OKU Laboratory

1 ms 3D Feedback Microscope

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The 3D measurement of the micro space is demanded in specific fields like biology. In particular, the high-speed measurement is demanded when the target object is moving.

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 One way to rapidly measure the 3D information is to aquire an image of the object to be measured by scanning the focal position of the microscope in the optical axis direction. This way is suitable for the high-speed measurement in which feedback is required because it can reconstruct the 3D information with a relatively simple procedure. However, it has been difficult  to rapidly measure the 3D information since the drive frequency of existing Z scanners is not high enough. To solve this problem, Tunable Acoustic Gradient index (TAG) lens, which can rapidly vary the focal position, was developed in recent years.

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 TAG lens is a kind of liquid lens which can change its focal length by modifying the optical characteristics of the shape of the liquid interface, and can change the focal length by varying the refractive power. The focus varying cycle of TAG lens is from 50 k to 500 kHz. In principle, the high-speed 3D measurement can be implemented by using TAG lens because a number of images can be acquired while rapidly varying the focal position. However, it is necessary to measure the information in a short period of 0.1 to 1 us in order to extract information only at a specific focal position. An image sensor achieving such short exposure time has the limitation, and when an image is captured by such short exposure time, the luminance of the image is very low. Therefore, it is impractical.

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 To solve this problem, a method, which a particular focal planes were captured as color components of the color image by synchronizing the color strobe lights and the focus varying cycle of TAG lens, was proposed. We address a development of high-speed 3D feedback microscope system which 3D information is calculated from captured focal planes and feedbacked, by using a principle of this method.