Photon Response Research Articles

Ultrafast Topological Engineering in Metamaterials.

Transient optical heating provides an efficient way to trigger phase transitions in naturally occurring media through ultrashort laser pulse irradiation. A similar approach could be used to induce topological transitions in the photonic response of suitably engineered artificial structures known as metamaterials. Here, we predict a topological transition in the isofrequency dispersion contours of a layered graphene metamaterial under optical pumping. We show that the contour topology transforms from elliptic to hyperbolic within a subpicosecond timescale by exploiting the extraordinary photothermal properties of graphene. This new phenomenon allows us to theoretically demonstrate applications in engineering the decay rate of proximal optical emitters, ultrafast beam steering, and dynamical far-field subwavelength imaging. Our study opens a disruptive approach toward ultrafast control of light emission, beam steering, and optical image processing.

Giant Photonic Response of Mexican-Hat Topological Semiconductors for Mid-infrared to Terahertz Applications.

The mid-infrared (MIR), far-infrared (FIR), and terahertz (THz) frequencies are the least developed parts of the electromagnetic spectrum for applications. Traditional semiconductor technologies like laser diodes and photodetectors are successful in the visible light range but are still confronted with great challenges when extended into the MIR/FIR/THz range. In this paper, we demonstrate that topological insulators (TIs), especially those with Mexican-hat band structure (MHBS), provide a route for overcoming these challenges. The optical responses of MHBS TIs can be 1-2 orders of magnitude larger than that of normal semiconductors at the optical transition edge. We explore the databases of topological materials and discover a number of MHBS TIs whose bandgaps lie between 0.05 and 0.5 eV and possess giant gains (absorption coefficients) on the order of 104-105 cm-1 at the transition edge. These findings may significantly boost potential MIR/FIR/THz applications such as photon sources, detectors, ultrafast electro-optical devices, and quantum information technologies.

Simultaneous remediation of methylene blue and Cr(VI) by mesoporous BiVO4 photocatalyst under visible-light illumination

Porous photocatalysts with large surface areas are more photoactive than compact solid counterparts, owing to their larger surface areas and porous structure, which enhance the adsorption and confinement of light, thus improving the reaction between pollutants and photocatalysts. This paper reports the mechanisms involved in the enhanced photocatalytic activity of two kinds of porous BiVO4 catalysts, named p-BVO-1 and p-BVO-2, which are fabricated by a template-free and alcohol-hydrothermal method, respectively. Characterization, photoelectrochemical and optical measurements, reactive species detection, UV–vis, and XPS analyses were conducted. The results show that the introduction of oxygen vacancies and prolonging effect of light within the pore structure can enhance the photon response and charge separation and transfer, which help to elevate the photocatalytic performance. The simultaneous photocatalysis test of p-BVO-1 for methylene blue (MB) and Cr(VI) showed that the addition of Cr(VI) enhanced MB adsorption by forming an MB-Cr-MB complex, and MB promoted the photoreduction of Cr(VI) by scavenging h+ and ⋅O2−, which may oxidize Cr(III) to Cr(VI). The results indicate that ⋅O2− and h+ are mainly deployed to degrade MB, while e− reduces Cr(VI) ions, thereby favoring the separation of electron-hole pairs.

Advanced Theragenerative Biomaterials with Therapeutic and Regeneration Multifunctionality

AbstractAll tissues and organs can be affected by diseases, and treatments for these diseases can cause damage to surrounding healthy tissues and organs. Therefore, treatment is required that involves disease therapy alongside tissue/organ regeneration. The design, construction, and biomedical applications of biomaterial platforms with both disease‐therapeutic and tissue‐regeneration multifunctionalities are in demand, which are herein referred to as theragenerative (abbreviation of therapy and regeneration) biomaterials. Due to the rapid development of theragenerative biomaterials in versatile biomedical applications, this progress report aims to summarize, discuss, and highlight the rational construction of distinctive theragenerative biomaterials with intrinsic therapeutic performance and tissue‐regeneration bioactivity. Based on the intrinsic response to either external physical triggers (e.g., photonic response or magnetic‐field response) or endogenous disease microenvironments (e.g., mild acidity or overexpressed hydrogen peroxide) and tissue‐regeneration bioactivity, these theragenerative biomaterials are extensively explored in various biomedical fields, including bone‐tumor therapy/regeneration, bone antibacterial therapy/regeneration, skin‐tumor therapy/regeneration, skin antibacterial therapy/regeneration, breast‐tumor therapy/adipose‐tissue regeneration, and osteoarticular‐tuberculosis therapy/bone‐tissue regeneration. The challenges faced and future developments of these distinctive theragenerative biomaterials are discussed, as are methods for further promoting their clinical translation.

