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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 13, Iss. 4 — Feb. 21, 2005
  • pp: 1085–1089
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Gain-switched Tm3+-doped double-clad silica fiber laser

Yun-Jun Zhang, Bao-Quan Yao, You-Lun Ju, and Yue-Zhu Wang  »View Author Affiliations


Optics Express, Vol. 13, Issue 4, pp. 1085-1089 (2005)
http://dx.doi.org/10.1364/OPEX.13.001085


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Abstract

A gain-switched Tm-doped double-clad silica fiber laser operating at a wavelength of approximately 2µm with moderate output energy of 14.7mJ per pulse and a slope efficiency of 39.5% (with respect to launched pump energy) is realized pumped at 1.064µm from a Nd:YAG laser. The gain-switched fiber laser pulses are built up by a series of relaxation spikes, and every spike pulse duration is nearly 1µs. The output wavelength becomes longer, and the slope efficiency increases with the increase in fiber length.

© 2005 Optical Society of America

1. Introduction

Rare-earth-doped fiber lasers offer an excellent combination of high efficiency and spatial beam quality. In many applications there is a requirement of short high peak-power pulses as sources for distributed and remote gas sensing [1

1. H. Tai, K. Yamamoto, and M. Uchida, “Long-distance simultaneous detection of methane and acetylene by using diode lasers coupled with optical fibers,” IEEE Photon. Technol. Lett. 4, 804–807 (1992). [CrossRef]

]. In the 2µm spectral region, the damage threshold of the human eye is high (about 1J/cm2), and lasers operating in that wavelength range are considered eye-safe and find practical application in laser range finding and eye-safe lidar, surgery in medicine, ultra-low-loss long-span communications, nonlinear-frequency conversion applications, long-distance optical time-domain reflectometry, and heterodyne detection applications[2

2. Ashraf F. El-Sherif and Terence A. King, “Analysis and Optimization of Q-Switched Operation of a Tm3+-Doped silica Fiber Laser Operating at 2µm,” IEEE J. Quantum Electron. 39, 759–765 (2003). [CrossRef]

].

Q-switched Tm3+-doped silica fiber lasers generate high-peak-power and relatively long-duration pulses, ranging from 100 ns to several hundred nanoseconds [3

3. P. S. Golding, S. D. Jackson, and P.-K. Tsai, “Efficient high power operation of a Tm-doped silica fiber laser pumped at 1.319µm,” Opt. Commun. 175, 179–183 (2000). [CrossRef]

5

5. Ashraf F. El-Sherif and Terence A. King, “High-peak-power operation of a Q-switched Tm3+-doped silica fiber laser operating near 2µm,” Opt. Lett. 28, 22–24 (2003). [CrossRef] [PubMed]

]. Mode-locked Q-switched Tm3+-doped silica fiber lasers can generate high-peak-power, high repetition frequency, and short-duration pulses of several hundred femtoseconds [6

6. LE. Nelson, E. P. Ippen, and H. A. Haus, “Broadly tunable sub-500 fs pulses from an additive-pulse mode-locked thulium-doped fiber ring laser,” Appl. Phy. Lett. 67, 19–21 (1995). [CrossRef]

,7

7. R. C. Sharp, D. E. Spock, and N. Pan, “190-fs passively mode-lock thulium fiber laser with a low threshold,” Opt. Lett. 21, 881–883 (1996). [CrossRef] [PubMed]

]. The pulse energy from the fiber laser is limited by power density considerations, and the intra-cavity elements used in the systems make the laser cavity complex. Gain-switched fiber lasers are convenient to use as pulse pump sources. For applications requiring a few hundred nanoseconds pulse duration in the 2µm spectral region, a feasible solution is use of gain-switched Tm3+-doped silica fiber lasers [8

8. B. C. Dickinson, S. D. Jackson, and T. A. King, “10mJ total output from a gain-switched Tm-doped fiber laser,” Opt. Commun. 182, 199–203 (2000). [CrossRef]

,9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

]. The goal of this investigation is to examine the characteristics of the gain-switched Tm3+-doped double-clad silica fiber lasers pumped at 1.064µm.

