Window material limits
- Microscopy Cluster (Unlicensed)
The beamline purchases general IR slides from Crystran in the UK. A comprehensive list of materials for optical windows and their technical data can be found HERE.
The materials most commonly used for transmission experiments are CaF2 and BaF2, their transmission throughput are shown below.
Figure: Transmission throughput of various thicknesses of [Left] CaF2 and [Right] BaF2 slides/windows. Click on each image to enlarge the graphic.
For longer wavelengths below the cutoff limit of CaF2 and BaF2, the beamline has diamond windows which are (mostly) transparent through the whole infrared spectrum including far-IR (THz) (see figure below). If you are particularly interested in acquiring information below 1000 cm-1, please contact a Beamline Scientist to discuss the technical aspects of the project.
Figure: [Left] Transmission throughput of diamond. [Right] Conversion table between wavenumber (cm-1) and wavelength (μm).
Comparison of IR window material using the narrowband and wideband detector
Figure [left]: Example spectra of a salt crystal extracted from a mature gouda cheese mounted on different IR window materials
NARROWBAND detector
Transmission acquisition mode
36× objective (NA = 0.5)
IR windows were: 0.5 mm CaF2 (blue), 0.5 mm BaF2 (red), diamond window from the micro-compression cell (black)
32 co-added scans
40 kHz, 4 cm-1 resolution
11.1 μm aperture
5 spectra averaged
Spectra max-min normalised on the band at 1100 cm-1
Figure [right]: Example spectra of a salt crystal extracted from a mature gouda cheese mounted on different IR window materials
WIDEBAND detector
Transmission acquisition mode
36× objective (NA = 0.5)
IR windows were: 0.5 mm CaF2 (blue), 0.5 mm BaF2 (red), diamond window from the micro-compression cell (black)
32 co-added scans and 256 co-added scans*
40 kHz, 4 cm-1 resolution
11.1 μm aperture
3 spectra averaged
Spectra max-min normalised on the band at 1100 cm-1
*The wideband detector has ~10× less detectivity (sensitivity) compared with the narrowband detector, therefore more co-added scans are required to achieve similar signal-to-noise.