Routine Beamline Performance Checks

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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%


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