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Optics, Volume 4, Issue 1 (March 2023) – 17 articles

Cover Story (view full-size image): This review article aims to highlight the potential diagnostic applications of gold nanoparticles in ophthalmology. More specifically, attention will be drawn to using AuNPs as contrast agents (CAs) in optical coherence tomography (OCT) and photoacoustic imaging (PAI), which are two novel imaging modalities for the visualization of the eye. The addition of a contrast agent has been proposed for image improvement, and AuNPs are attractive candidates for this purpose. The in vitro, ex vivo, and in vivo studies investigating and supporting this concept will be presented thoroughly to elucidate whether AuNPs are eligible for imaging enhancement owing to their optical characteristics. View this paper
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12 pages, 1571 KiB  
Article
Nonperturbative Generation of Harmonics by Nanometer-Scale Localized Electronic States on the Surface of Bulk Materials and Nano-Films
by Jozsef Seres, Enikoe Seres, Eva Céspedes, Leyre Martinez-de-Olcoz, Miguel Zabala and Thorsten Schumm
Optics 2023, 4(1), 246-257; https://doi.org/10.3390/opt4010017 - 13 Mar 2023
Cited by 1 | Viewed by 1253
Abstract
The generation of high-order harmonics in solid crystals has received considerable attention recently. Using a driver laser with 0.8 µm wavelength and 28 fs ultrashort pulses, we present experimental results, accompanied with theoretical considerations, suggesting that the actual sources of the harmonics are [...] Read more.
The generation of high-order harmonics in solid crystals has received considerable attention recently. Using a driver laser with 0.8 µm wavelength and 28 fs ultrashort pulses, we present experimental results, accompanied with theoretical considerations, suggesting that the actual sources of the harmonics are nanometer-sized localized and transient electronic states on the surface of the materials when the laser intensity is in the non-perturbative regime. Adaptation of the bond model of the harmonic generation into the non-perturbative regime and including the quantum features of the process provide a localized excitation approach that correctly describes the measured polarization dependence of the harmonic signal, reflecting the microscopic surface structure and symmetries of the examined materials. Full article
(This article belongs to the Special Issue Opto-Thermo-Mechanical Interactions in Nano-Objects and Metasurfaces)
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19 pages, 3036 KiB  
Article
Optimized Design and Simulation of Optical Section in Electro-Reflective Modulators Based on Photonic Crystals Integrated with Multi-Quantum-Well Structures
by Mohammad Mahdi Khakbaz Heshmati and Farzin Emami
Optics 2023, 4(1), 227-245; https://doi.org/10.3390/opt4010016 - 01 Mar 2023
Viewed by 8882
Abstract
In the design of photonic integrated circuits (PICs), the optical connections of the PIC surface, along with the electronic components of the chips, are significant issues. One of the optoelectronics components that utilizes these surface connections are electro-reflective modulators, consisting of an optical [...] Read more.
In the design of photonic integrated circuits (PICs), the optical connections of the PIC surface, along with the electronic components of the chips, are significant issues. One of the optoelectronics components that utilizes these surface connections are electro-reflective modulators, consisting of an optical section and an electronic section. In this paper, a novel scheme of two-dimensional photonic crystals (PhCs) is presented for the optical and reflective sections of this device. This design is two-dimensional; thus, it has less volume than the current bulky structures. The finite element method is utilized to simulate and optimize the scheme of PhCs and gold layer parameters. Furthermore, optimization of design parameters is accomplished through the Nelder–Mead method. Moreover, the modeling and simulation of the proposed hybrid PhCs has been investigated according to the structural parameters with tolerance. These tolerances, related to the nanorods’ radius and lattice constants, are considered to justify and vindicate the fabrication technology limitations and conditions. In the “on” state of the modulator, the light transmission ratio is 98% for a 903 nm wavelength with a 45° angle of deflection and incident light, nd the bandwidth is 20 nm. For an 897 nm wavelength with a 41° angle, the transmission ratio is 95%, and the bandwidth is 7 nm. Full article
(This article belongs to the Special Issue Novel Optical Materials and Device)
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13 pages, 2895 KiB  
Article
Laser Beam Jitter Control Based on a LabVIEW FPGA Control System
by Delin Zhang, Jingxin Cheng and Yuanqin Xia
Optics 2023, 4(1), 214-226; https://doi.org/10.3390/opt4010015 - 24 Feb 2023
Viewed by 1635
Abstract
The thermal blooming effect, platform jitter, and other effects of laser beam propagation cause serious deviation, which will have a negative impact on laser tracking systems. It is important to ensure that the laser beam does not deviate. Based on a fast steering [...] Read more.
