Abstract: Systems and methods for analysing a time-domain signal are described. The method comprising: in a mixer (150), mixing the time-decay signal (115) with a local oscillator signal (122) generated by a local oscillator (120), resulting in a mixed signal from which a Fourier transformed time-decay signal is generated comprising a fundamental transformed time decay signal at the fundamental frequency of the local oscillator signal (122) and a plurality of transformed time-decay signals at a plurality of frequencies; and determining the magnitude of each of the transformed time-decay signals at the fundamental frequency and at a frequency other than the fundamental frequency.

Abstract: Methods and apparatuses of generating and processing a real-time time-domain cavity ringdown spectroscopy (CRDS) signal from absorbing species in an optical detection system having an optical ringdown cavity using off-axis paths are provided. At least one modulated light signal is generated using one or more light sources, each modulated at specified modulation frequency. Each modulated signal has harmonic frequency components and is input off-axis relative to the cavity's optical axis. The cavity contains mirrors arranged in a predetermined configuration. The optical axis is defined by a path passing through centers of mirrors. The modulated light signal is resonated off axis without astigmatic optical elements to produce CRDS signal and passes at least twice through cavity and across the mirrors without interfering with itself. An overall path length through cavity is greater than path length of optical axis. A photodetector detects the CRDS signal, which is demodulated dependent upon selected harmonics.

Abstract: Methods and apparatuses (500) of generating and processing a real-time time-domain cavity ringdown spectroscopy (CRDS) signal from absorbing species m an optical detection system having an optical ringdown cavity (200) using off-axis paths (230) are provided. At least one modulated light signal (570) is generated using one or more light sources (520), each modulated at specified modulation frequency. Each modulated signal has harmonic frequency components and is input off-axis (230) relative to the cavity's optical axis (220). The cavity contains mirrors (210, 212, 214; 310; 410; 510, 512, 514) arranged in a predetermined configuration. The optical axis (220) is defined by a path passing through centers of mirrors (210, 212, 214; 310; 410; 510, 512, 514). The modulated light signal (570) is resonated off axis (230) without astigmatic optical.

Abstract: Systems and methods for analysing a time-domain signal are described. The method comprising: in a mixer (150), mixing the time-decay signal (115) with a local oscillator signal (122) generated by a local oscillator (120), resulting in a mixed signal from which a Fourier transformed time-decay signal is generated comprising a fundamental transformed time decay signal at the fundamental frequency of the local oscillator signal (122) and a plurality of transformed time-decay signals at a plurality of frequencies; and determining the magnitude of each of the transformed time-decay signals at the fundamental frequency and at a frequency other than the fundamental frequency.