Abstract

Near-field scanning optical microscope (NSOM) probe designs consisting of a subwavelength aperture offset of either a metallic or metal-coated dielectric cantilevered tip are investigated using finite-difference time-domain calculations. The offset aperture and metal-coated dielectric tip couple surface plasmons that illuminate the tip apex, which results in a single-lobed probing optical spot having a full-width half maximum (FWHM) similar to the apex diameter. Since the surface plasmons converge at the apex, an offset-apertured probe promises significantly higher throughput light intensities than an apertured NSOM having a comparable spot FWHM.

© 2007 Optical Society of America

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References

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  1. E. H. Synge, "A suggested method for extending microscopic resolution into the ultra-microscopic region," Philosophy Magazine 6, 356-362 (1928).
  2. D. W. Pohl, W. Denk, and M. Lanz, "Optical stethoscopy: Image recording with resolution λ/20," Appl. Phys. Lett. 44, 651-653 (1984).
    [CrossRef]
  3. A. Lewis, M. Isaacson, A. Harotunian, and A. Muray, "Development of a 500-Å Spatial-Resolution Light-Microscope : I. Light is Efficiently Transmitted Through l/16 Diameter Apertures," Ultramicroscopy 13, 227 (1984).
    [CrossRef]
  4. H. A. Bethe, "Theory of diffraction by small holes," Phys. Rev. 66, 163-182 (1944).
    [CrossRef]
  5. T. Thio, H. J. Lezec, T. W. Ebbesen, K. M. Pellerin, G. D. Lewen, A. Nahata, and R. A. Linke, "Giant optical transmission of sub-wavelength apertures: physics and applications," Nanotechnology 13, 429-432 (2002).
    [CrossRef]
  6. A. Dechant, S. K. Dew, S. E. Irvine, and A. Y. Elezzabi, "High-transmission solid-immersion apertured optical probes for near-field scanning optical microscopy," Appl. Phys. Lett. 86, 013102 (2005).
    [CrossRef]
  7. A. Naber, D. Molenda, U. C. Fischer, H.-J. Maas, C. Höppener, N. Lu, and H. Fuchs, "Enhanced Light Confinement in a Near-Field Optical Probe with a Triangular Aperture," Phys. Rev. Lett. 89, 210801 (2002).
    [CrossRef] [PubMed]
  8. J. A. Matteo, D. P. Fromm, Y. Yuen, P. J. Schuck, W. E. Moerner, and L. Hesselink, "Spectral analysis of strongly enhanced visible light transmission through single C-shaped nanoapertures," Appl. Phys. Lett. 85, 648-650 (2004).
    [CrossRef]
  9. E. X. Jin and X. Xu, "Enhanced optical near field from a bowtie aperture," Appl. Phys. Lett. 88, 153110 (2006).
    [CrossRef]
  10. F. Zenhausern, M. P. O'Boyle, and H. K. Wickramasinghe, "Apertureless near-field optical microscope," Appl. Phys. Lett. 65, 1623-1625 (1994).
    [CrossRef]
  11. J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-Enhanced Fluorescence Microscopy at 10 Nanometer Resolution," Phys. Rev. Lett. 93, 180801 (2004).
    [CrossRef] [PubMed]
  12. L. Gomez, R. Bachelot, A. Bouhelier, G. P. Wiederrecht, S. Chang, S. K. Gray, F. Hua, S. Jeon, J. A. Rogers, M. E. Castro, S. Blaize, I. Stefanon, G. Lerondel, and P. Royer, "Apertureless scanning near-field optical microscopy: a comparison between homodyne and heterodyne approaches," J. Opt. Soc. Am. B 23, 823-833 (2006).
    [CrossRef]
  13. U. C. Fischer and M. Zapletal, "The concept of a coaxial tip as a probe for scanning near-field optical microscopy and steps towards a realization," Ultramicroscopy 42, 393-398 (1992).
    [CrossRef]
  14. T. Leinhos, O. Rudow, M. Stopka, A. Vollkopf, and E. Oesterschulze, "Coaxial probes for scanning near-field microscopy," J. Microsc. 194, 349-352 (1999).
    [CrossRef]
