Digital Fresnel holography beyond the Shannon limits

Linearity and Optimum-Sampling in Photon-Counting Digital Holographic Microscopy

In the image plane configurations frequently used in digital holographic microscopy (DHM) systems, interference patterns are captured by a photo-sensitive array detector located at the image plane of an input object. The object information in these patterns is localized and thus extremely sensitive to phase errors caused by nonlinear hologram recordings (grating profiles are either square or saturated sinusoidal) or inadequate sampling regarding the information coverage (undersampled around the Nyquist frequency or arbitrarily oversampled). Here, we propose a solution for both hologram recording problems through implementing a photon-counting detector (PCD) mounted on a motorized XY translation stage. In such a way, inherently linear (because of a wide dynamic range of PCD) and optimum sampled (due to adjustable steps) digital holograms in the image plane configuration are recorded. Optimum sampling is estimated based on numerical analysis. The validity of the proposed approach is confirmed experimentally.

Multiwavelength off-axis digital holography with an angle of more than 40 degrees and no beam combiner to generate interference light

We propose single-shot multiwavelength digital holography with an extremely large incident angle and show the digital recording of multiple object waves at multiple wavelengths with an angle of more than 40 degrees and no beam combiner to generate interference light. Both the avoidance of the crosstalk between the object waves at different wavelengths and the space-bandwidth extension are simultaneously achieved with a single-shot exposure of a monochromatic image sensor and a reference beam even when the wavelength difference between the object waves is small. An extremely large angle can be set by utilizing the signal theory. An angle of up to 40.6 degrees was introduced, interference fringes with an 818 nm period at the wavelength of 532 nm were generated, and an image sensor recorded a two-wavelength-multiplexed hologram. Resolution improvement was experimentally demonstrated using two-wavelength digital holography with the wavelengths of 640 and 532 nm.

Quality assessment of combined quantization-shot-noise-induced decorrelation noise in high-speed digital holographic metrology

this paper discusses on the influence of decorrelation noise induced by quantization and shot-noise when recording digital holograms at very high frame rate. A criterion based on the coherence factor of the hologram phase difference is proposed. The main parameters of interest are the ratio between the reference and the object waves and the sensor dynamics, depending on the photo-electron capacity of pixels. The study is based on a full numerical simulation of the holographic process, which provides useful rules. This leads to define the optimal conditions for recording at very-high frame rate with minimization of the decorrelation noise. Experimental results obtained with frame rate at 50kHz confirm the proposed approach.

Recovering the size of nanoparticles by digital in-line holography

The development of methods to measure the size of nanoparticles is a challenging topic of research. The proposed method is based on the metrology of the stable vapor bubble created by thermal coupling between a laser pulse and the nanoparticle in a droplet. The measurement is realized by digital in-line holography. The size of the nanoparticle is deduced from numerical simulations computed with a photo-thermal finite element method.

Digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA)

Single-shot digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA) is proposed. Both amplitude and quantitative phase distributions of waves containing multiple wavelengths are simultaneously recorded with a single reference arm in a single monochromatic image. Then, multiple wavelength information is separately extracted in the spatial frequency domain. The crosstalk between the object waves with different wavelengths is avoided and the number of wavelengths recorded with both a single-shot exposure and no crosstalk can be increased, by a large spatial carrier that causes the aliasing, and/or by use of a grating. The validity of Multi-SPECTRA is quantitatively, numerically, and experimentally confirmed.

Filtering role of the sensor pixel in Fourier and Fresnel digital holography

Digital holography is a modern imaging technique whereby a propagated object wave interferes with a known (spherical or plane) reference wave at a plane where a digital sensor is situated. The resulting intensity distribution is recorded by a CCD or CMOS sensor array to produce a digital hologram. This digital hologram can be processed in several ways to isolate the real image term. Using a propagation algorithm, the object wave can be numerically reconstructed from this real image term. Several factors limit the performance of such imaging systems, such as the finite extent of the sensor array and the finite size of the equally spaced sensor pixels, which average the light intensity incident upon them. Theoretical results indicate that in a Fresnel-based system the role of these finite-size pixels is to attenuate higher spatial frequencies by convolving the reconstructed signal with a rectangular function of equal size to the light-sensitive area of the pixel. However, when a spherical reference wave is used, as is the case with "lensless" Fourier-based systems, spatial frequencies will not be attenuated; rather it is the complex amplitude of the reconstructed signal that will be attenuated. In this manuscript we explore this question in more detail, providing new theoretical and experimental results. By assuming a fully developed speckle field for the object wave, we examine the first-order statistical distributions for the integrated intensity of the object wave, and the interference term, using numerical simulations. We show that the statistical distribution of the interference term can be changed, by varying the sphericity of the reference wave. Experimental results are provided where we compare the performance of a Fresnel and Fourier holographic system as a function of pixel size.