Fabrication of whispering gallery modes microcavity during optical trapping ASHIDA LAB TOYOTA...
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Transcript of Fabrication of whispering gallery modes microcavity during optical trapping ASHIDA LAB TOYOTA...
Fabrication ofwhispering gallery modes microcavity during optical trappingASHIDA LAB
TOYOTA YUSUKE
Contents Introduction ・ optical cavity ・ whispering gallery modes (WGM) microcavity Motivation Radiation force Experimental method & set up Result Future plan
Optical cavity
d
2d = n λ resonate
application・ laser・ increase of non-linear optical effect・ light amplifier
vacuum
Q-factor & mode volume
Q = τ ντ : photon lifetime in cavityν : resonance frequency
dloss
mode volume
the smaller mode volume become,the more light reflect.
low Q-factor
many losses
WGM Microcavity
High Q-factor despite small mode volume
Wave optics
LASERWave
LASERGeometric
Geometric optics
Mode number Mode number n, m, l
For example
A variety of mode numbersmake 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 <http://resolver.caltech.edu/CaltechETD:etd-06072004-085555>
Mode number l
l = 4 l = 3
half wavelength
Mode number m
m = 0
m = l - 2
m = l
m = 0
m = l - 2
m = l
Free spectra range
Wavelength
Wavelength
FSRl
FSRm Oblate sphere
sphere l = 2
l = 3
l = 4
l = 2l = 3l = 4
inte
nsity
inte
nsity
Previous work
sample
Ablation laser
Laser ablation in superfluid He Melting of optical fiber
CO2 laser
Optical fiber2 K
Fabricate Multiple microcavities at one timeImpossible to select size
Oblate sphereLimited materialPossible to select size
Motivation Size selectivity, high sphericity, a variety of material
Optical trap
trap beam
CO2 laser
surface tensionHow to form sphere ??
Radiation force
Gradient force
Dissipative forceOptical manipulation
Optical trap
Experimental method
Dual beam trap
Gradient force
Optical trap
Dissipative force
d
importantd is longer than that of single beam trap.
Optical trap
Optically trapped single SiO2 microsphere
Set upTi:sapphire laser 784 nm, 1.8 W
CO2 laser 10.6 μm
Polarized BS
L1L2
CF
White light
spectrometer
λ/2
L1
White light
spectrometer
90°
L1 f = 8.00 mm NA = 0.5L2 f = 100 mm
Experimental step
Gradient force
Optical trap
Ultrasonic nebulizer
Ethanol droplet : silica = 3000 : 1
Experimental step① Measure scattering light
White light
CO2 laser
② Melt
③ Measure scattering light again
Result in
tens
ity (a.
u.)
750700650600550wavelength (nm)
scattering spectra calculated spectra 90° direction( ) calculated spectra all direction( )
Result
Blue shift
inte
nsity
(a.
u.)
750700650600550
wavelength (nm)
before melting CO2 (1.2 W) CO2 (2.6 W) CO2 (3.8 W) CO2 (4.2 W)
Result
Blue shift
inte
nsity
(a.
u.)
670665660655650
wavelength (nm)
before melting CO2 (1.2 W) CO2 (2.6 W) CO2 (3.8 W) CO2 (4.2 W)
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.
Future plan
White light
CO2 laser
Semiconductor microparticle (NOT sphere)