OSA's Digital Library

Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 2, Iss. 9 — Sep. 1, 2012
  • pp: 1209–1218
« Show journal navigation

Mid-IR volumetric Bragg grating based on LiF color center crystal

Dmitry V. Martyshkin, Anton V. Fedorov, Anitha Arumugam, David J. Hilton, Vladimir V. Fedorov, and Sergey B. Mirov  »View Author Affiliations


Optical Materials Express, Vol. 2, Issue 9, pp. 1209-1218 (2012)
http://dx.doi.org/10.1364/OME.2.001209


View Full Text Article

Acrobat PDF (1537 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We have demonstrated volumetric Bragg gratings (VBGs) for mid-IR spectral range based on LiF color center (LiF:CC) crystals. γ-irradiated LiF:CC crystals feature strong absorption bands in the visible and near-IR spectral range, where selective color center photo-bleaching allows for the LiF refractive index modification. The absence of active absorption in LiF:CC crystals at wavelengths longer than 1.3 μm results in a VBG that is stable under mid-IR irradiation. Our calculations predict a ~60% diffraction efficiency over 1-6 μm spectral range, which could be realized in a ~1 cm long VBG. To verify this, we fabricated periodic structures in LiF:CC crystals using an amplified femtosecond Ti:sapphire laser. Diffraction at 1.56 μm is demonstration of a phase grating in LiF and is a proof of the feasibility of LiF:CC crystals for mid-IR VBG applications.

© 2012 OSA

1. Introduction

2. Experimental results

LiF crystals were γ-irradiated at 300 K with a dose of 2x108 rad using a 60Co source to produce CCs. After irradiation, the LiF sample was cleaved and polished to the size 5x5x5 mm3. After the absorption spectra measurements the crystal was mounted on a translational stage, which has computer controlled periodic spacing movement programmed through Thorlabs APT System Software.

One of the strongest absorption bands in LiF:CC crystal centered at 445 nm represents overlapped absorption bands of F2 and F3+ CCs. Excitation into this band causes not only transformation of F2 and F3+ CCs but also triggers a number of photochemical processes resulting in crystal bleaching. The basic initial photo induced processes under excitation into F2-F3+ absorption band include color center photo-ionization, dissociation and recharging:

F2+ωF2++e
(1)
F3++eF3
(2)
F3++ωF+F2+
(3)

The first process shows direct photo-ionization of the F2 CCs; the second describes capture of the electron released due to F2 CCs photo-ionization by F3+ CCs; and the third process illustrates photo dissociation of the F3+ CCs. The F2+ CCs obtained from the process (1) are not stable at room temperature (RT) and decay with several hours life-time. Irradiation with a shorter wavelength also includes processes of the photo ionization and photo dissociation of the F3 CCs:

F3+ω=F3++e
(4)

Finally, irradiation into the absorption band of F CCs may result in CCs annihilation, via the return of interstitial electrically neutral fluoride ions (Hi) to the lattices nodes:

F+ω(F)*+Hi[Fion]
(5)

Therefore, irradiation by light with a wavelength shorter than F2-F3+ absorption band provides beaching of different types of CCs. However, high absorption coefficient in the visible spectral range limits the radiation penetration depth. For that reason in our experimental setup we used fs Ti:sapphire laser operating at 790 nm where absorption coefficient is more than two order of magnitude smaller. High peak power of the fs laser allows utilization of a wide range of photo induced processes due to multi-photon excitation mechanisms, including three-photon excitation of F CCs.

We used Ti:sapphire laser radiation with an average power 400 mW, operating at 1 kHz repetition rate, and 35fs pulse duration. Laser radiation with 1 cm beam diameter was focused by cylindrical lens with a 15 mm focal distance on LiF crystal surface. The beam width on the crystal surface was ~1.53 µm. Some of the photo-induced processes enable migration of the excited CCs in the crystalline lattice. This migration could decrease the contrast of the photo-induced grating. Therefore, to demonstrate feasibility of the proposed approach we fabricate grating with a relatively large period comparing to the writing beam width. The crystal was irradiated for 5 seconds to produce a single groove (bleached stripe), then the sample was mechanically shifted 12 µm or 24 µm by using a computer controlled system and re-exposed to laser radiation. The procedure was repeated for 100 times, to produce 100 grooves. Two series of periodic gratings with 12 µm and 24 µm periods were fabricated. Optical microscopy images of the gratings are shown in the Fig. 1
Fig. 1 Optical microscopy image of 83 grooves/mm (A) and 42 grooves/mm (B) diffraction gratings.
. These images were obtained using transmitted light through the sample. We have not observed any changes using reflected light, i.e. due to optical damage of the crystal.

