Photon counting and multi-spot spectroscopy
An example system can include a support and two or more sensor elements mounted to the support. Each sensor element can be electrically connected to a common electrical node and may include: a respective quench resistor connected to a respective internal node; and a respective photodiode (PD) connected to the respective internal node; a differentiating element fed by at least one of the photodiodes; a first readout electrode fed by the common electrical node; and a second readout electrode fed by the differentiating element. The common electrical node may be connected to at least one of the quench resistors or at least one of the photodiodes.
1 . A silicon photomultiplier (SiPM) system, comprising:
an SiPM array, comprising:
a plurality of photosensors, each photosensor including a quench resistor coupled in series with a Geiger-mode avalanche photodiode (APD),
a first electrode configured to provide an output signal of the SiPM array, the output signal comprising an amalgamation of the plurality of APD signals;
a second electrode configured to provide a biasing voltage to each of the plurality of photosensors;
a differentiator coupled to the first electrode and configured to differentiate the output signal of the SiPM array as a function of time to thereby amplify events in the output signal associated with incidence of photons thus enabling identification of two or more photons closely incident in time in range of nanoseconds, the differentiator configured to generate a differentiated signal from the output signal; and
a pulse counting circuit coupled to the differentiator and configured to generate pulses associated with the differentiated signal.
2 . The SiPM system according to claim 1 , wherein the pulse counting circuit includes a buffer and a comparator with a threshold.
3 . The SiPM system according to claim 2 , wherein the threshold is an adaptive threshold based on an envelope of the photon signal.
4 . The SiPM system according to claim 3 , wherein the pulse counting circuit delays the photon signal so as to arrive concurrently at the comparator with the adaptive threshold.
5 . The SiPM system according to claim 4 , wherein the pulse counting circuit further includes a counter and memory configured to store time information of the photon signal corresponding to pulses counted by the pulse counting circuit.
6 . The SiPM system according to claim 1 , wherein the differentiator includes a resistor-capacitor (RC) high-pass filter.
7 . The SiPM system according to claim 6 , wherein the capacitor of the RC high- pass filter is coupled to the first electrode and the resistor of the RC high-pass filter couples the capacitor to ground, such that a node between the capacitor and the resistor provides output of the differentiator.
8 . The SiPM system according to claim 6 , wherein the differentiator further includes an amplifier configured to buffer the output of the differentiator.
9 . A particle detection optical system, comprising:
at least two narrow-band illumination sources, the at least two narrow-band illumination sources comprising a first source and a second source configured to provide respective beams;
a flow chamber;
an optical arrangement, wherein the optical arrangement is configured to direct respective beams from each of the at least two narrow-band illumination sources through respective spaced- apart locations disposed along a longitudinal axis of the flow chamber, wherein the optical arrangement is further configured to direct a first beam from a first source of the at least two narrow-band illumination sources along an illumination axis;
an optical sensor configured to provide an output signal associated with the first beam, the optical sensor arranged substantially on the illumination axis and optically positioned after the flow chamber; and
a controller configured to:
operate the first source of the at least two narrow-band illumination sources, establish a baseline associated with the output signal,
detect a variation as compared to the baseline in the output signal at a first time, and enable the second source of the at least two narrow-band illumination sources at a second time, the second time being substantially a predetermined time interval after the first time;
the optical sensor includes a silicon photomultiplier (SiPM) array, comprising:
a plurality of photosensors, each photosensor including a quench resistor coupled in series with a Geiger-mode avalanche photodiode (APD),
a first electrode configured to provide an output signal of the SiPM array, the output signal comprising an amalgamation of the plurality of APD signals,
a second electrode configured to provide a biasing voltage to each of the plurality of photosensors,
a differentiator coupled to the first electrode and configured to differentiate the output signal of the SiPM array, as a function of time to thereby amplify events in the output signal associated with incidence of photons thus enabling identification of two or more photons closely incident in time in nanosecond range, the differentiator configured to generate a differentiated signal from the output signal, and
a pulse counting circuit coupled to the differentiator and configured to generate pulses associated with the differentiated signal, wherein the pulse counting circuit includes a buffer and a comparator with a threshold, wherein the threshold is an adaptive threshold based on an envelope of the photon signal, wherein the pulse counting circuit delays the photon signal so as to arrive concurrently at the comparator with the adaptive threshold, and wherein the pulse counting circuit further includes a counter and memory configured to store time information of the photon signal corresponding to pulses counted by the pulse counting circuit.
10 . The particle detection optical system according to claim 9 , wherein the differentiator includes a resistor-capacitor (RC) high-pass filter.
11 . The particle detection optical system according to claim 10 , wherein the capacitor of the RC high-pass filter is coupled to the first electrode and the resistor of the RC high-pass filter couples the capacitor to ground, such that a node between the capacitor and the resistor provides output of the differentiator.
12 . The particle detection optical system according to claim 11 , wherein the differentiator further includes an amplifier configured to buffer the output of the differentiator.
13 . The particle detection optical system according to claim 9 , wherein the output signal is selected from the group consisting of a photocurrent, a charge, a photon-count output from a photodiode or sensor element, a plurality of signals from a split photodiode, a plurality of signals from a position-sensitive photodetector, and any combination thereof.
14 . The particle detection optical system according to claim 13 , further comprising a flow system configured to move samples through the flow chamber in a flow direction at a flow rate.
15 . The particle detection optical system according to 14 , wherein the respective spaced-apart location associated with the second source of the at least two narrow-band illumination sources is downstream of the location associated with the first source of the at least two narrow-band illumination sources along the flow direction.
16 . The particle detection optical system according to 15 , wherein the predetermined time interval substantially corresponds to amount of time required for a sample to move at the flow rate from the spaced-apart location associated with the first source of the at least two narrow-band illumination sources and the spaced-apart location associated with the second source of the at least two narrow-band illumination sources.
17 . The particle detection optical system according to claim 9 , the controller further configured to selectively cycle through the at least two narrow-band illumination sources.
18 . The particle detection optical system according to claim 9 , the controller further configured to disable the second source of the at least two narrow-band illumination sources upon expiration of a second predetermined time interval after enabling the second source of the at least two narrow-band illumination sources.