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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 8 — Apr. 9, 2012
  • pp: 8915–8919
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11 W narrow linewidth laser source at 780nm for laser cooling and manipulation of Rubidium

S. S. Sané, S. Bennetts, J. E. Debs, C. C. N. Kuhn, G. D. McDonald, P. A. Altin, J. D. Close, and N. P. Robins  »View Author Affiliations


Optics Express, Vol. 20, Issue 8, pp. 8915-8919 (2012)
http://dx.doi.org/10.1364/OE.20.008915


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Abstract

We present a narrow linewidth continuous laser source with over 11 W output power at 780 nm, based on single-pass frequency doubling of an amplified 1560 nm fibre laser with 36% efficiency. This source offers a combination of high power, simplicity, mode quality and stability. Without any active stabilization, the linewidth is measured to be below 10 kHz. The fibre seed is tunable over 60 GHz, which allows access to the D2 transitions in 87Rb and 85Rb, providing a viable high-power source for laser cooling as well as for large-momentum-transfer beamsplitters in atom interferometry. Sources of this type will pave the way for a new generation of high flux, high duty-cycle degenerate quantum gas experiments.

© 2012 OSA

1. Introduction

The rapid progress of atomic physics over the past few decades has largely hinged upon the development of high power, narrow linewidth laser sources for manipulating and probing atoms. Increased laser power allows for higher flux and collection efficiency in magneto-optical traps [1

1. S. Jollenbeck, J. Mahnke, R. Randoll, W. Ertmer, J. Arlt, and C. Klempt “Hexapole-compensated magneto-optical trap on a mesoscopic atom chip,” Phys. Rev. A 83, 043406 (2011). [CrossRef]

], as well as further improvements in lattice-based cooling techniques [2

2. M. Olshanii and D. Weiss, “Producing Bose-Einstein condensates using optical lattices,” Phys. Rev. Lett. 89, 090404 (2002). [CrossRef] [PubMed]

]. In atom interferometry, narrow linewidth, high power near-resonant lasers are a prerequisite to achieving higher sensitivities with large-momentum-transfer beamsplitting [3

3. H. Muller, S. Chiow, Q. Long, S. Herrmann, and S. Chu “Atom interferometry with up to 24-photon-momentum-transfer beam splitters,” Phys. Rev. Lett. 100, 180405 (2008). [CrossRef] [PubMed]

5

5. S. S. Szigeti, J. E. Debs, J. J. Hope, N. P. Robins, and J. D. Close “Why momentum width matters for atom interferometry with Bragg pulses,” New J. Phys. 14, 023009 (2012). [CrossRef]

].

In recent years a great deal of effort has focused on the development of high power narrow linewidth CW sources at 589 nm primarily for sodium guide star applications, but also for laser cooling. Currently doubling raman fibre lasers in an external resonant cavity have demonstrated powers of 50W [8

8. L. R. Taylor, Y. Feng, and D. B. Calia, “50W CW visible laser source at 589nm obtained via frequency doubling of three coherently combined narrow-band Raman fibre amplifiers,” Opt. Express 18, 8540–8555 (2010). [CrossRef] [PubMed]

] and doubling efficiencies of 86% at 25W [9

9. Y. Feng, L. R. Taylor, and D. B. Calia, “25 W Raman-fiber-amplifier-based 589 nm laser for laser guide star,” Opt. Express 17, 19021–19026 (2009). [CrossRef]

]. Another approach by Chiow et al. used a modified Coherent 899 Ti:sapphire laser to achieve 6W of light at 852 nm by injection locking. Frequency stabilization to a high-finesse optical cavity resulted in a linewidth of < 1 kHz [10

10. S. Chiow, S. Herrmann, H. Muller, and S. Chu “6 W, 1 kHz linewidth, tunable continuous-wave near-infrared laser,” Opt. Express 17, 5246 (2009). [CrossRef] [PubMed]

]. This technology allowed for efficient high-order Bragg diffraction in the largest area atom interferometer produced to date [11

11. S.-Y. Lan, P.-C. Kuan, B. Estey, P. Haslinger, and H. Müller “Influence of the Coriolis force in atom interferometry,” accepted Phys. Rev. Lett. (2012).

]. Diode pumped alkali vapour lasers have now demonstrated 48W in Cs [12

12. B. V. Zhdanov, J. Sell, and R. J. Knize, “Multiple laser diode array pumped Cs laser with 48W output power,” Electr. Lett. 44, 582–583 (2008). [CrossRef]

].

