Metrology

WAVEFRONT PHASE


Wooptix WFP is capable of achieving spatial resolutions orders of magnitude higher than conventional wave front sensors.


By measuring the reflected light from a surface we can provide a detailed elevation map of the surface, with the advantage of needing only one shot (no scanning needed) and high levels of accuracy and precision.

Wooptix WFP Working principle:

Imagine we send a narrow light beam to a surface at a particular angle, if the surface is flat, the reflected light will always fall in the same position of the sensor. If the surface slope differs from the perfect flatteness, the reflected light ray will fall in a different part of the sensor. The difference in distance from the two positions is proportional to the local surface slope.

This is the “Triangulation Reflection Method”, a well known metrology method. The disadvantage is that only gives one data point at one time, meaning that, to measure a surface needs some robot arm, or translation stage to scan all the surface area.

Wooptix WFP solution is also based in measuring displacements of light rays, but there is no need of scanning, since we can measure large areas in one shot. Basically we launch a bunch of light rays against a surface and capture the reflected light. As in the “Triangulation Reflection Method”, the deflection of each light ray gives the local slope of the surface.

It can be seen that the main difficult here is the identification of each light ray path to estimate the surface slope. It is easy when there is only 1, but when launching millions of light rays it becomes much more complicated.

Next figure, shows the image captured from a defect in a car paint sample and its reconstructed surface map. Note the heights on the surface map are in meters, that means the central bump height is about 12 microns!

Our Wavefront Phase technique to measure specular surfaces allows, as shown in the figures below, knowing with nanometer accuracy the topography of a flat mirror with 50 milimeters diameter from just a single measure (fig.1, left). Compared with the market´s groundtruth, the Chromatic confocal microscope, it can be observed overlapped to the warpage, the raster scanning noise induced by the confocal microscope to be able to capture all the surface of the mirror (fig.1, centre). The transversal profile of the sample describes a comparison between the two technologies in order to evaluate the softness and accuracy of the measures with the Wooptix´s sensor (fig. 1, right) versus the noisy profile from the confocal measure.

In adittion, the time invested by the confocal to scan the whole surface takes several minutes while the Wooptix sensor takes just miliseconds in order to capture just one topography map with all the complete information of the mirror.

So, accuracy, speed and quality in the measures are guaranteed by Wooptix´s sensor.

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