Understanding How A Surface Profiler Works

By Author: Vishal Khosla
Total Articles: 19
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Scanning of a sample is done vertically by an optical profiler. As the sample moves via the focal plane, it causes interference. The instrument does not allow every height level of the test object to reach maximum focus at the same time.

Industries require surface profiler for measurement of surface shapes, finishes and roughness. There are applications where use of surface profiler becomes critical to ensure quality. It becomes imperative for them to source surface profiler from a supplier that can be relied on for the quality of instrument.

The equipment makes use of light wavelength for measuring surface shapes, finishes and roughness. Properties of light wave are used for evaluating the optical pathway variation between the reference surface and the examination surface.

Constructive interference and destructive interference come into being when the beam splitter distance to the reference mirror equalizes the distance of the light splitter to the test surface. Interference fringes are produced, thanks to the split beams with variation in the length of beam light.

The interference beam is focused ...
... into a digital camera that views the destructive interference areas as darker and constructive interference areas as lighter. In an interference image, each transition from light to dark indicates one-half a wavelength of difference between the test path and the reference path.

Calculation of height differences across a surface in fractions of a wave is possible if the wavelength is known. A 3D surface map can be obtained from the height differences. Optical pathway variation is the outcome of changing height in the test side. Digital camera is used to differentiate the focused interference beam.

Scanning of the object is done vertically by the instrument. The object causes interference as it moves via the focal plane. Mechanism in the surface profiler is such that every height level of the test object does not reach maximum focus at the same time. Precise measurements provided by optical profiler make it useful when micro-measurement of surface difference is needed.

Many industries use the instrument for data storage and optics. They deploy it for measuring the volume, slope of diffraction gratings of binary lenses and radius of curvature. The surface profiler makes exact measurement by ensuring that adequate light from the surface returns to the material. The instrument fits in for measurement of metals, paper, paint, ink, plastic, glass and epoxies. It can also be used for analyzing cumulative effects of sawing, polishing and grinding. The technology can be deployed for large step height measurement and applications where a three dimensional map of a surface is important. It also comes handy where sampling location selection may lead to different results. The profiler works perfectly for measuring fragile surfaces as well as roughness modeled three dimensionally. However, it has some limitations. It won’t work in high slopes where light is reflected past the material.

A top-notch instrument provides advanced data analysis on any platform. Choice of a surface measurement system depends on various requirements including precision, automation, speed, vertical range and configuration flexibility.

On a state-of-the-art optical profiler, you can expect unique, complex algorithm and latest generation hardware. Combination of blue and white LED provides superior quality XYZ resolution images. Multi-color LED is used to generate real color images of sample. These profilers can measure longer profiles than previously possible in a single acquisition.

Author of this article is associated with Rtec Instruments, a California based company that deals in surface profiler, vacuum tribometer, ball on disk tester, high temperature tribometer, nano indentation, atomic force microscope and other instruments.