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A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 36060

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Dr. Paulo A. Ribeiro

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Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
Interests: thin films; functional molecular systems; sensors and transducers; electrical and optical properties of materials; biomedical sciences
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. David Andrews

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School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
Interests: fundamental molecular photonics and energy transport; optomechanical forces and nonlinear optical phenomena
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Dr. Pablo Albella

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Department of Applied Physics, University of Cantabria, 39005 Santander, Spain
Interests: plasmonics; sensing; nanophotonics; light-matter interaction; nanoantennas

Dr. Maria Raposo

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Guest Editor

Laboratory for Instrumentation, Biomedical Engineering and Radiation Physics (LIBPhys-NOVA), Department of Physics, NOVA School of Science and Technology, NOVA University of Lisbon, Campus FCT-NOVA, 2829-516 Caparica, Portugal
Interests: disease diagnosis; biosensors; biomarker; human health monitoring
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Optical systems are ubiquitous in modern society, with an ever-increasing number of applications, covering Medical Sciences as vision technologies, surgical instrumentation, medical imaging and health monitoring; Featured Optical Materials for new generation of sensors and devices; Space Science Instrumentation as telescopes, lenses, spectrometers; Telecommunications as optical fiber technology, information processing, quantum computing; Industry, from cutting, welding, precision metrology and process control, energy harvesting, modern lightening and Military/Weaponry Technology, to name but a few examples. Furthermore, all of these technologies are nowadays crucial to performing applied research in areas such as chemistry and biology, providing fundamental analysis tools. The success of optical and photonic systems and technologies in high-end scientific research has also found its way into everyday consumer products such as printers, displays, discs, cameras and eyeglasses, not to forget that optical fiber is crucial to telecommunications in general and internet in particular. This special issue will precisely feature three different tracks on Photonics, Optics, and Lasers, covering both theoretical and practical aspects.

Dr. Paulo A. Ribeiro
Prof. David Andrews
Dr. Pablo Albella
Dr. Maria Raposo
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

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Published Papers (11 papers)

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Research

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13 pages, 2104 KiB

Open AccessArticle

Sulfophosphate Glass Doped with Er³⁺ and TiO₂ Nanoparticles: Thermo-Optical Characterization by Photothermal Spectroscopy

by Zeinab Ebrahimpour, Humberto Cabrera, Fahimeh Ahmadi, Asghar Asgari and Joseph Niemela

Photonics 2021, 8(4), 115; https://doi.org/10.3390/photonics8040115 - 08 Apr 2021

Cited by 5 | Viewed by 2277

Abstract

In this work, time-resolved thermal lens and beam deflection methods were applied to determine the thermo-optical properties of Er³⁺ doped sulfophosphate glass in which different concentrations of Titanium dioxide (TiO₂) nanoparticles (NPs) were embedded. Thermal diffusivity (

D

), thermal [...] Read more.

D

), thermal conductivity (

κ

), and the temperature coefficient of the optical path length (

d s / d T

) were determined as a function of NPs concentrations. Moreover, the growth of TiO₂ NPs inside the amorphous glass matrix was evidenced by Transmission Electron Microscopy (TEM) images as well as through optical effects such as refractive index change of the glass. The outcomes indicated relatively high values for

D

and κ as well as a low

d s / d T

as required for most optical components used for laser media. The addition of TiO₂ NPs with concentration of dopants up to 0.6 mol% improved the optical properties of the glass samples but did not affect its thermal properties. The results indicate that the enhanced optical and thermal performance of the proposed co-doped glass fits the quality standards for materials used in photonic devices. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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16 pages, 2849 KiB

Open AccessEditor’s ChoiceArticle

Engineering of TiO₂ or ZnO—Graphene Oxide Nanoheterojunctions for Hybrid Solar Cells Devices

