Laser-induced plasmas in ambient air for incoherent broadband cavity-enhanced absorption spectroscopy

The emission from a laser-induced plasma in ambient air, generated by a high power femtosecond laser, was utilized as pulsed incoherent broadband light source in the center of a quasi-confocal high finesse cavity. The time dependent spectra of the light leaking from the cavity was compared with those of the laser-induced plasma emission without the cavity. It was found that the light emission was sustained by the cavity despite the initially large optical losses of the laser-induced plasma in the cavity. The light sustained by the cavity was used to measure part of the S₁ ← S₀ absorption spectrum of gaseous azulene at its vapour pressure at room temperature in ambient air as well as the strongly forbidden γ-band in molecular oxygen: b¹Σ⁺_g (ν¹ =2) ← X³Σ^-_g(νⁿ =0).