Why ordinary light is coherent

Simply, the emission is spontaneous, and photons emitted when transitions occur are out of phase incoherent.

However, some materials have higher energy states with higher lifetimes Such energy states are referred to as metastable states. Atoms or molecules can be pumped to their metastable states by supplying energy from the outside.

Once pumped to a metastable state, they exist for a long time without returning to the ground. So, the percentage of the atoms that exist at the metastable state can be largely increased by pumping more and more atoms or molecules to the metastable state from the ground state. This situation is completely opposite to the normal situation.

So, this situation is called population inversion. However, an atom that exists in a metastable state can be stimulated to de-excite by an incident photon. During the transition, a new photon is emitted. If the material medium is in the population inversion state, the new photon will stimulate another excited atom.

Eventually, the process will become a chain reaction emitting a flood of identical photons. They are coherent in phase , monochromatic single color and directional travels in the same direction. This is the basic laser action. The unique properties of laser light such as coherence, directionality, and narrow frequency range are the key advantages used in laser applications.

Based on the type of lasing mediums, there are several types of lasers namely solid state lasers, gas lasers, dye lasers and semiconductor lasers. Today, lasers are being used in many different applications while more new applications are being developed. Ordinary light is incoherent. Photons emitted by an ordinary light source are out of phase. Laser light is coherent.

Photons emitted by a laser light source are in phase. Ordinary light is polychromatic. It covers a wide range of frequencies. A mixture of waves having different frequencies. Laser light is monochromatic. A quantum of electromagnetic energy is called a photon.

The energy carried by each photon is proportional to its frequency. An atom or molecule of a substance usually does not emit energy; it is then said to be in a low-energy or ground state. When an atom or molecule in the ground state absorbs a photon, it is raised to a higher energy state, and is said to be excited. The substance spontaneously returns to a lower energy state by emitting a photon with a frequency proportional to the energy difference between the excited state and the lower state.

In the simplest case, the substance will return directly to the ground state, emitting a single photon with the same frequency as the absorbed photon. In a laser or maser, the atoms or molecules are excited so that more of them are at higher energy levels than are at lower energy levels, a condition known as an inverted population.

Laser light is used in metal cutting machines , laser printers , eye surgeries , tattoo removal , barcode readers and fiber optic technology. Today, lasers are used in many different applications , and more and more new applications are being developed every day.

He completed his master's degree at Gazi University Industrial Design Engineering Department and continues his education in the doctorate program of the same department. Your email address will not be published. Wednesday, September 2, - Related Posts. What Is Zhaga? Author Laser Laser Light Light. Cancel reply Your email address will not be published. LED Technology. LED Lighting. Lighting Design. Plant Growing.