Pulse symmetry modulation in BBO/Cr 4+ :YAG doubly Q-switched Nd:YAG laser

Symmetric pulses are of great importance for applications related to the temporal pulse profile, where temporal symmetry directly affects energy deposition, processing accuracy, and ranging performance. Nd:YAG is a mature gain medium widely used for acquiring high energy, high peak power nanosecond pulses because of its excellent thermal conductivity, moderate upper-state lifetime, and other advantages. However, the pulse symmetry of Q-switched Nd:YAG laser has received relatively little attention. Active Q-switching of Nd:YAG usually produces a clearly asymmetric pulse. In this paper we reported a diode-pumped, doubly Q-switched Nd:YAG laser operating at 1 kHz with highly symmetric pulse profiles, realized by simultaneously incorporating an electro-optic modulator and a Cr⁴⁺:YAG saturable absorber into the resonator. The effects of pump energy and output coupler transmittance on pulse symmetry were systematically investigated. At a pump energy of 1.83 mJ and 50% transmittance, the doubly Q-switched laser achieved a symmetry factor of 1.00, representing a relative increase of 81.8% compared with the purely electro-optic Q-switched Nd:YAG. The obtained highly symmetric pulses exhibited a spectral linewidth of 0.24 nm at a central wavelength of 1064.2 nm, together with beam quality factors of M X 2 = 1.26 and M Y 2 = 1.23.