Contrast Modulation Research Articles

Classification Matters More: Global Instance Contrast for Fine-Grained SAR Aircraft Detection

Since significant intra-class differences and inconspicuous inter-class variations, fine-grained aircraft detection in synthetic aperture radar (SAR) images is challenging. And the inherent lack of detailed features and severe noise interference in SAR images make it difficult to learn class-specific feature representations. Current detection approaches focus more on localization accuracy and ignore classification performance, which is more critical in fine-grained detection. To address the above challenges, we present GICNet: Global Instance Contrast for fine-grained SAR aircraft detection. A Global Instance-level Contrast (GIC) module is proposed to improve inter-class divergences and intra-class compactness. With a specially constructed global instance set, GICNet can contrast a large number of different aircraft targets while keeping a small batch size. Furthermore, we design a novel quality-aware focal loss (QAFL) to facilitate the accurate classification of well-localized aircraft targets. Meanwhile, to maintain localization performance, we develop a new edge-aware bounding-box refinement (EABR) module to refine predicted coarse bounding boxes. Experimental results show that our GICNet outperforms current advanced detectors and achieves a new state-of-the-art performance on the GaoFen-3 SAR aircraft detection dataset. Especially, GICNet also has advantages in reducing misclassification and recognizing well-located targets.

Absorption Coefficient and Optical Contrast Modulation through Side Chain Engineering of Electrochromic Polymers

Conjugated polymers can be electrochemically bleached to achieve colored-to-transmissive electrochromic switching. This work presents a side chain engineering approach to enhance colored state absorptivity of an electrochromic polymer, while maintaining high transmissivity in the bleached state. A series of dioxythiophene copolymers with systematic variations in their branched alkyl side chains have been used to understand side chain influence on solubility, aggregation, film morphology and optical constants. By increasing the chromophore density through an appropriate choice of side chains, the absorption coefficient of the colored polymer can be improved by almost 50%, with minimal influence on bleached-state absorption coefficients over the visible region. As such, solution-processed films of high absorbance can be prepared using thin polymer layers to achieve fast electrochromic switching and highly transmissive bleached states. Under optimized conditions, optical contrasts nearing 80% can be reached at the wavelength of maximum absorbance, among the highest reported for solution-processed, cathodically coloring electrochromic polymers. The improved absorption coefficients are especially useful in enhancing the electrochromic performance in the low transmittance regime (colored state transmittance <20%), providing useful insights for designing high contrast electrochromic materials.

Near-field radiative modulator driven by anisotropic hyperbolic polaritons in biaxial hyperbolic materials

α-phase molybdenum trioxide (α-MoO3) is an excellent biaxial hyperbolic material, whose thermal radiation properties depend highly on the crystal directions. The directional properties of thermal radiation can be controlled by changing the crystal directions of α-MoO3, which provides a novel path for the modulation of thermal radiation. In this work, we find that the near-field radiative heat transfer (NFRHT) between two α-MoO3 nanoparticles (NPs) mediated by an α-MoO3 planar substrate clearly depends on the crystal directions of α-MoO3. Due to the strong directionality of the localized hyperbolic polaritons in the NPs and the volume-confined hyperbolic polaritons in the substrate, we can achieve an effective modulation of the NFRHT by mechanical rotation. Numerical results show that the max modulation contrast could reach 60 when the planar substrate is a semi-infinite medium. The contribution of the vacuum, scattering, and cross terms under the influence of anisotropic NPs are analyzed separately to reveal the mechanism. Moreover, we investigate the effects of rotation angle and thickness of planar substrate on the modulation of NFRHT. Finally, we discuss the effects of rotating NPs on the performance of near-field radiative modulator. This work will guide the design of high-performance thermal radiative modulators based on anisotropic many-body systems.

