Nonlinear microscopy (NM) enables us to investigate the morphology or monitor the
physiological processes of the skin through the use of ultrafast lasers. Fiber (or
fiber-coupled) lasers are of great interest because they can easily be combined with
a handheld, scanning nonlinear microscope. This latter feature greatly increases the
utility of NM for pre-clinical applications and in vivo tissue imaging. Here, we present
a fiber-coupled, sub-ps Ti-sapphire laser system being optimized for in vivo, stain-free,
3D imaging of skin alterations with a low thermal load of the skin. The laser is pumped
by a low-cost, 2.1 W, 532 nm pump laser and delivers 0.5-1 ps, high-peak-power pulses
at a similar to 20 MHz repetition rate. The spectral bandwidth of the laser is below
2 nm, which results in a low sensitivity for dispersion during fiber delivery. The
reduction in the peak intensity due to the increased pulse duration is compensated
by the lower repetition rate of our laser. In our proof-of-concept imaging experiments,
a similar to 1.8 m long, commercial hollow-core photonic bandgap fiber was used for
fiber delivery. Fresh and frozen skin biopsies of different skin alterations (e.g.,
adult hemangioma, basal cell cancer) and an unaffected control were used for high-quality,
two-photon excitation fluorescence microscopy (2PEF) and second-harmonic generation
(SHG) z-stack (3D) imaging.
