The cost of Nichia blue/violet laser diodes is high because of their patent monopoly. They patented the C-axis cut of sapphire crystal wafers that is necessary to grow these diodes on. So far the only other material they grow on is silicon carbide, but it doesn't match GaN lattice that well making high power impossible, is much harder than sapphire and adds about 3 to 5 V on top of the 4 to 5 V nitride voltage drop basically cooking the poor little diode. :-(

A typical laser diode is diffraction limited with an emitting area of about 1 um by 3 um. An LED will emit from the surface of its chip over a full hemisphere. In order to radiate over only a limited angle, a lens is added but with idea optics Violet Laser 100mW , the emitting area is still effectively the .3 mm x .3 mm or so area of the LED. This is about 30,000 times that of the laser diode. With the typical 5 mm molded lens, it is more like 1,000,000 times the area. That means the intensity and optical density of the laser diode can be over a million times that of the LED.

This is at low currents, maybe around or possibly under half a milliamp for the usual ones with maximum rated current of 30 mA. These are noticeably nonlinear with efficiency peaking near or maybe under half a milliamp. They are so nonlinear in favor of low currents that they are sometimes referred to as "low current red" and most "low current red" LEDs are these groene laser 50mW . Ones in non-tinted packages often glow orangish or sometimes even yellowish orange at currents that they operate safely at - a secondary spectral band in the yellowish green does not lose efficiency at higher currents the way the main red band does. These LEDs are distinguished by a nominal peak wavelength of 690 to 700 nm.

A commercially-made Schmidt-Cassegrain or Maksutov telescope could project a small spot from an LED at a considerable distance groene laser 200mW . These both use a fairly fast (low f/number) primary mirror and a diverging (negative focal length) secondary mirror to give the net effect of a long focal length slow (f/10 to f/12) optical system. I have a 4 inch diameter SCT with 1.2 m focal length; the 8 inch SCTs are generally 2 m focal length. A 4 inch SCT is pretty small and light weight; 4 inches diameter, maybe a foot long, and a few pounds.

When economical, these shorter wavelength laser diodes will represent the enabling technology for yet another revolution in the storage capacity of optical drives (at least a factor of two better than even DVD). Compared to the 4.5 GB capacity of one surface, one side of a DVD, a DUD (Digital Ultra Disc/k) drive would hold about 13 GB/surface based on the wavelength difference alone (635/400 squared). The developers of the DVD standard have already (as of Spring, 2002) developed a DUD standard so the World will be ready and waiting when the cost of blue-violet laser diodes drops to a reasonable level. As if we need yet another new standard. :)