Abstract

The guided modes of sub-wavelength diameter air-clad optical fibers exhibit a pronounced evanescent field. The absorption of particles on the fiber surface is therefore readily detected via the fiber transmission. We show that the resulting absorption for a given surface coverage can be orders of magnitude higher than for conventional surface spectroscopy. As a demonstration, we present measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules at ambient conditions, revealing the agglomeration dynamics on a second to minutes timescale.

© 2007 Optical Society of America

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References

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  1. V. Bordo and H.-G. Rubahn, Optics and spectroscopy at surfaces and interfaces (Wiley-VCH, Weinheim 2006).
  2. Ph. H. Paul and G. Kychakoff, "Fiber-optic evanescent field absorption sensor," Appl. Phys. Lett. 51, 12-14 (1987).
    [CrossRef]
  3. A. Messica, A. Greenstein, and A. Katzir, "Theory of fiber-optic, evanescent-wave spectroscopy and sensors," Appl. Opt. 35, 2274-2284 (1996).
    [CrossRef] [PubMed]
  4. Xh. Fang and W. Tan, "Imaging single fluorescent molecules at the interface of an optical fiber probe by evanescent wave excitation," Anal. Chem. 71, 3101-3105 (1999).
    [CrossRef] [PubMed]
  5. S. Simhony, I. Schnitzer, A. Katzir, and E. M. Kosower, "Evanescent wave infrared spectroscopy of liquids using silver halide optical fibers," J. Appl. Phys. 64, 3732-3734 (1988).
    [CrossRef]
  6. R. A. Potyrailo, S. E. Hobbs, and G. M. Hieftje, "Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development," Fresen. J. Anal. Chem. 362, 349-373 (1998).
    [CrossRef]
  7. B. D. Gupta, H. Dodeja, A. K. Tomar, "Fiber-optic evanescent field absorption sensor based on a U-shaped probe," Opt. Quantum Electron. 28, 1629-1639 (1996).
    [CrossRef]
  8. H. Tai, H. Tanaka, and T. Yoshino, "Fiber-optic evanescent-wave methane-gas sensor using optical absorption for the 3.392-m line of a He-Ne laser," Opt. Lett. 12, 437-439 (1987).
    [CrossRef] [PubMed]
  9. J. Lou, L. Tong and Z. Ye, "Modeling of silica nanowires for optical sensing," Opt. Express 13, 2135-2140 (2005).
    [CrossRef] [PubMed]
  10. M. D. Marazuela and M. C. Moreno-Bondi, "Fiber-optic biosensors - an overview," Anal. Bioanal. Chem. 372, 664-682 (2002).
    [CrossRef] [PubMed]
  11. H. Proehl, Th. Dienel, R. Nitsche, and T. Fritz, "Formation of solid-state excitons in ultrathin crystalline films of PTCDA: from single moleules to molecular stacks," Phys. Rev. Lett. 93, 097403 (2004).
    [CrossRef] [PubMed]
  12. F. Le Kien, J. Q. Liang, K. Hakuta, and V. I. Balykin, "Field intensity distributions and polarization orientations in a vacuum-clad subwavelength-diameter optical fiber," Opt. Commun. 242, 445-455 (2004).
    [CrossRef]
  13. S. R. Forrest, "Ultrathin organic films grown by organic molecular beam deposition and related techniques," Chem. Rev. 97, 1793-1896 (1997).
    [CrossRef]
  14. T. A. Birks and Y. W. Li, "The shape of fiber tapers," J. Lightwave Technol. 10, 432-438 (1992).
    [CrossRef]
  15. J. D. Love and W. M. Henry, "Quantifying loss minimisation in single-mode fibre tapers," Electron. Lett. 22, 912-914 (1986).
    [CrossRef]
  16. S. R. Forrest and Y. Zhang, "Ultrahigh-vacuum quasiepitaxial growth of model van der Waals thin-films, I. Theory," Phys. Rev. B 49, 11297-11308 (1994).
  17. The absorption cross section of PTCDA was calculated from the molar extinctions coefficient ∑ of PTCDA in solution [M. Hoffmann, K. Schmidt, T. Fritz, T. Hasche, V. M. Agranovich, and K. Leo, "The lowest energy frenkel and charge-transfer excitons in quasi-one-dimensional structures: application to MePTCDI and PTCDA crystals," Chem. Phys. 258, 73-96 (2000)] according to ⌠ = 2.303/NA ×∑. We note that the averaged ⌠ on the fiber may differ from the value obtained in solution by a factor of the order of one due to geometric reasons and differences in the refractive indices.
  18. H. Proehl, R. Nitsche, Th. Dienel, K. Leo, and T. Fritz, "In situ differential reflectance spectroscopy of thin crystalline films of PTCDA on different substrates," Phys. Rev. B 71, 165207 (2005).
  19. The offset accounts for the fact that spectrum B still contains a monolayer component and thus an admixture of spectrum A.

