Infrared Single-shot Spectroscopy

We developed together with Dr. Ritter from the group of Prof. Hegemann (Experimental Biophysics, HUB) a mid-infrared spectrometer specifically suitable for microsecond time-resolved measurements of non-cyclic or slow cycling processes.

The spectrometer is currently commissioned at the IRIS beamline and will overcome the limit of conventional time-resolved Fourier-transform techniques such as step-scan FTIR which require cyclic systems where the reaction cascade is to be triggered thousands of times and in quick succession. The spectrometer combines a fast linear detector array with the highly brilliant synchrotron radiation source and a dispersive spectrometer core.

The spectral resolution is 5.6 cm-1 at 1800 cm‑1, reaches 4 cm‑1 in the amide-I range (1600 cm‑1), and is 1.2 cm‑1 at 1100 cm-1 making the spectrometer specifically suitable e.g. for the investigation of protein structural changes. The currently achieved signal-to-noise ratio of 400:1 within an acquisition time of 16 µm is expected to exceed 1000:1 when the spectrometer is fully adapted to the IRIS beamline.

Schematic view of the single shot mid-infrared spectrometer.

Infrared light from the BESSY II synchrotron source is focused to an entrance aperture after passing the sample. A folding mirror (M1) is used to guide the light into the dispersive core consisting of the Féry prism and the spherical mirror M2. This setup is based on spherical surfaces in aplanatic conditions, thus achieving a planar image. The FPA detector cold shield requires utilization of a re-imager. To record time-resolved absorbance changes, the photoreaction in the sample is started using a trigger laser.

References:

  1. Schade, U.; Ritter, E.; Hegemann, P.; Aziz, E.F.; Hofmann, K.P.: Concept for a single-shot mid-infrared spectrometer using synchrotron radiation. , Vibrational Spectroscopy 75 (2014), p. 190-195
    doi:10.1016/j.vibspec.2014.07.004
  2. Ritter, E.; Puskar, L.; Bartl, F.J.; Aziz, E.F.; Hegemann, P.; Schade, U.: Time-resolved infrared spectroscopic techniques as applied to channelrhodopsin. , Frontiers in Molecular Biosciences 2 (2015), p. 1-7
    doi:10.3389/fmolb.2015.00038