Cd-S photocells have peak response to green / green-yellow (as the human eye.)
They have a wide response nonetheless.
Photodiodes are more sensitive still and have even wider "bandwidths".
Then you're using a laser, a high-intensity source, with it.
You're not going to come up with an optical filter that'll radically attenuate all but your desired narrow green wavelength. (Not inexpensively so, anyway.)
It's possible that you could considerably attenuate, with mylar tape or something, all light (wavelengths) such that only a laser's intensity could get through.