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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 20 — Sep. 24, 2012
  • pp: 22308–22313
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Laser-written waveguides in KTP for broadband Type II second harmonic generation

Fredrik Laurell, Thomas Calmano, Sebastian Müller, Peter Zeil, Carlota Canalias, and Günter Huber  »View Author Affiliations


Optics Express, Vol. 20, Issue 20, pp. 22308-22313 (2012)
http://dx.doi.org/10.1364/OE.20.022308


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Abstract

Femto-second laser writing was used to fabricate waveguides in a z-cut KTP sample with losses below 0.8 dB/cm. They were used for efficient, broad bandwidth, Type II birefringent second harmonic generation to the green. The temperature and wavelength bandwidth were, 28⁰C∙cm and 0.85 nm∙cm, respectively.

© 2012 OSA

1. Introduction

In this paper we use a two line laser waveguide writing procedure, which provide low loss, circular single-mode waveguides in KTP. These were evaluated by Type II frequency doubling and provided broadband phasematching and close to the theoretically expected efficiency, i.e. with an undamaged crystal structure in the guiding region and a maintained nonlinearity.

2. Laser-written waveguides

Three dimensional micro-structures can be fabricated in several dielectrics utilizing nonlinear absorption processes with focused femtosecond lasers [8

8. B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchik, B. W. Shore, and M. D. Perry, “Nanosecond-to-femtosecond laser-induced breakdown in dielectrics,” Phys. Rev. B Condens. Matter 53(4), 1749–1761 (1996). [CrossRef] [PubMed]

]. Stress-induced changes of the refractive index can be used for waveguiding and channel waveguides can simply be made by focusing the laser radiation inside the sample, while it is translated. Straight waveguides as well as more complex passive structures as splitters and couplers have been made this way [9

9. D. Homoelle, S. Wielandy, A. L. Gaeta, N. F. Borrelli, and C. Smith, “Infrared photosensitivity in silica glasses exposed to femtosecond laser pulses,” Opt. Lett. 24(18), 1311–1313 (1999). [CrossRef] [PubMed]

12

12. K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 x 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Express 14(6), 2335–2343 (2006). [CrossRef] [PubMed]

]. In crystalline materials, like KTP, the refractive index change occurs due to stress-induced birefringence and/or lattice modification close to the focus region. Waveguiding can then, depending on the material and the writing condition, either occur in the modified region (Type I waveguides) or adjacent to it (Type II waveguides) [10

10. S. Nolte, M. Will, J. Burghoff, and A. Tünnermann, “Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics,” Appl. Phys., A Mater. Sci. Process. 77(1), 109–111 (2003). [CrossRef]

]. In the latter case writing of two closely placed tracks leads to good confinement as well as low loss [13

13. S. M. Eaton, H. Zhang, P. R. Herman, F. Yoshino, L. Shah, J. Bovatsek, and A. Y. Arai, “Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate,” Opt. Express 13(12), 4708–4716 (2005). [CrossRef] [PubMed]

].

Active devices like lasers and amplifiers have been obtained in rare-earth doped glasses [14

14. M. Ams, P. Dekker, G. D. Marshall, and M. J. Withford, “Monolithic 100 mW Yb waveguide laser fabricated using the femtosecond-laser direct-write technique,” Opt. Lett. 34(3), 247–249 (2009). [CrossRef] [PubMed]

], and also in different crystalline laser hosts like Neodymium doped Y3Al5O12-crystals (Nd:YAG) and Nd:YAG ceramics. Utilizing the two trace writing technique obtaining low loss waveguides, has made it possible to obtain laser emission with high slope efficiencies (> 60%) and output power (>1.3 W) [15

15. T. Calmano, J. Siebenmorgen, O. Hellmig, K. Petermann, and G. Huber, “Nd:YAG waveguide laser with 1.3 W output power, fabricated by direct femtosecond laser writing,” Appl. Phys. B 100(1), 131–135 (2010). [CrossRef]

]. Recently even better results were obtained with Yb:YAG fs-written waveguides where a slope efficiency of 75% and an output power of nearly 0.8W was demonstrated [16

