This paper describes a simple method for the real time measurement of the optical diameter and the spa-tial peak spectral intensity of the axially symmetric arc plasmas. The method only uses the integrated radia-tion intensities across the plasma column and along the central line of plasma cross section, which are meas-ured by a 2-channel programmable digital storage oscilloscope to obtain continuously the temporal variation of the optical diameter and the spatial peak spectral intensity of the plasmas. This method was applied to a Hg arc plasma and it was found out that the optical diameter had no tem-poral variation even if the discharge current was varied.
We developed a near-field scanning optical microscope (NSOM) giving infrared spectra in an area smaller than the diffraction limit of the infrared light. The developed NSOM features a probe which is equipped with a slit aperture to improve the efficiency in collecting the near-field light. The illumination light is generated with a Michelson interferometer as an interference light and the transmission spectrum of sample at the local position is given through the slit of probe. The experimental results with a test chart and a two-layered film show that the spatial resolution of the IR-NSOM developed depends only on the slit width and not on the wavelength of the illumination light. The spatial resolution of the microscope has been numerically analyzed with finite-difference time-domain (FD-TD) method.