The thermal blooming effect, platform jitter, and other effects of laser beam propagation cause serious deviation, which will have a negative impact on laser tracking systems. It is important to ensure that the laser beam does not deviate. Based on a fast steering mirror, a CMOS camera, and a Flex RIO system, a laser beam jitter control system is designed and implemented. The error is detected by camera and compensated for by the fast steering mirror (FSM), which is controlled by the Flex RIO device. By using LabVIEW and MATLAB, a closed loop model is realized. The results show that the system response is highly stabilized and has a short rise time, providing a reference for engineering applications. Full article
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16 pages, 7037 KiB  
Article
Compact Optical System Based on Scatterometry for Off-Line and Real-Time Monitoring of Surface Micropatterning Processes
by Marcos Soldera, Sascha Teutoburg-Weiss, Nikolai Schröder, Bogdan Voisiat and Andrés Fabián Lasagni
Optics 2023, 4(1), 198-213; https://doi.org/10.3390/opt4010014 - 24 Feb 2023
Cited by 1 | Viewed by 1346
Abstract
In this study, a scatterometry-based monitoring system designed for tracking the quality and reproducibility of laser-textured surfaces in industrial environments was validated in off-line and real-time modes. To this end, a stainless steel plate was structured by direct laser interference patterning (DLIP) following [...] Read more.
In this study, a scatterometry-based monitoring system designed for tracking the quality and reproducibility of laser-textured surfaces in industrial environments was validated in off-line and real-time modes. To this end, a stainless steel plate was structured by direct laser interference patterning (DLIP) following a set of conditions with artificial patterning errors. Namely, fluctuations of the DLIP process parameters such as laser fluence, spatial period, and focus position are introduced, and also, two patterning strategies are implemented, whereby pulses are deliberately not fired at both deterministic and random positions. The detection limits of the system were determined by recording the intensities of the zero, first, and second diffraction order using a charge-coupled device (CCD) camera. As supported by topographical measurements, the system can accurately calculate spatial periods with a resolution of at least 100 nm. In addition, focus shifts of 70 µm from the optimum focus position can be detected, and missing patterned lines with a minimum width of 28 µm can be identified. The validation of this compact characterization unit represents a step forward for its implementation as an in-line monitoring tool for industrial laser-based micropatterning. Full article
(This article belongs to the Section Laser Sciences and Technology)
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27 pages, 3615 KiB  
Review
Optical Fiber Based Temperature Sensors: A Review
by Rahul Kumar Gangwar, Sneha Kumari, Akhilesh Kumar Pathak, Sai Dheeraj Gutlapalli and Mahesh Chand Meena
Optics 2023, 4(1), 171-197; https://doi.org/10.3390/opt4010013 - 23 Feb 2023
Cited by 13 | Viewed by 6732
Abstract
The current generation is witnessing a huge interest in optical waveguides due to their salient features: they are of low cost, immune to electromagnetic interference, easy to multiplex, have a compact size, etc. These features of optical fibers make them a useful tool [...] Read more.
The current generation is witnessing a huge interest in optical waveguides due to their salient features: they are of low cost, immune to electromagnetic interference, easy to multiplex, have a compact size, etc. These features of optical fibers make them a useful tool for various sensing applications including in medicine, automotives, biotechnology, food quality control, aerospace, physical and chemical monitoring. Among all the reported applications, optical waveguides have been widely exploited to measure the physical and chemical variations in the surrounding environment. Optical fiber-based temperature sensors have played a crucial role in this decade to detect high fever and tackle COVID-19-like pandemics. Recognizing the major developments in the field of optical fibers, this article provides recent progress in temperature sensors utilizing several sensing configurations including conventional fiber, photonic crystal fiber, and Bragg grating fibers. Additionally, this article also highlights the advantages, limitations, and future possibilities in this area. Full article
(This article belongs to the Special Issue Opto-Thermo-Mechanical Interactions in Nano-Objects and Metasurfaces)
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15 pages, 14646 KiB  
Article
Innovative Approaches for Organizing an Inclusive Optics and Photonics Conference in Virtual Format
by Alba de las Heras, Ana I. Gómez-Varela, María-Baralida Tomás, Rosa Ana Perez-Herrera, Luis Alberto Sánchez, Francesca Gallazzi, Beatriz Santamaría Fernández, Mario Garcia-Lechuga, Maria Vinas-Pena, Martina Delgado-Pinar and Verónica González-Fernández
Optics 2023, 4(1), 156-170; https://doi.org/10.3390/opt4010012 - 15 Feb 2023
Cited by 1 | Viewed by 1856
Abstract
The COVID pandemic is forcing the renewal of scientific conferences, offering opportunities to introduce technological and inclusive developments. Our analysis focuses on the implementation of inclusive practices for female and early-career researchers in a virtual scientific conference. This organization approach was applied in [...] Read more.