2. Experiments

The absorption section of Tm3+-doped silica fiber at 1.064µm is 1.2×10-26 m2[9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

], but the absorption section of Tm3+-doped silica fiber at 790nm is 5×10-25 m2[10

10. Jianqiu Xu, Mahendra Prabhu, Jianren Lu, and Ken-ichi Ueda, “Efficient double-clad thulium-doped fiber laser with a ring cavity,” Appl. Opt. 40, 1983–1988 (2001). [CrossRef]

]. Pumped at 1.064µm region, the Tm3+-doped fiber lasers use single-clad silica fiber, for example, CW output powers generates >1W at slope efficiencies of 37%[11

11. D. C. Hanna, I. R. Pery, and J. R. Lincoln, “1-watt thulium doped CW fiber laser operation at 2-µm,” Opt. Commun. 80, 52–56 (1990). [CrossRef]

] and gain-switched pulse output generates 1.5mJ per pulse at slope efficiencies of 20%[9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

]. Another major drawback pumped at 1.064µm is the strong pump ESA present. Pumped photons are absorbed from the 3F4 and 3H4 levels to the 3F2,3 and 1G4 energy levels (the absorption section is 3.2×10-25 m2 and 3.0×10-25 m2 respectively, and see the simplified energy level diagram in Fig. 1) [9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

].

Fig. 1. Simplified energy level diagram of the six lowest energy of Tm3+ showing the relevant cross sections, pump and laser transitions.

As we know, this investigation is the first time to examine the gain-switched Tm3+-doped double-clad silica fiber lasers pumped at 1.064µm. In order to increase the absorption ratio of pumping laser pulse energy, we use a relatively long fiber.1 (35m, our fiber maximum length), a fiber.2 (8m), and a short fiber.3 (1m) which is used to be contrasted. The Tm3+-doped double-clad silica fiber is purchased from OFTC of Australian Photonics. Its core diameter is 18µm with a NA 0.158. The inner-clad diameter is 300µm with a shape of D and NA 0.37. The Tm3+-doped concentration is 1.3wt.% in the fiber core. The fiber has an effective absorption coefficient ~0.008m-1 (calculated according to [16

16. Stuart D. Jackson and Simon Mossman, “Efficiency dependence on the Tm3+ and Al3+ concentrations for Tm3+-doped silica double-clad fiber lasers,” Appl. Opt. 42, 2702–2707 (2003). [CrossRef] [PubMed]

]) at 1.064µm. The Nd:YAG pump laser pulse duration is ~100µs, and pumped with a single frequency flashlamp. The maximum total output energy is nearly 100mJ per pulse. No attempts are made to restrict oscillation to TEM00 and hence the laser output is quite multimode.

In the experiment, shown schematically in Fig. 2., the cavity uses Fresnel reflections from the cleaved ends of the fiber as feedback. A dichronic (R>90 at 1.064µm and T>99 at 1.8~2.1µm) butts to the distal end of the fiber, so the unabsorbed pump laser energy can be reflected to the fiber once more and the reflection is <0.1% at 1.8~2.1µm. With a lens f=50mm, the coupling efficiency can reach >50%. When the coupling position is best adjusted, the 467nm blue fluorescence associated with spontaneous emission from 1G4 energy level is visible.

Fig. 2. Experimental setup of gain-switched Tm3+-doped double-clad silica fiber lasers.

3. Results and discussion

Fig. 3. Measured temporal characteristics from the 8-m-long gain-switched fiber laser which has 59mJ launched. The CH2 is the output laser pulse and the CH1 is the pump pulse.
Fig. 4. Measured output laser pulse temporal characteristics from the 8-m-long gain-switched fiber laser which has 59mJ launched.
Fig. 5. Measured temporal characteristics from the 35-m-long gain-switched fiber laser which has 59mJ launched. The CH2 is the output laser pulse and the CH1 is the pump pulse.
Fig. 6. Measured output laser pulse temporal characteristics from the 35-m-long gain-switched fiber laser which has 59mJ launched.

