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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 27 — Dec. 19, 2011
  • pp: 26810–26815
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Efficient 1645 nm continuous-wave and Q‑switched Er:YAG laser pumped by 1532 nm narrow-band laser diode

Liang Zhu, Mingjian Wang, Jun Zhou, and Weibiao Chen  »View Author Affiliations


Optics Express, Vol. 19, Issue 27, pp. 26810-26815 (2011)
http://dx.doi.org/10.1364/OE.19.026810


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Abstract

Energy transfer upconversion induced thermal effects are mainly responsible for the low efficiency of laser diode pumped Er:YAG lasers. The current work adopts Er:YAG rods with 0.25% Er3+ doping concentration, instead of the commonly used rods with 0.5% Er3+ doping concentration. Results show that the thermal effect is greatly alleviated. A continuous-wave output of 10.2 W is obtained using 31 W incident pump power. Optical–optical efficiency is approximately 33%. Slope efficiency, with respect to the absorbed pump power, is as high as 83%, which is close to the quantum efficiency. In a Q-switched operation, 7 mJ pulses with a pulse width of ~65 ns are obtained at 100 Hz PRF.

© 2011 OSA

1. Introduction

Multi-watt lasers emitting in the eye-safe band have important applications in many aspects, such as range finding, spectroscopy, Doppler wind lidar, and so on [1

1. Y. Liu, J. Liu, and W. Chen, “Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar,” Chin. Opt. Lett. 9(9), 090604–090607 (2011). [CrossRef]

,2

2. C. Gao, S. Zhu, W. Zhao, Z. Cao, and Z. Yang, “Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate,” Chin. Opt. Lett. 7(7), 611–613 (2009). [CrossRef]

]. One of the most promising eye-safe lasers, 1645 nm hybrid fiber-bulk erbium lasers, has been proven to be effective in achieving high output power and good beam quality [3

3. Y. E. Young, S. D. Setzler, K. J. Snell, P. A. Budni, T. M. Pollak, and E. P. Chicklis, “Efficient 1645-nm Er:YAG laser,” Opt. Lett. 29(10), 1075–1077 (2004). [CrossRef] [PubMed]

7

7. J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron. 15(2), 361–371 (2009). [CrossRef]

]. The best results were reported to be a 60 W output with a slope efficiency of 80% for a continuous-wave (CW) operation [5

5. D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm,” Opt. Lett. 31(6), 754–756 (2006). [CrossRef] [PubMed]

] and 30 mJ pulses with a pulse width less than 20 ns at 20 Hz PRF for a Q-switched operation [7

7. J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron. 15(2), 361–371 (2009). [CrossRef]

]. This two-step method, however, adds complexity, weight, and volume. In addition, the optical–optical efficiency of the two-step system is limited by the efficiency of the first step: 1532 nm fiber lasers pumped by 976 nm laser diodes (LDs). Consequently, only 28% optical–optical efficiency is achieved for the two-step system [5

5. D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm,” Opt. Lett. 31(6), 754–756 (2006). [CrossRef] [PubMed]

,7

7. J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron. 15(2), 361–371 (2009). [CrossRef]

].

Due to its simple structure and potential for relatively high optical–optical efficiency, room temperature LD-directly pumped 1645 nm Er:YAG lasers have been developed intensively in recent years [4

4. S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe erbium lasers,” IEEE J. Sel. Top. Quantum Electron. 11(3), 645–657 (2005). [CrossRef]

,8

8. D. Garbuzov, I. Kudryashov, and M. Dubinskii, “110W(0.9J) pulsed power from resonantly diode-laser-pumped 1.6-μm Er:YAG laser,” Appl. Phys. Lett. 87(12), 121101 (2005). [CrossRef]

10

10. N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express 18(13), 13673–13678 (2010). [CrossRef] [PubMed]

]. High efficiency is prevented by two serious problems. First, there is conflict between the broad bandwidth of LD (~10 nm [10

10. N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express 18(13), 13673–13678 (2010). [CrossRef] [PubMed]

]) and the narrow absorption bandwidth of Er:YAG crystals (~1 nm for the highest peak, around 1532 nm). Second, the energy transfer upconversion (ETU) induces a strong thermal effect.

