Abstract

Our work focuses on combining ultrafast time resolved spectroscopy with the subwavelength spatial resolution of Near-field Scanning Optical Microscopy (NSOM). We use a variant of the equal pulse correlation (EPC) [1] in combination with NSOM by sending both pump and probe pulses through a sub-200-nm NSOM tip [2]. While other workers in the field have sent one or both pulses to the sample via conventional far-field optics, our technique has two unique features which may be advantageous, and which form the subject of this paper. The first is an apparent decrease in the depth of field, and the second is the possibility to measure carrier transport with submicron spatial resolution. An arrangement sending both "pump" and "probe" pulses through the NSOM tip [3] may be advantageous when applying NSOM to "thick" samples, such as semiconductor materials and devices, because it appears to have a shallow depth of field built-in to it. We present measurements which put an upper bound on the depth of field in this type of experiment and show the main features of the data can be qualitatively reproduced by a simple dipole model.

© 1996 Optical Society of America