Recent progress in digital holography with dynamic diffractive phase apertures [Invited].

Digital holography with diffractive phase apertures is a hologram recording technique in which at least one of the interfering waves is modulated by a phase mask. In this review, we survey several main milestones on digital holography with dynamic diffractive phase apertures. We begin with Fresnel incoherent correlation holography (FINCH), a hologram recorder with an aperture of a diffractive lens. FINCH has been used for many applications such as 3D imaging, fluorescence microscopy, superresolution, image processing, and imaging with sectioning ability. FINCH has played an important role by inspiring other digital holography systems based on diffractive phase aperture, such as Fourier incoherent single-channel holography and coded aperture correlation holography, which also are described in this review.

Roadmap on Digital Holography-Based Quantitative Phase Imaging.

Quantitative Phase Imaging (QPI) provides unique means for the imaging of biological or technical microstructures, merging beneficial features identified with microscopy, interferometry, holography, and numerical computations. This roadmap article reviews several digital holography-based QPI approaches developed by prominent research groups. It also briefly discusses the present and future perspectives of 2D and 3D QPI research based on digital holographic microscopy, holographic tomography, and their applications.

Single-plane and multiplane quantitative phase imaging by self-reference on-axis holography with a phase-shifting method.

A new quantitative phase imaging approach is proposed based on self-reference holography. Three on-axis interferograms with different values of the phase filter are superposed. The superposition yields a more accurate phase map of the wavefront emerging from the object, compared with standard off-axis interferometry. Reduced temporal noise levels in the measured phase map and efficient phase recovery process for optically thin and thick transmissive phase objects highlight the applicability of the suggested framework for various fields ranging from metrology to bio-imaging. Qualitative phase imaging is also done online without altering the optical configuration. Qualitative phase detections of multiple planes of interest are converted to quantitative phase maps of the multiplane scene by a rapid phase contrast-based phase retrieval algorithm, from a single camera exposure and with no moving parts in the system.

Phase contrast-based phase retrieval: a bridge between qualitative phase contrast and quantitative phase imaging by phase retrieval algorithms.

In the last five decades, iterative phase retrieval methods have drawn a lot of interest across the research community as a non-interferometric approach to recover quantitative phase distributions from one (or more) intensity measurement. However, in cases where a unique solution does exist, these methods often require oversampling and high computational resources, which limit the use of this approach in important applications. On the other hand, phase contrast methods are based on a single camera exposure, but provide only a qualitative description of the phase; thus, they are not useful for applications in which the quantitative phase description is needed. In this Letter, we establish a combined approach based on the two above-mentioned methods to overcome their respective drawbacks. We show that a modified phase retrieval algorithm easily converges to the correct solution by initializing the algorithm with a phase-induced intensity measurement, namely with a phase contrast image of the examined object. Accurate quantitative phase measurements for both binary and continuously varying phase objects are demonstrated to support the suggested system as a single-shot quantitative phase contrast microscope.

Coded aperture correlation holographic microscope for single-shot quantitative phase and amplitude imaging with extended field of view.

Recently, a method of recording holograms of coherently illuminated three-dimensional scene without two-wave interference was demonstrated. The method is an extension of the coded aperture correlation holography from incoherent to coherent illumination. Although this method is practical for some tasks, it is not capable of imaging phase objects, a capability that is an important benefit of coherent holography. The present work addresses this limitation by using the same type of coded phase masks in a modified Mach-Zehnder interferometer. We show that by several comparative parameters, the coded aperture-based phase imaging is superior to the equivalent open aperture-based method. As an additional merit of the coded aperture approach, a framework for increasing the system's field of view is formulated and demonstrated for both amplitude and phase objects. The combination of high sensitivity quantitative phase microscope with increased field of view in a single camera shot holographic apparatus, has immense potential to serve as the preferred tool for examination of transparent biological tissues.

Doubling the acquisition rate by spatial multiplexing of holograms in coherent sparse coded aperture correlation holography.

Optical, spatial, or temporal multiplexing is a well-known approach to optimize the performance of imaging systems. Following the recent discovery about the capability to record a coherent hologram in an interferenceless working mode, we propose a motionless method to spatially multiplex more than one hologram in a single camera exposure. Using the rather simple multiplexing framework based on coded aperture correlation holography, we effectively increase the acquisition rate of dynamic scenes and the holographic data compression by two-fold. Quantitative or qualitative phase microscopy and acquisition of a bipolar hologram from a single camera shot, experimentally confirm the applicability of the suggested technique.

Interferenceless and motionless method for recording digital holograms of coherently illuminated 3D objects by coded aperture correlation holography system.

Optical recording of digital holograms by coherent light traditionally involves interference between object and reference waves, which complicates the image acquisition process and decreases the power efficiency. In this work, we take the coded aperture correlation holography technique one step forward to record coherent digital holograms of three-dimensional scenes, without wave interference and in a motionless working mode. In addition to the explicit benefits of integrating interferenceless holographic imaging system with coherent illumination, the suggested method enables fast image acquisition implied by its inherent high signal-to-noise ratio. Experimental validation for diffusely reflective objects is also provided, making this relatively simple system appropriate for studying and using the speckle phenomena in coherent digital holography.