How Does a Laser Work?

The background and principle of laser generation is a physical model. The laser has a very pure color, almost no divergent directivity, and extremely high luminous intensity. Because of these magical properties, the laser has a series of applications in various fields.

Background and principle of laser generation

An excited atom cannot stay at a high energy level for a long time. Even if there is no external effect, it will spontaneously transition from a high energy level to a low energy level and radiate a photon. Because this spontaneous emission of the atom is completely independent, the direction of the photon emitted by different atoms is completely different. Suddenly, photons propagating in all directions appear in the working material. Assuming that the working material has a cylindrical shape, some of these spontaneous radiation photons must propagate in the direction of its central axis, and most of them have a certain angle with the central axis. The photons of the latter type centrifugal de Germany quickly escape from the side of the working material, and have little effect on the generation of the laser. The photons of the former type of concentric and concentric moving along the center axis of the working material will cause the path The stimulated radiation of an atom at a high energy level produces a photon that has the same frequency, the same phase, and propagates in the same direction. This photon "worked together and fought side by side" with the photon that induced it, inspiring other atoms to radiate the same photons as them. Keep going like this, make the number of photons from 1 to 2, from 2 to 4, ... at an amazing speed and grow exponentially. Even more amazing is that because all these photons are generated by successively stimulated radiation, this makes them all have the same frequency, the same initial phase, the same polarization state, and propagate in the same direction.

In theory, as long as the working substance is long enough, no matter how weak the initial spontaneous radiation is, it can always be amplified to a certain intensity. However, in actual lasers, in general, the working substance is neither necessary nor particularly long (the exception is the recently developed lasers that use optical fibers as the working substance). It is common practice to put a reflection at each end of the laser. The mirror allows light to be reflected back and forth through the working substance and is continuously amplified. In order to make full use of light energy, the medium is often placed in a condensing cavity, which together with the end-face mirror forms a laser resonant cavity.

As can be seen from the above discussion, as a kind of light, laser light, like other light in nature, is generated by the transition of atoms (or molecules, ions, etc.), and is caused by spontaneous radiation. The difference is that ordinary light sources are generated by spontaneous radiation from beginning to end, so they contain components with different frequencies (or different wavelengths and different colors) and propagate in all directions. Lasers only rely on spontaneous radiation for the first extremely short period of time, and subsequent processes are completely determined by stimulated radiation. It is for this reason that the laser has a very pure color, almost no divergent directivity, and extremely high luminous intensity. It is these magical properties that make lasers have a series of incredible and compelling applications in various fields. ^[1]