Abstract
Optical trapping is used for many studies. However, optical trapping traps only very small droplets. Therefore, observation of the trapped droplet is difficult. We tried to observe the droplet with several observation systems. First, an objective lens with a variable iris is used. The iris cuts scattering light of trapping laser. Second, a telecentric lens is used instead of the objective lens. The telecentric lens catches only parallel ray. Shape of droplets can be observed without scattering light. Third, a color filter and backlight are used to cut almost all laser light and observe droplets as shade. In this, droplets are too unclear to observe. To count droplets, first and second ways are used. However, to observe in detail, this observation system needs to be improved.
