Accelerated phase retrieval using adaptive support and statistical fringe processing of phase estimates.

A technique for accelerated multiple-plane phase retrieval is demonstrated by creating adaptive support through the statistical analysis of phase estimates. Its technical advantage arises from, what we believe to be, the first time use of both phase estimates and a statistical metric, enabling the fast generation of noise-robust support masks. This results in a fourfold improvement in convergence speed when compared to the conventional multiple-plane method.

Enhanced multiple-plane phase retrieval using adaptive support.

In the single-plane phase retrieval method, the use of a fixed object support is not efficient and could lead to inaccurate reconstructions. While there have been adaptive support strategies for the single-plane method, numerical processing is slow because such strategies are based in the space domain. Here, an adaptive support strategy based in the Fourier domain in conjunction with the multiple-plane phase retrieval method is presented and demonstrated through simulations and experiments.

Accelerated single-beam multiple-intensity reconstruction using unordered propagations.

In conventional multiple-plane phase retrieval method, the wave propagations that proceed in the same ordered sequence could slow down convergence or lead to stagnation. In this Letter, a novel, to the best of our knowledge, algorithmic technique to accelerate phase retrieval using an unordered sequence of propagations is demonstrated experimentally. The main advantage of the technique is the significant increase in the change in amplitude, a key and essential element for a successful iterative phase retrieval.

Enhanced intensity variation for multiple-plane phase retrieval using a spatial light modulator as a convenient tunable diffuser.

In the multiple-plane phase retrieval method, a tedious-to-fabricate phase diffuser plate is used to increase the axial intensity variation for a nonstagnating iterative reconstruction of a smooth object wavefront. Here we show that a spatial light modulator (SLM) can be used as an easily controllable diffuser for phase retrieval. The polarization modulation at the SLM facilitates independent formation of orthogonally polarized scattered and specularly reflected beams.

Enhanced deterministic phase retrieval using a partially developed speckle field.

A technique for enhanced deterministic phase retrieval using a partially developed speckle field (PDSF) and a spatial light modulator (SLM) is demonstrated experimentally. A smooth test wavefront impinges on a phase diffuser, forming a PDSF that is directed to a 4f setup. Two defocused speckle intensity measurements are recorded at the output plane corresponding to axially-propagated representations of the PDSF in the input plane.

Vibration detection using focus analysis of interferograms.

This paper proposed an automated technique for vibration detection using statistical focus measure to evaluate interferogram contrast. An interferogram sequence from a Mach-Zehnder interferometer setup is recorded (frame rate: 24 fps) and the gray-level variance (GLVA) is plotted versus time. Occurrence of induced vibration in the setup causes a decrease in the interferogram contrast which, in turn, manifests as an evident rapid drop in the variance plot.

Numerical correction of optical vortex using a wrapped phase map analysis algorithm.

We demonstrate experimentally a technique for the numerical correction of an optical vortex with a unitary topological charge. A developed algorithm based on the axial behavior of a reconstructed wavefront is used in the detection of the optical vortex. Optimizations of the number of axial phase maps and the window size used in the algorithm yield the precise coordinates of the vortex eye.

Single-plane multiple speckle pattern phase retrieval using a deformable mirror.

A design for a single-plane multiple speckle pattern phase retrieval technique using a deformable mirror (DM) is analyzed within the formalism of complex ABCD-matrices, facilitating its use in conjunction with dynamic wavefronts. The variable focal length DM positioned at a Fourier plane of a lens comprises the adaptive optical (AO) system that replaces the time-consuming axial displacements in the conventional free-space multiple plane setup. Compared with a spatial light modulator, a DM has a smooth continuous surface which avoids pixelation, pixel cross-talk and non-planarity issues.

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.

Phase microscopy of technical and biological samples through random phase modulation with a diffuser.

A technique for phase microscopy using a phase diffuser and a reconstruction algorithm is proposed. A magnified specimen wavefront is projected on the diffuser plane that modulates the wavefront into a speckle field. The speckle patterns at axially displaced planes are sampled and used in an iterative phase retrieval algorithm based on a wave-propagation equation.

