How to calculate dark count from data collected?

[physicsclaus]

Homework Statement

How to calculate dark count from data collected?

Relevant Equations

I cannot find it

Hello everyone, I am trying to measure the dark count from a measurement a SPDC source. Although I collected data from the signal generator, I do not know how to obtain dark count rates per second.

I only know the following definition
Dark counts refer to the tiny amount of DC current in the absence of light input. An additional fluctuating current with zero mean value caused by thermal fluctuation is not called a dark current. When extremely small optical powers need to be detected, we need to consider dark count. Thus, dark count will limit single photon detection capability.

The following is the data extracted:
Detection rate ch.2 (counts/s): 124
Detection rate ch.4 (counts/s): 612
Coincidence rate (pairs/s): 0
Delay (ns): 0

Delay (ns), Coincidence rate (pairs/sec)

-20, 0
-18, 0
-16, 0
-14, 0
-12, 0
-10, 0
-8, 0
-6, 0
-4, 0
-2, 0
0, 0
2, 0
4, 0
6, 0
8, 0
10, 0
12, 0
14, 0
16, 0
18, 0
20, 0

Time (s), Ch2 (counts/sec), Ch4 (counts/sec), Coincidence (pairs/sec) (delay: 0 ns)

0, 124, 612, 0
1, 115, 609, 0
2, 126, 589, 0
3, 122, 564, 0
4, 125, 627, 0
5, 120, 555, 0
6, 105, 630, 0
7, 105, 584, 0
8, 115, 586, 0
9, 128, 604, 0
10, 138, 597, 0
11, 101, 548, 0
12, 118, 596, 0
13, 107, 611, 0
14, 122, 538, 0
15, 136, 632, 0
16, 110, 609, 0
17, 131, 582, 0
18, 117, 602, 0
19, 127, 605, 0
20, 130, 632, 0
21, 126, 621, 0
22, 132, 617, 0
23, 138, 574, 0
24, 127, 615, 0
25, 118, 605, 0
26, 143, 588, 0
27, 125, 594, 0
28, 117, 594, 0
29, 132, 608, 0
30, 114, 586, 0
31, 130, 632, 0
32, 138, 576, 0
33, 128, 619, 0
34, 126, 601, 0
35, 114, 613, 0
36, 129, 631, 0
37, 120, 586, 0
38, 125, 576, 0
39, 110, 551, 0
40, 110, 624, 0
41, 108, 587, 0
42, 122, 562, 0
43, 117, 597, 0
44, 127, 580, 0
45, 122, 600, 0
46, 117, 598, 0
47, 120, 569, 0
48, 112, 628, 0
49, 116, 540, 0
50, 123, 574, 0
51, 129, 579, 0
52, 126, 606, 0
53, 119, 594, 0
54, 129, 590, 0
55, 128, 629, 0
56, 112, 584, 0
57, 121, 574, 0
58, 110, 624, 0
59, 120, 586, 0
60, 110, 602, 0

I generated some graphs from jupyter notebook, still it does not make sense to me.

I have also found the respective maximum values
Time (s) 60
Ch2 (counts/sec) 143
Ch4 (counts/sec) 632
Coincidence (pairs/sec) (delay:6ns) 0
dtype: int64

and also the respective mean values
Time (s) 30.000000
Ch2 (counts/sec) 121.508197
Ch4 (counts/sec) 595.508197
Coincidence (pairs/sec) (delay:6ns) 0.000000
dtype: float64

I hope someone could give me some insights of how to calculate the dark count, thank you so much for your time!

 

[Drakkith]

Were the Ch2 measurements taken with no light source?

 

[physicsclaus]

Were the Ch2 measurements taken with no light source?

Yes, there is no light source in it .

 

[Steve4Physics]

Yes, there is no light source in it .

Since there is no light source producing the Ch2 readings, why do you think the Ch2 counts are non-zero? What is producing the Ch2 counts?

