There are purpose-made laser diode driver ICs out there.
Which will do things like give you control of threshold
current. Not to mention being way, way faster and
likely more current-drive-capable.
If you want the Darlington to turn off quicker (like the
same timescale as turnon) you have to pay attention
to the second base, its discharge time (which is handled,
how?) needs to be on the order of turnon time that is
fed by emitter follower front end at very low net
impedance. You probably don't want that impedance
presented as a full time load at that node. You might
look at a squaring circuit, but I think you just want to
walk away from '70s discrete technology and embrace
the '90s.