The COVID pandemic is forcing the renewal of scientific conferences, offering opportunities to introduce technological and inclusive developments. Our analysis focuses on the implementation of inclusive practices for female and early-career researchers in a virtual scientific conference. This organization approach was applied in the XIII Spanish Optical Meeting (RNO2021), which was also characterized by avatars interacting in an online metaverse. The effectiveness of inclusive policies and novel technological tools was evaluated using the participation data and a post-conference survey. Our study reveals the high impact of inclusive actions and a strong interest in the scientific community to explore conference advances. Full article
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10 pages, 3318 KiB  
Article
Design and Optical Analysis of a Refractive Aspheric Intraocular Lens with Extended Depth of Focus
by Kunqi Li, Xiaoqin Chen, Yayan Bian, Yuwei Xing, Xiaolan Li, Dongyu Liu and Yongji Liu
Optics 2023, 4(1), 146-155; https://doi.org/10.3390/opt4010011 - 31 Jan 2023
Cited by 1 | Viewed by 1569
Abstract
To obtain a continuous range of clear vision for pseudophakic eyes, a design of intraocular lens (IOL) with extended depth of focus (EDoF) was proposed. The IOL was optimized with a multi-configuration approach based on a pseudophakic eye model and the optical performances [...] Read more.
To obtain a continuous range of clear vision for pseudophakic eyes, a design of intraocular lens (IOL) with extended depth of focus (EDoF) was proposed. The IOL was optimized with a multi-configuration approach based on a pseudophakic eye model and the optical performances of the designed IOL were analyzed. The modulation transfer function (MTF) values remain above 0.2 at 50 lp/mm for object distance ranging from 0.35 m to infinity in both photopic vision and mesopic vision over a field of 4°. The optical performances remain stable when the pupil diameter changes from 2.25 mm to 5 mm. Besides, the presented theoretical analyses show the designed IOL has good optical performances for polychromatic light and corneal asphericity. The above shows that the IOL exhibits an excellent ability for pseudophakic eyes to see the object in a continuous range of distance. Full article
(This article belongs to the Special Issue Advances in Vision Optics, Myopia Control and Refractive Surgery)
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8 pages, 4732 KiB  
Article
Direct Laser Writing of Computer-Generated Holograms by Photodissolution of Silver in Arsenic Trisulfide
by Arjun Karimbana Kandy, Cedric Sebastien Martins Figueiredo, Manuel Fernandez Merino, Antoine Bourgade, Jean-Yves Natoli, Konstantinos Iliopoulos and Julien Lumeau
Optics 2023, 4(1), 138-145; https://doi.org/10.3390/opt4010010 - 31 Jan 2023
Cited by 3 | Viewed by 1212
Abstract
Photodissolution is a process that is well known for its ability to cause inclusion of silver into the matrix of a chalcogenide layer, changing its optical properties. In this paper, using e-beam deposition, we developed Ag (74 nm)/As2S3 (355 nm) [...] Read more.
