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What is the laser

The letters in the word laser stand for Light Amplification by Stimulated Emission of Radiation. A laser is an unusual light source. It is quite different from a light bulb or a flash light. Lasers produce a very narrow beam of light. This type of light is useful for lots of technologies and instruments—even some that you might use at home!

A laser is different. Lasers do not occur in nature. However, we have figured ways to artificially create this special type of light. Lasers produce a narrow beam of light in which all of the light waves have very similar wavelengths. The laser’s light waves travel together with their peaks all lined up, or in phase. This is why laser beams are very narrow, very bright, and can be focused into a very tiny spot.

Because laser light stays focused and does not spread out much (like a flashlight would), laser beams can travel very long distances. They can also concentrate a lot of energy on a very small area.

working principle of laser

A laser is created when electrons in the atoms in optical materials like glass, crystal, or gas absorb the energy from an electrical current or a light. That extra energy “excites” the electrons enough to move from a lower-energy orbit to a higher-energy orbit around the atom’s nucleus. A laser takes advantage of the quantum properties of atoms that absorb and radiate particles of light called photons. When electrons in atoms return to their normal orbit—or “ground” state—either spontaneously or when “stimulated” with a light or other energy source, even another laser in some cases, they emit more photons.

Light moves in waves. Ordinary visible light, say from a household light bulb or a flashlight, comprises multiple wavelengths, or colors, and are incoherent, meaning the crests and troughs of the light waves are moving at different wavelengths and in different directions.

In a laser beam, the light waves are “coherent,” meaning the beam of photons is moving in the same direction at the same wavelength. This is accomplished by sending the energized electrons through an optical “gain medium” such as a solid material like glass, or a gas.

The particular wavelength of light is determined by the amount of energy released when the excited electron drops to a lower orbit. The levels of energy introduced can be tailored to the material in the gain medium to produce the desired beam color.

A mirror on one side of the laser’s optical material bounces the photon back toward the electrons. The space between mirrors, or the “cavity,” is designed so the photon desired for the particular type of optical gain medium are fed back into the medium to stimulate the emission of an almost exact clone of that photon. They both move in the same direction and speed, to bounce off another mirror on the other side to repeat the cloning process.

Two become four, four become eight and so on until the photons are amplified enough for them to all move past the mirrors and the optical material in perfect unison. Think of them as synchronized members of a marching band in the Rose Parade. And that unison gives the laser its power. Laser beams can stay sharply focused over vast distances, even to the moon and back.

Types of Laser

Laser classes start at Class 1 and end at Class 4.  The higher the number in the classification, the greater hazard potential the laser system has.  These laser classifications are identified on the laser system and often Roman numerals are used to identify the class number.  The identification process is accomplished by affixing a label onto the product.  Along with text warnings, these labels include information pertaining to the wavelength, total output power and laser classification.

Class 1
Class 1 laser systems are intrinsically safe.  Under normal operating conditions, these lasers do not pose potential health hazards.  Special design considerations are used to prevent human access to laser radiation during operation.

Class 2
Class 2 laser systems are low power, visible lasers.  The eye’s natural blinking reflex caused by bright light aversion will protect the user.  There are some potential hazards if directly viewed for an extended period of time.  A CAUTION label is required for Class 2 lasers.

Class 3
Class 3a laser systems are also required to have a CAUTION label and on some cases require a DANGER label.  The light aversion reflex should protect the user if only viewed momentarily.  A hazard may be present if viewed with collecting optics such as during an optical alignment process.

Class 3b laser systems can produce a hazard if viewed directly or by viewing secondary beams.  Typically, these lasers will not produce hazardous reflections from a matte surface.  These systems have a DANGER label affixed and although the potential for eye damage is present, the risk for fire or skin hazards is low.  Laser safety eyewear is recommended while using these lasers

Class 4
Class 4 laser systems present hazards to both the eye and skin.  The hazards can be present from direct, secondary and diffuse reflections.  A DANGER label is affixed to all Class 4 laser systems.  Class 4 lasers can also damage materials in or around the laser area and ignite flammable substances.  Laser safety eyewear is required while using these lasers.

Lasers Application

Lasers have been around since 1960, although the idea goes back to 1900 (see “A Legacy of Lasers and Laser Fusion Pioneers”).

Today, lasers come in many sizes, shapes, colors, and levels of power, and are used for everything from surgery in hospitals, to bar code scanners at the grocery store, and even playing music, movies, and video games at home. You might have undergone LASIK surgery, which corrects your vision by using a tiny laser to reshape the cornea of your eye.

Some lasers, such as ruby lasers, emit short pulses of light. Others, like helium–neon gas lasers or liquid dye lasers, emit light that is continuous. NIF, like the ruby laser, emits pulses of light lasting only billionths of a second. Laser light does not need to be visible. NIF beams start out as invisible infrared light and then pass through special optics that convert them to visible green light and then to invisible, high-energy ultraviolet light for optimum interaction with the target.