Temporally and spatially incoherent holography using photorefractive multiple quantum well devices

Abstract

Summary form only given. Near infrared radiation offers the potential for medical diagnostic and functional imaging in biological tissue since the absorption of a typical tissue in this region is at a minimum. However, the scattering of light in tissue in this spectral region is a significant problem and much research has been motivated by the desire to recover image information in the presence of this scattered light. In particular, various schemes have been devised to form images using ballistic (or unscattered) light, which is normally obscured by the presence of the highly diffuse background. These techniques include spatial filtering, time gating and coherence gating. Photorefractive holography is a coherence gating technique like OCT but it differs in that it is a 'whole field' imaging technique that acquires all the pixel information in parallel. When imaging in the reflection geometry using backscattered light, coherence gating can also provide depth-resolved (time-of-flight) image information. The coherence length of the light source primarily determines the depth resolution. Photorefractive MQW devices have been used to record spectrally resolved holograms, as well as recording images direct-to-video through scattering media. The authors are motivated by the desire to develop an imaging technique for applications such as skin cancer detection. For this task imaging through solid scattering media is an important issue.