⚡ Laser light

Image: Laser light, described in 1917 by Albert Einstein (1879-1955), is blue, green or red, that is to say composed of a single color, all the other colors being subtle mixtures of colors.
In 1960, the American physicist Théodore Maiman (1927-2007) obtained for the first time a laser emission by means of a ruby crystal.

Blue, green or red light

Natural or artificial light (light daylight, incandescent lamp, LED, etc.) is a light composed of a superposition of all the colors, that is to say a chaotic electromagnetic wave that propagates in all directions. It is not a wave with a regular and consistent length but rather a messy lapping on the surface of the water.
Laser light (Light Amplification Stimulated Emission of Radiation) is natural light stripped of all colors except one.
Although it is possible to make lasers of multiple colors and going in multiple directions both the most popular and efficient laser is the monochrome and unidirectional laser. Laser light is either blue, green or red, that is, composed of a single color (primary color), all other colors are mixtures of colors (secondary colors). Ex: a carrot absorbs blue, its color is therefore a subtle mixture of all colors except blue.
It is the length of the optical cycle (period and frequency) which determines the color of the laser radiation.
Laser light is neat and can travel in a straight line without distortion over very large distances provided it is amplified. The image one can retain of a laser light compared to natural light is that of a regiment marching in step unlike a crowd which moves in disorder.
Stimulated light is an amplification obtained by the emission of two photons from the energy of a single photon. Thus the laser light will be stimulated so as to be easily manipulated. Thanks to mirrors we can propagate it where we want, as far as we want, and increase the power as we want. Notable examples are the laser guide stars used to tune astronomical observations or the world's most powerful megajoule laser to test nuclear fusion.

NB: According to the equations of James Clerk Maxwell (1831-1879), light is a self-propagating electromagnetic transverse wave with electric and magnetic components where electric and magnetic fields oscillate at right angles to each other and propagate perpendicularly to the direction in which they move indefinitely unless absorbed by the intermediate matter.
In other words, each type of field - electric and magnetic - generates the other in order to propagate the entire composite structure in empty space at the finite speed of light.

Uses of laser light

Image: Electronic cloud taken with an attosecond laser. We see here the characteristic structure of the orbital of the nitrogen molecule N2. The first image is the calculated image, the second is the experimentally reconstructed image and the third image is theoretically reconstructed.

Laser light is not only used for the decoration of performance halls.
The uses of the laser are numerous, they are even the mark of our time. They range from the ultra low power diode (0.000001 watt) found in optical drives to the megajoule laser (10¹⁵ watts) designed to experiment with controlled nuclear fusion.
Indeed, laser light has invaded our daily lives. It is found in supermarkets (barcode reading), in IT (DVD, Blu-ray, laser printer reading), in information transport (optical fiber), in precision measurements in physics (distance Earth/Moon, atom photography), in industry (laser range finder, radar, laser cutting, welding, engraving), in medicine (eye surgery, dermatology, laser scalpel), in defense (weapon simulation nuclear), in research (fusion controlled plasma), in astronomy (laser telemetry on satellites, adaptive optics with the laser guide star).
Coherent invisible lasers are also produced from microwaves (maser) used in particular in interferometry, metrology and in atomic clocks.
In order to increase the power, pulsed lasers are also produced. Pulsed lasers emit light intermittently. They are used to observe physical phenomena that move very quickly. Indeed, when we pulse an ultra-short flash of light, we can capture an ultra-brief image of an ultra-fast object. The femtosecond laser is used as a strobe, in order to take photographic images with an extremely short exposure time. For that it is necessary to light very intensely.
The advantage that we have with the laser is that we can concentrate the light and increase its power over an extremely short period of time, the shorter the duration the greater the power is high.
In one attosecond (10 ^-18 seconds), light travels the diameter of an atom while in one second it travels the Earth / Moon distance. This ultra-short duration is adapted to the movements of the molecules of matter and even to the movements of electrons in atoms. With the femtosecond laser, we can achieve high peak powers (up to 100 joules per pulse) as in large petawatt systems. Various applications make use of all or parts of these unique properties of light (research, industry, biomedical field). From the attosecond laser we can photograph the electronic clouds around their atomic nuclei. By shaping light pulses that are both ultra-intense and ultra-short, we can get into the heart of matter.