A yellow to magenta multielectrochromic, pH sensor polymer based on 2,5-di(thienyl)pyrrole modified with methyl orange azo dye

The enhancement of optical contrast and color modulation of π-conjugated polymers may be achieved by incorporating organic dyes through modification of the monomer chemical structure. Methyl orange (MO) azo dye is widely used as a pH indicator, changing its color from orange to red depending on the medium, which makes it a promising strategy to attain polymer materials with innovative optoelectronic properties. A 2,5-di(thienyl)pyrrole (SNS) derivatized with MO, namely SNS-MO has been synthesized with 95% yield and characterized by 1H NMR, 13C NMR, FT-IR and mass spectroscopy techniques. Polymer films of PSNS-MO were electrodeposited onto ITO/glass surface by cyclic voltammetry in (C4H9)4NBF4/CH3CN electrolyte. The PSNS-MO films showed yellow orange color in the neutral state (E = 0.00 V) and light magenta in the oxidized state (E = 0.65 V), presenting chromatic contrast (Δ%T) at 496 and 1010 nm of 14.0 and 23.0, respectively, electrochromic efficiency (η) in the range of 83.90 – 308.10 cm2 C−1 and switching time < 3.5 s. The polymer films were also investigated in Phosphate Buffered Saline (PBS) solutions and after exposure to HCl vapors, in which the color varied from reddish brown at pH = 0.0 to yellowish orange at pH = 4.0. These results show the importance of incorporating azo dyes into the structure of the conjugated polymer to obtain original and advanced materials, since PSNS-MO films are promising for application as active layers in optoelectronic devices and pH optical sensors.

Compact Numerical Modeling of Indirect Time-of-Flight CMOS Image Sensors

A pixel-level compact numerical model, including input optical, pixel parameter, modulation gate clock, and readout noise for indirect time-of-flight (i-ToF) sensor, is proposed. The modulation contrast (Cmod) of the pixel and the depth characteristics, including depth accuracy and depth noise, are obtained with the iterative and Monte Carlo methods. The rationality of the demodulation process is verified through the pixel parameter Cmod with technology computer-aided design (TCAD) simulation and test. Then, the prediction results of the depth accuracy under nonideal conditions are obtained, which is consistent with the theoretical analysis and measurements. Finally, the depth noise is characterized. The model results give an excellent agreement with the measurement results. The proposed development of such a compact model presents an essential convenience toward for the design and circuit-level simulation and can provide the prediction of i-ToF sensor characteristics.

Arbitrary shaped abruptly autofocusing beams

Arbitrary shaped abruptly autofocusing beam (AAB) with initial launch angle modulation is proposed and demonstrated in this paper. Usually, arbitrary shaped Airy beams, which are constructed by substituting various shape functions into circular model, do not own abruptly autofocusing properties because their parabolic trajectories would not intersect at a same point. The modulation for initial launch angles of trajectories is necessary for these beams to re-obtain abruptly autofocusing properties. With the launch angle modulation, the abruptness and intensity contrast of focusing could be as intensive as the circular AAB. The rectangle, star, ellipse shaped AAB are mainly investigated in this paper. Other shaped AAB can be constructed with similar method.

Behavioral signatures of Y-like neuronal responses in human vision

Retinal ganglion cells initiating the magnocellular/Y-cell visual pathways respond nonlinearly to high spatial frequencies (SFs) and temporal frequencies (TFs). This nonlinearity is implicated in the processing of contrast modulation (CM) stimuli in cats and monkeys, but its contribution to human visual perception is not well understood. Here, we evaluate human psychophysical performance for CM stimuli, consisting of a high SF grating carrier whose contrast is modulated by a low SF sinewave envelope. Subjects reported the direction of motion of CM envelopes or luminance modulation (LM) gratings at different eccentricities. The performance on SF (for LMs) or carrier SF (for CMs) was measured for different TFs (LMs) or carrier TFs (CMs). The best performance for LMs was at lower TFs and SFs, decreasing systematically with eccentricity. However, performance with CMs was bandpass with carrier SF, largely independent of carrier TF, and at the highest carrier TF (20 Hz) decreased minimally with eccentricity. Since the nonlinear subunits of Y-cells respond better at higher TFs compared to the linear response components and respond best at higher SFs that are relatively independent of eccentricity, these results suggest that behavioral tasks employing CM stimuli might reveal nonlinear contributions of retinal Y-like cells to human perception.

