March 15, 2014 / Vol. 39, No. 6 / OPTICS LETTERS
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1/f noise in external-cavity InGaN diode laser at 420 nm wavelength for atomic spectroscopy X. Zeng and D. L. Boïko* Centre Suisse d’Électronique et de Microtechnique, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland *Corresponding author: [email protected] Received February 5, 2014; accepted February 6, 2014; posted February 19, 2014 (Doc. ID 204496); published March 14, 2014 We have extensively studied the frequency noise and relative intensity noise spectra in a tunable external-cavity InGaN diode laser at blue (420 nm) wavelengths. We report flicker (1∕f ) frequency-noise behavior at low Fourier frequencies measured using offset frequency-absorption spectroscopy on 85 Rb vapor cells, which yields an estimated lasing linewidth of 870 kHz. From considerations of high-dislocation density in III nitride epitaxy, 1∕f noise and linewidth were expected to be larger than in conventional III-V lasers. Surprisingly, the measured noise characteristics are comparable to or better than those of near-infrared distributed feedback lasers and externalcavity diode lasers. The noise-reduction mechanism is attributed to the wavelength dependence of 1∕f noise. We discuss challenges in atomic spectroscopy applications caused by defects and mode-clustering effect in GaN lasers. Using the Hakki–Paoli analysis in an aged laser diode, we provide possible explanation about the origin of observed mode clustering. © 2014 Optical Society of America OCIS codes: (140.2020) Diode lasers; (140.3600) Lasers, tunable; (140.7300) Visible lasers; (270.2500) Fluctuations, relaxations, and noise; (300.6260) Spectroscopy, diode lasers. http://dx.doi.org/10.1364/OL.39.001685
Wavelength tunable semiconductor lasers with narrow linewidths, such as external-cavity diode lasers (ECDLs), distributed feedback lasers (DFBs), or vertical-cavity surface emitting lasers (VCSELs) are vital for many applications in atomic physics, spectroscopy, and frequency standards. III-V alloy-based tunable lasers for interrogating D lines of alkali atoms in the near-infrared (NIR) spectral range (e.g., D1 and D2 lines in Cs and Rb atoms) are common, and their noise features are well established. On the other hand, blue–violet tunable lasers based on the group III nitride material are far less common, even though they are necessary tools for interrogating atomic transitions such as the Rb 5S1∕2 − 6P3∕2 (420.18 nm wavelength), Rb 5S1∕2 − 6P1∕2 (421.55 nm), Sr 5S0 − 5P1 (460.7 nm), Sr ion 2S1∕2 − 2P1∕2 (421.55 nm), Ca 4S1∕2 − 4P1∕2 (398.8 nm), and Yb 4S0 −4P1 (398.9 nm). Currently, GaN-based DFBs [1,2] and electrically pumped VCSELs [3,4] are not yet adequately mature for atomic spectroscopy due to challenges of group III nitride epitaxy and processing. GaN-based ECDLs are the most mature and common [5–10], and a few commercial models are available. Most of these ECDLs achieve free-running lasing linewidth on the order of several MHz, though, with active frequency stabilization on a reference, the lasing linewidth can be as low as 7 kHz [10]. The typical mode-hop-free frequency-tuning range is 20–30 GHz, though a tuning range up to 110 GHz has been reported [9]. However, so far all available blue-violet tunable semiconductor lasers lack vital information on the white and flicker noise contributions in frequency noise (FN) and relative intensity noise (RIN) spectra. For the majority of semiconductor lasers, the integral noise features such as the linewidth and RIN are defined by flicker (1∕f ) noise due to generationrecombination processes through recombination centers in defects (e.g., dislocations) [11]. The dislocation density in as-grown GaN laser epitaxy is relatively 0146-9592/14/061685-04$15.00/0
high (>1 × 105 cm−2 [12]) compared to the well-matured conventional III-V materials ( 0.14) [29]. A strong wavelength and cavitylength dependences may explain why low-frequency RIN PSD in our 420 nm ECDL is comparable with that of 852 nm DFB laser despite higher defect density in GaN and, hence, higher amplitude of 1∕f noise sources. The lower RIN PSD in the 780 nm ECDL is attributed to the much lower defect density in technologically matured III-V epitaxy. The origin of excessive RIN PSD in the 423 nm ECDL from [26] is not known. The authors would like to thank the Swiss National Science Foundation (FNS) for funding this research. References 1. R. Hofmann, V. Wagner, H.-P. Gauggel, F. Adler, P. Ernst, H. Bolay, A. Sohmer, F. Scholz, and H. C. Schweizer, IEEE J. Sel. Top. Quantum Electron. 3, 456 (1997).