An enhancement of different length of the fiber.1, fiber.2 and fiber.3 leads to a variation in the fiber laser spectrums (given in Fig. 7.). The spectrum characteristics are measured by the monochromator WDG30 with a grating of 300 strip/mm and blaze wavelength 2µm. A PbS detector is used to monitor the pulses energy from the monochromator output slit. The output laser peak wavelength of fiber.1, fiber.2 and fiber.3 is 2.04µm, 2.0µm and 1.92µm respectively. In the approximately 2µm spectral region, the shorter wavelength laser has higher reabsorption losses with the silica fiber length increasing [12

12. Stuart D. Jackson and Terence A. King, “Dynamics of the output of heavily Tm-doped double-clad silica fibre lasers,” J. Opt. Soc. Am. B 16, 2178–2188(1999). [CrossRef]

]. The intrinsic absorption peak of silica is at 1.94µm, so the relatively shorter laser wavelength has more intrinsic loss with the fiber length increasing [13

13. Stuart D. Jackson, “Cross relaxation and energy transfer upconversion process relevant to the function of 2µm Tm3+-doped silica fibre lasers,” Opt. Commun. 230, 197–203 (2004). [CrossRef]

]. Because the reabsorption losses and the intrinsic absorption losses are relatively less in the fiber.3, the output laser is similar to the spontaneous radiation fluorescent spectrum [14

14. Stuart D. Jackson and Terence A. King, “Theoretical Modeling of Tm-Doped Silica Fiber Lasers,” J. Lightwave Technol. 17, 948–956 (1999). [CrossRef]

]. The output laser spectrums from fiber.1 and fiber.2 are concordant to the general laser spectrum characteristics, and have a relatively narrow line width, though there are no specific cavity mirrors.

Fig. 7. Spectrums of the output lasers with the fiber length 35m, 8m and 1m which has 59mJ launched.

The fiber laser pulse energy (measured with the Newport energy meter 818-J25) from the three fiber lasers as a function of the launched pump energy is shown in Fig. 8.. The launched pump energy is measured by the cutback method. The output laser pulse energy from fiber.1 reaches the maximum 14.7mJ per pulse. (For the Fresnel cavity, it is assumed that equal amounts of laser energy are emitted from each end of the fiber and therefore pulse energy measurements made at the distal end of the fiber are doubled [8

8. B. C. Dickinson, S. D. Jackson, and T. A. King, “10mJ total output from a gain-switched Tm-doped fiber laser,” Opt. Commun. 182, 199–203 (2000). [CrossRef]

].). The variation in the slope efficiencies and thresholds for the three fiber lasers is shown in Fig. 9. The slope efficiency increases with the fiber length increasing. The absorption ratio of the double-clad fiber is much smaller than the single-clad fiber and there exists amounts of unabsorbed pump energy, so the longer fiber can absorb more pump pulse energy and acquire more gain than the shorter one.

Fig. 8. Total output pulse energy from the gain-switched fiber laser as a function of the launched pump energy.
Fig. 9. Measured slope efficiencies and thresholds as a function of fiber length.

4. Conclusion

In conclusion, we have presented >14mJ of total gain-switched fiber laser output from a Nd:YAG cladding-pumped Tm-doped silica fiber laser. The maximum slope efficiency is 39.5% (with respect to the launched pump energy), which to our knowledge is the highest slope efficiency that has been reported pumped at 1.064µm in a similar cavity. A series of relaxation spikes from the gain-swirched fiber lasers are observed and have potential applications in surgery and others areas requiring pulse duration of a few hundred nanoseconds. The output peak wavelengths are 2.04, 2.0, and 1.92µm with fiber lengths of 35, 8, and 1m. Because the pump pulse characteristics and cavity are similar to those in Ref. [9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

], it is convenient to contrast our results to single-clad fiber results from Ref. [9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

]. The output energy from fiber 1 and fiber 2 have not saturated appearances during the launched pumped pulse energy range from 27 to 73mJ, but in Ref. [9

9. Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

] there are saturated appearances during the launched pumped pulse energy range from 6 to 24mJ; thus with Tm3+-doped double-clad fiber, the pulse energy can be greater than with single-clad fiber. There are more fiber laser spike pulses from the double-clad fiber than from the single-clad fiber during a pump pulse duration. The high-energy pulse is easily coupled into the double-clad fiber. With heavily Tm3+-doped big-core-diameter fiber to increase absorbed ratio and optimal length, the fiber laser will further increase the output energy and slope efficiency.

