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Photonics, Volume 8, Issue 12 (December 2021) – 70 articles

Cover Story (view full-size image): Quantum entanglement is a cornerstone of upcoming quantum technologies such as quantum computation and quantum cryptography. The topics of particular interest are complex quantum states with more than two particles and a large number of entangled quantum levels. As it is usually impossible to reconstruct an experimental setup that produces such states, searching for interesting experiments requires the random simulation of millions of setups and calculation of the respective output states. In this work, we show that machine learning models can provide significant improvements over random searching, since an LSTM neural network can learn to model quantum experiments by predicting output state characteristics for given setups. This approach not only allows for a faster search, but is an essential step towards the automated design of multiparticle, high-dimensional quantum experiments. View this paper
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14 pages, 7063 KiB  
Article
Step Surface Profile Measurement Based on Fringe Projection Phase-Shifting Using Selective Sampling
by Songsong Zhang and Haisong Huang
Photonics 2021, 8(12), 592; https://doi.org/10.3390/photonics8120592 - 20 Dec 2021
Cited by 1 | Viewed by 2350
Abstract
Fringe projection is a non-contact optical method that is widely used in the optical precision measurement of complex stepped surfaces. However, the accuracy of the fringe phase extraction employed has a direct impact on the measurement precision of the surface shape. Where phase-shifting [...] Read more.
Fringe projection is a non-contact optical method that is widely used in the optical precision measurement of complex stepped surfaces. However, the accuracy of the fringe phase extraction employed has a direct impact on the measurement precision of the surface shape. Where phase-shifting measurement is used, the classical equal step phase extraction algorithm can only be used to measure simple and smooth surfaces, and leads to measurement errors on complex stepped surfaces, which affects the accuracy of the phase extraction. In addition, the iterative process lasts for a long time, resulting in a low efficiency. This paper proposes a step-by-step phase-shifting extraction algorithm based on selective sampling to measure the contour of the stepped surface. Firstly, the fringe pattern is sampled at equal intervals to reduce the iterative calculation time. Finally, the accurate measurement phase is calculated by the alternating iteration method. The phase extraction accuracy and iteration times are compared in experimental measurements between classical iterative algorithms such as four-step phase-shifting algorithms and the variable phase shift phase interpolation algorithm based on selective sampling. It is shown that the variable frequency phase-shifting extraction algorithm based on selective sampling has a shorter operation time, smaller error, and higher accuracy than the traditional iterative algorithm in fringe projection measuring complex stepped surfaces. Full article
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26 pages, 4960 KiB  
Review
Optical Phenomena in Mesoscale Dielectric Particles
by Oleg V. Minin and Igor V. Minin
Photonics 2021, 8(12), 591; https://doi.org/10.3390/photonics8120591 - 19 Dec 2021
Cited by 40 | Viewed by 3511
Abstract
During the last decade, new unusual physical phenomena have been discovered in studying the optics of dielectric mesoscale particles of an arbitrary three-dimensional shape with the Mie size parameter near 10 (q~10). The paper provides a brief overview of these phenomena [...] Read more.
During the last decade, new unusual physical phenomena have been discovered in studying the optics of dielectric mesoscale particles of an arbitrary three-dimensional shape with the Mie size parameter near 10 (q~10). The paper provides a brief overview of these phenomena from optics to terahertz, plasmonic and acoustic ranges. The different particle configurations (isolated, regular or Janus) are discussed, and the possible applications of such mesoscale structures are briefly reviewed herein in relation to the field enhancement, nanoparticle manipulation and super-resolution imaging. The number of interesting applications indicates the appearance of a new promising scientific direction in optics, terahertz and acoustic ranges, and plasmonics. This paper presents the authors’ approach to these problems. Full article
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12 pages, 4162 KiB  
Article
Output Pulse Characteristics of a Mamyshev Fiber Oscillator
by Haili Han, Nan-Kuang Chen, Liqiang Zhang, Yanru Xie, Zhen Tian, Yicun Yao, Yuanchuan Huang and Xia Zhang
Photonics 2021, 8(12), 590; https://doi.org/10.3390/photonics8120590 - 18 Dec 2021
Cited by 5 | Viewed by 2489
Abstract
The dependence of the output pulse characteristics of a Mamyshev fiber oscillator on cavity parameters is investigated in detail. We analyze the change in pulse spectrum bandwidth, pulse duration, dechirped pulse duration and chirp with the change in fiber group velocity dispersion, fiber [...] Read more.
The dependence of the output pulse characteristics of a Mamyshev fiber oscillator on cavity parameters is investigated in detail. We analyze the change in pulse spectrum bandwidth, pulse duration, dechirped pulse duration and chirp with the change in fiber group velocity dispersion, fiber nonlinearity, gain, and filters by putting forward a numerical model. In particular, as one of the most important components, the effect of filters bandwidth and the central wavelength interval between them is discussed. The passive fibers are classified into two kinds according to their locations in the cavity, which are the one before the gain fiber and the one after the gain fiber. Numerical simulation results show that a wide spectrum can be obtained by increasing the nonlinearity of the second passive fiber, while the change in nonlinearity of the first passive fiber has a weak effect on spectrum broadening. A wide spectrum could also be obtained by increasing the nonlinearity or the small-signal gain coefficient of the gain fiber. A Yb-doped Mamyshev fiber oscillator is demonstrated. The results show the increase in pump power, which agrees reasonably well with the numerical simulation results. Full article
(This article belongs to the Special Issue Mode Locked Fiber Laser)
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29 pages, 5984 KiB  
Article
Thermal Fringe Formation during a Hologram Recording Using a Dry Photopolymer
by Friedrich-Karl Bruder, Thomas Fäcke and Thomas Rölle
Photonics 2021, 8(12), 589; https://doi.org/10.3390/photonics8120589 - 18 Dec 2021
Cited by 2 | Viewed by 2103
Abstract
In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe [...] Read more.