Tailoring ZnO Spontaneous Emission with Plasmonic Radiative Local Density of States Using Cathodoluminescence Microscopy

Cathodoluminescence can probe photonic responses of nanostructures at high spatial and energy resolution, providing a powerful tool to investigate the radiative properties under electron excitation...

Design of artificial climate chamber for screening tea seedlings’ optimal light formulations

A multi-channel photon sensor (MPS) capable of measuring Red Photon Flux Density (RPFD), Blue Photon Flux Density (BPFD) and Photosynthetic Photon Flux Density (PPFD) based on silicon photodiodes and filters is designed. At the same time, the FPGA-based environmental control system realizes the closed-loop control of RPFD, BPFD and PPFD by reading the data collected by the MPS that slides up and down according to the height of the canopy of the plant and using the PWM signal to control the LED light board’s red and blue channel. Based on the above method, the article completed an Artificial Climate Chamber (ACC) that realizes the automatic regulation of PPFD and RPFD/BPFD (R/B) of plant canopy that are the key parameters for determining the light formulations of plant lighting and environmental parameters including temperature, relative humidity, CO2 concentration, photoperiod etc. At a significantly lower cost, the MPS’s photon response curve is close to the ideal value, and the linear response R2 of the calibration exceeds 0.999. After setting the parameters for 30 s, the RPFD, BPFD and PPFD control error of the ACC are 1.43%, 1.39% and 0.71%, respectively. The paper also used tea seedlings as materials to explore the physiological and biochemical indexes of leaves under different R/B and PPFD. By comparing the biomass accumulation, free amino acid, tea polyphenols, polyphenols / amino acid ratio and other key parameters, PPFD = 100μmol∙m-2∙s-1 and R/B = 1/3 is the optimal light formulations for artificial light cultivation of tea seedlings.

Complex photonic response reveals three-dimensional self-organization of structural coloured bacterial colonies.

Vivid colours found in living organisms are often the result of scattering from hierarchical nanostructures, where the interplay between order and disorder in their packing defines visual appearance. In the case of Flavobacterium IR1, the complex arrangement of the cells in polycrystalline three-dimensional lattices is found to be a distinctive fingerprint of colony organization. By combining analytical analysis of the angle-resolved scattering response of in vivo bacterial colonies with numerical modelling, we show that we can assess the inter-cell distance and cell diameter with a resolution below 10 nm, far better than what can be achieved with conventional electron microscopy, suffering from preparation artefacts. Retrieving the role of disorder at different length scales from the salient features in the scattering response enables a precise understanding of the structural organization of the bacteria.

Determination of 1-propanol, ethanol, and methanol concentrations in water based on a one-dimensional phoxonic crystal sensor.

