Noise in an infrared radiation detector operating on the basis of frequency conversion

The fluctuation–dissipation theorem and the field equations for a crystal are used to derive expressions for the power of the noise generated by thermal fluctuations in the crystal and by the background radiation. These sources of noise are compared with that due to spontaneous parametric luminescence. It is shown that the parametric luminescence noise predominates in the near infrared, whereas in the middle and far infrared the thermal and background sources of noise are more important (unless they are reduced by cooling).