OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 9 — May. 6, 2013
  • pp: 10667–10675
« Show journal navigation

Upconversion emission obtained in Yb3+-Er3+ doped fluoroindate glasses using silica microspheres as focusing lens

C. Pérez-Rodríguez, S. Ríos, I. R. Martín, L. L. Martín, P. Haro-González, and D. Jaque  »View Author Affiliations


Optics Express, Vol. 21, Issue 9, pp. 10667-10675 (2013)
http://dx.doi.org/10.1364/OE.21.010667


View Full Text Article

Acrobat PDF (1089 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

An intensity enhancement of the green upconversion emission from a codoped Er3+ -Yb3+ fluoroindate glass has been obtained by coating the glass surface with silica microspheres (3.8 µm diameter). The microspheres focus an incoming beam (λ ≈950 nm) on the surface of the fluoroindate glass. The green emission (λ ≈545 nm) of the Er3+ ions located in the microsphere focus was measured with a microscope in reflection mode, being the peak intensity 4.5 times the emission of the bare substrate. The transversal FWHM of the upconversion spot was experimentally determined by deconvolution with the experimental Point Spread Function of the system, obtaining a value of 309 nm. This value is in good agreement with Finite-Difference Time-Domain simulations taking into account the magnification of the image due to the microsphere.

© 2013 OSA

1. Introduction

In the recent years a wide range of applications have been developed based in the research in dielectric microcavities such as microspheres and microcylinders. Among their known characteristics these systems exhibit high Q factors with narrow resonances [1

1. A. B. Matsko, Practical Applications of Microresonators in Optics and Photonics, (CRC Press, Pasadena, Calif., 2009).

] making them useful in several kinds of sensing applications [2

2. G. Adamovsky and M. V. Otügen, “Morphology-dependent resonances and their applications to sensing in aerospace environments,” J. Aerosp. Comp. Inf. Commun. 5(10), 409–424 (2008). [CrossRef]

,3

3. L. L. Martín, C. Pérez-Rodríguez, P. Haro-González, and I. R. Martín, “Whispering gallery modes in a glass microsphere as a function of temperature,” Opt. Express 19(25), 25792–25798 (2011). [CrossRef] [PubMed]

] and microlasers [4

4. M. Mohageg, A. B. Matsko, and L. Maleki, “Lasing and up conversion from a nominally pure whispering gallery mode resonator,” Opt. Express 20(15), 16704–16714 (2012). [CrossRef]

].

Furthermore, under certain conditions, they can produce a narrow beam with a waist under the Abbe diffraction limit called photonic nanojet [5

5. A. Heifetz, S.-C. Kong, A. V. Sahakian, A. Taflove, and V. Backman, “Photonic Nanojets,” J Comput Theor Nanosci 6(9), 1979–1992 (2009). [CrossRef] [PubMed]

]. Experimental measurements of the 3-D intensity profile of a nanojet have been performed by P. Ferrand et al [6

6. P. Ferrand, J. Wenger, A. Devilez, M. Pianta, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Direct imaging of photonic nanojets,” Opt. Express 16(10), 6930–6940 (2008). [CrossRef] [PubMed]

]. Their measurements reveal that a 3 µm diameter sphere under plane wave illumination at 520 nm can give rise to a focal spot with Full With at Half Maximum (FWHM) of 270 nm in good agreement with the Finite-Difference Time-Domain (FDTD) simulations.

The application of Photonic nanojets in a variety of fields as biomedicine, imaging, photonics and material science has been studied recently. In the work of Ref [7

7. K. W. Allen, A. Darafsheh, and V. N. Astratov, “Photonic nanojet-induced modes: from physics to applications,” 2011 13th International Conference on Transparent Optical Networks 1–4 (2011).

] several microspheres, arranged linearly as a chain, periodically focus the light, giving place to photonic nanojet induced modes that could be a tool to reach ultra precise laser surgery. Array structures are reported in Ref [8

8. Y. P. Rakovich, M. Gerlach, J. F. Donegan, K. I. Rusakov, and A. A. Gladyshchuk, “Mode manipulation in system of coupled microcavities with whispering gallery modes,” Opt. Spectrosc. 108(3), 385–390 (2010). [CrossRef]

], where triangles and rings of 5, 6 and 7 nodes formed by dye coated microspheres emit in the far field in a similar way as fluorescence molecules. These structures have been called photonic molecules and can be used to manipulate photons in micrometric scale. In reference [9

9. Z. Wang, W. Guo, L. Li, B. Luk’yanchuk, A. Khan, Z. Liu, Z. Chen, and M. Hong, “Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope,” Nat Commun 2, 218 (2011). [CrossRef] [PubMed]

] Wang et al. have enhanced the resolution of a microscope under white light illumination up to 50 nm by locating a microsphere on the surface of a sample. This significant improvement in resolution opens the door to the imaging of virus, DNA and molecules.

