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You can't get more direct than this in terms of proving that photons exist!
The particular case of the double-slit experiment will be discussed at: single particle double slit experiment.
Video 7. How to use an SiPM - Experiment Video by SensLTech (2018) Source.
Video 8. Single-photon detectors - Krister Shalm by Institute for Quantum Computing (2013) Source.