by Duarte Carreira, Paulo A. Ribeiro, Maria Raposo and Susana Sério

Photonics 2021, 8(3), 75; https://doi.org/10.3390/photonics8030075 - 12 Mar 2021

Cited by 7 | Viewed by 3232

Abstract

It is currently of huge importance to find alternatives to fossil fuels to produce clean energy and to ensure the energy demands of modern society. In the present work, two types of hybrid solar cell devices were developed and characterized. The photoactive layers of the hybrid heterojunctions comprise poly (allylamine chloride) (PAH) and graphene oxide (GO) and TiO₂ or ZnO films, which were deposited using the layer-by-layer technique and DC-reactive magnetron sputtering, respectively, onto fluorine-doped tin oxide (FTO)-coated glass substrates. Scanning electron microscopy evidenced a homogeneous inorganic layer, the surface morphology of which was dependent on the number of organic bilayers. The electrical characterization pointed out that FTO/(PAH/GO)₅₀/TiO₂/Al, FTO/(PAH/GO)₃₀/ZnO/Al, and FTO/(PAH/GO)₅₀/ZnO/Al architectures were the only ones to exhibit a diode behavior, and the last one experienced a decrease in current in a low-humidity environment. The (PAH/GO)₂₀ impedance spectroscopy study further revealed the typical impedance of a parallel RC circuit for a dry environment, whereas in a humid environment, it approached the impedance of a series of three parallel RC circuits, indicating that water and oxygen contribute to other conduction processes. Finally, the achieved devices should be encapsulated to work successfully as solar cells. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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12 pages, 1774 KiB

Open AccessArticle

Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability

by Maria Raposo, Carlota Xavier, Catarina Monteiro, Susana Silva, Orlando Frazão, Paulo Zagalo and Paulo António Ribeiro

Photonics 2021, 8(3), 70; https://doi.org/10.3390/photonics8030070 - 04 Mar 2021

Viewed by 1881

Abstract

Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device reliability, particularly in complex aqueous environments such as wastewater. In this work, the stability of GO layers in layer-by-layer (LbL) films of polyethyleneimine (PEI) and GO was investigated. The results led to the following conclusions: PEI/GO films grow linearly with the number of bilayers as long as the adsorption time is kept constant; the adsorption kinetics of a GO layer follow the behavior of the adsorption of polyelectrolytes; and the interaction associated with the growth of these films is of the ionic type since the desorption activation energy has a value of 119 ± 17 kJ/mol. Therefore, it is possible to conclude that PEI/GO films are suitable for application in optical fiber sensor devices; most importantly, an optical fiber-based interrogation setup can easily be adapted to investigate in situ desorption via a thermally stimulated process. In addition, it is possible to draw inferences about film stability in solution in a fast, reliable way when compared with the traditional ones. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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13 pages, 6877 KiB

Open AccessArticle

Single Headlamp with Low- and High-Beam Light

by Shang-Ping Ying, Bing-Mau Chen, Han-Kuei Fu and Chen-Yu Yeh

Photonics 2021, 8(2), 32; https://doi.org/10.3390/photonics8020032 - 27 Jan 2021

Cited by 4 | Viewed by 4795

Abstract

Generally, automobiles are typically equipped with separate headlamp lanterns for generating low- and high-beam light. Compared with separate headlamp lanterns, a single headlamp producing both low- and high-beam light can be more compact and have less mechanical complexity. The single headlamp structure has become a main emphasis of research that manufacturers will continue to focus great efforts on in the future. A novel design of a single headlamp generating both low- and high-beam light is proposed in this study. The proposed headlamp consists of a compound ellipsoidal reflector, a baffle plate, a condenser lens, and LED array devices generating low- and high-beam light. The compound ellipsoidal reflector comprises a primary ellipsoidal reflector for generating low-beam light and a secondary ellipsoidal reflector for generating high-beam light. Monte Carlo ray tracing simulations were performed to confirm the optical characteristics of the proposed design. A prototype of the proposed headlamp was also fabricated and assembled to verify the design’s effectiveness. The simulated and measured illuminance distributions of the low-beam and high-beam light had the desired light patterns. Moreover, all the simulated and measured illuminances of each point and line met the ECE R112 regulation for low-beam and high-beam light. The proposed headlamp in this study is feasible for the application of single headlamp generating both low- and high-beam light. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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18 pages, 6403 KiB

Open AccessEditor’s ChoiceArticle

Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser

by Simone Di Mitri, Andrea Latina, Marcus Aicheler, Avni Aksoy, David Alesini, Graeme Burt, Alejandro Castilla, Jim Clarke, Hector Mauricio Castañeda Cortés, Michele Croia, Gerardo D’Auria, Marco Diomede, David Dunning, Massimo Ferrario, Alessandro Gallo, Anna Giribono, Vitaliy Goryashko, Andrea Mostacci, Federico Nguyen, Regina Rochow, Jessica Scifo, Bruno Spataro, Neil Thompson, Cristina Vaccarezza, Alessandro Vannozzi, Xiaowei Wu and Walter Wuensch Show full author list Hide full author list

