Coherent anti-Stokes Raman scattering microscopy with near-infrared ps pulses synchronized within 50 fs

Abstract

Coherent anti-Stokes Raman Scattering (CARS) microscopy [1] has enjoyed a resurgence following a series of recent improvements such as co-linear excitation geometry [2], and epi-direction detection [3]. An additional refinement has been the use of synchronized ps Ti:Sapphire lasers [4, 5]. Due to their wide tunability, ability of access the fingerprint region (1000 to 2000 cm − 1) and near-infrared center wavelengths, these lasers are almost the ideal light source for CARS imaging. However, the relative timing jitter between the two lasers has remained a fundamental limitation. As CARS is inherently a multi-photon (four-wave mixing) microscopy technique, the presence of timing jitter is directly mapped to fluctuations in the CARS signal itself. In this work, we utilize a new locking method to reduce the timing jitter to below 50 fs. At this level of jitter, stability of the CARS signal is nearly shot-noise limited.