Radiant Exitance Research Articles

The dark art of light curing in dentistry

ObjectiveThis study was designed to show that the commonly reported irradiance values that are quoted in most publications inadequately describe the light output from light curing units (LCUs). MethodsThe total spectral radiant power (mW) output from 12 contemporary LCUs was measured with a fiberoptic spectroradiometer and a calibrated integrating sphere. Five recordings were taken for each LCU and exposure mode. In addition, the irradiances (mW/cm²) delivered at 0-mm, 5-mm and 10-mm distances were recorded through a 6-mm diameter aperture and the radiant exposures (J/cm²) from the LCUs were calculated. Light beam profiles from the LCUs were recorded using a beam profiler, and the images were overlaid on a molar tooth to simulate a clinical setting. Data were analyzed using ANOVA followed by Tukey post-hoc test (α = 0.05). ResultsThe mean power outputs from the LCUs ranged from 380 to 2472 mW (p < 0.0001). The highest irradiance was recorded from the Cicada CV 215-G7 (3091 mW/cm² in its highest mode) and the lowest from the Radii Cal CX (731 mW/cm²). The emission spectra differed, even among the multi-peak and single-peak LCUs. Radiant exposures from the entire light tip ranged from 18.3 J/cm², Radii Cal CX, in its standard 25 s exposure mode to 3.9 J/cm² from the Monet Laser in a 3 s exposure setting. Half (50 %) of the measured irradiance values from the LCUs differed from the manufacturers' value by more than 10 %. There were significant differences in the impact of distance from the tip. The beam profiles visually highlighted the varying effects of distance from the LCU tip among different units. ConclusionThere were significant differences in the emission spectra, power outputs, tip diameters, irradiances, radiant exposures, and the effect distance from the light tips. These differences underline the importance of manufacturers and researchers correctly measuring and reporting the output from the LCU to ensure that research is reproducible and that patients receive acceptable dental restorations. Clinical SignificanceThis article alerts clinicians, researchers and journal editors that providing only the tip irradiance (radiant exitance) value from the LCU is no longer sufficient. Manufacturers and researchers should include information on the spectral radiant power, emission spectrum, tip diameters, and also the effect of distance on the irradiance and radiant exposure, beam profiles and tooth access information when describing an LCU.

Properties of InSb photodiodes fabricated by ion implantation

InSb photodiodes were fabricated by ion implantation method. The electrical and photoelectrical properties of the photodiodes in the operating temperature range of 69…115 K were investigated. The test structures were fabricated as a part of the developed technological route. The value R0 A0, which is the product of the dynamic resistance and the diode area, was ~2·104 Ohm·cm2 at the operating temperature of 77 K for the diodes with the topological area of 0.01 mm2. The avalanche effect as well as the influence of background radiation on the I–V characteristics and dynamic resistance of the diodes were observed. The integrated ampere-watt responsivity of the fabricated InSb photodiodes to a radiant exitance of a blackbody with the temperature of 500 K was determined. The operating temperature of the InSb diode, at which the thermal and fractional noises were equal to each other, was 115 K under the conditions of the presence of background radiation with the temperature of 293 K in the aperture angle FOV ~ 30°.

Monomer elution and shrinkage stress analysis of addition-fragmentation chain-transfer-modified resin composites in relation to the curing protocol

ObjectiveThe purpose was to compare the effects of rapid (3 s) and conventional (20 s) polymerization protocols (PP) of mono- and multichip LED curing units (LCU) on shrinkage stress (SS) and monomer elution (ME) in bulk-fill resin-based composites (RBC) with and without addition-fragmentation chain-transfer (AFCT) monomer. MethodsCylindrical (5x4mm) specimens were prepared from two RBCs containing different AFCT monomers (Filtek OneBulk-FOB; Tetric PowerFill-TPF) and one without (Tetric EvoCeram Bulk-TEC). After soaking for 3, 10, and 14 days (75 % ethanol), ME was quantified using standard monomers by High-Performance Liquid Chromatography. SS was measured from the start of polymerization to 5 min using a Materials Testing Machine. The radiant exitance of LCUs was measured using a spectrophotometer. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05). ResultsAFCT-modification significantly decreased ME (p < 0.001). ME was reduced by half by day 10 and by one tenth by the end of the 14-day compared to the 3-day sampling. ME itself was dependent, whereas the percentage of monomers released was independent of the PP used (p > 0.05). FOB showed the lowest SS (p < 0.001), while there was no significant difference between TPF and TEC (p = 0.124). Both ME and SS were significantly influenced by material type and PP. SignificanceThe incorporation of the AFCT monomer reduced ME, but this was inversely related to a decrease in exposure time. SS values reduced by rapid PP in parallel with increasing ME values. The utilization of the AFCT molecule in conjunction with an appropriate resin-, initiator-system is of significant consequence for the kinetics of polymerization and the incorporation of monomers into the network.

