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Near-field Raman imaging using optically trapped dielectric microsphere

Near-field Raman imaging using optically trapped dielectric microsphere. Johnson Kasim et.al. Optics Express(2008) . Outline. Introduction To overcome the diffraction limit Raman spectroscopy Experiment Setup Results C onclusion. To overcome the diffraction limit.

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Near-field Raman imaging using optically trapped dielectric microsphere

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  1. Near-field Raman imaging using optically trapped dielectric microsphere Johnson Kasimet.al. Optics Express(2008)

  2. Outline • Introduction • To overcome the diffraction limit • Raman spectroscopy • Experiment Setup • Results • Conclusion

  3. To overcome the diffraction limit • Going through particles with light • Injecting light stop on sample Light spot ~100 nm Scattering light Particle 1 Particle 2 Sample Resolution (~wavelength/2) Resolution (~light spot)

  4. Raman Spectroscopy

  5. Advanced point the method • Simply to deliver the laser light by fiber • Fiber is keep at a close distance(~tens nm) • Very low laser power(typically 100nW) • Taking a long time(e.q.~10hours) • By using optical tweezers mechanism • The laser is focused to a spot smaller than above method • Taking a short time(e.q.~10minutes)

  6. Experiment Setup o Spot size

  7. Raman spectra from SiGe and poly-Si

  8. Raman images of periodic poly-Si line

  9. Raman images of gold nano-patterns

  10. Conclusion • Report a new design in performing high-resolution near-field Raman imaging • Scanning a 3µm diameter polystyrene microsphere using optical tweezers mechanism • Laser spot size (84nm) • Reducing laser spot size about (48nm by using a 0.5µm diameter polystyrene microsphere • If we reduce brownian motion effect ,obtain better small resolution.

  11. Timetable • Mechanical setup • Beam alignment • Test tapping force • Galvanometer control by function generator • Tracking laser setup • Connect QPD to OT301 • Connect computer to SR830 • GPID card • Convert Adapter(RS232)

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