Mode converted ion cyclotron wave (ICW) has been observed with phase contrast imaging (PCI) in
plasmas in Alcator C‐Mod [1, 2]. The measurements were carried out with the optical heterodyne technique using acousto‐optic
modulators which modulate the CO2
laser beam intensity near the ion cyclotron frequency . With recently improved calibration of the PCI system using a calibrated sound wave source, the measurements have been compared with the full‐wave code TORIC, as interpreted by a synthetic diagnostic. Because of the line‐integrated nature of the PCI signal, the predictions are sensitive to the exact wave field pattern. The simulations are found to be in qualitative agreement with the measurements.