there are a few tutorials on this site about scanlines, look them up,
BUT:
basicly there are 2 ways to do this:
First the "i can do it myself way":
Depending on the effect you make a new document thats 2x2, 3x3, 6x6, 7x7 or 8x8 pixels (wide and high). In our case for diagonal lines you need 3x3 pixels.
Then zoom in (to see something

) to the max. Suppose that is 3200x .
Fill the layer with 1 of the 2 colors your gonna use, most of the time that would be white (not in my case); and set the foreground color to the second (that would be mostly black).
Then take the pensil tool and make sure you got a 1-pixel hard round tip
then just draw the pattern.
Select all (ctrl+a) and edit > define pattern
then you can close the document and go to your document where you want it applied.
Go to your image and apply it on a seperate layer, lower the opacity (a lot) and change the layer mode (sometimes).
Pictures:
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