Microlenses metrology with digital holographic microscopy

Digital holographic Microscopy (DHM) is an imaging modality reconstructing the wavefront in a numerical form, directly from a single digitalized hologram. It brings quantitative data derived simultaneously from the amplitude and phase of the complex reconstructed wavefront diffracted by the object and it is used to determine the refractive index and/or shape of the object with accuracy in the nanometer range along the optical axis. DHM comprises a microscope objective to adapt the sampling capacity of the camera to the information content of the hologram. This paper illustrates some of the possibilities offered by DHM for micro-optics quality control. Actual results obtained by DHM, yielding an axial precision up to 3.7 nm, will be compared with measurements performed with interferometers by SUSS MicroOptics SA and with the profiles measured with a mechanical scanning probe instrument (Alpha step 200 from Tencor Instrument). Two different micro-lenses arrays where tested: a quartz refractive lenses array (observed with transmission DHM) and a Silicon refractive lens array (observed with reflection DHM).