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Show Basics: How a Laser Works

Making Light
By Bob Mueller, Lightspeed Design Group

The word LASER is an acronym. It stands for Light Amplification by the Stimulated Emission of Radiation. By "radiation", however, the acronym refers to a radiant vibration, not an emission of radioactive particles. In other words, the emissions of lasers are in the form of light, and the frequencies can range anywhere from infra-red to ultraviolet. Those lasers of interest to the laser display industry, however, are mostly those whose output is visible (from red to deep blue).

As the acronym suggests, lasers work through a process called stimulated emission. The lasers we typically employ are called ion gas lasers, due to the fact that they utilize a gas or a mixture of gases as the lasing medium. These work because certain gases are "easily" coerced to produce visible light through this process.

The stimulation comes in the form of electricity, which excites the atoms of the gas: as the electrons in these atoms are given more energy, they tend to jump to a higher orbit. These unnaturally high orbits, however, don't last long, and the electrons fall back to their proper orbital shells, to be once again excited by the influx of electricity. It is this process of the electrons returning to their original orbits that creates the laser light we see (actually, it's more appropriate to call it a jump, for an electron falls from orbit in a span of time infinitesimally small): During this jump back down, the extra energy is released from each atom as a packet called a photon (light). Moreover, if this photon collides with another already excited atom, that atom is also stimulated to emit a photon...but this new photon will be vibrating perfectly in step (in-phase) with the colliding photon, and will be traveling on the exact same course.

Photons are released, however, in haphazard directions. In order to get them aligned into the tight beam of light with which we're familiar, the tubes in which the atoms of gas are excited must be mirrored on both ends. Any photon that now happens to randomly travel exactly perpendicular with the mirrors on both ends (which inevitably happens) will cause a remarkable chain of events: The drama begins with the photon's 'cloning' when it bounces off the mirror and collides with another excited atom. Those two in-phase photons then collide with two more excited atoms, making four photons traveling in-phase, and exactly down the length of the laser tube. This process is then repeated in a geometric progression of photons parading exactly down the laser tube, colliding with more excited atoms, creating more photons, reflecting off the mirrors, and repeating and amplifying the process over and over again.

The laser light we see is finally released through the front mirror, whose reflective coating was designed to be partially transparent. In this way, a small percentage of those perfectly aligned photons is allowed to escape, forming the thin, straight, coherent, and beautiful beams we call LASER light.

Different colors of light, as specific frequencies, are produced by different gases. Argon gas, for instance, produces colors ranging from emerald green to beautiful deep blues. Krypton gas produces a palette from deep reds to light blues. A laser incorporating a mixture of these two gases can produce all the colors unique to those individual gases... simultaneously. It is these Krypton/Argon mixed-gas ion lasers that are typically utilized in laser projection hardware.

To sum up, laser light provides a quality of light unmatched by any other light source in the world: It's coherent, meaning again that the waves of light are vibrating perfectly in step with each other (in-phase); It's monochromatic, meaning that only very pure, specific frequencies (colors) of light are created (though several frequencies can be created simultaneously with the same laser); and it's low-divergent, meaning it keeps its power contained within a narrow, barely widening beam.

But there's something more, as well: Synergy. The above qualities together, somehow provide more than merely the sum of their parts. In human emotive terms, laser light has a sparkle. Its radiance, its breathtakingly pure, glowing colors, and its sheer elegance somehow imbue it with an intangible, almost magical power to plug directly into our emotions. Its synergistic qualities reach out to us in a way we do not comprehend, and we are touched by this uniquely wonderful lightform.
Indeed, we are drawn to it like a moth to the moon...

Bob Mueller is art director for Lightspeed Design Group and past winner of ILDA's Career Achievement Award.

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Images from top:
Laser Images, Inc.,
Laserland GmbH,
Laser Systems Europe