OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 4 — Feb. 13, 2012
  • pp: 4518–4524
« Show journal navigation

Terahertz emission from Indium Oxide films grown on MgO substrates using sub-bandgap photon energy excitation

Elmer S. Estacio, Christopher T. Que, Fritz C. B. Awitan, Jan Isaac Bugante, Francesca Isabel de Vera, Jonathan Azares, Jessica Afalla, Jeffrey de Vero, Armando S. Somintac, Roland V. Sarmago, Arnel A. Salvador, Kohji Yamamoto, and Masahiko Tani  »View Author Affiliations


Optics Express, Vol. 20, Issue 4, pp. 4518-4524 (2012)
http://dx.doi.org/10.1364/OE.20.004518


View Full Text Article

Acrobat PDF (831 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

Indium oxide (In2O3) films grown by thermal oxidation on MgO substrates were optically excited by femtosecond laser pulses having photon energy lower than the In2O3 bandgap. Terahertz (THz) pulse emission was observed using time domain spectroscopy. Results show that THz emission saturates at an excitation fluence of ~400 nJ/cm2. Even as two-photon absorption has been excluded, the actual emission mechanism has yet to be confirmed but is currently attributed to carriers due to weak absorption from defect levels that are driven by a strain field at the interface of the substrate and the grown film.

© 2012 OSA

1. Introduction

In this work, we experimentally demonstrate THz emission from photo-excited In2O3 films on single crystal MgO (100) prepared by thermal oxidation. The MgO substrate is so chosen due of its excellent transmission properties both in the optical and THz-frequency regimes, high-melting temperature, and low electrical conductivity [16

16. M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004). [CrossRef]

]. Results show that even at an excitation photon energy which is lower than the bandgap, the In2O3 films exhibited THz emission. Additionally, the dependence of the THz emission on the oxidation temperature and excitation fluence was also studied in an attempt to explain the underlying THz radiation mechanism.

2. Experiment

The In2O3 thin films were formed via thermal oxidation of Indium films deposited on single crystal MgO (001) substrates. The MgO substrates were primarily cleaned, rinsed and blow-dried. Indium metal with 99.999% purity was then thermally evaporated on the substrates at a rate of 6Å/s in a 3x10−5-Torr vacuum environment. A quartz crystal sensor indicated the indium film thickness to be ~1500Å. The samples were then oxidized in ambient air at three different temperatures (350°C, 450°C, and 550°C). Initial thin film characterization was carried out via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The THz emission was measured using standard THz-time domain spectroscopy (THz-TDS) methods. The optical excitation was provided for by a p-polarized mode-locked Ti:Sapphire laser delivering ~80 femtosecond pulses at a central wavelength of 800 nm with a repetition rate of 82 MHz. The samples were excited at a 45ο incidence with an average pump power of 150 mW, loosely focused to a beam spot size of ~1 mm. The THz radiation was collected in the specular reflection direction and focused to the detector using appropriate off-axis paraboloid mirrors. The THz temporal waveforms were detected by a Hamamatsu LT-GaAs dipole-type photoconductive antenna, switched by a variable time-delayed 20 mW optical pulse.

3. Results and discussion

The THz-TDS data plots for sub-bandgap optical excitation (800 nm, 600 nJ/cm2 fluence) of the three samples are shown in Fig. 2
Fig. 2 THz-TDS plots for the In2O3/MgO films oxidized at 350°C, 450°C, 550°C. The sample oxidized at 450°C exhibited the most intense THz emission. The inset shows the corresponding Fourier-transform spectra of the TDS data. The THz emission is centered at ~1 THz, and having frequency components of up to 2 THz. A signal-to-noise ratio dynamic range of more than 1 order of magnitude for the 450°C-oxidized sample illustrates implies intense THz emission.
. To confirm that the THz transients did not originate from the MgO, a bare substrate was also tested yielding no THz emission. The 450°C film exhibited the most intense THz emission, followed by the In2O3/MgO film oxidized at 550°C. The 350°C film has a slightly weaker THz emission compared with the 550°C sample. The corresponding Fourier-transform amplitude spectra of the TDS waveforms (inset) revealed spectrally symmetric emission having a central frequency at 1 THz, with frequency components extending up to ~2 THz. The signal amplitude of the THz transients was approximately 10 times less than that of SI-GaAs and is two orders weaker than the THz emission from p-InAs. A recent survey of semiconductor surface THz emitters reported that p-InAs is currently the most intense semiconductor surface THz emitter [18