On the other hand several studies have been focused on the enhancement of single molecule fluorescence in the vicinity of metal nanoparticles [10

10. S. Kühn, U. Håkanson, L. Rogobete, and V. Sandoghdar, “Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna,” Phys. Rev. Lett. 97(1), 017402 (2006). [CrossRef] [PubMed]

,11

11. Y. Zhang, R. Zhang, Q. Wang, Z. Zhang, H. Zhu, J. Liu, F. Song, S. Lin, and E. Y. B. Pun, “Fluorescence enhancement of quantum emitters with different energy systems near a single spherical metal nanoparticle,” Opt. Express 18(5), 4316–4328 (2010). [CrossRef] [PubMed]

] and dielectric microspheres [12

12. S. Lecler, S. Haacke, N. Lecong, O. Crégut, J.-L. Rehspringer, and C. Hirlimann, “Photonic jet driven non-linear optics: example of two-photon fluorescence enhancement by dielectric microspheres,” Opt. Express 15(8), 4935–4942 (2007). [CrossRef] [PubMed]

14

14. D. Gérard, A. Devilez, H. Aouani, B. Stout, N. Bonod, J. Wenger, E. Popov, and H. Rigneault, “Efficient excitation and collection of single-molecule fluorescence close to a dielectric microsphere,” J. Opt. Soc. Am. B 26(7), 1473–1478 (2009). [CrossRef]

] with applications in biophotonics. Dielectric microspheres have been preferred because although metalic nanostructures are capable of generating strong electromagnetic fields in their vicinity, giving rise to a higher excitation of molecules, they also produce losses due to the quenching of the fluorescence emission.

In Ref [14

14. D. Gérard, A. Devilez, H. Aouani, B. Stout, N. Bonod, J. Wenger, E. Popov, and H. Rigneault, “Efficient excitation and collection of single-molecule fluorescence close to a dielectric microsphere,” J. Opt. Soc. Am. B 26(7), 1473–1478 (2009). [CrossRef]

] Gérard et al. obtained a tiny spot with subwavelength dimensions in both axial and transversal directions by illuminating a 2 µm dielectric microsphere with a tightly focused gaussian beam. Due to the interaction of the microsphere tiny spot and a single fluorescent molecule, they have obtained an enhancement of the fluorescence up to a factor of 2.2, being a key factor the axial confinement of the focal spot that cannot be obtained under plane wave illumination.

Non-linear processes have been studied in Ref [12

12. S. Lecler, S. Haacke, N. Lecong, O. Crégut, J.-L. Rehspringer, and C. Hirlimann, “Photonic jet driven non-linear optics: example of two-photon fluorescence enhancement by dielectric microspheres,” Opt. Express 15(8), 4935–4942 (2007). [CrossRef] [PubMed]

] where silica microspheres were added to a rhodamine B dye solution. The authors observed a two-photon fluorescent enhancement of 30% in presence of microspheres when the sample was illuminated with a focused laser pulse. It has to be noticed that the results correspond to the emission averaged over a large area of the sample, and so the results of the enhancement of a single sphere were not reported.

Among fluorescence materials the choice of glasses doped with Rare Earths (RE) seems to be advantageous since they are efficient emitters that present well known upconversion processes. In upconversion processes two or more photons are sequentially absorbed leading to the emission in a shorter wavelength. From these processes emissions in the infrared, visible and UV can be obtained. The upconversion intensity depends on the n-th power of the excitation intensity, where n is the number of photons involved. In this work a glass doped with Er3+ and Yb3+ has been covered with silica microspheres with the aim of producing an enhancement of the upconversion intensity in the focal region of each microsphere. The microsphere focus the incident beam in a small region of the sample, producing a gain in the excitation per unit area in the focal region. Furthermore, due to the upconversion process, the sample emits with the nth power of the excitation intensity, optimizing the emission compared, as an example, with fluorophores whose emission has a linear dependence with the excitation intensity. Moreover at low powers fluorophores can suffer from the photobleaching that destroys their fluorescence after some characteristic time. On the contrary glasses doped with RE ions show a luminescence stable in time.

