CAS Projekte

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). mehr

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. mehr

The CAS laboratory is home to a THz Time-Domain Spectrometer (TDS1008, BATOP). The TDS uses an ultrafast laser (λ=785 nm, Δt_pulse=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). mehr

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. mehr