Skip to main content
Technical Information - Far-IR beamline
Far Infrared

Technical Information - Far infrared


The IFS 125/HR Brüker spectrometer (figure 1) utilises a Michelson interferometer with an optical path length of 942 cm for single-sided data acquisition; optics f/6.5. This instrument has three internal light sources: Hg-Arc lamp, 5-1000 cm-1; Globar source, 10-13000 cm-1; Tungsten lamp, 1000-25000 cm-1. The spectrometer is also equipped with an array of optical filters, detectors and beamsplitters offering continuous spectral coverage from the THz to the mid-IR regions. 

FAR IR instrumentation

Length of scanning arm of IFS 125/HR interferometer (arrow): 5 m

Sample compartment (circled) can fit multiple accessories.

Figure 1. The Bruker IFS125HR FTIR Spectrometer. 


Sample Analysis

The instrument can be connected to a multitude of accessories and components (table 4) via the sample compartment, allowing a variety of gas and condensed phase experiments to be conducted; see Samples for more information regarding available sample mounts. The instrument is operated under high vacuum conditions but sample compartment can be evacuated and vented independently from the rest of the spectrometer which makes sample changes more rapid. The sample compartment can also be purged with nitrogen gas if required. The spectrometer is remotely controlled using the OPUSTMsoftware v.6.5. 

The Far IR & HR beamline is equipped with a number of different detector types, allowing sample analysis across a wide spectral range. A series of narrow band pass IR Optical Filters are available to reduce the bandwidth (and thus the noise), and apertures ranging from 0.5-12 mm can be used to reduce the beam diameter. 

Table 1. Light Sources


Wavenumber Range /cm-1



Hg-Arc Lamp




Tungsten Lamp



 Table 2. Available Detectors


Wavenumber Range /cm-1

Si Bolometer


Si:B PhotoDetector




MCTN (narrow band)


MCTM (Medium band)



Table 3. Beamsplitters


Wavenumber Range /cm-1

6 μm Multilayer Mylar


75 μm Mylar


125 μm Mylar





Table 4. Accessories (see Samples for more information) 


Gas Phase Experiments

Condensed Phase Experiments

60 cm multipass glass cell for non-reactive samples.

Single disc holder for transmission studies; for pressed discs or self-supporting samples 13 mm diameter.

60 cm heated multipass glass cell for reactive samples; cell can be heated to approx. 80 °C.

N2ITRO Near Normal Incidence Transmission/Reflection Optics.

Enclosive Flow Cooling (EFC) cell;

cell is used for the study of gases, particulates and/or cluster species and can reach LN2 or LHe temperatures .

Cryogen-cooled Cryostat; for pressed discs or self-supporting samples 10 mm in diameter. Can be cooled to liquid nitrogen temperatures.

Grazing Incidence Angle (GIA);

for the study of thin films or monolayers.

Beamline Performance and Calibration

Figure 2 below shows a comparison between spectra recorded for a gaseous sample using a conventional thermal source (blue trace) and synchrotron radiation (red trace). The S/N obtained with the synchrotron is superior to that of a conventional thermal source by a factor of approximately 60.

scan far ir beamline

Figure 2. Synchrotron (red) vs conventional thermal source (blue): rotationally resolved spectra of a gaseous sample (0.001 cm-1 resolution).