16. T. Calmano, J. Siebenmorgen, A. Paschke, C. Fiebig, K. Paschke, G. Erbert, K. Petermann, and G. Huber, “Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser,” Opt. Mater. Express 1(3), 428 (2011). [CrossRef]

,17

17. J. Siebenmorgen, T. Calmano, K. Petermann, and G. Huber, “Highly efficient Yb:YAG channel waveguide laser written with a femtosecond-laser,” Opt. Express 18(15), 16035–16041 (2010). [CrossRef] [PubMed]

]. For nonlinear optical application laser written waveguides have, besides in KTP, been made in lithium niobate (LN), periodically poled lithium niobate (PPLN) [18

18. J. Burghoff, C. Grebing, S. Nolte, and A. Tünnermann, “Efficient frequency doubling in femtosecond laser-written waveguides in lithium niobate,” Appl. Phys. Lett. 89(8), 081108 (2006). [CrossRef]

,19

19. R. Osellame, M. Lobino, N. Chiodo, M. Marangoni, G. Cerullo, R. Ramponi, H. T. Bookey, R. R. Thomson, N. D. Psaila, and A. K. Kar, “Femtosecond laser writing of waveguides in periodically poled lithium niobate preserving the nonlinear coefficient,” Appl. Phys. Lett. 90(24), 241107 (2007). [CrossRef]

] and yttrium aluminum borate [20

20. N. Dong, J. Martínez de Mendivil, E. Cantelar, G. Lifante, J. Vázquez de Aldana, G. A. Torchia, F. Chen, and D. Jaque, “Self-frequency-doubling of ultrafast laser inscribed neodymium doped yttrium aluminum borate waveguides,” Appl. Phys. Lett. 98(18), 181103 (2011). [CrossRef]

].

3. Waveguide fabrication

A set of Type II, x-propagating, channel waveguides were produced in a z-cut flux grown KTP sample with the dimensions (10 × 5 × 1) mm3. Laser pulses from an amplified femtosecond laser system (Clark-MRX CPA- 2010) with a wavelength of 775 nm, a pulse duration of 150 fs, pulse energies up to 1 mJ, and a repetition rate of 1 kHz were focused 150 μm below the polished surface of the crystals using an aspheric lens (NA = 0.55, f = 4.5 mm). During the writing process, the crystals were translated transversally with respect to the incident fs-laser pulses by a motorized stage (Aerotech ABL 1000) with a velocity of 25 μm/s. The pulse energy was varied between 0.4 μJ and 4 μJ, and the threshold for material modification in this setup was approximately 0.6 μJ. The diameter of the focal spot in air was measured to be 2 μm (at 1/e2) by imaging the focus onto the sensor of a CCD-camera.

Several different pairs of parallel tracks were inscribed in the sample and the distance between two adjacent tracks was changed between 16 μm and 25 μm to obtain waveguides with different width. A pulse energy of 2.5 μJ gave both good confinement and low loss, which was then used for the waveguides described below. After track writing the end faces were polished and the final length, l, of the sample became 9.5 mm.

4. Waveguide characterization

The waveguide losses were quite low for all the waveguides. A conservative upper limit for the loss for the single-mode waveguides was estimated by coupling the HeNe laser beam through the waveguide and comparing the transmitted and the launched power. Taking the Fresnel losses at the two sample facets under consideration, but not the incoupling losses, gave a power loss below 0.8 dB/cm for both the TE and the TM mode.

