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Rapid Interferometry Data Acquisition From Zygo

26 May 2004

Standard phase shifting interferometry provides the highest precision and lowest mainframe uncertainty available. However, in some environments vibration and turbulence can severely affect interferometric measurements. This is a particular problem in applications with large air volumes such as long cavities or large test parts. Typical solutions have involved moving the test to a more stable environment, a QC or R & D laboratory or waiting until the area is quiet, weekends or at night. Rigging elaborate test set-ups to minimise the effects of environmentally induced measurement noise is another method.

A better solution is to use short burst of phase data collection followed by frame averaging thus freezing the effects of an unstable environment. The usual way of doing this is hardware based using multiple cameras or optical paths to segment the interferograms into a number of phase shifted images. Unfortunately this technique is complex and expensive.

The new ZYGO FlashPhase is a revolutionary computer based system which adds very high speed data acquisition to Zygo’s standard MetroPro software. Since FlashPhase does not modify the interferometer it does not affect the high performance of conventional phase shifting interferometry data. Traditionally PMI methods determine phase by modulating the cavity and capturing multiple intensity frames. This technique, however, takes too long to make measurements in an unstable environment. FlashPhase solves this problem by information extracted from each individual frame. Both set-up and calibration are easy to accomplish although with wavefront errors for large aperture systems being less than λ/20, calibration is often unnecessary. The frame averaging method also minimises noise and the number of frames over which averaging takes place can be selected to optimise measurements.

In extreme environments FlashPhase improves the performance of the Zygo VeriFire AT and GPI HS instruments dramatically. Camera shuttering is available in these systems and is software controlled and user selectable. Shuttering down to 30µSecs freezes frames in even the most hostile environments and once the frames are frozen the FlashPhase measurements proceed normally.

For more data on the FlashPhase click here.

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