Area coding method in frequency comb profilometryfused with optical interferometry for measuringcentimeter-depth object with nanometer-accuracy

Area coding masks in a frequency comb profilometer (FCP) based on a single-pixel imaging architecture are introduced for measuring a practical metal object that has weaker reflection than a specular object does. In such a case, it is important to increase the intensity of the encoded object light on the photodetector area because a photodiode operated at a high frequency of more than 1 GHz is generally small. The area-coding masks can concentrate more light on the focal point compared with random-coding masks that are commonly used. The increased intensity also increases the number of pixels in the FCP, and consequently accurate matching is achieved between the data obtained by optical interferometry and the FCP data. It was demonstrated that the introduction of area-coding masks increased the detected light intensity and allowed us to measure a practical metal object with 16 times more sampling points.