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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 24 — Nov. 21, 2011
  • pp: 24165–24170
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Tunable continuous-wave diamond Raman laser

Daniele C. Parrotta, Alan J. Kemp, Martin D. Dawson, and Jennifer E. Hastie  »View Author Affiliations


Optics Express, Vol. 19, Issue 24, pp. 24165-24170 (2011)
http://dx.doi.org/10.1364/OE.19.024165


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Abstract

Continuous-wave operation of a diamond Raman laser, intracavity-pumped by a diode-pumped InGaAs semiconductor disk laser (SDL), is reported. The Raman laser, which utilized a 6.5-mm-long synthetic single-crystal diamond, reached threshold for 5.3 W of diode laser pump power absorbed by the SDL. Output power up to 1.3 W at the first Stokes wavelength of 1227 nm was demonstrated with excellent beam quality and optical conversion efficiency of 14.4% with respect to absorbed diode laser pump power. Broad tuning of the Raman laser output between 1217 and 1244 nm was achieved via intracavity tuning of the SDL oscillation wavelength.

© 2011 OSA

1. Introduction

There is increasing interest in diamond as a very attractive gain medium for Raman lasers. This is due, amongst other reasons, to its broad optical transparency, high Raman gain coefficient (~15 cm/GW at 1 µm), large Stokes shift (1332 cm−1), and a thermal conductivity (~2000 W/m·K) 2 to 3 orders of magnitude greater than other crystalline Raman media. The development of synthetic single-crystal diamond, produced via chemical vapor deposition (CVD), has now matured to the point that large (few mm3), high optical quality single-crystals, suitable for intracavity use, are becoming commercially available [1

1. I. Friel, S. L. Geoghegan, D. J. Twitchen, and G. A. Scarsbrook, “Development of high quality single crystal diamond for novel laser applications,” Proc. SPIE 7838, 783819, 783819-8 (2010). [CrossRef]

]. Following these developments, efficient diamond Raman lasers have been successfully demonstrated in a variety of configurations. In pulsed operation, and pumped in an external resonant cavity, optical conversion efficiency up to 63.5% [2

2. R. P. Mildren and A. Sabella, “Highly efficient diamond Raman laser,” Opt. Lett. 34(18), 2811–2813 (2009). [CrossRef] [PubMed]

], slope efficiency of 84% [3

3. A. Sabella, J. A. Piper, and R. P. Mildren, “1240 nm diamond Raman laser operating near the quantum limit,” Opt. Lett. 35(23), 3874–3876 (2010). [CrossRef] [PubMed]

], and Stokes average output power of 24.5 W [4

4. J.-P. M. Feve, K. E. Shortoff, M. J. Bohn, and J. K. Brasseur, “High average power diamond Raman laser,” Opt. Express 19(2), 913–922 (2011). [CrossRef] [PubMed]

] have been reported. In the continuous-wave (cw) regime, synthetic diamond pumped within a Nd:YVO4 laser achieved a conversion efficiency of 11% and output power up to 1.6 W [5

5. W. Lubeigt, V. G. Savitski, G. M. Bonner, S. L. Geoghegan, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, “1.6 W continuous-wave Raman laser using low-loss synthetic diamond,” Opt. Express 19(7), 6938–6944 (2011). [CrossRef] [PubMed]

], and more recently, >5 W when pumped within a Nd:YLF laser [6

6. V. Savitski, J. Hastie, M. Dawson, D. Burns, and A. Kemp, “Multi-watt Continuous-wave Diamond Raman Laser at 1217 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDA_2.

]. All previously reported diamond Raman lasers have, however, been pumped by rare-earth-doped solid-state lasers for operation at fixed wavelengths.

In this paper, we present a tunable (1217-1244 nm) cw diamond Raman laser, achieved by pumping diamond within a 1060-nm-wavelength InGaAs semiconductor disk laser (SDL). Maximum output power of 1.3 W at 1227 nm and optical conversion efficiency up to 14.4% has been obtained. This is, to our knowledge, the first tunable diamond Raman laser; and in addition also shows competitive efficiency compared with previously reported cw crystalline Raman lasers (e.g [7

7. L. Fan, Y.-X. Fan, Y.-Q. Li, H. Zhang, Q. Wang, J. Wang, and H.-T. Wang, “High-efficiency continuous-wave Raman conversion with a BaWO(4) Raman crystal,” Opt. Lett. 34(11), 1687–1689 (2009). [CrossRef] [PubMed]

].). Importantly, the laser rivals the optical efficiency of SDLs designed for fundamental emission in the 1200-1300nm range [8

8. V.-M. Korpijärvi, M. Guina, J. Puustinen, P. Tuomisto, J. Rautiainen, A. Härkönen, A. Tukiainen, O. Okhotnikov, and M. Pessa, “MBE grown GaInNAs-based multi-Watt disk lasers,” J. Cryst. Growth 311(7), 1868–1871 (2009). [CrossRef]

].