2. Experimental description

The sample was obtained from a precursor Er-Yb codoped glass based on a fluoroindate matrix with the following composition in mol %: 37InF3, 20ZnF2, 20SrF2, 20BaF2, 0.75YbF3 and 2.25ErF3 (see Ref [15

15. I. R. Martín, P. Vélez, V. D. Rodríguez, U. R. Rodríguez-Mendoza, and V. Lavín, “Upconversion dynamics in Er 3 + -doped fluoroindate glasses,” Spectrochim. Acta [A] 55(5), 935–940 (1999). [CrossRef]

] for details). The microspheres (Cospheric Santa Barbara) were diluted in a conical tube and sonicated for 10 minutes to avoid clustering. A drop of the solution was taken with a micropipette and deposited on the sample. Finally, the sample surface was imaged by a microscope to ensure that microspheres were not stacked. A collimated 950 nm beam from a laser diode (L3-MSF03 JDS Uniphase) in continuous mode is collected by a microscope objective (Olympus Plan, NA = 0.9) giving rise to a converging beam which illuminates the sample. In order to calibrate the laser power a thermopile power sensor (Gentec UP19K-15S-H5-DO) was located on the sample’s position, setting the laser power to a value of 2 mW. Each microsphere focuses the incident beam in a narrow region of the glass, exciting the Er3+-Yb3+ ions, resulting in emissions centered at 545 nm and 660 nm due to upconversion processes. The light emitted by the sample re-enters the microscope objective and is focused by a lens in a CCD camera (ATK-16HR). Suitable filters (shortPass 600 nm FES0600 Thorlabs and shortPass 800 nm NT64-325 Edmundoptics) have been located before the CCD to select the green upconversion emission. The experimental set-up is shown in detail in Fig. 1
Fig. 1 Top view of the experimental setup. DL. Diode Laser, M. Mirror, XYZ. Three axis translation stage, BS. Beamsplitter, L. Lens, F. Filter and CCD. CCD detector. In the inset shows the front view of the ensemble designated by the arrow. S. sample and MO. Microscope objective.
. The PSF of the system has been measured using as point sources Tm3+-Yb3+ doped SrF2 nanoparticles with sizes below 8 nm diluted in distilled water. The procedure employed to avoid the formation of aggregates in the preparation of this sample is similar to the one described in the protocol of Ref [16

16. R. W. Cole, T. Jinadasa, and C. M. Brown, “Measuring and interpreting point spread functions to determine confocal microscope resolution and ensure quality control,” Nat. Protoc. 6(12), 1929–1941 (2011). [CrossRef] [PubMed]

]. Under excitation at 950 nm in the same experimental setup it is possible to detect upconversion emission from the individual nanoparticles at 480 nm. Fitting the measured emission spot to a gaussian distribution, a value of 350 nm for the transversal FWHM of the system PSF has been obtained.

3. Results and discussion

An image of an arrangement of five microspheres above the flat surface of an Er3+-Yb3+ codoped fluoroindate glass is shown in Fig. 2(a)
Fig. 2 (a) Left: Green upconversion emission of five microspheres located above an Er3+-Yb3+ codoped fluoroindate glass. (b) Right: 3D graph of the spatial intensity distribution of the green upconversion intensity corresponding to the left image.
and a 3-D representation of the intensity distribution of the green emission in Fig. 2(b). It can be observed that an intensity enhancement due to the upconversion emission has been obtained compared to the emission of the bare substrate. The intensity gain, defined as the ratio of the maximum intensity and the mean value of the emission from the substrate, was calculated obtaining a value of 4.5.

In order to know the characteristic of this emission, the emission spectrum of a bulk fluoroindate glass codoped with Er3+-Yb3+ has been measured under excitation at 950 nm as it is shown in Fig. 3
Fig. 3 Upconversion emission spectrum of a Er3+-Yb3+ codoped fluoroindate glass sample under excitation at 950 nm. Inset: Diagram energy levels of Er3+ and Yb3+ ions detailing ESA and ET upconversion process.
. The spectrum has been obtained selecting a region without microspheres. The main emission bands due to Er3+ electronic transitions are centered in the green at 545 nm (4S3/2 (2H11/2)→ 4I15/2) and in the red at 660 nm (4F9/24I15/2). These emissions are supported by the Excited State Absorption (ESA) of the Er3+ ion and/or the Energy Transfer (ET) processes from the 2F5/2 level of the Yb3+ ion, resonant with the 4I11/2 level of Er3+ ion as it is shown in the diagram of the inset of Fig. 3. By choosing a proper filter the 545 nm green emission has been selected.