You haven't provided any description of the setup. We are left to guess! What are the inputs to Ch2 and Ch4? Are the efficiencies of Ch2 and Ch4 identical? What coincidences are being detected? Why do the results show zero coincidences? Is the sole purpose to measure the dark count rate or is there some other objective? Etc.

 

[Drakkith]

Yes, there is no light source in it .

Then are the Ch2 counts/s not already the dark current/s? I'm not sure what your setup is, what sensors you're using, etc. For a CCD or CMOS camera sensor, I would take a 'dark frame', subtract the built-in bias via a bias frame, and then divide by the exposure time to get dark current per second for each pixel. I'm not quite sure how this works for a DC current from whatever your sensor is.

 

[physicsclaus]

Since there is no light source producing the Ch2 readings, why do you think the Ch2 counts are non-zero? What is producing the Ch2 counts?

You haven't provided any description of the setup. We are left to guess! What are the inputs to Ch2 and Ch4? Are the efficiencies of Ch2 and Ch4 identical? What coincidences are being detected? Why do the results show zero coincidences? Is the sole purpose to measure the dark count rate or is there some other objective? Etc.

Now I understand more why there is dark count measured in the photodetector. as far as I know, the photon light signal is converted into current so we can measure it. how the As you mentioned efficiency, do you know a way to calculate it? For the coincidence, I think it is due to the blockage of the output from the SPDC source with paper card so we cannot measure it. I should have mentioned this part. I have many measurements in this experiment, the first one is to measure the dark count. Thank you for your questions for clarity.

 

[physicsclaus]

Then are the Ch2 counts/s not already the dark current/s? I'm not sure what your setup is, what sensors you're using, etc. For a CCD or CMOS camera sensor, I would take a 'dark frame', subtract the built-in bias via a bias frame, and then divide by the exposure time to get dark current per second for each pixel. I'm not quite sure how this works for a DC current from whatever your sensor is.

Channel 2 corresponds to the probe and channel 4 correspond to the system. I do not know what sensor is this either. Thank you so much for your method of finding the dark count.

 

[Steve4Physics]

Channel 2 corresponds to the probe and channel 4 correspond to the system. I do not know what sensor is this either.

Where is the probe? What does the system consist of?

Consider providing a diagram of the setup showing clearly where the Ch2 and Ch4 signals come from. What is(are) the objective(s) of the experiment? Do you have an instruction sheet? Can you post it?

 

[physicsclaus]

Please kindly find all the images about the experiment. Can I ask questions other than dark count? I feel this experiment is so difficult for me complete.

 

[Steve4Physics]

Please kindly find all the images about the experiment. Can I ask questions other than dark count? I feel this experiment is so difficult for me complete.

The images of the text you posted seem to be in a random order without page numbers. I’ve looked through them and they seem to include Sections 2 -10 (but in random order) of some document - but there is no Section 1. Maybe Section 1 pulls the whole thing together.

This seems to be some sort of quantum entanglement/erasure/delayed-choice experiment, or similar. But I can’t see any clear statement of the overall objective/purpose.

There are a number of very specific steps to follow – your best bet might be to try following them and see what happens. Then the overall picture might become clearer.

I’m not knowledgeable in this area so it’s very difficult (for me, anyway) to offer any specific advice. Sorry I can’t help more.

[minor edit]

 

[Drakkith]

Okay, according to section 3, the 'probe' is simply one set of photons exiting the 2nd beamsplitter in port B, while the 'system' is the other set of photons exiting the 2nd beamsplitter in port A. So each photon pair is split into a probe photon and a system photon. Each photon beam is detected by its own separate detector.

I have zero experience with this, but I would think you would simply measure the output from each detector without the photon source turned on to get the dark current. Although if you already did this above then I don't know why Ch2 and Ch4 have wildly different counts unless they are different types or brands of detectors.

 

[physicsclaus]

Hello everyone, I have posted another question regarding the calculation of gating time, I hope someone can give me some guidance. I cannot find any way to do this calculation.

https://www.physicsforums.com/threa...m-the-rate-of-the-random-coincidence.1048708/