Thermal index gradient

The most significant feature of laser-induced thermal index change is the magnitude of drix/dTand dri2/dT. Fig. 2 is a plot of the thermal index gradients dri /dT and dri2/ dT) of PCB from experimental values of the refractive indexes [14]. 

One of the most striking features of the temperature dependence of the refractive indices of nematic hquid crystals is that the thermal index gradients (dn IdT and dn IdT) become extraordinarily large near the phase transition temperature (Figs. 3.7a and 3.7b). From Equations (3.46), (3.47), (3.40), and (3.41), we can obtain dm IdT and ldl 2 ... 

One of the most striking and important optical properties of Uqtrid crystals is their large birefringence throughout the whole optical spectrum (from near UV to the infrared). The large thermal index gradients noted in Table 9.1 for the visible-infrared spectram are a consequence of that. In Figures 9.10 and 9.11 the measured refractive... 

Thermal index gradients dnJdT lO- K 10 K (visible-infrared) 5CBat25°C 5CB near... 

Sources are often surrounded by a thermally insulated enclosure to reduce noise caused by refractive index gradients between the hot air near the source and cooler air in the fight path. Short-term fluctuations in spectral output are usually due to voltage fluctuations and can be overcome by use of a stabilized power supply. Long-term changes occur as result of changes in the source material due to oxidation or other high temperature reactions. These... 

Similar to the thermal lens effect is exploitation of the fact that a narrow probe laser beam exhibits deflection as a consequence of a refractive index gradient again, the amount of deflection can be measured using a position-sensitive photodetector. 

Bulk property detectors function by measuring some bulk physical property of the mobile phase, e.g., thermal conductivity or refractive index. As a bulk property is being measured, the detector responses are very susceptible to changes in the mobile phase composition or temperature these devices cannot be used for gradient elution in LC. They are also very sensitive to the operating conditions of the chromatograph (pressure, flow-rate) [31]. Detectors such as TCD, while approaching universality in detection, suffer from limited sensitivity and inability to characterise eluate species. 

A method for determining the alteration of the refractive index of a medium as a result of the temperature rise in the path of a beam of coherent light absorbed by the medium. Thermal lensing can also occur with pigmented proteins, and this phenomenon can influence the accuracy of concentration gradient measurements in small aperture flow cuvettes as well as in ultracentrifugation. 

Photothermal deflection spectroscopy — Photothermal deflection is a photothermal spectroscopic technique used to detect the changes in the refractive index of the fluid above an illuminated sample by the deflection of a laser beam. There are two sources from which the thermal deflection effect might appear. One of them is produced by a gradient in the refractive index after a thermal excitation where the density also varies with temperature, in the so-called mirage effect. And the other one is produced by the topographical deformation of the surface over which the laser beam is reflected. This effect is known as photothermo-elastic effect or surface photothermal deflection [i]. 

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