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消逝波增益耦合的石英球腔中的受激拉曼散射研究

消逝波增益耦合的石英球腔中的受激拉曼散射研究. 普小云 陈天江 王亚丽 ( 云南大学物理系 ) . 云南省物理学会 2005 年学术年会 云南蒙自. High Q Micro - Cavities:. Examples : - Droplets ( R. K. Chang group ); Silica micro-spheres ( H. J. Kimble group ); Micro-toroids ( K. J. Vahala group ) - Liquid pendant drops ( Ours ).

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消逝波增益耦合的石英球腔中的受激拉曼散射研究

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  1. 消逝波增益耦合的石英球腔中的受激拉曼散射研究消逝波增益耦合的石英球腔中的受激拉曼散射研究 普小云 陈天江 王亚丽 ( 云南大学物理系 )  云南省物理学会 2005年学术年会 云南蒙自

  2. High Q Micro - Cavities: • Examples : • - Droplets (R. K. Chang group); • Silica micro-spheres (H. J. Kimble group); • Micro-toroids (K. J.Vahala group) • - Liquid pendant drops ( Ours) Characteristics: Gain material = Cavities, cavities are composed by gain medium Xiao-Yun Pu, Chiu-Wah Chan,Wing-Kee Lee, Optics letters, Oct 2000, 25(20) 1514 Xiao-Yun Pu, Wing-Kee Lee, Optics letters, April 2000, 25(7) 466

  3. Is it possible to separate the gain medium from cavities ? Cylindrical Micro-cavity Pump lasing Dye lasing gain(Rhd. 6G dye in ethanol) Dye lasing Yes, since there exists evanescent wave coupling between the gain molecules outside and the resonator modes inside. Hee-Jong Moon, et al., Physical Review Letters, 85(15), Oct 2000, 3161

  4. How about Raman gain surrounding a micro-sphere ? Fabrication of quartz micro-spheres: Mirror Lens Fiber Lens Mirror Video monitor Diameter 30 ~ 300 m CO2 Laser Beam split Mirror

  5. Experimental Setup Water l=1; m=n Beam Calibration Focus Lens Optical Cell Spherical Cavity Pure Water YAG Laser L Light Collection Lens Long wave pass Filter Spectrum Acquiring System

  6. Experimental results - 1 P2′ P1′ 1, Spontaneous Raman Spectrum 10 pulses, Raman spectrum of water Filtered with FFT

  7. Experimental results - 2 P2 P1 2, Stimulated Raman Spectrum from Optical Cell L = 10 cm Spectrum Acquiring System One pulse, SRS spectrum of water, Ep =1.6 mJ

  8. Experimental results - 2 L = 10 cm Lowing down Ep =1.60 to 1.41mJ , no SRS can be seen. After inserting spherical cavity , SRS re-excited.

  9. Experimental results - 3 3, SRS Spectra with Evanescence Coupled Gain D = 96 m;  = 21.4 cm-1 Ep =1.41 mJ

  10. D = 126 m;  = 18.6 cm-1 D = 36 m; = 60.7 cm-1 D = 210 m; = 10.6 cm-1 D = 170 m; = 13.8 cm-1

  11. Explanation 1, Mode intervals of SRS Spectra Assuming: only first order WGM supporting SRS, the mode interval should be Where, n =1.457 is the refraction index of cavity; D is the diameter of a cavity used.

  12. Cavity diameter （mm）  (1st order value) （cm-1）  (Experimental value)（cm-1） 36 63.3 60.7 64 34.1 35.1 96 22.8 21.4 126 17.3 18.6 170 12.9 13.8 210 10.4 10.6 270 8.1 8.5

  13. 2, Why only the first order WGM supports SRS ? The model of Photonic atom: Arnold S., American Scientist 89, (2001) 214 The lower order number, the lower WGM locates in the voltage well; The depth of voltage well decreases with the relative refraction index (n). 2nd order ,1st order nc/no =n

  14. 3, How evanescence field changes with n ? Ethanol n↘ d＝3μm n ＝1.47  = 0.12 = evanescence field / total field↗ Which is benefit to the SRS Water d＝3μm n ＝1.50  = 0.11 (evanescence) ↗ → Q ↘ Vacuum d ＝3μm n ＝2.0  = 0.06 Which is not benefit to the SRS

  15. L = 10 cm 100 m 4, the comparison between two SRS processes • Assuming: Q =3107(>109 in the vacuum ); • w = 31015 s-1 (red light); Thus :  =Q /w =10-8 s ＞tlaser =7 10-9 s Gain length = 10 cm 6600 turns ! In the time interval tlaser(gain time) , Raman Photons run a distance of 206 cm, that is, Gain length~206 cm

  16. Conclusion 1, SRS can be excited from a micro-cavity via evanescence wave coupled gain ; 2, A micro-sphere can service as SRS signal sensor , which can be used in various Raman medium; 3, The related theory needs to be further developed.

  17. 谢 谢 !

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