When a microsphere is trapped near a surface by single-beam gradient force trapping, the standing wave is generated between the microsphere and the surface, where abrupt motion along the optical axis (jumping) is observed corresponding to displacement of the surface. This jumping distance is on the order of a few hundred nanometers. In the vicinity of the surface, intensity of retro-reflected light is increased so that the averaged position of the jumping is shifted up on the order of several micrometers. Therefore wide-range and high-resolution position measurement technique is required. In this article, we proposed to apply a chromatic confocal sensor to measure the axial position of the microsphere in the standing wave. It was experimentally validated that the position of the microsphere could be measured with a resolution of 10 nm and a measuring range of 3 µm.

当通过单束梯度力捕获将微球捕获在表面附近时，在微球和表面之间会产生驻波，在该驻波中会观察到沿光轴的突然运动（跳跃），这与表面的位移相对应。该跳跃距离约为几百纳米。在表面附近，回射光的强度增加，以使跳跃的平均位置向上移动几微米的数量级。因此，需要宽范围和高分辨率的位置测量技术。在本文中，我们建议应用彩色共聚焦传感器来测量微球在驻波中的轴向位置。