18. V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008). [CrossRef]

] and thus, the observed THz emission from the In2O3 samples are very weak. However, the surveyed high-quality low-bandgap semiconductors were grown using well-established growth techniques, and were excited at energies well above the bandgap; hardly comparable with the conditions in this current study. With a signal-to-noise ratio dynamic range of approximately 1 order of magnitude in the amplitude spectra, the observed THz emission is sufficiently intense to warrant interest and further investigation. The THz data suggest a correlation between THz radiation and the presence of the cubic (222)-oriented c-In2O3 phase because XRD results showed that the 450°C-oxidized sample, having the highest THz emission, also exhibited the strongest intensity for this particular peak assignment. The presence of this phase appears to favor slightly more intense THz emission but this assertion needs further experimental confirmation and will not be pursued in detail in this work. On the other hand, it is important to have a better understanding of the underlying THz radiation mechanism albeit for sub-bandgap optical excitation.

Initially, a two-photon absorption process was suspected. A two-photon photoconductive THz emission in ZnSe has been previously reported [19

19. J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003). [CrossRef]

]. However, our further experimental verifications showed that photocarrier generation due to this nonlinear process is unlikely. The 2nd harmonic (400 nm at 40 mW) of the 800 nm wavelength emission of the Ti:Sapphire laser was used to excite the 450°C sample in order to investigate above-bandgap optical excitation. Its THz emission was then compared with the emission for the fundamental-line excitation at the same power. The results are shown in the inset of Fig. 3
Fig. 3 Excitation fluence dependence of the THz emission from the 450°C-oxidized sample. The slope of the log-log plot indicates that the THz radiation mechanism is not a nonlinear optical process. The inset compares the THz emission from below-bandgap and above-bandgap excitation showing that the 800 nm wavelength pump is more efficient (the traces have been offset for ease of comparison); thereby ruling out a two-photon absorption process as the origin of the photo-carriers causing THz emission.
, wherein the above-bandgap pump yielded lower THz emission. In general, the probability two-photon absorption is orders of magnitude lower than the single photon case and the comparable THz emission intensities in the inset do not support a dominant two-photon scenario. Moreover, even though the number of photons in the short-wavelength excitation case is only half of the fundamental line pumping, a two-photon process should still have exhibited less efficient photo-carrier generation (and THz emission). The difference in the THz-TDS waveforms in the two excitation conditions, however, suggests that the origin of photocarrier generation that leads to THz emission are different. The above-bandgap excitation case exhibited an almost single-cycle THz transient while the THz emission due to sub-bandgap absorption was characterized by several cycles. This is an indication of differences in the photocarrier dynamics between 400 nm and 800 nm excitation cases that could be an interesting topic for succeeding studies.

The presence of these defects has been shown not to detrimentally affect the THz emission properties of the In2O3/MgO sample in a significant manner. The micron-scale grain structures could scatter incident NIR light but the optical quality of the sample in the THz region has not been compromised. Shown in Fig. 4
Fig. 4 In the transmission-type excitation geometry, the THz emission intensity does not vary much whether the sample was excited from the MgO substrate side or from the In2O3 film side. Even as the sample’s over-all optical transmission is relatively low due to strong scattering, its THz optical qualities are not compromised. The TDS waveforms have been shifted for ease of comparison.
is the comparison of the THz emission from the 450°C-oxidized sample in the transmission excitation geometry for the cases where the optical excitation was made incident on the film side and on the MgO substrate side. An important observation is that the peak intensities of the two signals are very much comparable. The intensity attenuation for the case of MgO substrate-side excitation is attributed to the attenuation of the excitation pump laser after passing through the MgO substrate, possibly due to reflection and optical scattering. As such, it can be deduced that: (a) the MgO substrate is sufficiently transparent to both the excitation beam and to THz radiation and (b) the In2O3 film is transparent to THz radiation.

4. Summary

This work experimentally demonstrated the generation of THz transients in polycrystalline In2O3 thin films on MgO substrates, prepared by thermal oxidation. Sufficiently intense THz emission can be observed even for excitation photon energy below the In2O3 bandgap of 2.9 eV. A comparison of the THz emission intensity between above- and sub-bandgap excitation initially suggested that a two-photon absorption process is not mainly responsible for the THz emission. This was confirmed by excitation fluence dependence measurements. The sub-bandgap absorption is currently attributed to weak absorption from defects and impurities although this has not been confirmed. Transmission excitation geometry THz measurements showed that the samples are sufficiently transparent in the THz region. Studies on the actual utilization of In2O3/MgO films in wide-bandgap PCA’s is beyond the scope of this work. However, results suggest that the necessity of short-wavelength excitation sources for such future devices may be circumvented owing to the observation of sub-bandgap excited THz emission from In2O3.

