Multiple Wavelengths Of Light Research Articles

Advances in Paper‐Based Photodetectors: Fabrications, Performances, and Applications

AbstractWith the development of wearable electronic technology, the flexible photodetectors have attracted widespread attention, and it is of great significance to develop flexible, eco‐friendly and low‐cost photodetectors. Cellulose paper, as a flexible, eco‐friendly, low‐cost, lightweight, customizable, biodegradable and renewable material, has received enthusiastic attention and rapid development in the field of photodetectors in recent years. In this review, it is focused on the research progress of paper‐based (PB) photodetectors. First, the fabrication methods of PB photodetectors are discussed, including electrode materials and optoelectronic functional materials. Then, this review systematically summarizes and analyzes the achievements of PB photodetectors on photoelectric performances (spectral response range, responsivity, detectivity, response/recovery times and on/off ratio) and flexibility characteristics (bending angle and bending cycle). In terms of key performance indicators, the PB photodetectors reported so far can detect multiple wavelengths of light from UV to near‐infrared with the maximum detectivity of 1013 Jones. In addition, the various applications of PB photodetectors is reviewed and discussed. Finally, it is look forward to the future development of PB photodetectors in terms of fabrication methods, photoelectric and flexible performances, and applications. With this review, it is hope that it will promoted the future development of PB photodetectors.

Improved multivariable algorithms for estimating oceanic particulate organic carbon concentration from optical backscattering and chlorophyll-a measurements

The capability to estimate the oceanic particulate organic carbon concentration (POC) from optical measurements is crucial for assessing the dynamics of this carbon reservoir and the capacity of the biological pump to sequester atmospheric carbon dioxide in the deep ocean. Optical approaches are routinely used to estimate oceanic POC from the spectral particulate backscattering coefficient bbp, either directly (e.g., with backscattering sensors on underwater platforms like BGC-Argo floats) or indirectly (e.g., with satellite remote sensing). However, the reliability of algorithms which relate POC to bbp is typically limited due to the complexity of interactions between light and natural assemblages of marine particles, which depend on variations in particle concentration, composition, and size distribution. This study expands on our previous work by analysis of an extended field dataset created with judicious data inclusion criteria with the aim to provide POC algorithms for multiple light wavelengths of measured bbp, which can be useful for applications with in situ optical sensors as well as above-water active or passive measurement systems. We describe an improved empirical multivariable approach to estimate POC from simultaneous measurements of bbp and chlorophyll-a concentration (Chla) to better account for the effects of variable particle composition on the relationship between POC and bbp. The multivariable regression models are formulated using a relatively large dataset of coincident measurements of POC, bbp, and Chla, including surface and subsurface data from the Atlantic, Pacific, Arctic, and Southern Oceans. We show that the multivariable algorithm provides reduced uncertainty of estimated POC across diverse marine environments when compared with a traditional univariate algorithm based on only bbp. We also propose an improved formulation of univariate algorithm based on bbp alone. Finally, we examine performance of several algorithms to estimate POC using our dataset as well as a dataset consisting of optical measurements from BGC-Argo floats and traditional POC measurements collected during a coincident research cruise in the Atlantic Ocean.

A biological camera that captures and stores images directly into DNA

The increasing integration between biological and digital interfaces has led to heightened interest in utilizing biological materials to store digital data, with the most promising one involving the storage of data within defined sequences of DNA that are created by de novo DNA synthesis. However, there is a lack of methods that can obviate the need for de novo DNA synthesis, which tends to be costly and inefficient. Here, in this work, we detail a method of capturing 2-dimensional light patterns into DNA, by utilizing optogenetic circuits to record light exposure into DNA, encoding spatial locations with barcoding, and retrieving stored images via high-throughput next-generation sequencing. We demonstrate the encoding of multiple images into DNA, totaling 1152 bits, selective image retrieval, as well as robustness to drying, heat and UV. We also demonstrate successful multiplexing using multiple wavelengths of light, capturing 2 different images simultaneously using red and blue light. This work thus establishes a ‘living digital camera’, paving the way towards integrating biological systems with digital devices.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

Utility of Continuous Pulse Co-Oximetry for Hemoglobin Monitoring in Pediatric Patients with Solid Organ Injuries at Level 1 Trauma Centers: A Pilot Study.

