scholarly journals The Structural Basis for Iridescent Colour Changes in Dermal and Corneal Irddophores in Fish

1989 ◽  
Vol 141 (1) ◽  
pp. 313-325 ◽  
Author(s):  
J. N. LYTHGOE ◽  
JULIA SHAND
Keyword(s):  
Refractive Index ◽  
High Refractive Index ◽  
Structural Basis ◽  
Wavelength Shift ◽  
Constructive Interference ◽  
Sand Goby ◽  
Pomatoschistus Minutus ◽  
Intercellular Matrix ◽  
Colour Changes ◽  
Low Refractive Index

The reflectance from the iridophores in the skin of the neon tetra Paracheirodon innesi (Myers) and the iridophores in the cornea of the sand goby Pomatoschistus minutus (Pallas) changes in response to light. In both cases the reflectance comes from the constructive interference of alternating plates of material of high and low refractive index. In the neon tetra the high refractive index plates are mainly guanine, and the low refractive index plates are cytoplasm. In the goby cornea the plates are made of intercellular matrix and cytoplasm, but it is not known which has the higher refractive index. In neon tetra dermal iridophores, the response to light is a shift to longer wavelength reflection without an accompanying increase in the amplitude of reflectance. In goby cornea, light can induce an increase in the amplitude of reflectance without a shift in wavelength. It is suggested that the wavelength shift is produced by an inflow of material into the iridophore and that the change in amplitude, without a shift in wavelength, is produced by a transfer of material, such as water, between the high and low refractive index layers of the multilayer stack.

Spectral reflectance and directional properties of structural coloration in bird plumage

2002 ◽  
Vol 205 (14) ◽  
pp. 2017-2027 ◽  
Author(s):  
D. Osorio ◽  
A. D. Ham
Keyword(s):  
Refractive Index ◽  
Spectral Tuning ◽  
Fixed Position ◽  
Constructive Interference ◽  
Structural Coloration ◽  
Spectrally Selective ◽  
Optical Effects ◽  
Selective Interference ◽  
Visual Properties ◽  
Low Refractive Index

SUMMARY Bird plumage is coloured both by pigments and by spectrally selective interference in the light reflected from feather barbs. These barbs are composites of high- and low-refractive-index materials, and light is reflected at refractive index boundaries. The spatial structure determines the wavelengths where constructive interference occurs and, hence, the spectral tuning. The spectral tuning of interference colours often varies with angles of illumination and reflection, which produces iridescence. Iridescence and other optical effects mean that interference coloration looks different from pigmentation and is visually striking. To study the optical and visual properties of structural plumage colours, we recorded the reflectance spectra of feathers and in particular their directional properties. A fixed spot on a feather was viewed from a fixed position, whilst the feather orientation and the angle of illumination were varied. We recognise two main types of coloration, `directional' and `diffuse'. Within these types, there is considerable variation, and five examples illustrate some features of structural plumage colours and suggest how their optical and visual properties can be measured and described.

The measurement of large optic axial angles with the universal stage

1966 ◽  
Vol 35 (273) ◽  
pp. 763-769
Author(s):  
M. Munro
Keyword(s):  
Refractive Index ◽  
Rapid Method ◽  
High Refractive Index ◽  
Optic Axis ◽  
Relative Speed ◽  
Accuracy And Precision ◽  
Direct Location ◽  
Speed Accuracy ◽  
Universal Stage ◽  
Low Refractive Index

SummaryA comparison has been made of the relative speed, accuracy, and precision of several methods of measuring large optic axial angles with the universal stage. It is concluded that a method based on the direct location of a single optic axis and the application of the Biot-Fresnel law will frequently be the most satisfactory when only the standard, low refractive index centre plate for the stage is available. If a centre plate of high refractive index is employed, however, good results can normally be obtained by using the more rapid method based on the direct location of both optic axes.

