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  • Editor: Xi-Cheng Zhang
  • Vol. 39, Iss. 16 — Aug. 15, 2014
  • pp: 4762–4765
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Controllable continuous-wave Nd:YVO4 self-Raman lasers using intracavity adaptive optics

Ran Li, Mike Griffith, Leslie Laycock, and Walter Lubeigt  »View Author Affiliations


Optics Letters, Vol. 39, Issue 16, pp. 4762-4765 (2014)
http://dx.doi.org/10.1364/OL.39.004762


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Abstract

A controllable self-Raman laser using an adaptive optics (AO)-based control loop featuring an intracavity deformable mirror is reported. This method has the potential to alleviate thermal lensing within the Raman and laser gain media, and enable solid-state Raman lasers to reach new power levels. A proof-of-concept experiment using a Nd:YVO4 self-Raman laser and resulting in 18% enhancement of the first Stokes output power is reported. Moreover, wavelength selection between two Raman laser outputs (λ=1109 and 1176 nm) emanating from the 379 and 893cm1 Raman shifts of YVO4, respectively, was achieved using this AO technique.

© 2014 Optical Society of America

Stimulated Raman scattering (SRS) is widely recognized as a practical and efficient approach to extend the spectral coverage of solid-state lasers operating in the near-infrared and visible spectra, especially when SRS is combined with second-harmonic generation or sum frequency generation [1

1. P. Cerny, H. Jelinkova, P. G. Zverev, and T. T. Basiev, Prog. Quantum Electron. 28, 113 (2004). [CrossRef]

3

3. H. M. Pask, P. Dekker, R. P. Mildren, D. J. Spence, and J. A. Piper, Prog. Quantum Electron. 32, 121 (2008). [CrossRef]

]. However, the nonelastic nature of SRS results in the dissipation of a significant portion of energy as heat in the Raman material. This inevitably leads to undesired thermo-optical distortions and impacts the performance of the Raman laser (especially when the Raman crystal is inserted within the laser cavity). This additional thermal lensing scales directly with the Raman laser output power and has been identified as the main limitation in power scaling crystalline Raman lasers operating in the continuous-wave (CW) regime [2

2. J. A. Piper and H. M. Pask, IEEE J. Sel. Top. Quantum Electron. 13, 692 (2007). [CrossRef]

,4

4. A. J. Lee, H. M. Pask, D. J. Spence, and J. A. Piper, Opt. Lett. 35, 682 (2010). [CrossRef]

]. The use of low-loss, low-birefringence synthetic diamond can significantly reduce the effects of SRS-induced thermal lensing in CW Raman lasers [5

5. W. Lubeigt, G. M. Bonner, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, Opt. Lett. 35, 2994 (2010). [CrossRef]

7

7. O. Kitzler, A. McKay, and R. P. Mildren, Opt. Lett. 37, 2790 (2012). [CrossRef]

]. In this Letter, we propose a method to reduce the effects of both SRS and laser-induced thermal lensing, leading to power scaling of crystalline Raman lasers. This method is based on a feedback control loop using adaptive optics (AO), which has been used to optimize the performance of solid-state lasers by compensating for the thermal lens effect within the laser gain medium [8

8. W. Lubeigt, G. Valentine, and D. Burns, Opt. Express 16, 10943 (2008). [CrossRef]

10

10. S. Piehler, B. Weichelt, A. Voss, M. A. Ahmed, and T. Graf, Opt. Lett. 37, 5033 (2012). [CrossRef]

].

In this Letter, the proof-of-concept implementation of this technique inside a crystalline Raman laser is reported for the first time to our knowledge. A bimorph deformable mirror (DM) was inserted as the end mirror in a self-Raman Nd:YVO4 laser cavity. In this so-called self-Raman configuration, laser conversion and SRS occurred within the same Nd:YVO4 crystal, which in turn became the subject of intense thermal buildup. Consequently, this self-Raman configuration was believed to be an ideal test bed to implement this feedback loop. In addition to power enhancement, this AO-based system was also used to control the wavelength of the output beam by selecting the Raman transitions of the YVO4 crystal used in this laser.

Fig. 1. Diagram of the Nd:YVO4 self-Raman laser incorporating the AO feedback loop.
Fig. 2. Actuator designation of the DM.

With no voltage applied to the DM, the laser was aligned to deliver a maximum Raman output power of 500 mW for an absorbed laser diode pump power of 10.8 W. In this case, the focal length of the first order of the thermal lens (fthl) present in the Nd:YVO4 crystal could be estimated to be 50mm. Using an ABCD-matrix software, the fundamental transverse mode radii of the fundamental (λ=1064nm) and Raman (λ=1176nm) laser fields at the center of the gain medium with and without thermal lensing are shown in Table 1. Only the radius of the Raman field was impacted by thermal lensing with a 20% increase.

