Precise alignment of laser beams used in heterodyne interferometry is vital and necessary to the precision, accuracy, and quality of the measurement, but off the shelf-based breadboard setups have a large physical footprint and many components that can introduce unwanted noise. Our lab creates optomechanical accelerometer devices including a fused silica resonator with a 5Hz natural frequency and uses a heterodyne displacement interferometer to readout the position of the test mass, which can then be used to determine the acceleration of the device. A novel compact fiber injector system design is presented here that reduces the footprint of the fiber collimator input of the heterodyne interferometer by an order of magnitude from a breadboard setup, down to 24 x 16 x 19 mm. This new injector system integrates both fibers of different frequencies directly onto the mount with the resonator, increasing stability and reducing entry points for vibrational noise while minimizing the optical path length difference between beams. Each beam can then be independently tilted and de-centered to maximize the fringe visibility at the output of the interferometer, using spring-loaded adjustment screws and secured in place with locking screws. An accelerometer using these injectors measured a displacement of 10^-9 m/√Hz at 10^-2 Hz in air with the test mass anchored, nearly identical to the previous breadboard setup while being much more compact and portable. I will present the design, integration onto an accelerometer, and the initial acceleration noise measurements taken using these fiber injector systems.

Fluorescence appears in most gemstones when exposed to specific irradiation, playing a crucial role in mineral identification and color treatments detection. Traditional visual evaluation under mercury vapor lamps has limitations, leading to inconsistencies in fluorescence analysis. This study introduces tunable laser-based spectroscopy for gemstone analysis. Unlike visual methods, spectroscopy enhances reliability by examining luminescence across the UV to NIR spectrum, while tunable laser provides different excitation wavelengths. The developed system targets gemstone treatments and synthetic material analysis, including diamonds and corundums (ruby and sapphires). Analysis of commercially valuable gemstones demonstrates the system’s capability in gemstone identification. Examples include laboratory-grown diamonds with natural diamond-like features, heat-treated and untreated natural blue sapphires, and the evaluation of the relationship between the orange emission feature and color stability in photochromic sapphires. These findings ensure transparency in the jewelry trade by identifying unclaimed treatments and synthetic materials, as well as contributing to a more comprehensive understanding of gemstone luminescence.

Thermal-electrical circuit modeling is a well-established technique for the quantification of power dissipation in electronic devices and optimizing cooling means, but rarely used in building construction and facility energy management. In contrary to pure numerical simulations, equivalent circuit methods allow the derivation of useful formulas and rules of thumb. In most cases, modeling using electro-thermal analogy is limited to stationary considerations. The recent paper is understood as a short follow up of an earlier publication on the use of non-linear equivalent circuit techniques, extending the models by dynamic behavior and distributed parameters. We present refinements of the modeling framework. Also, the time and cost efficient use of commercially available electrical network simulation software is discussed.

We introduce our cutting-edge panoramic camera – a True Panoramic Camera (TPC), designed for mobile smartphone applications. Leveraging prism optics and well-known imaging processing algorithms, our camera achieves parallax-free seamless stitching of images captured by dual cameras pointing in two different directions opposite to the normal. The result is an ultra-wide (140ox53o) panoramic Field-of-View (FOV) without the optical distortions typically associated with ultra-wide-angle lenses. Packed into a compact camera module measuring 22 mm (length) x 11 mm (width) x 9 mm (height) and integrated into a mobile testing platform featuring the Snapdragon 8 Gen 1 processor, the TPC demonstrates unprecedented capabilities of capturing panoramic pictures in a single shot and recording panoramic videos.

