Sub 100 nm resolution confocal focus-engineered coherent anti-Stokes Raman scattering microscopy under non-degenerate pumping condition

For the development of microscopic tools that can resolve non-fluorescent samples beyond the diffraction limit, we propose focus-engineered non-degenerate pumped coherent anti-Stokes Raman scattering (CARS) using spatial light modulator (SLM)-based phase shaping, liquid lens focus control, and confocal detection. Non-degenerate pumped CARS (ND-CARS) with frequency-doubled probe pulses resulted in approximately 75% improvement in resolution compared to that of degenerate CARS. Focal adjustment using the liquid lens facilitated the accurate overlapping of three beams. The circular π-phase modulation at the center of the probe-beam wavefront demarcated the net CARS focal volume into a sub 100 nm-scale core and surrounding side lobes. The confocal geometry detection setup successfully removed the side lobes, allowing optical imaging of 81 nm-sized zinc oxide particles at 87 nm, and edge-to-edge resolution was determined to be 103 nm.