Patent ID: 8164749

Claim:
An optical measurement apparatus, comprising: a container for storing a sample having particles dispersed movably in a medium; a power source for generating an AC or DC voltage; an electrode pair for generating an electric field having a space period in the container by application of the voltage from the power source; an irradiation optical system for applying a parallel light flux to a diffraction grating resulting from density distribution of the particles generated in the container by the application of the voltage; a detection optical system for detecting diffracted light generated from the parallel light flux passing through the diffraction grating; voltage control means for controlling to generate and annihilate the diffraction grating resulting from the density distribution of the particles in the container by the application of the voltage from the power source to the electrode pair and stoppage and modulation of the application of the voltage; and data processing means for taking in outputs of the detection optical system to execute the process of evaluating characteristics of the particles and/or the medium, wherein electrodes constituting the electrode pair include multiple mutually parallel linear electrode pieces and a connection part electrically connecting the respective electrode pieces to each other, respectively, electrode piece ununiformly-arranged areas including at least two of the linear electrode pieces arranged adjacently to each other, and electrode piece absent areas without the electrode pieces arranged therein are alternately formed in each of the electrodes, the electrodes are arranged so that the electrode piece ununiformly-arranged areas of one of the electrodes are positioned in the electrode piece absent areas of the other electrode, and the electrode pieces of the electrodes are in parallel with each other at regular intervals, and a relationship between width L of the electrode pieces of each of the electrodes and a space distance S between the electrode pieces is as follows: L /( L+S )≦0.3.