Cuticular interference reflectors in the golden pupae of danaine butterflies

1985 ◽  
Vol 226 (1244) ◽  
pp. 367-390 ◽  
Keyword(s):  
Refractive Index ◽  
Spectral Reflectance ◽  
Specimen Preparation ◽  
Constructive Interference ◽  
Pupal Development ◽  
Metallic Sheen ◽  
Colour Changes ◽  
Successive Formation ◽  
Absolute Reflectance ◽  
High Reflectance

In pupae of Euploea core and Amauris ochlea most of the cuticle displays a strong metallic golden or silvery lustre. The reflection colours appear between 24 and 48 h after pupation, first as blue and greenish hues which later turn into gold or silver, and vanish again about 24 h before emergence of the butterfly. If excised cuticle dries, the metallic sheen is lost and the cuticle becomes fully transparent. Absolute reflectance was measured by microspectrophotometry as over 70% from 550 to over 800 nm. At wavelengths below 550 nm, reflectance drops rapidly in golden cuticles and less so in silvery ones. Electron micrographs of reflecting cuticle show numerous alternating dense and clear layers (up to 250 pairs) in the endocuticle of reflecting regions (METAL-cuticle Multiple Endocuticular Thin Alternating Layers). Proceeding from outside to inside, the clear C-layers first systematically grow thicker and then thinner again, whereas the thickness of the dense D-layers remains fairly constant throughout the stack. The refractive index of D- and C-layers was determined as 1.58 and about 1.37, respectively. Computed spectral reflectance curves optimally match the measured spectra, if the thickness values are corrected for shrinkage during specimen preparation (C-layers, + 20 % ; D-layers, + 5 %). In conclusion the metallic reflection colours can be quantitatively attributed to constructive interference of light at the layers of METAL-cuticle; no pigment is involved. The colour changes during pupal development can be fully explained as the successive formation or decomposition of these layers. The importance of statistical and systematic variations of layer thickness and of the high numbers of layers is discussed with regard to the formation of biological broadband reflectors. Compared with other biological interference reflectors, danaine cuticular gold and silver mirrors show extremely high reflectance and optical precision.

Fabrication of Antireflective Films Composed of High and Low Refractive Index Layers Using Layer-by-Layer Self-Assembly Method

2007 ◽  
Vol 124-126 ◽  
pp. 559-562
Author(s):  
Jin Hye Bae ◽  
Jin Han Cho ◽  
Kook Heon Char
Keyword(s):  
Refractive Index ◽  
Self Assembly ◽  
Annealing Temperature ◽  
High Refractive Index ◽  
Multilayer Films ◽  
Layer By Layer ◽  
Assembly Method ◽  
Particle Layer ◽  
Refractive Index Layer ◽  
Low Refractive Index

We introduce a novel and versatile approach for controlling anti-reflective (AR) properties of multilayer films based on layer-by-layer (LbL) self-assembly (SA) method. For the fabrication of these films, blend (i.e., mixed) layers containing both polyanions (i.e., titanium precursor (TALH) and poly(sodium 4-styrenesulfonate) (PSS)) were assembled with polycation (i.e., poly(diallyldimethylammonium chloride) (PDAD)) for the formation of the high refractive index multilayers and on the other hand, the negatively charged silica particles with the diameter of about 100 nm were employed for low refractive index layer. The refractive index of TALH:PSS/PDAD multilayer was controlled by blending ratio and annealing temperature as TALH has the relatively high refractive index (n = 1.68) in comparison with that (n = 1.46) of conventional polyelectrolytes (PEs) at room temperature and furthermore these titanium precursors are partially changed into TiO2 with relatively high refractive indices (n = 1.50 ~ 1.81) at annealing temperature of 250 oC. In the case of silica particle layer used for low refractive index layer, the calculated refractive index was about 1.35 due to much vacancy among the adsorbed silica colloids although the inherent refractive index of silica material is about 1.45. As a result, the films composed of TALH:PSS/PDAD multilayers with tunable refractive index and silica colloidal layer can easily modulate the optical properties of multilayer films by blending ratio and heat treatment.

