CAS Projects




The CASAC (CAS Absorption Cell) Experiment
CASAC is a long-pathlength absorption spectrometer. The centerpiece of this spectrometer is a long-pathlength glass tube (3m-long x 5cm-diameter), which serves as the main flow cell. In the center is a region 2 meters in length, which has a large metal electrode at each end, wrapped with tubing on the outside of the cell, and is centered in a copper solenoid, enabling the ability to form a cooled, confined plasma from an appropriate mixture of gaseous precursors. Spectroscopy through the cell can then be performed in the range of 80–1100 GHz using Schottky-based multiplier chains (AMC, Virginia Diodes Inc.) and either Schottky detectors (VDI) or a hot-electron bolometer (QMC Instruments) for detection. Optionally, a wire-grid polarizer and retroreflector can be used to perform double-pass spectroscopy, which can help with saturation spectroscopy (i.e. Lamb Dip). more
CASJET (The Molecular Jet Experiment)
To extend the capabilities of the CAS laboratory for rotational spectroscopy a free-jet supersonic expansion experiment for probing low-temperature, unstable molecules has been developed. The instrument operates in the 80–1600 GHz range (4–0.2 mm) and can be combined with the CPFTS. The molecular beam, a gas generated by the mixture of different chemical samples connected to mass flow controllers, is injected into a high-vacuum expansion chamber (~10-5 Torr / 10-3 bar) through a 1-mm pinhole of a pulsed valve. The supersonic expansion allows the adiabatic cooling of the molecular beam, yielding temperatures in the range of approximately 7 to 20 K, depending on the buffer gas used, significantly lower than those reachable in the CASAC spectrometer (~ 80 K). The coupling of the molecular beam to the mm- and submm-wave radiation is obtained through a roof-top mirror placed inside the chamber, which also contains the aperture through which the molecular sample is injected. The production of unstable species is achieved by attaching a high-voltage low-current DC nozzle to the front of the valve, through which the molecules pass right after the pulsed valve and prior to free expansion. more
The TDS (THz Time-Domain Spectrometer)
The CAS laboratory is home to a THz Time-Domain Spectrometer (TDS1008, BATOP). The TDS uses an ultrafast laser (λ=785 nm, Δtpulse=100 fs) which provides, in combination with high-performance photo-conductive antennas, a large spectral bandwidth (0.05–5 THz) and a high dynamic range in signal. It is capable of pulse pump-probe delays up to 650 ps, and is thus compatible with a wide range of optically-active samples. The instrument has built-in mounts for small samples, and it can also be interfaced to a closed cycle, ultra-low vibration cryostat (CS210SFg-GMX, Advanced Research Systems). more
CASTRAP (Cryogenic Ion Trap)
The CAS cryogenic ion trap is a versatile tool that extends CAS laboratory domain to ion-molecule interaction at cold temperatures. Closed cycle cryostat allows us to reach temperatures lower than 4 K for the neutral buffer gas. The radio frequency 22 pole ion trap assures very well defined trapping and cooling conditions for the ions from the lightest ion H+ (mass 1) up to several hundred mass units. Differential pumping and complete separation of fore-vacuum of the ion source and the interaction regions allows studies with minimal influence of the ion precursor gas to the ion-neutral of choice interactions. more
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