SiPM Photon Detection Efficiency Calculator (PDE = FF × QE × Pt)

Understanding the photon detection efficiency calculator — concept and principle

This calculator finds the photon detection efficiency (PDE) of a silicon photomultiplier (SiPM), the share of incident photons that produce a counted signal. It can work from fill factor, quantum efficiency and avalanche trigger probability, from a photon-counting measurement or from photocurrent sensitivity and gain. It is used in particle physics, medical imaging and lidar.

How it is calculated

From components: PDE = FF × QE × P_t

Photon counting: μ = −ln P₀,light + ln P₀,dark; PDE = μ ÷ N_photons

Photocurrent: PDE = (hc/λ) × S ÷ (q M) = 1,240 × S ÷ (λ_nm × M)

• FF is the geometric fill factor, QE the quantum efficiency, P_t the trigger probability; P₀ the share of pulses with zero counts; S in A/W, M the gain.

The principle

A photon is counted only if three things happen in turn: it lands on a sensitive area, it creates an electron–hole pair, and that carrier sets off an avalanche. The probabilities multiply. In counting measurements the number of detected photons per pulse is Poisson-distributed, so the share of empty pulses gives the mean directly, and subtracting the dark result removes noise counts. The photocurrent method includes crosstalk and afterpulses, so it tends to overestimate the counting PDE.

Worked example

Default inputs: from components, FF = 60%, QE = 85%, P_t = 70%, wavelength 450 nm.

1. PDE = 0.60 × 0.85 × 0.70 = 35.7%.
2. Detected per 1,000 incident photons = 357.
3. Photon energy at 450 nm = 1,239.84 ÷ 450 = 2.755 eV.
4. The counting mean μ is only used in the counting method, so it shows —.

How to read the result

Higher PDE means more signal for the same light. Fill factor is usually the biggest loss in small-cell SiPMs; raising the overvoltage increases trigger probability but also dark counts and crosstalk. Always compare PDE at the same wavelength and overvoltage.

Common mistakes

• Using photocurrent PDE as if it were counting PDE.
• Forgetting the dark correction in counting measurements.
• Quoting PDE without the wavelength and overvoltage.

Frequently asked questions

Why does PDE rise with overvoltage?

A higher field makes it more likely that a carrier triggers an avalanche.

What is the fill factor?

The fraction of the device area that is sensitive to light.

Why use zero-count pulses?

For Poisson statistics, the share of empty pulses gives the mean without counting multi-photon events.

Why does photocurrent overestimate PDE?

It also counts crosstalk and afterpulses.

Sources: E. Garutti, "Silicon Photomultipliers for High Energy Physics Detectors", arXiv:1108.3166 (2011) · Hamamatsu Photonics, "MPPC, MPPC modules" technical information