Why photons? A psychoanalytic portrait of a scientist as a mature man.

Abstract: I will start with the origins: Maxwell theory, present five reasons to quantize, or maybe four? I will then discuss quantum theory of optical coherence, answering the question:  How to reconcile Maxwell with photons? I will describe shortly coherent states and squeezed states. I will then turn to strong field physics, starting with a historical introduction and description of the present times, where semi-classical theory is sufficient.  I will then mention the generation of Schrödinger cat states within atto-physics, answering the question: yes, we do need photons. At the end, I will discuss three mechanisms to exhibit quantumness of EM fields: i) Conditioning/post selection + applications; ii) Nonlinear effects induced by depletion/interband transitions, or dipole correlations; iii) Use quantum fields.