In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe formation. This deformation is caused mainly by the one-sided heating of the recording element, namely, the dry photopolymer–recording plate stack. It turned out that the main source for this heating was the heat of polymerization in the dry photopolymer released during the exposure interval. These insights were translated into a physical model with which quantitative predictions about thermal fringe formation can be made depending on the actual HOE recording geometry, recording conditions and characteristics of the dry photopolymer. Using this model, different types of large size HOEs, used as components to generate a steerable confined view box for a 23” diagonal size display demonstrator, could be recorded successfully without thermal fringe formation. Key strategies to avoid thermal fringe formation deduced from this model include balancing the ratio of lateral recording plate dimension R to its thickness h, recording the power density P or equivalently the exposure time texp at a fixed recording dosage E, and most importantly recording the the linear coefficient of thermal expansion (CTE) of the recording plate material. Suitable glass plates with extremely low CTE were identified and used for recording of the above-mentioned HOEs. Full article
(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)
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13 pages, 5064 KiB  
Article
Force Dependent Quantum Phase Transition in the Hybrid Optomechanical System
by Lingchao Li and Jian-Qi Zhang
Photonics 2021, 8(12), 588; https://doi.org/10.3390/photonics8120588 - 18 Dec 2021
Cited by 1 | Viewed by 1872
Abstract
The optomechanics shows a great potential in quantum control and precise measurement due to appropriate mechanical control. Here we theoretically study the quantum phase transition in a hybrid atom-optomechanical cavity with an external force. Our study shows, in the thermodynamic limit, the critical [...] Read more.
The optomechanics shows a great potential in quantum control and precise measurement due to appropriate mechanical control. Here we theoretically study the quantum phase transition in a hybrid atom-optomechanical cavity with an external force. Our study shows, in the thermodynamic limit, the critical value of quantum phase transition between the normal phase and super-radiant phase can be controlled and modified by the external force via the tunable frequency of optomechanics, then a force dependent quantum phase transition can be achieved in our system. Moreover, this force dependent quantum phase transition can be employed to detect the external force variation. In addition, our numerical simulations illustrate the sensitivity of the external force measurement can be improved by the squeezing properties of the quantum phase transition. Full article
(This article belongs to the Special Issue Optomechanics: Science and Applications)
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10 pages, 1670 KiB  
Article
Raman Spectroscopy Enables Non-Invasive Identification of Mycotoxins p. Fusarium of Winter Wheat Seeds
by Maksim N. Moskovskiy, Aleksey V. Sibirev, Anatoly A. Gulyaev, Stanislav A. Gerasimenko, Sergey I. Borzenko, Maria M. Godyaeva, Oleg V. Noy, Egor I. Nagaev, Tatiana A. Matveeva, Ruslan M. Sarimov and Alexander V. Simakin
Photonics 2021, 8(12), 587; https://doi.org/10.3390/photonics8120587 - 17 Dec 2021
Cited by 4 | Viewed by 2383
Abstract
Identification of specific mycotoxins p. Fusarium contained in infected winter wheat seeds can be achieved by visually recognizing their distinctive phenotypic species. The visual identification (ID) of species is subjective and usually requires significant taxonomic knowledge. Methods for the determination of various types [...] Read more.
Identification of specific mycotoxins p. Fusarium contained in infected winter wheat seeds can be achieved by visually recognizing their distinctive phenotypic species. The visual identification (ID) of species is subjective and usually requires significant taxonomic knowledge. Methods for the determination of various types of mycotoxins of the p. Fusarium are laborious and require the use of chemical invasive research methods. In this research, we investigate the possibility of using Raman spectroscopy (RS) as a tag-free, non-invasive and non-destructive analytical method for the rapid and accurate identification of p. Fusarium. Varieties of the r. Fusarium can produce mycotoxins that directly affect the DNA, RNA and chemical structure of infected seeds. Analysis of spectra by RS methods and chemometric analysis allows the identification of healthy, infected and contaminated seeds of winter wheat with varieties of mycotoxins p. Fusarium. Raman seed analysis provides accurate identification of p. Fusarium in 96% of samples. In addition, we present data on the identification of carbohydrates, proteins, fiber and other nutrients contaminated with p. Fusarium seeds obtained using spectroscopic signatures. These results demonstrate that RS enables rapid, accurate and non-invasive screening of seed phytosanitary status. Full article
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9 pages, 2594 KiB  
Communication
Photonic Nanojet Generation Using Integrated Silicon Photonic Chip with Hemispherical Structures
by Aneesh Vincent Veluthandath and Ganapathy Senthil Murugan
Photonics 2021, 8(12), 586; https://doi.org/10.3390/photonics8120586 - 17 Dec 2021
Cited by 3 | Viewed by 2117
Abstract
Photonic nanojet (PNJ) is a tightly focused diffractionless travelling beam generated by dielectric microparticles. The location of the PNJ depends on the refractive index of the material and it usually recedes to the interior of the microparticle when the refractive index is higher [...] Read more.
