The research focuses on isochromatic photoelastic fringe patterns in solid materials by using reflection mode in dark field polariscope. The optical setup consists of light source, polarizers, quarter wave plates, 577 nm optical pass filter, compensator and digital camera system. The fringe patterns were produced on the sample and fractional / integer number of fringe order was observed using Babinet compensator and digital camera system. The samples were circular and rectangular shape of PMMA coated with silver spray and compressed by hydraulic system at the top and the bottom. The results of the isochromatic fringe pattern were analyzed in horizontal and vertical positions. It was found that force and the number of isochromatic photoelastic fringe order depended on shape of sample, which reflects stress distribution behavior.
Photostress analysis system was used to study the stress distribution on a circular disk. A reflection polariscope was used to observe the surface strains from the recorded fringe patterns by digital camera. The shape of sample is a circular disk was pressed on the top and bottom and the polariscope produced fringe patterns from sample on the model being stressed. The results were analyzed, the fringe pattern looked different in various magnitude of force because the stress distribution in sample was changed with magnitude of force. Deformation can be determined from the fringe patterns.
The red-shift on fluorescent dyes spectra at high concentration was investigated by laser induce fluorescence technique. In this research, the fluorescent dyes (Rhodamine 6G, Rhodamine B, Fluorescein and Bromofluorescein) were used. The sample solutions were prepared with methanol solvent in the concentration range of 10<sup>-5</sup> to 10<sup>-3</sup> Molar and the temperature of sample solution was controlled at 25 °C by temperature control chamber. Then, the sample solution was illuminated by violet laser (405 nm) excitation source and the fluorescence spectra were recorded by CCD spectrometer. The result showed that the fluorescence spectra of all fluorescent dye solutions were dependent on concentration of fluorescent dyes. The position of fluorescence maximum intensity was shifted to a higher wavelength (red-shift) when the concentration increased because the dimer formation rate increases with increasing concentration, but the shifting of wavelength for each fluorescent dye solutions was different, which suggests the different rate of formation of dimer molecules in each fluorescent dye solutions.
The teaching and learning optics in Thailand is some how rather slowly developed. This is could possibly due to its importance, as seen by the educators and scientists in Thailand, was not so pronounced in the past. This made Thai scientists and researchers in many other disciplines lag of basic optics knowledge to getting involve with today advanced optics and photonics technologies. The need for high precision and high speed of the measurement and control in today experiment urges them to get involve in optics and photonics techniques more than ever before. At Chiang Mai university we offer 4-credit course: Optics and Spectroscopy. It covers a conventional optics course detail as referred in most conventional optics text books. Advanced optics course is also offered at higher level. The development of research activities utilizing optics and photonics techniques has been very slow due to the higher cost for most of the equipment involved. Very often that we have to assemble our own designed micro-computer-based equipment. The multi-scaler and a computer to serve as a photon correlator in dynamic light scattering (DLS) system to study correlation length in a liquid mixture at its critical point is one of the examples. The Ph.D. projects work in our section involve medical laser and electro-optics properties of a liquid mixture are some examples of our interest.