The Science Behind Laser

The term “Laser” is an abbreviation for “Light amplification by stimulated emission of radiation”. It has three distinct properties. It is monochromatic. It means that it is of a single wavelength and hence a single color. It is coherent. This means that the photons move in a periodic unison just like an army. It is unidirectional. This makes the beam dense and concentrated (highly collimated).

When a matter receives electrical or light energy in a proper amount, its atoms get excited. This energy is actually absorbed by the electrons in the atom. These electrons try to shake off this extra energy. By doing so, they come down to their natural (normal) state. When they shed the extra energy, the same becomes visible in the form of colored photons. The color (wavelength) signifies the state of excitation and the amount of energy released by an electron. Infrared has a larger wavelength than the ultraviolet.

Light or electrical energy brings the atoms of the lasing medium into an excited state. The lasing medium has a specific size, purity and concentration best suited for assisting stimulated emission. The electrons of the atoms reach a higher state of energy. This is an excited state. The electrons stay in this state for a very short interval of time. They immediately jump down to a lower state of energy. This meta-stable state is more comfortable.

It is just like children using a lift to reach the roof of a ten-floor apartment. When they fear that the lift facility might be closed, they get down to a floor from where they could easily step down using the stairs or just jump down to the ground floor. The stimulated jumping begins once a child takes an initiative.

The electrons in the excited state get down to a more comfortable lower state and emit the extra energy as light photons. There are an infinite number of electrons. A cascading effect begins. An infinite number of light photons having same wavelength and the same phase fill the space. Amplification and stimulation take place. A pair of mirrors on either side of the flash tube keep reflecting the photons. This further enhances the density and concentration of photons.

The mirror on the release side is half silvered. Sometimes, the central part is kept transparent. The reflecting photons further excite the electrons inside the flash tube. The number of light photons further increases. A coherent, monochromatic and unidirectional (highly collimated) light begins emanating through the disc. This is a laser beam.