  The Cherenkov Telescope Array (CTA) is the next generation of Imaging
Atmospheric Cherenkov Telescopes. It will reach a sensitivity and an energy
resolution with no precendent in very high energy gamma-ray astronomy. In order
to achieve this goal, the systematic uncertainties derived from the atmospheric
conditions shall be reduced to the minimum. Different instruments may help
account for these uncertainties. The Barcelona IFAE/UAB (acronyms for Institut
de F\'isica d'Altes Energies and Universitat Aut\`onoma de Barcelona,
respectively) and the Montpellier LUPM (Laboratoire Univers et Particules de
Montpellier) groups are building Raman LIDARs, devices which can reduce the
systematic uncertainties in the reconstruction of the gamma-ray energies from
20$%$ down to 5$%$. The Raman LIDARs subject of this work have coaxial 1.8 m
mirrors with a Nd-YAG laser each. A liquid light-guide collects the light at
the focal plane and transports it to the readout system. We are developping a
monochromator with the purpose of testing the readout chain of both LIDARs.
This device is composed of a system of filters and a photomultiplier, and will
be used to study a particular elastic channel. After characterizing the system,
we will build a polychromator to collect also the sparse Raman signal and will
optimize it to reduce every possible loss of signal. We report on the current
status of the LIDARs development and also the latest results on the different
characterization tests.
