Modeling of X‐ray‐Induced Refractive Index Changes in Poly(methyl methacrylate)

Abstract

The refractive index of bulk poly(methyl methacrylate) samples is modified by X-ray exposure. The intensity of the radiation is distributed over an energy range of 1 to 20 keV with a maximum at 3 keV. For an absorbed dose of about 1 kJ cm(-3), an increase of the refractive index of up to 3x10(-4) is observed. However, for much lower doses of about 10 J cm(-3) a decrease of 4x10(-4) appears. These refractive index changes, as well as the simultaneously arising radiation-induced thickness changes, are detected interferometrically. Based on these observations, on dose calculations, and on literature data, a model is proposed which describes quantitatively the observed refractive index changes. The refractive index increase is caused by a radiation-induced chemical alteration of the polymer composition, while the refractive index decrease is correlated with a decrease of mass density.

Effect of UV irradiation time on the structure and optical properties of Rose Bengal thin films

“…The normal dispersion is observed for wavelength > 600nm and in this wavelength range we can deduce the values of optical functions from the data of refractive index.UV irradiation reduces the value of the refractive index all over the spectra. The decrease of the refractive index with UV irradiation is related to the decrease of mass density of RB films (Andreas et al, 2005). Such behaviour has been reported in other organic semiconductor thin films El-Nahass et al, 2012;.…”

Influence of annealing temperature on structural and optical properties of nanocrystalline Platinum octaethylporphyrin (PtOEP) thin films

“…At longer wavelength, hm ? 0 the calculated value of the refractive index decreases by an amount Dn = 0.11 after annealing at 473 K. The decreasing of refractive index values is due to the decrease of mass density of PtOEP [48]. Fig.…”

Probing the Influence of X-rays on Aqueous Copper Solutions Using Time-Resolved in Situ Combined Video/X-ray Absorption Near-Edge/Ultraviolet−Visible Spectroscopy

“…With the advent of high-brilliance, highly focused X-ray beams from third-generation synchrotron sources, the observation of beam damage or beam influence in various types of samples is becoming more common and poses a number of problems. For example, it becomes difficult to determine the physical and chemical properties of the sample such as its structure or function. − This is especially important for the study of catalytic mechanisms since specific species, often considered as potential reaction intermediates and active sites, are formed in a reaction mixture. Normally such information is achieved under time-resolved measurement conditions, but one should be aware that the X-ray beam itself might induce the observed changes to the catalytic system under study, especially in circumstances where the experimental time resolution relies on increasing photon statistics rather than improvements in detector performance .…”