Illumination Intensity Research Articles

Photoelectrochemistry of Redox-Active Self-Assembled Monolayers Formed on n-Si/Au Nanoparticle Photoelectrodes.

Controlling the chemistry of the electrode-solution interface is critically important for applications in sensing, energy storage, corrosion prevention, molecular electronics, and surface patterning. While numerous methods of chemically modifying electrodes exist, self-assembled monolayers (SAMs) containing redox-active moieties are particularly important because they are easy to prepare, have well-defined interfaces, and can exhibit textbook photoelectrochemistry. Here, we investigate the photoelectrochemistry of redox-active SAMs on semiconductor/metal interfaces, where the SAM is attached to the metal site instead of the semiconductor. n-Si/Au photoelectrodes were fabricated using a benchtop electrodeposition procedure and subsequently modified by immersion in aqueous solutions of (ferrocenyl)hexanethiol and mercaptohexanol. We explored the relevant preparation conditions, finding that after optimization, we were able to obtain canonical cyclic voltammetry for a surface-bound redox molecule that could be turned on and off using light. We then characterized the optimized electrodes under varying illumination intensities, finding that the heterogeneous electron transfer kinetics improved under higher illumination intensities. These results lay the foundation for future studies of semiconductor/metal/molecule interfaces relevant to sensing and electrocatalysis.

Advancing biohydrogen production through indirect photolysis: Insights from numerical simulation using the lattice boltzmann method

Hydrogen production through biochemical reactions is regarded as one of the most potential alternative technologies for producing hydrogen because of its efficacy, renewability, and environmental friendliness. Indirect biophotolysis is one of the most potential biohydrogen production technologies. In this study, a platform based on a coupled lattice Boltzmann method with cellular automata (LBM-CA) was developed to investigate the effects of different illumination intensities and carbon dioxide (CO2) concentrations on indirect photolysis in a bioreactor. The bioreactor was divided into two distinct parts. The first part as a photobioreactor had a transparent window at the top wall of the bioreactor that allowed solar illumination to enter the domain to generate glucose through the conversion of CO2 to carbohydrates (such as glucose) while the second was opaque where hydrogen was produced from carbohydrates by microorganisms. The results show that in the first part of the bioreactor, biofilm grew once CO2 was available. However, there is a lag in the biofilm growthand biohydrogen production between the first and the second part of the bioreactor because they depend on glucose production in the first part. The biofilm concentration increased as illumination increased, especially in the early stages, while the biofilm growth mainly occurred in the first part of the bioreactor. Increasing illumination could increase biofilm concentration by 92.4 % and reduce the lag time. It is also observed that increasing CO2 concentration changed the normalized biofilm concentration considerably, from − 40.9 % to 18.8 %. This can be attributed to increased nutrient availability for microorganism growth and glucose production in the first part of biophotolysis, resulting in greater concentrations of glucose as the main nutrient in the next part. Changing the inlet concentration leads to variations in the normalized hydrogen concentration in the range of − 72.9 % to 49.5 %.

Light-induced multilevel resistive switching in cesium-doped lead-free halide double perovskite memory device

A series of (CH3NH3)2-xCsxAgBiBr6 films (x=0, 0.1, 0.2, 0.3, 0.4) were fabricated on ITO/glass substrates through the sol-gel method. 15 % Cs doping (x=0.3) was the optimal condition for enhancing the film quality and achieving nonvolatile bipolar resistive switching (BRS) performance in the devices. The on/off ratio in the (CH3NH3)1.7Cs0.3AgBiBr6 (Cs-MAABB-3)-based RS device reached 7.7×104, high and low resistance states were maintained for over 104 s. Under different light intensities with a wavelength of 430 nm, six distinct resistance states were recorded at −0.3 V in the Au/Cs-MAABB-3/ITO/glass device. These multilevel states remained after 5000 s and 650 cycles, indicating the excellent retention and endurance of multilevel RS memory in the Au/Cs-MAABB-3/ITO/glass device. The RS behavior in this device followed the trap-controlled space charge-limited current and conductive filament models. Cs-doping increased the concentration of intrinsic vacancies appropriately, leading to a more prominent RS effect. With varying intensities of illumination, the change of Schottky-like barrier at the Au/Cs-MAABB-3 interface, modulated by the photo-induced carriers, affected the multilevel resistance states in the device. The excellent multilevel RS performance was observed for the first time in the Cs-MAABB-3-based device. It presents broad possibilities for improving high-density memory in lead-free halide double perovskite-based devices.

