Here is a summary of the features, power output, power supply requirements, wavelengths, beam quality, cost, and applications of diode, helium-neon, argon/krypton ion, carbon dioxide lasers, helium-cadmium, and solid state lasers. There are many many other types but these represent the most common lasers available over the last 50 years - the the most common lasers available on the surplus market today.
* Diode lasers. Semiconductor laser diode 'chip' driven by low voltage power supply. Optical feedback from a monitor photodiode (commonly in the same package as the laser diode) is generally used for precise regulation of laser diode current.
Wavelengths: Red (635 nm, actually may appear slightly orange-red) through deep Red (670 nm) and beyond, IR (780 nm, 800 nm, 900 nm, 1,550 nm, etc.) up to several um). Near-UV, violet, and blue laser diodes are available from around 380 nm to 450 nm but are still very expensive. Green laser diodes have been produced in various research labs but until recently, only operated at liquid nitrogen temperatures, had very limited lifespans (~100 hours or worse), or both.
Beam quality: Fair to high depending on design. The raw beam is elliptical or wedge shaped and astigmatic. Correction requires additional optics (internal or external). Coherence length anywhere from a few mm to many meters.
Output power: 0.1 mW to 5 mW (most common), up to 100 W or more available. The highest power units are composed of arrays of laser diodes, not a single device and may exceed 100,000 W.
Some applications: CD/DVD players and CDROM/DVDROM drives, LaserDisc, MiniDisc, other optical storage drives; laser printers and laser fax machines; laser pointers; sighting and alignment scopes; measurement equipment; high speed fiber optic and free space communication systems; pump source for other lasers; bar code and UPC scanners; high performance imagers and typesetters, small (mostly) light shows; medical treatment (ophthalmic, uninary, and others).
High power laser diodes are the enabling technology for high efficiency Diode Pumped Solid State (DPSS) lasers and future energy efficient lighting.
Cost: $1 to $10,000 or more.
Comments: Inexpensive, low (input) power, very compact, but critical drive requirements. Many types of diode lasers are not suitable for holography or interferometry where a high degree of coherence and stability are required. However, see the section: Interferometers Using Inexpensive Laser Diodes since these common CD player and visible laser diodes may in fact be much better than is generally assumed. In addition, it has been reported that some inexpensive diode lasers appear to be even superior to traditional helium-neon lasers costing $Ks for holography. See the section: Holography Using Cheap Diode Lasers.