2. Diamond Raman laser configuration

3. Results and discussion

Figure 2
Fig. 2 Power transfer characteristic of the cw diamond Raman laser (red circles) using a 1.2% OC. Also plotted is the SDL intracavity power (open squares) measured via the calibrated signal leakage through a cavity folding mirror. The inset shows the far-field Raman laser beam profile, with M2~1.1, measured using a commercial beam profiler (Coherent BeamMaster).
shows the power transfer characteristic of the diamond Raman laser obtained with output coupling of ~1.2% at 1225 nm. The ‘absorbed’ diode pump power refers to the input power to the SDL gain structure after pump reflection losses of 19.7% at the surface of the uncoated diamond heatspreader. It is important to note that – in contrast to most conventional diode-pumped solid-state lasers – all pump power entering an SDL structure is absorbed. The Raman laser achieved a maximum output power of 1.3 W at 1227 nm for an absorbed diode pump power of 9 W (11.2 W incident pump power), resulting in a calculated optical conversion efficiency of 14.4%. For higher input power, the SDL was affected by thermal rollover [10

10. A. C. Tropper, H. D. Foreman, A. Garnache, K. G. Wilcox, and S. Hoogland, “Vertical-external-cavity semiconductor lasers,” J. Phys. D 37(9), R75–R85 (2004). [CrossRef]

], leading to a corresponding rollover of the Raman laser output power. The slope efficiency of the Raman laser before rollover was 36% with respect to absorbed diode pump power. From the known reflectivity of the cavity mirrors we were able to estimate the SDL intracavity power by measuring the leakage signal. The Raman laser threshold was reached when the SDL intracavity power was around 83 ± 10 W, corresponding to an average optical power density of ~4.6 MW/cm2 over the length of the diamond.

The 14.4% optical efficiency of the SDL-pumped diamond Raman laser is competitive with previously reported cw crystalline Raman lasers pumped by doped dielectric solid state lasers, despite the lower slope efficiencies of SDLs (typically ~40-50% for InGaAs SDLs). The highest optical conversion efficiency previously reported for a cw crystalline Raman laser is 13.2%, as demonstrated by Fan et al. using a 30-mm-long BaWO4 crystal [7

7. L. Fan, Y.-X. Fan, Y.-Q. Li, H. Zhang, Q. Wang, J. Wang, and H.-T. Wang, “High-efficiency continuous-wave Raman conversion with a BaWO(4) Raman crystal,” Opt. Lett. 34(11), 1687–1689 (2009). [CrossRef] [PubMed]

]. In this case the output coupling was only 0.2% and the slope efficiency was 15.3%; however, high optical efficiency was achieved by pumping several times above the Raman laser threshold. The cw diamond laser reported by Lubeigt et al. used a 4.1-mm-long diamond pumped within a Nd:YVO4 disk laser and 1% output coupling to demonstrate up to 1.6 W output power with slope efficiency of 18% and optical conversion efficiency of 11%, using a diamond with an absorption coefficient of <0.006 cm−1 [5

5. W. Lubeigt, V. G. Savitski, G. M. Bonner, S. L. Geoghegan, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, “1.6 W continuous-wave Raman laser using low-loss synthetic diamond,” Opt. Express 19(7), 6938–6944 (2011). [CrossRef] [PubMed]

]. The absorption loss for the diamond we used was measured to be <0.004 cm−1 [9

9. V. Savitski, D. Burns, and A. Kemp, “Low-loss synthetic single-crystal diamond: Raman gain measurement and high power Raman laser at 1240 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper CA12_2.

], corresponding to an estimated round-trip loss of ~0.5%. The AR-coatings on the diamond crystal contribute an additional round-trip loss of ~0.5%; however, the separate arm of the Raman laser cavity allows the optimization of the SDL pump beam and Raman beam overlap in the diamond. In addition, the high reflectivity dichroic mirror removes the losses associated with the conventional laser medium from the Raman laser cavity. These attributes, together with the slightly higher output coupling c.f [5

5. W. Lubeigt, V. G. Savitski, G. M. Bonner, S. L. Geoghegan, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, “1.6 W continuous-wave Raman laser using low-loss synthetic diamond,” Opt. Express 19(7), 6938–6944 (2011). [CrossRef] [PubMed]

]. of 1.2%, lead to higher slope efficiency of 36%.