A CMOS-Compatible Photonic Demodulator With Low-Power Consumption for Time-of-Flight Image Sensor

This article presents a CMOS-compatible low-power photonic demodulator for time-of-flight (ToF) CMOS image sensor. The proposed device called the junction-assisted photonic demodulator (JAPD) uses electric field applied through two guide electrodes to facilitate the collection of optically generated minority carriers but using a p-n junction to prevent direct majority carrier current. A prototype of the JAPD has been fabricated in a 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> standard CMOS foundry process. Experimental results show that it can achieve a low-power consumption of 29 fW per pixel and a high modulation contrast (MC) of 98%. Through process optimization, it is shown that the optical window can be fully depleted during the demodulation process. In TCAD simulation, the frequency response can be significantly improved by ensuring full depletion of the optical window.

The experience of extended &lt;i&gt;in vitro&lt;/i&gt; human embryo cultivation in a culture medium containing endometrium cells. A pilot study

BACKGROUND: At present, the knowledge on initial human embryogenesis stages is limited to the period of development from zygote to blastocyst. The creation of models based on the interaction between the embryo and endometrium in vitro, which accurately imitate the in vivo processes, represents the major way for implantation and post-implantation evaluation. Currently, no reports have been made on models reflecting the both processes simultaneously: the interaction of the embryo with the substrate, which represents many aspects of normal implantation, and the early post-implantation embryo development. The creation of a relevant model would allow investigation of implantation and early post-implantation processes as a whole.&#x0D; AIM: The aim of this study was to evaluate the vitality and developmental potential of human embryos from the day 6 blastocyst stage during their extended co-incubation with the endometrium in a culture medium specifically designed for cultivation to the blastocyst stage.&#x0D; MATERIALS AND METHODS: Embryos obtained in assisted reproductive technology programs were cultivated from the day 6 blastocyst stage up to 14 days of development in vitro in a culture medium designed for cultivation to the blastocyst stage, in the presence of endometrium cells. On day 14 of development, embryos and endometrial samples were first evaluated under an inverted microscope using Hoffman modulation contrast, then transferred to a special mold and impregnated with paraffin for cytoblock preparation. Obtained blocks were sliced, stained with hematoxylin and eosin and morphologically assessed.&#x0D; RESULTS: The first sample visual assessment on day 14 of cultivation in a culture medium with endometrium cells revealed a viable developing embryo with no signs of degradation. During the histological examination, the endometrial sample corresponded to the secretory phase of the cycle. The morphological assessment of the conceptus detected trophoblast cells. The second sample visual assessment on the day 14 of cultivation in a culture medium with endometrium cells revealed a viable embryo with no signs of degradation, which was in direct contact with the endometrial component. A histological examination detected a secretory endometrial fragment of the surface (luminal) epithelium. During the morphological assessment of the embryo, trophoblast cells were detected.&#x0D; CONCLUSIONS: The data obtained indicate the ability of the embryo to further develop from the day 6 blastocyst stage up to 14 days in a culture medium specifically designed for cultivation to the blastocyst stage, in the presence of endometrium cells. The latter can serve as an experimental model for both in vitro endometrial receptivity evaluation and intercellular interactions during implantation investigation.

