Autofocus Measurement

The principle
In the autofocus principle condensed light is focused from a laser diode onto the specimen surface. The reflected light is directed to a focus detector, which measures deviations from the ideal focus to within a few nanometers. The deviation in focus generates an error, which is used to re-focus the objective. The position of the objective represents an absolute measurement of the height.

Measurement principle of the autofocus control circuit

A precise digital position measurement system enables high resolution down to 25 nm

The advantages
The autofocus sensor is remarkable for its high vertical resolution. With a measurement range of 1.5 mm it resolves down to 20 nm. It is therefore capable of fast form and roughness measurement simultaneously.

Because of its high dynamics the AF2000 sensor performs best on surfaces with varying reflection coefficients.

Specifications

Sensor		Camera
Spot size [µm]	1,5	Integrated in-axis camera
Vertical resolution [µm]	0,020	Field of view [mm]	0,6x0,8
Measurement frequency [Hz]	10,000
Stand off [mm]	2 or 5	Laser diode	Class I
Linearity [%]	<0,08	Wavelength [nm]	630

The AF2000 sensor