hi,
i ve rendered this image following a tutorial and now i have no idea how to get rid of this noisy caustic and get instead of it more smooth caustics.
cheers
Is this in yafray?
oh, i did not mention ist? yes it is 
It’d be a good idea to tell us how you exactly did the caustics…probably show us the tutorial and tell us if you went along with it exactly. Without knowing your setup it’s hard to say how to improve the caustics (for me, at least). But probably you should tone down the intensity a bit, right now the caustics look way too strong.