Abstract

Low-coherence interferometry techniques such as OCT [1] and whole-field coherence gated imaging, e.g. [2], often require high average power broadband sources for application in turbid media such as biological tissue. We present a tunable, diode-pumped, all-solid-state, c.w. broadband laser source that provides up to ~ 100 mW average power in a single spatial mode and avoids the complexity of mode-locked lasers. By spatially dispersing the laser spectrum within the diode-pumped gain medium [3], we demonstrate a low-cost broadband high brightness source, based on 3-mirror Cr:LiSAF and Cr:LiSGaF lasers (figure 1) that will potentially scale to higher powers and can be applied to other gain media. We readily obtain tunable spectra (e.g. figure 2) with bandwidths up to ~ 15 nm and have also applied this radiation to 3-D imaging through turbid media using depth resolved photorefractive holography. Spectral widths exceeding 65 nm have also been observed but such spectra are discontinuous (we attribute the observed spectral modulation to scattering inhomogeneities in the laser crystals). We note that we were able to couple this broadband radiation into a single-mode optical fibre with 80% efficiency.

© 2000 IEEE