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Optics Express

Optics Express

  • Editor: J. H. Eberly
  • Vol. 8, Iss. 10 — May. 7, 2001
  • pp: 585–589
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Spectroscopic properties of lead fluoroborate glasses doped with ytterbium

Luciana R. P. Kassab, Sonia H. Tatumi, Alessandro S. Morais, Lilia C. Courrol, Niklaus U. Wetter, and V. L. R. Salvador  »View Author Affiliations


Optics Express, Vol. 8, Issue 10, pp. 585-589 (2001)
http://dx.doi.org/10.1364/OE.8.000585


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Abstract

A new lead fluoroborate glass (PbO-PbF2-B2O3) doped with ytterbium (Yb:PbFB) is presented. Samples with different concentrations of Yb3+ were produced and had their emission cross-sections, fluorescence lifetimes and minimum pump intensities determined. They have high refractive index of 2.2 and a density of 4.4 g/cm3. For a doping level of 1.153×1020 ions/cm3, the fluorescence lifetime, after excitation at 968 nm, is 0.81 ms, which is comparable to Yb:tellurite laser glass. Also, an emission band at 1022 nm is measured with emission cross-section of approximately 1.07×10-20 cm2 and fluorescence effective linewidth of 60 nm, which is comparable to Yb:phosphate laser glass.

© Optical Society of America

1. Introduction

Only recently, studies of lead oxyfluoride (PbO-PbF2) [9

9. P. Nachimuthu, R. Jagannathan, V. N. Kumar, and D. N. Rao, “Absorption and emission spectral studies of Sm3+ and Dy3+ ions in PbO-PbF2 glasses,” J. Non-Cryst. Solids 217, 215–223 (1997). [CrossRef]

] and lead borate glasses (PbO-B2O3) [10

10. M. B. Saisudha and J. Ramakrishna, “Effect of host glass on the optical absorption properties of Nd3+, Sm3+, and Dy3+ in lead borate glasses,” Phys. Rev. B 53, 6186–6196 (1995). [CrossRef]

] doped with rare-earth were reported. In this paper, we present optical and physical properties of a new lead fluoroborate glass (PbO-PbF2-B2O3), doped with different concentrations of ytterbium (Yb:PbFB), produced at the Laboratory of Glasses and Datation of the Faculty of Technology of São Paulo. The optical and physical properties were determined by means of absorption, luminescence and its associated lifetime, refractive index and density measurements. Calculations of spontaneous emission probability and emission cross-sections were performed.

2. Experimental Procedure

The glasses presented in this work are prepared with 99.99% pure elements (all products from Fluka and Aldrich). Different concentrations of Yb2O3 (0.5 to 2.0 mol%) were added to the following glass matrix: (mol%) 43.5H3BO3 - 22.5PbCO3 - 34.0PbF2. They are melted in air at 1000 °C for approximately one hour and a half, using alumina crucibles. Next, the melt is poured into pre-heated brass molds for a quick solidification and then annealed at 400 °C (below the glass transition temperature) for 12 h. Yellow colored, transparent and homogeneous samples were obtained. Glass samples with two polished faces and 3 mm thickness are used for refractive index, absorption, emission and lifetime measurements. Specimen surfaces must be polished, flat and parallel. We used a Carl Zeiss microscope with a 10x objective lens to measure the refractive index. The refractive index of 2.2 was determined by means of the “apparent depth method” [11

11. F. Donald Bloss, An Introduction to the Methods of Optical Crystallography, (Holt, Rinehart and Winston, Inc, USA, 1961).

]. This method relates the physical thickness of a transparent specimen to its optical thickness (apparent thickness). The absorption spectra were measured using a Carry Spectrometer in the range 920–1120 nm at room temperature. The emission spectra were obtained by exciting the samples with a GaAlAs laser diode (Optopower A020) at 968 nm. This diode system contains a broad area semiconductor laser with a maximum of 20 W of continuous output power operating at 964 nm. The diode laser beam is treated with a beamshaper [12

12. N. U. Wetter, “High Efficiency Pumping Scheme for Diode Bars” in Proceedings of the 2000 Conference on Lasers and Electro-Optics (Technical Digest. European Physical Society -Mulhouse, Nice, 2000), pp. 60–61.