Photoluminescence spectra of a LiF CC crystal before and after Ti:sapphire laser irradiation are depicted in Fig. 2
Fig. 2 Photoluminescence spectra of LiF CC crystals a) before laser irradiation, b) area of the crystal adjacent to the bleached stripe, c) bleached stripe (irradiated area), and d) bleached stripe after 12 hours.
. The photoluminescence (PL) spectra were measured under excitation by Argon laser at 514 nm. The PL spectrum of the sample before fs-irradiation consists of F2 and F3+ bands with maxima at 670 nm and 530 nm, correspondingly. The exposure to fs laser radiation produced bleached areas (stripes or grooves of diffraction grating) that were clearly visible to the eye. The color of bleached area changed from brown to light green indicating ionization of F2 and formation of F2+color centers. The PL spectra of the bleached area are shown in Fig. 2c and demonstrate substantial decrease of signal intensity in 600-800 nm spectral range corresponding to PL of F2 CCs and appearance of a new band around 900 nm corresponding to PL of F2+ CCs [4

4. T. T. Basiev and S. B. Mirov, Room Temperature Tunable Colour Center Lasers (Laser Science and Technology) (Harwood Academic Publishers GmbH, 1994).

,5

5. T. T. Basiev, S. B. Mirov, and V. V. Osiko, “Room-temperature color center lasers,” IEEE J. Quantum Electron. 24(6), 1052–1069 (1988). [CrossRef]

]. The F2+ CCs are unstable at room temperature and disappear after a 12-24 hour time period [4

4. T. T. Basiev and S. B. Mirov, Room Temperature Tunable Colour Center Lasers (Laser Science and Technology) (Harwood Academic Publishers GmbH, 1994).

,5

5. T. T. Basiev, S. B. Mirov, and V. V. Osiko, “Room-temperature color center lasers,” IEEE J. Quantum Electron. 24(6), 1052–1069 (1988). [CrossRef]

]. Figure 2d shows that after 12 hours the intensity of PL band at 900 nm decreases and PL band intensity of F2 CC slightly recovers. The photoluminescence imaging of 84 grooves/mm and 42 grooves/mm diffraction gratings is shown in Figs. 3
Fig. 3 Photoluminescence imaging and optical microscopy image of 83 grooves/mm diffraction grating. a) as prepared, b) same as (a) zoomed in 500-600 μm region, c) 12 hours after preparation, d) same as (c) zoomed in 500-600 μm region. The photoluminescence imaging was performed using PL integral intensity in 650-700 μm spectral region, the scanning was performed using XY translation stage with 1 μm step.
and 4
Fig. 4 Photoluminescence imaging and optical microscopy image of 42 grooves/mm diffraction grating. a) as prepared, b) same as (a) zoomed in 500-600 μm region, c) 12 hours after preparation, d) same as (c) zoomed in 500-600 μm region. The photoluminescence imaging was performed using PL integral intensity in 650-700 μm spectral region, the scanning was performed using XY translation stage with 1 μm step.
. The scanning was done by using XY translation stage with 100 nm precision and 1 µm lateral resolution of the Confocal Micro-Raman System.

The photoluminescence imaging of 84 grooves/mm and 42 grooves/mm diffraction gratings is shown in Figs. 3 and 4. The scanning was done by using XY translation stage with 100 nm precision and 1 µm lateral resolution of the Confocal Micro-Raman System.