Photonic nanojet (PNJ) is a tightly focused diffractionless travelling beam generated by dielectric microparticles. The location of the PNJ depends on the refractive index of the material and it usually recedes to the interior of the microparticle when the refractive index is higher than 2, making high index materials unsuitable to produce useful PNJs while high index favours narrower PNJs. Here we demonstrate a design of CMOS compatible high index on-chip photonic nanojet based on silicon. The proposed design consists of a silicon hemisphere on a silicon substrate. The PNJs generated can be tuned by changing the radius and sphericity of the hemisphere. Oblate spheroids generate PNJs further away from the refracting surface and the PNJ length exceeds 17λ when the sphericity of the spheroid is 2.25 The proposed device can have potential applications in focal plane arrays, enhanced Raman spectroscopy, and optofluidic chips. Full article
(This article belongs to the Section Optoelectronics and Optical Materials)
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22 pages, 6551 KiB  
Article
Holographic Optical Lenses Recorded on a Glassy Matrix-Based Photopolymer for Solar Concentrators
by Maria Antonietta Ferrara, Fabio Borbone and Giuseppe Coppola
Photonics 2021, 8(12), 585; https://doi.org/10.3390/photonics8120585 - 17 Dec 2021
Cited by 3 | Viewed by 2269
Abstract
Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a [...] Read more.
Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a half is enough to meet the world’s electricity consumption for a complete year. Generally, solar concentrators are used to collect the solar radiation and to concentrate it at a single focal point. These devices consist in a set of mirrors or mechanical structures to reduce the area of a photovoltaic cell, which is typically very expensive. Volume transmission phase holographic optical elements could be opportunely designed and realized to obtain a simple, lightweight, compact and inexpensive planar solar concentrator. With the aim of bringing scientific attention to this still developing topic, in this work we critically report a complete investigation on a new photopolymeric material obtained by sol-gel reactions used as possible recording material for volume holographic solar concentrators; as a proof of concept, both terrestrial and extreme environments, such as space, are considered as potential applications. Full article
(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)
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24 pages, 63776 KiB  
Article
Parametric Mid-Spatial Frequency Surface Error Synthesis
by Timothy Hefferan, Logan Graves, Isaac Trumper, Soojong Pak and Daewook Kim
Photonics 2021, 8(12), 584; https://doi.org/10.3390/photonics8120584 - 16 Dec 2021
Viewed by 2068
Abstract
Standard mid-spatial frequency tooling mark errors were parameterized into a series of characteristic features and systematically investigated. Diffraction encircled and ensquared energy radii at the 90% levels from an unpowered optical surface were determined as a function of the root-mean-square surface irregularity, characteristic [...] Read more.
Standard mid-spatial frequency tooling mark errors were parameterized into a series of characteristic features and systematically investigated. Diffraction encircled and ensquared energy radii at the 90% levels from an unpowered optical surface were determined as a function of the root-mean-square surface irregularity, characteristic tooling mark parameters, fold mirror rotation angle, and incident beam f-number. Tooling mark frequencies on the order of 20 cycles per aperture or less were considered. This subset encompasses small footprints on single-point diamond turned optics or large footprints on sub-aperture tool polished optics. Of the characteristic features, off-axis fabrication distance held the highest impact to encircled and ensquared energy radii. The transverse oscillation of a tooling path was found to be the second highest contributor. Both impacts increased with radial tooling mark frequency. Full article
(This article belongs to the Special Issue Advances in Optical Metrology)
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10 pages, 3968 KiB  
Communication
Monolithic, Optically Coupled, Multi-Section Mid-IR Quantum Cascade Lasers
by Kamil Pierściński, Dorota Pierścińska, Grzegorz Sobczak, Aleksandr Kuźmicz, Krzysztof Chmielewski, Katarzyna Krajewska and Piotr Gutowski
Photonics 2021, 8(12), 583; https://doi.org/10.3390/photonics8120583 - 16 Dec 2021
Viewed by 2323
Abstract
Mid-infrared (mid-IR λ ≈ 3–12 μm), single-mode-emission Quantum Cascade Lasers (QCLs) are of significant interest for a wide range of applications, especially as the laser sources are chosen for laser absorption spectroscopy. In this work, we present the design, fabrication and characterization of [...] Read more.
Mid-infrared (mid-IR λ ≈ 3–12 μm), single-mode-emission Quantum Cascade Lasers (QCLs) are of significant interest for a wide range of applications, especially as the laser sources are chosen for laser absorption spectroscopy. In this work, we present the design, fabrication and characterization of multi-section, coupled-cavity, mid-IR quantum cascade lasers. The purpose of this work is to propose a design modification for a coupled-cavity device, yielding a single-mode emission with a longer range of continuous tuning during the pulse, in contrast to a 2-section device. This effect was obtained and demonstrated in the work. The proposed design of a 3-section coupled-cavity QCL allows for a single-mode emission with 35 dB side-mode suppression ratio. Additionally, the time-resolved spectra of the wavelength shift during pulse operation, show a continuous tuning of ~3 cm−1 during the 2 μs pulse. The devices were fabricated in a slightly modified, standard laser process using dry etching. Full article
(This article belongs to the Section Lasers, Light Sources and Sensors)
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27 pages, 2485 KiB  
Review
Application of Reflectance Indices for Remote Sensing of Plants and Revealing Actions of Stressors
by Anastasiia Kior, Vladimir Sukhov and Ekaterina Sukhova
Photonics 2021, 8(12), 582; https://doi.org/10.3390/photonics8120582 - 16 Dec 2021
Cited by 25 | Viewed by 4017
Abstract
Environmental conditions are very changeable; fluctuations in temperature, precipitation, illumination intensity, and other factors can decrease a plant productivity and crop. The remote sensing of plants under these conditions is the basis for the protection of plants and increases their survivability. This problem [...] Read more.
