Another SPM related technique. An optic fibre is stretched and thinned such that it has a very sharp point. It is then coated such that only a small hole at the end of the fibre can transmit light. The tip is brought very close to the surface. The tip-surface distance can be measured via the force acting between the two. Light can be shone down the fibre, or light can be detected via the fibre from a 'distant' light source. The tip is scanned across the surface as in STM. NSOM (also known as SNOM), can detect objects below the diffraction limit (down to the nm regime) and thus represents a powerful new technique in optical microscopy.