Green laser in projector

Hi!

I've been building a 8-line laser projector using a green laser (200mW) and a spinning polygonal mirror to scan along the horizontal axis. To power the laser, I'm amplifyng the microcontroller's modulated digital output through a transistor (BC548) and connecting the collector to the laser's battery contacts. I've fairly succeeded, but the beginning of the each line is darker than the end. Also, the lines with more pixels seem brighter than the other ones. It looks like the laser takes some time to power up, which is undesirable to my project, as it turns on and off at rates of 20kHz. Should I try to disassemble the laser, remove the diode and build a LM317 driver? Is there any other circuit I could use to power the laser using it's built-in driver? I'm too scared about "killing" my laser, since my project is working already and these lasers aren't cheap.

Thanks!

Have you confirmed that the current to the pump diode is proportional to the micro-controller's output? I suspect a filter cap in the driver is softening the pulses. Pics would be nice.

Hi!
I don't have anything here but my laptop's crappy camera. Anyway, the built-in module looks pretty much like this one: http://repairfaq.org/sam/laserpic/grn06.jpg. It includes an 8-pin ST chip labeled "358 eZ927", some resistors and a 10uF tantalum capacitor. The laser pointer I've got was exactly this: http://i.imgur.com/oI8cI.jpg.
I've managed to remove the module (carefully), so I have now the diode. I've tried to power it up using an LM317 current regulator with a 10 R resistor (0.125 A) and I got barely no current through the diode. Now I'm using 5 R (0.25 A) and still nothing. Do you guys think I've already blown it or it's current requirements are even higher?
Thanks!

Ok, I've found the built-in module schematic, here in the forum:
http://laserpointerforums.com/f42/making-ttl-driver-dx-200mw-greenie-51916.html
I'll try to adapt the TTL modulator and I'll let you know what happens.
Thanks so far!

Please tell me you left the diode inside its heat sink.

I don't think that design will work at the speeds you need. There are filter caps in the driver that prevent sudden and drastic changes in current.