Evaluation of 278 New Bluephase Style Light Curing Units Purchased Over Six Years.

This study measured 278 new curing lights (LCUs) to determine if they met the manufacturer's specifications. Over a 6-year period, the light output from 278 Bluephase Style LCUs was measured before the LCUs were given to students (41 in 2017, 44 in 2018, 46 in 2019, 48 in 2020, 50 in 2021, and 49 in 2022). The radiant exitance (mW/cm²) from each year was compared using ANOVA and Tukey- Kramer multiple comparisons test with adjustment for the unequal sample sizes (α=0.05). The results were also compared against the manufacturer's stated radiant exitance of 1200 mW/cm². The 278 LCUs delivered an average (± standard deviation) radiant exitance of 1203 ± 16.7 mW/cm². The lowest radiant exitance was 1149 mW/cm² and the highest was 1257 mW/cm². Although there were statistically significant differences in the LCUs from each year, these values were within the manufacturer's tolerance of values of ± 10%. Approximately 13% of the emitted light was below 420 nm, and 87% was above 420 nm. These new LCUs were all multiple peak LCUs that emitted an average radiant exitance of 1,203 mW/cm² (range 1149 to 1257 mW/cm². Purchasers of the Style LCU can be confident that their new LCU will meet the manufacturer's specifications.

Path guiding for wavefront path tracing: A memory efficient approach for GPU path tracers

We propose a path-guiding algorithm to be incorporated into the wavefront style of path tracers (WFPTs). As WFPTs are primarily implemented on graphics processing units (GPUs), the proposed method aims to leverage the capabilities of the GPUs and reduce the hierarchical data structure and memory usage typically required for such techniques. To achieve this, our algorithm only stores the radiant exitance on a single global sparse voxel octree (SVO) data structure. Probability density functions required to guide the rays are generated on-the-fly using this data structure. The proposed approach reduces the scene-related persistent memory requirements compared to other path-guiding techniques while producing similar or better results depending on scene characteristics. To our knowledge, our algorithm is the first one that incorporates path guiding into a WFPT.

Evaluation of Radiant Power of the Light Curing Units Used in Clinics at Governmental and Privates Dental Faculties.

To evaluate the radiant power of the light cure units (LCUs) in relation to their type, radiant exitance, number of years in clinical use, and condition of LCUs tips in governmental and public clinics in Dental Faculties in Sana'a City. LCUs were collected from different colleges at Sanaa City, Yemen, then LCU data as type, clinical age (<1 year, between 1-5 and ˃ 5-years), tip condition was visually inspected for damage and adhering debris, and the radiant exitance values of the tested LCUs. Radiant exitance values were subcategorized into three groups: <400, 400-850, and >850 mW/cm², labeled as inadequate, marginal, and adequate radiant exitances, respectively. A Woodpecker radiometer was used with a mode lasting of 20 seconds was used with each LCU. Descriptive statistics of the different parameters were evaluated with SPSS version 25. One-way ANOVA and Mann-Whitney tests were performed to determine the mean difference between the groups with a significance value of ˂ 0.05 was considered. Two hundred twenty-three LCUs were surveyed, and the majority were Light-emitting diode (LED). Forty-nine (21.9%), 117 (52.4%), 57 (25.6%) recorded lesser than, 400-850, and more than 850 mW/cm², respectively. Radiant exitances of < year-old units were found to be higher than those of units used for ˃ 5 years with significant differences (p=0.001). The ANOVA test showed significant differences between the radiant exitance with clinical age and LCU tip conditions and a strong correlation p ˃ 0.050. LED curing lights were the most used in the tested Dental Faculties. More than half of the used LCU offered sufficient radiant exitance. Clinical age, the presence or absence of composite buildups, and damage to curing tips showed significantly affect radiant exitance values.

