NUMERICAL-SIMULATION OF IR-SPECTROSCOPIC EXPERIMENTS

In this work we demonstrate the application of numerical simulation fo r the investigation of the light distribution in an optical system, su ch as an FT-IR microscope. Because of the complexity of simulating the optical arrangement of a complete IR-microscope we have applied a pro gram based on a Monte Carlo type wavelength-dependent ray-tracing tech nique (SPRAY). The program is capable of computing spectral features i n a complex three-dimensional system. Spectral Features of organic lay ers and bodies are calculated from the real and imaginary parts of the dielectric functions determining the interaction of light with the ma terial considered. The dielectric functions can be derived from variou s models. Previous work has shown that for organic substances a harmon ic oscillator model can be used with sufficient accuracy. As microscop y usually exploits plane sample carriers, which do not seriously affec t the path of the IR-beam, we calculated and rested cylindrical and sp herical carriers, resulting in a higher energy throughput to the detec tor. In the simulation virtual screens could be placed before, inside and after the carrier to visualize the path of the radiation and the f ocusing effects, corroborating the experimental results. This work dem onstrates the importance of wavelength-dependent numerical simulation of IR-spectroscopic experiments. The software developed offers a valua ble tool for the verification of experimentally obtained IR-spectrosco pic results and for the development and optimization of optical system s.