroscopy in the THz spectral region have great potential as analytical tools in the field of heritage science. THz technology has several valuable features specifically for the investigation of art and archaeology objects such as no radiation risk, low power, non-contact and reflection mode allowing non-contact spectroscopic imaging and non-destructive tomography.
Based on the successful and promising applications of THz technology in Cultural Heritage Science, a THz time-domain spectrometer has been added to the equipment portfolio of the Italian node of the European Research Infrastructure for Heritage Science (E-RIHS.it) through SHINE (StrengtHening the Italian Nodes of E-RIHS) project. This THz instruments is a part of the FIXLAB platforms, and it can operate in transmission and reflection modes and is equipped with a mechanical planar scanner to perform imaging in both measurement configurations.