Figure 3 shows that, for the 84 grooves/mm (12 µm period) grating, the caustic of the Ti:sapphire laser beam after focusing by 15 mm cylindrical lens was sufficient to produce grating with a good contrast. An intensity decrease can be seen in Figs. 3a and 3c and is due to poor parallelism of the crystal surfaces that results in the microscope defocusing during scanning over the lateral 1.2 mm distance. A similar defocusing was observed for the 42 grooves/mm grating, as shown in Figs. 4a and 4c, with an improved grating contrast, as expected due to a smaller overlap of the bleached and unbleached zones of the crystal. The PL signal intensity slightly increased after 12 hours in both cases, as shown in Figs. 4c and 5c
Fig. 5 Image of the diffraction pattern of 532 and 632 nm radiations obtained with a 12 μm period grating; left- position of the zero order; b and a-first order diffraction of 532 nm and 632 laser beams, respectively.
, compared to initial observations shown in Fig. 3.

Diffraction grating efficiencies were characterized at normal incidence using three different CW lasers. In these experiments, we measured the efficiency of Raman-Nath diffraction to the first order at normal incidence. The laser beams were slightly focused on the grating surfaces to insure the beam size smaller than the size of the grating. The sets of calibrated neutral filters were used to increase a dynamic range of the photo-detectors. Figure 6
Fig. 6 Absorption spectra of the LiF CCs crystal.
shows image of the diffraction pattern of the radiation of He-Ne (0.632 μm) as well as second harmonic radiation of the Nd:YAG (0.532μm) lasers.

3. Discussion

To estimate the refractive index change induced by color centers we used Kramers-Kronig Relations between real (n) and imaginary parts (κ) of the refractive index [17

17. M. Fox, Optical Properties of Solids (Oxford Master Series in Condensed Matter Physics) (Oxford Univ. Press, 2001).

21

21. K. Peiponen and J. Riissanen, “On the linear and non-linear refractive index of F colour centres as a function of temperature,” J. Phys. Chem. 17(31), 5617–5620 (1984).

].
Δn(ω)=1πP+κ(ω)ωωdω
(6)
κ(ω)=1πP+n(ω)1ωωdω,
(7)
where Δn is refractive index change induced by absorption κ(ω). The change of the refractive index in the Alkali -halide crystals due to CC absorption was studied in several publications, however most researchers were focused on the near-infrared and visible spectral ranges [18

18. M. Montecchi, R. M. Montereali, and E. Nichelatti, “Refractive index modification from color centres in dielectric confining structures,” Opt. Mater. 17(1–2), 347–350 (2001). [CrossRef]

21

21. K. Peiponen and J. Riissanen, “On the linear and non-linear refractive index of F colour centres as a function of temperature,” J. Phys. Chem. 17(31), 5617–5620 (1984).

]. We have numerically calculated refractive index change induced by CCs absorption bands. The strongest absorption line of the CCs crystal belongs to the F- centers. An F- center is an anionic vacancy trapped a single-electron. It is the simplest CC in the crystals with the highest concentration compared to other possible CCs. In LiF crystals, the absorption band of the F- CCs is located at 248 nm, the absorption coefficient can reach 1000 cm−1 in highly irradiated crystal [22

22. S. B. Mirov and T. T. Basiev, “Progress and trends in color center lasers,” Proc. SPIE 2138, 248–262 (1994). [CrossRef]

]. Using this value for α(ω) and the Kramers-Kronig relations, Eq. (6) estimates the refractive index change using:
Δn=α0λ04π(2(ωω0)/Δω)1+(2(ωω0)/Δω)2
(8)
where α0=4πk0λ0 is a maximum absorption coefficient and Δω is a FWHM of the absorption line. The maximum value of Δnmax is equal to Δnmax = 1/2κ0 at ω = ω0 ± Δω/2 and for low frequency limit ω<<Δω<ω0 the change of the refractive index is:
Δn(0)=α0λ04πΔω2ω0=nmaxΔωω0
(9)
For the most fundamental F-band in LiF color center crystal (λ0 = 248 nm, ΔfFWHM/f0 = 0.155) and absorption coefficient of α0 = 500 cm-1, the estimated Δnmax = 5 × 10−4 and Δn(0) = 0.8 × 10−4.

