GroundWinds New Hampshire

Interferometer and Control Electronics

The interferometer system consists of three interferometers and a dielectric blocking filter. The blocking filter is intended to remove broadband sunlight from the return measurement.

The output from the receive fiber is connected to the filter etalon. The filter etalon's function is to remove sidebands that are likely to be present in the signal from background.

The output of the filter interferometer is connected to the molecular etalon using a fiber optic cable. The light that passes through the molecular interferometer is sent into a CLIO and detected by a streaking CCD camera. The light that is reflected from the molecular etalon is captured by another fiber and presented to the aerosol etalon. The light that passes through the aerosol etalon is sent into a CLIO and detected by a streaking CCD camera. The light that is rejected by the aerosol etalon is collected by yet another fiber optic and put into a photo multiplier tube (PMT). This PMT is used to measure a photometric return and has value both for detecting density and for monitoring the performance of the interferometer.

The entire interferometer is contained in a pressure and temperature controlled vessel. Changes in pressure and temperature change the refractive index of the air in the gap of the etalons, and can cause a shift in the measured spectrum as well as an overall degradation of resolving power. Drastic changes in temperature (> 5 C) can adversely affect parts of the system as mechanical deformation occurs. Thermal distortion of the etalon plates is detrimental to the performance of the system. The chamber is purged with extra dry nitrogen and sealed. This dry environment is also very favorable to the etalon coatings. Hermetic feed-throughs are used for the many electrical connections that must be fed into the chamber.

Filter Interferometer:

Molecular Interferometer:

Aerosol Interferometer:

Inteferometer System (shows all three channels mounted to the chamber base):

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