how to use diffractive diffuser for laser

i want to use a diffuser for the laser . the diffuser used is a diffractive diffuser . can any body tel me how to fit the diffuser and what al specifications i have to look for in the diffuser if i have to cover a big area around 4 meters at about 800 meters .im using a red laser .please help

Have you tried googling for laser diffusers? Assuming they're commercially available the manufacturer should be able to provide the information you want.