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Ashida lab Toyota yusuke

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1 Ashida lab Toyota yusuke
Fabrication of whispering gallery modes microcavity during optical trapping Ashida lab Toyota yusuke

2 Contents Introduction ・optical cavity
・whispering gallery modes (WGM) microcavity Motivation Radiation force Experimental method & set up Result Future plan

3 Optical cavity d 2d = n λ resonate application ・laser
・increase of non-linear optical effect ・light amplifier d vacuum

4 Q-factor & mode volume Q = τ ν τ : photon lifetime in cavity
ν : resonance frequency mode volume the smaller mode volume become, the more light reflect. d many losses loss low Q-factor

5 WGM Microcavity High Q-factor despite small mode volume Wave optics
Geometric optics High Q-factor despite small mode volume Wave optics Wave LASER Geometric LASER

6 Mode number Mode number n, m, l n = 1 For example
A variety of mode numbers make a variety of mode patterns. Fundamental WGM n = 1 Kippenberg, T.J.A. Nonlinear optics in ultra-high-Q whispering-gallery optical microcavities. (2004). at < >

7 Mode number l half wavelength l = 4 l = 3

8 Mode number m m = 0 m = l - 2 m = l m = l m = l - 2 m = 0

9 Free spectra range sphere Oblate sphere intensity l = 2 FSR l l = 4
Wavelength l = 3 FSR m Oblate sphere intensity l = 4 Wavelength

10 Previous work Laser ablation in superfluid He Melting of optical fiber
sample 2 K Optical fiber Ablation laser CO2 laser Fabricate Multiple microcavities at one time Impossible to select size Oblate sphere Limited material Possible to select size

11 Motivation Optical trap
Size selectivity, high sphericity, a variety of material Optical trap CO2 laser trap beam How to form sphere ?? surface tension

12 Radiation force Optical manipulation Optical trap Dissipative force
Gradient force Optical trap

13 Experimental method Optical trap Dual beam trap Dissipative force d
Gradient force important d is longer than that of single beam trap.

14 Optical trap Optically trapped single SiO2 microsphere

15 Set up Ti:sapphire laser 784 nm, 1.8 W CF λ/2 L1 f = 8.00 mm NA = 0.5
CO2 laser 10.6 μm Polarized BS L1 L2 CF White light spectrometer λ/2 L1 f = 8.00 mm NA = 0.5 L2 f = 100 mm White light spectrometer 90° L1

16 Experimental step Optical trap Gradient force Ultrasonic nebulizer
Ethanol droplet : silica = 3000 : 1

17 Experimental step ① Measure scattering light ② Melt
CO2 laser White light ② Melt ③ Measure scattering light again

18 Result

19 Result Blue shift

20 Result Blue shift

21 Summary We achieved optical trapping of a single SiO2 microsphere
and observed WGM spectra. We melted the optically trapped single SiO2 microsphere and observed blue shift of the WGM spectra.

22 Future plan Semiconductor microparticle (NOT sphere) CO2 laser
White light

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