Autofocus Fourier single-pixel microscopy

Single-pixel microscopy enables observation of micro samples in invisible wave bands. Finding the focus position is essential to capture a clear image of a sample but could be difficult for single-pixel microscopy particularly in invisible wave bands. It is because the structured patterns projected onto the sample would be invisible and searching for the focus position manually could be exhausting. Here, we report an autofocus method for Fourier single-pixel microscopy. The reported method allows one to find the focus position without recording or reconstructing a complete image. The focus position is determined by the magnitude summation of a small number of Fourier coefficients, which enables fast autofocus. The reported method is experimentally demonstrated in imaging various objects in both visible and near-infrared wave bands. The method adds practicability to a single-pixel microscopy.