Calculator Inputs
Formula Used
| Method | Equation |
|---|---|
| Photon/Count | QE = Ne,primary / Nph,active, where Nph,active = Ninc × T × (1 − R) × FF. |
| Power + Current | QE = (I/q) / (Pactive / (hc/λ)), with Pactive = P × T × (1 − R) × FF. |
| Responsivity | QEext = (Rresp · h · c) / (q · λ). Corrected QE estimate ≈ QEext / (T × (1 − R) × FF). |
Symbols: h is Planck’s constant, c is the speed of light, q is the elementary charge, λ is wavelength, T is transmission, R is reflectance, and FF is fill factor.
How to Use This Calculator
- Select a method that matches your measurements: counts/electrons, optical power with photocurrent, or responsivity.
- Enter optical corrections if your power/photon number is measured before losses. Keep defaults (1, 0, 1) if you already reference the detector’s active area.
- Add dark/background terms for low-light measurements. Subtraction improves accuracy, especially with long integrations.
- Set gain parameters if your detector has internal multiplication. This avoids reporting a QE inflated by gain.
- Press Calculate. The results appear above the form, and you can export them as CSV or PDF.
Example Data Table
| Case | Method | Inputs (summary) | Estimated QE (%) |
|---|---|---|---|
| A | Photon/Count | Ninc=2.5e12, Signal=1.8e11 counts, e/count=1, M=1, T=0.95 | ~7.6 |
| B | Power + Current | λ=532 nm, P=0.20 mW, I=12 uA, Id=0.2 uA, T=0.90 | ~79 |
| C | Responsivity | R=0.55 A/W, λ=850 nm, optical factor=1.00 | ~80 |
Examples are illustrative and may not match a specific detector technology.
This article explains how the calculator’s inputs map to real detector measurements, so you can interpret quantum efficiency results consistently across instruments, wavelengths, and optical setups.
1) What quantum efficiency represents
Quantum efficiency (QE) is the fraction of incident photons that produce collected charge carriers. A QE of 0.80 means roughly 80 out of 100 photons contribute to measurable signal. In practice, QE depends on absorption, carrier collection, and how your readout defines “detected.”
2) External versus internal definitions
External QE refers to photons arriving at the detector package or reference plane, while internal (or active-area) QE refers to photons that actually reach the sensitive region. Losses from windows, filters, and reflections can shift results noticeably. Optical factor corrections help reconcile these definitions.
3) Wavelength and material dependence
QE is strongly wavelength dependent because absorption depth and reflection change with photon energy. Silicon devices often peak in the visible and decline in the infrared, while InGaAs extends sensitivity into the near‑IR. When comparing devices, always report the wavelength used for the measurement.
4) Reference planes and coupling losses
Many labs measure optical power before the final optic, fiber, or window. The calculator lets you apply transmission, reflectance loss, and fill factor to estimate photons at the active area. This is essential when you benchmark setups that differ in filters, focusing optics, or sensor geometry.
5) Dark signal, background, and integration time
At low light, dark current and background counts can dominate. Subtracting dark and background terms using the same integration time reduces bias in QE. If the net signal becomes negative after subtraction, it indicates your signal is below noise or the subtraction terms were overestimated.
6) Gain and multiplication effects
Avalanche photodiodes, image intensifiers, and electron‑multiplying sensors can include internal gain. Gain increases signal but does not create additional photons, so a naïve ratio can exceed 100%. The gain input converts measured output electrons back to primary electrons, yielding a physically interpretable QE.
7) Calibration and uncertainty management
Reliable QE needs calibrated optical power, stable wavelength, and known beam geometry. Common uncertainty sources include power meter calibration, wavelength error, coupling drift, and dark-current temperature dependence. For best practice, repeat measurements, document optical factor assumptions, and propagate errors when publishing results.
8) Using results for design decisions
High QE improves signal-to-noise, lowers required illumination, and reduces exposure time. Use the percent QE to compare detectors at the same wavelength and reference plane. Use corrected QE to evaluate intrinsic sensor performance, then pair it with noise and bandwidth metrics for system-level selection.
FAQs
1) Why can QE be greater than 100%?
QE can exceed 100% when internal multiplication gain is present or when the photon rate is underestimated. Use the gain setting and verify power, wavelength, and optical factor reference plane to obtain a meaningful primary-electron QE.
2) What is the optical factor used for?
It converts photons or power measured at a reference plane into photons reaching the active area. It combines transmission, reflectance loss, and fill factor so you can compare measurements taken with different optics or detector packaging.
3) Should I enter reflectance as a loss or as reflectivity?
Enter reflectance as a fraction of light reflected away (a loss). For example, 0.04 represents a 4% reflection loss. The calculator uses (1 − reflectance) when computing the optical factor.
4) How do I estimate incident photons from optical power?
Compute photon energy E = hc/λ, then photon count N = (P × t)/E. If your power is measured before losses, apply transmission and reflectance terms so the photon count matches the detector’s active area.
5) Which method should I choose?
Use the counts method for photon-counting or integrated readout data, the power+current method for photodiode measurements with a power meter, and the responsivity method when you have a manufacturer or calibrated responsivity curve at a given wavelength.
6) Does fill factor apply to all sensors?
Fill factor mainly applies to pixelated arrays, masked regions, or sensors with micro-structures where only part of the area is photosensitive. For fully active photodiodes, set fill factor to 1 unless you know an effective active fraction.
7) What temperature effects should I consider?
Dark current and dark counts often rise with temperature, changing the net signal used for QE. If you compare measurements across days or devices, record temperature and repeat dark measurements under the same conditions for consistent subtraction.