Abstract

We present an imaging scheme that takes advantage of the superior lateral resolution of volume holographic imaging (VHI)[1] and a-priori surface information about the object to build a profilometer that can resolve 50µm longitudinal features at a working distance of ≈ 50 cm with a single VHI camera. We discuss the scheme and present experimental results of surface profiles of MEMS devices.

© 2003 Optical Society of America

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References

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  1. G. Barbastathis and D.J. Brady, �??Multidimensional tomographic imaging using volume holography,�?? Proceedings of the IEEE 87, 2098-2120, (1999).
    [CrossRef]
  2. G. Barbastathis, M. Balberg and D. J. Brady, �??Confocal microscopy with a volume holographic filter,�?? Opt. Lett. 24, 811-813 (1999).
    [CrossRef]
  3. A. Sinha and G. Barbastathis, �??Volume holographic telescope,�?? Opt. Lett. 27, 1690-1692 (2002).
    [CrossRef]
  4. W. Liu, D. Psaltis and G. Barbastathis, �??Real-time spectral imaging in three spatial dimensions,�?? Opt. Lett. 27, 854-856 (2002).
    [CrossRef]
  5. A. Sinha, W. Sun, T. Shih and G. Barbastathis, �??Volume holographic imaging in the transmission geometry,�?? to appear in Appl. Opt.
  6. D. Marr, Vision, (W. H. Freeman & Co, 1982).
  7. G. Binnig, C. F. Quate and C. Gerber, �??Atomic Force Microscope,�?? Phys. Rev. Lett., 56, 930-933 (1986).
    [CrossRef] [PubMed]
  8. M. Born and E. Wolf, Principles of optics, (Pergamon Press, Cambridge, UK, 1998).
  9. J. White, H. Ma, J. Lang and A. Slocum, �??An instrument to control parallel plate separation for nanoscale flow control,�?? Rev. Sc. Instruments 74, 4869-4875 (2003).
    [CrossRef]

Appl. Opt.

A. Sinha, W. Sun, T. Shih and G. Barbastathis, �??Volume holographic imaging in the transmission geometry,�?? to appear in Appl. Opt.

IEEE

G. Barbastathis and D.J. Brady, �??Multidimensional tomographic imaging using volume holography,�?? Proceedings of the IEEE 87, 2098-2120, (1999).
[CrossRef]

Opt. Lett.

Phys. Rev. Lett.

G. Binnig, C. F. Quate and C. Gerber, �??Atomic Force Microscope,�?? Phys. Rev. Lett., 56, 930-933 (1986).
[CrossRef] [PubMed]

Rev. Sc. Instruments

J. White, H. Ma, J. Lang and A. Slocum, �??An instrument to control parallel plate separation for nanoscale flow control,�?? Rev. Sc. Instruments 74, 4869-4875 (2003).
[CrossRef]

Other

M. Born and E. Wolf, Principles of optics, (Pergamon Press, Cambridge, UK, 1998).

D. Marr, Vision, (W. H. Freeman & Co, 1982).

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Figures (9)

Fig. 1.
Fig. 1.

Schematic for PR–VHI (a) Recording (b) Readout using a collimated point source.

Fig. 2.
Fig. 2.

Diffracted intensity pattern observed on CCD for defocused point source.

Fig. 3.
Fig. 3.

PR–VHI using a line source to reduce scanning required (a) Schematic (b) Intensity pattern observed on CCD.

Fig. 4.
Fig. 4.

Depth resolution degrades slightly when using a line readout as opposed to a point readout. The PR–VHI system had an objective lens with f=50.2 mm and a=5 mm; θ s=25°. The volume hologram was 2 mm thick crystal of LiNbO3 with diffraction efficiency η=5% recorded using a doubled Nd:Yag laser with λ=532 nm.

Fig. 5.
Fig. 5.

(a) PR–VHI metrology system at normal incidence (b) Inclined PR–VHI system to exploit a-priori object information.

Fig. 6.
Fig. 6.

Depth resolution improves by taking advantage of a-priori object information. The PR–VHI sensor had f=460 mm, a=5mm and F=50.2 mm for the same LiNbO3 crystal used in Fig.4.

Fig. 7.
Fig. 7.

Surface scan of microturbine with surface features ≈ 225µm, (a) Image of Microturbine captured using CCD, (b) PR–VHI image of turbine with the top surface in focus, (c)&(d) PR–VHI images focused 50µm and 150µm below the top surface. (e) PR–VHI image focused on the base of the turbine 250µm below the top surface. Note that there is a complete contrast reversal in between images (b) and (e).

Fig. 8.
Fig. 8.

Surface scan of nanogate which has surface features ≈ 150µm, (a) Image of nanogate captured using CCD, (b) PR–VHI image of device with the top surface in focus, (c)&(d) PR–VHI images focused 50µm and 100µm below the top surface. (e) PR–VHI image focused on the base of the turbine 150µm below the top surface. Note that there again is a complete contrast reversal in between images (b) and (e).

Fig. 9.
Fig. 9.

Schematic of proposed PR–VHI system to perform high resolution metrology at long working distance.

Equations (5)

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I ( x , y ) I b = circ ( ( x θ s F ) 2 + y 2 F a δ f 2 ) sinc 2 ( L θ s λ ( x F θ s ) ) ,
Δ z FWHM = 5.34 λ f 2 θ s a L .
Δ x B = 2 λ f θ s L .
I ( x , y ) I b = rect ( ( x θ s F ) F a δ f 2 ) rect ( y b δ f ) sinc 2 ( L θ s λ ( x F θ s ) ) ,
Δ z FWHM ( P R ) opt = 5.34 r min λ f 2 θ s a 2 × L .

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