Environmental conditions are very changeable; fluctuations in temperature, precipitation, illumination intensity, and other factors can decrease a plant productivity and crop. The remote sensing of plants under these conditions is the basis for the protection of plants and increases their survivability. This problem can be solved through measurements of plant reflectance and calculation of reflectance indices. Reflectance indices are related to the vegetation biomass, specific physiological processes, and biochemical compositions in plants; the indices can be used for both short-term and long-term plant monitoring. In our review, we considered the applications of reflectance indices in plant remote sensing. In Optical Methods and Platforms of Remote Sensing of Plants, we briefly discussed multi- and hyperspectral imaging, including descriptions of multispectral and hyperspectral cameras with different principles and their efficiency for the remote sensing of plants. In Main Reflectance Indices, we described the main reflectance indices, including vegetation, water, and pigment reflectance indices, as well as the photochemical reflectance index and its modifications. We focused on the relationships of leaf reflectance and reflectance indices to plant biomass, development, and physiological and biochemical characteristics. In Problems of Measurement and Analysis of Reflectance Indices, we discussed the methods of the correction of the reflectance indices that can be used for decreasing the influence of environmental conditions (mainly illumination, air, and soil) and plant characteristics (orientation of leaves, their thickness, and others) on their measurements and the analysis of the plant remote sensing. Additionally, the variability of plants was also considered as an important factor that influences the results of measurement and analysis. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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12 pages, 21541 KiB  
Communication
A High Precision Fiber Optic Fabry–Perot Pressure Sensor Based on AB Epoxy Adhesive Film
by Yanan Zhang, Shubin Zhang, Haitao Gao, Danping Xu, Zhuozhen Gao, Zheyu Hou, Jian Shen and Chaoyang Li
Photonics 2021, 8(12), 581; https://doi.org/10.3390/photonics8120581 - 16 Dec 2021
Cited by 11 | Viewed by 2022
Abstract
This paper proposes a Fabry–Perot pressure sensor based on AB epoxy adhesive with ultra-high sensitivity under low pressure. Fabry–Perot interference, located between single-mode fiber (SMF) and hollow-core fiber (HCF), is an ultra-thin AB epoxy film formed by capillary action. Then the thick HCF [...] Read more.
This paper proposes a Fabry–Perot pressure sensor based on AB epoxy adhesive with ultra-high sensitivity under low pressure. Fabry–Perot interference, located between single-mode fiber (SMF) and hollow-core fiber (HCF), is an ultra-thin AB epoxy film formed by capillary action. Then the thick HCF was used to fix the HCF and SMF at both ends with AB epoxy adhesive. Experimental results show that when the thickness of AB epoxy film is 8.74 μm, and the cavity length is 30 μm, the sensor has the highest sensitivity. The sensitivity is 257.79 nm/MPa within the pressure range of 0–70 kPa. It also investigated the influence of the curing time of AB epoxy on the interference spectrum. Experiments showed that the interference spectrum peak is blue-shifted with the increase of curing time. Our study also demonstrated the humidity stability of this pressure sensor. These characteristics mean that our sensor has potential applications in the biomedical field and ocean exploration. Full article
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23 pages, 5825 KiB  
Article
Numerical Simulation of Enhancement of Superficial Tumor Laser Hyperthermia with Silicon Nanoparticles
by Olga I. Sokolovskaya, Ekaterina A. Sergeeva, Leonid A. Golovan, Pavel K. Kashkarov, Aleksandr V. Khilov, Daria A. Kurakina, Natalia Y. Orlinskaya, Stanislav V. Zabotnov and Mikhail Y. Kirillin
Photonics 2021, 8(12), 580; https://doi.org/10.3390/photonics8120580 - 15 Dec 2021
Cited by 8 | Viewed by 3116
Abstract
Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in [...] Read more.
Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in water and ethanol as agents for laser tumor hyperthermia, we numerically simulated effects of heating a millimeter-size nodal basal-cell carcinoma with embedded nanoparticles by continuous-wave laser radiation at 633 nm. Based on scanning electron microscopy data for the synthesized SiNPs size distributions, we used Mie theory to calculate their optical properties and carried out Monte Carlo simulations of light absorption inside the tumor, with and without the embedded nanoparticles, followed by an evaluation of local temperature increase based on the bioheat transfer equation. Given the same mass concentration, SiNPs obtained by the laser ablation of silicon nanowires in ethanol (eSiNPs) are characterized by smaller absorption and scattering coefficients compared to those synthesized in water (wSiNPs). In contrast, wSiNPs embedded in the tumor provide a lower overall temperature increase than eSiNPs due to the effect of shielding the laser irradiation by the highly absorbing wSiNPs-containing region at the top of the tumor. Effective tumor hyperthermia (temperature increase above 42 °C) can be performed with eSiNPs at nanoparticle mass concentrations of 3 mg/mL and higher, provided that the neighboring healthy tissues remain underheated at the applied irradiation power. The use of a laser beam with the diameter fitting the size of the tumor allows to obtain a higher temperature contrast between the tumor and surrounding normal tissues compared to the case when the beam diameter exceeds the tumor size at the comparable power. Full article
(This article belongs to the Special Issue Topical Problems of Biophotonics)
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10 pages, 4291 KiB  
Communication
Multi-Lane Mirror for Broadband Applications of the Betatron X-ray Source
by Marek Raclavský, Krishna P. Khakurel, Uddhab Chaulagain, Marcel Lamač and Jaroslav Nejdl
Photonics 2021, 8(12), 579; https://doi.org/10.3390/photonics8120579 - 15 Dec 2021
Cited by 5 | Viewed by 2676
Abstract
A new generation of small-scale ultrafast X-ray sources is rapidly emerging. Laser-driven betatron radiation represents an important class of such ultrafast X-ray sources. With the sources driving towards maturity, many important applications in material and biological sciences are expected to be carried out. [...] Read more.