5. Second harmonic generation experiments

6. Conclusions and outlook

Future work should include attempts to get higher confinement by inducing larger refractive index change through laser writing. That would result in a smaller overlap area, Aovl, between the fundamental and SH modes, which will increase the efficiency, as the waveguide over bulk conversion efficiency scales as [4

4. F. Laurell, “Periodically poled materials for miniature light sources,” Opt. Mater. 11(2-3), 235–244 (1999). [CrossRef]

];
λFl2NeffAovl,
(2)
where Neff is the average refractive index for the TE00 and TM00 modes. Furthermore, a shorter phasematching wavelength and even larger bandwidth can be obtained for KTP if the waveguide instead is written in the y-direction. Risk et al. demonstrated noncritical Type II phasematching at 994 nm with a bandwidth of 175 °C·cm in the y-direction of bulk KTP [25

25. W. P. Risk, R. N. Payne, W. Lenth, C. Harder, and H. Meier, “Noncritically phasematched frequency doubling using 994 nm dye and diode laser radiation in KTiOP04,” Appl. Phys. Lett. 55(12), 1179–1181 (1989). [CrossRef]

]. Finally, by using this laser writing technique for PPKTP would enable even more efficient frequency conversion, flexible phasematching throughout the transparence region of KTP and other attractive features of quasi-phase matching.

Acknowledgments

The authors would like acknowledge technical support from Hanna Al-Maawali and financial support from the Linnaeus Center ADOPT financed by the Swedish Science Council, the Deutsche Forschungsgemeinschaft (Graduate School 1355) and the Joachim Herz Stiftung.

References and links

1.

J. D. Bierlein and H. Vanherzeele, “Potassium titanyl phosphate: properties and new applications,” J. Opt. Soc. Am. B 6(4), 622–633 (1989). [CrossRef]

2.

M. G. Roelofs, P. A. Morris, and J. D. Bierlein, “Ion exchange of Rb, Ba, and Sr in KTiOPO4,” J. Appl. Phys. 70(2), 720–728 (1991). [CrossRef]

3.

F. Laurell, J. B. Brown, and J. D. Bierlein, “Sum‐frequency generation in segmented KTP waveguides,” Appl. Phys. Lett. 60(9), 1064–1066 (1992). [CrossRef]

4.

F. Laurell, “Periodically poled materials for miniature light sources,” Opt. Mater. 11(2-3), 235–244 (1999). [CrossRef]

5.

P. Bindner, A. Boudrioua, J. C. Loulergue, and P. Moretti, “Formation of planar optical waveguides in potassium titanyl phosphate by double implantation of protons,” Appl. Phys. Lett. 79(16), 2558–2561 (2001). [CrossRef]

6.

S. Campbell, R. R. Thomson, D. P. Hand, A. K. Kar, D. T. Reid, C. Canalias, V. Pasiskevicius, and F. Laurell, “Frequency-doubling in femtosecond laser inscribed periodically-poled potassium titanyl phosphate waveguides,” Opt. Express 15(25), 17146–17150 (2007). [CrossRef] [PubMed]

7.

C. Tu, Z. Huang, K. Lou, H. Liu, Y. Wang, Y. Li, F. Lu, and H. T. Wang, “Efficient green-light generation by frequency doubling of a picosecond all-fiber ytterbium-doped fiber amplifier in PPKTP waveguide inscribed by femtosecond laser direct writing,” Opt. Express 18(24), 25183–25191 (2010). [CrossRef] [PubMed]

8.

B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchik, B. W. Shore, and M. D. Perry, “Nanosecond-to-femtosecond laser-induced breakdown in dielectrics,” Phys. Rev. B Condens. Matter 53(4), 1749–1761 (1996). [CrossRef] [PubMed]

9.

D. Homoelle, S. Wielandy, A. L. Gaeta, N. F. Borrelli, and C. Smith, “Infrared photosensitivity in silica glasses exposed to femtosecond laser pulses,” Opt. Lett. 24(18), 1311–1313 (1999). [CrossRef] [PubMed]

10.

S. Nolte, M. Will, J. Burghoff, and A. Tünnermann, “Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics,” Appl. Phys., A Mater. Sci. Process. 77(1), 109–111 (2003). [CrossRef]

11.

A. M. Kowalevicz, V. Sharma, E. P. Ippen, J. G. Fujimoto, and K. Minoshima, “Three-dimensional photonic devices fabricated in glass by use of a femtosecond laser oscillator,” Opt. Lett. 30(9), 1060–1062 (2005). [CrossRef] [PubMed]

12.

