How does a band pass filter increase the time of arrival of photons?

In summary, a band pass filter increases the time of arrival of photons by allowing only a specific range of frequencies to pass through while blocking others. This selective filtering reduces the number of photons that can reach the detector, effectively delaying their arrival. Additionally, the filter can introduce phase shifts in the transmitted light, further contributing to the altered timing of the detected photons.
  • #1
Daniel Petka
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TL;DR Summary
If a very short (laser) pulse attenuated to single photon intensity passes through a narrow band pass filter, do the photons get detected at random times?
Here is my thought experiment: Let's say I attenuate a very short laser pulse to single photon intensity. Due to the uncertainty principle, I know the time of arrival of the photons, but not their energy. So let's reverse that by splitting the pulse in its spectral components with a diffraction grating and passing the spectrum through a slit. The photons that pass through the slit will have a defined energy, but not a defined time of arrival, because each new photon arrives on a random spot and so it's also random if it passes through the slit. This seems logical (kind of). But now let's pass the pulse directly through a narrow band pass filter instead. The photons should still appear randomly. Is that true? If yes, it's extremely counter intuitive. It's as if the band pass filter can delay a photon randomly. How does this happen, what's going on here physically? It has to be true because, well, Fourier Transform, but I don't get why.
 
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  • #2
The filter can the thought of as a "measuring apparatus", which induces a "collapse" of initial superposition (of states with different energies) into a state with well defined energy. The collapse is "nonlocal", in the sense that it does not respect the principle that wave cannot "change" faster than light. As always, the exact physical meaning of "nonlocal collapse" depends on the choice of interpretation (Copenhagen, Bohm, many worlds, ...).
 
  • #3
Demystifier said:
The filter can the thought of as a "measuring apparatus", which induces a "collapse" of initial superposition (of states with different energies) into a state with well defined energy. The collapse is "nonlocal", in the sense that it does not respect the principle that wave cannot "change" faster than light. As always, the exact physical meaning of "nonlocal collapse" depends on the choice of interpretation (Copenhagen, Bohm, many worlds, ...).
Thank you for the reply! This is probably one of those cases where intuition fails
 
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FAQ: How does a band pass filter increase the time of arrival of photons?

What is a band pass filter?

A band pass filter is an electronic device or optical component that allows signals or photons within a certain frequency or wavelength range to pass through while attenuating frequencies or wavelengths outside that range. It is commonly used in various scientific and engineering applications to isolate specific spectral components.

How does a band pass filter work?

A band pass filter works by using a combination of optical coatings, materials, or electronic components that are designed to resonate at specific frequencies or wavelengths. These components either absorb or reflect unwanted frequencies, allowing only the desired range to pass through. This selective transmission is achieved through constructive and destructive interference patterns.

Why would a band pass filter affect the time of arrival of photons?

The time of arrival of photons can be affected by a band pass filter due to the dispersion properties of the filter material. When photons pass through the filter, their speed can be altered depending on the wavelength. This change in speed can cause a delay in the time it takes for the photons to reach their destination, effectively increasing their time of arrival.

What is the relationship between the filter's bandwidth and the time of arrival of photons?

The bandwidth of the filter determines the range of wavelengths that can pass through it. A narrower bandwidth means that only a very specific range of wavelengths can pass, which can result in a greater dispersion effect and thus a longer delay in the time of arrival of the photons. Conversely, a wider bandwidth allows a broader range of wavelengths to pass with less dispersion, resulting in a shorter delay.

How can the time delay introduced by a band pass filter be measured?

The time delay introduced by a band pass filter can be measured using time-resolved spectroscopy or other time-of-flight measurement techniques. By comparing the arrival times of photons passing through the filter with those of a reference path (without the filter), the delay can be quantified. This requires precise timing equipment and often involves the use of ultrafast lasers and detectors.

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