Short-Wavelength Infrared Organic Light-Emitting Diodes from A-D-A'-D-A Type Small Molecules with Emission beyond 1100nm.

Short-wavelength infrared (SWIR) organic light-emitting diodes (OLEDs) have attracted great interest due to their potential applications in biological imaging, infrared lighting, optical communication, environmental monitoring, and surveillance. Due to an intrinsic limitation posed by the energy-gap law, achieving high-brightness in SWIR OLEDs remains a challenge. Herein, the study reports the use of novel A-D-A'-D-A type small molecules NTQ and BTQ for high-performance SWIR OLEDs. Benefiting from multiple D-A effect in conjugated skeleton, the small molecules NTQ and BTQ exhibit narrow optical gaps of 1.23 and 1.13eV, respectively. SWIR electroluminescence (EL) emission from OLEDs based on NTQ and BTQ is achieved, with emission peaks at 1140 and 1175nm, respectively. Not only owing to a negligible efficiency roll-off across the full range of applied current density but also the ability to afford a high operation current density of 5200mA cm-2 , the resultant SWIR OLEDs based on NTQ exhibit a maximal radiant exitance of =1.12mW cm-2 . Furthermore, the NTQ-based OLEDs also possess sub-gap turn-on voltage of 0.85V, which is close to the physical limits derived from the generalized Kirchhoff and Planck equation. This work demonstrates that A-D-A'-D-A type small molecules offer significant promise for NIR/SWIR emitting material innovations.

The Study of Forced Power Supply Modes of a Xenon Flash Tube with Reinforced Electrode Assemblies

An INP‑16/350 xenon flash tube based on reinforced electrode assemblies was developed. As compared to the similar serially produced lamp INP‑16/580, the new lamp has the same dimensions but reduced discharge gap and reduced filling gas pressure. A stable quasi-arc operating mode of the lamp was reached with duration of radiation pulses of up to ten seconds when forcing power supply. The amplitude on time dependences of the lamp’s radiant exitance are formed by means of computer control of the temporal shape of the thyristor rectifier current pulses. For studying of the thermal overloads of the lamps, the methodology and IR-range optical pyrometry means were designed both, for the quartz bulb and for the electrode. The dependence of the latter’s temperature on energy deposition was studied using two custom-made radiometers. The load and radiation characteristics of the new lamp and the said analogue were compared. The new lamp is capable to operate rather reliably with high-power supply and energy deposition overload of up to 100 times in the single second-long flash mode with natural air cooling.

Blue Laser for Polymerization of Bulk-Fill Composites: Influence on Polymerization Kinetics.

The objective of this study was to compare the polymerization kinetics of bulk-fill resin composites cured with a LED-curing device and a diode laser (449 nm). Three bulk-fill composites were light-cured with constant radiation exposure at 10 J/cm2 by varying radiant exitance and curing time. The following three light-curing protocols were used: (I) 3300 mW/cm2 for 3 s; (II) 2000 mW/cm2 for 5 s; and (III) 1000 mW/cm2 for 10 s. The degree of conversion (DC) was monitored in real time at a data acquisition rate of 2 spectra/s over a 5-min period and again after seven days using Fourier transform infrared spectroscopy. DC amounted to 30.9-61.7% at 4-mm depth after 5 min. DC values of two sculptable composites were significantly higher with the laser, regardless of the curing protocol used, but not for the flowable composite. The maximum polymerization rate (2.0-22.1%/s) was less affected by the type of curing device for one of the composites, while the other two composites achieved significantly higher values when cured with the laser. Laser curing generally increased the DC and the maximum polymerization rate while it shortened the onset of the maximum reaction rate. New handheld laser devices with adjustable power have the potential to be used as a photopolymerization light source for new generations of bulk-fill composites.