Photonics 2020, 7(4), 125; https://doi.org/10.3390/photonics7040125 - 04 Dec 2020

Cited by 4 | Viewed by 3430

Abstract

The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75–300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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17 pages, 11347 KiB

Open AccessEditor’s ChoiceArticle

Coherent Beam Combining Using an Internally Sensed Optical Phased Array of Frequency-Offset Phase Locked Lasers

by Lyle E. Roberts, Robert L. Ward, Craig Smith and Daniel A. Shaddock

Photonics 2020, 7(4), 118; https://doi.org/10.3390/photonics7040118 - 28 Nov 2020

Cited by 8 | Viewed by 3706

Abstract

Coherent beam combining can be used to scale optical power and enable mechanism-free beam steering using an optical phased array. Coherently combining multiple free-running lasers in a leader-follower laser configuration is challenging due to the need to measure and stabilize large and highly dynamic phase differences between them. We present a scalable technique based on frequency-offset phase locking and digitally enhanced interferometry to clone the coherence of multiple lasers without the use of external sampling optics, which has the potential to support both coherent and spectral beam combining, and alleviates issues of voltage wrapping associated with actuating feedback control using electro-optic modulators. This technique was demonstrated experimentally using a tiled-aperture optical phased array in which the relative output phase of three free-running lasers was stabilized with an RMS output phase stability of

λ / 104

. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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10 pages, 2395 KiB

Open AccessArticle

Characterization of Absorption Losses and Transient Thermo-Optic Effects in a High-Power Laser System

by Lukasz Gorajek, Przemyslaw Gontar, Jan Jabczynski, Jozef Firak, Marek Stefaniak, Miroslaw Dabrowski, Tomasz Orzanowski, Piotr Trzaskawka, Tomasz Sosnowski, Krzysztof Firmanty, Marcin Miczuga, Jaroslaw Barela and Krzysztof Kopczynski

Photonics 2020, 7(4), 94; https://doi.org/10.3390/photonics7040094 - 22 Oct 2020

Cited by 1 | Viewed by 2380

Abstract

(1) Background: The modeling, characterization, and mitigation of transient lasers, thermal stress, and thermo-optic effects (TOEs) occurring inside high energy lasers have become hot research topics in laser physics over the past few decades. The physical sources of TOEs are the un-avoidable residual absorption and scattering in the volume and on the surface of passive and active laser elements. Therefore, it is necessary to characterize and mitigate these effects in real laser systems under high-power operations. (2) Methods: The laboratory setup comprised a 10-kW continuous wave laser source with a changeable beam diameter, and dynamic registration of the transient temperature profiles was applied using an infrared camera. Modeling using COMSOL Multiphysics enabled matching of the surface and volume absorption coefficients to the experimental data of the temperature profiles. The beam quality was estimated from the known optical path differences (OPDs) occurring within the examined sample. (3) Results: The absorption loss coefficients of dielectric coatings were determined for the evaluation of several coating technologies. Additionally, OPDs for typical transmissive and reflective elements were determined. (4) Conclusions: The idea of dynamic self-compensation of transient TOEs using a tailored design of the considered transmissive and reflecting elements is proposed. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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10 pages, 734 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tunable THz Pulses Generation in Non-Equilibrium Magnetized Plasma: The Role of Plasma Kinetics

by Anna V. Bogatskaya, Nelli E. Gnezdovskaia and Alexander M. Popov

Photonics 2020, 7(4), 82; https://doi.org/10.3390/photonics7040082 - 24 Sep 2020

Cited by 1 | Viewed by 2547

Abstract

In this paper the theoretical model to consider the influence of kinetic properties of nonequilibrium two-color plasma during the THz pulses generation in the presence of static magnetic field is developed. It is shown that applying a static magnetic field on a gas along the direction of propagation of an ionizing two-color laser pulse allows one to produce two-frequency emissions in THz range with tunable central frequency and bandwidth, which are strongly dependent on electron velocity distribution function (EVDF) formed in the plasma as well as relations between collisional, plasma and cyclotron frequencies. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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14 pages, 5446 KiB