Considering that Er:YAG has a relatively broader absorption bandwidth at around 1470 nm, compared with that at around 1532 nm, LDs lasing 1470 nm lasers are often used, although this method has lower quantum efficiency [4

4. S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe erbium lasers,” IEEE J. Sel. Top. Quantum Electron. 11(3), 645–657 (2005). [CrossRef]

,8

8. D. Garbuzov, I. Kudryashov, and M. Dubinskii, “110W(0.9J) pulsed power from resonantly diode-laser-pumped 1.6-μm Er:YAG laser,” Appl. Phys. Lett. 87(12), 121101 (2005). [CrossRef]

10

10. N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express 18(13), 13673–13678 (2010). [CrossRef] [PubMed]

]. CW operations with 0.5% Er3+ doped Er:YAG slab have obtained 6.1 W CW output with approximately 33 W incident pump power, resulting in an optical–optical efficiency of 19% [10

10. N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express 18(13), 13673–13678 (2010). [CrossRef] [PubMed]

]. One of the few studies [4

4. S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe erbium lasers,” IEEE J. Sel. Top. Quantum Electron. 11(3), 645–657 (2005). [CrossRef]

] on Q-switched operations pumped in this manner reported 38 mJ pulses with pulse widths of 60 ns, but the authors admitted that the pumping system used was highly inefficient.

Volumetric Bragg grating was used to obtain narrow-band 1470 and 1532 nm pump sources with a loss of less than 10%. By adopting the former, 80 W CW output was achieved with a 0.5% Er3+ doped Er:YAG slab [11

11. I. Kudryashov, A. Katsnelson, N. Ter-Gabrielyan, and M. Dubinskii, “Room temperature power scalability of the diode-pumped Er:YAG eye-safe laser,” in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optical Society of America, 2009), paper CWA2.

,12

12. I. Kudryashov, N. Ter-Gabrielyan, and M. Dubinskii, “Resonantly diode-pumped Er:YAG laser: 1470-nm vs. 1530-nm CW pumping case,” Proc. SPIE 7325, 732505 (2009). [CrossRef]

]. The maximum optical–optical efficiency for both pump sources was around 25%. Narrow-band 1532 nm LDs (less than 1 nm) have recently become commercially available, and they have been used as pump sources for Er:YAG lasers using 0.5% Er3+ doped conventional rod crystals [13

13. M. Eichhorn, “High-power resonantly diode-pumped CW Er3+:YAG laser,” Appl. Phys. B 93(4), 773–778 (2008). [CrossRef]

] and novel fiber-like crystals [14

14. S. Bigotta and M. Eichhorn, “Q-switched resonantly diode-pumped Er3+:YAG laser with fiberlike geometry,” Opt. Lett. 35(17), 2970–2972 (2010). [CrossRef] [PubMed]

] as gain media. In the latter work, 14.5 W CW output was obtained with approximately 42 W incident pump power, resulting in an optical–optical efficiency of approximately 35%. Q-switched pulses with 8 mJ pulse energy and 70 ns pulse width were also generated.

The current work investigates the performance of LD directly-pumped Er:YAG lasers with a 0.25% Er3+ doped Er:YAG rod. The results are compared with those of a 0.5% Er3+ doped Er:YAG rod with the same crystal length. The performance of the Q-switched 0.25% Er3+ doped Er:YAG rod is also studied and presented.

2. Experimental setup

3. Results and discussions

Improvements in the lasers with 0.25% doped rods can be attributed to three reasons. First, the ETU was alleviated by lower doping concentration. Thus, the energy waste caused by the ETU was reduced. Second, alleviation of the ETU resulted in less heat generation, thus lengthening the focal length of the thermal lens. This increased the spot size of the fundamental laser mode and reduced the pump areas mismatched by the laser modes. Therefore, the ETU was reduced further. Third, since the lower laser level was the upper Stark sub-level of 4I15/2 [7

7. J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron. 15(2), 361–371 (2009). [CrossRef]

], its population density decreased due to the decrease in the temperature of the 0.25% doped rods. Hence, the re-absorption loss is reduced.