Photodissolution is a process that is well known for its ability to cause inclusion of silver into the matrix of a chalcogenide layer, changing its optical properties. In this paper, using e-beam deposition, we developed Ag (74 nm)/As2S3 (355 nm) bilayers and characterized the photodissolution kinetics when exposed to actinic radiation. We showed that local complete silver photodissolution at the micron scale can be achieved. Based on this result, we then developed amplitude-based computer-generated holograms using direct laser writing. CW lasers with beam shaping and short pulse lasers with beam scanning were both implemented. Elements with 8.5 µm and <1 µm spatial resolution and close to theoretical intensity distribution, respectively, were successfully demonstrated. Full article
(This article belongs to the Special Issue Laser-Assisted Micro- and Nano-Fabrications)
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6 pages, 1336 KiB  
Article
Optical Isolation of the Amplifier Cavity in XG-III PW Beamline
by Zhenhai Wu, Jiao Long, Jun Zhang, Qian Xiong, Xiongjun Zhang and Dongxia Hu
Optics 2023, 4(1), 132-137; https://doi.org/10.3390/opt4010009 - 28 Jan 2023
Viewed by 1029
Abstract
Optical isolation with high-quality, large-aperture polarizers is commonly used in high-power laser facilities to suppress retro-reflected pulses. However, it is hard to manufacture these polarizers. We propose an approach of optical isolation with two plasma-electrode Pockels cells instead of large-aperture polarizers. In this [...] Read more.
Optical isolation with high-quality, large-aperture polarizers is commonly used in high-power laser facilities to suppress retro-reflected pulses. However, it is hard to manufacture these polarizers. We propose an approach of optical isolation with two plasma-electrode Pockels cells instead of large-aperture polarizers. In this approach, Nd:glass slabs placed at the Brewster′s angle are used as polarizers. The analysis results and the application performances in the Xingguang (Star Light) XG-III PW beamline indicate that this approach can supply good protection to optical components in laser facilities. Full article
(This article belongs to the Special Issue Laser–Matter Interaction)
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32 pages, 1391 KiB  
Article
Spin–Orbital Coupling and Conservation Laws in Electromagnetic Waves Propagating through Chiral Media
by Hyoung-In Lee
Optics 2023, 4(1), 100-131; https://doi.org/10.3390/opt4010008 - 18 Jan 2023
Cited by 1 | Viewed by 1405
Abstract
This study examines the characteristics of the electromagnetic waves that propagate through an unbounded space filled with a homogeneous isotropic chiral medium. The resulting characters are compared to those of the electromagnetic waves propagating through an achiral free space. To this goal, we [...] Read more.
This study examines the characteristics of the electromagnetic waves that propagate through an unbounded space filled with a homogeneous isotropic chiral medium. The resulting characters are compared to those of the electromagnetic waves propagating through an achiral free space. To this goal, we form energy conservation laws for key bilinear parameters in a chiral case. Due to a nonzero medium chirality, conservation laws turn out to contain extra terms that are linked to the spin–orbit coupling, which is absent for an achiral case. In this way, we identified where the neat hierarchy exhibited by the achiral case among the key bilinear parameters is destroyed by a medium chirality. As an example, we took a plane wave for the chiral case to evaluate those bilinear parameters. Resultantly, the conservation laws for a chiral case are found to reveal inconsistencies among several bilinear parameters that constitute the conservation laws, thereby prompting us to establish partial remedies for formulating proper wave-propagation problems. Therefore, adequate applications of boundary conditions are found to be necessary after examining typical problems available from the literature. Full article
(This article belongs to the Collection Feature Paper Collection of Emerging Trends on Optics)
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26 pages, 4059 KiB  
Review
Gold Nanoparticles as Contrast Agents in Ophthalmic Imaging
by Alexandra Kavalaraki, Ellas Spyratou, Maria Anthi Kouri and Efstathios P. Efstathopoulos
Optics 2023, 4(1), 74-99; https://doi.org/10.3390/opt4010007 - 18 Jan 2023
Cited by 6 | Viewed by 2469
Abstract
Over the past few years, tremendous research concerning the possibilities of gold nanoparticles in medicine has been conducted. Gold nanoparticles (AuNPs) are considered to be unique nanostructures due to their extraordinary chemical and physical properties. This review article aims to bring into light [...] Read more.
