Number 30 (Story #5), April 18 1991 by Phillip F. Schewe and Ben Stein PHOTON SCANNING TUNNELING MICROSCOPY (PSTM) and near-field scanning optical microscopy (NSOM) are two new techniques that use photons instead of tunneling electrons to image surface structure. Although neither PSTM or NSOM can match the atomic-scale resolution of more conventional scanning microscopes, they are both able to achieve resolutions smaller than the wavelength of the light, the traditional limit for optical microscopy; also they can image non-conducting samples. PSTM, developed at Oak Ridge National Lab (Robert Warmack, 615-974-3342), employs a sharp probe which detects small pulses of light that emerge when the surface being imaged is illuminated from below. In NSOM, developed by AT&T Bell Labs (Eric Betzig, 201-582-3737), light shoots down a very thin glass pipette and reflects from a piece of the sample smaller than the light's wavelength; this technique that may be valuable in checking microcircuit chips. (Science, 5 April.)