Hemorrhage is a major cause of preventable death in injured children. Monitoring after admission often requires multiple blood draws, which have been shown to be stressful in pediatric patients. The Rainbow-7 device is a continuous pulse co-oximeter that measures multiple wavelengths of light, permitting continuous estimation of the total hemoglobin level. The purpose of this study was to evaluate the utility of the noninvasive hemoglobin measurement for monitoring pediatric trauma patients admitted with solid organ injury (SOI). This is a prospective, dual-center, observational trial for patients under age 18 admitted to a Level I pediatric trauma center. Following admission, blood was routinely measured as per current SOI protocols. Noninvasive hemoglobin monitoring was initiated after admission. Time-synced data for hemoglobin levels was compared to that taken using blood draws. Data was evaluated using bivariate correlation, linear regression, and Bland-Altman analysis. Over a 1-year period, 39 patients were enrolled. Mean age was 11 (±3.8) years. Forty-six percent (n = 18) of patients were male. Mean ISS was 19 ± 13 The average change in hemoglobin levels between laboratory measurements was -0.34 ± 0.95 g/dL and the average change in noninvasive hemoglobin was -0.12 ± 1.0 g/dL/measurement. Noninvasive hemoglobin values were significantly correlated with laboratory measurements (p < 0.001). Trends in laboratory hemoglobin measurements were highly correlated with changes in noninvasive levels (p < 0.001). Bland-Altman analysis demonstrated similar deviation from the mean throughout the range of hemoglobin values, but the differences between measurements was increased by anemia, African American race, and elevated SIPA score and ISS. Noninvasive hemoglobin values demonstrated correlation with measured hemoglobin concentration as isolated measurements and trends, although results were affected by skin pigmentation, shock, and injury severity. Given the rapid availability of results and the lack of requirement of venipuncture, noninvasive hemoglobin monitoring may be a valuable adjunct for pediatric solid organ injury protocols. Further study is required to determine its role in management. III, Study Type: Diagnostic Test.

Development of a Target-to-Sensor Mode Multispectral Imaging Device for High-Throughput and High-Precision Touch-Based Leaf-Scale Soybean Phenotyping

Image-based spectroscopy phenotyping is a rapidly growing field that investigates how genotype, environment and management interact using remote or proximal sensing systems to capture images of a plant under multiple wavelengths of light. While remote sensing techniques have proven effective in crop phenotyping, they can be subject to various noise sources, such as varying lighting conditions and plant physiological status, including leaf orientation. Moreover, current proximal leaf-scale imaging devices require the sensors to accommodate the state of the samples during imaging which induced extra time and labor cost. Therefore, this study developed a proximal multispectral imaging device that can actively attract the leaf to the sensing area (target-to-sensor mode) for high-precision and high-throughput leaf-scale phenotyping. To increase the throughput and to optimize imaging results, this device innovatively uses active airflow to reposition and flatten the soybean leaf. This novel mechanism redefines the traditional sensor-to-target mode and has relieved the device operator from the labor of capturing and holding the leaf, resulting in a five-fold increase in imaging speed compared to conventional proximal whole leaf imaging device. Besides, this device uses artificial lights to create stable and consistent lighting conditions to further improve the quality of the images. Furthermore, the touch-based imaging device takes full advantage of proximal sensing by providing ultra-high spatial resolution and quality of each pixel by blocking the noises induced by ambient lighting variances. The images captured by this device have been tested in the field and proven effective. Specifically, it has successfully identified nitrogen deficiency treatment at an earlier stage than a typical remote sensing system. The p-value of the data collected by the device (p = 0.008) is significantly lower than that of a remote sensing system (p = 0.239).

Multiwavelength Optoelectronic Synapse with 2D Materials for Mixed-Color Pattern Recognition.

Neuromorphic visual systems emulating biological retina functionalities have enormous potential for in-sensor computing, with prospects of making artificial intelligence ubiquitous. Conventionally, visual information is captured by an image sensor, stored by memory units, and eventually processed by the machine learning algorithm. Here, we present an optoelectronic synapse device with multifunctional integration of all the processes required for real time object identification. Ultraviolet-visible wavelength-sensitive MoS2 FET channel with infrared sensitive PtTe2/Si gate electrode enables the device to sense, store, and process optical data for a wide range of the electromagnetic spectrum, while maintaining a low dark current. The device exhibits optical stimulation-controlled short-term and long-term potentiation, electrically driven long-term depression, synaptic weight update for multiple wavelengths of light ranging from 300 nm in ultraviolet to 2 μm in infrared. An artificial neural network developed using the extracted weight update parameters of the device can be trained to identify both single wavelength and mixed wavelength patterns. This work demonstrates a device that could potentially be used for realizing a multiwavelength neuromorphic visual system for pattern recognition and object identification.

