Choosing a method

Render Properties → Sampling → Method has two entries.

• Path Tracing is Cycles as you know it, and the default. Photon Caustics and Path Guiding build on it.
• Bidirectional is for caustics and for light from small or hidden lamps. Vertex Merging is an option under it.

Neither is better for everything. Stay on Path Tracing; switch to Bidirectional for caustics seen directly and for small or hidden lamps, and compare at equal render time rather than equal samples.

Baking. Photon Caustics, Bidirectional and Vertex Merging also work when you bake a texture: Combined, or Diffuse, Glossy or Transmission with Indirect ticked. Photons and Merge Radius then count pixels of the baked image instead of the render. For animation, leave Animate Seed off so that a still caustic bakes the same in every frame.