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)