Thermal relaxation time and photothermal optomechanical force in sliced photonic crystal silicon nanobeams

Optomechanical devices based on sliced silicon photonic crystal nanobeams could have several use cases in future quantum technologies, especially as quantum transducers between different quantum systems. To create the required pure mechanical states at low temperatures, an understanding of photon absorption, thermal relaxation, and the associated photothermal force is crucial. Here, we characterize the strength of the photothermal force in sliced silicon nanobeam resonators. We extract the thermal relaxation time separately from phonon ray tracing simulations, allowing us to study the strength of the photothermal optomechanical effect without the uncertainty from the thermal relaxation time. With this information, we can put strict upper bounds to the photothermal force and photon absorption ( β parameter) in the devices without knowledge of the cavity photon population. The methods we employ can easily be adapted to other geometries and devices for the study of the photothermal effects.