Recording Of Multiple Holograms Research Articles

Grating-based in-line geometric-phase-shifting incoherent digital holographic system toward 3D videography.

Incoherent digital holography (IDH) with a sequential phase-shifting method enables high-definition 3D imaging under incoherent lights. However, sequential recording of multiple holograms renders IDH impractical for 3D videography. In this study, we propose grating-based in-line geometric-phase-shifting IDH. Our method divides orthogonal circularly polarized lights into four copies with a fabricated phase grating and subsequently creates self-interference holograms with geometric phases introduced by a segmented linear polarizer. This enables single-shot recording of holograms without the need for a specially designed image sensor, such as a polarization-sensitive sensor. Moreover, the achievable spatial resolution is higher than that of off-axis methods. As a proof-of-principle experiment, we demonstrated snapshot and video recording of 3D reflective objects using our IDH method. The results confirmed the feasibility of the proposed method.

Separating twin images in digital holographic microscopy using weak scatterers.

When using inline digital holographic microscopy (DHM) and placing the hologram plane within a particle suspension, both real and virtual images come into focus during reconstruction, limiting our ability to resolve three-dimensional (3D) particle distribution. Here, we propose a new method to distinguish between real and virtual images in the 3D reconstruction field. This new method is based on the use of weak scatterers, and the fact that the real and virtual images of weak scatterers display distinct intensity distributions along the optical axis. We experimentally demonstrate this method by localizing and tracking 1 µm particles in a 3D volume with a particle concentration ranging from 200 to 6000particles/mm3. Unlike previous approaches to address the virtual image problem, this method does not require the recording of multiple holograms or the insertion of additional optical components. The proposed method allows the hologram plane to be placed within the sample volume, and extends the capability of DHM to measure the 3D movements of particles in deep samples far away from the optical window.

Holographic performance of silicon polymer films based on photoswitchable molecules

Holographic silicon polymer films based on photoswitchable molecules are studied with respect to their performance for hologram recording, with photoswitchable ruthenium sulfoxide complexes as an example. Our systematic study reveals that it is possible to record elementary holographic lossy gratings with outstanding quality with respect to their dynamics and in- and off-Bragg read-out features. Furthermore, the possibility for the recording of multiple holograms within the same volume element via angular multiplexing as well as the recording with continuous-wave and a fs-laser pulse train is successfully demonstrated. At the same time, a strong limitation of the maximum diffraction efficiency in the order of ∼ 10−3 is found that cannot be counterbalanced by either the tuning of material (thickness, concentration, ...) or recording parameters (repetition rate, wavelength, ...). This limitation – being severe for any type of holographic applications – is discussed and compared with the performance of high-efficient single-crystalline reference holographic media. We conclude that the potential of sulfoxide compounds may be hidden in holography until it becomes possible to synthesize polymer films with appropriate three-dimensional structural arrangement of the photoswitchable compounds.

Three-dimensional-object recognition by use of single-exposure on-axis digital holography

On-axis phase-shifting digital holography requires recording of multiple holograms. We describe a novel real-time three-dimensional- (3-D-) object recognition system that uses single-exposure on-axis digital holography. In contrast to 3-D-object recognition by means of a conventional phase-shifting scheme that requires multiple exposures, our proposed method requires only a single digital hologram to be synthesized and used to recognize 3-D objects. A benefit of the proposed 3-D recognition method is enhanced practicality of digital holography for 3-D recognition in terms of its simplicity and greater robustness to external scene parameters such as moving targets and environmental noise factors. We show experimentally the utility of the single-exposure on-axis digital holography-based 3-D-object recognition method.

Multiple recording of rainbow holograms on the same section of a photosensitive material

A technology is proposed for multiple recording of holograms on the same section of thin recording media using the technique for obtaining rainbow holograms. It is shown that in this case the individual holograms can be reconstructed and read independently of one another. Experimental results are presented.

Thermal fixing of multiple holographic gratings in magnesium oxide lithium niobate crystal

The photorefractive properties of 4% mol magnesium oxide doped lithium niobate have been investigated at room temperature. The recording and erasing time constants were measured as a function of intensity and analyzed by using the two active species (electron-hole) model. The results were used to compute the exposure schedule for multiple hologram recording. We have recorded grating of five holograms by angular multiplexing at room temperature and fixed them by means of a thermal cycling procedure. The highest diffraction efficiency of a fixed grating is up to 50% of an unfixed one.

Absorption effects in photorefractive volume-holographic memory systems I Beam depletion

We consider how absorption-induced beam depletion alters the index-modulation profile, the diffracted beam profile, and the Bragg selectivity of volume holograms. We derive theoretical equations that consider beam depletion (in the absence of two-beam coupling) and compare these with experimental observations. We also derive a smart scheduling technique whereby such absorption effects can be compensated for during the scheduled recording of multiple holograms. In our smart scheduling approach, during recording the profile of the input signal beam is modified such that during recall its output profile is uniform.

Recording of multiple holograms in photopolymer films

Multiple images were recorded in DuPont HRF-150 photopolymer as transmission holograms by using angle multiplexing. Agreement with Kogelnik's two-wave diffraction theory for phase gratings, the time considerations and its effect on dynamic range, the necessity of a pre-illumination pulse, and good image quality at readout are reported.

Volume‐type multiple hologram memory using PMMA thick films

AbstractPhotosensitive polymers such as PMMA (polymethyl methacrylate) are favorable materials for volume‐type hologram; properties of PMMA thick films not studied as yet, will be described in the present report. the validity of a dynamic coupled‐wave theory (in which a saturation effect is considered) is shown. the maximum hologram memory density of a photosensitive particle model is discussed; a differential scattering cross section 0.33 mm2 and maximum photosensitive particle density 3 × 1011/cm3 are obtained. These figures predict a maximum memory density which is an order of magnitude larger than that of a Kodak 649F plate. With a PMMA film several hundreds μm thick the possibility of 100‐fold multiple hologram recording and image reconstruction is confirmed.

Theory of holograms formed using a coded reference beam

An analysis is made of the properties of holograms formed using a coded reference beam. It is shown that coding of a reference transparency by pseudorandom binary sequences is optimal in multiple recording of holograms. A method is suggested for constructing a correlation deflector in a system of optically matched filters based on the properties of pseudorandom sequences.

Multiple recording of holograms with a coded reference wave

Theoretical and experimental investigations were made of the dependence of the quality of a reconstructed image on the ratio of the scales of inhomogeneities of the object and glass-plate diffuser fields. It is shown that the ratio of the signal to the noise resulting from recording of many holograms in one element improves if the random structure of the reference wave field is of the small-scale type. The improvement is proportional to the ratio of the typical scales of inhomogeneities of the object and the reference wave fields.

Multiple-exposure recording of holograms in the case of an extended reference-beam source

The multiple recording of holograms in the same region of a light-sensitive surface is considered in the case of an extended reference-beam source. It is shown that such a reference beam makes it possible to achieve the multiple recording of holograms of extended sources employing small deflections of the reference beam. A description is given of experiments in which up to 50 holograms were recorded on the same plate.

Multiple Recording of Holograms

Multiple Recording of Holograms