Laser is one of the important inventions of humanity, known as the “brightest light”. In daily life, we can often see various laser applications, such as laser beauty, laser welding, laser mosquito killers, and so on. Today, let’s have a detailed understanding of lasers and the principles behind their generation.

What is a laser?

Laser is a light source that uses a laser to generate a special beam of light. A laser generates lasing light by inputting energy from an external light source or power source into the material through the process of stimulated radiation.

A laser is an optical device composed of an active medium (such as gas, solid, or liquid) that can amplify light and an optical reflector. The active medium in a laser is usually a selected and processed material, and its characteristics determine the output wavelength of the laser.

The light generated by lasers has several unique characteristics:

Firstly, lasers are monochromatic light with very strict frequencies and wavelengths, which can meet some special optical needs.

Secondly, laser is coherent light, and the phase of light waves is very consistent, which can maintain relatively stable light intensity over long distances.

Thirdly, lasers are highly directional light with very narrow beams and excellent focusing, which can be used to achieve high spatial resolution.

Laser is a light source

The principle of laser generation

The generation of laser involves three basic physical processes: stimulated radiation, spontaneous emission, and stimulated absorption.

Stimulated radiation

Stimulated radiation is the key to laser generation. When an electron at a high energy level is excited by another photon, it emits a photon with the same energy, frequency, phase, polarization state, and propagation direction in the direction of that photon. This process is called stimulated radiation. That is to say, a photon can “clone” an identical photon through the process of stimulated radiation, thereby achieving amplification of light.

Spontaneous emission

When an atom, ion, or molecule’s electron transitions from a high energy level to a low energy level, it releases photons of a certain amount of energy, which is called spontaneous emission. The emission of such photons is random, and there is no coherence between the emitted photons, which means their phase, polarization state, and propagation direction are all random.

Stimulated absorption

When an electron at a low energy level absorbs a photon with an energy level difference equal to its own, it can be excited to a high energy level. This process is called stimulated absorption.

In lasers, a resonant cavity composed of two parallel mirrors is usually used to enhance the stimulated radiation process. One mirror is a total reflection mirror, and the other mirror is a semi reflection mirror, which can allow a portion of the laser to pass through.

The photons in the laser medium reflect back and forth between two mirrors, and each reflection produces more photons through the stimulated radiation process, thereby achieving amplification of light. When the intensity of light increases to a certain extent, laser is generated through a semi reflecting mirror.