Particle counter

Inventors

Matsuda, Tomonobu • SHIMMURA, Masaki • SAITOU, Mitsuaki • Yamakawa, Yuki

Assignees

Rion Co Ltd

Abstract

Provided is a particle counter including: a light source; a light superimposition unit configured to superimpose light beams; an irradiation optical system configured to irradiate a fluid in a flow passage with one of a plurality of light beams from the light source; a detection optical system configured to make a part of scattered light beams by a particle in the fluid enter the light superimposition unit; a reference optical system configured to split another one of the plurality of light beams into a plurality of reference light beams and makes the reference light beams enter the light superimposition unit; and a counting unit configured to count the particles on the basis of detection signals corresponding to an interference light beam received by a light receiver. The interference light beam is generated by interference between the scattered light beam and one of the reference light beams at the light superimposition unit, and is received by the light receiver corresponding to the reference light beam.

Core Innovation

The invention is a particle counter designed to count small-size particles in a fluid with improved signal-to-noise (S/N) ratios. It includes a light source that emits a beam which is split into multiple light beams. One of these beams irradiates a fluid flowing through a flow passage, forming a detection area. Scattered light beams from particles in the fluid are collected by a detection optical system and made to enter a light superimposition unit together with multiple reference light beams obtained by splitting another one of the initial light beams via a diffraction optical system. Interference light beams are generated by interference between the scattered light beams and the corresponding reference light beams and are detected by light receivers corresponding to each reference light beam.

The particle counter detects scattered light beams traveling along the travelling direction of the fluid, which enhances changes in optical path length due to particle movement, producing a higher frequency and amplitude change in the interference light signal. The use of multiple reference light beams created by a diffraction grating allows spatially separated detection of particles, which increases detection area and counting efficiency. The design also includes apparatus to control the intensity, polarization, and wave front shape of reference light beams to approximately match those of scattered light beams, enhancing interference quality. A difference calculation between two oppositely phased interference signals further improves measurement sensitivity.

The problem solved is the difficulty in detecting and counting small particles, especially those 30 nm or less, in fluids such as chemical solutions where background noise from scattered light generated by the fluid medium is substantial. Previous counters were limited in sensitivity due to background noise and detection inefficiencies, particularly when using single reference light beams or multi-divided photodetectors with limited effective area. This invention achieves higher sensitivity and counting efficiency by using interference detection with multiple reference light beams and specific optical configurations.

Claims Coverage

The patent contains several independent claims outlining the core inventive features related to a particle counter system employing interference between scattered light beams and multiple reference light beams created from a split light source. There are two principal independent claims encapsulating these inventive features.

The independent claims cover a particle counter system using interference between scattered light from particles and multiple spatially split reference light beams derived from a coherent light source, employing detection schemes using light superimposition units such as beam splitters to generate dual interference light beams and differential detection to enhance counting sensitivity and efficiency.

Stated Advantages

Documented Applications