In this paper, we present a demonstration of digital holography at the rate of 1,000,000 fps, which is the fastest speed in digital holography. Up to now, we have confirmed the validity of parallel phase-shifting digital holography in many fields.
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This technique records multiple phase-shifted holograms with single-shot exposure, which can achieve a high-speed recording, and it can acquire a clear reconstructed image free from the zeroth-order diffraction image and the conjugate image by applying phase-shifting calculation ( 5). To overcome the problem of phase-shifting digital holography, we proposed parallel phase-shifting digital holog-raphy ( 6)-( 22). However, this technique is useless for measuring 3D information of high-speed moving objects because multiple exposures for recording the phase-shifted holograms are needed. By the phase-shifting calculation, the zeroth-order diffraction image and the conjugate image are remove from the object image. In this technique, a PZT-driven mirror is introduced in the reference beam arm to record four phase-shifted holograms. To solve this problem, phase-shifting digital holography ( 5) was proposed. However, the undesired images, such as the zeroth-order diffraction image and the conjugate image are superimposed on the object image in in-line digital holography, so that the quality of the reconstructed image is degraded and the measurement precision is decreased. That means in-line digital holography is more suitable for highspeed recording than off-axis digital holography. Especially, the pixel size of high-speed camera is larger than general camera to record as many photons as possible in extreme short exposure time.
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Therefore, pixel pitch of image sensors is too large to record fine interference fringes. In general, pixel sizes of CCD or CMOS image sensors are few micrometers. In off-axis configurations, the reference beam and the object beam come to the image sensor with a relative angle, and the interval of the interference fringes decreases with the relative angle increasing. One is in-line digital holography ( 3) and the other one is off-axis digital holog-raphy ( 4).
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The recording method are grouped in two main categories according to the incident angle between object beam and reference beam. In this technique, a hologram containing 3D information of the object is recorded by an image sensor such as a charge-coupled devices (CCDs) or complementary metal-oxide semiconductors (CMOSs), and both the intensity images and phase images are reconstructed on computer. Digital holography ( 1), ( 2) is a useful technique for recording and reconstructing 3D information of objects without scanning. Three-dimensional (3D) measurement for dynamic objects is required in many fields such as living cell measurement, product inspection, particle measurement, flow measurement, shock wave analysis, and so on.