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Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 2, Iss. 10 — Oct. 1, 2012
  • pp: 1416–1424
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Waveguide-like structures written in transparent polycrystalline ceramics with an ultra-low fluence femtosecond laser

Gabriel R. Castillo-Vega, Elías H. Penilla, Santiago Camacho-López, Guillermo Aguilar, and J. E. Garay  »View Author Affiliations


Optical Materials Express, Vol. 2, Issue 10, pp. 1416-1424 (2012)
http://dx.doi.org/10.1364/OME.2.001416


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Abstract

We present a laser processing study of optically transparent ytrria stabilized zirconia (YSZ) ceramics (ZrO2-8 mol. % Y2O3) using unamplified femtosecond (fs) laser pulses of a few nJ and high repetition rate (70 MHz). The ceramics were fabricated using current activated pressure assisted densification (CAPAD) and have fine grain size and minimal porosity, producing a transparent material. Irradiation using fs laser pulses caused permanent changes in the optical properties of the irradiated zone. These laser written structures were found to confine He-Ne laser light (632 nm) in effect functioning as waveguide like structures and were written into the YSZ ceramics using a remarkably low per-pulse energy (5nJ). The number of passes with the laser i.e total incident pulses per unit area was found to significantly affect the waveguide writing. We believe that waveguides are regions were the concentration of oxygen vacancies and/or their associated free electrons have been altered by laser irradiation. We are not aware of previous reports of low fluence fs laser pulses being used to influence vacancy related defects to produce waveguides in ceramics. This new mechanism opens the door for writing strictures in optical ceramics with lower power than previously thought feasible.

© 2012 OSA

1. Introduction

Waveguides in optical media are an essential part of a wide variety of important optical devices. In recent years, pulsed laser processing has become an established method for writing waveguides in optical materials; successful examples using femtosecond (fs) laser pulses exist for glasses and single crystals [1

1. K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, “Writing waveguides in glass with a femtosecond laser,” Opt. Lett. 21(21), 1729–1731 (1996). [CrossRef] [PubMed]

6

6. C. N. Borca, V. Apostolopoulos, F. Gardillou, H. G. Limberger, M. Pollnau, and R. P. Salathe, “Buried channel waveguides in Yb-doped KY(WO4)2 crystals fabricated by femtosecond laser irradiation,” Appl. Surf. Sci. 253(19), 8300–8303 (2007). [CrossRef]

]. In recent years transparent polycrystalline ceramics have been receiving significantly increased attention for optical applications such as laser source materials [7

7. A. Ikesue and Y. L. Aung, “Ceramic laser materials,” Nat. Photonics 2(12), 721–727 (2008). [CrossRef]

], solid state lighting [8

8. E. H. Penilla, Y. Kodera, and J. E. Garay, “Simultaneous synthesis and densification of transparent, photoluminescent polycrystalline YAG by current activated pressure assisted densification (CAPAD),” Mater. Sci. Eng. B 177(14), 1178–1181 (2012). [CrossRef]

] and light manipulation [9

9. J. R. Morales, N. Amos, S. Khizroev, and J. E. Garay, “Magneto-optical Faraday effect in nanocrystalline oxides,” J. Appl. Phys. 109(9), 093110 (2011). [CrossRef]

]. Ceramics offer high temperature and chemical stability and relatively efficient fabrication compared to glasses and single crystals thus promising to increase the application space for optical materials. These advantages have prompted investigations and various successful demonstrations of waveguide written in ceramics [10

10. G. A. Torchia, P. F. Meilán, A. Rodenas, D. Jaque, C. Mendez, and L. Roso, “Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics,” Opt. Express 15(20), 13266–13271 (2007). [CrossRef] [PubMed]

,11

11. G. A. Torchia, A. Rodenas, A. Benayas, E. Cantelar, L. Roso, and D. Jaque, “Highly efficient laser action in femtosecond-written Nd:yttrium aluminum garnet ceramic waveguides,” Appl. Phys. Lett. 92(11), 111103 (2008). [CrossRef]

].

