M. Emam-Ismail

Influence of γ-irradiation on optical parameters of electron beam evaporated ZnSe1−xTex nanocrystalline thin films

In the present paper, we reported the effect of γ-irradiation with different doses (100–300 kGy) on the optical parameters of nanocrystalline ZnSe1−xTex (x=0.0, 0.2, 0.5, 0.7, 1.0) thin films. In the wavelength range 400–2500 nm, the optical parameters of the as-deposited and γ-irradiated were extracted from transmission spectra using the Swanepoel method. It was found that the refractive index of the investigated films increases with increasing the doses of γ-radiation. Such post-irradiation increase in the refractive index was attributed to the increase of the density of the investigated films with irradiation doses due to structure transformation induced by thermal effects during irradiation. In addition, the refractive index dispersions of both as-deposited and γ-irradiated of nanocrystalline ZnSe0.8Te0.2 films are found to follow the single oscillator model. The calculated single oscillator parameters; oscillator strength Ed, static refractive index no, increased after irradiation while the oscillator energy Eo, reduced after irradiation. The absorption coefficient was found to increase with the increase of the doses of γ-radiation. Furthermore, the obtained optical energy gap of nanocrystalline ZnSe1−xTex films was found to decrease with increasing the doses of the γ-radiation which is attributed to the increase of the telluride (Te) atoms or defects after irradiation. This is confirmed by the decrease in the Urbach energy Ee after radiation. The γ-irradiation stimulated increase in the absorption coefficient and change in the optical parameters, which can be utilized for industrial dosimetric and detector purposes.

Birefringence dispersion of polyethylene and cellulose triacetate sheets used as photonic wave retarders

Abstract. In a wide spectral range of 400 to 1000 nm, the channeled spectra formed from the interference of polarized white light are used to extract the dispersion of phase birefringence Δn(λ) of polyethylene and cellulose triacetate (CTA) polymer sheets. The Δn(λ) of polyethylene and CTA sheets is fitted to Cauchy dispersion function with relative error of order 1.2×10−4 and 4×10−4, respectively. The dispersion of group birefringence Δng(λ) of polyethylene and CTA is also calculated and fitted to Ghosh dispersion function with relative error of order 7×10−4 and 5×10−4, respectively. Furthermore, the phase and group retardations introduced by polyethylene and CTA sheets are also calculated. The amount of phase retardation confirms that polyethylene and CTA sheets can act as multiple order half and quarter wave plates working at many different wavelengths through the spectral range 400 to 1000 nm. For polyethylene and CTA sheets, a large difference between group and phase retardance is observed at a short wavelength (λ≈400u2009u2009nm), while such difference progressively diminished at a long wavelength (λ≈1000u2009u2009nm). Finally, a zero order polyethylene quarterwave plate working at 544 nm and dual wavelength CTA quarterwave plate working at 510 and 680 nm are experimentally realized.