(Invited) Soft Wireless Optofluidic and Optoelectronic Implants for Advanced Chronic Neural Interfacing

Optogenetics and neuropharmacology holds immense promise for dissection of neural circuits and cellular signaling in freely behaving animals. However, the full potential of their in vivo applications is limited by the use of conventional tools such as cannulas for drug delivery and fiber optics for photostimulation. These traditional approaches greatly damage neural tissue near the implant, hinder integration with different modalities, and severely limit the animal’s natural behavior and movement, mainly due to their rigid construction, bulky design, and tethered operation, respectively. Furthermore, current methods lack spatiotemporal control of drug delivery, wireless control, and multi-functionality.To address these fundamental limitations in in vivo neuroscience, we have developed soft wireless optofluidic and optoelectronic implants, which can provide wireless delivery of light and/or drugs in awake, moving animals. The devices consist of ultrathin and flexible probes, which integrate microscale inorganic light-emitting diodes and/or microfluidic channels, and wireless interface with an independent power supply. This design enables compact, lightweight and soft system, thus enabling seamless implantation and operation in the brain without causing disturbance of naturalistic behavior. With integration of smartphone control, replaceable drug cartridges for long-term drug delivery, and wireless energy harvesters for intervention-free charging, they can further facilitate chronic neural interfacing to uncover the basis for brain functions and neuropsychiatric diseases. We have successfully demonstrated chronic wireless capabilities of these devices in freely moving animals that can repeatedly deliver multiple wavelengths of light and drugs for long periods of time to manipulate animals’ behavior. The unique capabilities of the soft wireless implants forecasts their broad utility in chronic in vivo neuropharmacology and optogenetics for various neuroscience research and clinical applications.

Constraining delay time distribution of binary neutron star mergers from host galaxy properties

ABSTRACT Gravitational wave (GW) observatories are discovering binary neutron star mergers (BNSMs), and in at least one event we were able to track it down in multiple wavelengths of light, which allowed us to identify the host galaxy. Using a catalogue of local galaxies with inferred star formation histories and adopting a BNSM delay time distribution (DTD) model, we investigate the dependence of BNSM rate on an array of galaxy properties. Compared to the intrinsic property distribution of galaxies, that of BNSM host galaxies is skewed towards galaxies with redder colour, lower specific star formation rate, higher luminosity, and higher stellar mass, reflecting the tendency of higher BNSM rates in more massive galaxies. We introduce a formalism to efficiently make forecast on using host galaxy properties to constrain DTD models. We find comparable constraints from the dependence of BNSM occurrence distribution on galaxy colour, specific star formation rate, and stellar mass, all better than those from dependence on r-band luminosity. The tightest constraints come from using individual star formation histories of host galaxies, which reduces the uncertainties on DTD parameters by a factor of three or more. Substantially different DTD models can be differentiated with about 10 BNSM detections. To constrain DTD parameters at 10 per cent precision level requires about one hundred detections, achievable with GW observations on a decade time-scale.

An approach for correcting optical paths of different wavelength lasers in diffusive medium based on Monte Carlo simulation

Near-infrared spectroscopy (NIRS) generally uses multiple wavelengths of light to obtain functional information. When different wavelengths are employed together, their optical paths are different in the medium and it can potentially cause errors. In this study, we introduced an approach of correcting optical paths when laser sources are used. Laser can be approximated by a point source in a diffusive medium and its depth depends on the wavelength. By multiplying the ratio of detected weights emitted from different point sources, they are conceptually moved to the same position. Monte Carlo simulation was implemented to accumulate required data. As an example for verifying this method, optical properties of the white matter of the brain was used. All combinations of four wavelengths (400, 550, 700, and 850 nm) and six source-detector distances (0.5 mm to 3.0 mm at intervals of 0.5 mm) were simulated. Under the same example conditions, the difference between the simulation results and this method was about ‘1.28%’. The results showed that this approach is applicable to short source-detector distance conditions.

Functional interrelation of MYC2 and HY5 plays an important role in Arabidopsis seedling development.