A potential drawback to the widespread application of waveguide structures in ceramic-based devices is the relatively high power that is necessary to induce permanent optical changes in ceramics i.e. for waveguide writing. Here we present a method for writing waveguides in transparent polycrystalline ceramics using fs laser pulses with remarkably low energy of 5nJ. This laser energy is orders of magnitude lower than previously reported for waveguide writing in ceramics. Such low energy required for writing waveguides should make these optical ceramics more amenable to industrial application leading to their integration in devices.

2. Experimental procedure

2.1 Ceramic fabrication

Commercial (Tosoh Corporation, Tokyo, Japan) nanocrystalline 8YSZ powder with a reported grain size of 50 nm was densified using current activated pressure assisted densification (CAPAD). Each of the samples was prepared in a graphite die with 19 mm inner diameter. Temperature was measured using a grounded N- type thermocouple placed in a hole drilled halfway through the thickness of the die. The CAPAD processing was done in a custom built apparatus that has been described before [12

12. S. R. Casolco, J. Xu, and J. E. Garay, “Transparent/translucent polycrystalline nanostructured yttria stabilized zirconia with varying colors,” Scr. Mater. 58(6), 516–519 (2008). [CrossRef]

]. 1.5 g of 8YSZ powder was loaded into the die for each sample. The pressure in the system was raised to 106 MPa before the current was applied.

When this pressure was reached, the current heated the sample to 1200 °C using a heating rate of 200 °C/min. Samples were held for 10 min at final pressure and temperature. The samples were mechanically polished for microstructural and optical characterization. The densified samples were fractured and examined using scanning electron microscopy (SEM) (Phillips FEI). Figure 1
Fig. 1 (a) SEM micrograph of the thermally etched surface of an 8YSZ sample produced via CAPAD at 1200⁰C with a 10 min hold time at temperature, 106 MPa (b) Photograph of the same 8YSZ on top of backlit text showing transparency of the ceramic.
shows an SEM micrograph and optical photograph of a typical sample. The sample was annealed for 8 hours in air at 750 °C, in order to thermally etch the surface.

2.2 Ceramic annealing

2.3 Femtosecond laser processing

When a femtosecond laser pulse is focused inside a transparent material the irradiance reached in the focal volume may induce nonlinear absorption through a combination of multiphoton absorption, avalanche ionization and tunneling ionization [15

15. K. Itoh, W. Watanabe, S. Nolte, and C. B. Schaffer, “Ultrafast processes for bulk modification of transparent materials,” MRS Bull. 31(08), 620–625 (2006). [CrossRef]

]. If enough energy is deposited in the material through this nonlinear absorption, permanent structural changes such as refractive index changes can be induced. Since the nonlinear absorption can be only reached for high irradiances, the changes are induced only in the focal volume. Therefore, by simply translating the sample with respect to the focus and using a continuous train of pulses it is possible to induce permanent changes in the material in a reproducible and controlled manner. In this work we used this technique to write waveguide-like structures in the YSZ ceramic.

For the laser processing of the ceramics a homemade Ti:sapphire oscillator with a central wavelength of 800 nm, a repetition rate of 70 MHz, a maximum on-target per pulse energy of 5 nJ and a pulse duration (FWHM) of about 66 fs was used. The laser beam was focused on the surface sample through a lens of 0.6 N.A. and a focal distance f1 = 4 mm. To find and visualize the beam waist onto the sample (ω0 = 1.9 µm, zR = 7.8 µm) we used a lens of focal distance f2 = 500 mm and a CCD camera (PL-A774, Pixelink). This system was set in a configuration similar to an image relay arrangement. The samples were translated with a constant speed of 530 µm/s and perpendicular to the incident beam as shown in Fig. 2
Fig. 2 Schematic of laser processing set-up.
. To determine the refractive index change threshold, a series of about 2 mm long lines were written varying the number of laser scans and the per pulse delivered energy by using an attenuator made of a combination a half- wave plate and a polarizer.

