  We study experimentally blast wave dynamics on a weakly interacting fluid of
light. The fluid density and velocity are measured in 1D and 2D geometries.
Using a state equation arising from the analogy between optical propagation in
the paraxial approximation and the hydrodynamic Euler's equation, we access the
fluid hydrostatic and dynamic pressure. In the 2D configuration, we observe a
negative differential hydrostatic pressure after the fast expansion of a
localized over-density, which is a typical signature of a blast wave for
compressible gases. Our experimental results are compared to the Friedlander
waveform hydrodynamical model. Velocity measurements are presented in 1D and 2D
configurations and compared to the local speed of sound, to identify supersonic
region of the fluid. Our findings show an unprecedented control over
hydrodynamic quantities in a paraxial fluid of light.
