Production environments and challenging test set-ups commonly present a troublesome and persistent challenge in achieving reliable and precise optical metrology using standard Phase-Shifting Interferometry (PSI) – namely, isolating the measurement equipment and test samples from the negative effects of vibration.

Watch: Demonstration of QPSI™ vibration-tolerant interferometry in a production area

Measurements taken in vibration-prone environments typically encounter fringe print-through errors, rendering the data unacceptable. One traditional method commonly used to overcome these negative effects is to take many repeated measurements over time and average them. This method has limited effectiveness and can take a long time.

There are solutions available that attempt to correct a poor environment in order to mitigate its undesirable effects. A typical solution is to use a vibration isolation table, and sometimes facilities are completely renovated in order to establish a "metrology" grade environment. These solutions are expensive, and even cost-prohibitive for some operations, leading ZYGO engineers to come up with an innovative solution – QPSI™ technology.

Animated comparison of a PSI measurement with fringe print-through
due to vibration, and the same surface measured with
QPSI™ technology – free of print-through.

In developing QPSI™ technology, ZYGO collaborated with manufacturing operations where vibration, typically originating from machining or polishing equipment, has been problematic. QPSI™ technology uses a patented algorithm to reduce or eliminate measurement errors due to common sources of vibration, delivering precision measurements in less-than-desirable environments.

QPSI™ technology maintains the accuracy of a true Fizeau interferometer configuration, and eliminates the need to take many measurement averages to reduce the effects of a production environment. Unlike vibration isolation tables and chambers, no additional hardware is required. There is no special set-up or calibration needed, and cycle times are typically within a second or two of standard PSI measurements. Therefore, from the operator's perspective, taking a measurement using QPSI™ technology is no different than taking a standard PSI measurement.

The budget-friendly QPSI vibration-tolerant interferometry solution is offered with every ZYGO interferometer system that is capable of phase measuring interferometry.