Manipulating Soliton Polarization in Soliton Self-Frequency Shift and Its Application to 3-Photon Microscopy in Vivo

Abstract

Soliton self-frequency shift (SSFS) enables energetic femtosecond pulse generation and deep-brain 3-photon microscopy (3PM) in animal models in vivo. The signal level in 3PM is currently limited by the available soliton energy. Here we propose a new maneuverable physical parameter that enables more energetic soliton generation through SSFS in a photonic-crystal (PC) rod. Through both theory and experiment, we demonstrate that circularly-polarized solitons are 1.5 times more energetic than previously reported linearly-polarized solitons. We further demonstrate comparative 3PM of the white matter layer in the mouse brain in vivo with both circularly-polarized and linearly-polarized solitons. The 3.7 times higher 3PM signal excited with circularly-polarized solitons indicates that this novel nonlinear optical technique is promising for 3PM.