Coherent Source is the source of waves that produce waves with the same frequency, same wavelength, and constant phase or constant phase difference. Coherent Sources are important in wave optics as they provide conditions for interference of waves to produce highly focussed and directional beam of light.

In this article, we will learn about coherent source, its types, characteristics, how to produce coherent source, its application and difference between coherent and incoherent source in detail.

What is Coherent Source?

Coherent Source refers to the sources that produce waves with a constant phase relation. In simple terms these sources generate waves in which the crests and troughs of emitted waves align or maintain a consistent phase difference as they move through space-time. This phase consistency allows the waves to interact predictably either in constructive interference or destructively, creating such phenomena as patterns of interference.

Coherent Source of Light

Coherent Source of Light are those light-emitting sources that emits light of the same frequency, same wavelength and same phase or constant phase difference

Coherent Source Example

Laser is an excellent example of Coherent Source. Let’s understand why laser is an coherent source

• In a laser, emitted light waves are in phase.
• This causes sharp and predictable interference patterns.
• It coherence enables the laser to emit a focused highly directional beam of light.
• Lasers are considered essential for applications like cutting, medical procedures and fiber optic data transmission due to coherent properties.
• Unlike common light sources with random wave phases, lasers produce waves that oscillate together to enable predictability and control.

Types of Coherent Sources

There are two types of coherence which are mentioned below:

• Temporal Coherence Sources
• Spatial Coherence Sources

Temporal Coherence Sources

Temporal Coherence determines whether phase relationships between waves are stable over time for such phenomena as interference patterns. It measures the consistency with which peaks and troughs of waves align as they travel.

• This coherence is critical in applications such as interferometry, guaranteeing accurate measurements.
• It is influenced by factors such as the source characteristics and propagation medium.
• Lasers often have high temporal coherence which provides very stable phase.
• On the other hand, larger sources may have reduced coherence times.
• Temporal coherence understanding helps in developing systems for efficiency and reliability.

Spatial Coherence Sources

Spatial coherence relates to phase consistency of waves at two or more different points in space but not over time. It defines how well waves maintain their phase coherence in various spatial positions.

• This coherence is vital in fields like imaging as it determines resolution and clarity.
• Spatial coherence is affected by character of the source and propagation conditions.
• High spatial coherence results in sharp wave fronts and focused beams.
• This facilitates enhanced performance and accuracy in optical systems based on spatial coherence.

Characteristics of Coherent Sources

Coherent Sources have several features that allow them to be distinguished from incoherent sources, especially if the characteristics of emitting waves with regular phase relationships are considered. Here are some key characteristics of coherent sources:

• Waves appear with a stable and constant phase relationship in time or space, so the patterns of interference that they form will be predictable.
• They are often described as monochromatic as they radiate light of one color or a very narrow range of colors resulting in sharp colours or spectral purity.
• The phase of emitted waves are highly aligned that results in highly directional beams, enabling focused and controlled propagation for different uses.
• Coherent Source ensures temporal stability, meaning they present constant phase relationships over time is imperative for methods such as interferometry and the ones involving time domain measurements.
• Coherent Source maintain uniformity in space by maintaining a stable phase relation between spatial locations that influence imaging quality, holography and spatially resolving features.
• Coherent Sources are able to produce highly focused beams, especially in lasers because of the coherence and synchrony at which photons are discharged.
• They exhibit very narrow linewidths in their emission spectra and this high degree of frequency stability as well as purity is vital to precision measurements and spectral applications.
• Coherent Source possess a large coherence length, meaning interference effects can be observed over significant distances or path differences which makes interferometric techniques and extended coherence applications easier.

How to Produce Coherent Sources?

Since, the availability of Coherent Source of light is not so easy, there are two ways with the help of which we can produce coherent sources of light:

By Dividing the Wavefront

Coherent Sources can be made by splitting the wavefront. For this purpose we can use different mirrors, lenses or prism. We can also use method’s like, Young’s Double Slit Expriment, Fresnel Method etc. to achieve the same

By Dividing the Amplitude

Dividing the amplitude is another method of producing coherent sources of light. Amplitude is divided by separating the amplitude of the incident beam of light into different parts using partial reflection and refraction.

Interference and Coherence

Interference means the phenomenon that takes place when two or more waves are superimposed over one another, thereby creating a resultant wave of whose amplitude and phase depend on characteristics of individual waves. Depending on the phase relationship between two waves that happens to overlap, interference can produce an amplification of the combined wave’s amplitude by adding with each other if in constructive condition or attenuation through destructive interaction.