2005 (2)

J. Lou, L. Tong and Z. Ye, "Modeling of silica nanowires for optical sensing," Opt. Express 13, 2135-2140 (2005).
[CrossRef] [PubMed]

H. Proehl, R. Nitsche, Th. Dienel, K. Leo, and T. Fritz, "In situ differential reflectance spectroscopy of thin crystalline films of PTCDA on different substrates," Phys. Rev. B 71, 165207 (2005).

2004 (2)

H. Proehl, Th. Dienel, R. Nitsche, and T. Fritz, "Formation of solid-state excitons in ultrathin crystalline films of PTCDA: from single moleules to molecular stacks," Phys. Rev. Lett. 93, 097403 (2004).
[CrossRef] [PubMed]

F. Le Kien, J. Q. Liang, K. Hakuta, and V. I. Balykin, "Field intensity distributions and polarization orientations in a vacuum-clad subwavelength-diameter optical fiber," Opt. Commun. 242, 445-455 (2004).
[CrossRef]

2002 (1)

M. D. Marazuela and M. C. Moreno-Bondi, "Fiber-optic biosensors - an overview," Anal. Bioanal. Chem. 372, 664-682 (2002).
[CrossRef] [PubMed]

1999 (1)

Xh. Fang and W. Tan, "Imaging single fluorescent molecules at the interface of an optical fiber probe by evanescent wave excitation," Anal. Chem. 71, 3101-3105 (1999).
[CrossRef] [PubMed]

1998 (1)

R. A. Potyrailo, S. E. Hobbs, and G. M. Hieftje, "Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development," Fresen. J. Anal. Chem. 362, 349-373 (1998).
[CrossRef]

1997 (1)

S. R. Forrest, "Ultrathin organic films grown by organic molecular beam deposition and related techniques," Chem. Rev. 97, 1793-1896 (1997).
[CrossRef]

1996 (2)

B. D. Gupta, H. Dodeja, A. K. Tomar, "Fiber-optic evanescent field absorption sensor based on a U-shaped probe," Opt. Quantum Electron. 28, 1629-1639 (1996).
[CrossRef]

A. Messica, A. Greenstein, and A. Katzir, "Theory of fiber-optic, evanescent-wave spectroscopy and sensors," Appl. Opt. 35, 2274-2284 (1996).
[CrossRef] [PubMed]

1994 (1)

S. R. Forrest and Y. Zhang, "Ultrahigh-vacuum quasiepitaxial growth of model van der Waals thin-films, I. Theory," Phys. Rev. B 49, 11297-11308 (1994).

1992 (1)

T. A. Birks and Y. W. Li, "The shape of fiber tapers," J. Lightwave Technol. 10, 432-438 (1992).
[CrossRef]

1988 (1)

S. Simhony, I. Schnitzer, A. Katzir, and E. M. Kosower, "Evanescent wave infrared spectroscopy of liquids using silver halide optical fibers," J. Appl. Phys. 64, 3732-3734 (1988).
[CrossRef]

1987 (2)

1986 (1)

J. D. Love and W. M. Henry, "Quantifying loss minimisation in single-mode fibre tapers," Electron. Lett. 22, 912-914 (1986).
[CrossRef]

Anal. Bioanal. Chem. (1)

M. D. Marazuela and M. C. Moreno-Bondi, "Fiber-optic biosensors - an overview," Anal. Bioanal. Chem. 372, 664-682 (2002).
[CrossRef] [PubMed]

Anal. Chem. (1)

Xh. Fang and W. Tan, "Imaging single fluorescent molecules at the interface of an optical fiber probe by evanescent wave excitation," Anal. Chem. 71, 3101-3105 (1999).
[CrossRef] [PubMed]

Appl. Opt. (1)

Appl. Phys. Lett. (1)

Ph. H. Paul and G. Kychakoff, "Fiber-optic evanescent field absorption sensor," Appl. Phys. Lett. 51, 12-14 (1987).
[CrossRef]

Chem. Rev. (1)

S. R. Forrest, "Ultrathin organic films grown by organic molecular beam deposition and related techniques," Chem. Rev. 97, 1793-1896 (1997).
[CrossRef]

Electron. Lett. (1)

J. D. Love and W. M. Henry, "Quantifying loss minimisation in single-mode fibre tapers," Electron. Lett. 22, 912-914 (1986).
[CrossRef]

Fresen. J. Anal. Chem. (1)

R. A. Potyrailo, S. E. Hobbs, and G. M. Hieftje, "Optical waveguide sensors in analytical chemistry: today’s instrumentation, applications and trends for future development," Fresen. J. Anal. Chem. 362, 349-373 (1998).
[CrossRef]

J. Appl. Phys. (1)

S. Simhony, I. Schnitzer, A. Katzir, and E. M. Kosower, "Evanescent wave infrared spectroscopy of liquids using silver halide optical fibers," J. Appl. Phys. 64, 3732-3734 (1988).
[CrossRef]

