Evanescent Wave Microscopy and White Light Spectroscopy

The evanescent field of a propagating waveguide mode can be used in various ways in microscopy. It basically serves as the illumination source for samples located on the surface of a waveguide. Therefore the microscopy slide has to carry a waveguide at its surface.
On the other hand, by coupling white light into a waveguide device and monitoring the out coupled spectrum one should yield information about the absorption of anything located in the evanescent field. The unique possibility to use either TE or TM modes offers an independent insight in in-lane and out-of-plane absorptions independently.

The evanescent light as the illuminating source of any microscopic object on the surface of the waveguide can serve many purposes. It can be used for:

• scattering light microscopy, where a contast arises from low and high scattering areas
• fluorescence microscopy, where the evanescent field excites chromophores
• absorption phenomena

The objects may vary from inorganic and organic particles or patterned surfaces to biological objects like cells. The wavelength of illumination can easily be chosen, as well as the intensity. To some extend the depth profile can be adjusted by applying the right waveguide mode. Another option is to define a destinct polarisation state by using either TE or TM modes or a combination of both.

For the white light microscopy an adequate coupling mechanism has to be used. The outcoupled intensity will be analysed by means of a spectrometer.