While a Brewster-cut crystal could be used to reduce reflection losses, the enlargement of the intracavity beam would increase the Raman laser threshold. Higher output power and higher optical conversion efficiency is therefore expected to be achieved via SDL power scaling so that the diamond Raman laser may be pumped many more times above threshold. For example, an InGaAs SDL with up to 20 W output power (>2.8 kW intracavity power) in a single transverse mode has previously been demonstrated [12

12. B. Rudin, A. Rutz, M. Hoffmann, D. J. H. C. Maas, A.-R. Bellancourt, E. Gini, T. Südmeyer, and U. Keller, “Highly efficient optically pumped vertical-emitting semiconductor laser with more than 20W average output power in a fundamental transverse mode,” Opt. Lett. 33(22), 2719–2721 (2008). [CrossRef] [PubMed]

].

The beam propagation factors of the ~1055 nm output from the SDL were measured during Raman conversion to be M2horizontal = 2.05 and M2vertical = 1.82. Turning off the Raman laser via slight misalignment of the dichroic mirror led to improvement in the SDL beam quality: M2horizontal = 1.5 and M2vertical = 1.4. This is consistent with the losses associated with preferential Raman conversion of lower order transverse modes resulting in the oscillation of higher order transverse modes in the SDL. At maximum output power, the beam propagation factors of the Raman laser were M2horizontal = 1.14 and M2vertical = 1.05. Compared with the KGW Raman laser we reported earlier [11

11. D. C. Parrotta, W. Lubeigt, A. J. Kemp, D. Burns, M. D. Dawson, and J. E. Hastie, “Continuous-wave Raman laser pumped within a semiconductor disk laser cavity,” Opt. Lett. 36(7), 1083–1085 (2011). [CrossRef] [PubMed]

], the beam quality of the diamond Raman laser is clearly superior, despite tighter focusing in the Raman crystal. We attribute this to the very high thermal conductivity of diamond (~600 times greater than that of KGW), which is therefore much less susceptible to thermal aberration. Indeed, based on the approximations in [13

13. J. A. Piper and H. M. Pask, “Crystalline Raman lasers,” IEEE J. Sel. Top. Quantum Electron. 13(3), 692–704 (2007). [CrossRef]

], we estimate the magnitude of the thermal lens focal length to be greater than 0.5 m in diamond but less than 0.05 m in KGW. That is to say the thermal lens is at least an order of magnitude weaker in the diamond Raman laser.

The SDL beam was constrained by the Brewster surfaces of the BRF to be horizontally polarized, and therefore parallel to a <111> axis of the diamond crystal. The Raman laser, which had no such constraints (aside from minor cavity anisotropy) was also measured to be horizontally polarized, parallel to <111>. This is consistent with the polarized diamond Raman laser threshold measurements reported by Sabella et al. [3

3. A. Sabella, J. A. Piper, and R. P. Mildren, “1240 nm diamond Raman laser operating near the quantum limit,” Opt. Lett. 35(23), 3874–3876 (2010). [CrossRef] [PubMed]

].

Rotation of the BRF allowed the tuning of the SDL and therefore of the Raman laser. For an absorbed diode pump power of 9 W and using ~1.2% OC, the Raman laser operated over the range 1217-1244 nm (SDL range 1047-1067 nm), with output power exceeding 1 W over a 10 nm range (see Fig. 3
Fig. 3 Tuning of the Raman laser via rotation of the intracavity BRF for an absorbed pump power of 9 W. The dashed line shows the variation in the output coupler transmission, as measured by the supplier.
). The SDL in a similar configuration but without Raman conversion tunes between ~1040-1070nm. This would equate to potential tuning of the Raman laser between about 1207 and 1248nm. Whilst differences in set-up preclude a rigorous comparison, the smaller tuning of the Raman laser achieved experimentally suggests that the varying reflectivity of the Raman laser output coupler, which had increased transmission at shorter wavelengths (Fig. 3), played a role in limiting the tuning range.

The laser emission linewidth was measured using an optical spectrum analyzer with 0.01 nm resolution, and a typical output spectrum thus observed is shown in Fig. 4
Fig. 4 Typical emission spectrum of the Raman laser, taken using an optical spectrum analyzer with 0.01 nm resolution. Inset: plotted on a log scale.
. The use of the BRF narrowed the SDL linewidth to ~0.25 nm full width at half maximum (FWHM), whereas the Raman linewidth was 0.22 nm.