At the 780nm Rb wavelength, tunable Ti:sapphire and Alexandrite lasers have demonstrated up to 6W, offering the option of injection locking [13

13. J. Walling, O. Peterson, and R. Morris, “Tunable CW alexandrite laser,” IEEE J. Quantum Electron. 16, 120–121 (1980). [CrossRef]

]. Zweiback et. al have demonstrated 28W from a diode pumped alkali vapour laser [14

14. J. Zweiback and W. F. Krupke “28W average power hydrocarbon-free rubidium diode pumped alkali laser,” Opt. Express 18, 1444–1449 (2010). [CrossRef] [PubMed]

]. By cascading two PPLN crystals, Thompson et al. were able to obtain 20% SHG efficiency and generate 900mW of light at 780 nm [15

15. R. J. Thompson, M. Tu, D. C. Aveline, N. Lundblad, and L. Maleki “High power single frequency 780nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals,” Opt. Express 11, 1709 (2003). [CrossRef] [PubMed]

]. Recently the atomic physics community has also begun to investigate the possibility of using compact cw frequency-doubled sources for portable atom interferometry based sensors [16

16. F. Lienhart, S. Boussen, O. Carat, N. Zahzam, Y. Bidel, and A. Bresson “Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm,” Appl. Phys. B 89, 177 (2007). [CrossRef]

,17

17. V. Ménoret, R. Geiger, G. Stern, N. Zahzam, B. Battelier, A. Bresson, A. Landragin, and P. Bouyer “Dual-wavelength laser source for onboard atom interferometry,” Opt. Lett. 36, 4128 (2011). [CrossRef] [PubMed]

].

In this paper we present a compelling argument to move to a doubled laser system in atomic physics labs working with Rubidium. We have produced a 11.4 W cw laser at 780.24 nm with a 6 kHz linewidth by single-pass frequency doubling in a single PPLN cystal. The doubling efficiency is 36%. The setup is simple and robust, relying on a narrow-linewidth fiber laser [18

18. NP Photonics, The Rock.

] to provide a highly stable seed, and a low noise 30 W fibre amplifier [19

19. IPG photonics.

] to generate the high powers required for efficient doubling.

2. Apparatus

The experimental setup is shown in Fig. 1. The source is an amplifed NP Photonics Rock fibre laser with a centre wavelength of 1560.48 nm and a tuning range of ±30GHz. Only ±150 MHz tuning is readily available via piezo control, otherwise the laser must be tuned with temperature. This laser has a specified linewidth of < 5 kHz integrated over 100 ms. The output frequency appears nearly insensitive to acoustic noise, particularly compared to an external cavity diode laser. We do observe a slow thermal drift of the seed laser, which is easily counteracted by a low bandwidth servo loop with an error signal provided by saturation spectroscopy of Rubidium with the doubled light. The 1560.48 nm seed is amplified by an IPG Photonics fiber amplifier with a maximum output power of 30 W. The amplified beam has a 1/e2 diameter of 1.1 mm and is linearly polarized.

Fig. 1 Schematic of the experimental setup. The seed and fiber amplifier are not shown in the diagram. PPLN - periodically-poled lithium niobate crystal, HWP - half-wave plate, QWP - quarter-wave plate, PBS - polarizing beamsplitter. After the oven, the 780nm and 1560nm light are separated by the dichoric mirrors.

Using a single plano-convex lens with a 50 mm focal length, this beam is focused into the centre of a 40 mm long periodically-poled lithium niobate (PPLN) cystal. The crystal is 1 mm thick and has five 1 mm wide gratings, each with a different domain period [20

20. PPLN crystal supplied by Covesion Ltd.

]. In this work we have used a grating with a 19.5 μm domain period. The crystal is housed inside a temperature-stabilized oven on a three-axis translation stage, and held at 81.60 °C for optimal phase matching. The polarisation of the light incident on the crystal is controlled using a λ/2 waveplate, which is optimized to achieve maximum doubling efficiency.

The linearly polarised 780 nm light exiting the crystal is filtered by two dichroic mirrors and collimated with a 100 mm lens. This light is analyzed via saturated absorption spectroscopy using rubidium vapor, which also provides the locking signal for the seed laser (a fibre modulator is used to generate the necessary frequency sidebands for locking). The remaining 1560 nm light reflected by the dichroic mirrors can be used for dipole trapping. The optical setup is robust and compact, and does not require any active control of the optical components, with the exception of temperature-stabilizing the PPLN crystal.

