Study of lasing on the 4F3/2 → 4I13/2 secondary transition of Nd3+ ions in a phase-conjugate Nd3+ : YAG laser

Lasing at a wavelength of 1.34 μm on the ⁴F_3/2 → ⁴I_13/2 secondary transition of Nd3+ ions in a phase-conjugate (PC) Nd³⁺ : YAG laser under four-wave mixing in a laser medium is theoretically and experimentally investigated. The influence of the amplified spontaneous emission at a wavelength λ = 1.064 μm on the parameters of phase-conjugate generation of the Nd³⁺ : YAG laser at λ = 1.34 μm under passive Q switching by a V³⁺ : YAG crystal using two-, three-, and four-loop open cavity schemes is analysed by mathematical simulation. It is shown that there is an optimal initial transmission of a passive Q switch (PQS), the value of which decreases with increasing number of cavity feedback loops. The generation in the Nd³⁺ : YAG laser at λ = 1.34 μm with an open PC multiloop cavity is experimentally obtained and studied for the first time. Emission in the form of a train of seven pulses with a total energy of 0.25 J and individual pulse energy and duration of 36 mJ and 150 ns, respectively, is obtained with an initial PQS transmission of 74%. The angular divergence of the laser beam is found to be 0.7 mrad at quality factors M²_x = 1.2 and M²_y = 1.1.