A new generation of small-scale ultrafast X-ray sources is rapidly emerging. Laser-driven betatron radiation represents an important class of such ultrafast X-ray sources. With the sources driving towards maturity, many important applications in material and biological sciences are expected to be carried out. While the last decade mainly focused on the optimization of the source properties, the development of such sources into user-oriented beamlines in order to explore the potential applications has recently taken off and is expected to grow rapidly. An important aspect in the realization of such beamlines will be the implementation of proper X-ray optics. Here, we present the design of a multi-lane X-ray mirror as a versatile focusing device covering a wide spectral range of betatron X-rays. The expected photon flux in the focal plane of such optics was also estimated through geometrical simulations. Full article
(This article belongs to the Special Issue Advances in X-ray Optics)
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9 pages, 13411 KiB  
Article
Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD
by Manijeh Razeghi, Junhee Lee, Lakshay Gautam, Jean-Pierre Leburton, Ferechteh H. Teherani, Pedram Khalili Amiri, Vinayak P. Dravid and Dimitris Pavlidis
Photonics 2021, 8(12), 578; https://doi.org/10.3390/photonics8120578 - 14 Dec 2021
Cited by 6 | Viewed by 2445
Abstract
Gallium oxide (Ga2O3) thin films of various thicknesses were grown on sapphire (0001) substrates by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa), high purity deionized water, and silane (SiH4) as gallium, oxygen, and silicon precursors, [...] Read more.
Gallium oxide (Ga2O3) thin films of various thicknesses were grown on sapphire (0001) substrates by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa), high purity deionized water, and silane (SiH4) as gallium, oxygen, and silicon precursors, respectively. N2 was used as carrier gas. Hall measurements revealed that films grown with a lower VI/III ratio had a dominant p-type conduction with room temperature mobilities up to 7 cm2/Vs and carrier concentrations up to ~1020 cm−3 for thinner layers. High resolution transmission electron microscopy suggested that the layers were mainly κ phase. Microstrip field-effect transistors (FETs) were fabricated using 2D p-type Ga2O3:Si, channels. They achieved a maximum drain current of 2.19 mA and an on/off ratio as high as ~108. A phenomenological model for the p-type conduction was also presented. As the first demonstration of a p-type Ga2O3, this work represents a significant advance which is state of the art, which would allow the fabrication of p-n junction based devices which could be smaller/thinner and bring both cost (more devices/wafer and less growth time) and operating speed (due to miniaturization) advantages. Moreover, the first scaling down to 2D device channels opens the prospect of faster devices and improved heat evacuation. Full article
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12 pages, 17615 KiB  
Article
Laser 3D Printing of Inorganic Free-Form Micro-Optics
by Diana Gonzalez-Hernandez, Simonas Varapnickas, Greta Merkininkaitė, Arūnas Čiburys, Darius Gailevičius, Simas Šakirzanovas, Saulius Juodkazis and Mangirdas Malinauskas
Photonics 2021, 8(12), 577; https://doi.org/10.3390/photonics8120577 - 14 Dec 2021
Cited by 33 | Viewed by 5082
Abstract
A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the [...] Read more.
A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the heat-treatment results in converting the material to inorganic substances. The produced miniature optical elements are characterized and their optical performance is demonstrated. Finally, the concept is validated for manufacturing compound optical components such as stacked lenses. This is an opening for new directions and applications of laser-made micro-optics under harsh conditions such as high intensity radiation, temperature, acidic environment, pressure variations, which include open space, astrophotonics, and remote sensing. Full article
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11 pages, 4079 KiB  
Article
Dual-Band, Polarization-Insensitive, Ultrathin and Flexible Metamaterial Absorber Based on High-Order Magnetic Resonance
by Duong Thi Ha, Bui Son Tung, Bui Xuan Khuyen, Thanh Son Pham, Nguyen Thanh Tung, Nguyen Hoang Tung, Nguyen Thi Hoa, Vu Dinh Lam, Haiyu Zheng, Liangyao Chen and YoungPak Lee
Photonics 2021, 8(12), 574; https://doi.org/10.3390/photonics8120574 - 14 Dec 2021
Cited by 10 | Viewed by 2258
Abstract
We demonstrate a dual-band, polarization-insensitive, ultrathin and flexible metamaterial absorber (MA), based on high-order magnetic resonance. By exploiting a flexible polyimide substrate, the thickness of MA came to be 1/148 of the working wavelength. The absorption performance of the proposed structure was investigated [...] Read more.
We demonstrate a dual-band, polarization-insensitive, ultrathin and flexible metamaterial absorber (MA), based on high-order magnetic resonance. By exploiting a flexible polyimide substrate, the thickness of MA came to be 1/148 of the working wavelength. The absorption performance of the proposed structure was investigated for both planar and bending models. In the case of the planar model, a single peak was achieved at a frequency of 4.3 GHz, with an absorption of 98%. Furthermore, additional high-order absorption peaks were obtained by the bending structure on a cylindrical surface, while the fundamental peak with a high absorption was maintained well. Our work might be useful for the realization and the development of future devices, such as emitters, detectors, sensors, and energy converters. Full article
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12 pages, 7962 KiB  
Article
A Smartphone-Based Detection Method of Colloidal Gold Immunochromatographic Strip
by Shiqun Jin, Lihao Bai, Guo Xia, Long Ma, Jiangtao Wang, Zhiming Li and Fei Cai
Photonics 2021, 8(12), 576; https://doi.org/10.3390/photonics8120576 - 13 Dec 2021
Viewed by 2386
Abstract
The outbreak of the new coronavirus (SARS-CoV-2) infection has become a global public health crisis. Antigen detection strips (colloidal gold) can be widely used in novel coronavirus clinical screening and can even be extended to home self-testing, which provides a practical and effective [...] Read more.
