Medical fiber lasers and example application to laser nerve stimulation

Summary form only given. As an example of the medical applications of fiber lasers, a CW Tm³⁺-silica fibre laser is described which has been designed for nerve activation and pain stimulation. The output wavelength near 2 μm is close to a tissue-OH absorption peak, with negligible absorption by hemoglobin or melanin, and tunability over about 70 nm. The thermal stimulus arising from the absorption effectively activates pain-specific, partially myelinated A-delta and unmyelinated C nerve fibres. The laser output is pulse modulated to provide control of pulse duration, inter-pulse time intervals or pulse sequences, and tuned to give control over the depth location of the activated nociceptors. The controlled pain stimulation is monitored by functional brain imaging, based on EEG, PET and fMRI, giving cerebral activation with spatial and temporal resolution. Interest in this system includes understanding of the mechanism and physiology of pain processing and behavior and pain management.