Nanoscale Thermotropic Phase Transitions Enhance Photothermal Microscopy   Signals
  The photothermal heterodyne imaging technique enabled studies of individual weakly absorbing nano-objects in various environments. It uses a photo-induced change in the refractive index of the environment. Taking advantage of the dramatic index of refraction change occurring around a thermotropic liquid crystalline phase transition, we demonstrate a 40-fold signal-to-noise ratio enhancement for gold nanoparticles imaged in 4-Cyano-4'-pentylbiphenyl (5CB) liquid crystals over those in a water environment. We studied the photothermal signal as a function of probe laser polarization, heating power, and sample temperature quantifying the optimal enhancement. This study established photothermal microscopy as a valuable technique for inducing and/or detecting local phase transitions at the nanometer scales. 
A. Nicholas G. Parra-Vasquez (LP2N), Laura Oudjedi (LP2N), Laurent   Cognet (LP2N), Brahim Lounis (LP2N)
physics.optics cond-mat.mtrl-sci