Create

Then duplicate this layer 4 times and merge the duplicated layer together, you will have the following effect:


Rename this layer as “lines” after the merge.
Step 4
Again we duplicate the “lines” layers 3 times, and you will see the colour of the the spectrum become clearer:

Then we merge those duplicated layer together, then use the Free Transform tool to resize it into the following:

Then we can use the Warp Tool (Ctrl + T and right-click select “Warp”), transform it into the following shape:

And here is the effect after warping: