Thin Glass

Innovative technology enables form measurement of both front and back surfaces of thin optics, simultaneously. 

Thin Glass Disk Mounted for MeasurementDriven by the demand for smaller and smaller consumer products and semiconductor devices, manufacturers require thin planar optics for an array of applications.

This puts the responsibility on the material and optics manufacturers to ensure the glass is flat and free of material deformities which can cause distortion and affect end-use functionality.

Measuring the surfaces of thin, plane-parallel optics has been historically problematic because multiple reflections from the front and back surface are returned to the interferometer.

Multiple Overlapping Fringe PatternsThis results in a complex pattern of overlapping interference fringes make it very difficult – if not impossible – for traditional phase-shifting interferometry (PSI) techniques to obtain reliable measurements.

Several techniques have been developed to overcome the limitations of measuring thin plane-parallel optical components with PSI, such as coating the back surface to reduce or eliminate the secondary reflection. Applying black paint, coloring with a dark marker, or spreading petroleum jelly on the back surface takes time, adds undesirable steps to the metrology process, and carries the risk of damaging or distorting a thin component when applying or removing the coating.

Measurement of Thin Glass Optical ComponentZYGO provides a more advanced solution, Fourier-transform phase-shifting interferometry (FTPSI). This enables easy characterization of the front and back surface, optical and physical thickness variation, and material homogeneity of thin plane parallel glass. FTPSI makes it possible to distinguish between the front and back surfaces and characterize the quality of both in a single measurement, even if they are less than a millimeter thick.

Need more information, or expert assistance with your measurement application? Contact ZYGO today.

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