Near-field optical spectroscopy using an incoherent light source

We present a method to perform near-field optical spectroscopy. It consists of an apertureless near-field optical microscope combined with an incohere nt light source and a monochromator. We show that the optical response of t he tip depends both on the wavelength and the tip apex shape. The experimen tal optical response of the tips is in good agreement with the predicted th eoretical one. The near-field optical spectrum obtained on a gold island in the visible spectrum range (lambda=400-600 nm) is presented and shows that the method is reliable to perform spectroscopic measurements on submicrome ter-sized objects. (C) 2000 American Institute of Physics. [S0003-6951(00)0 2204-X].