Amplified spontaneous emission on sodium D-lines using nonresonant optical pumping

We describe experiments on the excitation of amplified spontaneous emission on the D-lines of sodium (D₂ = 588.9 nm; D₁ = 589.6 nm) with longitudinal optical pumping with a large detuning from the D₂ line toward shorter wavelengths. The radiation spectra are measured, showing gain on both lines, at a Na concentration of (1-5) × 1014 cm^-3, buffer gas (helium) pressure of 600 Torr at the working temperature, and pumping power density of more than 1.5 MW/cm². The time characteristics show that the output radiation varies versus the concentration of sodium atoms in the active medium. The dependences of radiation absorption at the D-lines of sodium on the concentration of Na atoms and buffer gas pressure are given.