Hi, What is the equation for a E field of a single pulse of a laser? If that laser is shined onto say a grating spectroscope (square law detector), how can I go about deriving an expression for Intensity as a function of frequency at the output of the spectroscope? I know that the square law detector will measure Energy which is the square of the E field (and some proportionality factor that I don't know). I also know Intensity equation, I = 1/2 Epsilon * c * E^2 where Epsilon is the permittivity in vacuum. But that doesnt seem to apply here since it has no dependence on frequency. Any help is much appreciated.