We note that the CCs absorption bands are better approximated by Gaussian shape due to a strong electron-phonon coupling. This requires a numerical calculation of Cauchy's integral in Eq. (6). For these calculations, we measured absorption coefficients of the prepared samples with different thicknesses (from hundreds of micron to several mm) to increase accuracy of measurement of absorption coefficients of different CCs. The experimental data of the absorption spectra are shown in Fig. 6a. Due to a high absorption coefficient, we could not use the direct measurements of the maximum of the F-band, however, it can also be estimated from the band shape and position of the maximum measured from the low irradiated samples. For refractive index calculations, we fit the measured absorption spectra in the frequency domain using Gaussian absorption bands of the F center and 10 other aggregate CCs. The fitting results are shown using gray curves in Fig. 6b and summarized in the Table 1

Table 1. Results of the Absorption Spectrum Deconvolution by Gaussian Bandsa

table-icon
View This Table
. The bands positions and their bandwidths used in the fitting are in a good agreement with previously reported data [4

4. T. T. Basiev and S. B. Mirov, Room Temperature Tunable Colour Center Lasers (Laser Science and Technology) (Harwood Academic Publishers GmbH, 1994).

7

7. K. J. Teegarden and B. J. Thompson, Selected Papers on Color-Center Lasers (SPIE Press Book) (SPIE, 2003).

]. The most dominant bands are F band at 248 nm with absorption coefficient 675 cm−1 and band at 450 nm which results from overlapping of the F2 and F3+ bands with a total absorption coefficient equal to 314 cm−1.

Calculation of the refractive index change using Eq. (6) was performed with MAPLE 4 software and compared to the analytical solution for the Lorentz bands. The absorption index changes induced by color centers are shown in the Fig. 7
Fig. 7 The calculation of refractive index changes induced by color centers. The black curve shows the results of calculations taking into account all color centers in the sample and the red curve shows the results including only absorption by two major bands (F and F2 & F3+).
. The black curve shows the results for Δn induced by all color centers in the sample and the red curve shows the results only for the absorption by two bands (F and F2 & F3+). As one can see from the calculation, Δn≥10−4 can be obtained in the near-mid-IR spectral range (1300-3000 nm). Consideration of only two major absorptions bands at 248 and 450 nm (F and F2 &F3+) reduces the Δn calculated value only on 30%. This analysis of the LiF CC crystal absorption spectra demonstrated that one can obtain Δn> 10−4 in the near-mid-IR spectral range (1.3-6.0 µm).

The measurements of the diffraction efficiencies allow us to estimate the induced Δn at 1.56 μm. The first-order Raman-Nath diffraction could be calculated using equation [23

23. H. Nishihara, M. Haruna, and T. Suhara, Optical Integrated Circuits (McGraw-Hill, 1989).

]:
η1=J12(2|k|l)=J12(πΔnlGλ)(kl)2=(πΔnlGλ)2
(10)
where J1 is the Bessel function of order 1 and lG is thickness of the diffraction grating. There are two major factors that are limiting depth of the photo-induced grating. The first factor is the beam divergence which results in decreasing of the irradiation flux. The second is spatial overlap of adjacent lines. As the result of divergence (Θ = 2λ/πw0) the writing beams with separation Λ will overlap at a distance lgΛ/Θ=ð2Λw0/ë. Using parameters Λ = 12 μm and w0 = 1.53 μm, the estimated grating thickness is lg≈37 μm.In the gratings with a 24 μm period, the beams will overlap at twice the distance and result in greater diffraction efficiency, which was observed in our experiments. The change of the refractive index calculated from experimental results was Δn≈1.9 × 10−4. The reflection efficiency of the VBG could be estimated using the following equation [23

23. H. Nishihara, M. Haruna, and T. Suhara, Optical Integrated Circuits (McGraw-Hill, 1989).

]:
η=[tanh(πLλ(Δn))]2
(11)
where L is the length of the periodic structure. The required length of the periodic structure with R = 60% can be found as follows:

πLλ0(δn)1
(12)

Using Δn~10−4, the required length of the diffraction grating is L = 0.5-1 cm for λ0 = 1.5-6 μm. In current experimental setup, the beam divergence is the limiting factor for the grating thickness. This limitation could be overcome by using interference method for grating writing. However, it will require careful optimization of exposition time to maximize grating efficiency. Current technology enables fabrication of homogeneously colored LiF crystals with typical sizes larger than 10 cm. The grating 1.5-6 μm period and 1 cm length could be fabricated using standard holographic method or direct e-beam writing.