3. Results and discussion

3.1 Waveguide-like structure fabrication

A top view optical micrograph of a series of waveguide-like structures on as processed YSZ is shown in Fig. 3
Fig. 3 Optical micrograph (in transmission) of the waveguide-like structures written in the YSZ ceramic using varying energies a) 3.6, b) 4.6 and c) 5 nJ per pulse. The inset number over the structures indicates the number of scans along the same track.
. These figures show the effects of varying the energy pulse per [(a)3.6, (b) 4.6 and (c) 5 nJ] and the number of passes at each energy. The micrographs reveal that with each of the laser energies in this study, pulsed laser processing produced written structures that are brighter compared to the surrounding material, indicating a permanent change in the optical properties of the irradiated region. This color change can be caused by a change in absorption coefficient, refractive index or both as will be discussed below.

It is worth emphasizing the extremely low per pulse energy used to write the structures. The energies used here (3.6 nJ to 5 nJ) are at least three or four orders of magnitude lower than previously reported in the literature for laser-induced index trimming in transparent crystals and ceramics [5

5. G. A. Torchia, C. Méndez, L. Roso, and J. O. Tocho, “Optical spectroscopy in channel waveguides made in Nd:YAG crystals by femtosecond laser writing,” J. Lumin. 128(5-6), 754–756 (2008). [CrossRef]

,6

6. C. N. Borca, V. Apostolopoulos, F. Gardillou, H. G. Limberger, M. Pollnau, and R. P. Salathe, “Buried channel waveguides in Yb-doped KY(WO4)2 crystals fabricated by femtosecond laser irradiation,” Appl. Surf. Sci. 253(19), 8300–8303 (2007). [CrossRef]

,10

10. G. A. Torchia, P. F. Meilán, A. Rodenas, D. Jaque, C. Mendez, and L. Roso, “Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics,” Opt. Express 15(20), 13266–13271 (2007). [CrossRef] [PubMed]

,11

11. G. A. Torchia, A. Rodenas, A. Benayas, E. Cantelar, L. Roso, and D. Jaque, “Highly efficient laser action in femtosecond-written Nd:yttrium aluminum garnet ceramic waveguides,” Appl. Phys. Lett. 92(11), 111103 (2008). [CrossRef]

]. The lowest (threshold energy) for writing is 3.6 nJ (I = 4.4 x 1011 W/cm2, F = 31 mJ/cm2). In order to verify that we worked below the ablation threshold, we analyzed the irradiated zones by SEM. We did not find any evidence of ablation.

We also found that the number of scans plays an important role in waveguide writing at all energies. For example at 3.6 nJ (Fig. 3(a)) at a low number of scans (100) no visible change was observed while increasing the number of scans to 150 produced a weak visible change and at 200 scans, the wave-guide structure is clearly visible. The effect of scans was similar at higher energies (Figs. 3(b) and 3(c)); Increasing scan numbers produce more clearly demarcated structures. The dependence on the total number indicates that the total incident pulses per unit area on the sample is important.

Equation (1) suggest that there are two possibilities for controlling [VO˙]: 1) The concentration ofVO¨ can vary or 2) The trapped electron, ecan become de-coupled from the VO¨. Both mechanisms are feasible with pulsed laser processing.

Mechanism 1) requires the thermally driven diffusion of oxygen vacancies. fs laser irradiation could increase the temperature of the samples to temperatures where oxygen vacancies have sufficient mobility to cause significant diffusion. This is feasible because of the time between successive delivered pulses (14 ns, i.e. 70 MHz repetition rate), which for this material, could be much shorter than the characteristic time for thermal diffusion out of the focal volume. As a result, the delivered train of laser pulses deposits energy faster than the time required for heat diffusion to occur, leading to a high temperature rise of the material over the focal region [19

19. C. B. Schaffer, A. Brodeur, J. F. García, and E. Mazur, “Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy,” Opt. Lett. 26(2), 93–95 (2001). [CrossRef] [PubMed]

,20

20. C. Schaffer, J. Garcia, and E. Mazur, “Bulk heating of transparent materials using a high repetition-rate femtosecond laser,” Appl. Phys., A Mater. Sci. Process. 76(3), 351–354 (2003). [CrossRef]

]. For long enough laser exposures, the heat deposited by the successive pulses of the oscillator diffuses towards the surrounding material inducing changes beyond the focal volume. This can be seen in Fig. 3(c) where the width of the structures is larger than the diameter of the laser spot (≈4 µm). Eaton et al. [21

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

,22

22. S. M. Eaton, H. Zhang, M. L. Ng, J. Li, W. J. Chen, S. Ho, and P. R. Herman, “Transition from thermal diffusion to heat accumulation in high repetition rate femtosecond laser writing of buried optical waveguides,” Opt. Express 16(13), 9443–9458 (2008). [CrossRef] [PubMed]

] noticed that using a high-repetition rate femtosecond laser it is possible to reach high temperatures by heat accumulation processes.

