Transient
De luz-wiki
The initial phase of an alternating field has played a minor role in the force exerted by the field over a free charge. The main reason being that in most cases the transient behaviour has a slowly varying envelope.
However, in recent times either with passive or active schemes, very short optical pulses have been achieved. These pulses may contain only a few oscillations and the slowly varying envelope condition is no longer fulfilled.
The external field is often set
