Tracking submicron particles in a micro­channel by microscopic holography

F M Xiao1, L Wang2, R Luo2* S Liu1

1Department of Thermal Power Engineering, North China Electric Power University, Beijing 102206, China

2State Key Lab of Power Systems, Dept of Thermal Eng., Tsinghua University, Beijing 100084, China.

*e­mail: ruiluo@tsinghua.edu.cn

ABSTRACT

Three­dimensional tracking of submicron particles in flows in a micro­channel was carried out using in­ line holographic microscopy. In­line holograms of a fixed 0.5µm fluorescent particle at different optical axial positions, i.e. defocus distances, were obtained and were compared with its laser induced fluorescent (LIF) diffraction patterns to determine the accurate relationship between them and the defocus distances. The holograms of flows seeded with the 0.5 µm particles in the micro­channel were preprocessed by the background subtraction to remove diffraction noises from the micro­channel and other non­moving objects. The particles in each hologram were then identified and located to obtain their two­dimensional positions. The defocus distances of those particles were determined from their each hologram pattern instead of a direct reconstruction. Finally the three­dimensional position and velocity of each particle were obtained.

Keywords In­line hologram, Microscopy holography, Submicron particle, Micro­channel