# Duration of wave packet (photon) vs coherent time

• coke
In summary, coherence time refers to the length of time a pulse of light remains coherent, while the duration of the wave packet is the time difference between the leading and trailing edge of the pulse. The coherence time is related to the bandwidth of the pulse and can be measured using a Mach-Zender interferometer. Generally, the coherence time is equal to twice the length of the cavity.
coke
hi, can anyone kindly explain to me what's 'coherent time' and 'duration of wave packet (photon)' in white light interference ?

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.

## 1. What is a wave packet?

A wave packet refers to a localized group of waves that travel together as a single unit.

## 2. What is a photon?

A photon is a fundamental particle of light and other forms of electromagnetic radiation. It carries energy and behaves both as a particle and a wave.

## 3. What is the duration of a wave packet?

The duration of a wave packet is a measure of how long the wave packet exists before it spreads out and dissipates. It is typically expressed in terms of the time it takes for the packet to spread to twice its original size.

## 4. What is coherent time?

Coherent time refers to the duration of time during which a wave packet maintains its coherence, meaning the waves within the packet remain in phase with each other. This is important for the transmission and detection of information.

## 5. How does the duration of a wave packet relate to its coherent time?

The duration of a wave packet and its coherent time are inversely related. This means that as the duration of a wave packet increases, its coherent time decreases. This is because as the packet spreads out, the waves within it become more out of phase with each other, leading to a decrease in coherence.

• Optics
Replies
8
Views
1K
• Optics
Replies
1
Views
1K
• Optics
Replies
7
Views
2K
• Optics
Replies
54
Views
5K
• Quantum Physics
Replies
7
Views
464
• Optics
Replies
4
Views
2K
• Optics
Replies
18
Views
2K
• Optics
Replies
4
Views
1K
• Special and General Relativity
Replies
13
Views
2K