  15. H. G. Frey, F. Keilmann, A. Kriele, and R. Guckenberger, "Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe," Appl. Phys. Lett. 81, 5030-5032 (2002).
    [CrossRef]
  16. H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-Resolution Imaging of Single Fluorescent Molecules with the Optical Near-Field of a Metal Tip," Phys. Rev. Lett. 93, 200801 (2004).
    [CrossRef] [PubMed]
  17. T. H. Taminau, R. J. Moerland, F. B. Segerink, L. Kuipers, and N. F. van Hulst, "λ/4 Resonance of an Optical Monopole Antenna Probed by Single Molecule Fluorescence," Nano Lett. 7, 28-33 (2007).
    [CrossRef]
  18. K. Tanaka, M. Tanaka, and T. Sugiyama, "Creation of strongly localized and strongly enhanced optical near-field on metallic probe-tip with surface plasmon polaritons," Opt. Express 14, 832-846 (2006).
    [CrossRef] [PubMed]
  19. H. G. Frey, C. Bolwien, A. Brandenburg, R. Ros, and D. Anselmetti, "Optimized apertureless optical near-field probes with 15 nm optical resolution," Nanotechnology 17, 3105-3110 (2006).
    [CrossRef]
  20. Y. Mitsuoka, T. Niwa, S. Ichihara, K. Kato, H. Muramatsu, K. Nakajima, M. Shikida, and K. Sato, "Microfabricated silicon dioxide cantilever with subwavelength aperture," J. Microsc. 202, 12-15 (2001).
    [CrossRef] [PubMed]
  21. G. Schürmann, W. Noell, U. Staufer, N. F. de Rooij, R. Eckert, J. M. Freyland, and H. Heinzelmann, "Fabrication and characterization of a silicon cantilever probe with an integrated quartz-glass (fused-silica) tip for scanning near-field optical microscopy," Appl. Opt. 40, 5040-5045 (2001).
    [CrossRef]
  22. L. Aeschimann, Apertureless Scanning Near-Field Optical Microscope Probe for Transmission Mode Operation (University of Neuchâtel, Switzerland, 2004).
  23. M. Y. Jung, S. S. Choi, and I. W. Lyo, "Micromachined Si3N4-Tip on Cantilever for Parallel SFM and NSOM Applications," Microelectronic Engineering 46, 427-430 (1999).
    [CrossRef]
  24. P. N. Minh, T. Ono, and M. Esashi, "High throughput aperture near-field scanning optical microscopy," Rev. Sci. Instrum. 71, 3111-3117 (2000).
    [CrossRef]
  25. K.-B. Song, E.-K. Kim, S.-Q. Lee, J. H. Kim, and K.-H. Park, "Fabrication of a high-throughput cantilever-style-aperture tip by the use of the Bird’s-beak effect," Jpn. J. Appl. Phys. 42, 4353-4356 (2003).
    [CrossRef]
  26. E. Kretschmann and H. Raether, "Radiative Decay of Non-Radiative Surface Plasmons Excited by Light," Zeitschrift für Naturforschung A  23, 2135 (1968).
  27. A. Taflove, Computational Electrodynamics: The Finite-Difference Time-Domain Method (Artech House, Boston, 1995).
  28. P. B. Johnson and R. W. Christy, "Optical Constants of Noble Metals," Phys. Rev. B 6, 4370-4379 (1972).
    [CrossRef]
  29. G. Leveque, C. G. Olson, and D. W. Lynch, "Reflectance spectra and dielectric functions for Ag in the region of interband transitions," Phys. Rev. B 27, 4654-4660 (1983).
    [CrossRef]
  30. J.-P. Berenger, "A Perfectly Matched Layer for the Absorption of Electromagnetic Waves," J. Computational Phys. 114, 185-200 (1994).
    [CrossRef]
  31. S. Patanè, E. Cefali, A. Arena, P. G. Gucciardi, and M. Allegrini, "Wide angle near-field optical probes by reverse tube etching," Ultramicroscopy 106, 475-479 (2006).
    [CrossRef] [PubMed]
  32. L. Novotny, D. W. Pohl, and B. Hecht, "Scanning near-field optical probe with ultrasmall spot size," Opt. Lett. 20, 970-972 (1995).
    [CrossRef] [PubMed]
  33. A. Dogariu, T. Thio, and L. J. Wang, "Delay of light transmission through small apertures," Opt. Lett. 26, 450-452 (2001).
    [CrossRef]
  34. H. J. Lezec and T. Thio, "Diffracted evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays," Opt. Express 12, 3629-3651 (2004).
    [CrossRef] [PubMed]

