  We investigate experimentally and theoretically the coherent and incoherent
processes in open 3-level ladder systems in room temperature gases and identify
in which regime electromagnetically induced transparency (EIT) occurs. The
peculiarity of this work lies in the unusual situation where the wavelength of
the probe field is shorter than that of the coupling field. The nature of the
observed spectral features depends considerably on the total response of
different velocity classes, the varying Doppler shifts for bichromatic
excitation fields, on optical pumping to additional electronic states and
transit time effects. All these ingredients can be absorbed in a model based on
optical Bloch equations with only five electronic states.
