Compared with passive techniques, differential absorption lidar (DIAL) offers several advantages in remote CO₂ sensing, such as relatively high spatial resolution, high measurement specificity, and avoidance of interference from other gases. DIAL typically requires a pair of single-frequency pulses corresponding to on-line and off-line CO₂ absorption spectra.The single-frequency Q-switched double-pulse laser is an effective pumping source in DIAL systems.

Researchers at Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques ——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) designed a laser diode dual-end-pumped injection-seeded single-frequency Q-switched double-pulse Nd:YAG laser using a modified ramp-fire technique. [Laser Phys. Lett. 10 (2013) 035001] The laser is capable of producing a pair of Q-switched single-frequency 1064 nm laser pulses in one pump period.Every pulse has an output energy of up to 10 mJ, width of nearly 20 ns, and interval of about 200 _s between two Q-switched pulses. The optical-to-optical efficiency of this laser is about 22.4% and its slope efficiency is 28%. A narrow spectrum linewidth of less than 28.6 MHz with a frequency of jitter around 1 MHz over 2 min may be obtained, and a beam quality of 1.23 in the horizontal direction and 1.31 in the vertical direction is detected.