First of all, do it in a team of 5 - it will be easier.
You can do the task every 20 hours - so if you fail first time, don't worry and try again.
Get Ratha in the line of laser and then let him loose to the right side of the room (corner). Don't allow him to go up (one person is blocking his way).
Use utori on the laser and keep shooting at it with wands / bolts etc.
Use flasks when you can.
If he teleports somwhere, you can use harp in the middle of the room, to summon him (each person 3 times) and he'll be in the middle. Then block his path in a way to allow him to move only one sqm a time.
You have 10 min to complete the task.