] and focused by a single f=5 cm lens. Close to the focus, and for a depth of focus of 2 mm, the beam has a rectangular profile, with transverse dimensions of approximately 260×260 µm. During the emission measurements, the sample is pumped by the diode laser beam, chopped at 40 Hz with 7.5 W, of diode output power, and focused onto the sample with a lens of 5 cm focal length. The emission from the sample is analyzed with a 0.5 m monochrometer (Spex) and a Germanium detector. The signal was intensified with an EG&G7220 lock-in amplifier and processed by a computer. The lifetimes of excited Yb3+ ions are measured using a pulsed laser excitation (4 ns) from an OPO pumped by a frequency doubled Nd:YAG laser (Quantel). The signal is detected by a fast S-20 extended type photomultiplier detector and analyzed using a signal processing Box-Car averager (PAR 4402). The density, of 4.4 g/cm3 was measured with the Archimedes method. The concentration of Yb3+ ions (as well as the other compounds of the glass) were determined by the X-ray Fluorescent Spectrometry with wavelength dispersion (resolution of ±0.01) and used to determine the absorption cross-section.

3. Results

Figure 1 presents the absorption spectrum for the sample doped with 1.153x1020 ions/cm3 of Yb3+, with 3 mm thickness, in order to show the optical transparency. Figure 2 shows absorption and emission cross-section spectra of all the samples produced.

Fig 1. Absorption spectrum for the lead fluoroborate glass (3 mm thickness) doped with 1.153x1020 ions/cm3 of Yb3+.

The fluorescence lifetimes measured (τf) are shown in Table 1. The highest value is 0.81 ms for the sample doped with 1.153×1020 ions/cm3 of Yb3+ and, as the concentration increases, the lifetime shortens gradually. The spontaneous emission probability (AR), presented in Table 1, and the emission cross-section (σem), shown in Figure 2, are calculated using the equations [5

5. X. Zou and H. Toratani, “Evaluation spectroscopic properties of Yb3+ doped glasses,” Phys. Rev. B 52, 15889–15897 (1995). [CrossRef]

] that follow:

AR=8πcn2(2J+1)λp4(2J+1)ρk(λ)dλ
(1)
σem(λ)=λ4ARg(λ)8πn2c
(2)

where c represents the velocity of light, n the refractive index, λp the absorption peak wavelength, ρ the concentration of Yb3+ ions, k(λ) the absorption coefficient, J′ and J the total momentum for the upper and lower levels and g(λ) the normalized line shape function of the fluorescence transition of Yb3+. Also seen in Table 1 is Δλeff, the fluorescence effective linewidth.

Fig 2. Absorption and emission cross-section spectra for lead fluoroborate glasses doped with Yb3+ for excitation at 968 nm.

Table 1:. Spectroscopic properties of Yb3+ doped lead fluoroborate glasses.

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From the point of view of laser operation, it is generally desirable for the emission cross-section to be as large as possible to provide for high gain and for the fluorescence lifetime to be long in order to permit high pulsed power.

Based on the considerations above, we come to the conclusion, that the sample with the best spectroscopic properties for a laser material is the one with 1.153×1020 ions/cm3 of Yb3+ (Table 1). The spectroscopic data of this sample are comparable to some Yb3+ doped laser glasses: Yb:YTG glass (a tellurite laser glass) has a fluorescence lifetime of 0.9 ms [6

6. C. Jiang, F. Gan, J. Zhang, P. Deng, and G. Huang, “Yb:tellurite laser glass with high emission cross-section,” Materials Letters 41, 209–214 (1999). [CrossRef]

]; Yb:PNK glass (a phosphate laser glass) has an emission cross-section of 1.08×10-20 cm2 [7