Open AccessEditor’s ChoiceArticle

Structural, Optical and Electrical Characterizations of Midwave Infrared Ga-Free Type-II InAs/InAsSb Superlattice Barrier Photodetector

by U. Zavala-Moran, M. Bouschet, J. P. Perez, R. Alchaar, S. Bernhardt, I. Ribet-Mohamed, F. de Anda-Salazar and P. Christol

Photonics 2020, 7(3), 76; https://doi.org/10.3390/photonics7030076 - 18 Sep 2020

Cited by 14 | Viewed by 4038

Abstract

In this paper, a full set of structural, optical and electrical characterizations performed on midwave infrared barrier detectors based on a Ga-free InAs/InAsSb type-II superlattice, grown by molecular beam epitaxy (MBE) on a GaSb substrate, are reported and analyzed. a Minority carrier lifetime value equal to 1 µs at 80 K, carried out on dedicated structure showing photoluminescence peak position at 4.9 µm, is extracted from a time resolved photoluminescence measurement. Dark current density as low as 3.2 × 10⁻⁵ A/cm² at 150 K is reported on the corresponding device exhibiting a 50% cut-off wavelength around 5 µm. A performance analysis through normalized spectral response and dark current density-voltage characteristics was performed to determine both the operating bias and the different dark current regimes. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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12 pages, 3786 KiB

Open AccessArticle

Cavity Ring-Down Spectroscopy for Molecular Trace Gas Detection Using A Pulsed DFB QCL Emitting at 6.8 µm

by Komlan S. Gadedjisso-Tossou, Lyubomir I. Stoychev, Messanh A. Mohou, Humberto Cabrera, Joseph Niemela, Miltcho B. Danailov and Andrea Vacchi

Photonics 2020, 7(3), 74; https://doi.org/10.3390/photonics7030074 - 14 Sep 2020

Cited by 16 | Viewed by 3398

Abstract

A trace gas sensor based on pulsed cavity ring-down spectroscopy (CRDS) was developed for measurement of the ν4 fundamental vibrational band of ammonia (NH₃) centered at 1468.898 cm⁻¹. A pulsed distributed feedback quantum cascade laser (DFB-QCL) operating at 6.8 µm (1470.58 cm⁻¹) quite well covered the absorption band of the ammonia and strong fundamental vibrational absorption bands of different molecular gases in this unexplored region. The cavity was partially evacuated down to 0.4 Atm by a turbo-molecular pump to reduce the partial interference between the NH₃ spectra and water near the absorption peak of ammonia. A sensitivity of nine parts per billion was reached for a measurement time of 120 s as well as an optical path length of 226 m. The device demonstrated high spectral performance and versatility due to its wide tuning range, narrow linewidth, and comparatively high-energy mid-IR radiation in the relatively unexplored 6.8 µm region, which is very important for high-resolution spectroscopy of a variety of gases. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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10 pages, 3972 KiB

Open AccessLetter

A Refractive Index Sensitive Liquid Level Monitoring Sensor Based on Multimode Interference

by Fan Zhang, Shuguang Li, Xin Yan, Xuenan Zhang, Fang Wang, Takenobu Suzuki, Yasutake Ohishi and Tonglei Cheng

Photonics 2020, 7(4), 89; https://doi.org/10.3390/photonics7040089 - 06 Oct 2020

Cited by 9 | Viewed by 2568

Abstract

According to the beam propagation method, a fiber refractive index-sensitive multimode interference (MMI) structure fabricated by splicing a self-made silica glass rod between two single mode fibers (SMF–NCF (no core fiber)–SMF structure) is proposed for liquid level monitoring. Theoretical and experimental investigation was carried out meticulously using a 4.5 cm and a 9.5 cm long silica glass rod. It is proved that the simple and economical sensor with the shorter length has high sensitivity, satisfactory repeatability, and favorable stability. The sensitivity climbs with the increase in refractive index of the measured liquid, which is 204 pm/mm for pure water, 265.8 pm/mm for 10% glycerin solution, and 352.5 pm/mm for 25% glycerin solution. The proposed sensor can be standardized in certain application circumstances to achieve accurate liquid level monitoring. Full article

(This article belongs to the Special Issue Photonics, Optics and Laser Technology)

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