Infrared and visible image fusion based on contrast enhancement guided filter and infrared feature decomposition

Infrared (IR) and visible (VIS) images represent the features of the scene at different wavelengths, and the features they contain have different properties. Therefore, the traditional weighted fusion strategy is challenging to preserve the different types of feature information. In addition, VIS images are highly susceptible to bad weather, which also seriously affects the quality of fused images in complex environments. To solve the above problems, we propose a feature enhancement fusion method. First, a fusion model called contrast enhancement guided filter (CEGF) is proposed. The new model enables the texture information of VIS images to be presented with the intensity of infrared pixels, which solves the problem of combining different attribute features and removes the influence of harsh lighting conditions. To improve the visibility of texture details under different lighting conditions, a contrast modulation factor is added to the cost function design of the filter to enhance the contrast of visible details. Second, we use a dual-scale decomposition strategy to enhance the infrared feature information of the fusion results. Finally, we apply the method of this paper with ten classical image fusion algorithms in two types of datasets. The visual effect and objective evaluation of the fusion results verify that the proposed method preserves the characteristics of the high contrast of IR images and improves the visibility of infrared scenes for subsequent target identification and detection.

A Comprehensive Introduction to Magnetic Resonance Imaging Relaxometry and Contrast Agents.

The development of imaging technologies allowing noninvasive observation through solid bodies has represented a breakthrough in medical diagnosis, facilitating the comprehension of biomolecular events underlying disease and the development of more efficient therapeutic approaches. Some of the traditional limitations of these techniques are nowadays fading away thanks to the combination of imaging with nanotechnology, allowing the development of novel functional biomaterials that increase the sensitivity of detection, enable sensitivity to specific targets, and facilitate the combination of therapeutic and diagnostic functions (theragnosis) with molecular platforms functioning simultaneously as imaging probes and drug delivery carriers. The design of such functional biomaterials requires a comprehensive understanding of the principles that govern the generation of signal and modulation of contrast for a given imaging modality to exploit its capabilities to the maximal level. In this sense, magnetic resonance imaging (MRI) is a technique that presents a complex relationship between the detected signal and the physical–chemical properties of its sourcing matter, allowing the generation of multiple image contrasts. Thus, while magnetic resonance imaging is a highly versatile imaging modality, it requires specific knowledge of its physical principles to take advantage of all of its possibilities. This work reviews the origin of the image signal and contrast in MRI and the concepts of relaxometry and MRI contrast agents.

Cascaded plasmon-induced transparency in spoof surface plasmon polariton waveguide

Manipulating spoof surface plasmon polaritons (SPPs) effectively has promising applications in developing ultracompact plasmonic circuits. Research on versatile components in planar spoof SPP waveguides has attracted widespread attention over the decades. In particular, cascaded chip-scale devices play an important role in enhancive buffering, highly-sensitive sensing and nonlinear interaction. Herein, we propose a novel strategy to manipulate the switching and slow wave features of spoof SPPs on the basis of plasmon-induced transparency (PIT) spectral responses. A combined module consisting of split square-ring resonators and electric-LC resonators is loaded with a spoof SPP waveguide along the propagating trajectory, where the destructive interference between the two resonators contributes to the PIT behavior and the group delay of the spoof SPPs. A modulation contrast of up to 16.2 dB is achieved for the spoof SPP transmission at the PIT peak frequency. The measurements are consistent with both full-wave simulations and theoretical calculations. Cascaded capabilities performed by installing multiple PIT modules at an interval of an equivalent wavelength are accomplished in the planar spoof SPP waveguide. The proposed strategy opens up fascinating prospects on highly integrated plasmonic circuits and networks.

Macaque V1 responses to 2nd-order contrast-modulated stimuli and the possible subcortical and cortical contributions.

Natural images comprise contours and boundaries defined by 1st-order luminance-modulated (LM) cues that are readily encoded by V1 neurons, and 2nd-order contrast-modulated (CM) cues that carry local, but not over-the-space, luminance changes. The neurophysiological foundations for CM processing remain unsolved. Here we used two-photon calcium imaging to demonstrate that V1 superficial-layer neurons respond to both LM and CM gratings in awake, fixating, macaques, with overall LM responses stronger than CM responses. Furthermore, adaptation experiments revealed that LM responses were similarly suppressed by LM and CM adaptation, with moderately larger effects by iso-orientation adaptation than by orthogonal adaptation, suggesting that LM and CM orientation responses likely share a strong orientation-non-selective subcortical origin. In contrast, CM responses were substantially more suppressed by iso-orientation than by orthogonal LM and CM adaptation, likely suggesting stronger orientation-specific intracortical influences for CM responses than for LM responses, besides shared orientation-non-selective subcortical influences. These results thus may indicate a subcortical-to-V1 filter-rectify-filter mechanism for CM processing: Local luminance changes in CM stimuli are initially encoded by orientation-non-selective subcortical neurons, and the outputs are half-wave rectified, and then summed by V1 neurons to signal CM orientation, which may be further substantially refined by intracortical influences.

