The pure and spectrally stable light emitted by the laser can be used in many ways.
Ruby Laser: The original laser was a ruby that was excited by a bright flashing light bulb, and the laser produced was a "pulsed laser" rather than a continuous steady beam. The beam quality produced by this laser is fundamentally different from the laser produced by the laser diodes we use today. This intense light emission, which lasts only a few nanoseconds, is ideal for capturing easily moving objects, such as holographic portraits of people. The first laser portrait was born in 1967. Ruby lasers require expensive rubies and produce only brief pulses of light.
He-Ne Laser: In 1960 scientists Ali Javan, William R.Brennet Jr. and Donald Herriot designed the He-Ne laser. It was the first gas laser, a type of equipment commonly used by holographic photographers. Two advantages:
1. Generate continuous laser output;
2. There is no need for flash bulbs for light excitation, but electricity for gas excitation.
Laser diode: Laser diode is one of the most commonly used lasers at present. The phenomenon of spontaneous recombination of electrons and holes on both sides of the PN junction of the diode to emit light is called spontaneous emission. When the photons generated by spontaneous emission pass through the semiconductor, once they pass near the emitted electron-hole pairs, they can be stimulated to recombine to generate new photons, which induce the recombination of excited carriers to emit new photons The phenomenon is called stimulated emission. If the injection current is large enough, the carrier distribution opposite to the thermal equilibrium state will be formed, that is, the population of the particles is reversed. When a large number of carriers in the active layer are reversed, a small amount of photons generated by spontaneous radiation will generate induced radiation due to the reciprocal reflection at both ends of the resonator, resulting in positive feedback of frequency-selective resonance, or a gain for a certain frequency. When the gain is greater than the absorption loss, coherent light with good spectral lines can be emitted from the PN junction—laser. The invention of laser diodes has made laser applications rapidly popular, and various applications such as information scanning, optical fiber communication, laser ranging, laser radar, laser discs, laser pointers, supermarket payment collection, etc., are constantly being developed and popularized.