Fast non-contact surface roughness measurements up to the micrometer range by dual-wavelength digital holographic microscopy

We present fast high-roughness and non-contact surface measurements by digital holographic microscopy (DHM). By using single- and dual-wavelength operation modes, coupled with advanced image stitching and non-measured points management methods, the technique enables two-dimensional roughness measurements up to the micrometer (N6). The sample is mechanically scanned over a surface up to 5 × 0.3 mm2 with 17 holograms each acquired in less than 500 µs, the corresponding phase images stitched together by software, and therefore providing multiple profiles measurement in the ISO definition in less than 30 s. The approach is validated by inspection of several different roughness standards and our technique is demonstrated to be in agreement with two existing well-known techniques in the field.