The mean value of the FWHM of the intensity peaks shown in Fig. 2 has been estimated by fitting the data to Gaussian profiles (see Fig. 5
Fig. 5 Intensity profile (dots) in a line that cross the center of a microsphere and Gaussian fitting (continuous line).
for a representative peak), obtaining a value of 609 nm. The FWHM of the focal spot produced by the sphere is enlarged by both the PSF of the system and the fact that the light emitted by the sample goes through the microsphere in its way to the CCD camera.

4. Conclusions

In a simple optical setup and with an easy sample preparation an intensity enhancement of 4.5 for the green upconversion emission of an Er3+-Yb3+ codoped fluoroindate glass has been obtained by focusing the incoming beam with a 3.8 µm silica microsphere. This value could be improved by properly choosing the size and refractive index of the microspheres. Measurements of the variation of the intensity emitted by the sample in the microsphere focus area and outside of the microsphere with the pump power allow to conclude that the microspheres do not affect the ESA and ET upconversion mechanisms. The size of the emitting area has been experimentally determined obtaining a FWHM of 309 nm in good agreement with the Finite-Difference Time-Domain simulations (320 nm). This size could be reduced by using upconversion processes requiring more participating photons (three or four) at shorter wavelengths. These results open a new method to improve the upconversion emission intensity in biological samples with rare earth doped nanoparticles that can be used as nano-sensors. Furthermore, in this kind of applications, it could be interesting to use optical trapping in order to shift the microspheres over the sample.

Acknowledgments

Authors thank Ministerio de Economía y Competitividad of Spain (MINECO) within The National Program of Materials (MAT2010-21270-C04-02/-03/-04), the National Program of Scientific Research (FIS2012-38244-C02-01), The Consolider-Ingenio 2010 Program (MALTA CSD2007-0045, www.malta-consolider.com), the EU-FEDER for their financial support, the FSE and ACIISI of Gobierno de Canarias for the project ID20100152 and FPI grant. We also thank The Governments of Spain and India for the award of a project within the Indo-Spanish Joint Programme of Cooperation in Science and Technology (PRI-PIBIN-2011-1153 / DST-INT-Spain-P-38-11).

References and links

1.

A. B. Matsko, Practical Applications of Microresonators in Optics and Photonics, (CRC Press, Pasadena, Calif., 2009).

2.

G. Adamovsky and M. V. Otügen, “Morphology-dependent resonances and their applications to sensing in aerospace environments,” J. Aerosp. Comp. Inf. Commun. 5(10), 409–424 (2008). [CrossRef]

3.

L. L. Martín, C. Pérez-Rodríguez, P. Haro-González, and I. R. Martín, “Whispering gallery modes in a glass microsphere as a function of temperature,” Opt. Express 19(25), 25792–25798 (2011). [CrossRef] [PubMed]

4.

M. Mohageg, A. B. Matsko, and L. Maleki, “Lasing and up conversion from a nominally pure whispering gallery mode resonator,” Opt. Express 20(15), 16704–16714 (2012). [CrossRef]

5.

A. Heifetz, S.-C. Kong, A. V. Sahakian, A. Taflove, and V. Backman, “Photonic Nanojets,” J Comput Theor Nanosci 6(9), 1979–1992 (2009). [CrossRef] [PubMed]

6.

P. Ferrand, J. Wenger, A. Devilez, M. Pianta, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Direct imaging of photonic nanojets,” Opt. Express 16(10), 6930–6940 (2008). [CrossRef] [PubMed]

7.

K. W. Allen, A. Darafsheh, and V. N. Astratov, “Photonic nanojet-induced modes: from physics to applications,” 2011 13th International Conference on Transparent Optical Networks 1–4 (2011).

8.

Y. P. Rakovich, M. Gerlach, J. F. Donegan, K. I. Rusakov, and A. A. Gladyshchuk, “Mode manipulation in system of coupled microcavities with whispering gallery modes,” Opt. Spectrosc. 108(3), 385–390 (2010). [CrossRef]

9.