4. Conclusion

We have demonstrated gamma irradiated LiF Color Center Crystals as a material for Volumetric Bragg Grating operating in the mid-IR spectral range. Our calculations have demonstrated that photorefractive effect based on color center bleaching could provide VBG efficiency ~60% over 1-6 μm spectral range. Periodic structures with 24 and 12μm periods in LiF:CC crystals were fabricated by fs radiation of Ti:sapphire laser. The fabricated structures have been characterized using Raman-Nath diffraction at 0.532, 0.632, and 1.56 μm. Experimentally obtained diffraction at 1.56 μm is a clear evidence of phase grating fabrication and feasibility of these materials for mid-IR VBG applications.

Acknowledgments

The authors would like to acknowledge funding support from National Science Foundation (NSF) EPS-0814103, 1158862 and ECCS-0901376. The work reported here partially involves intellectual property developed at the University of Alabama at Birmingham.

References and links

1.

A. A. Kaminskii, “Laser crystals and ceramics: recent advances,” Laser Photon. Rev. 1(2), 93–177 (2007). [CrossRef]

2.

S. Mirov, V. Fedorov, I. S. Moskalev, D. Martyshkin, and C. Kim, “Progress in Cr2+ and Fe2+ doped mid-IR laser materials,” Laser Photon. Rev. 4(1), 21–41 (2010). [CrossRef]

3.

S. B. Mirov, V. V. Fedorov, D. V. Martyshkin, I. S. Moskalev, M. S. Mirov, and V. P. Gapontsev, “Progress in mid-IR Cr2+ and Fe2+ doped II-VI materials and lasers,” Opt. Mater. Express 1(5), 898–910 (2011). [CrossRef]

4.

T. T. Basiev and S. B. Mirov, Room Temperature Tunable Colour Center Lasers (Laser Science and Technology) (Harwood Academic Publishers GmbH, 1994).

5.

T. T. Basiev, S. B. Mirov, and V. V. Osiko, “Room-temperature color center lasers,” IEEE J. Quantum Electron. 24(6), 1052–1069 (1988). [CrossRef]

6.

S. B. Mirov and T. T. Basiev, “Progress in color center lasers,” IEEE J. Sel. Top. Quantum Electron. 1(1), 22–30 (1995). [CrossRef]

7.

K. J. Teegarden and B. J. Thompson, Selected Papers on Color-Center Lasers (SPIE Press Book) (SPIE, 2003).

8.

F. Bonfigli, M. A. Vincenti, S. Almaviva, R. M. Montereali, E. Nichelatti, R. N. Nogueira, and H. J. Kalinowski, “Photo-induced gratings in thin color center layers on lithium fluoride,” Appl. Opt. 48(31), G38–G43 (2009). [CrossRef] [PubMed]

9.

A. Rocchetti, G. Assanto, R. M. Montereali, E. Nichelatti, and F. Somma, “Color-center waveguides in low-energy electron-bombarded lithium fluoride,” Appl. Phys. Lett. 88(26), 261111 (2006). [CrossRef]

10.

R. Montereali and M. Piccinini, “Optical gain of F2 color centres in LiF confining structures realised by electron-beam lithography,” Opt. Commun. 209(1-3), 201–208 (2002). [CrossRef]

11.

G. Cheng, Y. Wang, J. He, G. Chen, and W. Zhao, “Color center conversion by femtosecond pulse laser irradiation in LiF:F2 crystals,” Opt. Express 15(14), 8938–8942 (2007). [CrossRef] [PubMed]

12.

R. Montereali, S. Bigotta, M. Piccinini, M. Giammatteo, P. Picozzi, and S. Santucci, “Broad-band active channels induced by electron beam lithography in LiF films for waveguiding devices,” Nucl. Instrum. Methods Phys. Res. B 166-167, 764–770 (2000). [CrossRef]

13.

F. Mollenauer and D. H. Olson, “Broadly tunable lasers using color centers,” J. Appl. Phys. 46(7), 3109–3118 (1975). [CrossRef]

14.

