To see progress messages when rendering, set Verbosity Level to Progress messages in Render > Render Current Frame or Render > Batch Render >.
To render caustics
Caustics-receiving objects should have a high diffuse shader, for example, Lambert set to 0.8.
Select Windows > Rendering Editors > Render Settings or click the Render Settings window icon.
Caustics (in the Rendering Features section of the Features tab) is automatically enabled.
If the default settings are not sufficient to achieve the look you want (or to reduce render speed), tweak the caustics settings until you achieve the look you want. See Caustics and Global Illumination for more information.
If your scene contains caustics, global illumination or final gather, and you would like to see those effect during mental ray IPR, in Render View select IPR > IPR > Render Settings.