7. C. Jiang, H. Liu, Q. Zeng, X. Tang, and F. Gan, “Yb:phosphate laser glass with high emission cross-section,” J. Chem. and Phys. of Solids 61, 1217–1223 (2000). [CrossRef]

]; the product of τf.σem is 0.60×10-20 cm2ms in Yb:FP glass (a fluorophosphate laser glass) [13

13. V. Petrov, U. Griebner, D. Ehrt, and W. Seeber, “Femtosecond self mode locking of Yb:fluoride phosphate glass laser,” Opt. Lett. 22, 408–410 (1997). [CrossRef] [PubMed]

]. A complete comparison is given in Table 2 where the spectroscopic properties of some phosphate (QX,ADY,LY,PN,PNK), fluorophosphate (FP) and tellurite (YTG) laser glasses, reported in published papers [6

6. C. Jiang, F. Gan, J. Zhang, P. Deng, and G. Huang, “Yb:tellurite laser glass with high emission cross-section,” Materials Letters 41, 209–214 (1999). [CrossRef]

,7

7. C. Jiang, H. Liu, Q. Zeng, X. Tang, and F. Gan, “Yb:phosphate laser glass with high emission cross-section,” J. Chem. and Phys. of Solids 61, 1217–1223 (2000). [CrossRef]

,13

13. V. Petrov, U. Griebner, D. Ehrt, and W. Seeber, “Femtosecond self mode locking of Yb:fluoride phosphate glass laser,” Opt. Lett. 22, 408–410 (1997). [CrossRef] [PubMed]

,14

14. R. Koch et al., “Efficient room temperature cw Yb:glass laser pumped by a 946 nm Nd:YAG laser,” Optics Communications 134, 175–178 (1997). [CrossRef]

], are compared with lead fluoroborate glass, doped with 1.153×1020 ions/cm3 of Yb3+. Table 2 also presents the minimum pump intensity (Imin=1.69 kW/cm2), which is a measure for the ease of pumping the laser material, in an otherwise lossless oscillator, calculated by the following equation [15

15. L. D. Deloach, S. A. Payne, L. Smith, W. L. Kway, and W. F. Krupke, “Laser and spectroscopic properties of Sr5 (PO4)3 F:YB,” J. Opt. Soc. Am. B 11, 269–276 (1994). [CrossRef]

]:

Imin=βminIsat
(3)

where:

β=σabs(λ0)σem(λ0)+σabs(λ0)Isat=hcλpτfσabs(λp)

where σabs(λ0)=0.22×10-20 cm2 and σem(λ0)=1.07×10-20 cm2 are the absorption and the emission cross-sections, respectively, at the extraction wavelength (λ0=1022 nm); σabs(λp)=2.56×10-20 cm2 is the absorption cross-section at the laser pump wavelength (λp=968 nm) and Isat=9.9 kW/cm2 is the pump saturation intensity. The βmin=0.1705 parameter addresses the fact that Yb3+ doped materials are of quasi-four-level nature and suffer from ground-state absorption.

Table 2:. Spectroscopic properties of some laser glasses and the YAG crystal doped with Yb3+ [6,7,13,14,15].

table-icon
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It can be seen from above table, that PbFB has similar Imin as the well known laser materials YAG [15

15. L. D. Deloach, S. A. Payne, L. Smith, W. L. Kway, and W. F. Krupke, “Laser and spectroscopic properties of Sr5 (PO4)3 F:YB,” J. Opt. Soc. Am. B 11, 269–276 (1994). [CrossRef]

] and QX [7

7. C. Jiang, H. Liu, Q. Zeng, X. Tang, and F. Gan, “Yb:phosphate laser glass with high emission cross-section,” J. Chem. and Phys. of Solids 61, 1217–1223 (2000). [CrossRef]

,14

14. R. Koch et al., “Efficient room temperature cw Yb:glass laser pumped by a 946 nm Nd:YAG laser,” Optics Communications 134, 175–178 (1997). [CrossRef]

].

