Lower 5V output to 2V max
I think that you are reading the specification of the laser driver circuit incorrectly.  It would help if you can either post the exact specifications of the driver or post a link to a web page that describes the driver.  Please don't link to a PDF file - most people won't download a file to view it.

I strongly suspect that the laser driver circuit wants to see a TTL-compatible signal.  I'm inferring that from the 0.8V 'flip' voltage that you mention as well as the '2V max to turn it on'.  What that means is that the driver needs a voltage HIGHER than 2.0 Vdc to turn it ON and a voltage LESS than 0.8 Vdc to guarantee that it turns OFF.

If I am correct, you don't need to anything except connect the Arduino output pin directly to the control input pin on the laser driver circuit.  

Be sure to also connect your Arduino ground to the laser power supply ground.