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

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

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

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 <http://resolver.caltech.edu/CaltechETD:etd-06072004-085555>

Mode number l half wavelength l = 4 l = 3

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

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

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

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

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

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

Optical trap Optically trapped single SiO2 microsphere

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

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

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

Result

Result Blue shift

Result Blue shift

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 Semiconductor microparticle (NOT sphere) CO2 laser White light