Laser pointers emerged because of the widespread usage of the visible red laser diodes. From the perspective of diodes used to produce laser pointers, laser pointers can be separated into two categories. The one is pointer made from direct laser diodes (Direct diode pointers), and the other one is pointer made from diode pumped solid state (DPSS laser pointers).
Direct diode pointers can produce red or violet light (made from Blu-Ray lasers at 405 nm WL “nanometers wavelength”), and direct diode green will likely be available due to work of company KAAI. A variety of wavelengths fit red laser pointers, such as 635 nm, 650 nm, 660nm, 670 nm.
DPSS laser pointers are typically available at the following wavelengths, (blue) at 473 nm, (green) at 532 nm and (yellow) at 589 nm and (orange) at 593 nm, since light with wavelength about 555nm (green) is most sensitive for human eyes, all other visible colors are less bright than the same power level green. The apparent brightness of colors depend on the ratio with green, for example, blue at 488 nm being which is 2.6 times less than green. However, The apparent brightness of colors are not just decided by the wavelength, but also by its power level. Therefore, they can be balanced. 1 watt green laser at 514 nm appears to be as bright as a 2.6 watt blue laser at 488 nm. You can check a color chart to find out power levels and wavelengths of the colors, which appear same bright.
To buy a right DPSS laser pointer, you need to keep three things in your mind, the power level, the way the diodes are operated, and safety.
First, the power level here means the actual power level measured at the operating wavelength. Because a typical DPSS laser pointer has several laser wavelengths. You have to make sure the wavelength you need. For example, a typical green DPSS laser pointer has several laser wavelengths involved to generate a frequency doubled visible output. You measure the power. It is at 532nm, but this 532nm may generate from the other2 IR laser wavelengths. You actually get cheap laser pointers that output infra-red light (808 nm and 1064 nm). This can be very dangerous.
The second thing is the way the pump diodes are operated. The way can be pulsed (turned on and off at a fixed frequency) or CW constant wave (on constantly). It is easy to judge you bought a pulsed laser or a CW laser. The only thing you need to do is moving the beam quickly across the wall or ceiling to see if there is a chopped up line.
The last thing, most important, is about safety. Because the increasing power output is available today, the laser pointers can be very dangerous. The limit of laser pointer is 5milliwatts. However, some manufactures may produce much more powerful laser pointers, even as high as 500milliwatts to cater to clients. A 5milliwatt green laser at 532 nm would be enough to dazzle your night adjusted vision and possibly cause an automotive accident at say a hundred feet from the source. A 500milliwatt green laser could cause permanently damage to your vision.
Since widespread applications of laser and the safety issue, controls are needed to make the laser apply better and safely. Actually, Food and Drug Administration controlled lasers strictly.