K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 x 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Express 14(6), 2335–2343 (2006). [CrossRef] [PubMed]

13.

S. M. Eaton, H. Zhang, P. R. Herman, F. Yoshino, L. Shah, J. Bovatsek, and A. Y. Arai, “Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate,” Opt. Express 13(12), 4708–4716 (2005). [CrossRef] [PubMed]

14.

M. Ams, P. Dekker, G. D. Marshall, and M. J. Withford, “Monolithic 100 mW Yb waveguide laser fabricated using the femtosecond-laser direct-write technique,” Opt. Lett. 34(3), 247–249 (2009). [CrossRef] [PubMed]

15.

T. Calmano, J. Siebenmorgen, O. Hellmig, K. Petermann, and G. Huber, “Nd:YAG waveguide laser with 1.3 W output power, fabricated by direct femtosecond laser writing,” Appl. Phys. B 100(1), 131–135 (2010). [CrossRef]

16.

T. Calmano, J. Siebenmorgen, A. Paschke, C. Fiebig, K. Paschke, G. Erbert, K. Petermann, and G. Huber, “Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser,” Opt. Mater. Express 1(3), 428 (2011). [CrossRef]

17.

J. Siebenmorgen, T. Calmano, K. Petermann, and G. Huber, “Highly efficient Yb:YAG channel waveguide laser written with a femtosecond-laser,” Opt. Express 18(15), 16035–16041 (2010). [CrossRef] [PubMed]

18.

J. Burghoff, C. Grebing, S. Nolte, and A. Tünnermann, “Efficient frequency doubling in femtosecond laser-written waveguides in lithium niobate,” Appl. Phys. Lett. 89(8), 081108 (2006). [CrossRef]

19.

R. Osellame, M. Lobino, N. Chiodo, M. Marangoni, G. Cerullo, R. Ramponi, H. T. Bookey, R. R. Thomson, N. D. Psaila, and A. K. Kar, “Femtosecond laser writing of waveguides in periodically poled lithium niobate preserving the nonlinear coefficient,” Appl. Phys. Lett. 90(24), 241107 (2007). [CrossRef]

20.

N. Dong, J. Martínez de Mendivil, E. Cantelar, G. Lifante, J. Vázquez de Aldana, G. A. Torchia, F. Chen, and D. Jaque, “Self-frequency-doubling of ultrafast laser inscribed neodymium doped yttrium aluminum borate waveguides,” Appl. Phys. Lett. 98(18), 181103 (2011). [CrossRef]

21.

T. Y. Fan, C. E. Huang, B. Q. Hu, R. C. Eckardt, Y. X. Fan, R. L. Byer, and R. S. Feigelson, “Second harmonic generation and accurate index of refraction measurements in flux-grown KTiOPO4.,” Appl. Opt. 26(12), 2390–2394 (1987). [CrossRef] [PubMed]

22.

P. Jelger, M. Engholm, L. Norin, and F. Laurell, “Degradation-resistant lasing at 980 nm in a Yb/Ce/Al-doped silica fiber,” J. Opt. Soc. Am. B 27(2), 338–342 (2010). [CrossRef]

23.

Z. Y. Ou, S. F. Pereira, E. S. Polzik, and H. J. Kimble, “85% efficiency for cw frequency doubling from 1.08 to 0.54, µm,” Opt. Lett. 17(9), 640–642 (1992). [CrossRef] [PubMed]

24.

B. Boulanger, J. P. Fève, G. Marnier, B. Ménaert, X. Cabirol, P. Villeval, and C. Bonnin, “Relative sign and absolute magnitude of d2 nonlinear coefficients of KTP from second-harmonic-generation measurements,” J. Opt. Soc. Am. B 11(5), 750–757 (1994). [CrossRef]

25.