The outbreak of the new coronavirus (SARS-CoV-2) infection has become a global public health crisis. Antigen detection strips (colloidal gold) can be widely used in novel coronavirus clinical screening and can even be extended to home self-testing, which provides a practical and effective way for people to obtain health status information away from the crowd. In this paper, a colloidal gold detection system without complex devices is proposed, which is based on smartphone usage along with a mobile-phone software embedded with normalization algorithms and a special designed background paper. The basic principle of the device relies on image processing. First, the data of the green channel of the image captured by a smartphone are selected to be processed. Second, the calibration curves are established using standard black and white card, and the calibration values under different detection environments are obtained by calibration curves. Finally, to verify the validity of the proposed method, various standard solutions with different concentrations are tested. Results show that this method can eliminate the influence of different environments on the test results, the test results in different detection environments have good stability and the variation coefficients are less than 5%. It fully proves that the detection system designed in this paper can detect the result of colloidal gold immunochromatographic strip in time, conveniently and accurately in different environments. Full article
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11 pages, 2209 KiB  
Article
Optical Pump–Terahertz Probe Study of HR GaAs:Cr and SI GaAs:EL2 Structures with Long Charge Carrier Lifetimes
by Irina A. Kolesnikova, Daniil A. Kobtsev, Ruslan A. Redkin, Vladimir I. Voevodin, Anton V. Tyazhev, Oleg P. Tolbanov, Yury S. Sarkisov, Sergey Yu. Sarkisov and Victor V. Atuchin
Photonics 2021, 8(12), 575; https://doi.org/10.3390/photonics8120575 - 13 Dec 2021
Cited by 6 | Viewed by 2099
Abstract
The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various [...] Read more.
The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of surface and volume Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that, in most cases for HR GaAs:Cr and SI GaAs:EL2, Auger recombination mechanisms make the largest contribution to the recombination rate of nonequilibrium charge carriers at injection levels above ~(0.5–3)·1018 cm−3, typical of pump–probe experiments. At a lower photogenerated charge carrier concentration, the SRH recombination prevails. The derived charge carrier lifetimes, due to the SRH recombination, are approximately 1.5 and 25 ns in HR GaAs:Cr and SI GaAs:EL2, respectively. These values are closer to but still lower than the values determined by photoluminescence decay or charge collection efficiency measurements at low injection levels. The obtained results indicate the importance of a proper experimental data analysis when applying terahertz time-resolved spectroscopy to the determination of charge carrier lifetimes in semiconductor crystals intended for the fabrication of devices working at lower injection levels than those at measurements by the optical pump–terahertz probe technique. It was found that the charge carrier lifetime in HR GaAs:Cr is lower than that in SI GaAs:EL2 at injection levels > 1016 cm−3. Full article
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10 pages, 3552 KiB  
Article
Improving Multiphoton Microscopy by Combining Spherical Aberration Patterns and Variable Axicons
by Juan M. Bueno, Geovanni Hernández, Martin Skorsetz and Pablo Artal
Photonics 2021, 8(12), 573; https://doi.org/10.3390/photonics8120573 - 13 Dec 2021
Cited by 1 | Viewed by 1915
Abstract
Multiphoton (MP) microscopy is a well-established method for the non-invasive imaging of biological tissues. However, its optical sectioning capabilities are reduced due to specimen-induced aberrations. Both the manipulation of spherical aberration (SA) and the use of axicons have been reported to be useful [...] Read more.
Multiphoton (MP) microscopy is a well-established method for the non-invasive imaging of biological tissues. However, its optical sectioning capabilities are reduced due to specimen-induced aberrations. Both the manipulation of spherical aberration (SA) and the use of axicons have been reported to be useful techniques to bypass this limitation. We propose the combination of SA patterns and variable axicons to further improve the quality of MP microscopy images. This approach provides enhanced images at different depth locations whose quality is better than those corresponding to the use of SA or axicons separately. Thus, the procedure proposed herein facilitates the visualization of details and increases the depth observable at high resolution. Full article
(This article belongs to the Special Issue Laser Interaction with Materials)
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13 pages, 3816 KiB  
Article
Spontaneous Emission Enhancement by a Rectangular-Aperture Optical Nanoantenna: An Intuitive Semi-Analytical Model of Surface Plasmon Polaritons
by Xinyue Zhang, Xuelin Zhai, Can Tao, Ning Wang, Ying Zhong and Haitao Liu
Photonics 2021, 8(12), 572; https://doi.org/10.3390/photonics8120572 - 12 Dec 2021
Viewed by 2009
Abstract
The spontaneous-emission enhancement effect of a single metallic rectangular-aperture optical nanoantenna on a SiO2 substrate was investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons (SPPs) in the aperture, an intuitive and comprehensive SPP model was established. The [...] Read more.
The spontaneous-emission enhancement effect of a single metallic rectangular-aperture optical nanoantenna on a SiO2 substrate was investigated theoretically. By considering the excitation and multiple scattering of surface plasmon polaritons (SPPs) in the aperture, an intuitive and comprehensive SPP model was established. The model can comprehensively predict the total spontaneous emission rate, the radiative emission rate and the angular distribution of the far-field emission of a point source in the aperture. Two phase-matching conditions are derived from the model for predicting the resonance and show that the spontaneous-emission enhancement by the antenna comes from the Fabry–Perot resonance of the SPP in the aperture. In addition, when scanning the position of the point source and the aperture length, the SPP model does not need to repeatedly solve the Maxwell’s equations, which shows a superior computational efficiency compared to the full-wave numerical method. Full article
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10 pages, 2128 KiB  
Article
Reduction in DC-Drift in LiNbO3-Based Electro-Optical Modulator
by Aleksei Sosunov, Roman Ponomarev, Anton Zhuravlev, Sergey Mushinsky and Mariana Kuneva
Photonics 2021, 8(12), 571; https://doi.org/10.3390/photonics8120571 - 11 Dec 2021
Cited by 4 | Viewed by 3155
Abstract
This study involves the results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is [...] Read more.