Capillary Refill Time (CRT) is a traditional, semi-quantitative method used to estimate blood flow return to the skin after compression, with times over a few seconds deemed abnormal. Quantitative CRT (qCRT) aims to enhance traditional CRT by offering precise, mobile measurements crucial for telehealth. This study addresses important qCRT challenges, such as variation in skin phototype and the creation of a consistent, phototype-independent algorithm to reduce variability. We employed cross-polarized imaging and cocircular setups to reduce specular reflection, analyzing CRT decay across various color spaces in thirty-two volunteers of all Fitzpatrick phototypes. The sensing system was an RGB camera. We have showed that it is possible to produce qCRT results that are insensitive to phototype (melanin). However, the qCRT results, even for the same operational mechanics, show high sensitivity to the specific algorithm used for CRT determination. Since different algorithms exist to determine CRT, we discuss specific examples using two methods to analyze the CRT decay curve and three-color spaces (green channel, grayscale, and hemoglobin obtained by image processing).

When investigating magnetic nanoparticles (MNPs), interpreting the Verdet constant is not straightforward. The samples investigated in this work are monodispersed iron oxide (Fe3O4) MNPs with a diameter of 20nm, dissolved in ultra-high purity water. . The MNP samples were subjected to an AC magnetic field that enables lock-in detection. A simple view of the experiment would lead to the idea that superparamagnetic particles should result in a linear response and the observed intensity modulation (due to polarization modulation) should have a 1f response only. Instead, the observed behavior consists of not just the main 1f response but also includes 2nd, 3rd, 4th, and 6th harmonics in response to the AC magnetic field. These higher harmonics provide strong evidence of aggregate formation at this concentration and particle size. To better understand the source(s) of these higher harmonics and the possible role played by aggregation, we further measure samples in two related geometries – a double pass where light passes through the samples twice and a Michelson interferometer setup that allows us an independent measure the ratios of various harmonics.

This paper is intended as a short follow-up to our last publication on the use of polarization-based imaging techniques and metrology applications. With their increasing resolution, memory availability and computing capacity, smartphones have become a common means for image and video documentation, geodetic and metrological data acquisition and similar applications in recent years. We are investigating concepts for smartphone-based polarimetric image acquisition and evaluation in field measurement campaigns. Technical applications are, for example, the mobile examination of larger areas with regard to contamination, damage to coatings, corrosion and the like, but also artistic photography, e.g. for paintings and sculptures. In addition to pure data acquisition, image pre-processing and analysis can be carried out in the field by means of mobile image processing applications. In the paper we discuss such concepts, their feasibility and robust extensions for smartphones that could lead to applications that actually take advantage of the smartphone's mobility.

Remarkable strides have been made in the realm of efficiently sorting and analysing Orbital Angular Momentum (OAM) states of light through the application of geometric optical transformations employing mode sorters. In our study, we introduce a novel methodology that reconstructs OAM states of light through the demonstration of the reciprocity of light. This is achieved by operating a diffractive mode sorter in reverse, effecting an inverse geometric optical transformation that reverts simple lateral spots back to OAM modes of light. Our approach leveraged a Digital Micro-mirror Device (DMD) to encode a hologram, producing an array of spots mimicking the output of a traditional mode sorter. Our system is not only limited solely to the generation of scalar OAM modes, with a simple manipulation of the polarization of light we enhanced our system to encompass vector beam generation capabilities.

The ability to generate structured light with arbitrarily controlled polarization in a compact optical path has been a challenge over the last few years in the fields of optics and photonics. In this regard, our work proposes the design, fabrication, and characterization of new dielectric dual-functional meta-optics that generate orbital angular momentum beams with on-demand different vectorial behaviors acting only on the input polarization. The metaoptics are designed as an array of periodic subwavelength metastructures (so-called meta-atoms) composed of silicon nanofins on a silicon substrate, acting like half-wave plates that exploit both the geometric and dynamic phases. We prove the generation of dual-ring perfect vector beams and novel complex vectorial configurations: azimuthally-variant perfect vector beams and helico-conical vector beams. This design solution offers both compactness of the optical path and easy integration with other optical elements, suggesting intriguing applications in telecommunications, imaging, particle manipulation, and quantum information.

