# Coherent time vs duration time of the wave packet (photon)

• coke
In summary, the difference between "coherence time" and "coherence length" can be measured using different interferometers and is related to the frequency spread and size of a light source. For pulsed light, there may be competition between these two factors and it is not clear what would happen in certain cases. Overall, further research and experimentation may be needed to fully understand the effects of these factors on the behavior of light in different experiments.
coke
hi, i really confused about this two term. As i read from a book, ' in the Young's double slits experiment of light, if the time difference (that resulted from the path difference because of the two slits) is longer than the duration of each 'burst' (the photon),the received waves must come from different 'burst', which are unrelated and incoherent.'

i want to know if 'coherent time' = duration of the 'burst' (about nanosecond for white light). if they are equal, i can understanding the above statement. if they are not, can anyone explain clearly, in detail to me ? Thank you very very much!

"Coherence time" is related to the frequency spread (bandwidth) of a beam. Coherence time is most proeprly measured by a Mach-Zender/Michaelson interferometer- the coherence time is related to the difference in path lengths.

"Coherence length", sometimes called the coherence area, is related to the apparent size of a source, and is measured by a Young's double slit interferometer.

For pulsed light, I can see there being competition between the coherence time, the bandwidth, and the pulse duration, and it's not immediately clear what would happen in a Michaelson interferometer, except in the obvious cases of the pulses being coincident or completely missing each other.

Putting pulses through a double-slit interferometer poses no obvious difficulties, since the pulse width and size of the illuminated spot are not related to each other. Perhpas for sub fs pulses, there could be some interesting effects, but it could be hard to distinguish them from changes to a single-slit diffraction pattern.

Coherent time and duration time refer to different aspects of the wave packet (photon) in the context of the Young's double slit experiment. Coherent time refers to the amount of time that the wave packet maintains its coherence, or its ability to interfere with itself. This is typically on the order of nanoseconds for white light. Duration time, on the other hand, refers to the length of time that the wave packet exists before it is absorbed or interacts with another particle.

In the context of the Young's double slit experiment, it is important for the time difference between the two paths (resulting from the two slits) to be shorter than the coherent time of the wave packet. This ensures that the wave packet remains coherent and can interfere with itself, producing the characteristic interference pattern on the screen. If the time difference is longer than the coherent time, the wave packet will no longer be coherent and the interference pattern will not be observed.

In other words, the duration time of the wave packet is not directly related to its coherence. The duration time is simply the length of time that the wave packet exists before it is absorbed or interacts with another particle. The coherent time, on the other hand, is a measure of the wave packet's ability to maintain its interference properties. So, while the two terms are related in the sense that they both refer to time in the context of the wave packet, they are not equivalent and cannot be used interchangeably.

I hope this explanation helps to clarify the difference between coherent time and duration time in the context of the Young's double slit experiment. If you have any further questions, please do not hesitate to ask.

## What is the difference between coherent time and duration time of a wave packet?

Coherent time refers to the time period during which the phase relationship between different components of a wave packet remains constant. Duration time, on the other hand, is the time interval during which the wave packet has a significant amplitude. In other words, coherent time is about the coherence of the wave packet, while duration time is about its temporal extent.

## How do coherent time and duration time affect the behavior of a wave packet?

A longer coherent time indicates a more stable and well-defined wave packet, while a shorter coherent time results in a more spread out and less predictable wave packet. Similarly, a longer duration time means that the wave packet will have a longer temporal extent, while a shorter duration time results in a more localized wave packet.

## How are coherent time and duration time related to each other?

Coherent time and duration time are closely related, as they both describe different aspects of the same wave packet. Generally, a longer coherent time corresponds to a longer duration time, and vice versa. However, this relationship can vary depending on the specific properties of the wave packet.

## What factors influence the coherent time of a wave packet?

The coherent time of a wave packet is influenced by several factors, including the spectral width of the wave packet, the phase stability of the source, and the propagation medium. Additionally, the size and shape of the wave packet also play a role in determining its coherent time.

## How is the duration time of a wave packet measured?

The duration time of a wave packet can be measured using various techniques, such as time-resolved spectroscopy or autocorrelation. These methods involve analyzing the temporal profile of the wave packet and determining the time interval during which it has a significant amplitude. The exact measurement technique used may vary depending on the specific properties of the wave packet being studied.

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