The attributes in the Caustics group control the emission of photons, used to render caustics.
The Caustics group
Enable Caustics
Turning this attribute on will render a one-pass caustic map.
Number Of Photons
This attribute controls the number of photons in the caustic map. It is available only when Enable Caustics is turned on. The default number of photons is 50 000.
Number Of Bounces
This attribute controls the maximum number of specular and diffuse bounces allowed when rendering the caustic map.The default number of bounces is 10.