Shape and deformation measurements of 3D objects using volume speckle field and phase retrieval.

Shape and deformation measurement of diffusely reflecting 3D objects are very important in many application areas, including quality control, nondestructive testing, and design. When rough objects are exposed to coherent beams, the scattered light produces speckle fields. A method to measure the shape and deformation of 3D objects from the sequential intensity measurements of volume speckle field and phase retrieval based on angular-spectrum propagation technique is described here.

Numerical correction of aberrations via phase retrieval with speckle illumination.

What we believe to be a novel technique for wavefront aberration measurement using speckle patterns is presented. The aberration correction is done numerically. A tilted lens is illuminated with a partially developed speckle field, and the transmitted light intensity is sampled at axially displaced planes.

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.

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

Wavefronts incident on a random phase plate are reconstructed via phase retrieval utilizing axially displaced speckle intensity measurements and the wave propagation equation. Retrieved phases and phase subtraction facilitate the investigations of wavefronts from test objects before and after undergoing a small rotation or deformation without sign ambiguity. Angular displacement (Deltatheta) between incident planar wavefronts is determined from the light source vacuum wavelength (lambda) divided by the fringe spacing (Lambda).

Interferometric evaluation of angular displacements using phase retrieval.

Phase retrieval is carried out using sequential intensity measurements of a volume speckle field and a wave propagation equation. Retrieved phases and phase subtraction facilitate the analysis of wavefronts before and after undergoing a small rotation. Angular displacement between incident planar wavefronts is determined from the unwrapped phase difference, phase diffuser aperture diameter, and the light source wavelength.

Wavefront sensing using speckles with fringe compensation.

Wavefront sensing with numerical phase-error correction system is carried out using a random phase plate and phase retrieval using multiple intensity measurements of axially-displaced speckle patterns and the wave propagation equation. Various wavefronts with smooth curvatures incident on the developed phase plate (DPP) are examined: planar, spherical, cylindrical, and a wavefront passing through the side of a bare optical fiber. Spurious fringe pattern in the wavefront reconstructions due to a small tilt (Delta theta=0.

Random phase plate for wavefront sensing via phase retrieval and a volume speckle field.

A random phase plate is prepared by illuminating a photoresist plate with a fully developed speckle field and using the developed phase plate (DPP) as a diffuser. Wavefront sensing is implemented using phase retrieval based on the recording of speckle intensity patterns at various distances from the DPP and the wave propagation equation. The effects of the roughness height of the DPP on the phase retrieval are investigated.

Colored object recognition by digital holography and a hydrogen Raman shifter.

Multi-wavelength holography is demonstrated with a H(2) Raman shifter that is pumped with an elliptically-polarized pulsed 532 nm beam to produce temporally coherent, intense, polarized output lines. Digital holograms of two-dimensional colored objects are recorded using Raman output lines at 630.4 nm (S(05), Red), 532 nm (Rayleigh, Green) and 435.

Wavefront sensing with random amplitude mask and phase retrieval.

A light beam with an ideal wavefront that is transmitted or reflected from an object is modified by different characteristics of the object such as shape, refractive index, density, or temperature. Wavefront sensing therefore yields valuable information about the system or the changes happening to the system. A new method for wavefront sensing using a random amplitude mask and a phase retrieval method based on the Rayleigh-Sommerfeld wave propagation equation is described.

Complete wavefront reconstruction using sequential intensity measurements of a volume speckle field.

The recording of the volume speckle field from an object at different planes combined with the wave propagation equation allows the reconstruction of the wavefront phase and amplitude without requiring a reference wave. The main advantage of this single-beam multiple-intensity reconstruction (SBMIR) technique is the simple experimental setup because no reference wave is required as in the case of holography. The phase retrieval technique is applied to the investigation of diffusely transmitting and reflecting objects.

Pulsed full-color digital holography with a hydrogen Raman shifter.

We demonstrate pulsed full-color digital holography with a hydrogen Raman shifter as a single source of highly directional multiwavelength light. For the primary (blue, green, red) color channels we utilize the first three Stokes beam outputs (415.9, 502.