Film thickness test method - Double beam of light Microscope method

The instruments used in the dual-beam microscopy method are mainly used to measure surface roughness. Also useful for measuring the thickness of transparent and translucent coatings , especially anodized films on aluminum.

The instrument works by shining a beam at an incident angle of 45° onto the overburden surface, and a portion of the beam is reflected back from the overburden surface. The other part penetrates the coating and reflects off the coating-substrate interface. Two separate images can be seen from the microscope 's eyepiece, the distance of which is proportional to the thickness of the overlay, and the distance can be measured by adjusting the scale control knob.

This method should only be used when sufficient light is reflected back from the coating-substrate interface to obtain a clear image in the microscope .

The method is non-destructive for transparent or translucent covering layers, such as anodized films. In order to measure the thickness of the opaque coating, a small piece of the coating needs to be removed, so that a step that can refract so that the absolute value of the thickness of the coating can be measured. In this case, the method is destructive testing.

Measurement errors with dual-beam microscopy are typically less than 10%.