Found this on reddit..
http://en.wikipedia.org/wiki/Holographic_Versatile_Disc
"It employs a technique known as collinear holography, whereby a green and red laser beam are collimated in a single beam. The green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc. A red laser is used as the reference beam to read servoinformation from a regular CD-style aluminum layer near the bottom. "
"The system uses a green laser, with an output power of 1 watt which is quite high power for a consumer device laser. So a bigger challenge of the project for widespread consumer markets is to either improve the sensitivity of the polymer used, or develop and commoditize a laser capable of higher power output and suitable for a consumer unit."
Can you imagine getting a 1 watt green laser for $100 from Wal-Mart? I know this is only wikipedia. so I don't know how accurate the page is. It says that it was developed in 2004 so excuse me if there is already a topic on this.