oh, Marc
you can't do that, as you know, after one PBS, the lasers had s and p polaration 50%-50%, the PBS only transmission one polaration and reflect another, if you do that, you just waste one PBS and 2 lasers, you got the same power just like use one.
yeah ,you are right, wavelplate can change the light polarization but it will change both, remember both.
don't worry the reliable of 400mW green lasers, well lasers life time always more than 5000hours,up to 8000hours, some maybe 10000hours(this is always the LD expect life) please attention this threads:
http://www.photonlexicon.com/forums/...ead.php?t=3674.
Best regards!
Bridge