4. Conclusion

A new lead fluoroborate glass doped with different concentrations of ytterbium is presented. The samples exhibited a very good mechanical resistance under high-brightness diode laser pumping. The one with the best spectroscopic properties, doped with 1.153×1020 ions/cm3 of Yb3+, has fluorescence lifetime of 0.81 ms, emission cross-section of 1.07×10-20 cm2 at 1022 nm, fluorescence effective linewidth of 60 nm, high absorption cross-section of 2.56×10-20 cm2 at 968 nm, and Imin=1.69 kW/cm2. This new glass has very similar properties when compared to other known glasses which are also used as active laser media. These features make it a good candidate for laser action.

Acknowledgments

We would like to thank the support from Fundação de Amparo à Pesquisa do Estado de São Paulo.

References and links

1.

J. Nees et al., “Ensuring compactness, reliability and scalability for the next generation of high-field laser,” J. Quant. Electron 4, 376–384 (1998).

2.

A. Diening, P. E. A. Mobert, and G. Huber, “Diode pumping continuous wave, quasi-continuous-wave, and Q-switched laser operation of Yb,Tm:YLFB at 1.5 and 2.3 µm,” J. Appl. Phys. 84, 5900–5904(1998). [CrossRef]

3.

B. R. Judd, “Optical Absorption Intensities of Rare-Earth Ions,” Phys. Rev. 127, 750–761(1962). [CrossRef]

4.

G. S. Ofelt, “Intensities of Crystal Spectra of Rare-Earth Ions,” J. Chem. Phys. 37, 511–520 (1962). [CrossRef]

5.

X. Zou and H. Toratani, “Evaluation spectroscopic properties of Yb3+ doped glasses,” Phys. Rev. B 52, 15889–15897 (1995). [CrossRef]

6.

C. Jiang, F. Gan, J. Zhang, P. Deng, and G. Huang, “Yb:tellurite laser glass with high emission cross-section,” Materials Letters 41, 209–214 (1999). [CrossRef]

7.

C. Jiang, H. Liu, Q. Zeng, X. Tang, and F. Gan, “Yb:phosphate laser glass with high emission cross-section,” J. Chem. and Phys. of Solids 61, 1217–1223 (2000). [CrossRef]

8.

M. J. Weber, J. E. Lynch, D. H. Blackburn, and D. J. Cronin, “Dependence of the stimulated emission cross-section of Yb3+ on host glass composition, ” IEE J. Quantum Electron 19, 1600–1608 (1983). [CrossRef]

9.

P. Nachimuthu, R. Jagannathan, V. N. Kumar, and D. N. Rao, “Absorption and emission spectral studies of Sm3+ and Dy3+ ions in PbO-PbF2 glasses,” J. Non-Cryst. Solids 217, 215–223 (1997). [CrossRef]

10.

M. B. Saisudha and J. Ramakrishna, “Effect of host glass on the optical absorption properties of Nd3+, Sm3+, and Dy3+ in lead borate glasses,” Phys. Rev. B 53, 6186–6196 (1995). [CrossRef]

11.

F. Donald Bloss, An Introduction to the Methods of Optical Crystallography, (Holt, Rinehart and Winston, Inc, USA, 1961).

12.

N. U. Wetter, “High Efficiency Pumping Scheme for Diode Bars” in Proceedings of the 2000 Conference on Lasers and Electro-Optics (Technical Digest. European Physical Society -Mulhouse, Nice, 2000), pp. 60–61.

13.

V. Petrov, U. Griebner, D. Ehrt, and W. Seeber, “Femtosecond self mode locking of Yb:fluoride phosphate glass laser,” Opt. Lett. 22, 408–410 (1997). [CrossRef] [PubMed]

14.

R. Koch et al., “Efficient room temperature cw Yb:glass laser pumped by a 946 nm Nd:YAG laser,” Optics Communications 134, 175–178 (1997). [CrossRef]

15.

