Common causes:

• Gas sample pressure too high
• Running large aperture
• Interferometer not optimally aligned
• Poor choice of apodization function.

Suggestions:

For CO gas resolution test cell: re-evacuate gas cell to about 2 torr. Bleed in CO. Pump back down to 3 torr.

High resolution requires elimination of divergent rays in the interferometer. Small source aperture sizes ensure this criteria. It is not unusual to run apertures at a few percent of full open when running maximum resolution.

Re-align interferometer and laser to optimize resolution.

Try using boxcar apodization.