5. Conclusions

Acknowledgments

The authors would like to thank Dr Ian Friel of Element Six Ltd. for providing the diamond sample. This work was supported by the Engineering and Physical Science Research Council (EPSRC), UK, under grant EP/G00014X.

References and links

1.

I. Friel, S. L. Geoghegan, D. J. Twitchen, and G. A. Scarsbrook, “Development of high quality single crystal diamond for novel laser applications,” Proc. SPIE 7838, 783819, 783819-8 (2010). [CrossRef]

2.

R. P. Mildren and A. Sabella, “Highly efficient diamond Raman laser,” Opt. Lett. 34(18), 2811–2813 (2009). [CrossRef] [PubMed]

3.

A. Sabella, J. A. Piper, and R. P. Mildren, “1240 nm diamond Raman laser operating near the quantum limit,” Opt. Lett. 35(23), 3874–3876 (2010). [CrossRef] [PubMed]

4.

J.-P. M. Feve, K. E. Shortoff, M. J. Bohn, and J. K. Brasseur, “High average power diamond Raman laser,” Opt. Express 19(2), 913–922 (2011). [CrossRef] [PubMed]

5.

W. Lubeigt, V. G. Savitski, G. M. Bonner, S. L. Geoghegan, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, “1.6 W continuous-wave Raman laser using low-loss synthetic diamond,” Opt. Express 19(7), 6938–6944 (2011). [CrossRef] [PubMed]

6.

V. Savitski, J. Hastie, M. Dawson, D. Burns, and A. Kemp, “Multi-watt Continuous-wave Diamond Raman Laser at 1217 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDA_2.

7.

L. Fan, Y.-X. Fan, Y.-Q. Li, H. Zhang, Q. Wang, J. Wang, and H.-T. Wang, “High-efficiency continuous-wave Raman conversion with a BaWO(4) Raman crystal,” Opt. Lett. 34(11), 1687–1689 (2009). [CrossRef] [PubMed]

8.

V.-M. Korpijärvi, M. Guina, J. Puustinen, P. Tuomisto, J. Rautiainen, A. Härkönen, A. Tukiainen, O. Okhotnikov, and M. Pessa, “MBE grown GaInNAs-based multi-Watt disk lasers,” J. Cryst. Growth 311(7), 1868–1871 (2009). [CrossRef]

9.

V. Savitski, D. Burns, and A. Kemp, “Low-loss synthetic single-crystal diamond: Raman gain measurement and high power Raman laser at 1240 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper CA12_2.

10.

A. C. Tropper, H. D. Foreman, A. Garnache, K. G. Wilcox, and S. Hoogland, “Vertical-external-cavity semiconductor lasers,” J. Phys. D 37(9), R75–R85 (2004). [CrossRef]

11.

D. C. Parrotta, W. Lubeigt, A. J. Kemp, D. Burns, M. D. Dawson, and J. E. Hastie, “Continuous-wave Raman laser pumped within a semiconductor disk laser cavity,” Opt. Lett. 36(7), 1083–1085 (2011). [CrossRef] [PubMed]

12.

B. Rudin, A. Rutz, M. Hoffmann, D. J. H. C. Maas, A.-R. Bellancourt, E. Gini, T. Südmeyer, and U. Keller, “Highly efficient optically pumped vertical-emitting semiconductor laser with more than 20W average output power in a fundamental transverse mode,” Opt. Lett. 33(22), 2719–2721 (2008). [CrossRef] [PubMed]

13.

J. A. Piper and H. M. Pask, “Crystalline Raman lasers,” IEEE J. Sel. Top. Quantum Electron. 13(3), 692–704 (2007). [CrossRef]

14.

N. Schulz, J.-M. Hopkins, M. Rattunde, D. Burns, and J. Wagner, “High-brightness long-wavelength semiconductor disk lasers,” Laser Photonics Rev. 2(3), 160–181 (2008). [CrossRef]

15.

