Abstract

In femtosecond terahertz-pulse (T-ray) imaging of metal structures with dimensions of the order of the wavelength, it is observed that the T rays propagate faster than the vacuum speed of light. In the case of apertures this can be understood as a waveguide effect in which superluminal velocities are expected close to the cutoff frequency. However, the effect is also observed close to knife edges and in propagation past thin metal wires.

© 1999 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef]
  3. D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
    [CrossRef]
  4. S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
    [CrossRef]
  5. R. McElroy and K. Wynne, Phys. Rev. Lett. 79, 3078 (1997).
    [CrossRef]
  6. L. Brillouin, Wave Propagation and Group Velocity (Academic, New York, 1960).
  7. S. Y. Liao, Microwave Circuit Analysis and Amplifier Design (Prentice-Hall, Englewood Cliffs, N.J., 1987).

1998

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

1997

R. McElroy and K. Wynne, Phys. Rev. Lett. 79, 3078 (1997).
[CrossRef]

Q. Wu and X. C. Zhang, Appl. Phys. Lett. 71, 1285 (1997).
[CrossRef]

1996

D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
[CrossRef]

A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996).
[CrossRef]

Brener, I.

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

Brillouin, L.

L. Brillouin, Wave Propagation and Group Velocity (Academic, New York, 1960).

Heinz, T. F.

A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996).
[CrossRef]

Hunsche, S.

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

Jacobsen, R. H.

D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
[CrossRef]

Koch, M.

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

Liao, S. Y.

S. Y. Liao, Microwave Circuit Analysis and Amplifier Design (Prentice-Hall, Englewood Cliffs, N.J., 1987).

McElroy, R.

R. McElroy and K. Wynne, Phys. Rev. Lett. 79, 3078 (1997).
[CrossRef]

Mittleman, D. M.

D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
[CrossRef]

Nahata, A.

A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996).
[CrossRef]

Nuss, M. C.

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
[CrossRef]

Weling, A. S.

A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996).
[CrossRef]

Wu, Q.

Q. Wu and X. C. Zhang, Appl. Phys. Lett. 71, 1285 (1997).
[CrossRef]

Wynne, K.

R. McElroy and K. Wynne, Phys. Rev. Lett. 79, 3078 (1997).
[CrossRef]

Zhang, X. C.

Q. Wu and X. C. Zhang, Appl. Phys. Lett. 71, 1285 (1997).
[CrossRef]

Appl. Phys. Lett.

A. Nahata, A. S. Weling, and T. F. Heinz, Appl. Phys. Lett. 69, 2321 (1996).
[CrossRef]

Q. Wu and X. C. Zhang, Appl. Phys. Lett. 71, 1285 (1997).
[CrossRef]

IEEE J. Sel. Topics Quantum Electron.

D. M. Mittleman, R. H. Jacobsen, and M. C. Nuss, IEEE J. Sel. Topics Quantum Electron. 2, 679 (1996).
[CrossRef]

Opt. Commun.

S. Hunsche, M. Koch, I. Brener, and M. C. Nuss, Opt. Commun. 150, 22 (1998).
[CrossRef]

Phys. Rev. Lett.

R. McElroy and K. Wynne, Phys. Rev. Lett. 79, 3078 (1997).
[CrossRef]

Other

L. Brillouin, Wave Propagation and Group Velocity (Academic, New York, 1960).

S. Y. Liao, Microwave Circuit Analysis and Amplifier Design (Prentice-Hall, Englewood Cliffs, N.J., 1987).

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Figures (4)

Fig. 1
Fig. 1

Schematic diagram of the near-field T-ray imaging setup: The T rays are generated by optical rectification of a beam of 120-fs pulses at 800  nm in 110 ZnTe. The sample is positioned on the back of the generation crystal, in the near field of the T rays. BS, beam splitter; S, sample and generation crystal on an xy translation stage; F, Teflon filter; WP2, WP4, wave plates; DC, detection crystal; POL, polarizer; PD's, photodiodes.

Fig. 2
Fig. 2

T-ray images of 500-nm-thick aluminum lettering on a silicon-on-sapphire chip. (a) Image generated when the relative transit time of the pulse is plotted. The T rays are polarized parallel to the y axis. (b) Cross section at y=18.48 mm. The hatched areas indicate the position of the metal. Triangles, delay; squares, transmission.

Fig. 3
Fig. 3

T-ray image of a 100μm-diameter tinned-copper wire. (a) T-ray polarization parallel to the wire (the dashed line is the delay drift that is due to thickness variation in the ZnTe crystal). (b) Perpendicular polarization.

Fig. 4
Fig. 4

Time-domain traces of the T-ray pulses used in Fig.  3. Thick solid curve, free-space; dashed curve (shifted toward negative delay times), parallel polarization; solid curve (shifted toward positive delay times), perpendicular polarization.

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