Optics 101

Laser - The Structure, Physics and Applications of Laser

What is Laser
Structures of Laser
Structure of Laser - Laser Material
Structure of Laser - Pump Source
Structure of Laser - Optical Cavity
Physics of Laser
Laser Output
Applications of Laser

What is Laser

The word "laser" is actually an acronym that's stands for "Light Amplification by Stimulated Emission of Radiation". A laser typically emits a narrow and low-divergence beam of light with a wavelength that is well-defined. A laser is different to light sources such as incandescent light bulb in that light in emitted over a large spectrum of wavelength and into a large solid angle.

Structures of Laser

To put it in simple terms, a laser consists of three basic components:

  • Lasing Material
  • Pump Source
  • Optical Cavity

Structure of Laser - Laser Material

The lasing material, also commonly referred to as the laser medium or the gain medium. It is situated inside the optical cavity, and a method to supply energy to the lasing material. The gain medium is basically a material that can be a solid, liquid, or gas. It can also be molecules or atoms of a crystal. The gain medium is required to have appropriate optical properties and controlled size and shape, concentration and purity.

Structure of Laser - Pump Source

Electricity and light such as flash lamp or another laser are examples of pump sources. The laser medium absorbs this pump energy, which places some of the laser medium¡¦s particles into excited or high-energy quantum states.

Structure of Laser - Optical Cavity

The optical cavity is a type of cavity resonator. Inside the optical cavity, it contains a coherent light beam between reflective surfaces. The purpose of the reflective surfaces is to allow light to pass through the laser medium more than once before the light is lost through to diffraction or absorption or emitted from the output aperture. As the light beam passing through the laser medium and circulates through the optical cavity, the power of the circulating light beam can increase exponentially if the laser amplification in the laser medium is greater than the resonator losses.

Physics of Laser

As stated earlier, a laser is composed of a laser medium, pump source and an optical cavity. The laser medium transfers its external energy into laser beam. The molecules or atoms of a crystal are excited in the laser cavity; as a result more of the molecules or atoms are at a higher level of energy than at the lower energy level.

If the frequency of the photon is related to the difference in energy between the ground states and excited states strikes an excited atom, the atom is stimulated as it returns to the lower state of energy to release a second photon with the same frequency, in the phase with the bombarding photon as well as the same direction. This quantum mechanical process is referred to as stimulated emission.

When electricity and light such as flash lamp or another laser is added to the atoms of laser medium, the majority of electrons are excited to a higher level of energy state. When that number exceeds the number of electrons in the lower level of energy state, this will lead to a phenomenon known as population inversion. This energy state is unstable for the electrons, the electrons will remain in the high energy state for a short period of time and then they decay back to the low energy level. The decay or emission can happen in two ways: spontaneous or stimulated.

The light is amplified when the amount of stimulated emission or decay due to light that passes through is greater than the amount of absorption. This amplification will continue until there is a built up of sufficient energy for a burst of laser to be transmitted through the optical cavity. Strictly speaking, these are the necessary and crucial component of a laser.

Laser Output

The laser output can occur in several forms. It may be continuous constant-amplitude output, more commonly referred to as continuous wave or CW. It may also be pulsed output. This output method used techniques of Q-switching, mode locking or gain-switching. Much higher peak powers can be achieved in pulsed operation.

Applications of Laser

The applications of laser ranges include medical, defence, to research and industries. Here are some of the examples:

  • Medical - surgery, kidney stone treatment, eye treatment
  • Industrial - cutting, welding, material heat treatment
  • Defence - battle field, direct energy weapon, anti-missile
  • Research - spectroscopy, laser annealing, ablation, scattering and interferometers
  • Commercial - laser printers, laser pointers, compact disc players, barcode scanners

Source: AZoOptics

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