Easy 3D, non-contact surface profile measurements in air

Of the principles of laser scanning microscopes, the most basic is the confocal optical system. It has a pinhole with a circular opening at the position that conjugates the focal position of the objective lens (image forming position) to only detect light at the focused position. Although it is important to evenly illuminate a certain area for a typical optical microscope, in the confocal optical system the light emitted from the point light source is radiated by the objective lens so that the light converges to one point on the sample. In general, a specific wavelength of laser light that travels in a very straight line is used as the point light source so that a large amount of light converges at one point. This reduces unnecessary scattered light from the environment and improves contrast compared with ordinary optical microscopes, which evenly illuminate the sample.

The light reflects on the surface of the sample, goes back along the same optical path, is separated by the beam splitter, and converges on the pinhole. This optical system is only able to obtain information from the focal position as most of the reflected light from other focal planes is blocked at the pinhole. This means that the confocal optical system can act like a height sensor because of its narrow depth of focus while a conventional optical system cannot due to its large depth of field that includes data from several focal planes.