The discussion revolves around the relationship between the intensity of light and the amplitude of the wave in a photonics system, specifically focusing on whether these terms can be used interchangeably or if they represent distinct concepts. The conversation includes theoretical considerations and clarifications regarding the definitions of amplitude in different contexts.
Participants express differing views on the definitions and implications of amplitude and intensity, indicating that there is no consensus on whether these terms can be considered the same or if they should be treated distinctly.
The discussion highlights the complexity of terminology in physics, particularly regarding the definitions of amplitude in various mathematical and physical contexts, which may lead to misunderstandings.
chrisbaird said:The intensity of light is proportional to the square of the amplitude of the electric component of the wave. Intensity and wave amplitude can be thought of as basically the same thing.
chrisbaird said:Unfortunately, the word amplitude can mean different things. Mathematically, the amplitude of a vector is just its length, so by definition it never goes negative because negativity is contained in the directional part of the vector and not in the length. In physics, "amplitude". Also in mathematics, amplitude can refer to the magnitude of a complex number, which is also always positive. Finally in physics, "amplitude" can mean the part of the wave's functional form left after the waving part has been isolated away. Used in this sense, the amplitude can be negative. The problem is that EM waves are complex-valued, waving, vector fields. This means that the word "amplitude" is present in all three forms in EM waves, and we must be more specific in relaying which one is meant.
In my previous comment, I meant the amplitude in the sense of what is left when the waving part is put to the side. So if the wave is E = E0 cos(kx - ωt) then the light intensity is proportional to |E0|^2.