Design of Optical Thin Film Filter for Sensor Network

2015 ◽  
Vol 3 (1) ◽  
Author(s):  
Vahideh Khadem Hosseini ◽  
Mohammad Taghi Ahmadi
Keyword(s):  
Thin Film ◽  
Refractive Index ◽  
Silicon Dioxide ◽  
Human Body ◽  
High Refractive Index ◽  
Structural Factors ◽  
Optical Thin Film ◽  
Fabry Perot ◽  
Detection Of Objects ◽  
Low Refractive Index

Human body detection is very important especially in the countries prone to earthquakes. Fabry-Perot filter as an ideal option in this field needs to be explored. This filter is useful for detection of objects that have temperature around that of the human body. In the presented research, an optical thin film Fabry-Perot filter (FPF) at the wavelength about 8 um to 14 um is investigated. The important factors on transmission spectrum and the band width of filter are discussed. Additionally structural factors such as layers material and their thickness are explored. Various materials with high and low refractive index are examined by TFCalc3.5 for thin film layers. Germanium (Ge) with the refractive index 4.20 is selected for layer with high refractive index and Silicon Dioxide (SiO2) with the refractive index 1.46 is selected for low refractive index layer. Our simulation results lead to optimum parameters as: Germanium layer with 196nm thickness and Silicon Dioxide layer with 451nm thickness. Simulation of proposed filter indicated that the transfer coefficient is more than 90% in desired spectrum. Filter structure can be used on Infrared detectors to improve their resolutions and detection.

scholarly journals Strong coupling of single quantum dots with low-refractive-index/high-refractive-index materials at room temperature

2020 ◽  
Vol 6 (47) ◽  
pp. eabb3095
Author(s):  
Xingsheng Xu ◽  
Siyue Jin
Keyword(s):  
Quantum Dots ◽  
Refractive Index ◽  
Strong Coupling ◽  
Room Temperature ◽  
High Refractive Index ◽  
Colloidal Quantum Dots ◽  
Rabi Splitting ◽  
Pl Spectra ◽  
Dielectric Cavity ◽  
Low Refractive Index

Strong coupling between a cavity and transition dipole moments in emitters leads to vacuum Rabi splitting. Researchers have not reported strong coupling between a single emitter and a dielectric cavity at room temperature until now. In this study, we investigated the photoluminescence (PL) spectra of colloidal quantum dots on the surface of a SiO2/Si material at various collection angles at room temperature. We measured the corresponding reflection spectra for the SiO2/Si material and compared them with the PL spectra. We observed PL spectral splitting and regarded it as strong coupling between colloidal quantum dots and the SiO2/Si material. Upper polaritons and lower polaritons exhibited anticrossing behavior. We observed Rabi splitting from single-photon emission in the dielectric cavity at room temperature. Through analysis, we attributed the Rabi splitting to strong coupling between quantum dots and bound states in the continuum in the low-refractive-index/high-refractive-index hybrid material.

scholarly journals Modification of Low Refractive Index Polycarbonate for High Refractive Index Applications

2009 ◽  
Vol 2009 ◽  
pp. 1-8
Author(s):  
Gunjan Suri ◽  
Gouri Shankar Jha ◽  
Geetha Seshadri ◽  
Rakesh Kumar Khandal
Keyword(s):  
Refractive Index ◽  
Thermal Studies ◽  
High Refractive Index ◽  
Refractive Index Material ◽  
Optical Applications ◽  
Low Refractive Index

Polycarbonates and polythiourethanes are the most popular materials in use today, for optical applications. Polycarbonates are of two types which fall in the category of low refractive index and medium refractive index. The present paper describes the conversion of low refractive index polycarbonates into high refractive index material by the use of a high refractive index monomer, polythiol, as an additive. Novel polycarbonates, where the properties of refractive index and Abbe number can be tailor made, have been obtained. Thermal studies and refractive index determination indicate the formation of a new polymer with improved properties and suitable for optical applications.

scholarly journals Preparation of ultra-broadband antireflective coatings for amplifier blast shields by a sol–gel method

2017 ◽  
Vol 5 ◽  
Author(s):  
Huai Xiong ◽  
Bin Shen ◽  
Zhiya Chen ◽  
Xu Zhang ◽  
Haiyuan Li ◽  
...  
Keyword(s):  
Refractive Index ◽  
Sol Gel ◽  
High Refractive Index ◽  
Dip Coating ◽  
Scratch Resistance ◽  
Fused Silica ◽  
Antireflective Coating ◽  
Antireflective Coatings ◽  
Average Residual ◽  
Low Refractive Index