Efforts to Prevent Eye Fatigue Through Evaluation of Lighting Intensity (Illumination Level) in the Library at Muhammadiyah University Lamongan

Efforts to Prevent Eye Fatigue Through Evaluation of Lighting Intensity (Illumination Level) in the Library at Muhammadiyah University Lamongan

Comparative study of cadmium telluride solar cell performance on different TCO‐coated substrates under concentrated light intensities

AbstractConcentrating photovoltaics is an attractive route for achieving high power output with thin film solar cells, using low‐cost optics. In this work, the performance of CdTe:As thin film solar cells on two different transparent conducting oxide (TCO)‐coated substrates is investigated and compared under varying concentrated light intensities (1–6.3 Suns). Samples tested had CdZnS/CdTe:As devices deposited atop of either a soda‐lime glass with a fluorine‐doped tin oxide TCO or an ultra‐thin glass (UTG) with an aluminium zinc oxide TCO and ZnO high‐resistive transparent (HRT) layer. Device current density was found to increase linearly with increased light intensities, for both sample configurations. Power conversion efficiencies of both device samples decreased with increased light intensity, due to a decrease in fill factor. The fill factor, for both sample configurations, was affected by reducing shunt resistance with increasing illumination intensity. The two device types performed differently at the high illumination intensities due to their series resistance. Light‐soaking devices under 6.3 Suns illumination intensity for 90 min showed no significant performance degradation, indicative of relatively stable devices under the highest illumination intensity tested. Efficiency limiting factors are assessed, evaluated and discussed.

Light-Driven Multidirectional Bending in Artificial Muscles.

Using light to drive polymer actuators can enable spatially selective complex motions, offering a wealth of opportunities for wireless control of soft robotics and active textiles. Here, the integration of photothermal components is reported into shape memory polymer actuators. The fabricated twist-coiled artificial muscles show on-command multidirectional bending, which can be controlled by both the illumination intensity, as well as the chirality, of the prepared artificial muscles. Importantly, the direction in which these artificial muscles bend does not depend on intrinsic material characteristics. Instead, this directionality is achieved by localized untwisting of the actuator, driven by selective irradiation. The reaction times of this bending system are significantly - at least two orders of magnitude - faster than heliotropic biological systems, with a response time up to one second. The programmability of the artificial muscles is further demonstrated for selective, reversible, and sustained actuation when integrated in butterfly-shaped textiles, along with the capacity to autonomously orient toward a light source. This functionality is maintained even on a rotating platform, with angular velocities of 6°/s, independent of the rotation direction. These attributes collectively represent a breakthrough in the field of artificial muscles, intended to adaptive shape-changing soft systems and biomimetic technologies.

Study of defect density of copper vacancies in chalcogenide CuSbS2, CuSbSe2, CuBiS2, and CuBiSe2 heterojunction thin-film solar cells.

In the past decade, a new family of ternary chalcogenide absorber (TCA) materials MIMIIX2 (where MI = Cu, Ag, Pb; MII = Sb, Bi, In; and X = S, Se, Te) have been studied. The copper family of ternary chalcogenide CuSbS2 CuSbSe2 CuBiS2, and CuBiSe2 is an amazing absorber material for thin-film solar cells because of their suitable band gap, high absorption coefficient and inexpensive, nontoxic, environment friendly and sustainable nature. In the presented work, first time simulated defect density of copper vacancies in CuSbS2 (CAS), CuSbSe2 (CASe), CuBiS2 (CBS) and CuBiSe2 (CBSe) has based heterojunction thin-film solar cells (HJTFSCs) with buffer CdS, intrinsic i-ZnO, window ZnO: Al and back contact Mo and set the cell scheming ZnO: Al/i-ZnO/n-CdS/p-TCA/Mo using SCAPS 1D. Major focus of this paper is on the influence of copper vacancies defect density that impact on the performance of ternary chalcogenide with various parameters of solar cells, i.e. short-circuit current density (Jsc), open-circuit voltage (Voc), form factor (FF) and efficiency (η). The cell parameter set at constant temperature 300K, thickness 2.5μm, carrier density 5 × 1016cm-3, front internal transmission coefficient 1 and illumination intensity 100 mW/cm2 with AM1.5 sun light. This study clarifies the potential benefits to utilizing of ternary chalcogenide compounds as absorber material for solar cell fabrication.