D. V. Martyshkin, J. G. Parker, V. V. Fedorov, and S. B. Mirov, “Tunable distributed feedback color center laser using stabilized F2+** color centers in LiF crystal,” Appl. Phys. Lett. 84(16), 3022–3024 (2004). [CrossRef]

15.

T. Kurobori, H. Hibino, Y. Q. Chen, and K. Inabe, “Distributed-feedback color center lasers using F2 centers in KCl,” Jpn. J. Appl. Phys. 34(Part 2, No. 7B), L894–L896 (1995). [CrossRef]

16.

K. Kawamura, D. Takamizu, T. Kurobori, T. Kamiya, M. Hirano, and H. Hosono, “Nano-fabrication of optical devices in transparent dielectrics: volume gratings in SiO and DFB color center laser in LiF,” Nucl. Instrum. Methods Phys. Res. B 218, 332–336 (2004). [CrossRef]

17.

M. Fox, Optical Properties of Solids (Oxford Master Series in Condensed Matter Physics) (Oxford Univ. Press, 2001).

18.

M. Montecchi, R. M. Montereali, and E. Nichelatti, “Refractive index modification from color centres in dielectric confining structures,” Opt. Mater. 17(1–2), 347–350 (2001). [CrossRef]

19.

M. Montecchi, E. Nichelatti, A. Mancini, and R. M. Montereali, “Optical characterization of low-energy electron-beam-colored LiF crystals by spectral transmittance measurements,” J. Appl. Phys. 86(7), 3745–3750 (1999). [CrossRef]

20.

K.-E. Peiponen and A. Vaittinen, “Light-induced refractive index change in some F coloured alkali halide crystals,” J. Phys. Chem. 15(13), L415–L418 (1982).

21.

K. Peiponen and J. Riissanen, “On the linear and non-linear refractive index of F colour centres as a function of temperature,” J. Phys. Chem. 17(31), 5617–5620 (1984).

22.

S. B. Mirov and T. T. Basiev, “Progress and trends in color center lasers,” Proc. SPIE 2138, 248–262 (1994). [CrossRef]

23.

H. Nishihara, M. Haruna, and T. Suhara, Optical Integrated Circuits (McGraw-Hill, 1989).

OCIS Codes
(050.7330) Diffraction and gratings : Volume gratings
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(160.5320) Materials : Photorefractive materials

ToC Category:
Photorefractive Materials

History
Original Manuscript: April 16, 2012
Revised Manuscript: July 6, 2012
Manuscript Accepted: July 12, 2012
Published: August 7, 2012

Virtual Issues
Advances in Optical Materials (2012) Optical Materials Express

Citation
Dmitry V. Martyshkin, Anton V. Fedorov, Anitha Arumugam, David J. Hilton, Vladimir V. Fedorov, and Sergey B. Mirov, "Mid-IR volumetric Bragg grating based on LiF color center crystal," Opt. Mater. Express 2, 1209-1218 (2012)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-2-9-1209


