Calculate SiPM photon detection efficiency, fired microcells, saturation, signal-to-noise ratio, and dark count correction for silicon photomultiplier sensors.
Silicon Photomultipliers (SiPMs) are arrays of single-photon avalanche diodes (SPADs) operating in Geiger mode. Each microcell fires independently when it detects a photon, producing a standardized charge pulse. The total signal is the sum of all fired microcells.
Photon Detection Efficiency (PDE) is the probability that an incident photon triggers a microcell — it depends on overvoltage, wavelength, and fill factor. This calculator computes the expected number of photoelectrons, the saturation-corrected number of fired microcells, total output charge, dynamic range, and signal-to-noise ratio.
SiPMs have a finite number of microcells, so they saturate when many photons arrive simultaneously. The saturation model accounts for this: N_fired = N_total × (1 − exp(−Npe/N_total)). The calculator also adjusts dark count rate for temperature (DCR doubles every ~8°C).
Presets for popular SiPMs from Hamamatsu, SensL, and OnSemi let you quickly explore real device performance. This tool is essential for designing PET scanners, LiDAR detectors, fluorescence readers, and any photon counting system using SiPMs.
SiPMs are replacing traditional PMTs in many applications, but their nonlinear saturation, temperature-dependent noise, and correlated noise require careful analysis.
This calculator provides the essential SiPM performance metrics including saturation correction and temperature-adjusted dark count rates. The note above highlights common interpretation risks for this workflow. Use this guidance when comparing outputs across similar calculators. Keep this check aligned with your reporting standard.
Overvoltage: Vov = Vbias − Vbr. Photoelectrons: Npe = Nph × PDE. Fired microcells: Nfired = Ntot × (1 − exp(−Npe/Ntot)). Charge: Q = Nfired × Gain × q (q = 1.602×10⁻¹⁹ C). DCR(T) = DCR(25°C) × 2^((T−25°C)/8°C). SNR = Npe / √(Npe + DCR × t_gate).
Result: Npe = 40, Nfired = 39.6, saturation = 1.1%, Q = 10.8 fC
Overvoltage = 3 V. Npe = 100 × 0.40 = 40 photoelectrons. Nfired = 3600 × (1 − exp(−40/3600)) = 39.6 (negligible saturation). Charge = 39.6 × 1.7×10⁶ × 1.6×10⁻¹⁹ = 10.8 fC.
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Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use. ## Practical Notes
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Track units and conversion paths before applying the result. ## Practical Notes
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Keep this guidance aligned to the calculator’s expected inputs. ## Practical Notes
Use as a sanity check against edge-case outputs. ## Practical Notes
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Overvoltage (Vov) is the bias voltage above breakdown. Higher Vov increases gain, PDE, and detection probability but also increases dark counts, crosstalk, and afterpulsing.
Dark count rate approximately doubles every 8°C. Breakdown voltage increases ~20-50 mV/°C. Cooling a SiPM dramatically reduces noise — medical PET scanners often operate at −20°C.
The finite number of microcells. Once all microcells have fired, additional photons produce no additional signal. For linear response, keep Npe < 0.1 × Nmicrocells.
When one microcell fires, avalanche photons can trigger neighboring microcells. This "optical crosstalk" adds extra counts that inflate the apparent signal. It increases with overvoltage.
Charge carriers trapped during the avalanche are released after the microcell recharges, triggering a second avalanche. It produces delayed spurious counts on timescales of 10-100 ns.
SiPM PDE peaks at 400-450 nm (blue-green) for standard devices. UV-enhanced SiPMs peak at 350 nm. Near-infrared SiPMs use deeper junctions for sensitivity at 800-1000 nm.