Compared with the work by Chen et al., in which 74% of pump power was absorbed by a 0.25% doped, 4 cm rod [16

16. D. W. Chen, M. Birnbaum, P. M. Belden, T. S. Rose, and S. M. Beck, “Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues,” Opt. Lett. 34(10), 1501–1503 (2009). [CrossRef] [PubMed]

], the absorption of the pump power for the same rod in the current work was much lower (44.5%). The relatively broader bandwidth of the LD used (1 nm at maximum power) compared with the fiber laser (0.2 nm) in Ref. [16

16. D. W. Chen, M. Birnbaum, P. M. Belden, T. S. Rose, and S. M. Beck, “Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues,” Opt. Lett. 34(10), 1501–1503 (2009). [CrossRef] [PubMed]

] is one of the reasons for the lower pump power absorption, because the highest absorption peak of Er:YAG around 1532 nm is only approximately 1 nm. However, this alone does not explain the much lower absorption coefficient of the 0.25% doped rods compared with that the 0.5% doped rod in the current work. With incident power in a range of 0 to 31 W, the calculated average absorption coefficient of the 0.5% doped, 3 cm rod was approximately 3.5 times higher than that of the 0.25% doped, 3 cm rod. This may due to the varying extent of ETU in these two rods, because ETU will accelerate the recovery of the lower laser level population and, therefore, increase absorption. Additional work is required to understand this process better.

In the Q-switched operation, the 0.25% doped, 3 cm rod was chosen for its high slope efficiency and maximum output power. OCs with three different transmittances of 14%, 21%, and 30%, were used. No laser output was generated with the last transmittance. For the OC with a transmittance of 21%, only the performance under the short cavity length was obtained and recorded. The pulse energy and pulse width as a function of pulse repetition frequency (PRF) is shown in Figs. 3(a)
Fig. 3 Pulse energy (a) and pulse width (b) versus PRF in Q-switched operation.
and 3(b), respectively. Under 14% transmittance, 22 cm cavity length, and 8.2 W absorbed power, 7 mJ pulse with a pulse width of 65 ns was obtained.

Figure 4
Fig. 4 Comparison of output power between CW and Q-switched operation.
shows the average output power for both CW and Q-switched operations at T = 14% and L = 20 cm. The energy loss due to inefficient energy storage is negligible at 1 KHz PRF, but it becomes sufficiently strong at a PRF of less than 500 Hz.

4. Conclusion

Acknowledgment

We acknowledge Jiqiao Liu and Shuaiyi Zhang for their technical support and the Chinese Academy of Sciences Innovation Fund (Grant No: CXJJ-10-M50) for their financial support.

References and links

1.

Y. Liu, J. Liu, and W. Chen, “Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar,” Chin. Opt. Lett. 9(9), 090604–090607 (2011). [CrossRef]

2.

C. Gao, S. Zhu, W. Zhao, Z. Cao, and Z. Yang, “Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate,” Chin. Opt. Lett. 7(7), 611–613 (2009). [CrossRef]

3.

Y. E. Young, S. D. Setzler, K. J. Snell, P. A. Budni, T. M. Pollak, and E. P. Chicklis, “Efficient 1645-nm Er:YAG laser,” Opt. Lett. 29(10), 1075–1077 (2004). [CrossRef] [PubMed]

4.

S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe erbium lasers,” IEEE J. Sel. Top. Quantum Electron. 11(3), 645–657 (2005). [CrossRef]

5.

D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm,” Opt. Lett. 31(6), 754–756 (2006). [CrossRef] [PubMed]

6.

K. Spariosu, V. Leyva, R. A. Reeder, and M. J. Klotz, “Efficient Er:YAG laser operating at 1645 nm and 1617 nm,” IEEE J. Quantum Electron. 42(2), 182–186 (2006). [CrossRef]

7.

J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron. 15(2), 361–371 (2009). [CrossRef]

8.