Arabidopsis MYC2 bHLH transcription factor plays a negative regulatory role in blue light (BL)-mediated seedling development. HY5 bZIP protein works as a positive regulator of multiple wavelengths of light and promotes photomorphogenesis. Both MYC2 and HY5, belonging to two different classes of transcription factors, are the integrators of multiple signaling pathways. However, the functional interrelations of these two transcription factors in seedling development remain unknown. Additionally, whereas HY5-mediated regulation of gene expression has been investigated in detail, the transcriptional regulation of HY5 itself is yet to be understood. Here, we show that HY5 and MYC2 work in an antagonistic manner in Arabidopsis seedling development. Our results reveal that HY5 expression is negatively regulated by MYC2 predominantly in BL, and at various stages of development. On the other hand, HY5 negatively regulates the expression of MYC2 at various wavelengths of light. In vitro and in vivo DNA-protein interaction studies suggest that MYC2 binds to the E-box cis-acting element of HY5 promoter. Collectively, this study demonstrates a coordinated regulation of MYC2 and HY5 in blue-light-mediated Arabidopsis seedling development.

New, sensitive behavioral assay shows scorpions are attracted to multiple wavelengths of light

Scorpions fluoresce a bright green when under ultraviolet light, but the functional significance of the fluorescence is still unknown. A major challenge in studying scorpion fluorescence is the lack of efficient methods for testing the behavioral photosensitivity of scorpions. We have modified previous assays to produce a more sensitive testing device. The apparatus consists of a circular track made of a small Petri dish nested inside a larger one, with an LED shining from the inner chamber across a small sector of the track. We monitored the scorpions' movements in the arenas under three light wavelengths: ultraviolet (399 nm), yellow-green (566 nm), and red (630 nm); all wavelengths were matched to a nighttime light intensity (0.01 irradians). We also tracked each animal's movements in the absence of light as a control. The animals were attracted to 399 and 566 nm light and also showed some attraction to 630 nm. Furthermore, earlier studies suggest that scorpion photoreceptors form a homogeneous population that has been physiologically shown to be maximally sensitive to green wavelengths. We hypothesize that the photoreceptor population might be somewhat responsive to red light too, suggesting that the photoreceptors may respond to a broad spectrum of light or that the photoreceptor population may not be as homogeneous as previously thought. The strong response to UV light, as has been seen in other behavioral assays, remains enigmatic. Overall, this new assay is more sensitive than previous assays for detecting scorpion photoresponse and will be useful for future studies.

Multivariate analysis of Raman spectra of carbonaceous black drawing media for the in situ identification of historic artist materials

AbstractThe identification of black drawing materials in works of art on paper is often important for their conservation and crucial to gain insight about artists' methodologies and the historic use of drawing materials. Traditionally, conservators and curators have had to rely upon visual observation with multiple wavelengths of light and magnification to characterize the materials in drawings, a challenging task further complicated if the media have been manipulated by the artist. The use of carbon‐based pigments in black drawing materials, ranging from charcoals and chalks to pastels and crayons, can be verified in situ using Raman microspectroscopy based on the presence of the two broad spectral bands characteristic of carbonaceous materials. However, the subtle differences in these spectral features between pigments can be difficult to discern, especially in cases with high background fluorescence. Here, we utilized principal component analysis to distinguish a group of 14 reference black drawing materials, both contemporary and historic, in the Raman spectral region of 800–2,000 cm−1. The model generated successfully differentiates between charcoal, chalk, and fabricated stick media, with sensitivity to both the Raman bands of carbon‐based materials as well as the fluorescent background profile. We validated the model using Raman spectra of black media on 19th‐century French drawings from the J. Paul Getty Museum collection that were previously classified visually by microscopic evaluation.

Photochemical Mechanism of an Atypical Algal Phytochrome.

Phytochromes are bilin-containing photoreceptors that are typically sensitive to the red/far-red region of the visible spectrum. Recently, phytochromes from certain eukaryotic algae have become attractive targets for optogenetic applications because of their unique ability to respond to multiple wavelengths of light. Herein, a combination of time-resolved spectroscopy and structural approaches across picosecond to second timescales have been used to map photochemical mechanisms and structural changes in this atypical group of phytochromes. The photochemistry of an orange/far-red light-sensitive algal phytochrome from Dolihomastix tenuilepis has been investigated by using a combination of visible, IR and X-ray scattering probes. The entire photocycle, correlated with accompanying structural changes in the cofactor/protein, are reported. This study identifies a complex photocycle for this atypical phytochrome. It also highlights a need to combine outcomes from a range of biophysical approaches to unravel complex photochemical and macromolecular processes in multi-domain photoreceptor proteins that are the basis of biological light-mediated signalling.