Table 1. TEM00 Mode Radius at the Center of the Gain Medium for the Fundamental (λ=1064nm) and Raman (λ=1176nm) Fields with and without Thermal Lensing

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Fig. 3. Power transfer of the λ=1176nm output before optimization, including the post-optimization result.

Table 2. Zernike Coefficients before and after Power Scaling Investigation

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In addition to power scaling, this AO-based technique was also used as a means to select the wavelength of the Nd:YVO4 Raman laser. Neodymium-doped ortho-vanadates, such as Nd:YVO4 and Nd:GdVO4, have been shown to feature several Raman transitions [12

12. A. A. Kaminskii, K. Ueda, H. J. Eichler, Y. Kuwano, H. Kouta, S. N. Bagaev, T. H. Chyba, J. C. Barnes, G. M. A. Gad, T. Murai, and J. Lu, Opt. Commun. 194, 201 (2001). [CrossRef]

] leading to the development of Raman lasers based on secondary Raman transitions [13

13. F. Shuzhen, Z. Xingyu, W. Qingpu, L. Zhaojun, L. Lei, C. Zhenhua, C. Xiaohan, and Z. Xiaolei, Opt. Commun. 284, 1642 (2011). [CrossRef]

15

15. R. Li, R. Bauer, and W. Lubeigt, Opt. Express 21, 17745 (2013). [CrossRef]

]. Here, the AO system was used to rapidly modify the dynamics of the intracavity laser field, resulting in a switch between the primary (893cm1) and secondary (379cm1) Raman transitions of the Nd:YVO4 crystal. In this experiment, the laser cavity in Fig. 1 was slightly modified with the distance between the DM and the ROC=1m curved mirror set to 300 mm. At first, the laser resonator was aligned manually to only use the 379cm1 Raman shift with the DM actuators set at 0 V (i.e., focusing powers along x and y axes measured at 0.47 and 0.28 D, respectively), resulting in a 275 mW Raman laser output at λ=1109nm for an absorbed laser diode pump power of 8.2 W. The beam quality M2 factors along x and y transverse axes were measured to be 1.3 and 1.6 for the λ=1109nm laser output. Using an optical spectrum analyzer (Agilent 86140B), the full width at half-maximum (FWHM) linewidth of the first Stokes output (λ=1109nm) can be estimated at 0.15 nm at a resolution of 0.06 nm. The optical power transfer at λ=1109nm was measured as shown in Fig. 4. At a pump power of 10.1 W, 100mW of the λ=1176nm Raman output could also be observed in addition to the λ=1109nm line. The surface of the DM was then changed to an approximately flat shape by applying a voltage of 66 V to all actuators. In this way, the primary (893cm1) Raman shift was favored to the detriment of the 379cm1 shift. So, only the Raman laser at λ=1176nm could be observed with an output power of 340 mW and with beam quality M2 factors along x and y transverse axes measuring less than 1.1. The resulting FWHM linewidth of this Raman laser output was measured at 0.15 nm at a resolution of 0.06 nm. The optical power transfer of the λ=1176nm output obtained with the flat DM shape was measured as shown in Fig. 4. Again, at high pump powers (9.7 W), both Raman outputs could be observed with up to 100 mW of the λ=1109nm output. The Zernike coefficients before and after the wavelength switch are shown in Table 3.

Fig. 4. Power transfer of Raman lasers resulting from the 379cm1 transition (in red) and the 893cm1 transition (in black).

Table 3. Summary of Zernike Coefficients for Wavelength Control

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These two distinct experiments raise several discussion points.

In the wavelength control investigation, both Raman outputs could be observed simultaneously at pump powers above 9.5 W. Further investigation would be required to explain this Raman mode competition. However, it must be noted that the sum of their intensity meant that the total Raman output power was in line with the trend observed from lower powers.

This work has been supported by the UK EPSRC (grant number EP/K009982/1).

References

1.

P. Cerny, H. Jelinkova, P. G. Zverev, and T. T. Basiev, Prog. Quantum Electron. 28, 113 (2004). [CrossRef]

2.

J. A. Piper and H. M. Pask, IEEE J. Sel. Top. Quantum Electron. 13, 692 (2007). [CrossRef]

3.

H. M. Pask, P. Dekker, R. P. Mildren, D. J. Spence, and J. A. Piper, Prog. Quantum Electron. 32, 121 (2008). [CrossRef]

4.

A. J. Lee, H. M. Pask, D. J. Spence, and J. A. Piper, Opt. Lett. 35, 682 (2010). [CrossRef]

5.

W. Lubeigt, G. M. Bonner, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, Opt. Lett. 35, 2994 (2010). [CrossRef]

6.

V. G. Savitski, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, IEEE J. Quantum Electron. 48, 328 (2012). [CrossRef]

7.

O. Kitzler, A. McKay, and R. P. Mildren, Opt. Lett. 37, 2790 (2012). [CrossRef]

8.

W. Lubeigt, G. Valentine, and D. Burns, Opt. Express 16, 10943 (2008). [CrossRef]

9.

