Devices light-transmitting

The experimental set-up for the FCS measurement is illustrated schematically in Figure 8.6. A CW Ar laser (LGK7872M, LASOS lasertechnik GmbH) at 488 nm was coupled to a single mode optical fiber to isolate the laser device from an experimental table on which the confocal microscope system was constructed. This excitation laser light transmitted through the optical fiber was collimated with a pair of lenses, and then was guided into a microscope objective (lOOX, NA 1.35, Olympus). 

This type of sensitizer opens up new avenues for improving the near-IR response of dye-sensitized solar cells. In addition, important applications can be foreseen for the development of photovoltaic windows transmitting part of the visible light. Such devices would remain transparent to the eye, while absorbing enough solar energy photons in the near IR to render efficiencies acceptable for practical applications. 

The application of an external field onto many materials will induce optical anisotropy. If the applied field oscillates, a time-dependent modulation of the polarization of the light transmitted by the device will result. Modulators of this sort include photoelastic modulators (PEM) [30,31], Faraday cells [32], Kerr cells [32], and Pockel cells. 

There are materials, for example in the form of certain specially prepared polymer films, which, for light incident normal to the film, absorb to an extent dependent on the inclination of the plane of polarization to a unique axis in the plane of the film. Devices made from such films are termed polarizers approximately 60% of the incident unpolarized light is absorbed, and that part transmitted is plane polarized. The E vectors for the transmitted light are perpendicular to the high-absorbance direction. If the incident light is plane polarized, the intensity transmitted depends on the orientation of the polarizer axis with respect to the plane of polarization of the light. A device used in this mode is usually referred to as an analyser . 

Fig. 5.13. The resonant mirror device. The light from the soiuce is coupled through a prism Emd is totally reflected at the interface with the low refractive index layer, generating an evanescent field which couples light into the high refractive index waveguide layer The light transmitted through the waveguide also generates a evanescent field which interacts with the receptor layer.

The interface between the sample and the spectrometer is vital wherever a spectrometer is sited. The sample can be piped into the spectrometer or, in some cases the radiation used by the spectrometer can be transmitted to a convenient sample or probe location point using optical fibres or other light-pipe devices. The sample presented to the spectrometer must be representative of the material from which the measurement is required and the interaction between the radiation of the spectrometer and the sample must be suitable for the measurement to be made (sufficient power and suitably clean interface). 

Interference filters consist of a solid Fabry-Perot cavity. This is a device made of a sandwich of two partially reflective metallic layers separated by a transparent dielectric spacer layer. The partially reflective layers are made of higher refractive index than the dielectric spacer layer and are X/4 in thickness, where A is the peak wavelength (wavelength of maximum transmission) for the filter. The lower refractive index spacer layer is made to A/2 thickness. The thickness of the dielectric spacer layer determines the actual peak transmission wavelength for the filter. Only the A/2 light transmits with high efficiency the other wavelengths experience constructive interference between the multiple-order reflections from the two partially reflective layers. 

---