The main difference between Laser and Light is that Laser is referred to as coherent, monochromatic, and highly directional light, whereas light is referred to as incoherent and divergent because of the mixture of the electromagnetic waves that contain different wavelengths.
Laser vs. Light
The waves which came into existence because of the vibrations that occur between an electric field and a magnetic field are called electromagnetic waves. Both the laser and the light are considered as the electromagnetic waves. Because of this reason, they travel in a vacuum with the velocity of light. Nevertheless, laser light has properties that are very unique and cannot be seen in nature. Thus, it is considered to have very important properties.
Laser and light are frequently used in physics and are considered as the two important terms of this discipline of science. Sometimes we take laser as the form of the light. But the reality is that it is a light amplification of the radiations which are stimulated at the time of their emissions. We generally consider laser and light as the traveling photons. Both of them are different from each other in various ways.
We mainly differentiate laser and the light through the terms of the coherence. The laser is suggested as the monochromatic, coherent, and the unidirectional beam of light. Light present in the normal incandescent bulbs, on the flip side, emit photons according to their path of traveling, wavelengths, and their polarization. The laser is referred to as intense light, whereas ordinary light is not considered as an intense light.
Furthermore, the principle on which laser is based is stimulated emissions in which the photons get stimulated, and they emit photons on returning to their original energy states. Light, on the other hand, has a direction of travel and also has a whole range of energies. A laser is considered to be the type of electromagnetic wave which has a very specific color. Light, on the other side, is considered to be the type of electromagnetic wave, which is the sum of all the colors.
What is Laser?
The term “LASER” is an abbreviation for the Light Amplification by the Stimulated Emission of Radiation. Mostly atoms remain in the ground state because it is a stable state. Nevertheless, there also exists a small percentage of the atoms which are present at the excited or higher energy states. It is the temperature on which the percentage of the atoms at higher energy states depend. The number of atoms present at a given excited energy level increases as the temperature increases.
The lifespan of the excited state of the atoms is very short because of their instability. As a result, the excited atoms release their excess energy as photons and immediately de-excite to their ground states. These transitions do not demand any stimulus from outside and hence are called the probabilistic transitions. It is impossible to estimate the time that when an excited atom or molecule is getting de-excited. The transition process and the emission of the photons are random. We can say that the emission is spontaneous, and the emission of photons during transitions is out of phase (incoherent).
Nevertheless, some of the materials comprise higher energy states that have higher lifetimes. That energy states are called as the metastable states. Therefore, the atoms or molecules present in this state do not come back to their ground state immediately. We can also pump atoms or molecules to their metastable states by providing energy to them from the outside. They remain in the metastable state for a long time without returning to the ground. As a result, we can largely increase the percentage of the atoms at the metastable state by pushing more atoms or molecules from the ground state to the metastable state. This situation is called population inversion because it is completely opposite to the normal situation.
However, we can stimulate an atom to de-excite in a metastable state by an incident photon. A new photon is released during the transition. If the energy of the incoming photon is exactly equal to the difference of the energy between the ground state and the metastable state, then the frequency of the new photon, energy, the phase, and the direction will be the same to those of the incident photon. The new photon will be able to stimulate another excited atom if the population inversion state is the material medium. Ultimately, the process will convert into a chain reaction that will be responsible for emitting a flood of identical photons.
The emitted photons are monochromatic (single color), coherent (in-phase), and directional. We called this action as the basic laser action. The narrow frequency range, coherence, and directionality are some unique properties of laser light and are considered as the key advantages which are used in the laser applications. There are various types of lasers according to the type of lasing mediums, like gas lasers, dye lasers, solid-state lasers, and semiconductor lasers. We are using lasers in many different applications, and various new applications are being developed.
What is Light?
The fluorescent bulbs, the incandescent bulbs, which are also called the Tungsten filament bulbs and mainly the sunlight, are the most useful sources of ordinary light. According to theories, we came to know that any object having a temperature greater than the 0K (absolute zero) emits electromagnetic radiation. This is referred to as the basic concept that is being used in the incandescent bulbs. There is a Tungsten filament in an incandescent bulb.
When we switch on the bulb, then the applied potential difference enables the electrons to accelerate. As we all know that Tungsten has a high electrical resistance, therefore, the electrons collide with atomic cores within the shorter expanses. Because of the electron- atomic core collisions, they are involved in transferring some of their energy to the atomic cores, as the momentum of the electrons gets the change because of the collision. As a result of this transfer of energy, the Tungsten filament heats up.
The heated filament is involved in emitting the electromagnetic waves, which cover a wide range of frequency and turns into a blackbody. It is responsible for emitting IR, visible waves, microwaves, etc. But the useful part of this spectrum is its visible part. The sun is referred to as a super-heated blackbody. Because of this reason, it is involved in emitting a tremendous amount of energy, which is in the form of electromagnetic waves and is responsible for covering a wide range of frequency from radio waves to gamma rays. It is suggested that any heated body that emits radiation also emits the light waves.
At a given temperature, the Wien’s displacement law gives the wavelength which corresponds to the highest intensity of a blackbody. According to this law, the wavelength which corresponds to the highest intensity decreases as we increase the temperature. The wavelength which corresponds to the highest intensity of an object is considered to fall into the IR region at room temperature. Nevertheless, we can adjust the wavelength corresponding to the highest intensity by increasing the temperature of the body. But, the emission of the electromagnetic waves having other frequencies cannot be stopped. Because of this reason, such waves are not considered monochromatic.
It is obvious that all the ordinary light sources are referred to as divergent. Normally, we can say that ordinary light sources are involved in emitting the electromagnetic waves in all directions randomly. The phases of the emitted photons do not have any relationship. So, they are incoherent light sources. The waves emitted by the ordinary light sources are generally considered as polychromatic.
- The type of the electromagnetic wave which has a stimulated emission is called laser, whereas the type of the electromagnetic wave which has a spontaneous emission is called light.
- The laser is referred to as a coherent electromagnetic wave because the photons emitted by its source are in phase, on the other hand, light is referred to as an incoherent electromagnetic wave because the photons emitted by its source are out of phase.
- A laser is referred to as a monochromatic electromagnetic wave. Conversely, light is referred to as a polychromatic electromagnetic wave.
- A laser is referred to as a monochromatic electromagnetic wave; on the flip side, light is referred to as a polychromatic electromagnetic wave.
- The laser is considered as a highly directional electromagnetic wave; on the other side, light is considered as a divergent electromagnetic wave.
- The laser is involved in covering a very narrow range of the frequencies, while, light is involved in covering a wide range of the frequencies.
- As the laser is highly directional, so we can focus it on a very sharp spot, on the other hand, as light is divergent, so we cannot focus it on a sharp spot.
- The laser is the electromagnetic wave that has a very specific color, whereas light is the electromagnetic wave that comprises the sum of all the colors.
- The laser is referred to as intense light; on the flip side, ordinary light is not considered as an intense light.
- There are a lot of application of the laser which includes its usage in eye surgery, in the metal cutting machines, CD players, in nuclear fusion reactors, laser printing, tattoo removal, barcode readers, in laser cooling, holography, in fiber optic communication, etc., on the other hand, light has a usage in lighting a small area.
All of the above discussion concludes that both the laser and light are the types of electromagnetic waves. The former is referred to as a coherent electromagnetic wave and has a stimulated emission; on the other hand, the latter is referred to as an incoherent electromagnetic wave and has a spontaneous emission.