In vitro temperature changes in the pulp chamber caused by laser and Quadwave LED-light curing units.

The study evaluated the pulp temperature (PT) increase in Class I and V preparations when exposed to the Monet Laser (for1 and 3s), the PinkWave (for3 and 10s), the Valo Grand (for3 and 10s), the PowerCure, (for3 and 10s) and the SmartLite Pro (for10s). Non-retentive Class I and Class V cavities were prepared in one molar fixed in an acrylic plate and positioned in a warm water bath. The PT baseline was kept at 32°C to simulate physiological conditions. Two T-type thermocouples were inserted through the roots into the pulp chamber in two positions: close to the pulp horn and the buccal wall close to the Class V cavity. The water flow was adjusted to 0.026mL/min, and real-time temperature data were collected every 0.5s. PT measurements were made with the tip of the LCU 0 and 6mm away from the tooth surface. The radiant exitance (mW/cm2) and radiant exposure (J/cm2) were calculated. One-way ANOVA compared the effect of the pulpal flow, and ΔT values were subjected to two-way ANOVA, followed by Scheffe's post hoc tests. The Monet Laser used for 3s and the PinkWave used for 10s produced the greatest PT rise in the Class I cavity. The simulated pulpal flow did not influence the PT rise. Overall, cavities exposed at the 0mm distancehad higher ΔT values than groups at 6mm distance. The placement of a rubber dam for Class V restorations may prevent positioning LCUs directly over the cavity, which may affect the rise in PT.

Radiant Exitance of Old, New, and Damaged LED Light Curing Units.

This study aimed to determine the radiant exitance of new, damaged, and 16-year-old light-curing units (LCUs) with and without infection control barriers, and before and after removal of any debris. Old LCUs consisted of 62 SmartLite iQ2 lights (Dentsply Sirona, York, PA). New LCUs consisted of 58 SmartLite Focus (Dentsply Sirona) and 58 Valo Grand (Ultradent, South Jordan, UT, USA) LCUs. Each LCU was examined for damage and debris on its tip. A handheld radiometer (CheckUp with BlueLight Analytics app, Halifax, Nova Scotia, Canada ) was used to measure the radiant exitance using a 10-second exposure time. Measurements were made with and without infection control barriers. If debris was present, the radiant exitance was measured before and after removal of debris with and without the barriers. All measurements were repeated three times. The means of the measurements were used for statistical analyses, which consisted of paired t-tests, analysis of variance (ANOVA), and Tukey post-hoc analyses conducted with a 0.05 level of significance. Infection control barriers significantly reduced the radiant exitance of all LCUs, ranging from 4.35% to 6.91% depending upon the LCU and the presence of debris or damage. Clean undamaged SmartLite Focus (907 mW/cm2) and Valo Grand (Ultradent) LCUs (883 mW/cm2) with barriers had statistically higher radiant exitance than older clean undamaged SmartLite iQ2 (Dentsply Sirona) LCUs (719 mW/cm2) with barriers. All LCUs exceeded the recommended 400 mW/cm2 radiant power to cure 2 mm of Filtek Supreme Ultra shade A2 composite resin (3M ESPE, St Paul MN, USA). Infection control barriers, debris, damage, and age all significantly reduced radiant exitance of the lights.

Tailoring the 2D/3D Phase Segregation for Highly Efficient Si-Based Perovskite Light-Emitting Diodes

Si-based perovskite light-emitting diodes (PeLEDs) show immense potential in optoelectronic device fields by combining the advantages of a mature silicon platform with the impressive light-emitting properties of halide perovskites. However, their external quantum efficiencies (EQEs) have lagged far behind those of their conventional glass-based counterparts. Herein, the microcavity effect is employed to enhance the light extraction ratio of Si-based top-emission PeLEDs by fine-tuning the thicknesses of the functional layers. Meanwhile, the methylammonium chloride (MACl) additive is used to regulate the crystallization process and promote 2D/3D phase segregation in perovskite layer, endowing the film with a significantly improved photoluminescence quantum yield (PLQY) due to both the desired energy funneling from the 2D phase to the 3D phase and the trap passivation brought by the 2D phase. Owing to these synergistic strategies, the optimal devices exhibit a record EQE over 20% and an intense radiant exitance up to 155.9 mW cm–2 and thus represent the best performing Si-based PeLEDs ever reported to our knowledge.