W. P. Risk, R. N. Payne, W. Lenth, C. Harder, and H. Meier, “Noncritically phasematched frequency doubling using 994 nm dye and diode laser radiation in KTiOP04,” Appl. Phys. Lett. 55(12), 1179–1181 (1989). [CrossRef]

OCIS Codes
(190.4390) Nonlinear optics : Nonlinear optics, integrated optics
(220.4000) Optical design and fabrication : Microstructure fabrication
(130.7405) Integrated optics : Wavelength conversion devices

ToC Category:
Integrated Optics

History
Original Manuscript: July 17, 2012
Revised Manuscript: September 7, 2012
Manuscript Accepted: September 11, 2012
Published: September 14, 2012

Citation
Fredrik Laurell, Thomas Calmano, Sebastian Müller, Peter Zeil, Carlota Canalias, and Günter Huber, "Laser-written waveguides in KTP for broadband Type II second harmonic generation," Opt. Express 20, 22308-22313 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-20-22308


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References

  1. J. D. Bierlein and H. Vanherzeele, “Potassium titanyl phosphate: properties and new applications,” J. Opt. Soc. Am. B6(4), 622–633 (1989). [CrossRef]
  2. M. G. Roelofs, P. A. Morris, and J. D. Bierlein, “Ion exchange of Rb, Ba, and Sr in KTiOPO4,” J. Appl. Phys.70(2), 720–728 (1991). [CrossRef]
  3. F. Laurell, J. B. Brown, and J. D. Bierlein, “Sum‐frequency generation in segmented KTP waveguides,” Appl. Phys. Lett.60(9), 1064–1066 (1992). [CrossRef]
  4. F. Laurell, “Periodically poled materials for miniature light sources,” Opt. Mater.11(2-3), 235–244 (1999). [CrossRef]
  5. P. Bindner, A. Boudrioua, J. C. Loulergue, and P. Moretti, “Formation of planar optical waveguides in potassium titanyl phosphate by double implantation of protons,” Appl. Phys. Lett.79(16), 2558–2561 (2001). [CrossRef]
  6. S. Campbell, R. R. Thomson, D. P. Hand, A. K. Kar, D. T. Reid, C. Canalias, V. Pasiskevicius, and F. Laurell, “Frequency-doubling in femtosecond laser inscribed periodically-poled potassium titanyl phosphate waveguides,” Opt. Express15(25), 17146–17150 (2007). [CrossRef] [PubMed]
  7. C. Tu, Z. Huang, K. Lou, H. Liu, Y. Wang, Y. Li, F. Lu, and H. T. Wang, “Efficient green-light generation by frequency doubling of a picosecond all-fiber ytterbium-doped fiber amplifier in PPKTP waveguide inscribed by femtosecond laser direct writing,” Opt. Express18(24), 25183–25191 (2010). [CrossRef] [PubMed]
  8. B. C. Stuart, M. D. Feit, S. Herman, A. M. Rubenchik, B. W. Shore, and M. D. Perry, “Nanosecond-to-femtosecond laser-induced breakdown in dielectrics,” Phys. Rev. B Condens. Matter53(4), 1749–1761 (1996). [CrossRef] [PubMed]
  9. D. Homoelle, S. Wielandy, A. L. Gaeta, N. F. Borrelli, and C. Smith, “Infrared photosensitivity in silica glasses exposed to femtosecond laser pulses,” Opt. Lett.24(18), 1311–1313 (1999). [CrossRef] [PubMed]
  10. S. Nolte, M. Will, J. Burghoff, and A. Tünnermann, “Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics,” Appl. Phys., A Mater. Sci. Process.77(1), 109–111 (2003). [CrossRef]
  11. A. M. Kowalevicz, V. Sharma, E. P. Ippen, J. G. Fujimoto, and K. Minoshima, “Three-dimensional photonic devices fabricated in glass by use of a femtosecond laser oscillator,” Opt. Lett.30(9), 1060–1062 (2005). [CrossRef] [PubMed]
