  We report on the evolution of the charge density wave (CDW) and spin density
wave (SDW) order of a chromium film following photoexcitation with an ultrafast
optical laser pulse. The CDW is measured by ultrafast time-resolved x-ray
diffraction of the CDW satellite that tracks the suppression and recovery of
the CDW following photoexcitation. We find that as the temperature of the film
approaches a discontinuous phase transition in the CDW and SDW order, the time
scales of recovery increase exponentially from the expected thermal time
scales. We extend a Landau model for SDW systems to account for this critical
slowing with the appropriate boundary conditions imposed by the geometry of the
thin film system. This model allows us to assess the energy barrier between
available CDW/SDW states with different spatial periodicities.