Bayesian multi-exposure image fusion for robust high dynamic range ptychography.

The limited dynamic range of the detector can impede coherent diffractive imaging (CDI) schemes from achieving diffraction-limited resolution. To overcome this limitation, a straightforward approach is to utilize high dynamic range (HDR) imaging through multi-exposure image fusion (MEF). This method involves capturing measurements at different exposure times, spanning from under to overexposure and fusing them into a single HDR image. The conventional MEF technique in ptychography typically involves subtracting the background noise, ignoring the saturated pixels and then merging the acquisitions. However, this approach is inadequate under conditions of low signal-to-noise ratio (SNR). Additionally, variations in illumination intensity significantly affect the phase retrieval process. To address these issues, we propose a Bayesian MEF modeling approach based on a modified Poisson distribution that takes the background and saturation into account. The expectation-maximization (EM) algorithm is employed to infer the model parameters. As demonstrated with synthetic and experimental data, our approach outperforms the conventional MEF method, offering superior phase retrieval under challenging experimental conditions. This work underscores the significance of robust multi-exposure image fusion for ptychography, particularly in imaging shot-noise-dominated weakly scattering specimens or in cases where access to HDR detectors with high SNR is limited. Furthermore, the applicability of the Bayesian MEF approach extends beyond CDI to any imaging scheme that requires HDR treatment. Given this versatility, we provide the implementation of our algorithm as a Python package.

Photoinduced Charge Injection from Shallow Point Defects in Diamond into Water.

Thanks to its low or negative surface electron affinity and chemical inertness, diamond is attracting broad attention as a source material of solvated electrons produced by optical excitation of the solid-liquid interface. Unfortunately, its wide bandgap typically imposes the use of wavelengths in the ultraviolet range, hence complicating practical applications. Here, we probe the photocurrent response of water surrounded by single-crystal diamond surfaces engineered to host shallow nitrogen-vacancy (NV) centers. We observe clear signatures of diamond-induced photocurrent generation throughout the visible range and for wavelengths reaching up to 594 nm. Experiments as a function of laser power suggest that NV centers and other coexisting defects─likely in the form of surface traps─contribute to carrier injection, though we find that NVs dominate the system response in the limit of high illumination intensities. Given our growing understanding of near-surface NV centers and adjacent point defects, these results open new perspectives in the application of diamond-liquid interfaces to photocarrier-initiated chemical and spin processes in fluids.

Unpaired fundus image enhancement based on constrained generative adversarial networks.

Fundus photography (FP) is a crucial technique for diagnosing the progression of ocular and systemic diseases in clinical studies, with wide applications in early clinical screening and diagnosis. However, due to the nonuniform illumination and imbalanced intensity caused by various reasons, the quality of fundus images is often severely weakened, brings challenges for automated screening, analysis, and diagnosis of diseases. To resolve this problem, we developed strongly constrained generative adversarial networks (SCGAN). The results demonstrate that the quality of various datasets were more significantly enhanced based on SCGAN, simultaneously more effectively retaining tissue and vascular information under various experimental conditions. Furthermore, the clinical effectiveness and robustness of this model were validated by showing its improved ability in vascular segmentation as well as disease diagnosis. Our study provides a new comprehensive approach for FP and also possesses the potential capacity to advance artificial intelligence-assisted ophthalmic examination.

Why is gallium-doped silicon (sometimes) stable? Kinetics of light and elevated temperature induced degradation

Light and elevated temperature induced degradation (LeTID) can induce high power losses in photovoltaic modules built from various types of silicon wafers. After the industry's rapid transition from Boron- to Gallium-doping, it is still unclear how the new dopant atom affects the degradation process and why it entails an apparently higher resistance to LeTID. We treat identically processed Gallium-doped Czochralski silicon wafers at 16 different conditions by screening temperature and minority charge carrier density (in the following “injection”). The illumination source is regulated to keep the injection constant at each condition. This method allows for an improved quantitative analysis of the LeTID kinetics based on effective lifetime measurements. Our results show that Gallium-doping shifts the equilibrium between the formation of LeTID defects and their temporary recovery (TR) to the latter, leading to a reduced degradation extent at temperatures up to 80 °C. The efficacy of this TR-induced LeTID suppression depends delicately on both temperature and injection which explains why Gallium-doped silicon appears to be LeTID-immune at high illumination intensities. By accounting for the influence of TR, we extract activation energies and injection exponents that relate to the dominant defect transitions separately, revealing a large discrepancy to effective values reported in literature. The increased accuracy of our kinetic parameters enhances the reliability of existing efficiency models. Finally, we find that a degradation as expected under field conditions can be probed at a 100-fold accelerated rate in the lab. By shining light on LeTID kinetics in Gallium-doped silicon, we explain the dopant atoms' influence on the degradation behavior, establish a basis for precise yield modelling and formulate guidelines for accelerated test protocols.