D. Garbuzov, I. Kudryashov, and M. Dubinskii, “110W(0.9J) pulsed power from resonantly diode-laser-pumped 1.6-μm Er:YAG laser,” Appl. Phys. Lett. 87(12), 121101 (2005). [CrossRef]

9.

I. Kudryashov and A. Katsnelson, “Q-switch resonantly diode-pumped Er:YAG laser,” Proc. SPIE 7578, 75781D (2009).

10.

N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express 18(13), 13673–13678 (2010). [CrossRef] [PubMed]

11.

I. Kudryashov, A. Katsnelson, N. Ter-Gabrielyan, and M. Dubinskii, “Room temperature power scalability of the diode-pumped Er:YAG eye-safe laser,” in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optical Society of America, 2009), paper CWA2.

12.

I. Kudryashov, N. Ter-Gabrielyan, and M. Dubinskii, “Resonantly diode-pumped Er:YAG laser: 1470-nm vs. 1530-nm CW pumping case,” Proc. SPIE 7325, 732505 (2009). [CrossRef]

13.

M. Eichhorn, “High-power resonantly diode-pumped CW Er3+:YAG laser,” Appl. Phys. B 93(4), 773–778 (2008). [CrossRef]

14.

S. Bigotta and M. Eichhorn, “Q-switched resonantly diode-pumped Er3+:YAG laser with fiberlike geometry,” Opt. Lett. 35(17), 2970–2972 (2010). [CrossRef] [PubMed]

15.

J. W. Kim, J. I. Mackenzie, and W. A. Clarkson, “Influence of energy-transfer-upconversion on threshold pump power in quasi-three-level solid-state lasers,” Opt. Express 17(14), 11935–11943 (2009). [CrossRef] [PubMed]

16.

D. W. Chen, M. Birnbaum, P. M. Belden, T. S. Rose, and S. M. Beck, “Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues,” Opt. Lett. 34(10), 1501–1503 (2009). [CrossRef] [PubMed]

17.

N. P. Barnes, “Solid-state lasers from an efficiency perspective,” IEEE J. Sel. Top. Quantum Electron. 13(3), 435–447 (2007). [CrossRef]

18.

S. A. Payne, L. L. Chase, L. K. Smith, W. L. Kway, and W. F. Krupke, “Infrared cross-section measurements for crystals doped with Er3+, Tm3+, and Ho3+,” IEEE J. Quantum Electron. 28(11), 2619–2630 (1992). [CrossRef]

19.

M. Eichhorn, “Numerical modeling of diode-end-pumped high-power Er3+:YAG lasers,” IEEE J. Quantum Electron. 44(9), 803–810 (2008). [CrossRef]

OCIS Codes
(140.3480) Lasers and laser optics : Lasers, diode-pumped
(140.3500) Lasers and laser optics : Lasers, erbium
(140.3540) Lasers and laser optics : Lasers, Q-switched
(140.3580) Lasers and laser optics : Lasers, solid-state
(140.3613) Lasers and laser optics : Lasers, upconversion

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: August 11, 2011
Revised Manuscript: November 15, 2011
Manuscript Accepted: December 2, 2011
Published: December 15, 2011

Citation
Liang Zhu, Mingjian Wang, Jun Zhou, and Weibiao Chen, "Efficient 1645 nm continuous-wave and Q‑switched Er:YAG laser pumped by 1532 nm narrow-band laser diode," Opt. Express 19, 26810-26815 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-27-26810


