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Real-time, auto-focusing digital holographic microscope using graphics processors
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Image of FIG. 1.
FIG. 1.

The transmission based DHM setup. The laser beam is divided into two arms by the beam splitter BS1. The reference wave is modulated by a phase modulator (PM) and the object wave is transmitted through the specimen. Before joining the two arms of the interferometer by the second beam splitter BS2, object image is magnified by the microscope objective MO1. In order to compensate for the wave front curvature a similar objective MO2 is placed on the reference beam path. Finally, interference of the two beams is recorded by a CCD camera that is connected to a PC.

Image of FIG. 2.
FIG. 2.

Auto-focusing steps are shown using a recorded hologram of USAF resolution chart target. (a) 1024 × 1024 size hologram is scaled four times to 128 × 128 pixels. (b) Sharpness curve of the reconstructed image is calculated by using normalized-variance as the quality metric, the peak shows the correct focus distance (4 cm in this case). (c) Magnitude of reconstructed image at the focus distance.

Image of FIG. 3.
FIG. 3.

Generic architecture of an Nvidia GPU. SM stands for the shared memory.

Image of FIG. 4.
FIG. 4.

A picture of the digital holographic microscope.

Image of FIG. 5.
FIG. 5.

Flow of operations in an auto-focusing DHM.

Image of FIG. 6.
FIG. 6.

The figure shows the magnitude ((a), (c), (e)) and the phase ((b), (d), (f)) images of reconstructed holograms of human epithelial cells, photo-resist test sample, and USAF calibration chart in sequence.

Image of FIG. 7.
FIG. 7.

Error in focus calculation as a function of scaling. This is a plot of the percentage error of the focus distance estimated from the original hologram reconstruction and the scaled hologram reconstruction. For this figure, we have used holograms of USAF resolution target.


Generic image for table

Phase-shifting holography operation to recover the object wave from the recorded holograms.

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Focus distance estimation.

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Hologram reconstruction using angular spectrum method.

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Table I.

Hardware specifications of Geforce GTX 660 Ti.

Generic image for table
Table II.

Comparison of the timings for a single hologram reconstruction including the auto-focusing with 4 times scaling with an Intel Xeon W3670 CPU and a Nvidia Geforce GTX 660 Ti GPU.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Real-time, auto-focusing digital holographic microscope using graphics processors