Squeezed film damping at the nanoscale

01.01.2014, 00:00

Newsletter 7

The freely-suspended glass membranes in an evacuated dual-nanoweb fibre, driven at resonance by intensity-modulated light, exhibit a giant optomechanical nonlinearity. In recent experiments we investigated the effect of different gas pressures on the resonant frequency and Q-factor. As a consequence of the unusually narrow slot between the nanowebs (22 µm by 550 nm, the webs being ~440 nm thick), the gas-spring effect causes a pressure-dependent frequency shift that is ~15 times greater than typically measured in micro-electro-mechanical devices. On the other hand, squeezed-film damping causes the mechanical Q-factor to increase strongly as the pressure is reduced (see figure). The agreement between experiment and a model based on free-molecular energy transfer is remarkably good, especially since no free parameters are used. Squeezed-film damping and gas stiffness thus play key roles in determining the resonant frequency and Q-factor of the mechanical resonances. The results also show that in the low pressure regime, which is of great interest in many optomechanical systems and devices, an analytical solution can be sufficient to describe the squeezed-film damping effect in real structures.

Contact: johannes.koehler(at)mpl.mpg(dot)de
Group: Russell Division
Reference:  J. R. Koehler et al., Appl. Phys. Lett. 103, 221107 (2013).