# Thought experiments suggest problem with published work

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Gezstarski
A recent preprint ( https://arxiv.org/abs/2112.15157 ) seems to imply that the focussing properties of an optical system can depend on the bandwidth of the sensor, and even on that of the associated electronics! It is argued there that if the ‘frame rate’ of the sensor is very high, photons taking paths of different (optical) lengths through the optics will no longer be recorded in the same frame and so cannot interfere with each other.

I am not comfortable with the talk of photons interfering with one another – one should calculate the propagation as a wave and then evaluate the probability that a photon is absorbed, or interacts, at a given point – eg in a detector in the image plane. But the argument could be framed in terms of radiation’ instead of photons’ and it makes one think. Consider the following series of thought experiments:-

Suppose we have a system with a light source, a chromatic lens, and an imaging detector in the focal plane.

1) If the source of illumination were pulsed on the femtosecond timescale the spectrum would be broadened and the focal spot would be blurred by chromatic aberration.

2) If the light source was monochromatic and continuous but a shutter acting on the same timescale is introduced in the light path before the lens, then the effect must presumably be the same.

3) What if the shutter is after the lens?

4) What if instead of a shutter the detector is active only for very brief intervals?

5) What if it is continuously active but able to record the time of detection of every photon with femtosecond precision?

6) In (5) does the form of the recorded image depend on how you select the photons to include in the analysis – eg just those in short intervals like the pulses of a pulsed light source versus using all?

I believe that from (4) onwards the image is no longer blurred by chromatic aberration, but this implies that the logic in the preprint is ill-founded.

There are other issues with the remainder of the paper, but it would be good to get this one clear

ChanceLiterature and vanhees71

Staff Emeritus

vanhees71
Gold Member
This paper seems only on arXiv so far but one of the authors does have an extensive presence in the literature;

https://nanoptics.wordpress.com/publications/

The author is associated with the Department of Electrical and Computer Engineering, University of Utah.

Gezstarski
This paper seems only on arXiv so far but one of the authors does have an extensive presence in the literature;

https://nanoptics.wordpress.com/publications/

The author is associated with the Department of Electrical and Computer Engineering, University of Utah.
Sorry, I wrote "published" in error when trying to find a succinct header. It is a preprint and not yet published.

vanhees71
Staff Emeritus
Since the work isn't published, doesn't that that solve the problem? "These guys wrote a bad paper that failed to be published" - what is the problem here?

vanhees71
Gold Member
Sorry, I wrote "published" in error when trying to find a succinct header. It is a preprint and not yet published.
My suggestion is that you contact the lead author and discuss your concerns. The preprint invites you to do that.
Since the work isn't published, doesn't that that solve the problem? "These guys wrote a bad paper that failed to be published" - what is the problem here?
If it is a bad paper it damages the reputation of the researchers even to put it on arXiv. It would be good for all if the issues were cleared up. At this point it seems to me we really don't know if it failed peer review or just hasn't been published yet.

hutchphd, protonsarecool, vanhees71 and 1 other person
Gezstarski
My suggestion is that you contact the lead author and discuss your concerns. The preprint invites you to do that.

If it is a bad paper it damages the reputation of the researchers even to put it on arXiv. It would be good for all if the issues were cleared up. At this point it seems to me we really don't know if it failed peer review or just hasn't been published yet.
Irrespective of the status of the paper, I would be interested in reactions to my series of thought experiments.

Gezstarski
It doesn't have to be femtosecond, just sufficiently short that the spectrum is broadened. And it doesn't have to be a mechanical shutter.
The real question is whether the focussing of a chromatic optical system can be affected by the brevity or otherwise of the intervals (frames) during which the image is recorded in the same way that it can by pulsing the incident radiation and so broadening the source spectrum.

bob012345
Mentor
Irrespective of the status of the paper, I would be interested in reactions to my series of thought experiments.
Sorry, that is not how PF works. The paper needs to be published in a peer-reviewed journal before we can discuss it. Thread it now tied off (until the paper is published).