L. D. Deloach, S. A. Payne, L. Smith, W. L. Kway, and W. F. Krupke, “Laser and spectroscopic properties of Sr5 (PO4)3 F:YB,” J. Opt. Soc. Am. B 11, 269–276 (1994). [CrossRef]

OCIS Codes
(140.3380) Lasers and laser optics : Laser materials
(300.6360) Spectroscopy : Spectroscopy, laser

ToC Category:
Research Papers

History
Original Manuscript: March 7, 2001
Published: May 7, 2001

Citation
Luciana Kassab, Sonia Tatumi, Alessandro Morais, Lilia Courrol, Niklaus Wetter, and V. Salvador, "Spectroscopic properties of lead fluoroborate glasses doped with ytterbium," Opt. Express 8, 585-589 (2001)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-8-10-585


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References

  1. J. Nees et al., "Ensuring compactness, reliability and scalability for the next generation of high-field laser," J. Quant. Electron 4, 376-384 (1998).
  2. A. Diening, P. E. A. Mobert and G. Huber, "Diode pumping continuous wave, quasi-continuous-wave, and Q-switched laser operation of Yb,Tm:YLFB at 1.5 and 2.3 mm," J. Appl. Phys. 84, 5900 -5904(1998). [CrossRef]
  3. B. R. Judd, "Optical Absorption Intensities of Rare-Earth Ions," Phys. Rev. 127, 750- 761(1962). [CrossRef]
  4. G. S. Ofelt, "Intensities of Crystal Spectra of Rare-Earth Ions," J. Chem. Phys. 37, 511-520 (1962). [CrossRef]
  5. X. Zou, H. Toratani, "Evaluation spectroscopic properties of Yb3+ doped glasses," Phys. Rev. B 52, 15889-15897 (1995). [CrossRef]
  6. C. Jiang, F. Gan, J. Zhang, P. Deng, G. Huang, "Yb:tellurite laser glass with high emission cross-section," Materials Letters 41, 209-214 (1999). [CrossRef]
  7. C. Jiang, H. Liu, Q. Zeng, X. Tang, F. Gan, "Yb:phosphate laser glass with high emission cross-section," J. Chem. and Phys. of Solids 61, 1217-1223 (2000). [CrossRef]
  8. M. J. Weber, J. E. Lynch, D. H. Blackburn, D. J. Cronin, "Dependence of the stimulated emission cross-section of Yb3+ on host glass composition," IEE J. Quantum Electron 19, 1600-1608 (1983). [CrossRef]
  9. P. Nachimuthu, R. Jagannathan, V. N. Kumar, D. N. Rao, "Absorption and emission spectral studies of Sm3+ and Dy3+ ions in PbO-PbF2 glasses," J. Non-Cryst. Solids 217, 215-223 (1997). [CrossRef]
  10. M. B. Saisudha, J. Ramakrishna, "Effect of host glass on the optical absorption properties of Nd3+, Sm3+, and Dy3+ in lead borate glasses," Phys. Rev. B 53, 6186-6196 (1995). [CrossRef]
  11. F.Donald Bloss, An Introduction to the Methods of Optical Crystallography, (Holt, Rinehart and Winston, Inc, USA, 1961).
  12. N. U. Wetter, "High Efficiency Pumping Scheme for Diode Bars" in Proceedings of the 2000 Conference on Lasers and Electro-Optics (Technical Digest. European Physical Society -Mulhouse, Nice, 2000), pp. 60-61.
  13. V. Petrov, U. Griebner, D. Ehrt, W. Seeber, "Femtosecond self mode locking of Yb:fluoride phosphate glass laser," Opt. Lett. 22, 408-410 (1997). [CrossRef] [PubMed]
  14. R. Koch et al., "Efficient room temperature cw Yb:glass laser pumped by a 946 nm Nd:YAG laser," Optics Communications 134, 175-178 (1997). [CrossRef]
  15. L. D. Deloach, S. A . Payne, L. Smith, W. L. Kway, W. F. Krupke, "Laser and spectroscopic properties of Sr5 (PO4 )3 F:YB," J. Opt. Soc. Am. B 11, 269-276 (1994). [CrossRef]

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