Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution. This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution, to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity. Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform. With simulated optical measurement using H2O feature at 7185.6 cm−1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model, this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2 × 10−3. This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz, and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry. This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations, which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.

In this letter, we present a Michelson interferometer for the hyperfine spectrum measurement of an optically pumped far-infrared laser with a highest frequency resolution of 3-5 GHz. CH 3 OH gas with a purity of 99.9%, is pumped by the CO 2 9P36 and 9R10 laser lines to generate terahertz lasers with frequencies of 2.52 and 3.11 THz, respectively. Moreover, except for the center frequency, which is in good agreement with theoretical work, some additional frequencies on both sides of the center frequency are obtained at a frequency interval of 0.15 THz. Meanwhile, the mechanism behind the observed experimental results is also investigated.