Jacob Jonsson

Optical absorption in lithiated tungsten oxide thin films : Experiment and theory

Amorphous tungsten oxide exhibits electrochromism when intercalated with protons, lithium, sodium, and other ions. Thin films of the material were prepared by dc magnetron sputtering and then electrochemically intercalated with lithium. The optical absorption in the wavelength range of 300–2500nm was measured for a number of lithium concentrations. The optical absorption shows a maximum for lithium/tungsten ratios of 0.3–0.5. The optical spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with an extended site-saturation theory.

Spectral and global diffuse properties of high-performance translucent polymer sheets for energy efficient lighting and skylights

A visible and near-IR spectral study is presented for a translucent smooth polymer sheet in which dopant particles are clear polymer with a refractive index close to that of the clear polymer host. Diffuse, specular, and total reflectance and transmittance and absorptance as a function of sheet thickness and dopant levels approach ideal behavior for lighting applications. A fourth optical parameter, side loss S(T), is introduced to fully account for the measured data. This covers radiation that is trapped by total internal reflection (TIR) and travels sideways sufficiently far, including to the sheets edges, to miss detection on exit. S(T) has a strong spectral character, whereas total T and R spectra closely follow the spectrally flat wavelength dependence of the undoped clear sheet. Three distinct regimes are identified for the behavior with wavelength of the specular and diffuse components and are linked to rear surface TIR and side loss.

Optical properties of injection molded subwavelength gratings

We have fabricated injection molded subwavelength gratings for anti-reflection purposes superimposed upon a blazed grating structure in polycarbonate. The gratings are initially formed by electron-beam lithography and subsequently replicated using injection molding. There are several problems when trying to optically characterize a component such as a blazed transmittance grating. Standard spectrophotometers are not well suited for measuring transmittance in the different diffraction orders individually. Our sample size of 0.8x0.8 mm(2) is also a problem for standard instruments. First order transmittance has been measured for blazed gratings with single and double-sided AR-treatment and is transmittance is compared with with higher diffraction orders. Double-sided AR-treatment not only increase the total transmittance but also widens the wavelength range with high effectiveness of the first order diffraction.

Investigation of optical properties of injection moulded subwavelength gratings

Surface reflections from optical transmission components are in many cases unwanted and cumbersome. Thin film coating is the conventional technique used for anti-reflection treatment of optical components. In recent years subwavelength gratings have been studied as a replacement for thin films. Subwavelength gratings are microstructures that can be formed on one or both sides of a substrate. Typically an optical component needs to be AR-coated on both sides. We have fabricated injection moulded subwavelength gratings superimposed upon a blazed grating structure in polycarbonate. The gratings are initially formed by electron-beam lithography and subsequently replicated using the same process which is used to manufacture standard plastic compact discs (CDs). There are several problems when trying to characterize a component such as a blazed transmittance grating. First of all there is the spread of internal reflections. Light that is reflected inside the substrate is shifted in lateral position due to the angle of the grating. We have thoroughly investigated the effects of decrease in grating efficiency due to internal reflections and also tried to minimize these effects by appropriately treating both sides of the plastic CD.