scholarly journals Measurements of Photo-Induced Changes in Conjugated Polymers

1991 ◽  
Vol 228 ◽  
Author(s):  
Carleton H. Seager ◽  
Michael B. Sinclair ◽  
D. Mc Branch ◽  
A. J. Heeger ◽  
G. L. Baker
Keyword(s):  
Absorption Spectra ◽  
Light Transmission ◽  
Pump Light ◽  
General Shape ◽  
Experimental Conditions ◽  
Photothermal Deflection Spectroscopy ◽  
Highly Sensitive ◽  
Infra Red ◽  
Transmission Measurements ◽  
Induced Changes

ABSTRACTWe have used the highly sensitive technique of Photothermal Deflection Spectroscopy (PDS) to measure changes in the infra-red absorption spectra of MEHPPV, P3HT and Polydiacetylene-4BCMU induced by pumping these polymers with light above the π - π* transition energy. In contrast to previous chopped light transmission measurements of these effects, the PDS technique can directly measure the buildup or decay of the absorption coefficient, m, on the time scale of seconds to days. In the case of MEHPPV we observe that above-gap light causes the appearance of a broad infra-red peak in α, which continues to grow-in hours after the pump light is first applied. For this polymer the general shape of the absorption spectra in the unpumped state mimics the photo-induced changes, suggesting that remnant photo-induced states determine the maximum transparency observed under normal experimental conditions. For P3HT and to a lesser extent, MEHPPV, we also observe irreversible photo-induced absorption components which we tentatively identify with photo-induced oxidation of the polymer matrix.

scholarly journals Impact of Material Shade and Distance from Light Curing Unit Tip on the Depth of Polymerization of Composites

2017 ◽  
Vol 28 (5) ◽  
pp. 632-637 ◽  
Author(s):  
André L. Faria-e-Silva ◽  
Christopher Fanger ◽  
Lillian Nguyen ◽  
Demetri Howerton ◽  
Carmem S. Pfeifer
Keyword(s):  
Light Transmission ◽  
Degree Of Conversion ◽  
Experimental Conditions ◽  
Composite Surface ◽  
Infra Red ◽  
Light Curing ◽  
Different Depths ◽  
The Mean

Abstract This study aimed to evaluate the effect of the composite shade and distance from the light-curing unit (LCU) tip on the irradiance reaching the bottom of composite disks and on the depth of polymerization. Composites of three shades (opaque - OXDC, bleach - BXL, and A2) were inserted into molds with 3-mm of thickness positioned over a spectrometer and photo-activated with the LCU (Bluephase) tip placed at 0 or 1 cm from the composite surface. The mean irradiance reaching the bottom of composite was recorded during the entire photo-activation (30 s). Specimens (2 x 2 x 4 mm) were polymerized and used to map the degree of conversion achieved in different depths from irradiated surface. Specimens were sectioned into slices that were positioned over the platform of the infra-red microscope connected to the spectrometer to map the conversion. The conversion was measured in eight different depths every 500-µm. Increasing the distance of LCU tip reduced the irradiance only for A2. Interposing OXDC disks resulted in lowest values of irradiance and A2 the highest one. A tendency to decrease the conversion was observed towards the bottom of specimens for all experimental conditions, and the slope was more accentuated for OXDC. Differences among shades and distances from LCU tip were evident only beyond 1.5-2.0 mm of depth. In conclusion, both composite shade and distance from LCU tip might affect the light-transmission and depth of polymerization, while the effect of last was more pronounced.

scholarly journals Terahertz characterization of two-dimensional low-conductive layers enabled by metal gratings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Prashanth Gopalan ◽  
Yunshan Wang ◽  
Berardi Sensale-Rodriguez
Keyword(s):  
Optical Transmission ◽  
Terahertz Spectroscopy ◽  
Design Guidelines ◽  
Two Dimensional ◽  
Highly Sensitive ◽  
Transmission Measurements ◽  
Metal Gratings ◽  
Low Sensitivity ◽  
Non Destructive

AbstractWhile terahertz spectroscopy can provide valuable information regarding the charge transport properties in semiconductors, its application for the characterization of low-conductive two-dimensional layers, i.e., σs <  < 1 mS, remains elusive. This is primarily due to the low sensitivity of direct transmission measurements to such small sheet conductivity levels. In this work, we discuss harnessing the extraordinary optical transmission through gratings consisting of metallic stripes to characterize such low-conductive two-dimensional layers. We analyze the geometric tradeoffs in these structures and provide physical insights, ultimately leading to general design guidelines for experiments enabling non-contact, non-destructive, highly sensitive characterization of such layers.

scholarly journals Light transmission measurements and phototherapy eyepatches.

