Can this be used with a very precise photon detector module when I expose it to a very low photon source, resulting in max 200cps, signals of max 30ns width each? Will your counting circuit be able to count each of those incident photons?
Probably as these LEDs are actually very bad SPAD sensors with poor quantum efficiency and too much capacitance for those kinds of speed. We just use them as an instructional tool! For a 30ns pulse width you're going to need a professional SPAD detector with small active area and a reasonably fast oscilloscope. Maybe check out the APD430A from Thor, believe it or not, these have actually gotten cheaper over the years!
He's just using an ordinary LED and carefully adjusting the reverse bias voltage to a point just below where the LED breaks down (non-destructive avalanche breakdown). At this point, even just a single photon can put the LED over the edge and into breakdown. The circuit is feeding the LED through a resistor so when the LED breaks down, the voltage drops because the current rises and the resistor voltage drop increases. This takes the LED out of avalanche and the voltage rises back to the preset level, ready for another photon to arrive. There are special photon-counting avalanche photodiodes which have much higher performance - the main differences are that they have a much more stable avalanche threshold so you don't have to keep tuning it to stay right below breakdown. They also react to a higher fraction of photons which enter the diode (the LED might only react to 5 or 10% of them).
When the diode is in darkness, the count rate is very low (can be single digit), meaning that photons are triggering such events. The following is from Wikipedia: Avalanche photodiodes (APDs) are not single photon detectors. The experiment uses a single photon avalanche photodiode (SPAD). APDs are biased close to, but not exceeding the breakdown voltage of the semiconductor. This high electric field provides an internal multiplication gain only of the order of few hundreds, since the avalanche process is not diverging (also known as run-away avalanche) as in the case of SPAD avalanche discharges. The resulting avalanche current intensity is linearly related to the optical signal intensity. A SPAD, however, operates with a bias voltage above the breakdown voltage. Because the device is operating in this unstable above-breakdown regime, a single photon (or a single dark-current electron) can set off a significant avalanche of carriers. Practically, this means that in an APD, a single photon produces only tens or few hundreds of electrons, but in a SPAD a single photon triggers a current in the milliampere region (billions of billions of electrons per second) that can be easily "counted". Therefore, while the APD is a linear amplifier for the input optical signal with limited gain, the SPAD is a trigger device, and this triggering is what we are seeing in the experiment.
@jonathannewport8557 could this be build with a much more sensitive true spad, single photon avalanche detector?
Do you have more information on the circuit and code used on the MCU?
Can this be used with a very precise photon detector module when I expose it to a very low photon source, resulting in max 200cps, signals of max 30ns width each?
Will your counting circuit be able to count each of those incident photons?
Probably as these LEDs are actually very bad SPAD sensors with poor quantum efficiency and too much capacitance for those kinds of speed. We just use them as an instructional tool!
For a 30ns pulse width you're going to need a professional SPAD detector with small active area and a reasonably fast oscilloscope. Maybe check out the APD430A from Thor, believe it or not, these have actually gotten cheaper over the years!
how did you connect Excel to coolect data?
Where did you buy the SPAD chip? did you use optics?
He's just using an ordinary LED and carefully adjusting the reverse bias voltage to a point just below where the LED breaks down (non-destructive avalanche breakdown). At this point, even just a single photon can put the LED over the edge and into breakdown. The circuit is feeding the LED through a resistor so when the LED breaks down, the voltage drops because the current rises and the resistor voltage drop increases. This takes the LED out of avalanche and the voltage rises back to the preset level, ready for another photon to arrive. There are special photon-counting avalanche photodiodes which have much higher performance - the main differences are that they have a much more stable avalanche threshold so you don't have to keep tuning it to stay right below breakdown. They also react to a higher fraction of photons which enter the diode (the LED might only react to 5 or 10% of them).
The AND113R diodes are used for such projects. They are not specialized but have the avalanche property very prominent.
@@sbrehenywhere can I buy a specialized SPAD diode?
@@mix_dev6959 did you try to google? thorlabs, hamamatsu for example if you need lab grate.
2sc5707 кт315 czcams.com/video/Ju1UIuoVvCo/video.html
how did you say it give single photon signal
When the diode is in darkness, the count rate is very low (can be single digit), meaning that photons are triggering such events. The following is from Wikipedia:
Avalanche photodiodes (APDs) are not single photon detectors. The experiment uses a single photon avalanche photodiode (SPAD). APDs are biased close to, but not exceeding the breakdown voltage of the semiconductor. This high electric field provides an internal multiplication gain only of the order of few hundreds, since the avalanche process is not diverging (also known as run-away avalanche) as in the case of SPAD avalanche discharges. The resulting avalanche current intensity is linearly related to the optical signal intensity. A SPAD, however, operates with a bias voltage above the breakdown voltage. Because the device is operating in this unstable above-breakdown regime, a single photon (or a single dark-current electron) can set off a significant avalanche of carriers. Practically, this means that in an APD, a single photon produces only tens or few hundreds of electrons, but in a SPAD a single photon triggers a current in the milliampere region (billions of billions of electrons per second) that can be easily "counted". Therefore, while the APD is a linear amplifier for the input optical signal with limited gain, the SPAD is a trigger device, and this triggering is what we are seeing in the experiment.
how to design that circuit