Duration of wave packet (photon) vs coherent time

[coke]

hi, can anyone kindly explain to me what's 'coherent time' and 'duration of wave packet (photon)' in white light interference ?

 

[Claude Bile]

Coherence time is length of time a pulse of light will remain coherent for. Light pulses (or wavepackets if you like) become incoherent with time because the different frequency components drift out of phase with one another.

The duration of the wave packet is just the time difference between the leading and trailing edge of the pulse.

Claude.

 

[coke]

then does it mean that coherent time period is within the duration of a wave packet ?

 

[coke]

then does it mean that coherent time is within the duration of a wave packet ?

 

[Andy Resnick]

No- the coherence time is related to the bandwidth of a pulse, and is only related to the pulse time in diffraction-limited cases.

The coherence time means how well you can predict future values of the field (or intensity), and is typically measured by a Mach-Zender interfeometer.

As a rule of thumb, the coherence time (or equivalently, the maximum path difference in a M-Z interferometer) is given by twice the cavity length.