Optically Switchable NIR Photoluminescence of PbS Semiconducting Nanocrystals using Diarylethene Photoswitches.

Precisely modulated photoluminescence (PL) with external control is highly demanded in material and biological sciences. However, it is challenging to switch the PL on and off in the NIR region with a high modulation contrast. Here, we demonstrate that reversible on and off switching of the PL in the NIR region can be achieved in a bicomponent system comprised of PbS semiconducting nanocrystals (NCs) and diarylethene (DAE) photoswitches. Photoisomerization of DAE to the ring-closed form upon UV light irradiation causes substantial quenching of the NIR PL of PbS NCs due to efficient triplet energy transfer. The NIR PL fully recovers to an on state upon reversing the photoisomerization of DAE to the ring-open form with green light irradiation. Importantly, fully reversible switching occurs without obvious fatigue, and the high PL on/off ratio (>100) outperforms all previously reported assemblies of NCs and photoswitches.

Quantifying perceptual resolution for autostereoscopic three‐dimensional displays

AbstractThe perceptual experience issue is particularly important for autostereoscopic three‐dimensional (3D) displays since the perceptual resolution has a great correlation between panel resolution and other 3D display performances, but normally used effective resolution only considers the amount of information being sent to a certain viewing point. This work describes that the visual factors should be taken into consideration associated with resolution and contrast simultaneously to evaluate perceptual 3D resolution. We propose a quantitative evaluation of perceptual resolution of 3D displays from modulated contrast based on the contrast sensitivity function (CSF). A switchable parallax‐barrier display and a directional backlight display providing glasses‐free autostereoscopic vision are experimentally studied to verify the validity of the characterization. Due to the nonlinear response of the CSF threshold curve, less than 50% of the panel resolution in parallax‐barrier 3D displays is perceived, while the display with directional backlight illumination is shown to retain the panel resolution for perceptual experience as expected. We foresee that this study provides a practically objective paradigm to characterize the subjective perceptual resolution and the presented perceptual resolution can be served as a design guideline to achieve an improved 3D viewing experience.

Second-order texture gratings produce overestimation of height in depictions of rectangles and steps

The horizontal-vertical illusion (HVI) has been proposed as a method to increase the perceived height of steps, increase toe clearance and prevent falls. High contrast vertical stripes are placed on the step riser abutting a horizontal edge-highlighter creating ‘T’ junctions which are thought to promote the illusion. Various configurations of the HVI were tested including luminance gratings (L) and second-order modulations of contrast (CM), spatial frequency (FM) and orientation (OM). Observers were asked to compare the apparent height of gratings with that of either filled, unmodulated rectangles or unfilled rectangles. Rectangles were presented alone or as part of a step with a highlighter. In some conditions highlighters matched the properties of the grating; in others or not. In one critical experiment, the HVI was compared for steps with highlighters that were separated from the riser by a thin line and those where the risers and highlighters were continuous. All gratings except FM appeared taller when presented in the step configuration with a continuous, matching highlighter. This effect was greatly reduced when a thin line separated the grating from the highlighter and abolished for mis-matched highlighters and risers. In the rectangle conditions, all cues appeared taller than blank rectangles and L and CM appeared taller than filled-unmodulated rectangles. In conclusion, second-order cues may be useful for inducing the HVI onto steps. However, the ability of vertical stripes and edge-highlighters to accentuate perceived step height may be due to aggregation of the highlighter into the grating rather than the normal horizontal-vertical illusion.

