In this work, the content for an undergraduate-level holography workshop is presented. The session is divided into two parts: an instructional section and a hands-on application activity supported by research-grade open-source software. The first section starts with a brief theoretical review of conventional imaging, interference, and diffraction as the underlying physical phenomena. These concepts are then used for the description of the recording, processing, and reconstruction stages of analog holography, emphasizing in each case the phenomenology rather than the mathematical framework. Finally, the translation of these stages to digital holography is presented, introducing the principles of digital recording and numerical reconstruction. The contents of the instructional section are then applied in a lecturer-guided activity, in which the participants generate a computational off-axis hologram and calculate its reconstruction. All the operations are performed using the “Numerical Propagation” plugin of the open-source software ImageJ. This research-grade software allows the modeling and manipulation of complex-valued wavefields from a user-friendly graphical interface. It thus allows the participants to recreate step-by-step the recording and reconstruction stages of the holographic process, while directly identifying when each physical phenomenon is at play. The proposed content can be implemented either as a stand-alone workshop or as an applied component of an undergraduate optics course.
Since the discovery of the wave behavior of light, diffraction has been a cornerstone in optics. The teaching of the diffraction theory has been usually done theoretically based on a mathematical approach that could hinder the understanding of the physical phenomena. In this work, the simplicity in the architecture of an accessible, cost-effective, and 3D-printed digital lensless holographic microscope is used as an educational tool to study the diffraction theory by providing experimental validations of the phenomena for undergraduate students. The recording and reconstruction steps of the lensless holographic technique take the students to the bidirectionally of the diffraction phenomena in a completely hands-on approach. The integration of the theory with an accessible experimental setup generates an innovative way of teaching the diffraction phenomena in a classroom.
A single-shot procedure to reduce speckle noise in numerically computed complex-valued wavefields is presented. The method is supported by the possibility of numerically producing multiple speckle realizations of a calculated complex-valued wavefield to reduce the speckle noise through a noncoherent superposition of the produced realizations. Although the method is applied to digital holographic microscopy, it could be utilized in other techniques where a numerical representation of the complex-valued wavefield of interest can be obtained. Experimental results with nonbiological and biological samples are presented to support the feasibility of the method.
In phase-shifting digital holographic microscopy (PS-DHM), the reconstructed phase map is obtained after processing several holograms of the same scene with a phase shift between them. Most reconstruction algorithms in PS-DHM require an accurate and known phase shift between the holograms, requirement that limits the PS-DHM applicability. This work presents an iterative-blind phase shift extraction method based on the demodulation of the different components of the holograms using three-frame holograms with arbitrary and unequal phase-shifts. Both simulated and experimental results demonstrate the goodness and feasibility of the proposed technique.
A self-contained platform for realistic modeling of digital holographic microscopy (DHM) is presented. Amplitude and phase samples, imaged in different architectures, can be modeled to produce numerical DHM holograms that include all the parameters that are present in real experiments, providing an accessible way for newcomers to have a first approach to this research field. The platform is based on considering the imaging arm of the DHM that produces the object wave as the result of the convolution process between the geometrical-optics image prediction of the sample with the point spread function introduced by diffraction. The DHM hologram is produced by the amplitude superposition of complex-valued object wave with a reference wave of arbitrary description. The sampling of the analytically produced DHM holograms is set from the input discretized image according to the specifications of the digital camera aimed to be used. The feasibility of the realistic platform is exemplified by contrasting the wrong results of a nonrealistic simulation with experimental results to show the need for using a complete realistic simulation like the one presented; further applications of the platform to numerical modeling speckle noise reduction over samples with controlled levels of roughness, and phase-shifting DHM techniques, are included.
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