Polymerization Kinetics and Development of Polymerization Shrinkage Stress in Rapid High-Intensity Light-Curing.

This study investigated polymerization kinetics, linear shrinkage, and shrinkage stress development for six contemporary composite materials of different viscosities cured using radiant exitances of 1100–2850 mW/cm2. Real-time measurements of degree of conversion, linear shrinkage, and shrinkage stress were performed over 5 min using Fourier-transform infrared spectrometry, a custom-made linometer, and a custom-made stress analyzer, respectively. For most tested variables, the factor “material” had a higher effect size than the factor “curing protocol”. Maximum polymerization rate and maximum shrinkage stress rate were the most affected by changes in curing conditions. In contrast, no significant effects of curing conditions were identified within each material for shrinkage stress values measured at the end of the 5 min observation period. Linear shrinkage and shrinkage stress values measured after 5 min were closely correlated (R = 0.905–0.982). The analysis of polymerization kinetics suggested that the two composites specifically designed for rapid light-curing responded to higher radiant exitances differently than other composites. Polymerization kinetics and shrinkage stress behavior of contemporary restorative composite materials of different viscosities were overall more affected by material type than differences in curing conditions. Subtle differences in polymerization kinetics behavior shown by the two composites specifically designed for rapid high-intensity light-curing did not translate into significant differences in the development of polymerization shrinkage stress.

The Influence of Anisotropic Surface Reflection on Earth’s Outgoing Shortwave Radiance in the Lunar Direction

The variation in the radiation budget at Earth’s top of the atmosphere (TOA) represents the most fundamental metric defining the status of global climate change. The accurate estimation of Earth’s shortwave radiant exitance is of critical importance to study Earth’s radiation budget (ERB) at TOA. Measuring Earth’s outgoing shortwave radiance (OSR) is a key point to estimate Earth’s shortwave radiant exitance. Compared with space-borne satellite systems, Moon-based sensors (MS) could provide large-scale, continuous, and long-term data for Earth radiation observations, bringing a new perspective on ERB. However, the factors affecting the estimation of Earth’s OSR in the lunar direction have not yet been fully explored, for example, anisotropic surface reflection and the effects of clouds and aerosols on radiation budget. In this work, we only focused on the influence of anisotropic surface reflection. To evaluate the extent of this influence, we constructed a model to estimate Earth’s OSR in the lunar direction (EOSRiLD), integrating the variables of anisotropic surface reflection (scene types, solar zenith angles, viewing zenith angles, and relative azimuth angles) and radiant flux in Moon-viewed sunlit regions. Then, we discussed it over three time periods (Earth’s rotation, revolution period, and synodic month cycle) and analyzed the impact of three variables (area of the Moon-viewed sunlit region, scene types, and incident-viewing angular bins) on anisotropic EOSRiLD. Our results indicate that EOSRiLD based on the assumptions of anisotropic and isotropic reflection is different but they all show the same monthly cycle change, which is related to the area of the Moon-viewed sunlit region. At the beginning and end of the lunar month, the differences between anisotropy and isotropy are greatest in each cycle; when it is close to the first half of each cycle, there is a small difference peak. Both anisotropy and isotropy are caused by the relative azimuth angles between the Sun and Moon. In conclusion, even if the Moon-based platform has a wider scope than space-borne satellites, the difference is still large between anisotropy and isotropy. Therefore, we still need to consider the anisotropic surface reflection based on the Moon-based observation.

Can bulk-fill compromise the curing potential in deep cavities?