In this research, the photonic and phononic response of one-dimensional multilayer phoxonic crystals (PxCs) with normal incident of electromagnetic and acoustic waves is discussed. The presented design can work as a highly sensitive sensor for measuring three binary alcohol/water mixtures (i.e., 1-propanol/water, ethanol/water, and methanol/water) for a wide range of concentrations. The PxC sensor is able to detect small changes in the refractive index and longitudinal sound velocity of the alcohol/water mixture with initially neglecting the acousto-optical interaction. The sensor design is a defective structure as [$({\rm Si}/{\rm SiO}_2)^4 (\rm mixture\;wt. \%) {({{\rm SiO}_2}/{\rm Si})^4}$(Si/SiO2)4(mixturewt.%)(SiO2/Si)4]. Also, we studied the effects of changing mixture concentrations from 0 wt. % to 100 wt. % on the physio-chemical parameters and resonant mode frequency. In our results, we have achieved high performance for the three alcohol mixtures in both phononic and photonic sensors especially for low concentrations. For example, in the photonic sensor we obtained sensitivity, $Q$Q value, and figure of merit of 873 nm/RIU, 755, and ${290}\;{{\rm RIU}^{ - 1}}$290RIU-1, respectively, for methanol of concentration 10% in water. The phononic sensor showed higher results compared with the photonic sensor, as for ethanol with concentration 26.8% in water we obtained sensitivity, $Q$Q value, and figure of merit of ${37}\;{{\rm MHz/ms}^{ - 1}}$37MHz/ms-1, 1604, and ${8.4}\;{({\rm m/s})^{ - 1}}$8.4(m/s)-1, respectively. The proposed structure has different merits: operation at high temperatures, compact size, ease of fabrication, and feasibility of alcohol detection with two different methods that could be used in many chemical applications.

Nanoscale Nonlinear Spectroscopy with Electron Beams

We theoretically demonstrate the ability of electron beams to probe the nonlinear photonic response with nanometer spatial resolution, well beyond the capabilities of existing optical techniques. A...

Measurement of the relative response of small-electrode CMOS sensors at Diamond Light Source

This paper outlines the results of investigations into the effects of radiation damage in the mini-MALTA depleted monolithic pixel sensor prototype. Measurements were carried out at Diamond Light Source using a micro-focus X-ray beam, which scanned across the surface of the device in 2 μm steps. This allowed the in-pixel photon response to be measured directly with high statistics. Three pixel design variations were considered: one with the standard continuous n− layer layout and front-end, and extra deep p-well and n− gap designs with a modified front-end. Five chips were measured: one unirradiated, one neutron irradiated, and three proton irradiated. The standard design showed a decrease of 12% in pixel response after irradiation to 1e15 neq∕cm2. For the two new designs the pixel response did not decrease significantly after irradiation. A decrease of pixel response at high biasing voltages was observed. The charge sharing in the chip was quantified and found to be in agreement with expectations.

Few-Mode Fibers With Uniform Differential Mode Group Delay for Microwave Photonic Signal Processing

We present a novel design of few-mode fiber (FMF) with a uniform differential mode group delay (U-DMGD) among propagating modes and apply the FMF to a single-fiber delay line module for implementing microwave photonic finite impulse response (FIR) filters. By optimizing key parameters such as the core grading exponent and the dimension of the trench of FMF, a U-DMGD between adjacent modes among four modes (LP 01 , LP 11 , LP 02 and LP 31 ) over the entire C band is achieved. Wavelength dependence is entirely removed. An FIR microwave photonic filter (MPF) implemented using the designed 1-km FMF is investigated through numerical simulations. The free spectral range (FSR) of the MPF is 5.7 GHz, the 3-dB bandwidth is 1.26 GHz, and the main lobe-to-side lobe ratio (MSR) is 10.42 dB. Discussions on fabrication aspects have also been presented. The proposed single-fiber delay line structure based on FMF can significantly reduce the system complexity of microwave photonic signal processing.

Tailoring non-fullerene acceptors using selenium-incorporated heterocycles for organic solar cells with over 16% efficiency

The selenium substitution strategy was applied to develop two new A′-DAD-A′-type small molecular acceptors. The resulting selenium-incorporated molecules exhibit red-shifted absorption and an enhanced photon response, leading to high device efficiencies of over 16%.

Manipulation microwave photonic filter response of single microring by using optical frequency combs

We proposed a reconfigurable microwave photonic filter combining the multiple resonances of single microring resonator and optical frequency combs. By manipulating the number of comb lines, the frequency spacing of the comb lines and the relative power between the comb lines, the MPF can be reconfigured from a notch filter with ultra-high rejection ratio to a flat bandstop filter. The mechanism of the reconfigurable microwave photonic filter was clarified theoretically. And in experiments, a notch filter with an ultra-high RF rejection ratio exceed 60 dB and a flat stopband filter with a 10 dB rejection ratio and a stopband ripple less than 0.53 dB were easily reconfigured by manipulating the optical frequency comb lines.