J. Lightwave Technol. (1)

T. A. Birks and Y. W. Li, "The shape of fiber tapers," J. Lightwave Technol. 10, 432-438 (1992).
[CrossRef]

Opt. Commun. (1)

F. Le Kien, J. Q. Liang, K. Hakuta, and V. I. Balykin, "Field intensity distributions and polarization orientations in a vacuum-clad subwavelength-diameter optical fiber," Opt. Commun. 242, 445-455 (2004).
[CrossRef]

Opt. Express (1)

Opt. Lett. (1)

Opt. Quantum Electron. (1)

B. D. Gupta, H. Dodeja, A. K. Tomar, "Fiber-optic evanescent field absorption sensor based on a U-shaped probe," Opt. Quantum Electron. 28, 1629-1639 (1996).
[CrossRef]

Phys. Rev. B (2)

S. R. Forrest and Y. Zhang, "Ultrahigh-vacuum quasiepitaxial growth of model van der Waals thin-films, I. Theory," Phys. Rev. B 49, 11297-11308 (1994).

H. Proehl, R. Nitsche, Th. Dienel, K. Leo, and T. Fritz, "In situ differential reflectance spectroscopy of thin crystalline films of PTCDA on different substrates," Phys. Rev. B 71, 165207 (2005).

Phys. Rev. Lett. (1)

H. Proehl, Th. Dienel, R. Nitsche, and T. Fritz, "Formation of solid-state excitons in ultrathin crystalline films of PTCDA: from single moleules to molecular stacks," Phys. Rev. Lett. 93, 097403 (2004).
[CrossRef] [PubMed]

Other (3)

The absorption cross section of PTCDA was calculated from the molar extinctions coefficient ∑ of PTCDA in solution [M. Hoffmann, K. Schmidt, T. Fritz, T. Hasche, V. M. Agranovich, and K. Leo, "The lowest energy frenkel and charge-transfer excitons in quasi-one-dimensional structures: application to MePTCDI and PTCDA crystals," Chem. Phys. 258, 73-96 (2000)] according to ⌠ = 2.303/NA ×∑. We note that the averaged ⌠ on the fiber may differ from the value obtained in solution by a factor of the order of one due to geometric reasons and differences in the refractive indices.

V. Bordo and H.-G. Rubahn, Optics and spectroscopy at surfaces and interfaces (Wiley-VCH, Weinheim 2006).

The offset accounts for the fact that spectrum B still contains a monolayer component and thus an admixture of spectrum A.

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Figures (4)

Fig. 1.
Fig. 1.

(a) Intensity profile of the fundamental guided HE11 mode of an air-clad silica fiber in units of Nanowatts per λ 2 as a function of the distance d from the fiber surface in units of λ. Calculated according to [12] for unpolarized light, a total guided power of 1 nW, and a fiber radius of 0.253×λ. (b) Plot of 1/A eff and R/A eff in units of 1/λ2 and 1/λ, respectively, as a function of the fiber radius R in units of λ. Assuming a refractive index of 1.46, all plots in (a) and (b) hold universally for any λ.

Fig. 2.
Fig. 2.

Scheme of the experimental set-up. White light from a tungsten lamp is transmitted through a tapered fiber with a 500-nm diameter waist and analyzed by a CCD spectrograph. This allows to measure the absorbance of molecules deposited on the fiber waist with a high sensitivity.

Fig. 3.
Fig. 3.

Consecutive absorbance spectra. (a) Deposition of a sub-monolayer: more and more molecules still show a monomer-like spectrum. (b) Evolution of the spectral absorption of a constant molecule number. The shape varies continuously from monomer-like to oligomer-like. Thus we observe agglomeration of the molecules on the fiber surface.

Fig. 4.
Fig. 4.

Spectral investigation of the film ripening. Spectra for t=20-100 s can be modelled as a weighted sum of the spectra at t=20 s and t=100 s. As an example, we show the t=60 s spectrum and the corresponding model fit (see inset). The spectral weight of the t=20 s spectrum decays according to an offset exponential for t=20-100 s [19]. The corresponding fit yields a decay constant of 55(±1) s. The dotted line extrapolates the fit for t<20 s and t>100 s.

Equations (7)

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η ( λ ) = lg ( P sig ( λ ) P ref ( λ ) ) P abs ( λ ) ln ( 10 ) P ref ( λ ) ,
η free ( λ ) = θ σ ( λ ) ln ( 10 ) ,
θ min ln ( 10 ) η min ( λ ) σ ( λ ) .
A eff ( λ ) = P ref ( λ ) I surf ( λ ) .
P sig ( λ ) = P ref ( λ ) [ 1 σ ( λ ) A eff ] n ,
η fiber ( λ ) = lg ( P sig ( λ ) P ref ( λ ) ) n σ ( λ ) ln ( 10 ) A eff ( λ ) ,
η fiber ( λ ) θ σ ( λ ) ln ( 10 ) · 2 π RL A eff ( λ ) = η free ( λ ) ξ ( λ ) .

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