2. H. Schweizer, H. Gräbeldinger, V. Dumitru, M. Jetter, S. Bader, G. Brüderl, A. Weimar, A. Lell, and V. Härle, Phys. Status Solidi A 192, 301 (2002). 3. T. Onishi, O. Imafuji, K. Nagamatsu, M. Kawaguchi, K. Yamanaka, and S. Takigawa, IEEE J. Quantum Electron. 48, 1107 (2012). 4. G. Cosendey, A. Castiglia, G. Rossbach, J.-F. Carlin, and N. Grandjean, Appl. Phys. Lett. 101, 151113 (2012). 5. H. Leinen, D. Gläßner, H. Metcalf, R. Wynands, D. Haubrich, and D. Meschede, Appl. Phys. B 70, 567 (2000). 6. D. J. Lonsdale, A. P. Willis, and T. A. King, Meas. Sci. Technol. 13, 488 (2002). 7. L. Hildebrant, R. Knispel, S. Stry, J. R. Sacher, and F. Schael, Appl. Opt. 42, 2110 (2003). 8. O. M. Maragò, B. Fazio, P. G. Gucciardi, and E. Arimondo, Appl. Phys. B 77, 809 (2003). 9. J. Hult, I. S. Burns, and C. F. Kaminski, Appl. Opt. 44, 3675 (2005). 10. M. Horstjann, V. Nenakhov, and J. P. Burrows, Appl. Phys. B 106, 261 (2012). 11. S. Pralgauskaite, V. Palenskis, and J. Matukas, in Semiconductor Laser Diode Technology and Applications, D. S. Patil, ed. (InTech, 2012), pp. 133–160. 12. K. Motoki, SEI Tech. Rev. 70, 28 (2010). 13. GaAs wafer specifications from AXT Inc., http://www.axt .com/site/index.php?q=node/37. 14. S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, and H. Kiyoku, Appl. Phys. Lett. 69, 1568 (1996). 15. I. V. Smetanin and P. P. Vasil’ev, Appl. Phys. Lett. 100, 041113 (2012). 16. P. P. Vasil’ev, A. B. Sergeev, I. V. Smetanin, T. Weig, U. T. Schwarz, L. Sulmoni, J. Dorsaz, J. M. Lamy, J. F. Carlin, N. Grandjean, X. Zeng, T. Stadelmann, S. Grossmann, A. C. Hoogerwerf, and D. L. Boiko, Appl. Phys. Lett. 102, 121115 (2013). 17. A. S. Zubrilov, V. I. Nikolaev, D. V. Tsvetkov, V. A. Dmitriev, K. G. Irvine, J. A. Edmond, and C. H. Carter, Appl. Phys. Lett. 67, 533 (1995). 18. R. G. Waters, Prog. Quantum Electron. 15, 153 (1991). 19. I. Ratschinski, H. S. Leipner, F. Heyroth, W. Fränzel, O. Moutanabbir, R. Hammer, and M. Jurisch, J. Phys.: Conf. Ser. 281, 012007 (2011). 20. R. K. Sink, “Cleaved-facet group-III nitride lasers,” Ph.D. dissertation (University of California at Santa Barbara, 2000). 21. E. Caliebe and K. Niemax, J. Phys. B 12, L45 (1979). 22. D. A. Steck, “Rubidium 85 D Line Data,” http://steck.us/ alkalidata/rubidium85numbers.pdf. 23. L. D. Turner, K. P. Weber, C. J. Hawthorn, and R. E. Scholten, Opt. Commun. 201, 391 (2002). 24. G. Di Domenico, S. Schilt, and P. Thomann, Appl. Opt. 49, 4801 (2010). 25. M. Yamada, IEEE J. Quantum Electron. 30, 1511 (1994). 26. J. J. McFerran and A. N. Luiten, J. Opt. Soc. Am. B 27, 277 (2010). 27. C. Affolderbach and G. Mileti, Rev. Sci. Instrum. 76, 073108 (2005). 28. K. Matsuoka, K. Saeki, E. Teraoka, M. Yamada, and Y. Kuwamura, Proc. SPIE 6133, 61330P (2006). 29. R. J. Fronen and L. K. J. Vandamme, IEEE J. Quantum Electron. 24, 724 (1988).