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. A. A. Kaminskii, “Laser crystals and ceramics: recent advances,” Laser Photon. Rev.1(2), 93–177 (2007). [CrossRef]
  2. S. Mirov, V. Fedorov, I. S. Moskalev, D. Martyshkin, and C. Kim, “Progress in Cr2+ and Fe2+ doped mid-IR laser materials,” Laser Photon. Rev.4(1), 21–41 (2010). [CrossRef]
  3. S. B. Mirov, V. V. Fedorov, D. V. Martyshkin, I. S. Moskalev, M. S. Mirov, and V. P. Gapontsev, “Progress in mid-IR Cr2+ and Fe2+ doped II-VI materials and lasers,” Opt. Mater. Express1(5), 898–910 (2011). [CrossRef]
  4. T. T. Basiev and S. B. Mirov, Room Temperature Tunable Colour Center Lasers (Laser Science and Technology) (Harwood Academic Publishers GmbH, 1994).
  5. T. T. Basiev, S. B. Mirov, and V. V. Osiko, “Room-temperature color center lasers,” IEEE J. Quantum Electron.24(6), 1052–1069 (1988). [CrossRef]
  6. S. B. Mirov and T. T. Basiev, “Progress in color center lasers,” IEEE J. Sel. Top. Quantum Electron.1(1), 22–30 (1995). [CrossRef]
  7. K. J. Teegarden and B. J. Thompson, Selected Papers on Color-Center Lasers (SPIE Press Book) (SPIE, 2003).
  8. F. Bonfigli, M. A. Vincenti, S. Almaviva, R. M. Montereali, E. Nichelatti, R. N. Nogueira, and H. J. Kalinowski, “Photo-induced gratings in thin color center layers on lithium fluoride,” Appl. Opt.48(31), G38–G43 (2009). [CrossRef] [PubMed]
  9. A. Rocchetti, G. Assanto, R. M. Montereali, E. Nichelatti, and F. Somma, “Color-center waveguides in low-energy electron-bombarded lithium fluoride,” Appl. Phys. Lett.88(26), 261111 (2006). [CrossRef]
  10. R. Montereali and M. Piccinini, “Optical gain of F2 color centres in LiF confining structures realised by electron-beam lithography,” Opt. Commun.209(1-3), 201–208 (2002). [CrossRef]
  11. G. Cheng, Y. Wang, J. He, G. Chen, and W. Zhao, “Color center conversion by femtosecond pulse laser irradiation in LiF:F2 crystals,” Opt. Express15(14), 8938–8942 (2007). [CrossRef] [PubMed]
  12. R. Montereali, S. Bigotta, M. Piccinini, M. Giammatteo, P. Picozzi, and S. Santucci, “Broad-band active channels induced by electron beam lithography in LiF films for waveguiding devices,” Nucl. Instrum. Methods Phys. Res. B166-167, 764–770 (2000). [CrossRef]
  13. F. Mollenauer and D. H. Olson, “Broadly tunable lasers using color centers,” J. Appl. Phys.46(7), 3109–3118 (1975). [CrossRef]
  14. D. V. Martyshkin, J. G. Parker, V. V. Fedorov, and S. B. Mirov, “Tunable distributed feedback color center laser using stabilized F2+** color centers in LiF crystal,” Appl. Phys. Lett.84(16), 3022–3024 (2004). [CrossRef]
  15. T. Kurobori, H. Hibino, Y. Q. Chen, and K. Inabe, “Distributed-feedback color center lasers using F2 centers in KCl,” Jpn. J. Appl. Phys.34(Part 2, No. 7B), L894–L896 (1995). [CrossRef]
  16. K. Kawamura, D. Takamizu, T. Kurobori, T. Kamiya, M. Hirano, and H. Hosono, “Nano-fabrication of optical devices in transparent dielectrics: volume gratings in SiO and DFB color center laser in LiF,” Nucl. Instrum. Methods Phys. Res. B218, 332–336 (2004). [CrossRef]
  17. M. Fox, Optical Properties of Solids (Oxford Master Series in Condensed Matter Physics) (Oxford Univ. Press, 2001).
  18. M. Montecchi, R. M. Montereali, and E. Nichelatti, “Refractive index modification from color centres in dielectric confining structures,” Opt. Mater.17(1–2), 347–350 (2001). [CrossRef]
  19. M. Montecchi, E. Nichelatti, A. Mancini, and R. M. Montereali, “Optical characterization of low-energy electron-beam-colored LiF crystals by spectral transmittance measurements,” J. Appl. Phys.86(7), 3745–3750 (1999). [CrossRef]
  20. K.-E. Peiponen and A. Vaittinen, “Light-induced refractive index change in some F coloured alkali halide crystals,” J. Phys. Chem.15(13), L415–L418 (1982).
  21. K. Peiponen and J. Riissanen, “On the linear and non-linear refractive index of F colour centres as a function of temperature,” J. Phys. Chem.17(31), 5617–5620 (1984).
  22. S. B. Mirov and T. T. Basiev, “Progress and trends in color center lasers,” Proc. SPIE2138, 248–262 (1994). [CrossRef]
  23. H. Nishihara, M. Haruna, and T. Suhara, Optical Integrated Circuits (McGraw-Hill, 1989).

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