2007

T. H. Taminau, R. J. Moerland, F. B. Segerink, L. Kuipers, and N. F. van Hulst, "λ/4 Resonance of an Optical Monopole Antenna Probed by Single Molecule Fluorescence," Nano Lett. 7, 28-33 (2007).
[CrossRef]

2006

K. Tanaka, M. Tanaka, and T. Sugiyama, "Creation of strongly localized and strongly enhanced optical near-field on metallic probe-tip with surface plasmon polaritons," Opt. Express 14, 832-846 (2006).
[CrossRef] [PubMed]

H. G. Frey, C. Bolwien, A. Brandenburg, R. Ros, and D. Anselmetti, "Optimized apertureless optical near-field probes with 15 nm optical resolution," Nanotechnology 17, 3105-3110 (2006).
[CrossRef]

L. Gomez, R. Bachelot, A. Bouhelier, G. P. Wiederrecht, S. Chang, S. K. Gray, F. Hua, S. Jeon, J. A. Rogers, M. E. Castro, S. Blaize, I. Stefanon, G. Lerondel, and P. Royer, "Apertureless scanning near-field optical microscopy: a comparison between homodyne and heterodyne approaches," J. Opt. Soc. Am. B 23, 823-833 (2006).
[CrossRef]

E. X. Jin and X. Xu, "Enhanced optical near field from a bowtie aperture," Appl. Phys. Lett. 88, 153110 (2006).
[CrossRef]

S. Patanè, E. Cefali, A. Arena, P. G. Gucciardi, and M. Allegrini, "Wide angle near-field optical probes by reverse tube etching," Ultramicroscopy 106, 475-479 (2006).
[CrossRef] [PubMed]

2005

A. Dechant, S. K. Dew, S. E. Irvine, and A. Y. Elezzabi, "High-transmission solid-immersion apertured optical probes for near-field scanning optical microscopy," Appl. Phys. Lett. 86, 013102 (2005).
[CrossRef]

2004

J. A. Matteo, D. P. Fromm, Y. Yuen, P. J. Schuck, W. E. Moerner, and L. Hesselink, "Spectral analysis of strongly enhanced visible light transmission through single C-shaped nanoapertures," Appl. Phys. Lett. 85, 648-650 (2004).
[CrossRef]

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-Enhanced Fluorescence Microscopy at 10 Nanometer Resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

H. J. Lezec and T. Thio, "Diffracted evanescent wave model for enhanced and suppressed optical transmission through subwavelength hole arrays," Opt. Express 12, 3629-3651 (2004).
[CrossRef] [PubMed]

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-Resolution Imaging of Single Fluorescent Molecules with the Optical Near-Field of a Metal Tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

2003

K.-B. Song, E.-K. Kim, S.-Q. Lee, J. H. Kim, and K.-H. Park, "Fabrication of a high-throughput cantilever-style-aperture tip by the use of the Bird’s-beak effect," Jpn. J. Appl. Phys. 42, 4353-4356 (2003).
[CrossRef]

2002

H. G. Frey, F. Keilmann, A. Kriele, and R. Guckenberger, "Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe," Appl. Phys. Lett. 81, 5030-5032 (2002).
[CrossRef]

A. Naber, D. Molenda, U. C. Fischer, H.-J. Maas, C. Höppener, N. Lu, and H. Fuchs, "Enhanced Light Confinement in a Near-Field Optical Probe with a Triangular Aperture," Phys. Rev. Lett. 89, 210801 (2002).
[CrossRef] [PubMed]

T. Thio, H. J. Lezec, T. W. Ebbesen, K. M. Pellerin, G. D. Lewen, A. Nahata, and R. A. Linke, "Giant optical transmission of sub-wavelength apertures: physics and applications," Nanotechnology 13, 429-432 (2002).
[CrossRef]

2001

2000

P. N. Minh, T. Ono, and M. Esashi, "High throughput aperture near-field scanning optical microscopy," Rev. Sci. Instrum. 71, 3111-3117 (2000).
[CrossRef]

1999

T. Leinhos, O. Rudow, M. Stopka, A. Vollkopf, and E. Oesterschulze, "Coaxial probes for scanning near-field microscopy," J. Microsc. 194, 349-352 (1999).
[CrossRef]