O-177 Towards 3D Reconstructions of Human Preimplantation Embryo Development

Abstract Study question Can we use focal stacks collected through Hoffman modulation contrast (HMC) microscopy to generate 3D reconstructions of preimplantation embryos? Summary answer A machine learning system was designed to generate 3D meshes that approximate the structures of embryos captured on HMC microscopes up to the 8-cell stage. What is known already The 3D arrangement of cells in preimplantation human embryos is a topic of clinical interest, with significant associations between the cell arrangement and blastulation potential from as early as the 4-cell stage. In basic research, the use of confocal microscopy for generating 3D reconstructions is commonplace. However, the use of confocal microscopy in the IVF clinic is often infeasible due to cost and concerns for embryos’ wellbeing. The assessment of 3D cell arrangement in clinical settings can thus prove difficult and time-consuming as many embryologists rely on focal stacks captured through the HMC microscopes widely integrated into incubators. Study design, size, duration The study was a retrospective analysis of 581 Embryoscope focal stacks of embryos from 4 clinics collected between 2018 and 2020. The number of planes in each stack ranged from 7-11 and cell outlines were annotated along with the depths at which they were most in-focus. A deep learning system was designed to generate 3D reconstructions of the embryos. Two clinics’ data were used for training (N = 551) and the others’ for evaluation (N = 30). Participants/materials, setting, methods The deep learning system consisted of three stages: a super-resolution module, a cell segmentation module and a depth regression module. The super-resolution stage was used to predict missing planes in focal stacks that did not contain 11 focal planes; the segmentation module identified individual cells; the depth regression module identified the focal plane at which each cell was most “in-focus”. Meshes were then generated under the assumption that blastomeres’ dimensions are similar along each axis. Main results and the role of chance The superresolution module was evaluated by calculating the structural similarity index (SSIM; an image similarity measure ranging from 0-1) between predicted and true planes when tasked with predicting missing frames in focal stacks with up to 4 planes artificially removed (by uniform random sampling). The module achieved an SSIM of 0.80. The predictions were also evaluated by 2 embryologists, a clinician and a developmental biologist on a scale of 1-5 (1=very unrealistic; 3=usable; 5=very realistic), achieving a mean score of 4.11. The segmentation module was evaluated on the proportion of cells it managed to identify (91%) as well as the mean overlap between predicted cell segmentations and the ground truth (intersection-over-union of 0.86). The depth module was evaluated on the mean deviation of predictions from the true most “in-focus” plane (0.73 planes). 3D reconstructions generated by the system were evaluated with reference to the original focal stacks by 2 embryologists on a 1-5 scale similar to before, with a mean score of 3.72. The most common issues with the reconstructions identified by the embryologists were missing cells/fragments, incorrect cell shape due to obstruction by the well’s edge and imprecise depth predictions (with the “true” depth being between focal planes). Limitations, reasons for caution As previously mentioned, some reconstructions had inaccuracies. These would likely be ameliorated through modifications to the system modules and more training data. Moreover, the system was not trained or evaluated on morulae/blastocysts. Finally, each focal stack was analysed independently - future work may examine enforcing temporal consistency within timelapses. Wider implications of the findings This work serves as a first step towards unlocking data captured in IVF clinics for research into cell arrangement in preimplantation embryos. Combined with cell tracking, the system may be useful for research into cell fate. Moreover, the work may find clinical relevance in enabling easier assessment of cell arrangement. Trial registration number N/A

Inorganic photochromism material SrHfO3:Er3+ integrating multiple optical behaviors for multimodal anti-counterfeiting