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1/f noise in external-cavity InGaN diode laser at 420 nm wavelength for atomic spectroscopy X. Zeng and D. L. Boïko* Centre Suisse d’Électronique et de Microtechnique, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland *Corresponding author: [email protected] Received February 5, 2014; accepted February 6, 2014; posted February 19, 2014 (Doc. ID 204496); published March 14, 2014 We have extensively studied the frequency noise and relative intensity noise spectra in a tunable external-cavity InGaN diode laser at blue (420 nm) wavelengths. We report flicker (1∕f ) frequency-noise behavior at low Fourier frequencies measured using offset frequency-absorption spectroscopy on 85 Rb vapor cells, which yields an estimated lasing linewidth of 870 kHz. From considerations of high-dislocation density in III nitride epitaxy, 1∕f noise and linewidth were expected to be larger than in conventional III-V lasers. Surprisingly, the measured noise characteristics are comparable to or better than those of near-infrared distributed feedback lasers and externalcavity diode lasers. The noise-reduction mechanism is attributed to the wavelength dependence of 1∕f noise. We discuss challenges in atomic spectroscopy applications caused by defects and mode-clustering effect in GaN lasers. Using the Hakki–Paoli analysis in an aged laser diode, we provide possible explanation about the origin of observed mode clustering. © 2014 Optical Society of America OCIS codes: (140.2020) Diode lasers; (140.3600) Lasers, tunable; (140.7300) Visible lasers; (270.2500) Fluctuations, relaxations, and noise; (300.6260) Spectroscopy, diode lasers. http://dx.doi.org/10.1364/OL.39.001685
Wavelength tunable semiconductor lasers with narrow linewidths, such as external-cavity diode lasers (ECDLs), distributed feedback lasers (DFBs), or vertical-cavity surface emitting lasers (VCSELs) are vital for many applications in atomic physics, spectroscopy, and frequency standards. III-V alloy-based tunable lasers for interrogating D lines of alkali atoms in the near-infrared (NIR) spectral range (e.g., D1 and D2 lines in Cs and Rb atoms) are common, and their noise features are well established. On the other hand, blue–violet tunable lasers based on the group III nitride material are far less common, even though they are necessary tools for interrogating atomic transitions such as the Rb 5S1∕2 − 6P3∕2 (420.18 nm wavelength), Rb 5S1∕2 − 6P1∕2 (421.55 nm), Sr 5S0 − 5P1 (460.7 nm), Sr ion 2S1∕2 − 2P1∕2 (421.55 nm), Ca 4S1∕2 − 4P1∕2 (398.8 nm), and Yb 4S0 −4P1 (398.9 nm). Currently, GaN-based DFBs [1,2] and electrically pumped VCSELs [3,4] are not yet adequately mature for atomic spectroscopy due to challenges of group III nitride epitaxy and processing. GaN-based ECDLs are the most mature and common [5–10], and a few commercial models are available. Most of these ECDLs achieve free-running lasing linewidth on the order of several MHz, though, with active frequency stabilization on a reference, the lasing linewidth can be as low as 7 kHz [10]. The typical mode-hop-free frequency-tuning range is 20–30 GHz, though a tuning range up to 110 GHz has been reported [9]. However, so far all available blue-violet tunable semiconductor lasers lack vital information on the white and flicker noise contributions in frequency noise (FN) and relative intensity noise (RIN) spectra. For the majority of semiconductor lasers, the integral noise features such as the linewidth and RIN are defined by flicker (1∕f ) noise due to generationrecombination processes through recombination centers in defects (e.g., dislocations) [11]. The dislocation density in as-grown GaN laser epitaxy is relatively 0146-9592/14/061685-04$15.00/0
high (>1 × 105 cm−2 [12]) compared to the well-matured conventional III-V materials ( 0.14) [29]. A strong wavelength and cavitylength dependences may explain why low-frequency RIN PSD in our 420 nm ECDL is comparable with that of 852 nm DFB laser despite higher defect density in GaN and, hence, higher amplitude of 1∕f noise sources. The lower RIN PSD in the 780 nm ECDL is attributed to the much lower defect density in technologically matured III-V epitaxy. The origin of excessive RIN PSD in the 423 nm ECDL from [26] is not known. The authors would like to thank the Swiss National Science Foundation (FNS) for funding this research. References 1. R. Hofmann, V. Wagner, H.-P. Gauggel, F. Adler, P. Ernst, H. Bolay, A. Sohmer, F. Scholz, and H. C. Schweizer, IEEE J. Sel. Top. Quantum Electron. 3, 456 (1997).
