Synchronization-free all-solid-state laser system for stimulated Raman scattering microscopy

We introduce an extremely simple and highly stable system for stimulated Raman scattering (SRS) microscopy. An 8-W, 450-fs Yb:KGW bulk oscillator with 41 MHz repetition rate pumps an optical parametric amplifier, which is seeded by a cw tunable external cavity diode laser. The output radiation is frequency doubled in a long PPLN crystal and generates 1.5-ps long narrowband pump pulses that are tunable between 760 and 820 nm with >50 mW average power. Part of the oscillator output is sent through an etalon and creates Stokes pulses with 100 mW average power and 1.7 ps duration. We demonstrate SRS microscopy at a 30-μs pixel dwell time with high chemical contrast, signal-to-noise ratio in excess of 45 and no need for balanced detection, thanks to the favorable noise properties of the bulk solid-state system. Cw seeding intrinsically ensures low spectral drift. We discuss its application to chemical contrast microscopy of freshly prepared plant tissue sections at different vibrational bands.