Behavior of the population of the 4I11/2 level of Nd3+ in glasses interacting with high-power coherent radiation

An experimental method was developed for the determination of the rate of relaxation of the ⁴I_11/2 state and of the absorption cross section of the ⁴I_11/2–⁴F_3/2 transition. These parameters were deduced from the dependences of the intensity of the λ = 0.88 μ luminescence, excited as a result of the ⁴I_11/2–⁴F_3/2 transition by laser pulses of λ = 1.06 μ wavelength, on the energy density and duration of the laser pulses. Estimates of the relaxation time obtained for the investigated silicate (GLS-1) and phosphate (LGS-40, LGS-I) glasses, and also for a liquid based on POCl₃-SnCl₄, gave τ₂₁ < 2 nsec. A considerable increase in the population of the ⁴I_11/2 level occurred as a result of the Raman scattering of high-power coherent radiation by vibrations of the PO₄ group.