We have developed a computer program based on the geometrical optics approach proposed by Roosen to calculate the forces on dielectric spheres in focused laser beams. We have explicitly taken into account the polarization of the laser light and thd divergence of the laser beam. The model can be used to evaluate the stability of optical traps in a variety of different optical configurations.Our calculations explain the experimental observation by Ashkin that a stable single-beam optical trap, without the help of the gravitation force, can be obtained with a strongly divergent laser beam. Our calculations also predict a different trap stability in the directions orthogonal and parallel to the polarization direction of the incident light.Different experimental methods were used to test the predictions of the model for the gravity trap. A new method for measuring the radiation force along the beam axis in both the stable and instable regions is presented. Measurements of the radiation force on polystyrene spheres with diameters of 7.5 and 32 pm in a TEM,,-mode laser beam showed a good qualitative correlation with the predictions and a slight quantitative difference.The validity of the geometrical approximations involved in the model will be discussed for spheres of different sizes and refractive indices.

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A new type of glucose sensor based on luminescence quenching (LLJQUEN) is proposed. In this LUQUEN principle the concentration induced quenching is enlarged by radiationless (excited-state) energy transfer within the luminescent material. We describe the integrated optical detection part and the chemo-optical interface, in which the concentration induced optical changes are based on the binding of glucose. Some experiments on the internal energy transfer are reported, and the results are discussed.