Spectrophotometry

In this paper, we consider the problem of estimating the 3D position and intensity of multiple light sources without using any light probe or user interaction. The proposed approach is twofold and relies on RGB-D data acquired with a low cost 3D sensor. First, we separate albedo/texture and illumination using lightness ratios between pairs of points with the same reflectance property but subject to different lighting conditions. Our selection algorithm is robust in presence of challenging textured surfaces. Then, estimated illumination ratios are integrated, at each frame, within an iterative process to recover position and intensity of light sources responsible of cast shadows. Estimated lighting characteristics are finally used to achieve realistic Augmented Reality (AR).

We study the interaction of quasi-resonant light with point impurity atoms embedded into transparent solid dielectric in a waveguide focusing our attention on the case when interatomic separations are much larger that the wavelength of light. We demonstrate the effect of incomplete spontaneous decay of a single excited atom in a waveguide and extremely long-range dipole-dipole interaction between different atoms.

Electric Cell-substrate Impedance Sensing (ECIS) is an in vitro impedance measuring system to quantify the behavior of cells within adherent cell layers. To this end, cells are grown in special culture chambers on top of opposing, circular gold electrodes. A constant small alternating current is applied between the electrodes and the potential across is measured. The insulating properties of the cell membrane create a resistance towards the electrical current flow resulting in an increased electrical potential between the electrodes. Measuring cellular impedance in this manner allows the automated study of cell attachment, growth, morphology, function, and motility. Although the ECIS measurement itself is straightforward and easy to learn, the underlying theory is complex and selection of the right settings and correct analysis and interpretation of the data is not self-evident. Yet, a clear protocol describing the individual steps from the experimental design to preparation, realization, and analysis of the experiment is not available. In this article the basic measurement principle as well as possible applications, experimental considerations, advantages and limitations of the ECIS system are discussed. A guide is provided for the study of cell attachment, spreading and proliferation; quantification of cell behavior in a confluent layer, with regard to barrier function, cell motility, quality of cell-cell and cell-substrate adhesions; and quantification of wound healing and cellular responses to vasoactive stimuli. Representative results are discussed based on human microvascular (MVEC) and human umbilical vein endothelial cells (HUVEC), but are applicable to all adherent growing cells.

The paper sets forth basic principles in the design and use of spectrophotometers. §§ 1-4 deal with absorption spectrophotometry in its application to chemistry and includes consideration of the various methods in use, viz. photographic, visual, and photoelectric. The optimum conditions for each method are stated and the three types of method are compared. § 5 is concerned with spectrophotometry as a means of describing a radiation, as for instance in connexion with colorimetry, the comparison of light sources and quantitative spectrum analysis.

Chapter 6 - Applications of Raman and Infrared Microscopy to Materials and Biology

Most often, transmission and reflection properties and geometrical constraints (such as size) are the sole considerations in metamaterials design. Typically, power handling is of little concern as most applications are very low power. Here, we consider not only the complex transmission and reflection properties but also the magnitude of the electric fields in and around the structure when designing metamaterials for robustness in high power reflectarray applications.

