Methods and optical detection systems (200, 300, 800, 900) for generating and processing a real-time time-domain cavity ringdown spectroscopy (CRDS) signal (831, 931) from an absorbing species in an optical detection system (200, 300, 800, 900) having an optical ringdown cavity (200, 300) are disclosed. The optical ringdown cavity (200, 300) is adapted for accepting a sample of an absorbing species. One or more modulated light signals (241,243,245,341) are generated using one or more light sources (240, 242, 244, 340). The light source(s) (240, 242, 244, 340) is pulsed at a specified pulse rate(s). The modulated light signal(s) (241,243,245, 341) is resonated using the optical ringdown cavity (200, 300) comprising a plurality of mirrors (220, 230), or sets of mirrors (320, 330), to produce the CRDS signal (831, 931). The reflectivity of the mirrors (220, 230), or sets of mirrors (320, 330), is dependent upon the pulse rate of the modulated light signals (241,243,245,341). Different beamlines (212, 214, 216, 312, 314, 316) are established by the modulated light signal(s) (241,243,245, 341) and the mirrors (220, 230, 320, 330) interacting with the absorbing species sample.