Confocal-LIF 기법의 다층 매질 측정 시 굴절율 불일치에 따른 구면 수차 보정

Abstract

In this work, in measuring local quantities of micro-scale flows with the Confocal-LIF technique, an error due to spherical aberration was identified and a theoretical correction was proposed. The original objective lenses for a specified medium have a mismatch problem of refractive-indices that is critical when the measuring point enters deeply into the medium through thick windows. The index number of a correction collar (generally used for accurate focusing) of objective lenses is adjustable to minimize aberration. Thus, the depth of the focusing zone on the specific index was identified for the air medium. Then, a simple optical model for the collar-indexing was proposed. For a parallel laser light with Gaussian intensity, the predicted light energy distribution using the geometric ray tracing well matches with the measurement. Finally, the model has been demonstrated for accurate focusing along the depth direction in a multi-layer medium in using the Confocal-LIF technique.