Despite a significant focus on the photochemical and photoelectrical mechanisms underlying photobiomodulation (PBM), its complex functions are yet to be fully elucidated. To date, there has been limited attention to the photophysical aspects of PBM. One effect of photobiomodulation relates to the non-visual phototransduction pathway, which involves mechanotransduction and modulation to cytoskeletal structures, biophotonic signaling, and micro-oscillatory cellular interactions. Herein, we propose a number of mechanisms of PBM that do not depend on cytochrome c oxidase. These include the photophysical aspects of PBM and the interactions with biophotons and mechanotransductive processes. These hypotheses are contingent on the effect of light on ion channels and the cytoskeleton, the production of biophotons, and the properties of light and biological molecules. Specifically, the processes we review are supported by the resonant recognition model (RRM). This previous research demonstrated that protein micro-oscillations act as a signature of their function that can be activated by resonant wavelengths of light. We extend this work by exploring the local oscillatory interactions of proteins and light because they may affect global body circuits and could explain the observed effect of PBM on neuro-cortical electroencephalogram (EEG) oscillations. In particular, since dysrhythmic gamma oscillations are associated with neurodegenerative diseases and pain syndromes, including migraine with aura and fibromyalgia, we suggest that transcranial PBM should target diseases where patients are affected by impaired neural oscillations and aberrant brain wave patterns. This review also highlights examples of disorders potentially treatable with precise wavelengths of light by mimicking protein activity in other tissues, such as the liver, with, for example, Crigler-Najjar syndrome and conditions involving the dysregulation of the cytoskeleton. PBM as a novel therapeutic modality may thus behave as "precision medicine" for the treatment of various neurological diseases and other morbidities. The perspectives presented herein offer a new understanding of the photophysical effects of PBM, which is important when considering the relevance of PBM therapy (PBMt) in clinical applications, including the treatment of diseases and the optimization of health outcomes and performance.

Introduction: Light is a key factor in moderating human alertness, both subjective and objective. However, the methodology applies in research on the effects of exposure to light of different wavelengths and intensities on objective and subjective alertness varies greatly and evidence on objective alertness in particular is still inconclusive. Thus, the present, highly standardized within-subject laboratory study on N = 44 healthy males explored how LED light of different intensities (dim vs. bright light) and wavelengths (red vs. blue) affected objective (reaction time/RT) as well as subjective (sleepiness) alertness in the morning after wake-up. Methods: Participants spent two separate nights in the laboratory and were exposed to either one of the two light intensities or colors for 60 min after wake-up. Additionally, they indicated their sleepiness on the Karolinska Sleepiness Scale and participated in an auditory RT task before and after light intervention. It was hypothesized that both bright and blue light would lead to greater subjective and objective alertness when compared to dim and red light, respectively. Results: Results indicated that average RTs were longer for participants in the bright light condition (p = 0.004, f2 = 0.07) and that RTs decreased post-light exposure irrespective of light being dim or bright (p = 0.026, f2 = 0.07). However, dim versus bright light and RT did not interact (p = 0.758, f2 = 0.07). Chronotype was a significant covariate in the interaction of dim versus bright light and subjective sleepiness (p = 0.008, f2 = 0.22). There was no difference in RTs when comparing exposure to red or blue light (p = 0.488, f2 = 0.01). Findings on subjective sleepiness and light of different wavelengths revealed that sleepiness was reduced after light exposure (p = 0.007, f2 = 0.06), although the wavelength of light did not appear to play a role in this effect (p = 0.817, f2 = 0.06). Conclusion: Hence, neither of the hypotheses could be confirmed. However, they indicated that evening types might benefit from exposure to bright light regarding sleepiness, but not morning types.

This paper aims to establish a design system of the shading windows which achieve a balanced flows of visual information between the inside and the outside of a room. For this purpose, the relationship between the visibility level and the physical condition of the object seen through the shading of a window must be known. In this paper, the calculating method of the apparent luminance of a visual target seen through a lace curtain was established. In the calculating method, three optical properties of various race curtains, the rate of passage luminance, the property of transmission, and the property of reflection, are required. So these optical properties of five kinds of lace cloths which have different formal characteristics were measured.

The results of current microscopic investigations show that during the process of athermal photoablation the material surrounding the target is thermally stressed. In order to get more information of the target's thermal behaviour during light interaction and, furthermore, about the process itself, we developed a microthermocouple device with high spatial (um) and temporal (us) resolution. So far temperature measurements were carried out during excimer laser (351nm) irradiation with 250 to 1600 mJ/cm2 in single and repetition pulse mode. The measurements in polymers and in biological material gave the following results: 1) typical thermal effects like melting zones at polymer crater walls and tissue discoloration and smoke generation in biologic material. 2) In polymers as well as in biological materials the surface temperature increases with increasing energy density in single laser mode once the removal threshold is reached or exceeded. 3) The removal threshold depends on the heat capacity of the samples. The results indicate that photoablation of polymers and biological material (obtained with 351 nm short pulsed laser light wavelength of nearly 1000 mJ/cm2) is predominantly a photothermal process.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reflection and Transmission Properties of Common Construction Materials at 2.4 GHz Frequency