Local, nonlinear effects of cGMP and Ca2+ reduce single photon response variability in retinal rods.

The single photon response (SPR) in vertebrate photoreceptors is inherently variable due to several stochastic events in the phototransduction cascade, the main one being the shutoff of photoactivated rhodopsin. Deactivation is driven by a random number of steps, each of random duration with final quenching occurring after a random delay. Nevertheless, variability of the SPR is relatively low, making the signal highly reliable. Several biophysical and mathematical mechanisms contributing to variability suppression have been examined by the authors. Here we investigate the contribution of local depletion of cGMP by PDE*, the non linear dependence of the photocurrent on cGMP, Ca2+ feedback by making use of a fully space resolved (FSR) mathematical model, applied to two species (mouse and salamander), by varying the cGMP diffusion rate severalfold and rod outer segment diameter by an order of magnitude, and by introducing new, more refined, and time dependent variability functionals. Globally well stirred (GWS) models, and to a lesser extent transversally well stirred models (TWS), underestimate the role of nonlinearities and local cGMP depletion in quenching the variability of the circulating current with respect to fully space resolved models (FSR). These distortions minimize the true extent to which SPR is stabilized by locality in cGMP depletion, nonlinear effects linking cGMP to current, and Ca2+ feedback arising from the physical separation of E* from the ion channels located on the outer shell, and the diffusion of these second messengers in the cytoplasm.

Germanium/perovskite heterostructure for high-performance and broadband photodetector from visible to infrared telecommunication band

A high-performance and broadband heterojunction photodetector has been successfully fabricated. The heterostructure device is based on a uniform and pinhole-free perovskite film constructed on top of a single-crystal germanium layer. The perovskite/germanium photodetector shows enhanced performance and a broad spectrum compared with the single-material-based device. The photon response properties are characterized in detail from the visible to near-infrared spectrum. At an optical fibre communication wavelength of 1550 nm, the heterojunction device exhibits the highest responsivity of 1.4 A/W. The performance is promoted because of an antireflection perovskite coating, the thickness of which is optimized to 150 nm at the telecommunication band. At a visible light wavelength of 680 nm, the device shows outstanding responsivity and detectivity of 228 A/W and 1.6 × 1010 Jones, respectively. These excellent properties arise from the photoconductive gain boost in the heterostructure device. The presented heterojunction photodetector provides a competitive approach for wide-spectrum photodetection from visible to optical communication areas. Based on the distinguished capacity of light detection and harvesting from the visible to near-infrared spectrum, the designed germanium/perovskite heterostructure configuration is believed to provide new building blocks for novel optoelectronic devices.

Supercontinuum single-photon detector using multilayer superconducting nanowires

High-efficiency superconducting nanowire single-photon detectors (SNSPDs), which have numerous applications in quantum information systems, function by using the optical cavity and the ultrasensitive photon response of their ultra-thin superconducting nanowires. However, the wideband response of superconducting nanowires is limited due to the resonance of the traditional optical cavity. Here, we report on a supercontinuum SNSPD that can efficiently detect single photons over an ultra-broad spectral range from visible to mid-infrared light. Our detection approach relies on using multiple cavities with well-separated absorbed resonances formed by fabricating multilayer superconducting nanowires on metallic mirrors with silica acting as spacer layers. Thus, we are able to extend the absorption spectral bandwidth while maintaining considerable efficiency, as opposed to a conventional single-layer SNSPD. Our calculations show that the proposed supercontinuum SNSPD exhibits an extended absorption bandwidth with increased nanowire layers. Its absorption efficiency is greater than 70% over the entire range from 400 to 2500 nm (or 400 to 3000 nm), when using two-layer (or three-layer) nanowires. As a proof of principle, the SNSPD with bilayer nanowires is fabricated based on the proposed detector architecture with simplified geometrical parameters. The detector achieves broadband detection efficiency over 60% from 950 to 1650 nm. This type of detector may replace multiple narrow band detectors in a system and find uses in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy.

