Refractive Index Changes

Figure 1. shows the measured phase differenee derived using equation (6). A close match between the three sets of data points can be seen. Small jumps in the phase delay at 5tt, 3tt and most noticeably at tt are the result of the mathematical analysis used. As the cell is rotated such that tlie optical axis of the crystal structure runs parallel to the angle of polarisation, the cell acts as a phase-only modulator, and the voltage induced refractive index change no longer provides rotation of polarisation. This is desirable as ultimately the device is to be introduced to an interferometer, and any differing polarisations induced in the beams of such a device results in lower intensity modulation. 

In the papers referenced above it has been shown that depth resolutions around 2-3 pm collected with a 100 x microscope objective are possible. However, the depth resolution will degrade as one probes deeper into the sample this is a consequence of refraction caused by refractive index changes at the sample surface and boundaries within the sample. The greater the depth probed, the greater the dof becomes if an air objective is used the situation can be improved and aberrations minimised if an oil immersion objective is used [16,17],... 

Chomat M., Berkova D., Matejec V., Ctyroky J., Kasik I., The detection of refractive-index changes by using a sensing fiber with an inverted parabolic index profile, Proc. SPIE 3860 (1999), Boston. 

At concentrations greater than about 0.01 M, refractive index changes and the perturbing effect of solute molecules or ions on the charge distribution of their neighbours both affect the value of s. Positive or negative deviations may result. 

The sensors in this section can also be utilized to detect chemicals in liquid through the bulk solution refractive index change induced by the presence of target chemicals. Since no recognition molecules are used, this type of chemical sensing may usually have low specificity. However, these sensors may perform excellently in conjunction with other technologies such as capillary electrophoresis, mass spectrometer, and liquid chromatography in chemical detection. 

For the AJL8/APC polymer, saturation was not achieved until 250 h of exposure to the DNT vapor. However, the sensing polymer produces a detectable amount of refractive index change within a few minutes of exposure to DNT vapor of 100 ppb concentration. The response rate is thought to be limited by the diffusion of DNT molecules into the polymer. In the initial experiments reported here PMMA and polycarbonate were used as the host polymers. These polymers are relatively less permeable to DNT. The response rate is expected to improve if a more permeable polymer host is used. 

In this chapter, we will numerically analyze the effects of the HRI overlay on the cladding modes distribution with particular attention to its influence on the device sensitivity to the SRI changes and to the overlay refractive index changes. The structure to which we refer is depicted in Fig. 3.2. 

In many cases, only the relative refractive index change is of interest and the range of refractive index variation is small so the phase shift is less than 2n. In this case, the phase ambiguity issue can be avoided. The relative refractive index change can be calculated based on the spectral shift of the interferogram. 

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