In 3 of the Appollo lunar experiments astronauts left reflector panels on the moon so that laser beams from the earth could be reflected off the panels and back to earth.Lasers with lamda = 532 nm send pulses of 0.3 J to the moon and the round trip time is measured within delta t = 0.4 ns.In this way, the one way distance to the reflector on the moon is determined regularly within delta l = c*delta t/2 = 6 cm.The beams from the laser have a diameter of 5 km on the moon.(This is the result of the spreading due to diffraction and to athmospherical turbulence).The reflector panels contain 300 mirrors each of diameter 4 cm(a) Find the number of photons sent from the earth in a single pulse(b) find the fraction of these photons that strike anyone of the small mirrors.(c) find the angular divergence delta theta =lamda/d of the reflected beam from this mirror(d = mirror diameter)(d) What is the diameter of the reflected beam when it return to earth?(e)The return light is measured by a photomultipplier at the focus of a telescope.What fraction of the return light is captured by the telescope, whose diameter is 1 m(f) For a single pulse find the total number of photon captured by the the telescope from all all 300 mirrors.This experiment monitors the monn orbit within a few centimeters( compared to the earth-monn distance of 400 million meters) allowing stringent tests of competing theories of gravity.
In 3 of the Appollo lunar experiments astronauts left reflector panels on the moon so that laser beams from the earth could be reflected off the panels and back to earth.Lasers with lamda = 532 nm send pulses of 0.3 J to the moon and the round trip time is measured within delta t = 0.4 ns.In this way, the one way distance to the reflector on the moon is determined regularly within delta l = c*delta t/2 = 6 cm.The beams from the laser have a diameter of 5 km on the moon.(This is the result of the spreading due to diffraction and to athmospherical turbulence).The reflector panels contain 300 mirrors each of diameter 4 cm(a) Find the number of photons sent from the earth in a single pulse(b) find the fraction of these photons that strike anyone of the small mirrors.(c) find the angular divergence delta theta =lamda/d of the reflected beam from this mirror(d = mirror diameter)(d) What is the diameter of the reflected beam when it return to earth?(e)The return light is measured by a photomultipplier at the focus of a telescope.What fraction of the return light is captured by the telescope, whose diameter is 1 m(f) For a single pulse find the total number of photon captured by the the telescope from all all 300 mirrors.This experiment monitors the monn orbit within a few centimeters( compared to the earth-monn distance of 400 million meters) allowing stringent tests of competing theories of gravity.
