In this work we present experimental demonstration of focal-field engineering in infrared-sensitive third-order sum frequency generation (TSFG) microscopy by utilizing beam-shaping technique. Two photons of the input mid-infrared (MIR) beam at 3000 nm are upconverted to 615 nm in the presence of a single photon at 1040 nm through the TSFG process. The focal-field engineering scheme studied here improves optical resolution and contrast of the TSFG imaging. We observe best improvement of ~43 % in the central-lobe full-width half diameter with ~35% side-lobe strength of that of the central-lobe with the use of optimum phase-mask using isolated amorphous silicon (a-Si) nano disks as the sample. We compare the contrast enhancement between the experiments and simulations as a function of varying grating pitch and find good overall agreement between the two. In addition to annular phase masks, we also demonstrate edge contrast enhancement by imaging gratings with higher-order Hermite-Gaussian beams profile generated using horizontally partitioned 0-đťś‹ phase profile.
We present the coherent anti-Stokes Raman scattering (CARS) microscopy system that has been implemented by using a photonic crystal polarization maintaining optical fiber. Free space CARS system is hard in alignment and unstable in harsh environment. To overcome this problem the femto-second laser pulses of pump and the Stokes beams were delivered through the optical fiber, so that the system became less complex and robust to the surrounding environment. In order to confirm the feasibility of the fiber-based CARS system, the CARS images of polystyrene beads and zinc oxide (ZnO) are presented.
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