Why is my laser losing power?

Defective or dirty optics can cause power loss or beam alignment.

If the laser optics are dirty or have lost their coatings, it can loose power by not reflecting the laser beam properly.  Click here to have an understanding of optics refraction.

 
Why are antireflection coatings so important for optics?
These unwanted reflections off of glass surfaces are called Fresnel reflections.
They can lead to a lot of light being lost in a system with many different glass lenses, windows, prisms, and other optics.  Antireflection coatings minimize unwanted reflections so that the maximum amount of light transmits through an optical system.