Chirped Pulse FT Millimeter Wave Spectroscopy

Broadband chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is still a new spectroscopic technique in comparison to conventional absorption spectroscopy. It was developed in 2006 by the Brooks Pate research group. Because of some advantages over the conventional way of absorption spectroscopy it is already well established: The measured spectra are broadband and the measuring time is short. In general: A short microwave pulse with linearly in- or decreasing frequency (a chirp) is created, which causes a strong polarizing electromagnetic field. This field excites one or more rotational states of the molecules. After the chirp, the sample molecule emits a free induction decay (FID) signal for each transition back to the previous equilibrium state. This FID signal is received and Fourier transformed to get a spectrum. The mechanism is comparable with the nuclear magnetic resonance technique and is described in more detail elsewhere. The obtained rotational spectra, which are unique for each molecule due to quantum physical properties, can then be used for astrophysical data analysis.

We developed a new spectrometer for the frequency range between 75 and 110 GHz. There is a nozzle for a supersonic jet built in, as well as an extension to ignite a DC high voltage discharge.