Real-time Translational Velocity Measurement for High Speed Tracking of a Transparent Floating Cell by Optical Visualization

Abstract

This paper describes a real-time translational velocimetry for the high speed tracking of a transparent floating cell by the optical visualization. This tracking technique optically visualizes a transparent cell as the fringe of sinusoidal intensity distribution, and measures the velocity by a high-response PD (Photodiode). Conventionally, we proposed the optical visualization method which derives the specific spatial frequency component from the sample by introducing two pinholes as a spatial filter on the optical Fourier transform plane, and made transparent cell visualize as the fringe. However, to realize the high speed tracking, the real-time measurement of moving velocity for the fringe by PD is needed. Therefore, we detect the phase information that linearly varies in accordance with the fringe position. In this phase detection, the double slits with a phase different of π/2 is installed on the imaging surface, and each transmitted light is separately received by the split PD. Herewith, the output wave of sine and cosine can be simultaneously obtained. By calculating the phase information as the arctangent from the vector locus, instantaneous velocity can be measured. We verified the possibility of measuring velocity in real time using the pixel array of the CCD as virtual slits.