Photonics

10 pages, 2158 KiB

Open AccessArticle

Design Considerations for Integration of Terahertz Time-Domain Spectroscopy in Microfluidic Platforms

by Rasha Al-Hujazy and Christopher M. Collier

Photonics 2018, 5(1), 5; https://doi.org/10.3390/photonics5010005 - 10 Mar 2018

Cited by 11 | Viewed by 4484

Microfluidic platforms have received much attention in recent years. In particular, there is interest in combining spectroscopy with microfluidic platforms. This work investigates the integration of microfluidic platforms and terahertz time-domain spectroscopy (THz-TDS) systems. A semiclassical computational model is used to simulate the emission of THz radiation from a GaAs photoconductive THz emitter. This model incorporates white noise with increasing noise amplitude (corresponding to decreasing dynamic range values). White noise is selected over other noise due to its contributions in THz-TDS systems. The results from this semiclassical computational model, in combination with defined sample thicknesses, can provide the maximum measurable absorption coefficient for a microfluidic-based THz-TDS system. The maximum measurable frequencies for such systems can be extracted through the relationship between the maximum measurable absorption coefficient and the absorption coefficient for representative biofluids. The sample thickness of the microfluidic platform and the dynamic range of the THz-TDS system play a role in defining the maximum measurable frequency for microfluidic-based THz-TDS systems. The results of this work serve as a design tool for the development of such systems. Full article

(This article belongs to the Special Issue Microwave Photonics 2017)

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13 pages, 2943 KiB

Open AccessFeature PaperArticle

Efficiency Limits of Solar Energy Harvesting via Internal Photoemission in Carbon Materials

by Svetlana V. Boriskina, Jiawei Zhou, Zhiwei Ding and Gang Chen

Photonics 2018, 5(1), 4; https://doi.org/10.3390/photonics5010004 - 24 Feb 2018

Cited by 3 | Viewed by 5510

Abstract

We describe strategies to estimate the upper limits of the efficiency of photon energy harvesting via hot electron extraction from gapless absorbers. Gapless materials such as noble metals can be used for harvesting the whole solar spectrum, including visible and near-infrared light. The energy of photo-generated non-equilibrium or ‘hot’ charge carriers can be harvested before they thermalize with the crystal lattice via the process of their internal photo-emission (IPE) through the rectifying Schottky junction with a semiconductor. However, the low efficiency and the high cost of noble metals necessitates the search for cheaper abundant alternative materials, and we show here that carbon can serve as a promising IPE material candidate. We compare the upper limits of performance of IPE photon energy-harvesting platforms, which incorporate either gold or carbon as the photoactive material where hot electrons are generated. Through a combination of density functional theory, joint electron density of states calculations, and Schottky diode efficiency modeling, we show that the material electron band structure imposes a strict upper limit on the achievable efficiency of the IPE devices. Our calculations reveal that graphite is a good material candidate for the IPE absorber for harvesting visible and near-infrared photons. Graphite electron density of states yields a sizeable population of hot electrons with energies high enough to be collected across the potential barrier. We also discuss the mechanisms that prevent the IPE device efficiency from reaching the upper limits imposed by their material electron band structures. The proposed approach is general and allows for efficient pre-screening of materials for their potential use in IPE energy converters and photodetectors within application-specific spectral windows. Full article

(This article belongs to the Special Issue Nonlinear Dielectric Photonics and Metasurfaces)

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Graphical abstract

10 pages, 2317 KiB

Open AccessArticle

High Throughput AOTF Hyperspectral Imager for Randomly Polarized Light

by Ramy Abdlaty, John Orepoulos, Peter Sinclair, Richard Berman and Qiyin Fang

Photonics 2018, 5(1), 3; https://doi.org/10.3390/photonics5010003 - 22 Jan 2018

Cited by 26 | Viewed by 5476

Abstract

The acousto-optic tunable filter (AOTF) is one of the most used techniques for hyperspectral imaging (HSI), and is capable of fast and random wavelength access, high diffraction efficiency, and good spectral resolution. Typical AOTF-HSI works with linearly polarized light; hence, its throughput is limited for randomly polarized applications such as fluorescence imaging. We report an AOTF-based imager design using both polarized components of the input light. The imager is designed to operate in the 450 to 800 nm region with resolutions in the range of 1.5–4 nm. The performance characterization results show that this design leads to 68% improvement in throughput for randomly polarized light. We also compared its performance against a liquid crystal tunable filter (LCTF)-based imager. Full article

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2 pages, 143 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Photonics in 2017

by Photonics Editorial Office

Photonics 2018, 5(1), 2; https://doi.org/10.3390/photonics5010002 - 19 Jan 2018

Viewed by 2522

Abstract

Peer review is an essential part in the publication process, ensuring that Photonics maintains high quality standards for its published papers.[...] Full article

10 pages, 10533 KiB

Open AccessArticle

Terahertz Radome Inspection

by Fabian Friederich, Karl Henrik May, Bessem Baccouche, Carsten Matheis, Maris Bauer, Joachim Jonuscheit, Michael Moor, David Denman, Jamie Bramble and Nick Savage

Photonics 2018, 5(1), 1; https://doi.org/10.3390/photonics5010001 - 08 Jan 2018

Cited by 50 | Viewed by 6685

Abstract

Radomes protecting sensitive radar, navigational, and communications equipment of, e.g., aircraft, are strongly exposed to the environment and have to withstand harsh weather conditions and potential impacts. Besides their significance to the structural integrity of the radomes, it is often crucial to optimize the composite structures for best possible radio performance. Hence, there exists a significant interest in non-destructive testing techniques, which can be used for defect inspection of radomes in field use as well as for quality inspection during the manufacturing process. Contactless millimeter-wave and terahertz imaging techniques provide millimeter resolution and have the potential to address both application scenarios. We report on our development of a three-dimensional (3D) terahertz imaging system for radome inspection during industrial manufacturing processes. The system was designed for operation within a machining center for radome manufacturing. It simultaneously gathers terahertz depth information in adjacent frequency ranges, from 70 to 110 GHz and from 110 to 170 GHz by combining two frequency modulated continuous-wave terahertz sensing units into a single measurement device. Results from spiraliform image acquisition of a radome test sample demonstrate the successful integration of the measurement system. Full article

(This article belongs to the Special Issue Microwave Photonics 2017)

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Photonics, Volume 5, Issue 1 (March 2018) – 5 articles

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