As an important and efficient method of particles size measurement, laser scattering has attracted great interest in the last decades. The sheath flow method has received extensive attention for its specific characteristic in cell detection and other fields. In this work, we report on a study of sheath flow method in laser scattering particles size measurement. In the particles size measurement system, an optical fiber laser was used as laser source, the light sensitive was confined to circular region with a diameter of less than 10μm by micro-lens focusing structure. Based on the scattering theoretical analysis of the particle size distribution from the scattering light energy, an improved sheath flow structure is proposed to obtain accurate and reliable scattering light signal from the particle passing through sheath flow pool. The digital voltage signals were measured via the amplification circuit and the data acquisition card. Numerical calculations and experiment results show that the sheath flow system is effective in the laser scattering particles size measurement.
A novel design based on near forward light scattering detection system to measure size and concentration distribution of particles in liquids is reported. According to theory of Mie scattering, the influence of relative refractive index, particles size and wavelength on the detection results are discussed. A green optical fiber laser with 532nm was used as the excited light source. As a key part in the detection system, the focusing system using a lens structure to confine light sensitive area with Gauss distribution less than 80 μm<sup>2</sup>. The lateral size of the sample cell is limited to 100μm. In order to measure the particles in non-overlapping state and improve the accuracy and repeatability, a novel structure in the sample cell was used and particle velocity through the sample cell was controlled by high precision stepper motor control system of micro circulation pump. Particle light scattering signal acquisition was completed by the poly lens combination system, according to the receiving angle relative to the measured particle, which can adjust the light scattering direction to obtain better particles light scattering signal. Photoelectric signal conversion, amplification and acquisition are all the devices with high precision. The measurement results showed that the measurement system was accurate and stable when the particles size in the range of 0.5-5μm.