This study aims at fast and accurate sensing in dynamic conditions using the intrapulse laser technique. Integrated with a shock tube and three other independent lasers, the intrapulse laser was examined for both fundamental and practical applications across varying temperatures and pressures.
The spectral regions selected in this study range from 1914 to 1916 cm-1, including both NO and H₂O absorption peaks, enabling simultaneous measurements of NO and H₂O mole fraction as well as temperature using a two-line thermometry. The intrapulse laser operated at a 900 kHz repetition rate with a 200 ns pulse width, achieving a time resolution comparable to the fixed-wavelength method. The chirp rate of the intrapulse laser is 250-400 MHz, providing a spectral resolution of 0.0156-0.0197 cm-1. To correct the rapid passage effect observed under low-pressure conditions, a novel method of symmetrically flipping half of the unaffected spectrum has been proposed and validated. Specific experiments were designed to validate the capability of the intrapulse laser in accurately quantifying NO, H₂O and temperature. The results show that NO and H₂O measurements from the intrapulse laser aligned well with those from an ICL NO laser and a DFB H₂O laser, respectively. Additionally, the temperatures inferred by the intrapulse laser match well with calculations from one-dimensional shock equations. The average relative differences on NO mole fraction, H2O mole fraction and temperature are 4.5%, 7.0%, and 5.4%, respectively. In an application case, the intrapulse laser successfully captures the dynamic formation process of NO and H₂O and the associated temperature variations during NH₃ oxidation in the shock tube.
The results demonstrate good agreement with simulation results from a chemical mechanism. Thus, the intrapulse laser is a powerful technique that enables simultaneous measurements of multiple species and temperature in dynamic environments, combining the calibration-free advantage of the scanned-wavelength method with the high time resolution of the fixed-wavelength method.