This study involves the results of research on short-term and long-term DC-drifts in electro-optical modulators based on annealed proton exchange waveguides in LiNbO3 crystals after wafer pre-annealing. The relaxation time of the DC-drift of the operating point for a short-term drift is measured in minutes, and for a long-term drift it is measured in hours and days. DC-drift was measured by applying bias voltage and changing crystal temperature. The obtained results show significant impact on the stability of operating point in EO-modulators after treatment of defective structure of the near-surface layer of a LiNbO3 crystal. Treatment of the disturbed near-surface layer of a LiNbO3 crystal results in the simultaneous reduction in short-term DC-drift and increase in operation stability of electro-optical modulators during long-term measurement of temperature by activation energy calculation. Full article
(This article belongs to the Special Issue Photonic Integration: Technologies and Applications)
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16 pages, 2501 KiB  
Article
Maintaining Constant Pulse-Duration in Highly Dispersive Media Using Nonlinear Potentials
by Haider Zia
Photonics 2021, 8(12), 570; https://doi.org/10.3390/photonics8120570 - 11 Dec 2021
Viewed by 1756
Abstract
A method is shown for preventing temporal broadening of ultrafast optical pulses in highly dispersive and fluctuating media for arbitrary signal-pulse profiles. Pulse pairs, consisting of a strong-field control-pulse and a weak-field signal-pulse, co-propagate, whereby the specific profile of the strong-field pulse precisely [...] Read more.
A method is shown for preventing temporal broadening of ultrafast optical pulses in highly dispersive and fluctuating media for arbitrary signal-pulse profiles. Pulse pairs, consisting of a strong-field control-pulse and a weak-field signal-pulse, co-propagate, whereby the specific profile of the strong-field pulse precisely compensates for the dispersive phase in the weak pulse. A numerical example is presented in an optical system consisting of both resonant and gain dispersive effects. Here, we show signal-pulses that do not temporally broaden across a vast propagation distance, even in the presence of dispersion that fluctuates several orders of magnitude and in sign (for example, within a material resonance) across the pulse’s bandwidth. Another numerical example is presented in normal dispersion telecom fiber, where the length at which an ultrafast pulse does not have significant temporal broadening is extended by at least a factor of 10. Our approach can be used in the design of dispersion-less fiber links and navigating pulses in turbulent dispersive media. Furthermore, we illustrate the potential of using cross-phase modulation to compensate for dispersive effects on a signal-pulse and fill the gap in the current understanding of this nonlinear phenomenon. Full article
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10 pages, 2032 KiB  
Article
Soft X-ray Lensless Imaging in Reflection Mode
by Horia Popescu, Franck Fortuna, Renaud Delaunay, Nicolas Jaouen, Carlo Spezzani and Maurizio Sacchi
Photonics 2021, 8(12), 569; https://doi.org/10.3390/photonics8120569 - 11 Dec 2021
Viewed by 2110
Abstract
We report on the development and implementation of methodologies dedicated to soft X-ray imaging by coherent scattering in reflection mode. Two complementary approaches are tested, based on Fourier transform holography and on ptychography. A new method for designing holographic masks has been developed. [...] Read more.
We report on the development and implementation of methodologies dedicated to soft X-ray imaging by coherent scattering in reflection mode. Two complementary approaches are tested, based on Fourier transform holography and on ptychography. A new method for designing holographic masks has been developed. Our results represent a feasibility test and highlight the potential and limitations of imaging in reflection mode. Reflectivity is less efficient than transmission at soft X-ray wavelengths, hampering the acquisition of good quality images. Nonetheless, it has the potential to image a wider set of samples, notably those that are not transparent to soft X-rays. Although the images obtained so far are of modest quality, these results are extremely encouraging for continuing the development of coherent soft X-ray imaging in reflection mode. Full article
(This article belongs to the Special Issue Extreme-Ultraviolet and X-ray Optics)
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24 pages, 2376 KiB  
Review
Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety
by Yuqing Yang, Niamh Creedon, Alan O’Riordan and Pierre Lovera
Photonics 2021, 8(12), 568; https://doi.org/10.3390/photonics8120568 - 10 Dec 2021
Cited by 23 | Viewed by 4438
Abstract
Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such [...] Read more.
Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids. Full article
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15 pages, 4966 KiB  
Article
Fast Optimization Design of the Flexure for a Space Mirror Based on Mesh Deformation
by Fengchang Liu, Wei Li, Weiguo Zhao, Xiaodong Wang and Xiaoyu Wang
Photonics 2021, 8(12), 567; https://doi.org/10.3390/photonics8120567 - 10 Dec 2021
Cited by 2 | Viewed by 2049
Abstract
According to the requirements of high force-thermal stability and high performance of a space telescope, a space mirror assembly must not be influenced by environmental factors. In this study, a space mirror assembly under load conditions, such as gravity, thermal, and assembly error, [...] Read more.
