Stark-enhanced diode-laser spectroscopy of formaldehyde using a modified Herriott-type multipass cell

The combined use of a novel multipass cell and a sample modulation scheme based on the Stark effect in molecular spectra is used to suppress time dependent background signals, which in general limit spectrometer performance during measurements. A rapid background subtraction scheme, in which the external electric field was turned off on alternate scans, as well as a double modulation experiment show drift free, white noise limited characteristics up to integration times of more than 1000 s. This exceeds the generally obtained spectrometer stability by about one order of magnitude.