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References

  1. Y. Liu, J. Liu, and W. Chen, “Eye-safe, single-frequency pulsed all-fiber laser for Doppler wind lidar,” Chin. Opt. Lett.9(9), 090604–090607 (2011). [CrossRef]
  2. C. Gao, S. Zhu, W. Zhao, Z. Cao, and Z. Yang, “Eye-safe, high-energy, single-mode all-fiber laser with widely tunable repetition rate,” Chin. Opt. Lett.7(7), 611–613 (2009). [CrossRef]
  3. Y. E. Young, S. D. Setzler, K. J. Snell, P. A. Budni, T. M. Pollak, and E. P. Chicklis, “Efficient 1645-nm Er:YAG laser,” Opt. Lett.29(10), 1075–1077 (2004). [CrossRef] [PubMed]
  4. S. D. Setzler, M. P. Francis, Y. E. Young, J. R. Konves, and E. P. Chicklis, “Resonantly pumped eyesafe erbium lasers,” IEEE J. Sel. Top. Quantum Electron.11(3), 645–657 (2005). [CrossRef]
  5. D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Highly efficient in-band pumped Er:YAG laser with 60 W of output at 1645 nm,” Opt. Lett.31(6), 754–756 (2006). [CrossRef] [PubMed]
  6. K. Spariosu, V. Leyva, R. A. Reeder, and M. J. Klotz, “Efficient Er:YAG laser operating at 1645 nm and 1617 nm,” IEEE J. Quantum Electron.42(2), 182–186 (2006). [CrossRef]
  7. J. W. Kim, D. Y. Shen, J. K. Sahu, and W. A. Clarkson, “Fiber-laser-pumped Er:YAG lasers,” IEEE J. Sel. Top. Quantum Electron.15(2), 361–371 (2009). [CrossRef]
  8. D. Garbuzov, I. Kudryashov, and M. Dubinskii, “110W(0.9J) pulsed power from resonantly diode-laser-pumped 1.6-μm Er:YAG laser,” Appl. Phys. Lett.87(12), 121101 (2005). [CrossRef]
  9. I. Kudryashov and A. Katsnelson, “Q-switch resonantly diode-pumped Er:YAG laser,” Proc. SPIE7578, 75781D (2009).
  10. N. W. H. Chang, N. Simakov, D. J. Hosken, J. Munch, D. J. Ottaway, and P. J. Veitch, “Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm,” Opt. Express18(13), 13673–13678 (2010). [CrossRef] [PubMed]
  11. I. Kudryashov, A. Katsnelson, N. Ter-Gabrielyan, and M. Dubinskii, “Room temperature power scalability of the diode-pumped Er:YAG eye-safe laser,” in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, OSA Technical Digest (CD) (Optical Society of America, 2009), paper CWA2.
  12. I. Kudryashov, N. Ter-Gabrielyan, and M. Dubinskii, “Resonantly diode-pumped Er:YAG laser: 1470-nm vs. 1530-nm CW pumping case,” Proc. SPIE7325, 732505 (2009). [CrossRef]
  13. M. Eichhorn, “High-power resonantly diode-pumped CW Er3+:YAG laser,” Appl. Phys. B93(4), 773–778 (2008). [CrossRef]
  14. S. Bigotta and M. Eichhorn, “Q-switched resonantly diode-pumped Er3+:YAG laser with fiberlike geometry,” Opt. Lett.35(17), 2970–2972 (2010). [CrossRef] [PubMed]
  15. J. W. Kim, J. I. Mackenzie, and W. A. Clarkson, “Influence of energy-transfer-upconversion on threshold pump power in quasi-three-level solid-state lasers,” Opt. Express17(14), 11935–11943 (2009). [CrossRef] [PubMed]
  16. D. W. Chen, M. Birnbaum, P. M. Belden, T. S. Rose, and S. M. Beck, “Multiwatt continuous-wave and Q-switched Er:YAG lasers at 1645 nm: performance issues,” Opt. Lett.34(10), 1501–1503 (2009). [CrossRef] [PubMed]
  17. N. P. Barnes, “Solid-state lasers from an efficiency perspective,” IEEE J. Sel. Top. Quantum Electron.13(3), 435–447 (2007). [CrossRef]
  18. S. A. Payne, L. L. Chase, L. K. Smith, W. L. Kway, and W. F. Krupke, “Infrared cross-section measurements for crystals doped with Er3+, Tm3+, and Ho3+,” IEEE J. Quantum Electron.28(11), 2619–2630 (1992). [CrossRef]
  19. M. Eichhorn, “Numerical modeling of diode-end-pumped high-power Er3+:YAG lasers,” IEEE J. Quantum Electron.44(9), 803–810 (2008). [CrossRef]

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