All-solid-state sub-picosecond optical parametric oscillator laser system for multiphoton fluorescence imaging

We have developed a robust and reliable femtosecond synchronously pumped singly resonant optical parametric oscillator based on a 3mm long periodically poled lithium niobate (PPLN) crystal, with grating periods of 30 μm to 31,2 μm in 0.2 μm increments and utilised sum-frequency mixing to generate orange/red continuously tunable sub-picosecond radiation for application to two-photon fluorescence imaging. A coherent DPM-1000 diode-pumped, mode-locked, pulse compressed Nd³⁺:YLF laser (600 mW, 120 MHz, 400 fs, at 1047 nm) was used to pump the optical parametric oscillator. The practical performance of the laser system is discussed and imaging of a range of biologically significant samples is presented, including cardiac myocytes labelled with Indo-1 (Molecular Probes, Inc).