  Bolometers are a powerful and vital means of detecting light in the IR to THz
frequencies, and they have been adopted for a range of uses from astronomical
observation to thermal imaging. As uses diversify, there is an increasing
demand for faster, more sensitive room-temperature bolometers. To this end,
graphene has generated interest because of its miniscule heat capacity and its
intrinsic ultra-broadband absorption, properties that would allow it to quickly
detect low levels of light of nearly any wavelength. Yet, graphene has
disappointed its expectations in traditional electrical bolometry at room
temperature, because of its weakly temperature-dependent resistivity and
exceptionally high thermal conductivity. Here, we overcome these challenges
with a new approach that detects light by tracking the resonance frequency of a
graphene nanomechanical resonator. The absorbed light heats up and thermally
tensions the resonator, thereby changing its frequency. Using this approach, we
achieve a room-temperature noise-equivalent power of 7 pW/Hz^1/2, a value 100
times more sensitive than electrical graphene bolometers, and speeds (1.3 MHz)
that greatly surpass state-of-the-art microbolometers.