Objective: To determine the effect of the restorative technique, material’s opacity and the selected lightsources on the curing potential (CP) in deep cavities. Material and Methods: The radiant exitance (mW/cm2)of two light curing units (Bluephase G2 and Radii-Cal) was determined at 0 and 8 mm distance from a powermeter sensor (Ophir). Two bulk-fill composites of regular consistency (Opus, FGM; and Filtek One, 3M) and aconventional one (Sirius-Z, DFL) were considered and the level of their opacity were determined by a spherebasedspectrophotometer (SP60, X-Rite). The degree of C=C conversion (DC) was determined by spectroscopy(FTIR-ATR) at 0.05 and 8 mm depths and the CP considered the ratio between them. The “incremental technique”considered 4 increments of 2mm thickness each, whereas the “bulk-fill technique considered 2 increments of4mm-thickness. Data were submitted to analysis of variance and Tukey’s test (95%). Pearson’s correlation testswere performed to calculate the possible relation between curing potential and materials’ opacity. Results: Withthe incremental technique it was possible to achieve high CP regardless of the light source. The CP of bulk-fillcomposites was dependent on the light source, whereas Radii-Cal compromised the DC at 8 mm for both materials.The correlation between opacity and CP was dependent on the light source (r = 0.891707246 for Radii-Cal; r =0.515703768 for Bluephase G2). Conclusion: The bulk-fill technique was dependent on the light source whilethe incremental was not. The influence of materials’ opacity was dependent on the light curing unit.KEYWORDSConversion; Opacity; Resins; Light curing.

Relationship Between the Cost of 12 Light-curing Units and Their Radiant Power, Emission Spectrum, Radiant Exitance, and Beam Profile.

To correlate the radiant power (mW), radiant exitance (or tip irradiance in mW/cm2), emission spectrum (mW/cm2/nm), and beam irradiance profile of 12 light-curing units (LCUs) available in the Brazilian market with their market cost. Six LCUs that cost more than US$900 (Bluephase G4,VALO Grand, VALO Cordless, Radii Xpert, Elipar DeepCure-S, and Radii plus) and six low-cost LCUs costing less than US$500 (Radii Cal, Optilight Max, High Power LED 3M, Emitter D, Emitter C, and LED B) were examined. Radiant power (mW) and emission spectrum (mW/nm) were measured using an integrating sphere connected to a fiber-optic spectroradiometer. The internal tip diameter (mm) of each LCU was measured using a digital caliper and was used to calculate the average radiant exitance (mW/cm2). Irradiance profiles at the light tip were measured using a commercial laser beam profiler. The cost of each LCU in Brazil was correlated with internal tip diameter, radiant power, and tip irradiance. None of the low-cost LCUs were broad spectrum multiple peak LCUs. There was no correlation between the cost of the LCUs and their averaged tip irradiance; however, there was a high positive correlation between the cost of the LCUs and the radiant power and tip diameter. The VALO Grand, Elipar DeepCure-S, VALO Cordless, and Bluephase G4 all emitted a higher radiant power. They also had a significantly greater tip diameter than other LCUs. For the LCUs with a nonuniform output, some areas of the light tip delivered less than 400 mW/cm2, while other areas delivered more than 2500 mW/cm2. In general, LCUs that had a higher cost (US$971-US$1800) delivered more power (mW) and had a greater tip diameter (mm), which covered more of a tooth. In general, the low-cost LCUs (US$224-US$470) emitted a lower radiant power and had a smaller tip diameter.

Computational fluid dynamics–based modeling and optimization of flow rate and radiant exitance for 1,4-dioxane degradation in a vacuum ultraviolet photoreactor

1,4-Dioxane is one of the most persistent organic micropollutants in conventional drinking-water-treatment processes. Vacuum ultraviolet (VUV) treatment is a promising means of removing micropollutants such as 1,4-dioxane from source water, but this approach has not yet been implemented in a full-scale water treatment plant, partly because the operating parameters for pilot and full-scale VUV photoreactors have not been optimized. Here, we developed a computational fluid dynamics–based method for optimizing VUV photoreactor performance through energy-based analyses that take into account the effects of two important operating parameters—flow rate and radiant exitance. First, we constructed a computational fluid dynamics model and determined the sole parameter required for the model, the pseudo-first-order rate constant for the reaction of 1,4-dioxane, by simple batch experiment. Then, we validated the model by using a pilot-scale flow-through annular photoreactor. Finally, we used the validated model to examine the effects of flow rate and radiant exitance on the efficiency of 1,4-dioxane degradation in a virtual annular photoreactor. Radiation efficiency, which was defined as the ratio of the logarithmic residual ratio of 1,4-dioxane to the theoretical minimum logarithmic residual ratio (best possible performance) under the given operating conditions, was calculated as an energy-based index of cost-effectiveness. Radiation efficiency was found to increase with increasing flow rate but decreasing radiant exitance. An electrical energy per order (EEO) analysis suggested that VUV treatment under laminar flow was most economical when low-power lamps and a high flow rate were used. In contrast, VUV treatment under turbulent flow was suggested to be most economical when high-power lamps were used at a high flow rate.