According to the requirements of high force-thermal stability and high performance of a space telescope, a space mirror assembly must not be influenced by environmental factors. In this study, a space mirror assembly under load conditions, such as gravity, thermal, and assembly error, is considered. After the mirror is optimized, the surface shape error is reduced by 22%, and the mass is increased by 0.113 kg. In order to improve the efficiency of integration optimization, we present a fast optimization method using mesh deformation to be applied to the flexure. The size parameters of flexure and axial mount position are obtained by optimization. With our method, the single optimization time reduces from 10 min to 40 s, which can improve the efficiency of multi-objective optimization. The mirror assembly is fabricated and assembled based on optimization results. Finite element analysis (FEA) and test results for the space mirror assembly confirm the validity and feasibility of the fast optimization method, and we believe that the flexure based on fast optimization meets the requirements of a space mirror assembly for space applications. Full article
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45 pages, 7464 KiB  
Review
Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers
by Hossein Fathi, Mikko Närhi and Regina Gumenyuk
Photonics 2021, 8(12), 566; https://doi.org/10.3390/photonics8120566 - 10 Dec 2021
Cited by 18 | Viewed by 11232
Abstract
Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To [...] Read more.
Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers. Full article
(This article belongs to the Special Issue Specialty Optical Fibers, Fiber Lasers and Their Applications)
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23 pages, 1458 KiB  
Review
Power Scaling of CW Crystalline OPOs and Raman Lasers
by Soumya Sarang and Martin Richardson
Photonics 2021, 8(12), 565; https://doi.org/10.3390/photonics8120565 - 10 Dec 2021
Cited by 4 | Viewed by 2809
Abstract
Optical parametric oscillators (OPOs) and Raman lasers are two nonlinear-based laser technologies that extend the spectral range of conventional inversion lasers. Power and brightness scaling of lasers are significant for many applications in industry, medicine, and defense. Considerable advances have been made to [...] Read more.
Optical parametric oscillators (OPOs) and Raman lasers are two nonlinear-based laser technologies that extend the spectral range of conventional inversion lasers. Power and brightness scaling of lasers are significant for many applications in industry, medicine, and defense. Considerable advances have been made to enhance the power and brightness of inversion lasers. However, research around the power scaling of nonlinear lasers is lacking. This paper reviews the development and progress of output power of continuous-wave (CW) crystalline OPOs and Raman lasers. We further evaluate the power scalability of these two laser technologies by analyzing the cavity architectures and gain materials used in these lasers. This paper also discusses why diamond Raman lasers (DRLs) show tremendous potential as a single laser source for generating exceedingly high output powers and high brightness. Full article
(This article belongs to the Special Issue High-Power Lasers and Amplifiers)
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8 pages, 2856 KiB  
Communication
High Operating Temperature InAs/GaSb Superlattice Based Mid Wavelength Infrared Photodetectors Grown by MOCVD
by He Zhu, Jiafeng Liu, Hong Zhu, Yunlong Huai, Meng Li, Zhen Liu and Yong Huang
Photonics 2021, 8(12), 564; https://doi.org/10.3390/photonics8120564 - 10 Dec 2021
Cited by 5 | Viewed by 2477
Abstract
High operating temperature mid-wavelength InAs/GaSb superlattice infrared photodetectors with a single heterojunction structure grown by metal–organic chemical vapor deposition are reported. By inserting a fully-depleted wider-gap barrier layer between the absorber and the p-contact, “diffusion-limited” behavior has been achieved for the heterojunction “PNn” [...] Read more.
High operating temperature mid-wavelength InAs/GaSb superlattice infrared photodetectors with a single heterojunction structure grown by metal–organic chemical vapor deposition are reported. By inserting a fully-depleted wider-gap barrier layer between the absorber and the p-contact, “diffusion-limited” behavior has been achieved for the heterojunction “PNn” device, in contrast to the conventional pin homojunction device. The PNn device with a 50% cutoff wavelength of 4.5 μm exhibited a dark current of 2.05 × 10−4 A/cm2 and a peak specific detectivity of 1.28 × 1011 cm·Hz·W1 at 150 K and a reverse bias of −0.1 V. Full article
(This article belongs to the Special Issue Mid-Infrared Integrated Photonics)
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9 pages, 3481 KiB  
Communication
Improving Calibration Strategy for LIBS Heavy Metals Analysis in Agriculture Applications
by Vasily N. Lednev, Pavel A. Sdvizhenskii, Mikhail Y. Grishin, Evgeny A. Nikitin, Sergey V. Gudkov and Sergey M. Pershin
Photonics 2021, 8(12), 563; https://doi.org/10.3390/photonics8120563 - 09 Dec 2021
Cited by 8 | Viewed by 2039
Abstract
A new calibration procedure, known as mapping conditional-calibration laser-induced breakdown spectroscopy (LIBS), has been suggested to improve analysis results for heterogeneous samples. The procedure is based on LIBS elemental mapping, followed by signal conditioning in every sampling spot to skip signal outliers, then [...] Read more.
A new calibration procedure, known as mapping conditional-calibration laser-induced breakdown spectroscopy (LIBS), has been suggested to improve analysis results for heterogeneous samples. The procedure is based on LIBS elemental mapping, followed by signal conditioning in every sampling spot to skip signal outliers, then by finalizing the calibration curve construction. The suggested mapping conditional calibration procedure was verified for zinc analysis in soybean grist samples. The laser parameters correspond to those of the hand-held LIBS instrument in order to estimate the influence of sample surface heterogeneity under on-site analysis conditions. The laser spot (60 μm) was equal to or smaller than the typical size of grist particles (40–500 μm) but laser crater dimensions were significantly greater and varied widely (150–450 μm). The LIBS mapping of different spectral signals (atomic and ionic lines for major and minor components) was achieved. Elemental maps were normalized to achieve signal maps that were conditionally spotted to skip signal outliers. It was demonstrated that the suggested mapping conditional-calibration LIBS provided 15 ppm RMSECV for zinc determination in heterogeneous samples, which is typical for agricultural products. Full article
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