Coherence , Type of Coherence , Coherence Time , Coherence Length

         - : Coherence :- 


In physics if two wave sources have a constant phase difference and same frequency , and the same waveform then these sources are called coherent sources and this property is called coherence .

Type of Coherence:- Coherence are of following two types - 

1- Temporal Coherence 

2- Spatial Coherence 

1- Temporal Coherence :- If the phase difference between two points along the direction of wane propagation remains constant, the coherence is called temporal coherence . It is also called as longitudinal coherence, 

                   The degree to which correlation exists is known as the amount of longitudinal coherence. 

Image Source : Google

2- Spatial coherence :- If the phase difference between the two points on a plane perpendicular to the direction of propagation remains constant it is said to be spatial coherence. It is also known as trans vase or lateral coherence.

Image Source : Google

                  -: Coherence Time :-

 The average time for which the field remains sinusoidal is called  coherence time.     

                     𝞃c = 𝛌²/ 𝐂𝛥𝛌


                  -: Coherence Length :-

The length for which the field remains sinusoidal is called coherence length . It is represented by Lc .
                           
                          𝙇c = 𝛌²/ 𝞓𝝺
                                or
                           𝙇c=𝞜𝝺