  A design for photoacoustic mass sensors operating above 100 GHz is proposed.
The design is based on impulsive optical excitation of a pseudosurface acoustic
wave in a surface phononic crystal with nanometric periodic grating, and on
time-resolved extreme ultraviolet detection of the pseudosurface acoustic wave
frequency shift upon mass loading the device. The present design opens the path
to sensors operating in a frequency range currently unaccessible to
electro-acoustical transducers, providing enhanced sensitivity, miniaturization
and incorporating time-resolving capability while forgoing the piezoelectric
substrate requirement.