It is also possible that high electric field caused by the fs laser interaction with YSZ causes decoupling of electrons trapped in vacancies (Mechanism 2). Two types of oxygen vacancies have been identified in reduced cubic YSZ: T- and C-Type oxygen vacancies. The T-type vacancies occur in weakly reducing conditions, while the C-Type occurs in strongly reducing atmospheres. Merino and Orera showed that that the energy gaps between the T- and C-Type oxygen vacancies and the conduction band in reduced YSZ are ~3.3eV and ~2.6eV, respectively [23

23. V. M. Orera and R. I. Merino, “Correlation between intrinsic electron traps and electrical conductivity in stabilized zirconia,” Solid State Ionics 76(1-2), 97–102 (1995). [CrossRef]

]. Since we are irradiating the samples with λ = 800nm, corresponding to a photon energy of Eph = 1.55 eV it is apparently not possible to induce changes in the YSZ via Mechanism 2 with linear photonic absorption. However, since we are employing fs-laser pulses, the intensities are very high indicating the possibility of non-linear effects, in particular 2-photon absorption. The doublet of Eph is 3.10 eV which is enough energy to decouple trapped electrons from the C-type oxygen vacancies via Mechanism 2.

At this time it is not possible to say with certainty which mechanism is responsible of written structures in this work. Investigations are underway to elucidate the governing mechanism.

In order to determine whether the induced color change in the irradiated zones also led to a refractive index change, we analyzed the post-laser processed ceramics using a phase contrast microscope (Olympus, model BX41). Figure 4
Fig. 4 Phase contrast micrograph of a waveguide-like structure written at 5 nJ and 200 scans.
shows a phase contrast micrograph of a waveguide-like structure fabricated at 5 nJ per pulse energy (F = 44 mJ/cm2, I = 6.7 x 1011 W/cm2) and 200 scans. The micrograph reveals a high contrast between the resulting structure and the surrounding material. This clearly indicates a refractive index change over the irradiated track. The bright spots visible in sample are likely dust particles and/or other imperfections caused by polishing.

3.2 Annealing time influence

Table 1

Table 1. Laser Induced Changes in the YSZ Ceramic as a Function of the Annealing Time

table-icon
View This Table
shows the irradiation results in samples with different annealing time (i.e. different optical properties). All the results were obtained for a per pulse energy of 5 nJ (F = 44 mJ/cm2, I = 6.7 x 1011 W/cm2) and 200 scans. We found that the waveguide-like structures writing is easier for samples with a lower annealing time that have lower optical transmittance (higher linear absorption coefficient). This is further evidence that the waveguide writing process is an analogous effect to annealing, i.e is dependent on the concentration of oxygen vacancies in the sample[VO˙].

3.3 Light confinement in the pulsed laser written structures

The ability of the written structures to behave as an optical waveguide was proven by coupling a He-Ne laser trough a single mode optical fiber. The output of the waveguide was collected by a 10x microscope objective coupled to a CCD camera. Figure 5
Fig. 5 a) Light confinement in a waveguide-like structure written at 5 nJ and 200 scans. b) Coupling light in a zone out of the waveguide-like structure.
shows the waveguide-fiber coupling into a not-annealed sample. It can be seen that there is indeed light confinement in the written structures. These results also indicate that the change induced over the irradiated zone corresponds to a refractive index increment (positive Δn). We found that the structures written at higher energies present a better light confinement than those written at lower energies (not shown here). We also observed a better light confinement in structures written at higher number of scans. This confirms a higher refractive index increment over the irradiated zone for structures written at higher energies and higher number of scans.

