Abstract
In this paper we excite bound long range stripe plasmon modes with a highly focused laser beam. We demonstrate highly confined plasmons propagating along a 50 µm long silver stripe 750 nm wide and 30 nm thick. Two excitation techniques were studied: focusing the laser spot onto the waveguide end and focusing the laser spot onto a silver grating. By comparing the intensity of the out-coupling photons at the end of the stripe for both grating and end excitation we are able to show that gratings provide an increase of a factor of two in the output intensity and thus out-coupling of plasmons excited by this technique are easier to detect. Authors expect that the outcome of this paper will prove beneficial for the development of passive nano-optical devices based on stripe waveguides, by providing insight into the different excitation techniques available and the advantages of each technique.
Highlights
The use of plasmon waveguides for the development of sensitive nanoscale sensors and passive optical devices is a hot topic in photonics research [1,2,3]
The symmetric mode attenuation dramatically decreases with reducing metal thickness resulting in Long Range Surface Plasmon Polaritons (LRSPPs)
Whilst a number of theoretical papers based on stripe waveguide excitation in the visible predict the existence of bound LRSPP plasmon modes, there has been no experimental confirmation of this [10,11,12,13]
Summary
The use of plasmon waveguides for the development of sensitive nanoscale sensors and passive optical devices is a hot topic in photonics research [1,2,3]. They are one of the simplest waveguide structures that allow nanoscale confinement of the light in two dimensions They consist of a metallic rectangular bar surrounded by a dielectric medium, and theoretically can support LRSPPs which propagate micron distances at or near visible excitation. The plasmon mode supported by the waveguide leaks into the air region and its presence is detected via near field scanning optical microscopy techniques [14] Such waveguides do not provide the same level of field confinement in two dimensions due to the leaky nature of their modes. The position of the focused beam onto the grating was optimised for maximal output intensity at the stripe end This type of end coupling has been reported before for near IR excitation, and is known as broadside excitation [7]. Authors believe this work is the first attempt to excite bound LRSPP in the visible region
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