2. H. Schweizer, H. Gräbeldinger, V. Dumitru, M. Jetter, S. Bader, G. Brüderl, A. Weimar, A. Lell, and V. Härle, Phys. Status Solidi A 192, 301 (2002). 3. T. Onishi, O. Imafuji, K. Nagamatsu, M. Kawaguchi, K. Yamanaka, and S. Takigawa, IEEE J. Quantum Electron. 48, 1107 (2012). 4. G. Cosendey, A. Castiglia, G. Rossbach, J.-F. Carlin, and N. Grandjean, Appl. Phys. Lett. 101, 151113 (2012). 5. H. Leinen, D. Gläßner, H. Metcalf, R. Wynands, D. Haubrich, and D. Meschede, Appl. Phys. B 70, 567 (2000). 6. D. J. Lonsdale, A. P. Willis, and T. A. King, Meas. Sci. Technol. 13, 488 (2002). 7. L. Hildebrant, R. Knispel, S. Stry, J. R. Sacher, and F. Schael, Appl. Opt. 42, 2110 (2003). 8. O. M. Maragò, B. Fazio, P. G. Gucciardi, and E. Arimondo, Appl. Phys. B 77, 809 (2003). 9. J. Hult, I. S. Burns, and C. F. Kaminski, Appl. Opt. 44, 3675 (2005). 10. M. Horstjann, V. Nenakhov, and J. P. Burrows, Appl. Phys. B 106, 261 (2012). 11. S. Pralgauskaite, V. Palenskis, and J. Matukas, in Semiconductor Laser Diode Technology and Applications, D. S. Patil, ed. (InTech, 2012), pp. 133–160. 12. K. Motoki, SEI Tech. Rev. 70, 28 (2010). 13. GaAs wafer specifications from AXT Inc., http://www.axt .com/site/index.php?q=node/37. 14. S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, and H. Kiyoku, Appl. Phys. Lett. 69, 1568 (1996). 15. I. V. Smetanin and P. P. Vasil’ev, Appl. Phys. Lett. 100, 041113 (2012). 16. P. P. Vasil’ev, A. B. Sergeev, I. V. Smetanin, T. Weig, U. T. Schwarz, L. Sulmoni, J. Dorsaz, J. M. Lamy, J. F. Carlin, N. Grandjean, X. Zeng, T. Stadelmann, S. Grossmann, A. C. Hoogerwerf, and D. L. Boiko, Appl. Phys. Lett. 102, 121115 (2013). 17. A. S. Zubrilov, V. I. Nikolaev, D. V. Tsvetkov, V. A. Dmitriev, K. G. Irvine, J. A. Edmond, and C. H. Carter, Appl. Phys. Lett. 67, 533 (1995). 18. R. G. Waters, Prog. Quantum Electron. 15, 153 (1991). 19. I. Ratschinski, H. S. Leipner, F. Heyroth, W. Fränzel, O. Moutanabbir, R. Hammer, and M. Jurisch, J. Phys.: Conf. Ser. 281, 012007 (2011). 20. R. K. Sink, “Cleaved-facet group-III nitride lasers,” Ph.D. dissertation (University of California at Santa Barbara, 2000). 21. E. Caliebe and K. Niemax, J. Phys. B 12, L45 (1979). 22. D. A. Steck, “Rubidium 85 D Line Data,” http://steck.us/ alkalidata/rubidium85numbers.pdf. 23. L. D. Turner, K. P. Weber, C. J. Hawthorn, and R. E. Scholten, Opt. Commun. 201, 391 (2002). 24. G. Di Domenico, S. Schilt, and P. Thomann, Appl. Opt. 49, 4801 (2010). 25. M. Yamada, IEEE J. Quantum Electron. 30, 1511 (1994). 26. J. J. McFerran and A. N. Luiten, J. Opt. Soc. Am. B 27, 277 (2010). 27. C. Affolderbach and G. Mileti, Rev. Sci. Instrum. 76, 073108 (2005). 28. K. Matsuoka, K. Saeki, E. Teraoka, M. Yamada, and Y. Kuwamura, Proc. SPIE 6133, 61330P (2006). 29. R. J. Fronen and L. K. J. Vandamme, IEEE J. Quantum Electron. 24, 724 (1988).
