Routine Beamline Performance Checks
- Microscopy Cluster (Unlicensed)
Beam intensity and noise measurements
The beam intensity of a defined focus size on a sample and the observed baseline noise are recorded below. Typical noise values measured in reflectance with details of the measurement conditions are given below. The noise is assessed periodically in two 100 cm-1 regions as a %T spectrum calculated from two sequential “single beam” spectra collected under identical conditions.
Reference and sample = Gold mirror
Beam defining aperture = 5 × 5 microns at sample
Detector = Narrow-band MCT 50 micron element
Acquisition speed = 40 kHz
Number of scans = 128 averages
Apodisation = Beckmann-Harris
Zero filling = 2 levels
| 2450-2550 cm-1 | 1190-1290 cm-1 |
% noise | 0.02 | 0.05 |
Beamline calibration
Beamline calibration is undertaken by the staff in advance of users’ experiments, or following a change of beamline configuration during an experiment (e.g. from reflectance to ATR).
Signal-to-noise comparison
The signal-to-noise ratio is significantly improved by the use of the synchrotron source over a conventional lab-based mid-IR source, e.g. Globar. Figure 15 shows an approx. 20-40 fold improvement in the signal-to-noise when using the synchrotron source.
Figure: A comparison between the synchrotron and a conventional mid-IR source of the signal-to-noise recorded for the CH stretch absorption bands from a 5 mm spot on a biologcal tissue sample . FTIR spectral conditions: 128 co-added scans, 5×5 µm aperture, 4 cm-1 resolution.
RMS noise @ 2550 - 2450 cm-1:
Synchrotron 0.02 - 0.04%
Globar 0.8%