Abstract

We demonstrate a technique to measure the reflectance of colored objects, including blue, green, and yellow, hidden behind an opaque slab based on acoustically modulated laser speckle. One colored paper at a time was placed behind a 1 cm thick opaque slab with an air gap of 5 mm. Small periodic movements (nanometer scale) at 200 Hz were induced in the colored paper. A coherent red He–Ne laser illuminated the front of the slab, producing acoustically modulated speckle patterns, which were captured by a CCD camera. The magnitude of the time-varying speckle intensity is indicative of the hidden colored paper’s reflectance.

© 2012 Optical Society of America

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References

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  1. D. T. Delpy and M. Cope, Phil. Trans. R. Soc. B 352, 649 (1997).
    [CrossRef]
  2. D. A. Boas and A. K. Dunn, J. Biomed. Opt. 15, 011109 (2010).
    [CrossRef]
  3. S. L. Jacques and S. J. Kirkpatrick, Opt. Lett. 23, 879 (1998).
    [CrossRef]
  4. J. W. Goodman, in Laser Speckle and Related Phenomena, J. C. Dainty, ed. (Springer-Verlag, 1975).
  5. W. Leutz and G. Maret, Phys. B 204, 14 (1995).
    [CrossRef]
  6. S. Leveque-Fort, Appl. Opt. 40, 1029 (2001).
    [CrossRef]

2010 (1)

D. A. Boas and A. K. Dunn, J. Biomed. Opt. 15, 011109 (2010).
[CrossRef]

2001 (1)

1998 (1)

1997 (1)

D. T. Delpy and M. Cope, Phil. Trans. R. Soc. B 352, 649 (1997).
[CrossRef]

1995 (1)

W. Leutz and G. Maret, Phys. B 204, 14 (1995).
[CrossRef]

Boas, D. A.

D. A. Boas and A. K. Dunn, J. Biomed. Opt. 15, 011109 (2010).
[CrossRef]

Cope, M.

D. T. Delpy and M. Cope, Phil. Trans. R. Soc. B 352, 649 (1997).
[CrossRef]

Delpy, D. T.

D. T. Delpy and M. Cope, Phil. Trans. R. Soc. B 352, 649 (1997).
[CrossRef]

Dunn, A. K.

D. A. Boas and A. K. Dunn, J. Biomed. Opt. 15, 011109 (2010).
[CrossRef]

Goodman, J. W.

J. W. Goodman, in Laser Speckle and Related Phenomena, J. C. Dainty, ed. (Springer-Verlag, 1975).

Jacques, S. L.

Kirkpatrick, S. J.

Leutz, W.

W. Leutz and G. Maret, Phys. B 204, 14 (1995).
[CrossRef]

Leveque-Fort, S.

Maret, G.

W. Leutz and G. Maret, Phys. B 204, 14 (1995).
[CrossRef]

Appl. Opt. (1)

J. Biomed. Opt. (1)

D. A. Boas and A. K. Dunn, J. Biomed. Opt. 15, 011109 (2010).
[CrossRef]

Opt. Lett. (1)

Phil. Trans. R. Soc. B (1)

D. T. Delpy and M. Cope, Phil. Trans. R. Soc. B 352, 649 (1997).
[CrossRef]

Phys. B (1)

W. Leutz and G. Maret, Phys. B 204, 14 (1995).
[CrossRef]

Other (1)

J. W. Goodman, in Laser Speckle and Related Phenomena, J. C. Dainty, ed. (Springer-Verlag, 1975).

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Figures (4)

Fig. 1.
Fig. 1.

Reflectance spectra of five colored papers.

Fig. 2.
Fig. 2.

Experimental setup: LA, He–Ne laser; I1, iris 1; I2, iris 2; L, lens; DS, diffusive slab; R, reflector (color paper); CR, connecting rod; LS, loudspeaker; FG, function generator; PC, personal computer; TFG, two-channel function generator; AOM, acousto-optic modulator; D, AOM driver, and CCD, CCD camera.

Fig. 3.
Fig. 3.

Acoustically modulated (200 Hz) speckle intensity Iac over a range of laser repetition frequencies.

Fig. 4.
Fig. 4.

Normalized reflectance for colors blue, green, yellow, red, and white.

Equations (5)

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E(t)=j=1Najexp[i(ω0tk0lj)]=Aexp(iϕ)exp(iω0t),
I=EE*=(Eb+Em)(Eb+Em)*=Ab2+Am2+2AbAmcos(ϕbϕm).
Em(t)=j=1Namjexp[i(ω0tk0lj+mjsin(ωatϕmj))]=j=1Namjexp[i(ω0tk0lj)]×n=Jn(mj)exp[in(ωatϕmj)]=n=Am(n)exp[iϕm(n)]exp[i(ω0+nωa)t],
Am(n)exp[iϕm(n)]=j=1NamjJn(mj)exp[i(k0lj+nϕmj)],
I(t)=Idc+Iac(t)=Ab2+p=Am2(p)+2k=1p=Am(p)Am(p+k)×cos[kωat+ϕm(p)ϕm(p+k)]+2Ab[p=Am(p)cos[pωat+ϕbϕm(p)]],

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