Amplification of broad-spectrum (Δλ ≈ 4 nm) microsecond laser pulses in neodymium silicate and phosphate glasses

An equation is derived for the energy density of the amplified radiation allowing for the complex structure and inhomogeneous line broadening of the lasing transition in neodymium glass. It is shown that the effective cross section of induced transitions averaged over the pulse time, which is a function of the energy density of the amplified radiation, must be known for accurate calculations of amplifiers using this equation. The dumping of the inversion by a high-power 1 μs radiation pulse (Δλ ≈ 4 nm) was used to measure the effective cross section of stimulated transitions for GLS1, GLS8, and GLS24 glasses at various rates of excitation of the active medium. The measurements showed that the cross section depended on the rate of excitation of the active element: the cross section increasing with decreasing inversion. Amplifier diagrams were constructed for calculations in the range up to E_in = 13 J/cm² and E_out ≈ 25 J/cm².