This is the textbook and reference resource that instructors, students, and researchers in biomedical optics have been waiting for. Comprehensive and up to date, it covers a broad range of areas in biomedical optics, from light interactions at the single-photon and single-biomolecule levels, to the diffusion regime of light propagation in tissue. Subjects covered include spectroscopic techniques (fluorescence, Raman, infrared, near-infrared, and elastic scattering), imaging techniques (diffuse optical tomography, photoacoustic imaging, several forms of modern microscopy, and optical coherence tomography), and laser-tissue interactions, including optical tweezers. Topics are developed from the fundamental principles of physical science, with intuitive explanations, while rigorous mathematical formalisms of theoretical treatments are also provided. For each technique, descriptions of relevant instrumentation and examples of biomedical applications are outlined, and each chapter benefits from references and suggested resources for further reading, and exercise problems with answers to selected problems.

This is the textbook and reference resource that instructors, students, and researchers in biomedical optics have been waiting for. Comprehensive and up to date, it covers a broad range of areas in biomedical optics, from light interactions at the single-photon and single-biomolecule levels, to the diffusion regime of light propagation in tissue. Subjects covered include spectroscopic techniques (fluorescence, Raman, infrared, near-infrared, and elastic scattering), imaging techniques (diffuse optical tomography, photoacoustic imaging, several forms of modern microscopy, and optical coherence tomography), and laser-tissue interactions, including optical tweezers. Topics are developed from the fundamental principles of physical science, with intuitive explanations, while rigorous mathematical formalisms of theoretical treatments are also provided. For each technique, descriptions of relevant instrumentation and examples of biomedical applications are outlined, and each chapter benefits from references and suggested resources for further reading, and exercise problems with answers to selected problems.

Many conventional optoelectronic devices consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-structuring the constituent layers at length scales below the wavelength of light. The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical transmission, absorption, reflection, and refraction properties of device layers. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers may be used to enhance the performance of solar cells, photodetectors, and enable new imaging technologies. I will also demonstrate how the use of active nanoscale building blocks can facilitate the creation of active metafilm devices.

In predicting the reflectance, transmittance, and other optical properties of film-covered substrates, the films are usually modeled as uniform, plane parallel layers having constant (complex) refractive indices. However, it is well known that film structure is strongly influenced by the condition of the substrate onto which it is deposited. Optical scattering theories modify the above zero order assumptions by introducing microroughness on the substrate and film surfaces. In first order scattering theories the heights of surface microirregularities are assumed to be much less than the wavelength of light. In order to calculate the angular dependence of the scattered light,1 it is necessary to know the statistical properties of the microroughness, specifically the autocovariance function or its Fourier transform, the spectral density function. Recent experiments2,3 have shown that in some cases this information is not enough to correctly predict the complete angular scattering distribution; more detailed modeling of the film structure is needed. In order to better relate optical scattering of thin films to their structural and topographic features, we have made electron micrographs of replicas of film surfaces and their cross sections, and microtopographic measurements on films and bare substrates using a stylus-type profiling instrument having a lateral resolution ~ 0.1 to 0.2 μm. We have also obtained surface profiles from an analysis of microdensitometer traces of electron micrographs of surface replicas.4 Films studied include silver and multilayer dielectric stacks deposited onto microscope slides, fused quartz, and Zerodur substrates. When silver films are baked in vacuum, appreciable differences are observed in film structure, and large differences are also observed in the total scattering and its angular dependence. Measured scattering from various film-substrate combinations whose microstructural features have also been measured will be compared with theoretically predicted values. Further modifications to the theory have been proposed5 in order to better incorporate observed film microstructure into vector scattering theory.