We would like to control an existing machine called a truck probe with Arduino using a lazer sensor.
Any links so we know what you are talking about?
Lasers are not sensors they are emitters.
Many of us would like to do this as well -- however we have no idea what it is.
Can we help you in any way?
We did it using a barium hybrid initiator. Just make sure the covalent suppression is set to 11. Otherwise you get an inverted positron flow.
Barium, huh?
That's just crazy enough that it might work.
We were working though the alphabet, rather than the Periodic Table, and gave up at astatine.
Here is a link to see the machine in action. Go to 2:45 to see the one on a monorail. That is the unit we want to automate. The sensors (or emitters!) need to locate the trailer so the probe "knows" where to take sample.
I can't see where you gonna put an arduino, to read what? Truck's plates reading requires video recognition, same with a load
It looks like it samples corn or wheat from a bulk truck. Moisture maybe?
Shouldn't be that difficult to automate as long as the trucks parked in the same location each time and didn't move while the samples were being taken.
Hardhats anyone 
Video recognition is one way to do it. But every trailer is different, that is the challenge. We don't want to punch the cabin either!
I am still not very clear what you want to do.
If it is to find the limits of the open top in a truck, you can use a drag rod probe just like they do in a car wash to see where your windscreen is. Put a rod on the end of a pot with a spring and move it across the location of the truck. By taking the pot readings you can discover the profile of the truck.
Unexpectedly humorous response to the thread entitled "General".
"I'm here to amfruct the batterpomp, just until the rain lets up, you understand."
"By God, why didn't Herb tell me that!"