M. Y. Jung, S. S. Choi, and I. W. Lyo, "Micromachined Si3N4-Tip on Cantilever for Parallel SFM and NSOM Applications," Microelectronic Engineering 46, 427-430 (1999).
[CrossRef]

1995

1994

J.-P. Berenger, "A Perfectly Matched Layer for the Absorption of Electromagnetic Waves," J. Computational Phys. 114, 185-200 (1994).
[CrossRef]

F. Zenhausern, M. P. O'Boyle, and H. K. Wickramasinghe, "Apertureless near-field optical microscope," Appl. Phys. Lett. 65, 1623-1625 (1994).
[CrossRef]

1992

U. C. Fischer and M. Zapletal, "The concept of a coaxial tip as a probe for scanning near-field optical microscopy and steps towards a realization," Ultramicroscopy 42, 393-398 (1992).
[CrossRef]

1984

D. W. Pohl, W. Denk, and M. Lanz, "Optical stethoscopy: Image recording with resolution λ/20," Appl. Phys. Lett. 44, 651-653 (1984).
[CrossRef]

A. Lewis, M. Isaacson, A. Harotunian, and A. Muray, "Development of a 500-Å Spatial-Resolution Light-Microscope : I. Light is Efficiently Transmitted Through l/16 Diameter Apertures," Ultramicroscopy 13, 227 (1984).
[CrossRef]

1983

G. Leveque, C. G. Olson, and D. W. Lynch, "Reflectance spectra and dielectric functions for Ag in the region of interband transitions," Phys. Rev. B 27, 4654-4660 (1983).
[CrossRef]

1972

P. B. Johnson and R. W. Christy, "Optical Constants of Noble Metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

1944

H. A. Bethe, "Theory of diffraction by small holes," Phys. Rev. 66, 163-182 (1944).
[CrossRef]

1928

E. H. Synge, "A suggested method for extending microscopic resolution into the ultra-microscopic region," Philosophy Magazine 6, 356-362 (1928).

Appl. Opt.

Appl. Phys. Lett.

D. W. Pohl, W. Denk, and M. Lanz, "Optical stethoscopy: Image recording with resolution λ/20," Appl. Phys. Lett. 44, 651-653 (1984).
[CrossRef]

J. A. Matteo, D. P. Fromm, Y. Yuen, P. J. Schuck, W. E. Moerner, and L. Hesselink, "Spectral analysis of strongly enhanced visible light transmission through single C-shaped nanoapertures," Appl. Phys. Lett. 85, 648-650 (2004).
[CrossRef]

E. X. Jin and X. Xu, "Enhanced optical near field from a bowtie aperture," Appl. Phys. Lett. 88, 153110 (2006).
[CrossRef]

F. Zenhausern, M. P. O'Boyle, and H. K. Wickramasinghe, "Apertureless near-field optical microscope," Appl. Phys. Lett. 65, 1623-1625 (1994).
[CrossRef]

A. Dechant, S. K. Dew, S. E. Irvine, and A. Y. Elezzabi, "High-transmission solid-immersion apertured optical probes for near-field scanning optical microscopy," Appl. Phys. Lett. 86, 013102 (2005).
[CrossRef]

H. G. Frey, F. Keilmann, A. Kriele, and R. Guckenberger, "Enhancing the resolution of scanning near-field optical microscopy by a metal tip grown on an aperture probe," Appl. Phys. Lett. 81, 5030-5032 (2002).
[CrossRef]

J. Computational Phys.

J.-P. Berenger, "A Perfectly Matched Layer for the Absorption of Electromagnetic Waves," J. Computational Phys. 114, 185-200 (1994).
[CrossRef]

J. Microsc.

Y. Mitsuoka, T. Niwa, S. Ichihara, K. Kato, H. Muramatsu, K. Nakajima, M. Shikida, and K. Sato, "Microfabricated silicon dioxide cantilever with subwavelength aperture," J. Microsc. 202, 12-15 (2001).
[CrossRef] [PubMed]

T. Leinhos, O. Rudow, M. Stopka, A. Vollkopf, and E. Oesterschulze, "Coaxial probes for scanning near-field microscopy," J. Microsc. 194, 349-352 (1999).
[CrossRef]

J. Opt. Soc. Am. B

Jpn. J. Appl. Phys.