Figure 6
Fig. 6 Intensity profile at the output face of the waveguide-like structure for a transmitted beam for a wavelength of 632 nm.
shows the intensity profile at the output face of a waveguide written using 5 nJ (F = 44 mJ/cm2, I = 6.7 x 1011 W/cm2) and 200 scans. As it can be seen, the waveguide does not produce a single mode intensity distribution at the coupling wavelength (632 nm). This is shown in the inset picture of Fig. 6, which shows the mode intensity distribution of the waveguide. It presents two bright spots which could be two propagation modes of the waveguide. Another important point to note is that the transmittance of the YSZ ceramics increases with increasing wavelengths (see [13

13. J. E. Alaniz, F. G. Perez-Gutierrez, G. Aguilar, and J. E. Garay, “Optical properties of transparent nanocrystalline yttria stabilized zirconia,” Opt. Mater. 32(1), 62–68 (2009). [CrossRef]

]), suggesting that the transmittance of the waveguide structures should be higher at higher wavelengths. This opens the possibility for the use of this material in telecommunications applications (e.g. 1310 and 1550 nm); investigations are underway in this direction as well.

4. Conclusion

In conclusion, by using ultralow energy (5 nJ) and ultrafast (66 fs) laser pulses, we were able to write waveguide-like structures in the polycrystalline ceramic YSZ. The energy we used for writing these waveguide-like structures is at least three or four orders of magnitude lower than earlier reported for ceramics. To the best of our knowledge, these are the lowest energies ever reported for the successful writing of waveguides in a ceramic material. We found that the refractive index change increases with the pulse energy and the number of scans. We also found that the writing of these structures is easier for samples with low annealing time (high linear absorption coefficient).

Acknowledgments

Support of this work by CIMAV-AFOSR-CONACyT grant with J. Fillerup and J. Gonzalez as program managers is gratefully acknowledged. We also acknowledge partial support from the US Mexico Basic research initiative through grant FA9550-10-1-0212 and F0C06 and 2010-2011 UCMEXUS Collaborative Research Grant to SCL and GA. We would also like to thank H. Marquez Becerra fort helpful discussion on waveguides.

References and links

1.

K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, “Writing waveguides in glass with a femtosecond laser,” Opt. Lett. 21(21), 1729–1731 (1996). [CrossRef] [PubMed]

2.

K. Miura, J. Qiu, H. Inouye, T. Mitsuyu, and K. Hirao, “Photowritten optical waveguides in various glasses with ultrashort pulse laser,” Appl. Phys. Lett. 71(23), 3329–3331 (1997). [CrossRef]

3.

K. Hirao and K. Miura, “Writing waveguides and gratings in silica and related materials by a femtosecond laser,” J. Non-Cryst. Solids 239(1-3), 91–95 (1998). [CrossRef]

4.

C. Florea and K. Winick, “Fabrication and characterization of photonic devices directly written in glass using femtosecond laser pulses,” J. Lightwave Technol. 21(1), 246–253 (2003). [CrossRef]

5.

G. A. Torchia, C. Méndez, L. Roso, and J. O. Tocho, “Optical spectroscopy in channel waveguides made in Nd:YAG crystals by femtosecond laser writing,” J. Lumin. 128(5-6), 754–756 (2008). [CrossRef]

6.

C. N. Borca, V. Apostolopoulos, F. Gardillou, H. G. Limberger, M. Pollnau, and R. P. Salathe, “Buried channel waveguides in Yb-doped KY(WO4)2 crystals fabricated by femtosecond laser irradiation,” Appl. Surf. Sci. 253(19), 8300–8303 (2007). [CrossRef]

7.

A. Ikesue and Y. L. Aung, “Ceramic laser materials,” Nat. Photonics 2(12), 721–727 (2008). [CrossRef]

8.

E. H. Penilla, Y. Kodera, and J. E. Garay, “Simultaneous synthesis and densification of transparent, photoluminescent polycrystalline YAG by current activated pressure assisted densification (CAPAD),” Mater. Sci. Eng. B 177(14), 1178–1181 (2012). [CrossRef]

9.