This work introduces a novel method to significantly reduce the number of measurements needed for wavefront correction in strongly scattering media, as compared to traditional approaches. The key innovation lies in defining the beam using an annular angular spectrum rather than a 2D grid. We employ a Spatial Light Modulator (SLM) for both the preparation and sampling of the annular angular spectrum. The speckle pattern of the transmitted beam is evaluated at a single point of a detector, and the phase distribution is measured using three-step interferometry. The final correction to the transmitted beam is achieved by applying the conjugate phase onto the initial beam defined on the spatial light modulator. Remarkably, 64 measurements already provide a reasonably effective wavefront correction. However, optimal results are attained when the spatial azimuthal sampling frequency of the angular spectrum matches the transverse wave vector of the generated quasi-Bessel beam.

A novel digital laser setup with two controllable phase boundaries can generate complex structured beams. Experiments confirm the new configuration can generate vortex beams with controllable over both topological charge and intensity profiles. Not only vortex beams, but this cavity can also produce all kind of nondiffracting beam, including the Parabolic-Gauss beam, which was previously unattainable directly from laser cavities. This innovative digital laser configuration represents a versatile option for customizable structured beam laser facilitating wide-ranging applications.

The use of plastic optical fibers as sensors represents advantages due to the malleability of the material and the number of modulations it allows, in addition, it's a flexibility and low-cost material. Currently, optical couplers have also been developed in plastic fiber optics, due to their main use in telecommunications, and prices are increasingly affordable. In addition, the use of technologies in optics and photonics are more accepted in areas such as medicine, industry, beauty, sensors, and more. (1) In this work, a force sensor is achieved, based on beam modulation, made of a 2x2 (50:50) coupler of 1mm diameter Plastic Optical Fiber (POF), with a 10 cm POF joined to the output to generate a loop. This section was polished in D, V and cylindrical shapes, at 30% and 50% polished depth, using a visible spectrum, in 632.8 nm of an He-Ne laser source. The spectral response is obtained in a force range of 0-500 N which is gradually applied to the fiber polished section. A linear sensitivity of force-beam modulation is obtained.

In the promotion of Information and Communication Technology (ICT) in construction projects (i-Construction), as well as in the digitization of existing infrastructure (DX; Digital Transformation,) many improved distance measurement technologies enhance the efficient development and management of societal infrastructure. Infrastructure maintenance and management incorporate such technologies as small unmanned aerial vehicles (drones) and 3D laser scanners. Recently, the utilization of Mobile Mapping Systems (MMS) equipped with laser scanners has facilitated the acquisition of three-dimensional data in areas surrounding roads. MMS proves effective in measuring the three-dimensional shape of roadways as it acquires cloud point data. The data, represented by three-dimensional coordinates (x, y, z) aligned with the world geodetic system, can be seamlessly integrated into cyberspace on a computer. MMS utilizes a laser beam from a scanner installed on the vehicle, resulting in a measurement error of a few centimeters in the acquired cloud point data. However, the accuracy of the cloud point data significantly decreases in tunnels due to the absence of satellite positioning correction, leading to potential errors exceeding 1 meter. Presently, long distance [1 m to 30 m] measurement commonly relies on the Doppler effect. However, notable issues are the requirement for a stationary state and several seconds of measurement time to ensure accuracy. Hence, when mounted on a moving vehicle, poor quality data would be obtained. Similarly, the use of beacons or radar yields unreliable measured values for the vehicle movement. Even with autonomous navigation systems employing a gyro sensor and a speed sensor mounted on the vehicle to determine the point of travel, the cumulative error in position estimation gradually increases, particularly in locations where catching GPS satellites is challenging. Some essential sites on and around roads, such as tunnels and areas under elevated railway tracks, remain inaccessible for position information through GNSS (Global Navigation Satellite System,) limiting the full utilization of ICT technology. This study proposes a novel self-positioning system that integrates two laser devices and an image sensor to accurately acquire position information even in non-GNSS environments.

