All-solid-state sub-40-fs self-starting Cr4+:forsterite laser with holey-fiber beam delivery and chirp control for coherence-domain and nonlinear-optical biomedical applications

An all solid-state sub-40-fs self-starting Cr4+: forsterite laser with a wavelength tunable within the range of 1.21-1.29 mum adapted in its power, temporal, and spectral parameters for high-resolution optical coherence tomography (OCT) and nonlinear-optical tissue imaging is presented. Stable self-starting mode locking in the created laser is achieved both with and without semiconductor saturable-absorber mirrors, while the double-pulse regime of lasing permits time-resolved measurements on biological systems to he performed. Frequency doubling is implemented through second-harmonic generation in a 2.5-mm-long DCDA crystal, ensuring group-velocity matching for femtosecond pulses produced by the Cr: forsterite laser. A set of holey fibers with a period of the photonic-crystal structure of the cladding ranging from 468 nm to 32 mum ensure the tunability of the photonic band gap of the cladding within a broad spectral range, providing different waveguiding regimes for Cr4+: forsterite laser radiation.