Multiphoton signal increase due to repetition rate doubling in a photonic crystal rod

Abstract

Multiphoton microscopy (MPM) has benefitted dramatically from the development of fiber-based technology. Among these technologies, soliton self-frequency shift (SSFS) in photonic crystal (PC) rods uniquely combines high soliton energy (~100 nJ) and broad wavelength tuning range (>100 nm). Recently, high-energy, 1700-nm femtosecond pulses generated by SSFS in a PC rod enabled 3-photon microscopy of mouse hippocampus in vivo. Below damage threshold, acquisition speed is proportional to the repetition rate of the laser. Here we demonstrate a technique for increasing the soliton repetition rate in a PC rod. Through polarization division and polarization multiplexing, we can double the repetition rate of the optical solitons generated in a PC rod. The orthogonally polarized solitons have virtually the same spectrum, pulse width and energy. As an application, we demonstrate that compared with single-polarization soliton, imaging signals are increased by two fold in MPM using our technology, corresponding to the repetition rate doubling of the optical solitons. We expect this technology will help increase the imaging speed or signal levels in MPM. Besides, this technology may overcome the signal generation limit due to the maximum available soliton energy from solid-core PC rods.