Our linear astigmatism-free confocal off-axis collimator comprises two off-axis mirrors and one flat mirror with an aperture size of 73 mm and a focal length of 1200 mm. The off-axis mirrors, along with all other opto-mechanical parts, will be fabricated from the same material, such as aluminum alloy 6061-T6. This concept inherently creates an athermalized structure, meaning the entire system expands or contracts by the same amount as the thermal coefficient of expansion, ensuring that the image remains consistently in focus. We approached this collimator’s design as if it were an astronomical telescope, reversing the optical path directions, and conducted tolerance analysis using Optic Studio (ZEMAX) to define the opto-mechanical design requirements. The collimator’s target or telescope imaging sensor size is 4 × 4 mm, with a required imaging resolution of 13.7 cycles/mm at a wavelength of 750 nm. To achieve this, we divided the full field (4 × 4 mm) into 3 × 3 subfields, ensuring that the average Modulation Transfer Function (MTF) value exceeds 10%. We performed Monte-Carlo Simulations 5000 times to determine tolerance ranges with a 90% confidence level. Furthermore, we conducted stray light analysis for our off-axis collimator design. In comparison to typical on-axis Cassegrain designs, where baffles block some parts of the target rays and reduce intensity, our designed confocal off-axis collimator accommodates baffles without obstructing any light from the target.

Space-based long-baseline stellar interferometry has been envisioned for decades because it can bypass atmospheric disturbance and enable significant array scalability with high spectral and angular resolution. However, technological challenges have so far prevented the realization of these missions. The GLORIA project, a collaboration between the German Aerospace Center (DLR) and the Leibniz Institute for Astrophysics Potsdam (AIP), aims to advance the transition of near-infrared (NIR) stellar interferometry from ground-based to space-based observations. This initiative utilizes heterodyne interferometry to digitize delay lines, addressing the limitation of conventional mechanical rail systems used in ground-based interferometers to compensate for optical path differences necessary for achieving interference, which are impractical for space applications. By mixing NIR stellar radiation with a stable reference laser, the project intends to convert the signal into the radio regime, enabling delay line digitization while preserving crucial phase information essential for stellar image reconstruction. The first phase of the ground-testbed aims to establish a controlled testbed environment for tests of heterodyne interferometry. The second phase intends to simulate and measure astronomical conditions, leveraging the phase 1 setup adapted to replicate the complexities of a real stellar interferometer. The current progress of the testbed includes control over phase and amplitude for interferometric measurements with initial characterization of the heterodyne signal.

Here, simulations of a photoconductive scatterer in a system of two parallel dielectric resonators operating at a non-Hermitian degeneracy, or exceptional point (EP) are explored. Systems operating at an EP exhibit unique characteristics such as increased sensitivity to low-level perturbation that can be exploited to enhanced sensing applications. To elucidate this functionality, two-dimensional eigenfrequency simulations of this novel system operating at an EP with the scatterer is used to introduce perturbations to the system. The EP is identified through the variation of two physical parameters viz. the distance of the scatterer from the resonators and the gap between the resonators. A systematic parametric sweep of these variables shows the distinctive characteristics of a system with EPs including a crossing of real eigenfrequencies, repulsion of imaginary eigenfrequencies, simultaneous mode excitation, self-intersecting Riemann sheets, and eigenvalue splitting in response to perturbation. These results show how this EP-based systems can be used to significantly improve sensitivity low-level light detection.

This paper presents consecutive correction of the low- and high-order wavefront aberrations. To compensate for large-scale phase distortions bimorph deformable mirror was used with aperture 50 mm and 28 electrodes. The mitigation of the small-scale distortions was performed with 78-mm and 55 actuators wavefront corrector of the piezostack type. To investigate behavior of the laser beam two Shack-Hartmann wavefront sensors and far-field camera were used.

Laser beam shaping problem remains relevant for various applications of modern laser physics – from laser cutting of metals to wireless long-distance energy transmission. For example, the transformation of the original Gaussian profile into flat-top profile is necessary to improve the technology (material processing, holograms recording) while the doughnut-like profile ensures uniform temperature distribution on a target and increases the stability of various thermal processes, such as melting. To solve this problem the automated adaptive optical system with phase-only special light modulator and intensity analyzer are assembled and tested. The experimental results of the flat-top and doughnut-like intensity distributions formation are presented. We were able to concentrate ~60% and 75% of the initial beam energy for the doughnut-like and flat-top intensity distributions, correspondingly.