On the other hand, an entire wafer of VCSELs can be tested as a unit with each device evaluated for lasing threshold and power, and beam shape, quality, and stability, It is possible to form millions of VCSELs on a single wafer as a batch process and then test and evaluate the performance of each one automatically. The entire wafer can be burned in to eliminate infant mortalities and assure higher reliability of the final product. Each device can then be packaged or thrown away based on these findings.

Like their IR cousins, the typical maximum power from these devices is around 3 to 5 mW. Cost is in the $10 to $50 for the basic laser diode device - more with optics and drive electronics Ultrafire 16340 CR123 Batterij Lithium Oplaadbare . Higher power types (10s of mW) are also available but expect to spend several hundred dollars for something like a 20 mW module. Very high power diode lasers using arrays of laser diodes or laser diode bars with power output of WATTs or greater may cost 10s of thousands of dollars!

Due to the nature of the emitting junction which results in a wedge shaped beam and unequal divergence (10 x 30 degrees typical), a laser diode is somewhat astigmatic. In effect, the focal length required to collimate the beam in X and Y differs very slightly laserpointer 3000mw groen . Thus, an additional cylindrical lens or a single lens with an astigmatic curvature is required to fully compensate for this characteristic. However, the amount of astigmatism is usually small and can often be ignored. The general beam shape is elliptical or rectangular but this can be circularized by a pair of prisms.

The better way to deal with these laser diodes is to have them already mounted on a heat sink. But now we're talking about $100s for a single unit. But, for a number of reasons, the best type of high power laser diode to get is probably a fiber-coupled module. Then you don't have to mess with beam shape issues, the diode is safely tucked away out of harm, and the fiber output can easily be adapted to your favorite crystal shape laserpen 5000mw groen . Some power is lost in the coupling but it appears as though the specs I've seen are similar for the bare diode assembly and fiber-coupled module. Of course, the cost for such a module now appoaches that of a nicely equipped PC. :)

Low power edge emitting diodes usually operate in a single spatial mode for both axes. Edge emitting diodes more than about 100 mW are almost always multiple spatial mode in the slow (horizontal) axis, single mode in the fast (vertical) axis. Although it may take some effort (see below), a single mode diode can be focused or collimated with diffraction limited performance in both axes. This isn't possible even theoretically for a the slow axis of a multimode diode.