1991 ◽  
Vol 66 (1 Spec No) ◽  
pp. 59-61 ◽  
Author(s):  
J Robinson ◽  
M J Moseley ◽  
A R Fielder ◽  
S C Bayliss
Keyword(s):  
Light Transmission ◽  
Transmission Measurements

scholarly journals On the mechanism of boundary lubrication. II. Wear prevention by addition agents

1940 ◽  
Vol 177 (968) ◽  
pp. 103-118 ◽  
Keyword(s):  
High Pressures ◽  
Preceding Paper ◽  
Accurate Method ◽  
Polar Compounds ◽  
Experimental Conditions ◽  
Group V ◽  
Highly Sensitive ◽  
Local Pressures ◽  
Steel Balls ◽  
Long Chain

If two metal surfaces slide over each other in the presence of a lubricant and under high load, high pressures and temperatures prevail a t those isolated spots which actually carry the load, leading to wear and possibly to breakdown. The action of wear preventing agents under these conditions has been studied in detail and it has been found that such agents are effective through their chemical polishing action, by which the load becomes distributed over a larger surface and local pressures and temperatures are decreased. Especially effective are compounds containing phosphorus or other elements of group V of the periodic system. These have been found to form a metal phosphide or homolog on the surface which is able to alloy with the metal surface, lowering its melting point markedly, and by this action aiding greatly in maintaining a polish. The wear experiments were carried out with a highly sensitive and accurate method which uses metal-plated steel balls as its sliding elements. Under the experimental conditions additions of 1.5% triphenyl phosphine or triphenyl arsine in white oil gave wear prevention factors of 7.2 and 12.2 respectively (relative to pure white oil). A further addition of 1% of a long chain polar compound is able to double the wear prevention factor obtained with the polishing agents and wear prevention factors as high as 17.6 have been observed. The specifically physical action of the long-chain polar compounds is discussed in the preceding paper.

Ruby Laser Induced Changes in the Absorption Spectra of Sodium Decorated Sodium Chloride Crystals

1970 ◽  
Vol 25 (2) ◽  
pp. 229-236
Author(s):  
H. Kuzmany
Keyword(s):  
Absorption Spectra ◽  
Ruby Laser ◽  
Laser Light ◽  
Temperature Treatment ◽  
Laser Wavelength ◽  
Beam Path ◽  
General Increase ◽  
Annealing Conditions ◽  
Different Depths ◽  
Induced Changes

Abstract The effects of intense Q-switched ruby laser light on the absorption spectra of NaCl crystals, additively coloured by colloidal sodium were investigated at different depths along the laser beam path as well as after being subjected to different annealing conditions. A strong general increase in absorption was observed in the region where the laser light entered the crystal, while a strong decrease in absorption occurred in the colloid band, especially around the laser wavelength. This bleaching was accompanied by the generation of a new absorption band at ~ 1200 nm (~1.0eV) in the infrared, which, according to its sensitivty to temperature treatment, is not of colloidal origin, The energy denisty necessary for its generation was found to be about 400mJ/cm2. Its is suggested that the bleaching of the colloid band could be used for the storage of holograms.

scholarly journals Pattern of respiratory-induced changes in fingertip blood volume measured by light transmission

2011 ◽  
Vol 04 (08) ◽  
pp. 529-534 ◽  
Author(s):  
Meir Nitzan ◽  
Daniel Dayan ◽  
Eran Shalom ◽  
Yuval Slovik ◽  
Alan Murray
Keyword(s):  
Blood Volume ◽  
Light Transmission ◽  
Induced Changes
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