Optical Diagnostics and Renewable Energies
Optical Diagnostics and Renewable Energies
Optical Diagnostics and Renewable Energies

Dual-Track Raman Spectrometer

We use the dual-track test rig to analyse gas phase processes with the aid of Raman spectroscopy. We utilise the interaction between light and matter to obtain information about various processes such as catalytic systems along a 1D measurement volume. The inelastically scattered Raman signal behaves like a fingerprint of the molecules present in the sample volume. This makes it possible to derive both the species concentration and the temperature of the molecules along a 6 mm measuring range from the images generated, and all this with minimal intervention in the process under investigation. The Raman signal is excited with a 100 W continuous wave laser and then detected in our dual-track Raman spectrometer (DTRS) and broken down into its spectral components. The special feature of the spectrometer, as the name suggests, is that the signal is split into two separate optical beams by a beam splitter. Both signals are then imaged side by side on the sensor of a special camera. Depending on the experimental requirements, the two signals can be processed differently, as described in the following configurations.

 

Dual-resolution configuration: By integrating a transmission grating and a grism (combination of an optical grating and two prisms) into one of the two beam paths, it is possible to carry out simultaneous measurements with different spectral resolutions. This configuration was used, for example, to record the distribution of the nitrogen signal in measurements with high resolution using a grism and to determine the temperature in the sample volume on this basis. At the same time, all signals of the other required species were recorded with a broadband grating.

 

Polarisation separation configuration: In order to clean up the weak Raman signal from interference signals, such as those that occur in processes at high temperatures or through laser-induced fluorescence, the two beam paths were used to perform polarisation separation. The Raman signal has a high polarisation, while interference signals often do not have a uniform polarisation. If you now generate an image that is the same as the linear polarisation of the laser and another that has a polarisation rotated by 90°, the first contains the Raman signal with the interference signal and the second only the interference signal. If the two images are subtracted from each other, a pure Raman spectrum is obtained in the best case. By using the two beam paths of the spectrometer simultaneously, it is possible to compensate for temporal fluctuations in the process under investigation.

Optical Diagnostics and Renewable Energies

PubliCation

The Dual-Track Raman Spectrometer was published in Optics Express: https://opg.optica.org/oe/fulltext.cfm?uri=oe-32-14-24384&id=552326

PLANNED EXTENSIONS:

  • Integration of customised optics from Dioptic in order to be able to investigate processes at higher temperatures in the future
  • Extension of the test stand by a second laser, which is slightly shifted to the wavelength of the IPG-GLR (see SERDS)
  • Extension of the DTRS in order to be able to expose both beam paths separately from each other

EQUIPMENT

  • IPG Photonics GLR
    • CW laser
    • Maximum output power: 100 W
    • Wavelength: 532 nm
  • Teledyne Princeton Instruments SOPHIA camera
    • Back-illuminated CCD
    • 2048 x 2048 pixels
    • Quantum efficiency >95 %

Location

Laboratory C15 0.05

Research topics

RESPONSIBLE Team members