Nomenclature meaning? - (Nov/13/2020 )

Hi, I am making a research on a plant (Polygonum tinctorum), and I was given other names for it. like Persicaria tinctoria (Aiton) Spach & Pogalis tinctoria (Aiton) Raf.

What is the meaning ​of "Aiton", Spach. and Raf.? I can't find any botanical references in dictionaries or Internet. The meaning they give me don't make any sense.

Aiton and spach are the names of botanists who determined the names.