References and Links

1.

H. Tai, K. Yamamoto, and M. Uchida, “Long-distance simultaneous detection of methane and acetylene by using diode lasers coupled with optical fibers,” IEEE Photon. Technol. Lett. 4, 804–807 (1992). [CrossRef]

2.

Ashraf F. El-Sherif and Terence A. King, “Analysis and Optimization of Q-Switched Operation of a Tm3+-Doped silica Fiber Laser Operating at 2µm,” IEEE J. Quantum Electron. 39, 759–765 (2003). [CrossRef]

3.

P. S. Golding, S. D. Jackson, and P.-K. Tsai, “Efficient high power operation of a Tm-doped silica fiber laser pumped at 1.319µm,” Opt. Commun. 175, 179–183 (2000). [CrossRef]

4.

Ashraf F. El-Sherif and Terence A. King, “High-energy, high-brightness Q-switched Tm3+-doped fiber laser using an electro-optic modulator,” Opt. Commun. 218, 337–344 (2003). [CrossRef]

5.

Ashraf F. El-Sherif and Terence A. King, “High-peak-power operation of a Q-switched Tm3+-doped silica fiber laser operating near 2µm,” Opt. Lett. 28, 22–24 (2003). [CrossRef] [PubMed]

6.

LE. Nelson, E. P. Ippen, and H. A. Haus, “Broadly tunable sub-500 fs pulses from an additive-pulse mode-locked thulium-doped fiber ring laser,” Appl. Phy. Lett. 67, 19–21 (1995). [CrossRef]

7.

R. C. Sharp, D. E. Spock, and N. Pan, “190-fs passively mode-lock thulium fiber laser with a low threshold,” Opt. Lett. 21, 881–883 (1996). [CrossRef] [PubMed]

8.

B. C. Dickinson, S. D. Jackson, and T. A. King, “10mJ total output from a gain-switched Tm-doped fiber laser,” Opt. Commun. 182, 199–203 (2000). [CrossRef]

9.

Stuart D. Jackson and Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779–789 (1998). [CrossRef]

10.

Jianqiu Xu, Mahendra Prabhu, Jianren Lu, and Ken-ichi Ueda, “Efficient double-clad thulium-doped fiber laser with a ring cavity,” Appl. Opt. 40, 1983–1988 (2001). [CrossRef]

11.

D. C. Hanna, I. R. Pery, and J. R. Lincoln, “1-watt thulium doped CW fiber laser operation at 2-µm,” Opt. Commun. 80, 52–56 (1990). [CrossRef]

12.

Stuart D. Jackson and Terence A. King, “Dynamics of the output of heavily Tm-doped double-clad silica fibre lasers,” J. Opt. Soc. Am. B 16, 2178–2188(1999). [CrossRef]

13.

Stuart D. Jackson, “Cross relaxation and energy transfer upconversion process relevant to the function of 2µm Tm3+-doped silica fibre lasers,” Opt. Commun. 230, 197–203 (2004). [CrossRef]

14.

Stuart D. Jackson and Terence A. King, “Theoretical Modeling of Tm-Doped Silica Fiber Lasers,” J. Lightwave Technol. 17, 948–956 (1999). [CrossRef]

15.

M. Le Flohic, Pierre-Luc Francois, M. Jean-Yves Allain, and F. Sanchez, “Dynamics of the Transient of Emission in Nd3+-doped Fiber Laser,” IEEE J. Quantum Electron. 27, 1910–1921 (1991). [CrossRef]

16.

