Discuss Bill Compton's answer to: What's the diode laser products?and the function of diode laser peoducts?

Diode Lasers are actually ordinary LED's.  They emit coherent monochrhomatic light at a specific amplitude which varies by design from femtowatts (as used in passive recognition systems) to over 35 megawatts (used in satellite laser weapon systems).  This variety of light "sticks together" unlike other varieties of electromagnetic radiation.

These lasers are used in household eletronic devices, security systems, thermometers, and direction finding equipment.  Laser navigation systems were online fifteen years before GPS became a cost effective alternative. 

Laser rangefinders are used in architecture and construction virtually to the exclusion of all other techniques.  One may find a true level across a construction site more precisely than with spirit levels, because laser levels do not consider the curvature of the earth. 

For more information I have provided a link to Wikipedia which I believe will give you a basic understanding.

www.wikipedia.org/wiki/LED