FT_MW spectometres and ultrafast laser vaporization
Vaporization of labile biomolecules had been a serious problem that had hindered the investigation of solid compounds in the past and to solve this difficulty we have built a new spectrometer which implemented a ultrafast laser vaporization system to bring intact biomolecules into the gas-phase. The construction of this new spectrometer opened new perspectives for the investigation of multiple families of compounds.
The spectrorneter follows the original Balle-Flygare design, improved with recent advances in electronics and automation. Briefly, a supersonic jet expanding within a Fabry-Perot resonator is probed using short rnicrowave pulses. The pulse excitation suddenly brings the molecular ensemble intro coherence, inducing a macroscopic polarization. The following transient spontaneous emission or free-induced-decay (FID) is recorded in the fime-domain, and finally a Fourier-transform produces the frequency-domain spectrum displaying the resonance frequencies of the rotational transitions.
The instrument is based on Pate’s original design and allows the acquisition of the rotational spectra in the 6.0-18 GHz frequency range in a single molecular pulse. Briefly, a 1 chirped pulse is generated in an arbitrary waveform generator, covering 11 GHz. This broadband pulse is frequency-upconverted with a broadband mixer and amplified in a travelling wave tube amplifier. It is later broadcast inside a high vacuum chamber by using a horn antenna. The excitation induces polarization, resulting in a spontaneous molecular emission signal. This emission is collected with the aid of a second hom antenna and sent to a digital oscilloscope with a 20 GHz bandwidth. For each chirped pulse, the time domain signal is recorded in the scope. In the current set-up, 10 chirped pulses are used in each molecular pulse.