P. Yang, X. Lei, R. Yang, M. Ao, L. Dong, and B. Xu, Appl. Phys. B 100, 591 (2010). [CrossRef]

10.

S. Piehler, B. Weichelt, A. Voss, M. A. Ahmed, and T. Graf, Opt. Lett. 37, 5033 (2012). [CrossRef]

11.

W. Lubeigt, S. P. Poland, G. J. Valentine, A. J. Wright, J. M. Girkin, and D. Burns, Appl. Opt. 49, 307 (2010). [CrossRef]

12.

A. A. Kaminskii, K. Ueda, H. J. Eichler, Y. Kuwano, H. Kouta, S. N. Bagaev, T. H. Chyba, J. C. Barnes, G. M. A. Gad, T. Murai, and J. Lu, Opt. Commun. 194, 201 (2001). [CrossRef]

13.

F. Shuzhen, Z. Xingyu, W. Qingpu, L. Zhaojun, L. Lei, C. Zhenhua, C. Xiaohan, and Z. Xiaolei, Opt. Commun. 284, 1642 (2011). [CrossRef]

14.

J. Lin and H. M. Pask, Opt. Express 20, 15180 (2012). [CrossRef]

15.

R. Li, R. Bauer, and W. Lubeigt, Opt. Express 21, 17745 (2013). [CrossRef]

16.

D. Malacara, Optical Shop Testing, 2nd ed. (Wiley, 1992).

OCIS Codes
(010.1080) Atmospheric and oceanic optics : Active or adaptive optics
(140.3530) Lasers and laser optics : Lasers, neodymium
(140.3550) Lasers and laser optics : Lasers, Raman
(140.3580) Lasers and laser optics : Lasers, solid-state
(140.6810) Lasers and laser optics : Thermal effects

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: June 6, 2014
Revised Manuscript: July 9, 2014
Manuscript Accepted: July 11, 2014
Published: August 7, 2014

Citation
Ran Li, Mike Griffith, Leslie Laycock, and Walter Lubeigt, "Controllable continuous-wave Nd:YVO4 self-Raman lasers using intracavity adaptive optics," Opt. Lett. 39, 4762-4765 (2014)
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-39-16-4762


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References

  1. P. Cerny, H. Jelinkova, P. G. Zverev, and T. T. Basiev, Prog. Quantum Electron. 28, 113 (2004). [CrossRef]
  2. J. A. Piper and H. M. Pask, IEEE J. Sel. Top. Quantum Electron. 13, 692 (2007). [CrossRef]
  3. H. M. Pask, P. Dekker, R. P. Mildren, D. J. Spence, and J. A. Piper, Prog. Quantum Electron. 32, 121 (2008). [CrossRef]
  4. A. J. Lee, H. M. Pask, D. J. Spence, and J. A. Piper, Opt. Lett. 35, 682 (2010). [CrossRef]
  5. W. Lubeigt, G. M. Bonner, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, Opt. Lett. 35, 2994 (2010). [CrossRef]
  6. V. G. Savitski, I. Friel, J. E. Hastie, M. D. Dawson, D. Burns, and A. J. Kemp, IEEE J. Quantum Electron. 48, 328 (2012). [CrossRef]
  7. O. Kitzler, A. McKay, and R. P. Mildren, Opt. Lett. 37, 2790 (2012). [CrossRef]
  8. W. Lubeigt, G. Valentine, and D. Burns, Opt. Express 16, 10943 (2008). [CrossRef]
  9. P. Yang, X. Lei, R. Yang, M. Ao, L. Dong, and B. Xu, Appl. Phys. B 100, 591 (2010). [CrossRef]
  10. S. Piehler, B. Weichelt, A. Voss, M. A. Ahmed, and T. Graf, Opt. Lett. 37, 5033 (2012). [CrossRef]
  11. W. Lubeigt, S. P. Poland, G. J. Valentine, A. J. Wright, J. M. Girkin, and D. Burns, Appl. Opt. 49, 307 (2010). [CrossRef]
  12. A. A. Kaminskii, K. Ueda, H. J. Eichler, Y. Kuwano, H. Kouta, S. N. Bagaev, T. H. Chyba, J. C. Barnes, G. M. A. Gad, T. Murai, and J. Lu, Opt. Commun. 194, 201 (2001). [CrossRef]
  13. F. Shuzhen, Z. Xingyu, W. Qingpu, L. Zhaojun, L. Lei, C. Zhenhua, C. Xiaohan, and Z. Xiaolei, Opt. Commun. 284, 1642 (2011). [CrossRef]
  14. J. Lin and H. M. Pask, Opt. Express 20, 15180 (2012). [CrossRef]
  15. R. Li, R. Bauer, and W. Lubeigt, Opt. Express 21, 17745 (2013). [CrossRef]
  16. D. Malacara, Optical Shop Testing, 2nd ed. (Wiley, 1992).

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