Hello, I'm a student which needs to setup a HBT experiment in the lab and I have some questions. I already read this thread: https://www.physicsforums.com/showthread.php?t=757064 and it was very useful, so I'm asking for help from Cthugha or anyone who knows. My experimental setup is as following: Light from the the blue LED after passing through a 0.2[mm] pinhole, travels ~1.25[m] and is divided into 2 beams, each hits either the PMT #1 or PMT #2. Two signals from the detectors are being saved in a frequency of 1.25[GHz]. I perform a cross-correlation of the two signals in MATLAB. Problem: I did several runs - recorded the signals for 10 minutes, 40 minutes, 3 hours, 6 hours. In any of the runs the cross-correlation didn't show the peak (which corresponds to the photons correlation). After failing again and again I decided to check again my equipment for any misfitting to the theoretical basis of the experiment. Questions: 1. Light source. As I know, Brown and Twiss, in their original experiment used a mercury arc lamp, which is a thermal radiation source. I'm not sure if blue LED is a thermal radiation source or a single-photon. 2. Pinhole. I have different pinhole sizes, from 1um to 200um, but according to the theory - the more light PMTs receive, the higher the correlation, so I used the largest pinhole I have. The question is - do I have to use the lens before pinhole, in order to focus the light into it? 3. Maybe it's just a matter of time and I need far more than 6 hours of signals data? Thanks in advance.