Performance analysis of VCSEL using finite difference time domain method

Vertical Cavity Surface Emitting Laser (VCSEL) with significantly diverse structures has evolved with time for a different type of applications. A number of researchers used Finite Element Method (FEM) solver for computation of optical resonance modes in VCSEL but this method has a limitation of accuracy because it uses an approximate solution of partial differential equationsand integral equations. Furthermore, FEM is based either on eliminating the time derivatives completely or by rendering the partial differential equations into an equivalent ordinary differential equations. In this research work, we have used Finite Difference Time Domain (FDTD) method which elaborates the fine features of VCSEL and the accuracy of the VCSEL results got improved.The proposed approach is also beneficial for calculating reflectance for multiple wavelengths of light per simulation which is the major advantage over FEM. In this research paper, a new VCSEL structure is modeled and also numerically investigated by using proposed FDTD method. A complete analysis of VCSEL light emission, its electric field and Poynting vector are also evaluated at different points of light in thesecond window of optical communication. A rigorous evaluation in terms of spectrum analysis, transmission analysis and farfield projection analysis is done for wavelength ranging from 1310 nm to 1350 nm. Results show that the maximum power of 0.81 W is obtained at a wavelength of 1320 nm with maximum peak voltage of 1.4 V/m and 0.006 W/m2 Poynting vector.

Noninvasive hemoglobin measurement in pediatric trauma patients.

Hemorrhage is a major cause of preventable death secondary to traumatic injury. Diagnosis often requires multiple blood draws, which are psychologically stressful in pediatric patients. The Pronto device is a pulse co-oximeter that measures the total hemoglobin level using multiple wavelengths of light. The purpose of this study was to evaluate the accuracy of the noninvasive hemoglobin measurements relative to current invasive and point of care testing methods in pediatric trauma patients. We performed a prospective observational trial involving patients younger than 17 years presenting to a Level I pediatric trauma center. Following admission, blood was sampled from each patient for testing using an i-Stat device (point-of-care hemoglobin) and a complete blood count within our core laboratory (invasive hemoglobin). Noninvasive hemoglobin analysis was performed within 15 minutes of phlebotomy. Data were evaluated using Spearman correlation and Bland-Altman analysis. Over 2 years, 114 patients had attempted noninvasive hemoglobin measurements, with a success rate of 89%. Mean ± SD age was 9.2 ± 5.1 years. Ninety percent of admissions were for blunt injury, 3% penetrating, 5% near drowning, and 1% burns. Mean invasive hemoglobin was 12.6 ± 1.9 g/dL, mean point-of-care hemoglobin was 12.2 ± 2.0 g/dL, and mean noninvasive hemoglobin was 12.3 ± 1.6 g/dL. Noninvasive hemoglobin values were strongly correlated with both invasive and point of care measurements (R = 0.672 and R = 0.645, respectively; p < 0.001). Bland-Altman analysis comparing noninvasive to point-of-care and invasive hemoglobin levels resulted in an estimated bias of -0.39 and -0.49, respectively. Noninvasive hemoglobin values had excellent correlation with both invasive and point-of-care hemoglobin measurements, although the device was not successful for all patients. Given the rapid availability of results and the lack of requirement of venipuncture, noninvasive hemoglobin monitoring may be a valuable adjunct in the initial evaluation and monitoring of pediatric trauma patients. Diagnostic test study, level II.

Pulse Oximetry: Beyond SpO2.

