phase - conjugate optical coherence tomography methods and apparatus . pc - oct may be employed as a three - dimensional imaging technique of interest for biomedical and other imaging applications . it shares much of the source and detection convenience of conventional oct employing classical light sources , which is in clinical use in ophthalmology and is being developed for a variety of endoscopic optical biopsy instruments . pc - oct offers a two - fold improvement in axial resolution and immunity to group velocity dispersion , when compared with conventional oct , that is available from quantum optical coherence tomography . pc - oct does this without q - oct &# 39 ; s need for a non - classical light source and the attendant requirement of photon - coincidence counting detection . thus , in comparison with q - oct , pc - oct is capable of producing images in measurement times similar to those of conventional oct .