Research On Particle Velocimetry Based On Optical Time-stretch Microscopy

Determination of velocities of microscopic particles is of great importance in applied science and technology as well as fundamental research fields such as hematology and semiconductor industry process.Commonly used technologies include particle image velocimetry,fluorescence correlation spectroscopy,and laser Doppler velocimetry,which have shortcomings such as low speed measurable velocity,low particle throughput,low spatial resolution,and label-need.As an ultra-fast imaging technology,optical time-stretch microscopy has frame rate up to tens of MHz.Besides,optical time-stretch microscopy uses near-infrared light as a laser source,which is not invasive to living cells or tissues.Therefore,it is of great research value to use optical time-stretch microscopy technology for microscopic particle velocimetry.In this paper,particle velocimetry based on optical time-stretch microscopy technology is deeply studied.The dispersion Fourier transform of broadband pulsed laser in dispersion compensating fiber and the spatial dispersion of broadband pulsed laser on diffraction grating are researched in principle.These above two key technologies are combined and the resolution limit of optical time-stretch microscopy is derived.Aiming at the poor imaging quality caused by the fluctuation of pulse laser source stability in the actual experiment,this paper proposes a pulse laser source frequency detection method based on variance minimization and bisection method to solve this problem and reduce the pulse laser index requirements and hardware costs.This paper completed the programming on MATLAB,including the system's laser source frequency detection,data processing,image recovery,and particle velocimetry,which enhance the intelligence of the system.In this paper,the actual performance of the particle velocimetry based on optical time-stretch microscopy is verified by experiments.The actual flow velocity of polystyrene particles with different diameters in the microfluidic chip with different depths is measured,and the accuracy of the measurement results is verified by a high-precision flow sensor and COMSOL Multiphysics.The particle velocity reaches 2.51 m/s,the particle throughput reaches 10000 particles/s,the frame rate reaches 25 MHz,and the spatial resolution of the system reaches 2.2 ?m.The research and work of this paper provides a promising tool for label-free and high-throughput particle velocimetry at high velocity magnitudes.