Growing interest in precise measurements of methane concentration and distribution in the Earth's atmosphere is stimulating efforts to develop LIDAR systems in the spectral region of 1.65 um utilizing Path Differential Absorption techniques. The key element of such systems is a high energy optical source with good beam properties operating in the vicinity of a methane absorption line. In-band pumping Q-switched solid state lasers (SSLs) based on Er-doped active media are good candidates for this required optical source. The in-band pumping of SSLs allows for shifting a significant portion of the system thermal load from the gain medium to the pump diodes, thus greatly reducing gain medium thermal distortions deleterious to SSL power scaling with high beam quality. As the goal of this SBIR program, we propose to develop an efficient Q-switched SSL with pulse energy >1 mJ at 1000 Hz repetition rate with in-band laser diode pumping operating at a wavelength of 1651 nm well-matched to the principle absorption band used for the detection of methane in the Earth's atmosphere. Based on gallium garnet gain media, this SSL will also provide sufficient tunability for DIAL techniques. We will leverage legacy work carried out at PLI in the development of high energy Q-switched Er:YAG SSLs with in-band laser diode pumping, as well as an excellent legacy in the design and manufacturing of the pump laser diodes themselves.