Stereoscopic particle tracking for 3D touch, vision and closed-loop control in optical tweezers
Stereoscopic particle tracking for 3D touch, vision and closed-loop control in optical tweezers
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DOI：
10.1088/2040-8978/13/4/044003
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发表时间：
2011-04
影响因子：
2.1
通讯作者：
R. Bowman;D. Preece;G. Gibson;M. Padgett
中科院分区：
文献类型：
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作者：
R. Bowman;D. Preece;G. Gibson;M. Padgett
交互式3D微操作系统中的力测量可以让用户进行精细的调整，并通过触摸和视觉探索表面。我们提出了一个系统，以实现这一微米尺度上使用立体粒子跟踪结合全息光镊，它可以跟踪粒子与纳米精度。每个立体图像中的颗粒的2D跟踪给出每个颗粒的3D位置。使用应用于2D图像的每行和每列的1D“对称变换”，每个图像对花费不到200 µs，这可以在整个10 µm轴向范围内保持对颗粒的跟踪。所需的唯一参数是成像系统的几何形状，因此不需要针对不同的颗粒尺寸或折射率进行重新校准。因此，我们可以计算在1千赫下真实的时间内光学陷阱施加的力，从而使我们能够实现力反馈接口（环路速率为400 Hz）。结合我们的OpenGL全息计算引擎，该系统具有20 Hz的闭环带宽。这使我们能够通过主动反馈轴向稳定捕获的粒子，抵消一些布朗运动。对于我们在这里使用的弱陷阱（弹簧常数k <$2 pN µm − 1），这导致轴向刚度增加三倍。我们通过探测油滴来展示3D界面，在y-z平面上绘制其表面。
Force measurement in an interactive 3D micromanipulation system can allow the user to make delicate adjustments, and to explore surfaces with touch as well as vision. We present a system to achieve this on the micron scale using stereoscopic particle tracking combined with holographic optical tweezers, which can track particles with nanometre accuracy. 2D tracking of particles in each of the stereo images gives 3D positions for each particle. This takes less than 200 µs per image pair, using a 1D ‘symmetry transform’ applied to each row and column of a 2D image, which can maintain tracking of particles throughout the 10 µm axial range. The only parameters required are the geometry of the imaging system, and therefore there is no need to recalibrate for different particle sizes or refractive indices. Consequently, we can calculate the force exerted by the optical trap in real time at 1 kilohertz, allowing us to implement a force-feedback interface (with a loop rate of 400 Hz). In combination with our OpenGL hologram calculation engine, the system has a closed-loop bandwidth of 20 Hz. This allows us to stabilize trapped particles axially through active feedback, cancelling out some Brownian motion. For the weak traps we use here (spring constant k≈2 pN µm − 1), this results in a threefold increase in axial stiffness. We demonstrate the 3D interface by probing an oil droplet, mapping out its surface in the y–z plane.