K.-B. Song, E.-K. Kim, S.-Q. Lee, J. H. Kim, and K.-H. Park, "Fabrication of a high-throughput cantilever-style-aperture tip by the use of the Bird’s-beak effect," Jpn. J. Appl. Phys. 42, 4353-4356 (2003).
[CrossRef]

Microelectronic Engineering

M. Y. Jung, S. S. Choi, and I. W. Lyo, "Micromachined Si3N4-Tip on Cantilever for Parallel SFM and NSOM Applications," Microelectronic Engineering 46, 427-430 (1999).
[CrossRef]

Nano Lett.

T. H. Taminau, R. J. Moerland, F. B. Segerink, L. Kuipers, and N. F. van Hulst, "λ/4 Resonance of an Optical Monopole Antenna Probed by Single Molecule Fluorescence," Nano Lett. 7, 28-33 (2007).
[CrossRef]

Nanotechnology

H. G. Frey, C. Bolwien, A. Brandenburg, R. Ros, and D. Anselmetti, "Optimized apertureless optical near-field probes with 15 nm optical resolution," Nanotechnology 17, 3105-3110 (2006).
[CrossRef]

T. Thio, H. J. Lezec, T. W. Ebbesen, K. M. Pellerin, G. D. Lewen, A. Nahata, and R. A. Linke, "Giant optical transmission of sub-wavelength apertures: physics and applications," Nanotechnology 13, 429-432 (2002).
[CrossRef]

Opt. Express

Opt. Lett.

Philosophy Magazine

E. H. Synge, "A suggested method for extending microscopic resolution into the ultra-microscopic region," Philosophy Magazine 6, 356-362 (1928).

Phys. Rev.

H. A. Bethe, "Theory of diffraction by small holes," Phys. Rev. 66, 163-182 (1944).
[CrossRef]

Phys. Rev. B

P. B. Johnson and R. W. Christy, "Optical Constants of Noble Metals," Phys. Rev. B 6, 4370-4379 (1972).
[CrossRef]

G. Leveque, C. G. Olson, and D. W. Lynch, "Reflectance spectra and dielectric functions for Ag in the region of interband transitions," Phys. Rev. B 27, 4654-4660 (1983).
[CrossRef]

Phys. Rev. Lett.

J. M. Gerton, L. A. Wade, G. A. Lessard, Z. Ma, and S. R. Quake, "Tip-Enhanced Fluorescence Microscopy at 10 Nanometer Resolution," Phys. Rev. Lett. 93, 180801 (2004).
[CrossRef] [PubMed]

H. G. Frey, S. Witt, K. Felderer, and R. Guckenberger, "High-Resolution Imaging of Single Fluorescent Molecules with the Optical Near-Field of a Metal Tip," Phys. Rev. Lett. 93, 200801 (2004).
[CrossRef] [PubMed]

A. Naber, D. Molenda, U. C. Fischer, H.-J. Maas, C. Höppener, N. Lu, and H. Fuchs, "Enhanced Light Confinement in a Near-Field Optical Probe with a Triangular Aperture," Phys. Rev. Lett. 89, 210801 (2002).
[CrossRef] [PubMed]

Rev. Sci. Instrum.

P. N. Minh, T. Ono, and M. Esashi, "High throughput aperture near-field scanning optical microscopy," Rev. Sci. Instrum. 71, 3111-3117 (2000).
[CrossRef]

Ultramicroscopy

S. Patanè, E. Cefali, A. Arena, P. G. Gucciardi, and M. Allegrini, "Wide angle near-field optical probes by reverse tube etching," Ultramicroscopy 106, 475-479 (2006).
[CrossRef] [PubMed]

U. C. Fischer and M. Zapletal, "The concept of a coaxial tip as a probe for scanning near-field optical microscopy and steps towards a realization," Ultramicroscopy 42, 393-398 (1992).
[CrossRef]

A. Lewis, M. Isaacson, A. Harotunian, and A. Muray, "Development of a 500-Å Spatial-Resolution Light-Microscope : I. Light is Efficiently Transmitted Through l/16 Diameter Apertures," Ultramicroscopy 13, 227 (1984).
[CrossRef]

Other

E. Kretschmann and H. Raether, "Radiative Decay of Non-Radiative Surface Plasmons Excited by Light," Zeitschrift für Naturforschung A  23, 2135 (1968).

A. Taflove, Computational Electrodynamics: The Finite-Difference Time-Domain Method (Artech House, Boston, 1995).

L. Aeschimann, Apertureless Scanning Near-Field Optical Microscope Probe for Transmission Mode Operation (University of Neuchâtel, Switzerland, 2004).

