sentences:  Particularly when two-photon absorption is utilized, high-powered lasers may be required that can be bulky, difficult to cool, and pose safety concerns.Existing optical drives utilize continuous wave diode lasers operating at 780 nm, 658 nm, or 405 nm.3D optical storage drives may require solid-state lasers or pulsed lasers, and several examples use wavelengths easily available by these technologies, such as 532 nm (green).