Angular displacement and deformation analyses using a speckle-based wavefront sensor

Quantization analysis of speckle intensity measurements for phase retrieval

Speckle intensity measurements utilized for phase retrieval (PR) are sequentially taken with a digital camera, which introduces quantization error that diminishes the signal quality. Influences of quantization on the speckle intensity distribution and PR are investigated numerically and experimentally in the static wavefront sensing setup. Results show that 3 to 4 bits are adequate to represent the speckle intensities and yield acceptable reconstructions at relatively fast convergence rates. Computer memory requirements may be eased down by 2.4 times if a 4 bit instead of an 8 bit camera is used. This may facilitate rapid speckle data acquisition for dynamic wavefront sensing.

Quantitative phase microscopy using defocusing by means of a spatial light modulator

A new method for recovery the quantitative phase information of microscopic samples is presented. It is based on a spatial light modulator (SLM) and digital image processing as key elements to extract the sample's phase distribution. By displaying a set of lenses with different focal power, the SLM produces a set of defocused images of the input sample at the CCD plane. Such recorded images are then numerically processed to retrieve phase information. This iterative process is based on the wave propagation equation and leads on a complex amplitude image containing information of both amplitude and phase distributions of the input sample diffracted wave front. The proposed configuration is a non-interferometric architecture (conventional transmission imaging mode) where no moving elements are included. Experimental results perfectly correlate with the results obtained by conventional digital holographic microscopy (DHM).

Three-dimensional microscopy with single-beam wavefront sensing and reconstruction from speckle fields

Generally, 3D digital holographic microscopy requires the interference of the object wave with a known reference beam under coherent illumination to perform numerical focusing. This configuration may be challenging for some applications, including the use of exotic wavelengths such as x rays, miniaturized instrumentation, etc. Single-beam intensity measurement followed by phase retrieval techniques is attractive for wavefront sensing and reconstruction, including applications with low coherence. We use this method to construct a 3D microscope using volume speckle fields. Transparent phase objects are investigated using this principle. To the best of our knowledge, this is the first report on the application of this principle applied to microscopy.

Fast-convergent algorithm for speckle-based phase retrieval and a design for dynamic wavefront sensing

Wavefront reconstruction is carried out using sequentially recorded speckle patterns and an iterative phase retrieval method based on wave propagation. A novel fast-convergent algorithm that maintains the propagation distance in the iteration step equal to the distance between measurement planes is demonstrated. Employing the new algorithm, influences of the number of measurement planes, number of iterations, and uncertainties in the detector's transverse and axial positions on the rate of phase convergence are analyzed experimentally. A conceptual design for a dynamic wavefront sensor using arrays of beam splitters and detectors for parallel speckle recording is described.