Figure 1

Reflective speckle-based lens-less imaging microscopy system. (a) Experimental schematic; the incident and reflected beams are shown in red and green, respectively, for visibility. A 405 nm laser was used as a light source, and the incidence beam was relayed by a beam splitter (BS) before focusing on the sample. Optical diffuser (OD) for speckle pattern generation. The target is loaded onto the motorized stage and moved laterally to scan the illuminated positions. (b) Diffracted intensity images obtained for each illuminate position \({{\varvec{r}}}_{{\text{j}}}\) in the absence of OD. Images are distorted and blurred owing to the wavefront curvature caused by the diverged illumination. (c) Images numerically backpropagated to the sample plane \({\varvec{r}}\). The decrease in signal-to-noise ratio renders it impossible to restore high-resolution images using only a single measured intensity image. (d–e) Measured images obtained using a weak and strong diffuser, respectively. The diffuser characteristics determine the size and randomness of the illuminated speckle grains.