A laser is a device that emits a laser. There are six kinds of laser: solid laser, gas laser, dye laser, semiconductor laser, fiber laser and free electron laser.

Gas laser is a kind of laser which uses gas as gain medium and generally pumps gas discharge. Common gas types include atomic gases (he-ne lasers, inert gas ion lasers, metal vapor lasers), molecular gases (nitrogen lasers, carbon dioxide lasers), excimer gases, and special gas lasers that provide pumping energy through chemical reactions.

Helium neon laser (HeNe) and He is more than 75% to less than 15% of Ne a mixture of gases as gain medium, according to different working environment, can be issued a green (543.5 nm), yellow (594.1 nm), orange (612.0 nm), red (632.8 nm) and three kinds of near-infrared light (1152 nm, 1523 nm and 3391 nm), red (632.8 nm) is the most commonly used. The HeNe laser beams have a Gaussian distribution. The quality of the beams is very stable. Although the power is not high, the HeNe laser beams have excellent performance in the field of precision measurement.

Excimer molecules are unstable molecules that are produced by lasers of different wavelengths by filling a resonator with a mixture of different noble and halogen gases. Relativistic electron beams (energy greater than 200 kiloelectron volts) or transverse rapid pulsed discharges are commonly used to achieve excitation. When the unstable molecular bonds of the excited excimer break and the ground state atoms are dissociated, the energy of the excited state is released in the form of laser radiation. It is widely used in medical treatment, optical communication, semiconductor display, remote sensing, laser weapon and other fields.

The common inert gas lasers are argon ion (Ar+) and krypton ion (Kr+). Its energy conversion rate is up to 0.6%, and it can continuously and stably output 30-50W power for a long time with a life of over 1000h. It is mainly used in laser display, Raman spectrum, holography, nonlinear optics and other research fields, as well as in medical diagnosis, printing separation, material processing and information processing.

The gain medium used in the carbon dioxide laser is carbon dioxide mixed with helium and nitrogen, which can output far-infrared light with 9.6 m and 10.6 m wavelengths as the center. Carbon dioxide laser energy conversion rate is high, the output power can be from a few watts to tens of thousands of watts, plus very high beam quality, so that carbon dioxide laser in material processing, scientific research, national defense and medical have a wide range of applications.

Nitrogen molecular laser, using nitrogen as gain medium, can emit ULTRAVIOLET light of 337.1 nm, 357.7 nm and 315.9 nm, with peak power up to 45kW. It can be used as a pump light source for organic dye lasers and has been widely used in the fields of laser isotope separation, fluorescence diagnosis, ultra-high speed photography, pollution detection, medical care, agricultural breeding and so on. It can also be used to process submicron components because it is easier to focus small spots in the short wavelength.