Common causes:

• Beam blocked
• Low throughput accessory
• Poor environment
• Failing source
• Fogged beamsplitter
• Poorly tuned moving mirror control
• Failing detector
• Electronic fault

Suggestions:

Follow infrared beam (conceptually, as it is not visible). Make sure path is unobstructed. Does problem exist with accessories removed?

Reduce environmental vibrations.

Inspect beamsplitter for fogging, replace if necessary.

If poorly controlled moving mirror is suspected, try a different scanning velocity. However, if using a detector that has a considerable frequency response dependence, such as a DTGS detector, results may be ambiguous.

As last resort, swap detector/electronics/power supplies, one at a time.

Common causes:

• Noise is greater at high frequency: interferometer component misaligned
• Misaligned focussing mirror
• Scattering sample

Suggestions:

Align fixed interferometer mirror or other interferometer component with alignment capability.