Acknowledgments

A. Somintac, R. V. Sarmago, and A. Salvador acknowledge support from DOST and UP OVCRD.

References and links

1.

P. Gu and M. Tani, “Terahertz radiation from semiconductor surfaces,” in Terahertz Optoelectronics: Topics in Applied Physics, Vol. 97, K. Sakai, ed. (Springer-Verlag, 2005).

2.

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005). [CrossRef]

3.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005). [CrossRef]

4.

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000). [CrossRef]

5.

R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966). [CrossRef]

6.

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009). [CrossRef]

7.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

8.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010). [CrossRef]

9.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005). [CrossRef]

10.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009). [CrossRef]

11.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

12.

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007). [CrossRef]

13.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004). [CrossRef]

14.

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998). [CrossRef]

15.

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

16.

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004). [CrossRef]

17.

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

18.

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008). [CrossRef]

19.

J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003). [CrossRef]

20.

C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003). [CrossRef]

21.

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991). [CrossRef] [PubMed]

22.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009). [CrossRef]

23.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995). [CrossRef]

24.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008). [CrossRef]

25.

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009). [CrossRef] [PubMed]

26.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009). [CrossRef]

27.

K. Hess, Advanced Theory of Semiconductor Devices (Wiley Interscience, 2000).

OCIS Codes
(310.6860) Thin films : Thin films, optical properties
(300.6495) Spectroscopy : Spectroscopy, teraherz

ToC Category:
Thin Films

History
Original Manuscript: January 11, 2012
Revised Manuscript: February 2, 2012
Manuscript Accepted: February 2, 2012
Published: February 8, 2012

Citation
Elmer S. Estacio, Christopher T. Que, Fritz C. B. Awitan, Jan Isaac Bugante, Francesca Isabel de Vera, Jonathan Azares, Jessica Afalla, Jeffrey de Vero, Armando S. Somintac, Roland V. Sarmago, Arnel A. Salvador, Kohji Yamamoto, and Masahiko Tani, "Terahertz emission from Indium Oxide films grown on MgO substrates using sub-bandgap photon energy excitation," Opt. Express 20, 4518-4524 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-4-4518


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. P. Gu and M. Tani, “Terahertz radiation from semiconductor surfaces,” in Terahertz Optoelectronics: Topics in Applied Physics, Vol. 97, K. Sakai, ed. (Springer-Verlag, 2005).
  2. G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett.87(15), 151114 (2005). [CrossRef]
  3. S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett.87(26), 261112 (2005). [CrossRef]
  4. M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci.162–163, 492–498 (2000). [CrossRef]
  5. R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys.37(1), 299–302 (1966). [CrossRef]
  6. R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp.479(1–2), 840–843 (2009). [CrossRef]
  7. G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids352(23–25), 2311–2314 (2006).
  8. V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron.21(4), 360–363 (2010). [CrossRef]
  9. K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci.28(1), 9–17 (2005). [CrossRef]
  10. P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B79(20), 205211 (2009). [CrossRef]
  11. T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon.14(11), 27 (2008).
  12. P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B75(15), 153205 (2007). [CrossRef]
  13. R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett.84(23), 4810–4812 (2004). [CrossRef]
  14. N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys.84(1), 654–656 (1998). [CrossRef]
  15. H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films303(1–2), 216–221 (1997).
  16. M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett.85(2), 191–193 (2004). [CrossRef]
  17. M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films279(1–2), 1–3 (1996).
  18. V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys.9(2), 130–141 (2008). [CrossRef]
  19. J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett.83(14), 2967–2969 (2003). [CrossRef]
  20. C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met.139(3), 815–817 (2003). [CrossRef]
  21. B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett.67(19), 2709–2712 (1991). [CrossRef] [PubMed]
  22. J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett.95(5), 051912 (2009). [CrossRef]
  23. T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett.66(2), 121–123 (1995). [CrossRef]
  24. M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett.92(17), 171907 (2008). [CrossRef]
  25. A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett.4(6), 526–531 (2009). [CrossRef] [PubMed]
  26. E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett.94(23), 232104 (2009). [CrossRef]
  27. K. Hess, Advanced Theory of Semiconductor Devices (Wiley Interscience, 2000).

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.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited