This paper presents a comparative study on thermal lensing characteristics of a low temperature copper vapor laser (CVL) (LT-CVL as Copper-HBr laser) and a high temperature CVL (HT-CVL as elemental CVL). Interferometric techniques were used to study the combined thermal lens power of active gaseous medium and discharge sealing optical windows as well as that of the optical windows separately at different electrical input powers. As the input power varied from 2.7 to 4.6 kW, the combined thermal lens power varied from −1.4 to +0.94 km−1 for LT-CVL and from +1.4 to +13 km−1 for HT-CVL. The thermal lens power of the windows varied from +3 to +15 km−1 for HT-CVL. On the other hand, for LT-CVL, the thermal lens due to windows was very weak and could not be measured. It was observed that the origin of net thermal lensing mostly resides in the discharge tube windows owing to its higher temperature variation of refractive index as compared to that of gaseous active medium. The weaker thermal lens characteristics of an LT-CVL was attributed to its much lower working temperature and relatively flatter radial gas temperature profile than that of an HT-CVL.