Phase matching conditions, damage threshold, nonlinear and thermal properties of solid solution crystals GaSe1-xSx with the mixing ratio x ≤ 0.4 have been studied. Tunable СО2 laser SHG with GaSe0,867S0,133, GaSe0,71S0,29, and GaSe0,6S0,4 were investigated. The CO content in the atmosphere was measured with the lasers, being in the composition of TT differential absorption lidars.