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We report the implementation of an interferometric null test using a high-definition spatial light modulator (SLM) as a reconfigurable alternative to a computer-generated hologram. We detail the alignment process chain, including novel techniques using the SLM to project alignment fiducials on the test part. To validate the alignment protocol, we measure a mild off-axis conic with the SLM-based system and cross-validate with conventional interferometry within 30â nm root-mean-square (RMS) surface figure. Finally, we report the null test of a 65 mm clear aperture concave freeform with 91â µm peak-valley sag departure from the base sphere. The measured surface figure of the freeform is within 40 nm RMS compared to the measurement with a commercial metrology instrument.
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Optical vortices are widely used in optics and photonics, impacting the measurements and conclusions derived from their use. Thus, it is crucial to evaluate optical vortices efficiently. This work aims to establish metrics for evaluating optical vortex quality to support the implementation procedure and, hence, provide a tool supporting research purposes and technological developments. We propose to assess vortex quality using the following intensity parameters: eccentricity, cross-sectional peak-to-valley, cross-sectional peak difference, and the doughnut ratio. This methodology provides a low-cost, robust, and quantitative approach to evaluating optical vortices for each specific optical technology.
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In this work, we present a panoramic digital holographic system for the first time capable of obtaining 3D information of a quasi-cylindrical object by using a conical mirror. The proposed panoramic digital holographic system is able to scan the entire surface of the object to determine the amplitude and phase simultaneously. This paper demonstrates the feasibility of analyzing quasi-cylindrical objects in a short time (0.5 s) with a single camera and a minimum number of optical components. In addition, it can be applied to determine not only topographic measurement of the cylindrical surface but also measurements of radial deformations. Experimental results are presented at different magnifications, thus illustrating its capabilities and versatility.
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The lack of contrast represents a challenge in all imaging systems, including microscopy. This manuscript proposes the use of an azobenzene liquid crystal material as a Zernike filter in a phase-contrast configuration to enable label-free imaging. The novelty of the approach presented here is that it offers real-time adjustment of the contrast in images and prolonged-time observation. This is achieved with no SLM, any customized optical components, or mechanical elements, and voltage is not applied. Notably, the intensity level (0.95â mW/cm2) is well below photodamage or phototoxicity for bioimaging, allowing extended time monitoring of cells. Additionally, due to the large LC's birefringence (Δn=0.2), it is possible not only to visualize a phase object but also to adjust the contrast of stainless samples by just rotating the polarization with a large and continuous dynamic range of phase retardation. In future work, this will enable a simple implementation of differential phase-contrast microscopy and quantitative phase imaging. Due to the low-intensity illumination required, this system can be combined with other imaging techniques, such as tomography and fluorescence microscopy.
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A smart brute-force double random-phase encoding attack is presented that takes advantage of an unreported vulnerability: the smoothness of mean squared error (MSE) and correlation coefficient (CC) curves in a key-sensitivity analysis. The vulnerability reported here is made visible in a key-sensitivity analysis. It is shown that a modular arithmetic pre-coding provides significant robustness against this form of attack because the pre-coding creates a highly nonlinear, highly oscillatory MSE and CC curve in the key space. Knowledge of this new vulnerability and how to prevent this in the first place provides a better understanding of the robustness of various double random-phase encoding designs.
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A vibration-insensitive, single-shot phase-calibration method for phase-only spatial light modulators (SLM) is reported. The proposed technique uses a geometric phase lens to form a phase-shifting radial shearing interferometer to enable common-path measurements. This configuration has several advantages: (a) unlike diffraction-based SLM calibration techniques, this technique is robust against intensity errors due to misalignment; (b) unlike two-beam interferometers, this technique offers a high environmental stability; and (c) unlike intensity-based methods, the phase-shifting capability provides a phase uncertainty routinely in the order of ${2}\pi /100$2π/100. The experimental results show a significantly higher accuracy when compared to the diffraction-based approaches.
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This Letter proposes an optical encryption technique that disguises the information with modular arithmetic concepts and time-varying noise components that are unknown to the receiver. Optical encryption systems that use these techniques produce a nondeterministic system response, as well as noise like image data that can easily be generated with ordinary spatial light modulators. The principle of this technique is demonstrated for the double random phase encoding (DRPE) method. The conventional DRPE method has major vulnerabilities for Dirac signal and plain signal attacks, making them impractical for secure encryption. It is shown that the proposed encryption technique provides a robustness against these types of attacks, allowing optical DRPE to be employed in secure encryptions. Moreover, applications of this Letter are not limited to DRPE alone but can also be adopted by other optical encryption techniques such as fractional Fourier transform and Fresnel-transform-based techniques.
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A quantitative phase measuring technique is presented that estimates the object phase from a series of phase shifted interferograms that are obtained in a common-path configuration with unknown phase shifts. The derived random phase shifting algorithm for common-path interferometers is based on the Generalized Phase Contrast theory [pl. Opt.40(2), 268 (2001)10.1063/1.1404846], which accounts for the particular image formation and includes effects that are not present in two-beam interferometry. It is shown experimentally that this technique can be used within common-path configurations employing nonlinear liquid crystal materials as self-induced phase filters for quantitative phase imaging without the need of phase shift calibrations. The advantages of such liquid crystal elements compared to spatial light modulator based solutions are given by the cost-effectiveness, self-alignment, and the generation of diminutive dimensions of the phase filter size, giving unique performance advantages.
RESUMEN
Optical holographic interferometry (HI) is realized by two well-known techniques: double exposure holographic interferometry (DEHI) and real-time holographic interferometry (RTHI). However, the digital version of HI is typically realized numerically by DEHI. The main problem in digital implementation of RTHI is the lack of commercially available cameras and spatial light modulators with the same pixel size. This mismatch results in lateral and transversal magnifications of an object wavefront reconstruction. In real-time digital HI the reconstruction of an object in an initial state has to be superimposed on top of the loaded object. In this work, we present and analyze five approaches to overcome the mismatch problem, and the performance of these procedures is numerically quantified and compared. The experimental suitability of these approaches is investigated.