Neural-adjoint method for the inverse design of all-dielectric metasurfaces

All-dielectric metasurfaces exhibit exotic electromagnetic responses, similar to those obtained with metal-based metamaterials. Research in all-dielectric metasurfaces currently uses relatively simple unit-cell designs, but increased geometrical complexity may yield even greater scattering states. Although machine learning has recently been applied to the design of metasurfaces with impressive results, the much more challenging task of finding a geometry that yields a desired spectra remains largely unsolved. We propose and demonstrate a method capable of finding accurate solutions to ill-posed inverse problems, where the conditions of existence and uniqueness are violated. A specific example of finding the metasurface geometry which yields a radiant exitance matching the external quantum efficiency of gallium antimonide is demonstrated. We also show how the neural-adjoint method can intelligently grow the design search space to include designs that increasingly and accurately approximate the desired scattering response. The neural-adjoint method is not restricted to the case demonstrated and may be applied to plasmonics, photonic crystal, and other artificial electromagnetic materials.

The light-curing unit: An essential piece of dental equipment

This article describes the features that should be considered when describing, purchasing and using a light-curing unit (LCU). The International System of Units (S.I.) terms of radiant power or radiant flux (mW), spectral radiant power (mW/nm), radiant exitance or tip irradiance (mW/cm2 ), and the irradiance received at the surface (also in mW/cm2 ) are used to describe the output from LCU. The concept of using an irradiance beam profile to map the radiant exposure (J/cm2 ) from the LCU is introduced. Even small changes in the active tip diameter of the LCU will have a large effect on the radiant exitance. The emission spectra and the effects of distance on the irradiance delivered are not the same from all LCUs. The beam profile images show that using a single averaged irradiance value to describe the LCU can be very misleading. Some LCUs have 'hot spots' of high radiant exitance that far exceed the current ISO 10650 standard. Such inhomogeneity may cure the resin unevenly and may also be dangerous to soft tissues. Recommendations are made that will help the dentist when purchasing and then safely using the LCU. Dental manufacturers should report the radiant power from their LCU, the spectral radiant power, information about the compatibility of the emission spectrum from the LCU with the photoinitiators used, the active optical tip diameter, the radiant exitance, the effect of distance from the tip on the irradiance delivered, and the irradiance beam profile from the LCU.

Simultaneous reconstruction of nonlinear temperature-dependent properties in a 1D radiation-conduction medium

In this paper, a set of new data is proposed for the simultaneous reconstruction of thermal radiation and conduction properties in a radiation-conduction medium into the one-dimensional layer. The radiation problem is modeled by the modified discrete ordinates method, and the conduction-radiation heat transfer problem is solved via the finite volume approach. The inverse problem is solved using the particle swarm optimization algorithm. Various cases are solved in this paper. In the first section, the constant absorption coefficient and radiation-conduction parameters are reconstructed by measuring the exit radiation intensities. To increase the accuracy of results, a two-stage hybrid optimization algorithm is used in this section. In the first stage, the absorption coefficient is calculated, and in the second stage, the radiation-conduction parameter is obtained. In the second section, the ability of the proposed algorithm and the measured data for reconstruction of the temperature-dependent radiation-conduction parameter is tested. To improve the results' accuracy in this section, a set of new data is used. Consequently, the proposed algorithm with a modified objective function that uses new data is presented to decrease the Planck number's sensitivity to the measurement errors.