Consider a laser which emits photons with a wavelength of 1.55 micrometers. The laser has a lower electron level Ei and an upper electron level Eu. A power supply pours electrons into the upper energy level and these electrons fall down in a time T= 0.1 nanosecond to the lower level emitting photons. The laser is biased to produce 100 milliwatts of optical power.

Question

Consider a laser which emits photons with a wavelength of 1.55 micrometers. The laser has a lower electron level Ei and an upper electron level Eu. A power supply pours electrons into the upper energy level and these electrons fall down in a time T= 0.1 nanosecond to the lower level emitting photons. The laser is biased to produce 100 milliwatts of optical power. 
What is the current flowing in the laser if the efficiency of the laser to convert electrical energy to photon energy is 95 %?

Make an argument that the electrical current being converted to light is eN/T where N 
is the electron number in the upper level.