High dynamic range structured illumination microscopy based on per-pixel coding

Abstract Structured illumination microscopy (SIM) can achieve optical sectioning with high resolution, and have aroused extensive research interest. In SIM, a set of high-contrast illumination patterns are projected onto the sample to modulate the surface height information, and then, a decoding algorithm is applied to the modulated pattern images for high-quality optical sectioning. Applied to samples with large dynamic range of reflectivity, however, SIM may fail to achieve high quality sectioning for accurate surface reconstruction. Herein, an active digital micromirror device (DMD) based illumination method using per-pixel coded strategy is proposed in SIM to realize high-quality measurement for surface with complex reflection characteristics. In this method, the mapping relationship between DMD and the camera is established pixels by pixels, which enables the illumination intensity on the sample surface can be flexibly modulated by DMD pixel-level modulation corresponding to reflectivity distribution of the surface, and allows the camera pixels always to have reasonable exposure intensity for high precision measurement. More importantly, we put forward an adaptive light intensity control algorithm to improves the signal-to-noise ratio of acquired images without compromising modulation depth of pattern and measurement efficiency. Extensive comparative experiments were conducted and demonstrated that the proposed method can retrieve the surface morphology information of micro-scale complex reflectivity surfaces with high accuracy.

Response of multipolar retinal neurons to photodamage in the experiment

Purpose: to assess the reaction of multipolar retinal neurons to light irradiation depending on the intensity and duration of exposure. Material and methods. Outbred sexually mature white rats (n = 50, 100 eyes) weighing 180–200 g were exposed to continuous round-the-clock light (200, 3,500 lux; 1, 2, 7, 14, 30 days). The control group consisted of 25 non-irradiated animals (50 eyes). Using semifine sections, colored with toluidine blue, we counted the number of neurons in the ganglionic layer with karyopyknosis, focal and total chromatolysis. In the optic nerve, the percentage of degeneratively altered axons and the number of nerve fibers with deformation of the myelin sheath were calculated. Ultrastructural changes in neurons were studied using a JEM-100 CX-II electron microscope. Results. In the first days of the experiment (1, 2 days), reactive and destructive changes in organelles are observed in the perikaryons of multipolar retinal neurons. The granular endoplasmic reticulum becomes fragmented, loses part of its ribosomes, and vacuoles of varied sizes are formed from its cisterns. With an increase in the duration of exposure (7–30 days), degradation processes are increasing, all the more so after high-intensity (3,500 lux) light irradiation. The photodamage causes changes in all components of the optic nerve and is characterized by a destruction of organelles, a decrease in the number of elements of the cytoskeleton in the axon, and myelin sheath splitting. Conclusion. Changes in multipolar neurons of the retina after photodamage are primarily related to the content and distribution of the chromatophilic substance and depend on the intensity and duration of illumination.

Multifunctional organic salts synergize interfacial passivation for efficient PSCs

Fully inorganic metal halide perovskite solar cells (PSCs) exhibit high efficiency and excellent thermal stability. However, the presence of surface traps caused by oxygen vacancies in the electron transport layer leads to significant non-radiative charge recombination, which limits both the short-circuit current density (JSC) and photoelectric conversion efficiency (PCE). In this study, we propose a dual-purpose strategy by incorporating the multifunctional organic salt dopamine hydrochloride (DACl) as an additive into the electron transport layer. Firstly, DACl acts as a Lewis base when added to TiO2 films, facilitating improvements in electron transport properties and resulting in higher photovoltaic quality of subsequently deposited perovskite layers. This enhancement significantly improves overall photovoltaic performance. Secondly, DACl's electron-rich aromatic structure and -NH2 functional group can anchor undercoordinated Pb2+ ions and passivate defects within the perovskite film. Additionally, its -OH functional group and charged ion Cl- play crucial roles in improving perovskite grain size and crystallinity. As a result of these modifications, cell efficiency increased ∼35 %, from 9.37 % to 12.70 %, while short-circuit current density increased from 15.44 mA cm−2 to 17.80 mA cm−2 at an illumination intensity of 100 mW cm−2. These findings suggest that introducing DACl into the ETL layer is a promising approach for achieving efficient and stable PSCs.

