Sorry to throw this wobbly bit in, but these beamsplitters are typicaly 50/50 (ie 50 percent transmission and 50% reflectance)- that means you're only gonna get 50% power from each laser... and 50% plus 50% equals the initial power of one laser
Even using two right angled prisms cemented together in the typical beamsplitter arrangement (like two prisms glued together to make a cube) you're only gonna get 50/50 by definition... that's what a beamsplitter does, it erm... splits the beam. In actual fact you'll only get 50/50 in a perfect optical beamsplitter, in reality it'll be less that 50% due to absorbtion, diffraction and dispersion.
Sorry!
Oh also, if you're sticking a diverging or converging beam through a transmitting flat set at 45 degrees you'll get astigmatism, to correct for this you need to have a slight wedge in the beamsplitter- when I used to make interferometers I think the wedge was about 1 minute total indicated runnout, but this was at 633nm (visible) it'll be different at 10.6um (infarred).
I love deadlines- I like the whooshing sound they make as they fly by.