Gold Nanobumps Manipulate Light

Gold Nanobumps Fabricated by Femtosecond Laser System

A Ti:sapphire femtosecond laser is used to fabricate the artificial structure. An attenuator and a shutter with switching time of 30 ms are used for the control of the incident laser fluence and exposure time. The laser beam is expanded to a diameter of 6 mm by a spatial filter. A +/4 waveplate transforms the laser beam into circular polarization. Finally, the laser beam is focused by a high-numerical-aperture oil-immersion objective lens through the transparent substrate on the 30-nm Au film on cover glass. An Au nanobump with its height around 16 nm can be fabricated with average laser power of 240 mW for 30 ms. The artificial plasmonic structure formed by nanobumps is made and controlled by a threedimensional nanometer precision stage. The surface morphology of the artificial structure is characterized by an atomic force microscope (AFM).

Total Internal Reflection Microscope (TIRM) System

A total internal reflection microscope (TIRM) system based on an Olympus IX70 microscope and a Nd:YAG laser of 532 nm wavelength are used. A fiber illuminator is built up to control the incidence angle of total internal reflection. An oil-immersion objective is used for this purpose. The polarization of the incident beam is set by the polarizer. The reflected laser beam is blocked by the stop, and the scattering light and dark field image can be captured by a CCD camera. We can adjust the focal plane of the objective along the z-axis to construct the trajectories of scattered light in 3D. The inset shows that the surface plasmonic wave on the Au thin film is launched by a TM-polarized laser beam with an incident angle of 45°.

3D Plasmonic Micro Focusing

Backward and forward scattering of surface plasmonic wave interactions from gold nanobumps on the surface of a 30-nm gold thin film demonstrate three-dimensional (3-D) focusing and diverging properties. Fan-shaped forward scattering of an individual nanobump is observed. A quarter-circle structure composed of nanobumps is exploited to manipulate scattering from each nanobump. Experimental results show that 3-D propagation vectors generated by the gold nanobumps with their heights of 16 nm can deflect the surface plasmonic waves to produce 3-D focusing at 3.6 μm above the surface of the gold film. We clearly demonstrate that 3-D forward and backward focusing from gold nanobumps are with different amplitudes and directions of the vertical propagation vectors.

Light Manipulation by Gold Nanobumps

C. M. Chang, C. H. Chu, M. L. Tseng, Y.-W. Huang, H. W. Huang, B. H. Chen, D.-W. Huang, D. P. Tsai

Plasmonics 7(3), 563-569 (2012) [Link, Movie1, Movie2]

3D Plasmonic Micro Projector

Using the curved arrangement of Au nanobumps, the scattering of surface plasmon waves are transformed into spots at desired locations and altitudes in three-dimensional space. The light can be modulated into desired light patterns. This work is very promising for compact plasmonic circuitry, projection, live-cell imaging, optical sensing, and holography.

Three-dimensional plasmonic micro projector for light manipulation

C. M. Chang, M. L. Tseng, B. H. Cheng, C. H. Chu, Y. Z. Ho, H. W. Huang, Y.-C. Lan, D.-W. Huang, A. Q. Liu, Din Ping Tsai

Advanced Materials, in press (2012). [Link]

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