Supplementary Material (1)

» Media 1: MOV (1387 KB)     

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Figures (8)

Fig. 1.
Fig. 1.

Cross-sectional depiction of the geometries (not to scale) of the (a) OAMA, (b) OAMDA, and (c) a typical apertured NSOM tips. Results obtained from the typical apertured NSOM having parameters w=155 nm, h=80 nm, D=60 nm, and φ=45° is used as the baseline for all comparisons.

Fig. 2.
Fig. 2.

(a) Calculated field intensities illustrate the steady-state intensity distribution of an OAMDA probe. The polarization direction of the incident electric field is indicated by the arrow. Surface plasmons are coupled onto the outer and inner surfaces of the tip and propagate toward the apex. An enhanced electric field intensity is clearly observed at the sharp 40-nm apex. (b) (1.4 MB) Movie illustrating the side view of an OAMDA probe showing the dynamics of the intensity distribution. Note that the surface plasmon wave propagates both on the inner and the outer surfaces of the NSOM probe towards the apex.

Fig. 3.
Fig. 3.

Illumination spots obtained 20-nm from the apex of: (a) an OAMA probe having a 40-nm wide apex and (b) typical apertured NSOM probe with a 60 nm-wide opening. Both NSOM probes have similar FWHM of ~70 nm; however, the spot intensity distribution from the apertured NSOM probe is double-lobed. The scale bars represent 200 nm, and the linear color scales are in arbitrary units. [Media 1]

Fig. 4.
Fig. 4.

(a) Total intensity for an OAMA probe optical spot as a function of surface wave propagation length, L, calculated 20 nm from the probe apex. The dotted lines (black) represent Lorentzian fits to the peaks, and the solid (red) line represents the sum of the three Lorentzian lineshapes. The intensities are relative to those of the apertured NSOM of Fig. 1(c). (b) Spot full-width half-maximum as a function of the surface propagation length, L. In both 4(a) and 4(b), the probe has a fixed apex diameter of 40 nm, θ=11.3°, t=100 nm, and d=120 nm.

Fig. 5.
Fig. 5.

Total intensity calculated 20 nm from the apex of an OAMA probe as a function of (a) cantilever silver layer thickness for d=120 nm and (b) aperture diameter for t=80 nm. For both (a) and (b), other parameters include an apex of 40 nm diameter, L=4 µm, and θ=11.3°. Intensity values are relative to a conventional apertured probe of Fig. 1(c).

Fig. 6.
Fig. 6.

(a, c) The electric field lines in the offset aperture as a result of incident electric field polarization (parallel to the double-arrowed lines). The large circle represents the base of the tip while the smaller circle represents the aperture. (b, d) Intensity distributions in a calculated planar cut (at 1.2 µm from the apex) in the solid silver tip due to the polarizations shown respectively to their left. Note that the color scales are in arbitary units. An OAMA probe having a 40-nm apex, L=4 µm, θ=11.3°, t=100 nm, and d=320 nm is used for both polarizations.

Fig. 7.
Fig. 7.

Total intensity for an OAMDA probe as a function of the silver layer thickness on the silicon dioxide core. Intensities are calculated 20 nm from the 40-nm wide tip apex. Other parameters used for the calculations were L=4 µm, θ=11.3°, t=80 nm, and d=320 nm. Intensity values are relative to those of the apertured probe of Fig. 1(c).

Fig. 8.
Fig. 8.

(a) Total intensity for OAMDA probes calculated 20 nm from the tip apex as a function of the surface wave propagation length, L. The dotted lines (black) represent Lorentzian fits to the peaks and the solid (red) line represents the sum of the three Lorentzian lineshapes. The intensities are measured relative to those of the apertured NSOM of Fig. 1(c). (b) Spot full-width half-maximum as a function of the surface propagation length, L. In both 8(a) and 8(b), the probe has a tip apex diameter of 40 nm, θ=11.3°, t=80 nm, T=60 nm, and d=120 nm.

Equations (3)

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ε ( ω ) = ε 0 ε ε 0 ω p 2 ω 2 + i ω ν
ν d D d t + d 2 D d t 2 = ω p 2 ε 0 E + ν ε ε 0 d E d t + ε ε 0 d 2 E d t 2
L max ( n ) = λ SP 4 ( 1 + 2 n )

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