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