Optical frequency comb profilometry using a single pixel camera

We demonstrate an optical profilometer composed of an ultra-stabilized mode-locked femtosecond laser, a single pixel camera, and an optoelectronic interferometer. The combination of an optical frequency comb generated by the femtosecond laser and the optoelectronic interference in radio frequecny range enables us to measure an object with a large depth much more than a wavelength of light with a wide dynamic range giving no 2 pi phase ambiguity. The wide dynamic range is achieved by high stability of the optical frequency comb and easy selection of the frequency. The single pixel camera is used for two-dimensional imaging without a mechanical scanning. It is performed by spatial light modulation of an object beam, the coherent summation of the spatially-modulated object beam with a single photo detector, and an inverse matrix calculation. We selected two approaches to reduce the number of measurements. One was the compressive sensing that well reduced the number when an object is sparse. The other was the reversal signal generation method that reduced the number to one-half of the sampling points for any object. We demonstrated the surface profilometry for an object with the depth of several centimeters.