S. Calvez, J. E. Hastie, M. Guina, O. Okhotnikov, and M. D. Dawson, “Semiconductor disk lasers for the generation of visible and ultraviolet radiation,” Laser Photonics Rev. 3(5), 407–434 (2009). [CrossRef]

OCIS Codes
(140.3550) Lasers and laser optics : Lasers, Raman
(140.3580) Lasers and laser optics : Lasers, solid-state
(140.3600) Lasers and laser optics : Lasers, tunable
(140.7270) Lasers and laser optics : Vertical emitting lasers

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: August 22, 2011
Revised Manuscript: October 12, 2011
Manuscript Accepted: November 3, 2011
Published: November 11, 2011

Citation
Daniele C. Parrotta, Alan J. Kemp, Martin D. Dawson, and Jennifer E. Hastie, "Tunable continuous-wave diamond Raman laser," Opt. Express 19, 24165-24170 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-24-24165


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References

  1. I. Friel, S. L. Geoghegan, D. J. Twitchen, and G. A. Scarsbrook, “Development of high quality single crystal diamond for novel laser applications,” Proc. SPIE7838, 783819, 783819-8 (2010). [CrossRef]
  2. R. P. Mildren and A. Sabella, “Highly efficient diamond Raman laser,” Opt. Lett.34(18), 2811–2813 (2009). [CrossRef] [PubMed]
  3. A. Sabella, J. A. Piper, and R. P. Mildren, “1240 nm diamond Raman laser operating near the quantum limit,” Opt. Lett.35(23), 3874–3876 (2010). [CrossRef] [PubMed]
  4. J.-P. M. Feve, K. E. Shortoff, M. J. Bohn, and J. K. Brasseur, “High average power diamond Raman laser,” Opt. Express19(2), 913–922 (2011). [CrossRef] [PubMed]
  5. W. Lubeigt, V. G. Savitski, G. M. Bonner, S. L. Geoghegan, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, “1.6 W continuous-wave Raman laser using low-loss synthetic diamond,” Opt. Express19(7), 6938–6944 (2011). [CrossRef] [PubMed]
  6. V. Savitski, J. Hastie, M. Dawson, D. Burns, and A. Kemp, “Multi-watt Continuous-wave Diamond Raman Laser at 1217 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper PDA_2.
  7. L. Fan, Y.-X. Fan, Y.-Q. Li, H. Zhang, Q. Wang, J. Wang, and H.-T. Wang, “High-efficiency continuous-wave Raman conversion with a BaWO(4) Raman crystal,” Opt. Lett.34(11), 1687–1689 (2009). [CrossRef] [PubMed]
  8. V.-M. Korpijärvi, M. Guina, J. Puustinen, P. Tuomisto, J. Rautiainen, A. Härkönen, A. Tukiainen, O. Okhotnikov, and M. Pessa, “MBE grown GaInNAs-based multi-Watt disk lasers,” J. Cryst. Growth311(7), 1868–1871 (2009). [CrossRef]
  9. V. Savitski, D. Burns, and A. Kemp, “Low-loss synthetic single-crystal diamond: Raman gain measurement and high power Raman laser at 1240 nm,” in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper CA12_2.
  10. A. C. Tropper, H. D. Foreman, A. Garnache, K. G. Wilcox, and S. Hoogland, “Vertical-external-cavity semiconductor lasers,” J. Phys. D37(9), R75–R85 (2004). [CrossRef]
  11. D. C. Parrotta, W. Lubeigt, A. J. Kemp, D. Burns, M. D. Dawson, and J. E. Hastie, “Continuous-wave Raman laser pumped within a semiconductor disk laser cavity,” Opt. Lett.36(7), 1083–1085 (2011). [CrossRef] [PubMed]
  12. B. Rudin, A. Rutz, M. Hoffmann, D. J. H. C. Maas, A.-R. Bellancourt, E. Gini, T. Südmeyer, and U. Keller, “Highly efficient optically pumped vertical-emitting semiconductor laser with more than 20W average output power in a fundamental transverse mode,” Opt. Lett.33(22), 2719–2721 (2008). [CrossRef] [PubMed]
  13. J. A. Piper and H. M. Pask, “Crystalline Raman lasers,” IEEE J. Sel. Top. Quantum Electron.13(3), 692–704 (2007). [CrossRef]
  14. N. Schulz, J.-M. Hopkins, M. Rattunde, D. Burns, and J. Wagner, “High-brightness long-wavelength semiconductor disk lasers,” Laser Photonics Rev.2(3), 160–181 (2008). [CrossRef]
  15. S. Calvez, J. E. Hastie, M. Guina, O. Okhotnikov, and M. D. Dawson, “Semiconductor disk lasers for the generation of visible and ultraviolet radiation,” Laser Photonics Rev.3(5), 407–434 (2009). [CrossRef]

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