Photochromic materials usually have different physical and chemical properties when they are in different states. Inorganic photochromic materials are widely used in the fields of information storage, optical switches and sensors due to their long lifetime, good thermal stability and fatigue resistance. However, the current inorganic photochromic materials, possessing a unitary optical property, cannot fulfill the requirement of multimodal high-level security anti-counterfeiting. In this work, we report the multiple optical behaviors integrated inorganic photochromic Er3+-doped strontium hafnate ceramics. It integrates multiple optical functions, including photochromism, downshifting photoluminescence, up-conversion luminescence, afterglow, and thermoluminescence. The fluorescence modulation contrast (FMC) maximum of SrHfO3: Er3+ can achieve as high as to 77.21% in the mode of photochromism-driven the quenching of downshifting photoluminescence. The FMC maximum can approach 70.24% in the mode of photochromism-driven the quenching of up-conversion luminescence. By alternating the light stimulation and thermal field effect, both photochromism and fluorescence modulation exhibit excellent stability and robust fatigue resistance. The mechanisms of the observed photochromism, downshifting and up-conversion luminescence, fluorescence modulation, afterglow, and thermoluminescence were studied systematically. The combination of the multiple optical behaviors functionalizes the as-obtained material for versatile applications. As a proof of concept, a flexible film was designed and prepared, demonstrating the practical application of SrHfO3: Er3+ material for multimodal high-level security anti-counterfeiting.

Precision in iterative modulation enhanced single-molecule localization microscopy

Modulation enhanced single-molecule localization microscopy (meSMLM) methods improve the localization precision by using patterned illumination to encode additional position information. Iterative meSMLM (imeSMLM) methods iteratively generate prior information on emitter positions, used to locally improve the localization precision during subsequent iterations. The Cramér-Rao lower bound cannot incorporate prior information to bound the best achievable localization precision because it requires estimators to be unbiased. By treating estimands as random variables with a known prior distribution, the Van Trees inequality (VTI) can be used to bound the best possible localization precision of imeSMLM methods. An imeSMLM method is considered, where the positions of in-plane standing-wave illumination patterns are controlled over the course of multiple iterations. Using the VTI, we analytically approximate a lower bound on the maximum localization precision of imeSMLM methods that make use of standing-wave illumination patterns. In addition, we evaluate the maximally achievable localization precision for different illumination pattern placement strategies using Monte Carlo simulations. We show that in the absence of background and under perfect modulation, the information content of signal photons increases exponentially as a function of the iteration count. However, the information increase is no longer exponential as a function of the iteration count under non-zero background, imperfect modulation, or limited mechanical resolution of the illumination positioning system. As a result, imeSMLM with two iterations reaches at most a fivefold improvement over SMLM at 8 expected background photons per pixel and 95% modulation contrast. Moreover, the information increase from imeSMLM is balanced by a reduced signal photon rate. Therefore, SMLM outperforms imeSMLM when considering an equal measurement time and illumination power per iteration. Finally, the VTI is an excellent tool for the assessment of the performance of illumination control and is therefore the method of choice for optimal design and control of imeSMLM methods.

Solvent-induced lengthened conjugated chains in electrochromic PEDOT for enhanced optical modulation

Conjugated PEDOT is considered as a promising electrochromic (EC) material, while the unsatisfactory optical modulation contrast limits its applications. Enhancing the conjugated chain length has been proved to improve the EC performance of conjugated conductive polymers (CPs). Herein, a simple and effective solvent-induced approach is developed to prepare EC PEDOT with extended conjugated chains. A strong polarity solvent of acetonitrile is employed to electrochemically polymerize PEDOT on a well-designed Ni(OH)2 nanosheet arrays substrate, which facilitates a longer conjugated chain formed in the PEDOT molecules. Compared with the samples obtained in water, the acetonitrile-assistant prepared PEDOT demonstrates a superior EC behavior, including enhanced transmittance contrast (∼48% at 550 nm), fast response for coloring/bleaching (1.35 s/0.83 s), ultrahigh coloration efficiency (293.6 cm2 C-1) and improved cycling durability. Particularly, a stable optical modulation could be maintained in a wide temperature range (−10 to 100 °C) and harsh acidity environment. This work is anticipated to provide a novel and simple approach to lengthen the conjugated chains of EC PEDOT toward enhanced optical modulation and can also be applicable to various conjugated CPs.