FEBRUARY 1999 REPORT FOR

W. CHARLES SYMONS, III

While the majority of the NSOM instrument code was completed last month, system tests and modifications still needed to be performed. In order to adequately test the imaging capabilities of the Near-IR NSOM, a test sample was acquired from Ted Pella, Inc. This sample is a replica of a diffraction grating as seen in Figure 1 below. Specifically, the sample replicates a 2160 lines/mm diffraction grating with a line spacing of 0.463 µm. It remains to be determined whether or not this sample will adequately represent a thin-wire as utilized for the electromagnetic NSOM models being developed. However, during the testing of the NSOM instrument utilizing this sample, a cross-sectional image of the sample was obtained as seen in Figure 2 below.

Figure 1: Ted Pella Diffraction Grating Replica.

Figure 2: Near-IR NSOM Diffraction Grating Image Cross-Section.

At this point, the NSOM system is in the process of being modified. For example, in order to eliminate detector drift, the detector output has been capacitively coupled into the amplifier circuitry. In this manner, slow DC variations can be eliminated while the 650 Hz signal is passed with minimal attenuation. In addition to the NSOM modifications/improvements, preparation for the Pittsburgh Conference presentation entitled NEAR-IR SPECTRAL IMAGING BEYOND THE DIFFRACTION LIMIT is in the process of being completed. Furthermore, the FDTD NSOM code incorporating the Perfectly Matched Layer (PML) absorbing boundary conditions has been completed. However, testing and debugging of this code is currently in progress.