Z. Wang, W. Guo, L. Li, B. Luk’yanchuk, A. Khan, Z. Liu, Z. Chen, and M. Hong, “Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope,” Nat Commun 2, 218 (2011). [CrossRef] [PubMed]

10.

S. Kühn, U. Håkanson, L. Rogobete, and V. Sandoghdar, “Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna,” Phys. Rev. Lett. 97(1), 017402 (2006). [CrossRef] [PubMed]

11.

Y. Zhang, R. Zhang, Q. Wang, Z. Zhang, H. Zhu, J. Liu, F. Song, S. Lin, and E. Y. B. Pun, “Fluorescence enhancement of quantum emitters with different energy systems near a single spherical metal nanoparticle,” Opt. Express 18(5), 4316–4328 (2010). [CrossRef] [PubMed]

12.

S. Lecler, S. Haacke, N. Lecong, O. Crégut, J.-L. Rehspringer, and C. Hirlimann, “Photonic jet driven non-linear optics: example of two-photon fluorescence enhancement by dielectric microspheres,” Opt. Express 15(8), 4935–4942 (2007). [CrossRef] [PubMed]

13.

D. Gérard, J. Wenger, A. Devilez, D. Gachet, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Strong electromagnetic confinement near dielectric microspheres to enhance single-molecule fluorescence,” Opt. Express 16(19), 15297–15303 (2008). [CrossRef] [PubMed]

14.

D. Gérard, A. Devilez, H. Aouani, B. Stout, N. Bonod, J. Wenger, E. Popov, and H. Rigneault, “Efficient excitation and collection of single-molecule fluorescence close to a dielectric microsphere,” J. Opt. Soc. Am. B 26(7), 1473–1478 (2009). [CrossRef]

15.

I. R. Martín, P. Vélez, V. D. Rodríguez, U. R. Rodríguez-Mendoza, and V. Lavín, “Upconversion dynamics in Er 3 + -doped fluoroindate glasses,” Spectrochim. Acta [A] 55(5), 935–940 (1999). [CrossRef]

16.

R. W. Cole, T. Jinadasa, and C. M. Brown, “Measuring and interpreting point spread functions to determine confocal microscope resolution and ensure quality control,” Nat. Protoc. 6(12), 1929–1941 (2011). [CrossRef] [PubMed]

17.

M. Pollnau, D. R. Gamelin, S. R. Lüthi, H. U. Güdel, and M. Hehlen, “Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems,” Phys. Rev. B 61(5), 3337–3346 (2000). [CrossRef]

18.

S. Yang, A. Taflove, and V. Backman, “Experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet,” Opt. Express 19(8), 7084–7093 (2011). [CrossRef] [PubMed]

19.

S.-C. Kong, A. Sahakian, A. Taflove, and V. Backman, “Photonic nanojet-enabled optical data storage,” Opt. Express 16(18), 13713–13719 (2008). [CrossRef] [PubMed]

OCIS Codes
(110.0180) Imaging systems : Microscopy
(160.2540) Materials : Fluorescent and luminescent materials
(350.3950) Other areas of optics : Micro-optics

ToC Category:
Materials

History
Original Manuscript: November 14, 2012
Revised Manuscript: January 10, 2013
Manuscript Accepted: January 10, 2013
Published: April 24, 2013

Virtual Issues
Vol. 8, Iss. 6 Virtual Journal for Biomedical Optics

Citation
C. Pérez-Rodríguez, S. Ríos, I. R. Martín, L. L. Martín, P. Haro-González, and D. Jaque, "Upconversion emission obtained in Yb3+-Er3+ doped fluoroindate glasses using silica microspheres as focusing lens," Opt. Express 21, 10667-10675 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-9-10667


