Regular reflectance device

For investigations in the IR region, a great number of different devices have been constructed. In principle, the light beam coming out of the monochromator is directed onto the surface of the solid by a certain angle with mirrors or prisms, and the regular reflected beam is turned back to the detector. In some cases, this equipment can also be used in UV-VIS spectrophotometry. As an example, such a device is depicted in Fig. 4-54. 

Figure 4-54. Device for regular reflectance. DLS directed light source M surface mirror ...

In principle, these devices produce absorption spectra the sample is illuminated twice. Using UV-VIS sources with shorter wavelengths, some of the incident light is also absorbed, the rest of it is not only regularly reflected but also diffusely scattered, which causes a loss of energy, because only the specular reflected beam reaches the detector. 

The measurement of the polarization properties of light can be automated and improved by introducing a modulation of the polarization. Here a regular, time-dependent variation is introduced onto the optical properties of certain devices within either (or both) the PSG or PSA sections of the instrument. The modulation can be one of two types rotation of an optical element with fixed optical properties, or the modulation of the optical properties (retardation, for example) of an element with a fixed orientation. These are referred to as rotary modulators or field effect modulators, respectively. The latter name reflects the use of external fields (stress, electric or magnetic) to impart the modulation in these devices. In any case, a periodic oscillation is introduced into the signals that are measured that can effectively isolate specific optical properties in the sample. 

Light interacts with solid materials as scattering, absorption, transmission (transmittance), reflectance (both regular and diffuse), and diffraction. The purpose of spectroscopy is to quantify or qualify these interactions by the use of a variety of photon-produdng and photon-detection devices. The physics of these interaction phenomena and devices will be presented in this chapter. 

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