A comprehensive investigation of the synthesis, spectral, DFT, and optical properties of a novel oxadiazolyl-pyrano[3,2-c]quinoline for photosensor applications

The condensation reaction of pyranoquinoline-3-carbaoxldehyde 1 with benzohydraide afforded hydrazone 2 which upon oxidative cyclization yielded 6-ethyl-4‑hydroxy-3-(5-phenyl-1,3,4-oxadiazol-2-yl)-2H-pyrano[3,2-c]quinoline-2,5(6H)‑dione (EHPOPQ, 3). The DFT and B3LYP/6–311++G(d,p) basis set were used to compute the optimized molecular geometry. The global reactivity descriptors were examined and showed that hydrazone 2 exhibited high softness while aldehyde 1 had more electronegativity and high global electrophilicity. Subsequently, the reactive sites of the present compounds were located by tracing the MEP map. The GIAO method was used to calculate the 1H and 13C NMR. The current comprehensive investigation of the novel (EHPOPQ) reveals its significant potential for applications in nonlinear optics (NLO) and photovoltaics. Through high-level computational methods, EHPOPQ has an exceptionally high first hyperpolarizability (βtot) of 950 × 10−30 esu, which is substantially higher than that of the conventional NLO material urea. This high βtot value suggests that EHPOPQ could dramatically enhance the efficiency and performance of NLO devices such as frequency converters and optical modulators. In parallel, the detailed spectroscopic analysis of EHPOPQ's optical properties provided critical insights for photovoltaic applications. The optical band gap was measured to be 3.07 eV, indicating a direct band gap transition suitable for efficient light harvesting in solar cells. Additionally, dispersion parameters were carefully analyzed, which are essential for understanding the interaction of light with the material. The experimental characterization of EHPOPQ-based photovoltaic devices showed promising results. Current-voltage (J-V) measurements under varying illumination intensities revealed significant enhancements in the device's short-circuit current (from 1.2 µA to 4.3 µA) and open-circuit voltage (from 0.25 V to 0.47 V) as light intensity increased. These findings demonstrate the material's heightened photoresponsivity and suggest its potential as an efficient light conversion material for solar energy applications. These specific findings underline the importance of EHPOPQ in advancing both NLO and photovoltaic technologies, offering a pathway to more efficient and effective devices.

Composite polymer films with semiconductor nanocrystals for organic electronics and optoelectronics

Organic materials and, in particular, polymer films enhanced with certain nanocrystals have a potential for wide application in electronics and optoelectronics due to their organic flexibility, lightweight, simple integration, affordable manufacturing cost, and low environmental impact of their production. The purpose of this research is to investigate the electrical properties of polymer-based composite films containing Cd1–xCuxS nanocrystals in order to determine their prospects for use as conductive layers in organic electronics and optoelectronics. The paper contains a detailed description of the synthesis method of hybrid nanocomposite films based on peroxide reactive copolymer (PRC) with Cd1–xCuxS nanocrystals. The defect structure of the films is studied by analyzing the photoluminescence spectra. Current-voltage characteristics of the films with different Cd and Cu contents in the Cd1–xCuxS nanocrystals embedded into the polymer matrix, deposited on glass substrates are measured in the dark and under light illumination. The film conductivity is found to increase with the Cu content in the Cd1–xCuxS nanocrystals. The carrier transport corresponds to the Ohm law at low voltages and the space charge limited current (SCLC) or Poole–Frenkel mechanisms at higher ones. The conductivity of the polymer-based hybrid nanocomposite films has a weak dependence on the intensity of light illumination. The explanation of the obtained experimental results is proposed.