Newer pulse oximetry technology is available that uses multiple wavelengths of light and is thereby able to measure more than 2 forms of hemoglobin, including carboxyhemoglobin (SpCO), methemoglobin (SpMet), and total hemoglobin (SpHb). Several studies have shown relatively low bias, but poor precision, for SpCO compared with HbCO. Evaluations of SpMet have been conducted primarily in normal subjects. Clinical evaluations of SpHb suggest that it might not yet be accurate enough to make transfusion decisions. Respiratory waveform variability of the pulse oximeter plethysmogram might be useful to assess pulsus paradoxus in patients with airway obstruction; it might also be used to measure the breathing frequency. The change in pulse pressure over the respiratory cycle has been used to assess fluid responsiveness in mechanically ventilated patients, and similarly, the pulse oximetry plethysmogram waveform amplitude variability might be used to assess fluid responsiveness. However, there are limitations to this approach, and it remains to be determined how well it can be applied clinically using existing pulse oximetry technology. The pulse oximeter signal is probably useful for applications beyond SpO2 However, the current technology is not mature, and improvements are necessary. With technology improvements, the use of pulse oximetry to detect SpCO, SpMet, SpHb, pulsus paradoxus, breathing frequency, and fluid responsiveness is likely to improve in the future.

Use of Sub-bandgap Illumination to Improve Radiation Detector Resolution of CdZnTe

The performance of Cd1−x Zn x Te (CZT) materials for room-temperature gamma/x-ray radiation detection continues to improve in terms of material quality and detector design. In our prior publications, we investigated the use of multiple wavelengths of light (in the visible and infrared) to target charge carriers at various trap energies and physical positions throughout crystals. Light exposure significantly alters the charge mobility and improves carrier collection at the anode contact. This study presents an investigation of material performance as a radiation detector during such illumination. The decrease in charge trapping and increase in charge collection due to a higher probability of free electron release from traps contributed to an increase in the resolution-based performance of the detector through controlled illumination. We investigated the performance improvement of CZT crystals with previously known levels of intrinsic defects and secondary phases, at various voltages, light-emitting diode (LED) light wavelengths, and shaping times. Although our setup was clearly not optimized for radiation detector performance, it demonstrated substantial resolution improvements (based on full-width at half-maximum using 662-keV gamma rays from 137Cs upon illumination with 950-nm light) of 16% to 38% in comparison with unilluminated CZT under similar conditions. This manuscript includes discussion of the electrooptic behavior and its effect on performance. Additional testing and fabrication of a detector that incorporates such LED light optimization could lead to improved performance with existing detector-grade materials.

Nanoscale energy-route selector consisting of multiple photo-switchable fluorescence-resonance-energy-transfer structures on DNA

We report on a nanoscale energy-route selector consisting of multiple fluorescence resonance energy transfer (FRET) structures switched by external signaling with multiple wavelengths of light. In each FRET structure, a specific activator molecule is incorporated to a FRET pair of a donor and an acceptor to control the activation of the acceptor. Owing to this configuration, the FRET structures are switched independently, and an energy route is selected. Two photo-switchable FRET structures, one consists of Alexa Fluor 568 (donor), Cy5 (acceptor), and Alexa Fluor 405 (activator), and the other consists of Alexa Fluor 568 (donor), Cy5.5 (acceptor), and Cy3 (activator), were constructed using DNA strands modified with fluorescence molecules. Switching rates for the individual FRET structures were measured as 64 and 49 %, respectively. An energy-route selector was then assembled with the FRET structures which share a single donor. Experimental results demonstrate that the energy route can be changed repeatedly by activation control using three wavelengths of light.

Numerical Modeling of Sub-Wavelength Anti-Reflective Structures for Solar Module Applications.

This paper reviews the current progress in mathematical modeling of anti-reflective subwavelength structures. Methods covered include effective medium theory (EMT), finite-difference time-domain (FDTD), transfer matrix method (TMM), the Fourier modal method (FMM)/rigorous coupled-wave analysis (RCWA) and the finite element method (FEM). Time-based solutions to Maxwell’s equations, such as FDTD, have the benefits of calculating reflectance for multiple wavelengths of light per simulation, but are computationally intensive. Space-discretized methods such as FDTD and FEM output field strength results over the whole geometry and are capable of modeling arbitrary shapes. Frequency-based solutions such as RCWA/FMM and FEM model one wavelength per simulation and are thus able to handle dispersion for regular geometries. Analytical approaches such as TMM are appropriate for very simple thin films. Initial disadvantages such as neglect of dispersion (FDTD), inaccuracy in TM polarization (RCWA), inability to model aperiodic gratings (RCWA), and inaccuracy with metallic materials (FDTD) have been overcome by most modern software. All rigorous numerical methods have accurately predicted the broadband reflection of ideal, graded-index anti-reflective subwavelength structures; ideal structures are tapered nanostructures with periods smaller than the wavelengths of light of interest and lengths that are at least a large portion of the wavelengths considered.