Editing Photocathode (section)

=== Quantum Efficiency (QE) ===
[[Quantum efficiency]] is a unitless number that measures the sensitivity of the photocathode to light.  It is the ratio of the number of electrons emitted to the number of incident photons.<ref name=":0">[[Triveni Rao|Rao, T.]], & Dowell, D. H. (2013). ''An engineering guide to photoinjectors''. CreateSpace Independent Publishing.</ref>  This property depends on the wavelength of light being used to illuminate the photocathode.  For many applications, QE is the most important property as the photocathodes are used solely for converting photons into an electrical signal.


Quantum efficiency may be calculated from photocurrent (<math>I</math>), laser power (<math>P_{\text{laser}}</math>), and either the photon energy (<math>E_{\text{photon}}</math>) or laser wavelength (<math>\lambda_{\text{laser}}</math>) using the following equation.<ref name=":0" /><ref>{{cite journal |last1=Jensen |first1=Kevin L. |last2=Feldman |first2=Donald W. |last3=Moody |first3=Nathan A. |last4=O’Shea |first4=Patrick G. |title=A photoemission model for low work function coated metal surfaces and its experimental validation |journal=Journal of Applied Physics |date=15 June 2006 |volume=99 |issue=12 |pages=124905–124905–19 |doi=10.1063/1.2203720 |bibcode=2006JAP....99l4905J |url=https://doi.org/10.1063/1.2203720}}</ref>

<math display=block>
  \text{QE} = \frac{N_{\text{electron}}}{N_{\text{photon}}} 
  = \frac{I\cdot E_{\text{photon}}}{P_{\text{laser}}\cdot e}
  \approx \frac{ \overset{ [\text{amps}] }{I} \cdot 1240}{ \underset{ [\text{watts}] }{ P_{\text{laser} }} \cdot \underset{ [\text{nm}] }{ \lambda_{\text{laser} } }}
</math>