Stuart D. Jackson and Simon Mossman, “Efficiency dependence on the Tm3+ and Al3+ concentrations for Tm3+-doped silica double-clad fiber lasers,” Appl. Opt. 42, 2702–2707 (2003). [CrossRef] [PubMed]

OCIS Codes
(140.3510) Lasers and laser optics : Lasers, fiber
(140.3540) Lasers and laser optics : Lasers, Q-switched

ToC Category:
Research Papers

History
Original Manuscript: January 25, 2005
Revised Manuscript: January 24, 2005
Published: February 21, 2005

Citation
Yun Zhang, Bao-Quan Yao, You-Lun Ju, and Yue-Zhu Wang, "Gain-switched Tm3+-doped double-clad silica fiber laser," Opt. Express 13, 1085-1089 (2005)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-4-1085


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References

  1. H. Tai, K. Yamamoto, M. Uchida, “Long-distance simultaneous detection of methane and acetylene by using diode lasers coupled with optical fibers,” IEEE Photon. Technol. Lett. 4, 804-807 (1992). [CrossRef]
  2. Ashraf F. El-Sherif, Terence A. King, “Analysis and Optimization of Q-Switched Operation of a Tm3+- Doped silica Fiber Laser Operating at 2µm,” IEEE J. Quantum Electron. 39, 759-765 (2003). [CrossRef]
  3. P. S. Golding, S. D. Jackson, P.-K. Tsai, “Efficient high power operation of a Tm-doped silica fiber laser pumped at 1.319µm,” Opt. Commun. 175, 179-183 (2000). [CrossRef]
  4. Ashraf F. El-Sherif, Terence A. King, “High-energy, high-brightness Q-switched Tm3+-doped fiber laser using an electro-optic modulator,” Opt. Commun. 218, 337-344 (2003). [CrossRef]
  5. Ashraf F. El-Sherif, Terence A. King, “High-peak-power operation of a Q-switched Tm3+-doped silica fiber laser operating near 2µm,” Opt. Lett. 28, 22-24 (2003). [CrossRef] [PubMed]
  6. LE. Nelson, E. P. Ippen, H. A. Haus, “Broadly tunable sub-500 fs pulses from an additive-pulse modelocked thulium-doped fiber ring laser,” Appl. Phy. Lett. 67, 19-21 (1995). [CrossRef]
  7. R. C. Sharp, D. E. Spock, N. Pan, “190-fs passively mode-lock thulium fiber laser with a low threshold,” Opt. Lett. 21, 881-883 (1996). [CrossRef] [PubMed]
  8. B. C. Dickinson, S. D. Jackson, T. A. King, “10mJ total output from a gain-switched Tm-doped fiber laser,” Opt. Commun. 182, 199-203 (2000). [CrossRef]
  9. Stuart D. Jackson, Terence A. King, “Efficient Gain-Switched Operation of a Tm-Doped Silica Fiber Laser,” IEEE J. of Quantum Electron. 34, 779-789 (1998). [CrossRef]
  10. Jianqiu Xu, Mahendra Prabhu, Jianren Lu, Ken-ichi Ueda, “Efficient double-clad thulium-doped fiber laser with a ring cavity,” Appl. Opt. 40, 1983-1988 (2001). [CrossRef]
  11. D. C. Hanna, I. R. Pery, J. R. Lincoln, “1-watt thulium doped CW fiber laser operation at 2-µm,” Opt Commun. 80, 52-56 (1990). [CrossRef]
  12. Stuart D. Jackson, Terence A. King, “Dynamics of the output of heavily Tm-doped double-clad silica fibre lasers,” J. Opt. Soc. Am. B 16, 2178-2188(1999). [CrossRef]
  13. Stuart D. Jackson, “Cross relaxation and energy transfer upconversion process relevant to the function of 2µm Tm3+-doped silica fibre lasers,” Opt. Commun. 230, 197-203 (2004). [CrossRef]
  14. Stuart D. Jackson, Terence A. King, “Theoretical Modeling of Tm-Doped Silica Fiber Lasers,” J. Lightwave Technol. 17, 948-956 (1999). [CrossRef]
  15. M. Le Flohic, Pierre-Luc Francois, M. Jean-Yves Allain, F. Sanchez, “Dynamics of the Transient of Emission in Nd3+-doped Fiber Laser,” IEEE J. Quantum Electron. 27, 1910-1921 (1991). [CrossRef]
  16. Stuart D.Jackson, Simon Mossman, “Efficiency dependence on the Tm3+ and Al3+ concentrations for Tm3+-doped silica double-clad fiber lasers,” Appl. Opt. 42, 2702-2707 (2003). [CrossRef] [PubMed]

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