Abstract

The DIAL technique as applied employing Nd:YAG → dye-laser technology is quite powerful for monitoring NO₂, SO₂ and O₃ and some measuring systems are approaching operational status^1-3. However, it is of considerable interest to extend the applicability of such systems to a number of other atmospheric molecular constituents, e.g. NO, HCHO, Hg, CO, HCl, HF and CH_k. While NO₂, SO₂ and O₃ absorb in the visible and the easily accessible UV region (~300 nm), the measurement of the additional gases requires extensions of the wavelength region to short UV and IR wavelengths. With the high peak powers available with Nd:YAG based laser systems this is possible using Raman-shifting and frequency-mixing techniques. We are presently involved in a program aiming at the exploitation of these possibilities. At short UV wavelengths the atmospheric attenuation due to scattering is strong whereas low back-scattering is instead a problem in the IR region. Clearly, the pulse energies will be limited outside the well established wavelength regions and therefore the use of topographic targets or even retro-reflectors rather than atmospheric back-scattering can be necessary in many cases. Whereas low pulse energies can be problematic with a down- or up-converted dye-laser source, the continous tuning capability is an attractive feature. It is advantageous to use close-lying optimal on/off-resonance wavelengths, which eliminates differential albedo effects present for CO₂-laser systems.