A type of $\unicode[STIX]{x1D706}/4$–$\unicode[STIX]{x1D706}/4$ ultra-broadband antireflective coating has been developed using modified low refractive silica and high refractive silica layers by a sol–gel dip coating method for amplifier blast shields of the Shen Guang II high power laser facility (SG-II facility). Deposition of the first layer (high refractive index silica) involves baking at $200\,^{\circ }\text{C}$ in the post-treatment step. The second layer (low refractive index, $n=1.20$) uses low refractive index silica sol modified by acid catalysis. Thermal baking at temperatures no less than $500\,^{\circ }\text{C}$ for 60 min offers chemical stability, ethanol scratch resistance, and resistance to washing with water. The average residual reflection of dual-side-coated fused silica glass was less than 1% in the spectral range from 450 to 950 nm. Transmission gain has been evaluated by taking into account angular light, and the results show that the transmission gain increases with increasing light incidence. Even at $60^{\circ }$, the transmission spectrum of the broadband antireflective coating effectively covered the main absorption peak of Nd:glass.

Mechanism of reflexion in silvery layers of fish and cephalopods

1971 ◽  
Vol 178 (1050) ◽  
pp. 43-61 ◽  
Keyword(s):  
Refractive Index ◽  
Oblique Incidence ◽  
Normal Incidence ◽  
Rutilus Rutilus ◽  
High Refractive Index ◽  
Interference Microscopy ◽  
Osmotic Concentration ◽  
High Reflectivity ◽  
Refractive Index Material ◽  
Low Refractive Index

The highly reflecting structures found in the integuments and eyes of fish and cephalopods were studied. In all cases they consist of alternate layers of high and low refractive index ( n ) material (in fish, guanine and cytoplasm) and the high refractive index material is in the form of discrete plates. The highest reflectivity at a given wavelength λ 0 , together with the widest waveband of high reflectivity, would be given if these alternate layers all had an optical thickness of ¼ λ 0 . We have examined the possibility that fish and cephalopods can make ‘ideal' reflectors of this kind. The thicknesses ( t ) of the discrete plates released by scratching the reflecting layers were measured by interference microscopy, and it was found that although the plates from a region of a given colour sometimes varied greatly in surface area, their thicknesses were approximately constant. With one exception the optical thicknesses ( nt ) of the plates found in all the structures studied were between 100 and 200 nm. Many of the reflecting structures are highly coloured and in these there was almost always a good correlation between the wavebands best reflected and four times the optical thick­nesses of the plates which they contained. The most ventral scales in the juvenile sprat were studied in some detail. At normal incidence these scales reflect best a waveband around 720 nm and the guanine crystals which they contain all have optical thicknesses close to one quarter of this wavelength. The changes in colour with angle of viewing, and with changes in osmotic concentration of the medium in which these scales are placed, support the idea that the spaces between the crystals are ¼ λ 0 spaces. These scales have a high reflectivity to the lights penetrating best into the sea at the oblique angles of incidence from which the strongest intensities of daylight fall in life. Qualitative observations on scales from herring and from other regions on the sprat sup­ported the hypothesis that their guanine crystals were also arranged approximately in ¼ λ 0 stacks. Similar conclusions were reached for coloured surfaces found in the skin of the horse mackerel, the iris of the neon tetra, the reflecting tapeta of the dogfish and the spurdog, and in the eye of the squid, Loligo forbesi . In the scales of the roach, Rutilus rutilus , the crystals are of thicknesses which indicate that if in ‘ideal' ¼ λ 0 stacks they would at normal incidence appear red and at oblique incidence green, whilst in fact they are very little coloured. The crystals from the eyes of Callionymus lyra had 4 nt around 300 nm (in the u. v.) yet the reflexions given by piles of these crystals were bronze coloured. Possible explanations of these facts are given. In cephalopods the high refractive index plates are lozenge-shaped, flexible and of refrac­tive index about 1·56.

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