3. Results

The power in the second harmonic is plotted as a function of input power in Fig. 2. A maximum efficiency of 36% is achieved, giving 11.4 W of output power at 780 nm. These data were taken without any adjustment of the crystal temperature or alignment. This efficiency compares very favourably with more complex and lower power cavity-enhanced doubling systems at these wavelengths [21

21. J. Feng, Y. Li, X. Tian, J. Liu, and K. Zhang “Noise suppression, linewidth narrowing of a master oscillator power amplifier at 1.56nm and the second harmonic generation output at 780nm,” Opt. Express 16, 11871 (2008). [CrossRef] [PubMed]

]. The inset in Fig. 2 shows the spatial mode of the 780 nm light, after collimation from the doubler. By tuning the seed laser temperature and piezo, we can scan through all of the rubidium D2 transitions without a noticeable change in power.

Fig. 2 Measured second harmonic power as a function of input power from a single 40 mm PPLN crystal. The maximum output power is 11.4 Watts at 780 nm. The inset shows the spatial mode of the output.

To measure the linewidth of the 780 nm beam, a small portion of output power is directed through a fiber-coupled electro-optic phase modulator (modulation frequency 50 MHz) and then into an acoustically isolated unequal path length Mach-Zehnder inteferometer [22

22. F. Kéfélian, H. Jiang, P. Lemonde, and G. Santarelli, “Ultralow-frequency-noise stabilization of a laser by locking to an optical fiber-delay line,” Opt. Lett. 34, 914–916 (2009). [CrossRef] [PubMed]

]. One arm of the interferometer is passed through a 10 m single-mode optical fibre, giving a fringe spacing of 21 MHz. The output of the interferometer is monitored on a fast photodetector, and demodulation and low-pass filtering is used to generate an error signal which can be straightforwardly calibrated to the fringe spacing. The frequency noise spectrum obtained at the zero-crossing of the error signal is given in Fig. 3. Above 10 kHz, the measurement is limited by detector and electronic noise, aside from a peak at 500 kHz which corresponds to a noise feature in the seed laser. By integrating the noise spectrum over the range plotted in Fig. 3, we determine the linewidth of the frequency-doubled light to be 6 kHz over 100 ms, which is comparable to that of the NPP seed laser specified as < 5 kHz.

Fig. 3 Frequency noise spectrum measured using an unequal path length Mach-Zehnder interferometer as described in the text. The gray curve shows the detector noise. Integrating from 10 Hz to 5 MHz gives a linewidth of 6 kHz.

4. Conclusion

Acknowledgments

The authors would like to thank Tim Lam for his assistance with the linewidth measurement and Nikita Simakov for useful discussions. NPR thanks Nina and Alexander Robins for experimental support work. Specific product citations are for the purpose of clarification only and are not an endorsement by the authors or the ANU. This work was supported in part by the Australian Research Council Discovery program.

References and links

1.

S. Jollenbeck, J. Mahnke, R. Randoll, W. Ertmer, J. Arlt, and C. Klempt “Hexapole-compensated magneto-optical trap on a mesoscopic atom chip,” Phys. Rev. A 83, 043406 (2011). [CrossRef]

2.

M. Olshanii and D. Weiss, “Producing Bose-Einstein condensates using optical lattices,” Phys. Rev. Lett. 89, 090404 (2002). [CrossRef] [PubMed]

3.

H. Muller, S. Chiow, Q. Long, S. Herrmann, and S. Chu “Atom interferometry with up to 24-photon-momentum-transfer beam splitters,” Phys. Rev. Lett. 100, 180405 (2008). [CrossRef] [PubMed]

4.

S. Dimopoulos, P. W. Graham, J. M. Hogan, M. A. Kasevich, and S. Rajendran “Atomic gravitational wave interferometric sensor,” Phys. Rev. D 78, 122002 (2008). [CrossRef]

5.

S. S. Szigeti, J. E. Debs, J. J. Hope, N. P. Robins, and J. D. Close “Why momentum width matters for atom interferometry with Bragg pulses,” New J. Phys. 14, 023009 (2012). [CrossRef]

6.

K. B. MacAdam, A. Steinbach, and C. Wieman “A narrow-band tunable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb,” Am. J. Phys. 60, 1098 (1992). [CrossRef]

7.

