Interference mirrors

A difficulty arises because the photonic crystal structures for the visible region are not easy to fabricate. However, in this chapter we describe a facile extrusion method for fabricating polymers with a ID structure like that shown in Figure 2. The nanolayered polymeric structures can consist of many thousands of layers and have a modulation in the nonlinear refractive index in the direction normal to the surface of the layers. Such materials are the nonlinear analogue of polymeric multilayer interference mirrors. (10,11,12) They are also the ID analogue of the 2D photonic crystals studied by Lin et. al. (13) The latter workers demonstrated that photonic crystals do indeed provide an effective method for converting an intensity dependent refractive index into an intensity dependent transmission. 

Interference mirrors are dielectric thin film coatings where low- and high-refractive index layers alternate. The optical thickness of each of the layers is equal to quarter-wavelength QJAn). They are denoted as distributed Bragg mirrors or distributed Bragg reflectors (DBR), sometimes simply as Bragg mirrors. Other names include quarter-wave mirrors (QWM), quarterwave stacks (QWS) and highly reflective (HR) layers. 

Figure 4 Interference pettern created when regularly spaced atoms scatter an incident plane wave. A spherical wave emanates from each atom diffracted beams form at the directions of constructive interference between these waves. The mirror reflection—the (00) beam—and the first- and second-order diffracted beams are shown.

FIGURE 13.46 Nondispersive Infrared analyzer based on (d) interference filters and (b) gas correlation cechnictues. M = mirror, D = detector, S source, F = filter disk. WO = motor, FB = baud pass filter. SD = synchronous detection. C = correlation cell. N nitrogen filter. 

A characteristic dependence of the efficiency on the thickness of the active layer has also been observed for single layer polymer LEDs. This effect has been attributed to reflection of the EL light at the mirror-like metal electrodes resulting in characteristic interference maxima and minima depending on the thickness of the active layer and its refractive index [116). 

Front-silvered mirrors can be pohshed with optical rouge on a pad of chamois leather over cotton wool. Care is necessary because it is easy to polish completely through the silver. Back-silvered mirrors can be protected by first varnishing the silver and then painting the varnish. Front-silvered mirrors can be protected with a thin coat of lacquer, such as a dilute solution of cellulose nitrate in amyl acetate. The lacquer should not be too thin, or interference colours may be produced. 

Kijute 2.71 IIImttalion erf the X-ray standing wave held formed by the interference between the incident and reflected plane waves above a mirror surface t ee teat for detail ) After Bedivk ei cl (1990) Copyright 1990 by the AAAS... 

A reasonable objection to any in vitro model is whether it accurately mirrors the actual process. A strength of this model is that the peptides in the array, mounted on the microscope glass slide, are the very same as the antibody epitopes in the native proteins. Therefore, the types of formaldehyde-induced chemical reactions at or near the epitope are the same as would likely occur in a tissue sample. An additional strength of the model is that the experimental data using the peptide array completely account for the loss of immunoreactivity after formalin fixation and the recovery of immunoreactivity after antigen retrieval (Fig. 16.5). Nonetheless, our data do not prove that the model accurately represents formaldehyde reactions in tissue specimens. For example, our data do not exclude other causes of steric interference. 

This interferometric dilatometer consists of a rather simple and small Michelson interferometer, in which the two arms are parallel, and of a 4He cryostat, in which the sample to be measured is hold. The sample is cooled to 4 K, and data are taken during the warm up of the cryostat. The optical path difference between the two arms depends on the sample length hence a variation of the sample length determines an interference signal. The Michelson interferometer consists of a He-Ne stabilized laser (A = 0.6328 xm), two cube corner prisms, a beam splitter, three mirrors and a silicon photodiode detector placed in the focal plane of a 25 mm focal length biconvex lens (see Fig. 13.1). 

---