Coherence provide the potential condition for interference. We can say they Coherence and Interference are two features that complement each other. For constructive interference, coherence is the ideal condition that need to be satisfied.

Coherent Source and Incoherent Coherent Source

Coherent Sources are those which produce waves of same frequency, same wavelength and same phase. They are significant in producing highly focussed and directional beam of light. On the other hand, Incoherent Sources are those which produce waves of different phase, different frequency and different wavelengths. Let’s have a look on the difference between the two types of waves producing soources

Difference between Coherent and Incoherent Source

The difference between Coherent and incoherent source is tabulated below:

Applications of Coherent Source

Coherence, of both temporal and spatial nature is paramount in a wide range of scientific, engineering medical and technological applications. Here are some applications where coherence is crucial:

1. Interferometry: Coherence allows accurate measurements of distances, velocities and other parameters by monitoring interference patterns formed from the interaction of waves. This method is used in astronomy, metrology and optical testing.

2. Imaging and Microscopy: Coherence assists in getting high-resolution, depth-resolved imaging when techniques such as Optical Coherence Tomography OCT and confocal microscopy are used to obtain detailed visualization of biological tissues materials.

3. Holography: Capturing three-dimensional holographic images are possible only by Coherence. interference patterns formed by coherent light sources, enabling use in art , security and data storage services.

4. Communications: The coherent optical communication systems use phase-stable light sources to transmit data over the long distances with very low dispersion and attenuation, accordingly improving speed, reliability and bandwidth efficiency.

5. Laser Technology: Fundamental to lasers is coherence which allows them produces intense beams that are monochromatic and directional These beams find use in different areas including material processing , surgery, spectroscopy laserand research.

6. Spectroscopy: Coherence forms well-defined interference patterns that facilitate the analysis of molecular structures and interactions, providing spectral information for chemical analysis, environmental monitoring as well as characterization of materials.

7. Signal Processing: Coherence in radiofrequency and microwave engineering allows analysing and processing signals to use applications of radar, wireless communications or navigation systems

Significance of Coherent Source

The importance of a coherent source is its ability to generate consistent phase relationship waves and hence interference patterns that are predictable in precision applications as well for purposes of researching different fields like communication, medicine, optics among others This consistency makes it reliable and efficient in many technological or scientific ventures.

• Consistent source is characterized by waves with regular phase relationship; this allows predictable interference patterns helpful in experiments like interferometry and diffraction.
• Measurements with coherent sources are highly precise and their predictability ensures that particular use, like interferometry where tiny changes need to be detected is detectable.
• In communication systems such as fiber optics, coherent light sources allow efficient and reliable data transmission since signal degradation is minimized.
• Medical procedures have been significantly transformed by coherent sources such as lasers because of their precision which has offered better treatments and surgical techniques.
• Industries use coherent sources for activities such as cutting, welding and other precise applications that improve the efficiency of their operations.
• Credible sources have played a significant role in contributing to research regarding quantum optics, materials science and quantum mechanics resulting in advancements into understanding as well as technology development.
• Holography is a process of recording three dimensional images and it utilizes coherent sources to generate precise lifelike representations for objects.

Also, Read

• Young’s Double Slit Experiment
• Difference Between Diffraction & Interference
• Superposition and Interference
• Diffraction of Light

Coherent Source – Frequently Asked Questions (FAQs)

What is Meaning of Coherent Source?

Coherent Sources is a wave emitting source that produces waves that have the same frequency, same wavelength with a constant phase difference.

What are Incoherent Sources?

Incoherent sources generate waves that lack continuous phase relations and produce random interference patterns whenever the interaction of wave occurs.

Is Sun a Coherent Source of Light?

No, Sun is not a coherent source of light

What are the Examples of Coherent Source?

Lasers and speakers powered by electrical signals are two prominent examples of coherent sources

What are the Types of Coherent Sources?

There are two types of coherent sources namely, Temporal Coherent Sources and Spatial Coherent Sources

What is Interference?

Interference is the phenomena of superimposition of two waves

What is the difference between Coherent and Incoherent Sources?

The main difference between Coherent and Incoherent source is that Coherent Sources produce wave with same frequency and same phase or constant phase difference while incohent wave produces waves with the different frequency and phase