Knowledge Test

If the intensity is constant inside the laser beam, the emitted power is equal to : P=IΩ

where the solid angle of the beam is

Hence :

The photonic (or photon) laser flux is the ratio between its power and the energy of each photon (since the energy is the same for all the photons from the laser) :

The geometrical extent of the pencil defined by the solar rays that illuminate the panel (of area S ) under normal incidence is the following :

G=SΩsun, where Ωsun is the solid angle under which the sun is being seen from the panel, which then receives the following solar flux :

where Lsun is the sun radiance = K3Tsun4

There results that the panel irradiance is :

numerical application  : K3 = 1, 8 10-8 Wm-2sr-1K-4 (Stefan's constant) :

The radiance of the diffuse object under irradiance E is .

Since the sensor is an image forming system, the object is supposed to be larger than the sensor field of view and the flux incident upon its detector is : F =TopLobjetGcapteur.

From the results of the the main course, the geometrical extent of the conical beam that converges onto the the detector is : where Sd is the detector area.

One may conclude that the detector irradiance E' is given by :

If the propagating medium is perfectly transparent, the detector irradiance in an image forming sensor depends upon the object irradiance, upon its diffuse and the aperture number of the lens, but it is independent from the distance from the object. Hence the the flux received by the detector is constant whatever the distance.