Figure 4. AFM-IR measurements of circularly dichroic thermal expansion of the metasurface.
(a) Experimental setup. Light from a QCL passes through a quarter-wave plate (QWP) and illuminates the sample from CaF2 substrate. Local Ohmic heating of nanoantennas causes local heating and expansion of the polyethylene (PE) film and leads to cantilever deflection, which is detected by observing laser tracer beam deflection from cantilever, using position-sensitive photodetector (PSPD) and a lock-in amplifier, referenced by the QCL pulse repetition frequency. (b) COMSOL simulations of the temperature increase distribution in the polyethylene film at the end of a square QCL pulse with time duration T=200 ns and peak intensity I=1 kW cm−2 tuned to λ=9.1 μm, corresponding to the experimental conditions. (c) AFM-IR cantilever deflection on top of a PE-coated sample excited with RCP (left panel) and LCP (right panel) laser pulses at normal incidence through the CaF2 substrate.