Photothermal Frequency Response Characterization of Large Deformation Multi-layer Thin Film Structures

In this work, small signal AC photothermal actuation of a large deformation, out-of-plane thin film structure is demonstrated and the frequency response up to 1 kHz is experimentally measured for laser illumination at a wavelength of 1532 nm. Results from frequency sweeps at different AC modulated laser power levels are coincident with a sub-resonant single-pole thermal response with effective cutoff frequencies ∼50 Hz. The maximum angular motion magnitude was ∼1.5° observed at 38 W/cm2 average incident power and modulation frequencies < 10 Hz. No mechanical resonant modes were observed, which was in agreement with simulation using commercial FEA software and additional laser vibrometry performed. The photoactuation measured is attributed to the inherent photoabsorption inherent to a portion of the multilayer stack of the support arms of the structure combined with slight asymmetries in the geometry and alignment of the incident infrared laser. This works shows a viable means quantifying the precision in motion that can be expected for remote actuation of these types of structures via photo illumination.