  This paper presents a wide-ranging theoretical and experimental study of
non-adiabatic transient phenomena in a $\Lambda $ EIT system when a strong
coupling field is rapidly switched on or off. The theoretical treatment uses a
Laplace transform approach to solve the time-dependent density matrix equation.
The experiments are carried out in a Rb$^{87}$ MOT. The results show transient
probe gain in parameter regions not previously studied, and provide insight
into the transition dynamics between bare and dressed states.
