The atmospheric windows are important for the observation of the lower atmosphere and the surface of a terrestrial planet. An accurate knowledge of their transmission is essential for interpreting satellite and ground based infrared observations. In these atmospheric windows, the contributions of the far-wings and collision induced absorption, especially at high densities, become important, though difficult to be measured in the laboratory. Cavity ring down spectroscopy is the most sensitive tool to explore the weak absorption in atmospheric windows. This technique, coupled to a recently constructed atmospheric simulation chamber, offers a unique opportunity to investigate in Venus-like conditions CO2 absorptions in several near infrared atmospheric windows of Venus yet unexplored.