Scanning near-field optical microscopy using a slit-type probe is discussed. The slit-type probe has a width of much less than a wavelength, &lgr;, and a length on the order of &lgr;, and thus has high transmission efficiency. Two dimensional near-field images of objects have been constructed using an image reconstruction algorithm based on computerized tomographic imaging. Experiments performed at 60 GHz(&lgr;=5 mm)show that this type of near-field microscopy can achieve a spatial resolution of better than&lgr;/45for two dimensional imaging. A method for fabricating a submicron width slit probe at the end of an optical fiber is presented for extending this microscopy to optical waves. ©1997 American Institute of Physics.