Over the past few years, tremendous research concerning the possibilities of gold nanoparticles in medicine has been conducted. Gold nanoparticles (AuNPs) are considered to be unique nanostructures due to their extraordinary chemical and physical properties. This review article aims to bring into light the potential applications of gold nanoparticles for diagnostic purposes in ophthalmology. More specifically, attention will be drawn to the utilization of AuNPs as contrast agents (CAs) in optical coherence tomography (OCT) and photoacoustic imaging (PAI), which are two novel imaging modalities for the visualization of the eye. None of these techniques requires the use of an imaging adjuvant to function; however, the addition of a contrast agent has been proposed for image improvement, and AuNPs are attractive candidates for this purpose. The in vitro, ex vivo, and in vivo studies investigating and supporting this concept will be presented thoroughly to elucidate whether AuNPs are eligible for imaging enhancement owing to their optical characteristics. Full article
(This article belongs to the Special Issue Advances in Biophotonics Using Optical Microscopy Techniques)
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8 pages, 1215 KiB  
Article
White Photoluminescence in Dy-Doped Oxyfluoride Glasses
by Xianmei Chen, Artemiy V. Khamenok, Shaukat G. Khusainov, Mikhail V. Shestakov and Victor V. Moshchalkov
Optics 2023, 4(1), 66-73; https://doi.org/10.3390/opt4010006 - 17 Jan 2023
Cited by 2 | Viewed by 1680
Abstract
Dy3+-doped, Ag and Dy3+-co-doped, and Tm3+ and Dy3+-co-doped oxyfluoride glasses have been prepared by a conventional melt-quenching method. White and yellowish light emissions were generated in the glasses under excitation in the range from 350 to [...] Read more.
Dy3+-doped, Ag and Dy3+-co-doped, and Tm3+ and Dy3+-co-doped oxyfluoride glasses have been prepared by a conventional melt-quenching method. White and yellowish light emissions were generated in the glasses under excitation in the range from 350 to 390 nm. Changes in the excitation wavelength in the ultraviolet (UV) range do not significantly alter the emission tint of the Dy and Ag and Dy-co-doped glasses. On the contrary, the tint of the Tm and Dy co-doped glasses considerably varies under excitation in the same range. Full article
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11 pages, 2279 KiB  
Article
All-Optical Simultaneous Frequency Metamorphose Contingent on a Three Parallel SOA-MZIs Copula
by Hassan Termos, Ali Tharthar and Ali Mansour
Optics 2023, 4(1), 55-65; https://doi.org/10.3390/opt4010005 - 17 Jan 2023
Cited by 1 | Viewed by 1125
Abstract
In this treatise, we develop a standard modulation design to consummate concomitant frequency up mixing dependent on the three parallel SOA-MZIs by employing a sampling arrangement in Virtual Photonics Inc. (VPI) software. Each SOA-MZI is used to acquire a frequency output sampled signal [...] Read more.
In this treatise, we develop a standard modulation design to consummate concomitant frequency up mixing dependent on the three parallel SOA-MZIs by employing a sampling arrangement in Virtual Photonics Inc. (VPI) software. Each SOA-MZI is used to acquire a frequency output sampled signal at higher frequencies. Then, the amalgamation of these three mixed signals leads to a simultaneous up-conversion procedure. The peak and positive conversion gains (CGs) are compassed with the SOA-MZIs connected in parallel for frequency mixing for higher frequencies of data signals from 0.5 to 98 GHz, 1 to 98.5 GHz, and 1.5 to 99 GHz, concurrently, which are in connection with the control signal at the frequency of the fifth harmonic. Moreover, we assess the worth of the performance characterizations of the mixing system using orthogonal frequency division multiplexing (OFDM) complex modulated signals. This novel three parallel SOA-MZIs system is completed for the first time in order to achieve frequency transformation to higher frequencies. The numerically calculated CG, error vector magnitude (EVM), and bit error rate (BER) values are in exceptional concurrence with those procured through the VPI simulator. The upper bit rate that concurs the forward error correction (FEC) confines is 2 Gbit/s for OFDM modulations. The three parallel SOA-MZIs setup leads to well-recognized results and it is deemed as a superb system due to its good achievement. Subsequently, this system is analyzed in order to contrast with our previous systems based on a signal SOA-MZI and a cascaded SOA-MZIs link. Furthermore, this comparison shows that the three parallel SOA-MZIs system has perfect efficiency and quality. Full article
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16 pages, 12218 KiB  
Article
Active Optics—Progress in Modeling of Tulip-like Variable Curvature Mirrors
by Gerard R. Lemaitre, Pascal Vola and Patrick Lanzoni
Optics 2023, 4(1), 39-54; https://doi.org/10.3390/opt4010004 - 13 Jan 2023
Viewed by 1266
Abstract
We present new results obtained from the modeling of a tulip-like variable curvature mirror (VCM) in the case of a central force that reacts to its contour. From Nastran finite element analysis, we shows that 3-D optimizations, using non-linear static flexural option, with [...] Read more.