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. A. B. Matsko, Practical Applications of Microresonators in Optics and Photonics, (CRC Press, Pasadena, Calif., 2009).
  2. G. Adamovsky and M. V. Otügen, “Morphology-dependent resonances and their applications to sensing in aerospace environments,” J. Aerosp. Comp. Inf. Commun.5(10), 409–424 (2008). [CrossRef]
  3. L. L. Martín, C. Pérez-Rodríguez, P. Haro-González, and I. R. Martín, “Whispering gallery modes in a glass microsphere as a function of temperature,” Opt. Express19(25), 25792–25798 (2011). [CrossRef] [PubMed]
  4. M. Mohageg, A. B. Matsko, and L. Maleki, “Lasing and up conversion from a nominally pure whispering gallery mode resonator,” Opt. Express20(15), 16704–16714 (2012). [CrossRef]
  5. A. Heifetz, S.-C. Kong, A. V. Sahakian, A. Taflove, and V. Backman, “Photonic Nanojets,” J Comput Theor Nanosci6(9), 1979–1992 (2009). [CrossRef] [PubMed]
  6. P. Ferrand, J. Wenger, A. Devilez, M. Pianta, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Direct imaging of photonic nanojets,” Opt. Express16(10), 6930–6940 (2008). [CrossRef] [PubMed]
  7. K. W. Allen, A. Darafsheh, and V. N. Astratov, “Photonic nanojet-induced modes: from physics to applications,” 2011 13th International Conference on Transparent Optical Networks 1–4 (2011).
  8. Y. P. Rakovich, M. Gerlach, J. F. Donegan, K. I. Rusakov, and A. A. Gladyshchuk, “Mode manipulation in system of coupled microcavities with whispering gallery modes,” Opt. Spectrosc.108(3), 385–390 (2010). [CrossRef]
  9. Z. Wang, W. Guo, L. Li, B. Luk’yanchuk, A. Khan, Z. Liu, Z. Chen, and M. Hong, “Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope,” Nat Commun2, 218 (2011). [CrossRef] [PubMed]
  10. S. Kühn, U. Håkanson, L. Rogobete, and V. Sandoghdar, “Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna,” Phys. Rev. Lett.97(1), 017402 (2006). [CrossRef] [PubMed]
  11. Y. Zhang, R. Zhang, Q. Wang, Z. Zhang, H. Zhu, J. Liu, F. Song, S. Lin, and E. Y. B. Pun, “Fluorescence enhancement of quantum emitters with different energy systems near a single spherical metal nanoparticle,” Opt. Express18(5), 4316–4328 (2010). [CrossRef] [PubMed]
  12. S. Lecler, S. Haacke, N. Lecong, O. Crégut, J.-L. Rehspringer, and C. Hirlimann, “Photonic jet driven non-linear optics: example of two-photon fluorescence enhancement by dielectric microspheres,” Opt. Express15(8), 4935–4942 (2007). [CrossRef] [PubMed]
  13. D. Gérard, J. Wenger, A. Devilez, D. Gachet, B. Stout, N. Bonod, E. Popov, and H. Rigneault, “Strong electromagnetic confinement near dielectric microspheres to enhance single-molecule fluorescence,” Opt. Express16(19), 15297–15303 (2008). [CrossRef] [PubMed]
  14. D. Gérard, A. Devilez, H. Aouani, B. Stout, N. Bonod, J. Wenger, E. Popov, and H. Rigneault, “Efficient excitation and collection of single-molecule fluorescence close to a dielectric microsphere,” J. Opt. Soc. Am. B26(7), 1473–1478 (2009). [CrossRef]
  15. I. R. Martín, P. Vélez, V. D. Rodríguez, U. R. Rodríguez-Mendoza, and V. Lavín, “Upconversion dynamics in Er 3 + -doped fluoroindate glasses,” Spectrochim. Acta [A]55(5), 935–940 (1999). [CrossRef]
  16. R. W. Cole, T. Jinadasa, and C. M. Brown, “Measuring and interpreting point spread functions to determine confocal microscope resolution and ensure quality control,” Nat. Protoc.6(12), 1929–1941 (2011). [CrossRef] [PubMed]
  17. M. Pollnau, D. R. Gamelin, S. R. Lüthi, H. U. Güdel, and M. Hehlen, “Power dependence of upconversion luminescence in lanthanide and transition-metal-ion systems,” Phys. Rev. B61(5), 3337–3346 (2000). [CrossRef]
  18. S. Yang, A. Taflove, and V. Backman, “Experimental confirmation at visible light wavelengths of the backscattering enhancement phenomenon of the photonic nanojet,” Opt. Express19(8), 7084–7093 (2011). [CrossRef] [PubMed]
  19. S.-C. Kong, A. Sahakian, A. Taflove, and V. Backman, “Photonic nanojet-enabled optical data storage,” Opt. Express16(18), 13713–13719 (2008). [CrossRef] [PubMed]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited