Macroscopic multiphoton biomedical imaging using semiconductor saturable Bragg reflector modelocked Lasers

We report on the development of practical and user friendly lasers for multiphoton imaging of biological material. The laser developed for the work is a laser diode pumped Cr:LiSAF source modelocked using a saturable Bragg reflector as the passive modelocking element. From this system we routinely obtain 100fs pulses at a repetition rate 200MHz with an average output power of 20mW. The laser has a single operator control and is particularly suitable for use by non-laser specialists. We have used the source developed to image a range of biologically significant samples. The initial work has centred on the imaging of intact human dental tissue. The first two-photon images of dental tissue are reported showing the development of early dental disease from depths up to 500 mu m into the tooth. These results demonstrate the detection of carious lesions before the more conventional techniques currently used by dental practitioners. Work on other living intact biological tissue is also reported, in particular plants containing a genetically bred fluorescent marker to enable the examination of complete and intact living plant tissue.