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What is Laser?

Atoms at their resting energy state, or ground sta

The word laser is an acronym derived from the phrase “light amplification by stimulated emission of radiation.”

A laser-equipped device can generate a high-intensity light that is monochromatic, unidirectional, and parallel. These unique characteristics make the laser useful for commercial and medical applications. The image illustrates the operating principles of a laser device.

Atoms at their resting energy state, or ground state (E0), can be excited to a higher energy state (E*) when they absorb electrical, optical, or thermal energy.


The basic laser device consists of 3 components: (1) an active medium, or lasing medium; (2) an optical cavity, or resonator; and (3) an energizing source, or pump. The active medium in lasers may be a solid, liquid, or gas. Different active media emit different energies or wavelengths of light. However, they all operate with the same basic principles.

The resonator contains an active medium. At each end of the resonator, parallel reflectors or mirrors are placed facing each other. The front of the output mirror is designed to be partially reflective. It reflects only a portion of the light impinging on it, allowing some portion of the total energy or light to escape. The rear mirror is a total reflector that reflects 100% of the energy impinging on it. The pump source provide the energy (thermal, electric, or optical [eg, a flash lamp] for absorption by the active medium.


When the active medium is pumped with sufficient energy, a population inversion occurs, causing the spontaneous emission of photons. Some of these photons are reflected back and forth between the 2 mirrors (others are dissipated as heat) and then collide with atoms in the excited state; these collisions subsequently stimulate the emission of radiation. As other photons collide with excited atoms, energy within the resonator builds and is amplified by reflections between the parallel mirrors. At the front output mirror, a portion of the energy is permitted to escape. This energy is in the form of an intense beam of monochromatic (same wavelength), collimated (parallel, non diverging), and coherent (same direction) light.

Lasers work by emitting a wavelength of high energy light, which when focused on a certain skin condition (e.g. sun spots) will create heat and treat the problem via destruction (e.g. removing the sun spots). There are many different wavelengths (or colours) of lasers because each wavelength treats different things. That explains why so many models and types of lasers exist.


A laser generates a beam of very intense light. The major difference between laser light and light generated by white light sources (such as a light bulb) is that laser light is monochromatic, directional and coherent.

Coherent refers to synchronized phase of light waves. Incoherent light bulb vs. coherent laser

Collimated refers to the parallel nature of the laser beam. Laser light is emitted in a very thin beam, with all the light rays parallel. By focusing and defocusing this beam, a surgeon can vary its effect on tissue.

Monochromatic refers to the single (wavelength) colour of a laser beam. Ordinary white light is a mixture of colours, as you can demonstrate by shining sunlight through a prism. Because the wavelength of laser light determines its effect on tissue, the monochromatic property of laser light allows energy to be delivered to specific tissues in specific ways.




The electromagnetic spectrum includes energy ranging from gamma rays to electricity. Figure illustrates the total electromagnetic spectrum and wavelengths of the various regions.

Figure: Electromagnetic Spectrum



Ultraviolet radiation for lasers consists of wavelengths between 180 and 400 nanometers (nm). The visible region consists of radiation with wavelengths between 400 and 700 nm. This is the portion we call visible light. The infrared region of the spectrum consists of radiation with wavelengths between 700 nm and 1 mm. 

How are frequency and wavelength related?

Electromagnetic waves always travel at the same speed (299,792 km per second). This is one of their defining characteristics. In the electromagnetic spectrum there are many different types of waves with varying frequencies and wavelengths. They are all related by one important equation: Any electromagnetic wave's frequency multiplied by its wavelength equals the speed of light.

 Wavelength & Frequency are inversely proportional to each other i.e. if Wavelength increases, the frequency decreases & vice versa.



(in nanometers)


457 - 528 (514.5 and 488 most used)

Frequency doubled Nd:YAG


Helium Neon

543, 594, 612, and 632.8


337.5 - 799.3 (647.1 - 676.4 most used)



Laser Diodes

630 – 950


690 – 960



Hydrogen Fluoride

2600 – 3000

Erbium : Glass


Carbon Monoxide

5000 – 6000

Carbon Dioxide




​Common lasers & their wavelengths

The colour or wavelength of light being emitted depends on the type of lasing material being used. For example, if a Neodymium:Yttrium Aluminum Garnet (Nd:YAG) crystal is used as the lasing material, light with a wavelength of 1064 nm will be emitted. Table illustrates various types of material currently used for lasing and the wavelengths that are emitted by that type of laser. Note that certain materials and gases are capable of emitting more than one wavelength. The wavelength of the light emitted in this case is dependent on the optical configuration of the laser.


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