J. R. Morales, N. Amos, S. Khizroev, and J. E. Garay, “Magneto-optical Faraday effect in nanocrystalline oxides,” J. Appl. Phys. 109(9), 093110 (2011). [CrossRef]

10.

G. A. Torchia, P. F. Meilán, A. Rodenas, D. Jaque, C. Mendez, and L. Roso, “Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics,” Opt. Express 15(20), 13266–13271 (2007). [CrossRef] [PubMed]

11.

G. A. Torchia, A. Rodenas, A. Benayas, E. Cantelar, L. Roso, and D. Jaque, “Highly efficient laser action in femtosecond-written Nd:yttrium aluminum garnet ceramic waveguides,” Appl. Phys. Lett. 92(11), 111103 (2008). [CrossRef]

12.

S. R. Casolco, J. Xu, and J. E. Garay, “Transparent/translucent polycrystalline nanostructured yttria stabilized zirconia with varying colors,” Scr. Mater. 58(6), 516–519 (2008). [CrossRef]

13.

J. E. Alaniz, F. G. Perez-Gutierrez, G. Aguilar, and J. E. Garay, “Optical properties of transparent nanocrystalline yttria stabilized zirconia,” Opt. Mater. 32(1), 62–68 (2009). [CrossRef]

14.

J. E. Garay, “Current activated pressure assisted densification of materials,” Annu. Rev. Mater. Res. 40(1), 445–468 (2010). [CrossRef]

15.

K. Itoh, W. Watanabe, S. Nolte, and C. B. Schaffer, “Ultrafast processes for bulk modification of transparent materials,” MRS Bull. 31(08), 620–625 (2006). [CrossRef]

16.

R. Osellame, G. Della Valle, N. Chiodo, S. Taccheo, P. Laporta, O. Svelto, and G. Cerullo, “Lasing in femtosecond laser written optical waveguides,” Appl. Phys., A Mater. Sci. Process. 93(1), 17–26 (2008). [CrossRef]

17.

J. W. Chan, T. Huser, S. Risbud, and D. M. Krol, “Structural changes in fused silica after exposure to focused femtosecond laser pulses,” Opt. Lett. 26(21), 1726–1728 (2001). [CrossRef] [PubMed]

18.

M. Yoshimura, “Phase stability of zirconia,” Am. Ceram. Soc. Bull. 67, 1950–1955 (1988).

19.

C. B. Schaffer, A. Brodeur, J. F. García, and E. Mazur, “Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy,” Opt. Lett. 26(2), 93–95 (2001). [CrossRef] [PubMed]

20.

C. Schaffer, J. Garcia, and E. Mazur, “Bulk heating of transparent materials using a high repetition-rate femtosecond laser,” Appl. Phys., A Mater. Sci. Process. 76(3), 351–354 (2003). [CrossRef]

21.

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

22.

S. M. Eaton, H. Zhang, M. L. Ng, J. Li, W. J. Chen, S. Ho, and P. R. Herman, “Transition from thermal diffusion to heat accumulation in high repetition rate femtosecond laser writing of buried optical waveguides,” Opt. Express 16(13), 9443–9458 (2008). [CrossRef] [PubMed]

23.

V. M. Orera and R. I. Merino, “Correlation between intrinsic electron traps and electrical conductivity in stabilized zirconia,” Solid State Ionics 76(1-2), 97–102 (1995). [CrossRef]

24.

F. E. G. Henn, R. M. Buchanan, N. Jiang, and D. A. Stevenson, “Permittivity and AC Conductivity in yttria-stabilized zirconia: Application of a pairs-approximation model and determination of the binding energy of the oxygen vacancies,” Appl. Phys., A Mater. Sci. Process. 60(5), 515–519 (1995). [CrossRef]

OCIS Codes
(160.0160) Materials : Materials
(230.7370) Optical devices : Waveguides

ToC Category:
Artificially Engineered Structures

History
Original Manuscript: August 7, 2012
Manuscript Accepted: August 28, 2012
Published: September 20, 2012

Citation
Gabriel R. Castillo-Vega, Elías H. Penilla, Santiago Camacho-López, Guillermo Aguilar, and J. E. Garay, "Waveguide-like structures written in transparent polycrystalline ceramics with an ultra-low fluence femtosecond laser," Opt. Mater. Express 2, 1416-1424 (2012)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-2-10-1416


