laser engraver from dvd writer

I am working on laser engraver system with couple of my friends . I extracted a laser diode from a 16X dvd writer , and built a Lm317 laser driver , I am building my own laser aixiz module .

My questions are :

what is the focal length of the dvd lens so I can determine the beam diameter for the control system part ?

is there any way to build a ttl laser driver ?