| Scattering-type scanning near-field optical microscopy (s-SNOM) is a hybrid scanning probe/spectroscopic technique that can achieve a spatial resolution of tens of nanometers in the mid-infrared region. The scanning probe tip strongly localizes and enhances the spectroscopic capabilities, while recording sample topology. Although traditionally a monochromatic technique, making s-SNOM broadband is desirable; data acquisition becomes less time-consuming and there are fewer irreproducibilities. The most promising solution uses difference-frequency generation (DFG) to produce the broadband mid-IR light. Here I attempt to replicate an ultrashort DFG setup that has been shown to provide adequate illumination for and data from broadband s-SNOM experiments. To this effect I use two near-IR lasers -- one essentially monochromatic, the other a supercontinuum -- with ~80 fs pulse durations. At the time of writing, the broad mid-IR frequencies have not been observed, although temporal overlap of the pulses in the nonlinear medium, GaSe, has been confirmed through sum frequency generation. |
