Is Wavelength Doubling Laser a Real Technique?

[sparkle_pony]

I've heard of frequency doubling but is wavelength doubling a thing? If so, how efficient?

 

[UltrafastPED]

Frequency doubling divides the wavelength in half: http://www.rp-photonics.com/frequency_doubling.html

The inverse process also works, and is usually called parametric down conversion:
http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion

Your green laser pointer is an example of frequency doubling/second harmonic generation:
http://en.wikipedia.org/wiki/Laser_pointer#Green
See the schematic diagram on the right hand side - enlarge, and follow the red beam into the crystal which generates the green beam.