Subfemtosecond-resolved modulation of superfluorescence from ionized nitrogen molecules by 800-nm femtosecond laser pulses

Superfluorescence emission around 391 nm is generated when nitrogen molecules arc irradiated by a strong 800-nm pump laser and a delayed seed laser. The emission corresponds to the transition between N-2(+)(B-2 Sigma(+)(u), V '' = 0) and N-2(+)(X-2 Sigma(+)(g), nu = 0). When another weak 800-nm probe laser is injected and scanned after the pump laser, the superfluorescence intensity is observed to exhibit periodical modulation. The period is determined to be similar to 2.63 fs, corresponding to the transition frequency between N-2(+) (A(2)Pi(u), nu' = 2) and N-2(+)(X-2 Sigma(+)(g), nu = 0). Based on theoretical derivation, these observations can be attributed to the laser-induced population transfer and polarization variation between the relevant electronic states of ionized nitrogen molecules. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement