Abstract

We describe a dual-beam differential phase interferometer that performs direct phase measurement by using a rotating Ronchi grating filter. Two laser beams derived from a single source are focused onto the sample surface. The reflected light will retrace the same path and intersect at the back focus of the objective lens. Interference between the reflected rays will therefore produce intensity fringes with their spatial location governed primarily by the differential optical phase of the probes. When the fringes are projected onto a rotating grating filter with identical periodicity, the transmitted optical signal becomes an oscillating signal from which the optical phase can be measured by standard phase-sensitive techniques. This approach has the advantages of simple system configuration, effective isolation from environmental disturbance, and low-frequency operation, which permit the use of high impedance electronics with shot-noise-limited performance at low laser power.

© 1998 Optical Society of America

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References

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  1. K. J. Gasvik, Optical Metrology (Wiley, New York, 1995).
  2. C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
    [CrossRef]
  3. Y. Y. Hung, “Digital shearography versus TY-holography for non-destructive evaluation,” Opt. Lasers Eng. 26, 421–436 (1997).
    [CrossRef]
  4. M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
    [CrossRef]
  5. H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
    [CrossRef]

1997 (1)

Y. Y. Hung, “Digital shearography versus TY-holography for non-destructive evaluation,” Opt. Lasers Eng. 26, 421–436 (1997).
[CrossRef]

1994 (1)

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

1991 (1)

M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
[CrossRef]

1988 (1)

C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
[CrossRef]

Appel, R. K.

M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
[CrossRef]

C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
[CrossRef]

Gasvik, K. J.

K. J. Gasvik, Optical Metrology (Wiley, New York, 1995).

Ho, H. P.

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

Hung, Y. Y.

Y. Y. Hung, “Digital shearography versus TY-holography for non-destructive evaluation,” Opt. Lasers Eng. 26, 421–436 (1997).
[CrossRef]

Liu, M.

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

See, C. W.

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
[CrossRef]

Somekh, M. G.

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
[CrossRef]

C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
[CrossRef]

Valera, M. S.

M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
[CrossRef]

Appl. Phys. Lett. (1)

C. W. See, R. K. Appel, M. G. Somekh, “Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation,” Appl. Phys. Lett. 53, 10–12 (1988).
[CrossRef]

Electron. Lett. (1)

M. S. Valera, M. G. Somekh, R. K. Appel, “Common path differential intensity and phase profilometer using time division multiplexing,” Electron. Lett. 27, 719–720 (1991).
[CrossRef]

Meas. Sci. Technol. (1)

H. P. Ho, M. G. Somekh, M. Liu, C. W. See, “Direct and indirect dual-probe interferometers for accurate surface wave measurements,” Meas. Sci. Technol. 5, 1480–1490 (1994).
[CrossRef]

Opt. Lasers Eng. (1)

Y. Y. Hung, “Digital shearography versus TY-holography for non-destructive evaluation,” Opt. Lasers Eng. 26, 421–436 (1997).
[CrossRef]

Other (1)

K. J. Gasvik, Optical Metrology (Wiley, New York, 1995).

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Figures (5)

Fig. 1
Fig. 1

Wave-front collimation and formation of interference fringes with a convex lens.

Fig. 2
Fig. 2

Schematic of proposed dual-probe interferometer:PD’s, photodetectors.

Fig. 3
Fig. 3

Sinusoidal waveforms obtained from the signal and reference channels.

Fig. 4
Fig. 4

Measured differential step height of the photoresist stripe.

Fig. 5
Fig. 5

Experimental measurement drift of the interferometer.

Equations (6)

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E 1 = E 0   exp j ω 0 t - k x   sin   θ + z   cos   θ - ϕ , E 2 = E 0   exp j ω 0 t - k - x   sin   θ + z   cos   θ + ϕ ,
E = E 1 + E 2 = 2 E 0   exp j ω 0 t - kz   cos   θ cos ( kx   sin   θ + ϕ .
I = γ E 1 + E 2 E 1 + E 2 * = 2 γ E 0 2 cos 2 kx   sin   θ + ϕ 2 γ E 0 2 cos 2 kx θ + ϕ       θ   small ,
I = 2 γ E 0 2 cos 2 π x / L + 2 π δ / λ ,
P n = γ λ n X n X n + L / 2   2 E 0 2 cos 2 π x / L + 2 π δ / λ d x = γ λ n L E 0 2 - E 0 2 / π sin [ 2 π / L x n + 4 π / λ δ ,
P t =   P n 0 / 2 1 - 1 / π sin 2 π / L vt + 4 π / λ δ = P 0 / 2 1 - 1 / π sin 2 π / L vt + 4 π / λ δ .

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