L. Ricci, M. Weidemüller, T. Esslinger, A. Hemmerich, C. Zimmermann, V. Vuletic, W. König, and T. W. Hänsch “A compact grating-stabilized diode laser system for atomic physics,” Opt. Comm. 117, 541 (1995). [CrossRef]

8.

L. R. Taylor, Y. Feng, and D. B. Calia, “50W CW visible laser source at 589nm obtained via frequency doubling of three coherently combined narrow-band Raman fibre amplifiers,” Opt. Express 18, 8540–8555 (2010). [CrossRef] [PubMed]

9.

Y. Feng, L. R. Taylor, and D. B. Calia, “25 W Raman-fiber-amplifier-based 589 nm laser for laser guide star,” Opt. Express 17, 19021–19026 (2009). [CrossRef]

10.

S. Chiow, S. Herrmann, H. Muller, and S. Chu “6 W, 1 kHz linewidth, tunable continuous-wave near-infrared laser,” Opt. Express 17, 5246 (2009). [CrossRef] [PubMed]

11.

S.-Y. Lan, P.-C. Kuan, B. Estey, P. Haslinger, and H. Müller “Influence of the Coriolis force in atom interferometry,” accepted Phys. Rev. Lett. (2012).

12.

B. V. Zhdanov, J. Sell, and R. J. Knize, “Multiple laser diode array pumped Cs laser with 48W output power,” Electr. Lett. 44, 582–583 (2008). [CrossRef]

13.

J. Walling, O. Peterson, and R. Morris, “Tunable CW alexandrite laser,” IEEE J. Quantum Electron. 16, 120–121 (1980). [CrossRef]

14.

J. Zweiback and W. F. Krupke “28W average power hydrocarbon-free rubidium diode pumped alkali laser,” Opt. Express 18, 1444–1449 (2010). [CrossRef] [PubMed]

15.

R. J. Thompson, M. Tu, D. C. Aveline, N. Lundblad, and L. Maleki “High power single frequency 780nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals,” Opt. Express 11, 1709 (2003). [CrossRef] [PubMed]

16.

F. Lienhart, S. Boussen, O. Carat, N. Zahzam, Y. Bidel, and A. Bresson “Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm,” Appl. Phys. B 89, 177 (2007). [CrossRef]

17.

V. Ménoret, R. Geiger, G. Stern, N. Zahzam, B. Battelier, A. Bresson, A. Landragin, and P. Bouyer “Dual-wavelength laser source for onboard atom interferometry,” Opt. Lett. 36, 4128 (2011). [CrossRef] [PubMed]

18.

NP Photonics, The Rock.

19.

IPG photonics.

20.

PPLN crystal supplied by Covesion Ltd.

21.

J. Feng, Y. Li, X. Tian, J. Liu, and K. Zhang “Noise suppression, linewidth narrowing of a master oscillator power amplifier at 1.56nm and the second harmonic generation output at 780nm,” Opt. Express 16, 11871 (2008). [CrossRef] [PubMed]

22.

F. Kéfélian, H. Jiang, P. Lemonde, and G. Santarelli, “Ultralow-frequency-noise stabilization of a laser by locking to an optical fiber-delay line,” Opt. Lett. 34, 914–916 (2009). [CrossRef] [PubMed]

OCIS Codes
(020.1335) Atomic and molecular physics : Atom optics
(140.3515) Lasers and laser optics : Lasers, frequency doubled
(020.3320) Atomic and molecular physics : Laser cooling

ToC Category:
Atomic and Molecular Physics

History
Original Manuscript: February 13, 2012
Revised Manuscript: March 26, 2012
Manuscript Accepted: March 26, 2012
Published: April 2, 2012

Citation
S. S. Sané, S. Bennetts, J. E. Debs, C. C. N. Kuhn, G. D. McDonald, P. A. Altin, J. D. Close, and N. P. Robins, "11 W narrow linewidth laser source at 780nm for laser cooling and manipulation of Rubidium," Opt. Express 20, 8915-8919 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-8-8915