We present new results obtained from the modeling of a tulip-like variable curvature mirror (VCM) in the case of a central force that reacts to its contour. From Nastran finite element analysis, we shows that 3-D optimizations, using non-linear static flexural option, with an appropriate solution sequence, provide an accurate tulip-like VCM thickness distribution. This allows us to take into account boundary conditions, including the thin outer collarette and its link to a rigid ring. Modeling with a quenched stainless steel chromium substrate provides diffraction-limited optical surfaces. Rayleigh’s quarter-wave criterion is performed over a zoom range from flat up to f/3.5 convexity over a 13 mm clear aperture and 10 daN central force. The optical testing results of a prototype tulip-like VCM elaborated from the previous analytic theory, show quasi-diffraction-limited figures for a zoom range up to f/5. The present modeling results should significantly help in the future construction of such VCMs with a zoom range extended up to f/3.5. Full article
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26 pages, 7157 KiB  
Review
Recent Progress in Short and Mid-Infrared Single-Photon Generation: A Review
by Arianna Elefante, Stefano Dello Russo, Fabrizio Sgobba, Luigi Santamaria Amato, Deborah Katia Pallotti, Daniele Dequal and Mario Siciliani de Cumis
Optics 2023, 4(1), 13-38; https://doi.org/10.3390/opt4010003 - 12 Jan 2023
Cited by 3 | Viewed by 3020
Abstract
The generation of single photons in the mid-infrared spectral region is attracting the interest of scientific and technological research, motivated by the potential improvements that many important and emerging applications, such as quantum sensing, metrology and communication, could benefit from. This review reports [...] Read more.
The generation of single photons in the mid-infrared spectral region is attracting the interest of scientific and technological research, motivated by the potential improvements that many important and emerging applications, such as quantum sensing, metrology and communication, could benefit from. This review reports the progress in short and mid-infrared single photon generation, focusing on probabilistic sources based on the two non-linear processes of spontaneous parametric downconversion (SPDC) and four wave mixing (FWM). On one hand, numerical simulations of mid-infrared SPDC are described as a powerful tool to assist and guide the experimental realization, along with the implementation and engineering of novel non-linear materials. On the other hand, the advantages offered by FWM in silicon waveguides in terms of integration, miniaturization and manufacturability are presented, providing an optimal technology for integrated quantum applications. Full article
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2 pages, 185 KiB  
Editorial
Acknowledgment to the Reviewers of Optics in 2022
by Optics Editorial Office
Optics 2023, 4(1), 11-12; https://doi.org/10.3390/opt4010002 - 11 Jan 2023
Viewed by 759
Abstract
High-quality academic publishing is built on rigorous peer review [...] Full article
10 pages, 3362 KiB  
Communication
Spectral Optical Properties of Gray Matter in Human Male Brain Tissue Measured at 400–1100 nm
by Jamal H. Ali
Optics 2023, 4(1), 1-10; https://doi.org/10.3390/opt4010001 - 21 Dec 2022
Cited by 2 | Viewed by 2237
Abstract
Gray matter, in the outermost layer of the cerebral cortex, plays a significant role in processing important information, such as when reasoning and planning, in addition to influencing intelligence, emotion, memory, and language. In this paper, measurements of the optical properties, such as [...] Read more.
Gray matter, in the outermost layer of the cerebral cortex, plays a significant role in processing important information, such as when reasoning and planning, in addition to influencing intelligence, emotion, memory, and language. In this paper, measurements of the optical properties, such as the attenuation coefficients, scattering coefficients, scattering efficiency, and penetration depth of gray matter in the cerebral cortex were measured in the fresh brain tissue of a healthy human male at a spectral range of 400–1100 nm. Determining the optical properties of gray matter is important for developing NIR noninvasive diagnostic imaging techniques and therapy. The absorption spectra of the gray matter tissues obtained here showed clear peaks at 550 and 580 nm due to HBO2 and 970 nm due to water. The attenuation coefficient, transport length, and penetration depth for the gray matter were measured at 800 nm. The possible NIR optical imaging depth was roughly 3.8 mm, determined by the theoretical limit resulting from ballistic and snake photons. Using Beer’s law and the Mie model, the structural properties, such as the density of neurons, in the gray matter of human brain tissue, were investigated for the first time. The density of neurons in the examined gray matter tissue sample was estimated as roughly 40,000 neurons/mg. Full article
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