Single-mode operation of an injection-seeded alexandrite ring laser for application in water-vapor and temperature differential absorption lidar

A major improvement of a differential absorption lidar (DIAL) system for measurements of tropospheric water vapor and temperature is introduced. A Q-switched unidirectional alexandrite ring laser is injection seeded by a cw Ti:sapphire ring laser. Using an especially developed single-mode electronic, one starts the Q switch when the slave resonator is in resonance with the frequency of the Ti:sapphire laser. Long-term single-mode operation of the alexandrite laser is achieved. A single-shot spectral linewidth of <40 MHz and a frequency stability of 15 MHz rms can be specified. Thus what is to our knowledge the first single-mode DIAL system in the near infrared is presented.