Dopamine detection on activated reaction field consisting of graphene-integrated silicon photonic cavity.

Graphene is widely recognized as an outstanding and multi-functional material in various application fields such as electronics, photonics, mechanics, and life sciences. We propose a neurotransmitter sensor with ultra-small volume for detecting the photonic light-matter response. Such detection can be achieved using surface-activated monolayer graphene sheets and CMOS-compatible silicon-photonic circuits. Patterned pieces of CVD-grown graphene are integrated on the top of a silicon micro-ring resonator, which induce the adsorption of catecholamine molecules originated from the π-stacking effect. We used dopamine to demonstrate such detection and examine the sensitivity of graphene-dopamine coupling. To avoid high optical insertion loss and degradation of resonance characteristics caused by a graphene's extremely high optical absorption coefficient in the near infrared region, a ring resonator with adjusted coupling design is used to compensate for the drawbacks. Owing to the advanced nano-sensing platform and measurement system, an activated graphene-sensing surface of only ∼30 µm2/ch enables π coupling to dopamine with enough sensitivity to detect less than 10-µM solution concentration. The detection mechanism through the surface reaction is also verified by optical simulation and atomic force microscopy measurement, revealing that the flowing dopamine molecules can only occupy the outermost surface of graphene. We expect this sensor to contribute to the development of an innovative label-free and disposable bio-sensing platform with accurate, sensitive, and fast response.

Phonon-polaritonics: enabling powerful capabilities for infrared photonics

AbstractHere, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior – typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging.

Radiometric calibration of the SIMBIO-SYS STereo imaging Channel

The STereo imaging Channel (STC) is a double wide-angle camera developed to be one of the channels of the SIMBIO-SYS instrument onboard of the ESA BepiColombo mission to Mercury. STC main goal is to map in 3D the whole Mercury surface. The geometric and radiometric responses of the STC Proto Flight model have been characterized on-ground during the calibration campaign. The derived responses will be used to calibrate the STC images that will be acquired in flight. The aim is to determine the functions linking the detected signal in digital number to the radiance of the target surface in physical units. The result of the radiometric calibration consists in the determination of well-defined quantities: (1) the dark current as a function of the integration time and of the detector temperature, settled and controlled to be stable at 268 K; (2) the read out noise, which is associated with the noise signal of the read-out electronic; and (3) the fixed pattern noise, which is generated by the different response of each pixel. Once these quantities are known, the photon response and the photo-response non-uniformity, which represents the variation of the photon responsivity of a pixel in an array, can be derived. The final result of the radiometric calibration is the relation between the radiance of an accurately known and uniform source, and the digital numbers measured by the detector.

Electronics method to advance the coincidence time resolution with bismuth germanate

Exploiting the moderate Cherenkov yield from 511 keV photoelectric interactions in bismuth germanate (BGO) scintillators enables one to achieve a level of coincidence time resolution (CTR) appropriate for time-of-flight positron emission tomography (TOF-PET). For this approach, owing to the low number of promptly emitted light photons, single photon time resolution (SPTR) can have a stronger influence on achievable CTR. We have previously shown readout techniques that reduce effective device capacitance of large area silicon photomultipliers (SiPMs) can yield improvements in single photon response shape that minimize the influence of electronic noise on SPTR. With these techniques, sub-100 ps FWHM SPTR can be achieved with mm2 FBK near-ultra-violet high density (NUV-HD) SiPMs. These sensors are also useful for detecting Cherenkov light due to relatively high photon detection efficiency for UV light. In this work, we measured CTR for BGO crystals coupled to FBK NUV-HD SiPMs with a passive bootstrapping readout circuit that effectively reduces the SiPM device capacitance. A range of CTR values between 200 3 and 277 7 ps FWHM were measured for 3 3 3 and 3 3 15 mm3 crystals, respectively. This readout technique provides a relatively simple approach to achieve state-of-the-art CTR performance using BGO crystals for TOF-PET.