I think the laser in a rangefinder is only for pointing purpose. The range is measured by ultrasonic transceiver by measuring the time sound takes to travel to and fro.
Yes , right , laser is used for pointing.But I don think that sound is used. it is very difficult to focus sound to pointed target.Range is calculated from reflecting angle of laser beams.
I saw an sample project ( laser range finder ) on Servo MagazineBut i am not sure the number of issue.Simple range finder made with laser pointer and a webcam.