The word “laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. Lasers are used for a wide variety of purposes, including storing data on discs, cutting through materials, and even just pointing at things. Here are two common types of lasers and how they work.
Gas lasers consist of a tube of gas with mirrors on either end, one fully reflective, and the other partially reflective. When the tube is excited by an electric field, the electrons in the atoms of the gas (1) jump to a higher energy level (2), then immediately fall back down to their original level. When they fall, the excess energy is given off as photons, producing light (3). This light bounces between the two mirrors, which act as a resonant cavity for the light. Each pulse increases the intensity of the light, and when the light is intense enough, it shines through the less reflective mirror.
Diode lasers actually work much like gas lasers, except that special semi-conductor materials take the place of the gas. As a result of current flowing through the semiconductors, light is generated, and resonates in a mirrored cavity until it is intense enough to shine through. The resulting beam diverges rapidly after leaving the chip, so a lens is used to collimate the light, making the light rays parallel. Using semiconductors allows lasers to be smaller and less fragile.
Depending on the lasing medium (the gas in the laser tube, or the semiconductor materials used), lasers will produce different colors of light. This is because the electrons in different lasing mediums emit photons of different wavelengths. In the case of diode laser pointers, a laser shines through multiple materials to change the wavelength of the emitted light, resulting in different colors. The color of the laser is actually unrelated to the laser’s power, and different color lasers can all have equivalent power ratings.
Because of the way laser light is created, it is monochromatic (one color), containing only one wavelength of light. Laser light is also coherent, meaning all of the photons are in phase with one another. These properties set laser light apart from natural light, which is typically multichromatic and not coherent.
Not all lasers are created equal. Some lasers are safe for use by anyone, while others can cause severe burns or blindness if misused.
Two major organizations have created classifications for lasers based on their potential to cause harm: the Food and Drug Administration (FDA), and the International Electrotechnical Commission (IEC).