Optic simulation and optimization of a laser Doppler velocity profile sensor for microfluidic applications

Abstract

The application of laser Doppler velocimetry to microfluidic flows is usually prevented due the large size of the measurement volume of typically 100 µm. A significantly higher spatial resolution can be achieved with the concept of the laser Doppler velocity profile sensor. However, the resolution is limited by wavefront distortions caused by aberrations of the optical setup. In this work, optical simulation software was employed to investigate the aberrations caused by the profile sensor setup by going from ideal to real lenses step by step. As the main source for the aberrations, the aspheric lens for collimating the laser beams was identified. On the basis of this simulation the setup of the velocity profile sensor could be optimized. The sensor was employed to measure the velocity profile in a microchannel. A spatial resolution of 1.2 µm and a relative uncertainty of the velocity of 0.25% result, confirming the findings of the simulation. This demonstrates the potential of the optimized velocity profile sensor for flow measurements at the microscale.