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References

  1. S. Jollenbeck, J. Mahnke, R. Randoll, W. Ertmer, J. Arlt, and C. Klempt “Hexapole-compensated magneto-optical trap on a mesoscopic atom chip,” Phys. Rev. A83, 043406 (2011). [CrossRef]
  2. M. Olshanii and D. Weiss, “Producing Bose-Einstein condensates using optical lattices,” Phys. Rev. Lett.89, 090404 (2002). [CrossRef] [PubMed]
  3. H. Muller, S. Chiow, Q. Long, S. Herrmann, and S. Chu “Atom interferometry with up to 24-photon-momentum-transfer beam splitters,” Phys. Rev. Lett.100, 180405 (2008). [CrossRef] [PubMed]
  4. S. Dimopoulos, P. W. Graham, J. M. Hogan, M. A. Kasevich, and S. Rajendran “Atomic gravitational wave interferometric sensor,” Phys. Rev. D78, 122002 (2008). [CrossRef]
  5. S. S. Szigeti, J. E. Debs, J. J. Hope, N. P. Robins, and J. D. Close “Why momentum width matters for atom interferometry with Bragg pulses,” New J. Phys.14, 023009 (2012). [CrossRef]
  6. K. B. MacAdam, A. Steinbach, and C. Wieman “A narrow-band tunable diode laser system with grating feedback, and a saturated absorption spectrometer for Cs and Rb,” Am. J. Phys.60, 1098 (1992). [CrossRef]
  7. L. Ricci, M. Weidemüller, T. Esslinger, A. Hemmerich, C. Zimmermann, V. Vuletic, W. König, and T. W. Hänsch “A compact grating-stabilized diode laser system for atomic physics,” Opt. Comm.117, 541 (1995). [CrossRef]
  8. L. R. Taylor, Y. Feng, and D. B. Calia, “50W CW visible laser source at 589nm obtained via frequency doubling of three coherently combined narrow-band Raman fibre amplifiers,” Opt. Express18, 8540–8555 (2010). [CrossRef] [PubMed]
  9. Y. Feng, L. R. Taylor, and D. B. Calia, “25 W Raman-fiber-amplifier-based 589 nm laser for laser guide star,” Opt. Express17, 19021–19026 (2009). [CrossRef]
  10. S. Chiow, S. Herrmann, H. Muller, and S. Chu “6 W, 1 kHz linewidth, tunable continuous-wave near-infrared laser,” Opt. Express17, 5246 (2009). [CrossRef] [PubMed]
  11. S.-Y. Lan, P.-C. Kuan, B. Estey, P. Haslinger, and H. Müller “Influence of the Coriolis force in atom interferometry,” accepted Phys. Rev. Lett. (2012).
  12. B. V. Zhdanov, J. Sell, and R. J. Knize, “Multiple laser diode array pumped Cs laser with 48W output power,” Electr. Lett.44, 582–583 (2008). [CrossRef]
  13. J. Walling, O. Peterson, and R. Morris, “Tunable CW alexandrite laser,” IEEE J. Quantum Electron.16, 120–121 (1980). [CrossRef]
  14. J. Zweiback and W. F. Krupke “28W average power hydrocarbon-free rubidium diode pumped alkali laser,” Opt. Express18, 1444–1449 (2010). [CrossRef] [PubMed]
  15. R. J. Thompson, M. Tu, D. C. Aveline, N. Lundblad, and L. Maleki “High power single frequency 780nm laser source generated from frequency doubling of a seeded fiber amplifier in a cascade of PPLN crystals,” Opt. Express11, 1709 (2003). [CrossRef] [PubMed]
  16. F. Lienhart, S. Boussen, O. Carat, N. Zahzam, Y. Bidel, and A. Bresson “Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm,” Appl. Phys. B89, 177 (2007). [CrossRef]
  17. V. Ménoret, R. Geiger, G. Stern, N. Zahzam, B. Battelier, A. Bresson, A. Landragin, and P. Bouyer “Dual-wavelength laser source for onboard atom interferometry,” Opt. Lett.36, 4128 (2011). [CrossRef] [PubMed]
  18. NP Photonics, The Rock.
  19. IPG photonics.
  20. PPLN crystal supplied by Covesion Ltd.
  21. J. Feng, Y. Li, X. Tian, J. Liu, and K. Zhang “Noise suppression, linewidth narrowing of a master oscillator power amplifier at 1.56nm and the second harmonic generation output at 780nm,” Opt. Express16, 11871 (2008). [CrossRef] [PubMed]
  22. F. Kéfélian, H. Jiang, P. Lemonde, and G. Santarelli, “Ultralow-frequency-noise stabilization of a laser by locking to an optical fiber-delay line,” Opt. Lett.34, 914–916 (2009). [CrossRef] [PubMed]

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