Empa Eidgenossische Materialprufungs-und Forschungsanstalt

Irsweep Ag

Sensirion Ag

Markus Mangold

Lukas Emmenegger

Andreas Hugi

Urszula Szczepaniak

Akshay Nataraj

Bela Tuzson

Raphael Horvath

Michele Gianella

Jana Jágerská

Béla Tuzson

A vibrational circular dichroism (VCD) spectroscopy method and apparatus that can significantly reduce the measurement time needed to acquire a differential absorption spectrum compared to known approaches. A dual-comb is generated by superimposing the outputs from two quantum cascade laser sources, thus providing a third comb interferogram with beat frequencies higher than the polarization modulation frequency. Consequently, for each of the left and right circularly polarized light, the measurement signal measures transmission through the sample across the full wavelength range of interest during each period of the polarization modulation. A complete vibrational spectrum is thus acquired in each modulation of a polarization modulator, instead of only acquiring data for a single wavelength during each modulation of the polarization, as in dispersive or tunable laser VCD, or only a single Fourier component of the spectrum, as in Fourier transform VCD.

Vibrational circular dichroism spectroscopy

A dual-comb spectrometerwith two lasersserving as a local oscillator and an interrogator. The lasers output light beams with respective frequency combs C, Cof defined free spectral range, FSR. A detectorcan detect heterodyne mixing of the combined beams to detect an RF frequency comb C. Respective control signals are supplied to the lasers which have functional forms configured to cause the frequencies of the lasers' frequency combs C, Cto tune over a defined fraction of their FSR. This enables a reduction of the effective spectral sampling period by a factor equal to the ratio of the FSR to the spectral resolution of the spectrometer, which will typically be several orders of magnitude, so that the spectral sampling period can be reduced from the GHz to the MHz range, which in turn enables a gapless spectrum to be obtained in a short time.

Dual-comb spectroscopy

A Multi-pass optical cell () with an internal space () for laser spectroscopy is described, which is able to reduce or eliminate interference fringes appearing by performing laser absorption spectroscopy in the multi-pass optical cells () leading to improved absorption spectra. This is achieved by using a multi-pass optical cell () comprising an absorption mask () which is permanently or removable mountable in the internal space () in a rotatably fixed manner, where in a mask wall () a plurality of m apertures () is formed, in which the position of each aperture () is adapted to a predefinable propagation path of a main optical beam and/or the resulting reflection spot pattern () defined by the geometry of the multi-pass optical cell () and the used angle of incidence of an initial beam (), so that each aperture () is traversable by the main optical beam from a first side () to a second side ().

Method for reducing interference fringes in laser spectroscopy measurements using an absorption mask in combination with multi-pass optical cells

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Zurich, Switzerland

Markus Mangold