What Determines the Wavelength of a Laser?

The world’s first laser came into the world on May 16, 1960, a little over 60 years ago. Invented by Theodore Maiman, a PhD experimental physicist, it changed the world as we know it. Because of it, millions of blind people are now able to see and machine tools are able to precisely drill holes ranging from a few microns to several millimeters in diameter in the hardest of metals. Without the laser, there would be no smart bombs, supermarket bar code readers, precise navigation techniques for commercial aircraft, or certain life-saving cancer treatments. New and popular procedures that enable people to be rid of eyeglasses, remove unsightly moles, wrinkles and tattoos, and even streamline bikini lines would not exist.

Obviously, the same laser able to drill holes in metal cannot be used for cataract surgery, which is why different lasers operate at different wavelengths, from ultraviolet through the visible light spectrum to infrared. Although different lasers produce light of different wavelengths, all operate on the same basic principle.

Power versus wavelength

All matter, whether a solid, a liquid or a gas, is composed of atoms. Atoms consist of a nucleus made up of protons, neutrons, and a cloud of electrons that circle the nucleus in orbits defined by their various energy levels. A beam of energy, usually light consisting of many different wavelengths, like the beam of a flashlight, is used to excite the electrons to “jump” to a higher energy level.

If enough electrons are excited, the material can reach a state called “inversion.” The excited electrons can then be “stimulated” to drop back to their original state by “emitting” a photon. This photon will exactly match the photon that stimulated it in both wavelength and phase. These photons can then stimulate more photons to be emitted. This repeated process leads to an increase in the light output and is the reason for the name “laser” – Light Amplification by Stimulated Emission of Radiation. The power of a laser beam depends on the energy levels of the electrons in the atoms of the material used to produce it, generally called the “lasing” material.

The energy level of the photons produced by the lasing material is inversely proportional to the wavelength of the light produced by the lasing material. In other words, the shorter the wavelength of the light, the higher will be the energy of the photon. Although other factors such as the power source used to cause lasing and whether the laser beam is constant or pulsed, can affect it, it is generally the wavelength of the light that determines the power of the laser beam. Since different lasing materials produce light of different wavelengths, they also produce laser beams with different power levels.

The shortest wavelengths, from 10 to 400 nanometers (nm), produce ultraviolet (UV) light. Intermediate wavelengths, from 380 to 740 nm, produce visible (VIS) light from violet to red. The longest wavelengths, from 700 nm to 1 mm, produce infrared (IR) light which, like UV, is invisible to the human eye.

Maimon’s first laser used ruby (CrAlO3) to produce red light beam with a wavelength of 694 nm. Some other commonly used lasers, classified by type of lasing material, and their emission wavelengths include:

* Neodymium-doped yttrium aluminum garnet

Of course, regardless of its wavelength, the beam of a laser must be precisely controlled and directed. Lenses, windows and mirrors supplied by Esco Optics play an important role in assuring this precision. Learn more about Esco Optics Products here. Here are a couple of references that you might be interested in –  Types of Lasers.

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