Dual-spectrum laser source based on fiber continuum generation for integrated optical coherence and multiphoton microscopy

A single-laser dual-spectrum source designed for integrated optical coherence and multiphoton microscopy is demonstrated. The source implements the laser characteristics needed to optimally perform both modalities while extending the spectral range for this imaging technique. It consists of a widely tunable, mode-locked, Ti-sapphire laser with a portion of its output spectrally broadened via continuum generation in a photonic crystal fiber. The continuum-broadened beam allows for enhanced optical sectioning with optical coherence microscopy, while the unbroadened beam from the ultrashort-pulse Ti-sapphire laser optimally excites fluorescent markers. The noise power of the continuum-broadened beam is less than 1.1 dBmHz higher than the Ti-sapphire laser in the range from 1 Hz to 25 MHz, and the fiber shows no sign of damage after approximately 100 h of use. We demonstrate the use of this source across a wide spectral range by imaging green fluorescent protein-transfected mouse fibroblast cells costained with fluorescent dyes that are maximally excited at various wavelengths. Images of unstained in vivo human skin are also presented. This source extends the feasibility of this integrated imaging modality and will facilitate new investigations in in vivo microscopy, tissue engineering, and cell biology.