  12. K. Suzuki, V. Sharma, J. G. Fujimoto, E. P. Ippen, and Y. Nasu, “Characterization of symmetric [3 x 3] directional couplers fabricated by direct writing with a femtosecond laser oscillator,” Opt. Express14(6), 2335–2343 (2006). [CrossRef] [PubMed]
  13. S. M. Eaton, H. Zhang, P. R. Herman, F. Yoshino, L. Shah, J. Bovatsek, and A. Y. Arai, “Heat accumulation effects in femtosecond laser-written waveguides with variable repetition rate,” Opt. Express13(12), 4708–4716 (2005). [CrossRef] [PubMed]
  14. M. Ams, P. Dekker, G. D. Marshall, and M. J. Withford, “Monolithic 100 mW Yb waveguide laser fabricated using the femtosecond-laser direct-write technique,” Opt. Lett.34(3), 247–249 (2009). [CrossRef] [PubMed]
  15. T. Calmano, J. Siebenmorgen, O. Hellmig, K. Petermann, and G. Huber, “Nd:YAG waveguide laser with 1.3 W output power, fabricated by direct femtosecond laser writing,” Appl. Phys. B100(1), 131–135 (2010). [CrossRef]
  16. T. Calmano, J. Siebenmorgen, A. Paschke, C. Fiebig, K. Paschke, G. Erbert, K. Petermann, and G. Huber, “Diode pumped high power operation of a femtosecond laser inscribed Yb:YAG waveguide laser,” Opt. Mater. Express1(3), 428 (2011). [CrossRef]
  17. J. Siebenmorgen, T. Calmano, K. Petermann, and G. Huber, “Highly efficient Yb:YAG channel waveguide laser written with a femtosecond-laser,” Opt. Express18(15), 16035–16041 (2010). [CrossRef] [PubMed]
  18. J. Burghoff, C. Grebing, S. Nolte, and A. Tünnermann, “Efficient frequency doubling in femtosecond laser-written waveguides in lithium niobate,” Appl. Phys. Lett.89(8), 081108 (2006). [CrossRef]
  19. R. Osellame, M. Lobino, N. Chiodo, M. Marangoni, G. Cerullo, R. Ramponi, H. T. Bookey, R. R. Thomson, N. D. Psaila, and A. K. Kar, “Femtosecond laser writing of waveguides in periodically poled lithium niobate preserving the nonlinear coefficient,” Appl. Phys. Lett.90(24), 241107 (2007). [CrossRef]
  20. N. Dong, J. Martínez de Mendivil, E. Cantelar, G. Lifante, J. Vázquez de Aldana, G. A. Torchia, F. Chen, and D. Jaque, “Self-frequency-doubling of ultrafast laser inscribed neodymium doped yttrium aluminum borate waveguides,” Appl. Phys. Lett.98(18), 181103 (2011). [CrossRef]
  21. T. Y. Fan, C. E. Huang, B. Q. Hu, R. C. Eckardt, Y. X. Fan, R. L. Byer, and R. S. Feigelson, “Second harmonic generation and accurate index of refraction measurements in flux-grown KTiOPO4.,” Appl. Opt.26(12), 2390–2394 (1987). [CrossRef] [PubMed]
  22. P. Jelger, M. Engholm, L. Norin, and F. Laurell, “Degradation-resistant lasing at 980 nm in a Yb/Ce/Al-doped silica fiber,” J. Opt. Soc. Am. B27(2), 338–342 (2010). [CrossRef]
  23. Z. Y. Ou, S. F. Pereira, E. S. Polzik, and H. J. Kimble, “85% efficiency for cw frequency doubling from 1.08 to 0.54, µm,” Opt. Lett.17(9), 640–642 (1992). [CrossRef] [PubMed]
  24. B. Boulanger, J. P. Fève, G. Marnier, B. Ménaert, X. Cabirol, P. Villeval, and C. Bonnin, “Relative sign and absolute magnitude of d2 nonlinear coefficients of KTP from second-harmonic-generation measurements,” J. Opt. Soc. Am. B11(5), 750–757 (1994). [CrossRef]
  25. W. P. Risk, R. N. Payne, W. Lenth, C. Harder, and H. Meier, “Noncritically phasematched frequency doubling using 994 nm dye and diode laser radiation in KTiOP04,” Appl. Phys. Lett.55(12), 1179–1181 (1989). [CrossRef]

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