Abstract

In Digital holography Microscopes (DHM) implemented in the so-called “off axis” configuration, the object and reference wave fronts are not co-planar but form an angle of a few degrees. This results into two main drawbacks. First, the contrast of the interference is not uniform spatially when the light source has low coherence. The interference contrast is optimal along a line, but decreases when moving away from it, resulting in a lower image quality. Second, the non-coplanarity between the coherence plane of both wavefronts impacts the coherence vertical scanning measurement mode: when the optical path difference between the signal and the reference beam is changed, the region of maximum interference contrast shifts laterally in the plane of the objective. This results in more complex calculations to extract the topography of the sample and requires scanning over a much larger vertical range, leading to a longer measurement time. We have previously shown that by placing a volume diffractive optical element (VDOE) in the reference arm, the wavefront can be made coplanar with the object wavefront and the image plane of the microscope objective, resulting in a uniform and optimal interferogram. In this paper, we demonstrate a vertical scanning speed improvement by an order of magnitude. Noise in the phase and intensity images caused by scattering and non-uniform diffraction in the VDOE is analyzed quantitatively. Five VDOEs were fabricated with an identical procedure. We observe that VDOEs introduce a small intensity non-uniformity in the reference beam which results in a 20% noise increase in the extracted phase image as compared to the noise in extracted phase image when the VDOE is removed. However, the VDOE has no impact on the temporal noise measured from extracted phase images.

© 2013 OSA

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References

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2012 (2)

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

F. Dubois and C. Yourassowsky, “Full off-axis red-green-blue digital holographic microscope with LED illumination,” Opt. Lett.37(12), 2190–2192 (2012).
[CrossRef] [PubMed]

2011 (1)

2010 (2)

2002 (1)

U. Schnars and W. Jüptner, “Digital recording and numerical reconstruction of holograms,” Meas. Sci. Technol.13(9), 85–101 (2002).
[CrossRef]

2000 (1)

1999 (3)

Bally, G.

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

Bevilacqua, F.

Chmelik, R.

Cuche, E.

Depeursinge, C.

Ding, H.

Dubois, F.

Emery, Y.

Harasaki, A.

Joannes, L.

Jüptner, W.

U. Schnars and W. Jüptner, “Digital recording and numerical reconstruction of holograms,” Meas. Sci. Technol.13(9), 85–101 (2002).
[CrossRef]

Kemper, B.

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

Kolman, P.

Kosmeier, S.

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

Langehanenberg, P.

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

Legros, J. C.

Marquet, P.

Monemhaghdoust, Z.

Montfort, F.

Moser, C.

Popescu, G.

Schmit, J.

Schnars, U.

U. Schnars and W. Jüptner, “Digital recording and numerical reconstruction of holograms,” Meas. Sci. Technol.13(9), 85–101 (2002).
[CrossRef]

Wyant, J. C.

Yourassowsky, C.

Appl. Opt. (3)

Appl. Phys. B (1)

S. Kosmeier, P. Langehanenberg, G. Bally, and B. Kemper, “Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length,” Appl. Phys. B106(1), 107–115 (2012).
[CrossRef]

Meas. Sci. Technol. (1)

U. Schnars and W. Jüptner, “Digital recording and numerical reconstruction of holograms,” Meas. Sci. Technol.13(9), 85–101 (2002).
[CrossRef]

Opt. Express (3)

Opt. Lett. (2)

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Figures (7)

Fig. 1
Fig. 1

Vertical scanning. (a), (b) without, and (c) with, reference beam coherence plane tilt manipulation.

Fig. 2
Fig. 2

(a) VDOE which preserves the propagation direction and introduces a slight angle in coherence plane. (b) Fabricated device.

Fig. 3
Fig. 3

Optical set-up of the digital holographic microscope.

Fig. 4
Fig. 4

Example phase image resulting from the subtraction of a 5th order polynomial fit from the original phase image. Regions 1 to 5 of size 70 x 70 pixels are used to characterize the spatial phase.

Fig. 5
Fig. 5

Phase image resulting from subtraction of the original phase image with the reference phase hologram Selected regions 1 to 6 of size 2 x 2 pixels used to characterize the temporal phase noise.

Fig. 6
Fig. 6

Vertical scanning procedure.

Fig. 7
Fig. 7

(a) The resulting image obtained by the vertical scanning measurements which provides (b) the height line profile of the staircase sample.

Tables (3)

Tables Icon

Table 1 Relative change of standard deviation of the reference beam obtained without and with the VDOE in the path of reference beam.

Tables Icon

Table 2 Mean roughness (Ra) and maximum roughness (Rt) measured in five VDOES (top to bottom in the table) over five region of interest (left to right in the table) in the phase image of Fig. 4. Values represent the relative change obtained without and with the VDOE placed in the path of the reference arm.

Tables Icon

Table 3 Temporal standard deviation measured in [nm] in five regions shown in Fig. 5.

Metrics