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References

  1. K. M. Davis, K. Miura, N. Sugimoto, and K. Hirao, “Writing waveguides in glass with a femtosecond laser,” Opt. Lett.21(21), 1729–1731 (1996). [CrossRef] [PubMed]
  2. K. Miura, J. Qiu, H. Inouye, T. Mitsuyu, and K. Hirao, “Photowritten optical waveguides in various glasses with ultrashort pulse laser,” Appl. Phys. Lett.71(23), 3329–3331 (1997). [CrossRef]
  3. K. Hirao and K. Miura, “Writing waveguides and gratings in silica and related materials by a femtosecond laser,” J. Non-Cryst. Solids239(1-3), 91–95 (1998). [CrossRef]
  4. C. Florea and K. Winick, “Fabrication and characterization of photonic devices directly written in glass using femtosecond laser pulses,” J. Lightwave Technol.21(1), 246–253 (2003). [CrossRef]
  5. G. A. Torchia, C. Méndez, L. Roso, and J. O. Tocho, “Optical spectroscopy in channel waveguides made in Nd:YAG crystals by femtosecond laser writing,” J. Lumin.128(5-6), 754–756 (2008). [CrossRef]
  6. C. N. Borca, V. Apostolopoulos, F. Gardillou, H. G. Limberger, M. Pollnau, and R. P. Salathe, “Buried channel waveguides in Yb-doped KY(WO4)2 crystals fabricated by femtosecond laser irradiation,” Appl. Surf. Sci.253(19), 8300–8303 (2007). [CrossRef]
  7. A. Ikesue and Y. L. Aung, “Ceramic laser materials,” Nat. Photonics2(12), 721–727 (2008). [CrossRef]
  8. E. H. Penilla, Y. Kodera, and J. E. Garay, “Simultaneous synthesis and densification of transparent, photoluminescent polycrystalline YAG by current activated pressure assisted densification (CAPAD),” Mater. Sci. Eng. B177(14), 1178–1181 (2012). [CrossRef]
  9. J. R. Morales, N. Amos, S. Khizroev, and J. E. Garay, “Magneto-optical Faraday effect in nanocrystalline oxides,” J. Appl. Phys.109(9), 093110 (2011). [CrossRef]
  10. G. A. Torchia, P. F. Meilán, A. Rodenas, D. Jaque, C. Mendez, and L. Roso, “Femtosecond laser written surface waveguides fabricated in Nd:YAG ceramics,” Opt. Express15(20), 13266–13271 (2007). [CrossRef] [PubMed]
  11. G. A. Torchia, A. Rodenas, A. Benayas, E. Cantelar, L. Roso, and D. Jaque, “Highly efficient laser action in femtosecond-written Nd:yttrium aluminum garnet ceramic waveguides,” Appl. Phys. Lett.92(11), 111103 (2008). [CrossRef]
  12. S. R. Casolco, J. Xu, and J. E. Garay, “Transparent/translucent polycrystalline nanostructured yttria stabilized zirconia with varying colors,” Scr. Mater.58(6), 516–519 (2008). [CrossRef]
  13. J. E. Alaniz, F. G. Perez-Gutierrez, G. Aguilar, and J. E. Garay, “Optical properties of transparent nanocrystalline yttria stabilized zirconia,” Opt. Mater.32(1), 62–68 (2009). [CrossRef]
  14. J. E. Garay, “Current activated pressure assisted densification of materials,” Annu. Rev. Mater. Res.40(1), 445–468 (2010). [CrossRef]
  15. K. Itoh, W. Watanabe, S. Nolte, and C. B. Schaffer, “Ultrafast processes for bulk modification of transparent materials,” MRS Bull.31(08), 620–625 (2006). [CrossRef]
  16. R. Osellame, G. Della Valle, N. Chiodo, S. Taccheo, P. Laporta, O. Svelto, and G. Cerullo, “Lasing in femtosecond laser written optical waveguides,” Appl. Phys., A Mater. Sci. Process.93(1), 17–26 (2008). [CrossRef]
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