Recovering true FRET efficiencies from smFRET investigations requires triplet state mitigation

Single-molecule fluorescence resonance energy transfer (smFRET) methods employed to quantify time-dependent compositional and conformational changes within biomolecules require elevated illumination intensities to recover robust photon emission streams from individual fluorophores. Here we show that outside the weak-excitation limit, and in regimes where fluorophores must undergo many rapid cycles of excitation and relaxation, non-fluorescing, excitation-induced triplet states with lifetimes orders of magnitude longer lived than photon-emitting singlet states degrade photon emission streams from both donor and acceptor fluorophores resulting in illumination-intensity-dependent changes in FRET efficiency. These changes are not commonly taken into consideration; therefore, robust strategies to suppress excited state accumulations are required to recover accurate and precise FRET efficiency, and thus distance, estimates. We propose both robust triplet state suppression and data correction strategies that enable the recovery of FRET efficiencies more closely approximating true values, thereby extending the spatial and temporal resolution of smFRET.

Investigation on a novel hybrid system based on radiative sky cooling and split thermoelectric cooler driven by photovoltaic cell

This paper develops a novel cooling and heating system by integrating a novel split thermoelectric cooler (STEC) with photovoltaic power generation and radiative sky cooling. The system uses photovoltaic driven STEC modules to generate cooling and heating combined with radiative sky cooling to improve cooling capacity. By harnessing the distinctive characteristics of photovoltaic technology and radiative sky cooling, the new system is capable of operating continuously for 24 h without requiring any additional energy input. The system mathematical model is established, and the effects of STEC module number, solar illumination intensity, area ratio and ambient temperature on the performance are studied. Results demonstrate that the cooling efficiency of the system is 3.02 and the heating efficiency is 1.86 when the number of STEC modules is 3. In a year, the monthly average heat production of the system fluctuates due to changes in the solar illumination intensity, while the fluctuation of cooling capacity is small. The system cold production is larger than heat production, which is more suitable for application in the area with high demand for year-round refrigeration. The new system has good energy and economic performance with payback time being shorter than that of the photovoltaic-air conditioning system.

Randomized trial comparing the effects of a 3D head-up system and microscope eyepiece-assisted simulated vitrectomy with intraocular illumination on the ocular surface of an operator

BackgroundTo compare the effects of a 3D head-up system and microscope eyepiece-assisted simulated vitrectomy intraocular illumination on the ocular surface of an operator.MethodsThis was a prospective randomized controlled study. According to the application system, thirty ophthalmic operators (60 eyes) were randomly divided into 3D and eyepiece groups. Under different intensities of intraocular illumination, operators in both groups viewed the fundus model through a 3D display screen or microscopic eyepiece for 2 h. Objective examinations and a subjective symptom questionnaire were used immediately after the test to evaluate the ocular surface of the operators. Objective examinations included nonintrusion tear meniscus height (NIKTMH), nonintrusion break-up time (NIKBUT), and bulbar redness and strip meniscometry tube (SMTube) measurements. Statistical analyses were performed by using SPSS 26.0 software.ResultsAfter the test, the NIKTMH, NIKBUT and SMTube measurements decreased; however, the degree of change varied among the groups of different systems. The differences between the 3D group and the eyepiece group in NIKTMH measurements, SMTube measurements, subjective symptom scores (eye dryness, difficulty focusing, and cervical pain), and light intensity reaching the ocular surface of the operators were statistically significant (P < 0.05). All of the objective and subjective tests showed that the 3D group had fewer effects on the NIKTMH and SMTube measurements, and the subjective comfort of the 3D group was greater.ConclusionFor both 3D screens and eyepieces, simulated vitrectomy with intraocular illumination for two hours can lead to discomfort and abnormalities in the operator’s ocular surface; however, these abnormalities are less severe in the 3D group.Trial registrationThis trial was registered on December 22, 2022, at the Chinese Clinical Trials Registry with NO. ChiCTR2200066989.

Double-clad optical fiber as a single-point sensor of imaging quality for scanning laser system

We have developed a single-point optical sensor of imaging quality based on a double-clad optical fiber for laser beam scanning imaging systems. The optimal imaging quality, primarily affected by the accurate focusing, is determined by maximizing the ratio of the optical power coupled to the single-mode core and the inner multi-mode cladding of the double-clad fiber collecting the light scattered from the sample. We present simulations of the sensor’s performance at different levels of defocus and validate it experimentally by optimizing focus when imaging a scattering phantom and a living human eye with a scanning laser ophthalmoscope. In contrast to the existing image-based optimization procedures, our sensor provides feedback independent of illumination intensity or sample reflectivity that can be obtained for each image point, thus exceeding the imaging framerate. Importantly, our sensor can seamlessly be integrated with most laser scanning imaging systems, providing online feedback for correction optics.