Object Wave Intensity Research Articles

Iterative phase-retrieval-assisted off-axis terahertz digital holography.

In terahertz digital holography, the off-axis configuration is the appropriate choice when the investigated object is non-sparse and complex. The limitation of recording distance in the off-axis configuration restricts the imaging quality. Either low-resolution or spectra overlap can potentially occur. We propose an iterative phase-retrieval approach to improve the quality of reconstruction results obtained from an off-axis hologram. One additional capture of object wave intensity is recorded to perform iterative phase retrieval with off-axis reconstruction as the initial guess. Apodization operation can be applied to the object wave intensity capture to suppress undesired border diffraction effects. The image quality using the proposed method has been improved both from simulation and experimental verification.

Phase-shift extraction algorithm for blind phase-shifting holography based on the quotient of inner products

This paper presents a phase-shift extraction method for blind phase-shifting holography applications based on the quotient of inner products. The method only requires acquiring three-frame holograms with arbitrary unequal phase-shift values and the intensity of the reference wave, without requiring the object wave intensity. Two phase shift values can be extracted precisely using the algorithm, which can remove the background noise and DC component effects. Both simulated and experimental results have demonstrated the phase step retrieval accuracy and the feasibility of reconstructing the complex amplitude of the object wave.

A new estimation method for two-step-only quadrature phase-shifting digital holography

Two-step-only quadrature phase-shifting digital holography can reconstruct the original complex object using only two holograms without the additional recording of the reference wave intensity and the object wave intensity. Its success depends on the accurate estimation of the reference wave intensity from the two acquired holograms. The previous estimation method is relatively computational expensive. In this paper, we present a novel simple and effective method for estimating the reference wave intensity with low computational load. Simulation results are presented to demonstrate the effectiveness and speedup of the proposed method.

Partition calculation for zero-order and conjugate image removal in digital in-line holography

Conventional digital in-line holography requires at least two phase-shifting holograms to reconstruct an original object without zero-order and conjugate image noise. We present a novel approach in which only one in-line hologram and two intensity values (namely the object wave intensity and the reference wave intensity) are required. First, by subtracting the two intensity values the zero-order diffraction can be completely eliminated. Then, an algorithm, called partition calculation, is proposed to numerically remove the conjugate image. A preliminary experimental result is given to confirm the proposed method. The method can simplify the procedure of phase-shifting digital holography and improve the practical feasibility for digital in-line holography.

Double-image encryption on joint transform correlator using two-step-only quadrature phase-shifting digital holography

A new double-image encryption method on the joint transform correlator using two-step-only quadrature phase-shifting digital holography, based on the calculated intensity of reference beam is proposed. The technique realizes the double-image encryption using one random phase encoding on the joint transform correlator; and only records two quadrature-phase holograms on CCD camera without recording reference-wave intensity or object-wave intensity. With the acquired reference-wave intensity from 2-D correlation coefficient and the keys known, the clear retrieved image can be obtained at high speed by certain algorithm. Its feasibility and validity were verified by a series of computer simulations.

Parallel two-step phase-shifting microscopic interferometry based on a cube beamsplitter

Parallel two-step phase-shifting interferometry for microscopy is presented, and the recording condition for generalized two-step phase-shifting interferometry is discussed. A 45° tilted cube beamsplitter enables to replicate the orthogonally linear polarized object and reference waves into two parallel beams, respectively. As a consequence, two interferograms with quadrature phase shift are obtained along the two beams, and phase reconstructed with an improved algorithm. To reconstruct the phase distribution from the two-step phase-shifting interferograms, a certain recording condition should be satisfied. However, the recording condition has not ever been discussed before. In this paper, the recording condition for the two-step phase-shifting interferometry is derived and that is: the intensity of reference wave should be no less than two times object wave intensity.

Optimized two-step phase-shifting algorithm applied to image encryption

The two-step phase-shifting algorithm proposed previously is optimized, the original object wave field can be reconstructed by only one phase shift value in (0, π) and two interferograms, with the removal (or suppression) of background intensity (or dc term), and the additional measurements such as the object wave intensity, reference wave intensity, etc., are no longer required. Together with double random phase encoding technique in the Fresnel domain, the optimized two-step phase-shifting algorithm is then applied to image encryption system. The feasibility of the proposed scheme is verified by computer simulation. Furthermore, the sensitivity of geometrical keys has also been tested and analyzed.

Simple direct extraction of unknown phase shift and wavefront reconstruction in generalized phase-shifting interferometry: algorithm and experiments

An algorithm to extract the arbitrary unknown phase shift and then reconstruct the complex object wave in generalized phase-shifting interferometry (GPSI) without the iteration process and measurement of object wave intensity is proposed. This method can be used for GPSI of any frame number >or=2. Both computer simulations with smooth and diffusing object surfaces and optical experiments have verified the effectiveness of this method over a wide range of phase shifts with very satisfactory results.

A non-iterative method for phase-shift estimation and wave-front reconstruction in phase-shifting digital holography

This paper derives an analytical formula for extracting the amount of phase-shift in phase-shifting digital holography when the object wave intensity can be measured, which is obtained by simply solving the object wave reconstruction equation. Since it eliminates the requirements of approximation and iteration in existing techniques, a much faster processing speed can be obtained. It also has higher estimation accuracy than those iterative methods with a large iterative step size.

Speckle interferometry: three-dimensional deformation field measurement with a single interferogram

An electronic speckle interferometer, arranged for out-of-plane sensitivity and with an off-axis reference beam to produce spatial phase bias, is used for three-dimensional deformation field measurements. The complex amplitude of the object wave is calculated by application of a Fourier-transform method to a single interferogram. The change in phase after object deformation yields the out-of-plane component of the displacement field. The two in-plane components are obtained by cross correlation of subimages of the reconstructed object wave's intensity, a method that is also referred to as digital speckle photography. The Fourier-transform algorithm is extended and modified, leading to random measurement errors that are below widely accepted theoretical limits and also to an extended measuring range. These properties and the mutually combined information improve the accuracy of both methods compared with their usual single implementation. The performance is evaluated in experiments with pure out-of-plane, pure in-plane, and combined deformations and compared with theoretical values. An example of a practical application is given.