Duration of wave packet (photon) vs coherent time

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Discussion Overview

The discussion centers around the concepts of 'coherent time' and 'duration of wave packet (photon)' in the context of white light interference. Participants explore the definitions and relationships between these terms, particularly in relation to light pulses and their coherence properties.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants seek clarification on the definitions of coherent time and duration of wave packet in relation to white light interference.
  • One participant defines coherence time as the duration a light pulse remains coherent, noting that different frequency components can drift out of phase over time.
  • Another participant describes the duration of the wave packet as the time difference between the leading and trailing edges of the pulse.
  • There is a question about whether coherent time is contained within the duration of a wave packet, which is posed multiple times by different participants.
  • One participant argues that coherence time is related to the bandwidth of a pulse and is only connected to pulse time in specific cases, suggesting a more complex relationship.
  • This participant also mentions that coherence time is related to predictability of future values of the field and is typically measured using a Mach-Zender interferometer.
  • A rule of thumb is provided regarding coherence time being related to cavity length in interferometry, but this is presented as a general guideline rather than a definitive statement.

Areas of Agreement / Disagreement

The discussion reflects uncertainty and differing interpretations regarding the relationship between coherent time and the duration of a wave packet. No consensus is reached on whether coherent time is contained within the duration of a wave packet.

Contextual Notes

Participants express varying assumptions about the definitions and implications of coherence time and wave packet duration, indicating potential limitations in understanding the underlying physics.

coke
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hi, can anyone kindly explain to me what's 'coherent time' and 'duration of wave packet (photon)' in white light interference ?
 
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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.
 
then does it mean that coherent time period is within the duration of a wave packet ?
 
then does it mean that coherent time is within the duration of a wave packet ?
 
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.
 

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