Fig. 1. (a) Velocity measurement system schematic of double path; (b) double beam frequency difference diagram

Fig. 1. Schematic of the experimental system setup

Fig. 2. Relationship between the light-emitting diode (LED) output power and the driving current

Fig. 2. (a) Change in plume velocity and pressure in the combustion chamber with time when the rocket pry is stationary; (b) velocity measurement results when the rocket pry is sliding

Fig. 3. (a) Internal structure of flow velocity measurement instrument; (b) high-speed schlieren picture during the experiment

Fig. 3. (a) Original absorption spectra at different sulfur ion concentrations; (b) normalized absorption spectra before digital filtering; (c) normalized absorption spectra after digital filtering

Fig. 4. Sulfur ion absorbance as a function of sample concentration at 665 nm before and after applying the Savitzky-Golay (S-G) filter

Fig. 4. (a) Absorption spectrum Doppler shift signal; (b) ch1 channel flow velocity continuous measurement result

Fig. 5. Absorbance curves of CO2 molecules at temperature from 700 K to 1300 K

Fig. 5. 3D schematic of the multi-parameter in situ measurement sensor

Fig. 6. (a) Selected H2O absorption spectra; (b) temperature measurement result of flat flame burner

Fig. 7. Temperature and laser signal intensity under typical operating conditions of the scramjet engine

Fig. 8. Aero engine combustion chamber model and temperature concentration measurement results by TDLAS

Fig. 9. Concentration distribution simulation reconstruction. (a) Original concentration distribution;(b) concentration reconstruction results by traditional method; (c) concentration reconstruction results by two-step global optimization algorithm

Fig. 10. Interpolation beam layout geometry diagram. (a) Without rotation; (b) with an anticlockwise rotation of 90°

Fig. 11. Temperature and vapor concentration distribution reconstruction results of flat flame furnace

Fig. 12. Schematic diagram of turbofan engine nozzle outlet (a) and squared TDLAS measuring frame diagram (b)

Fig. 13. Directly reconstructed image of local grid (a) and interpolation processing result (b) of state MC

Fig. 14. (a) Standard temperature and humidity box of Anhui Meteorological Bureau; (b) comparison of TDLAS and cold mirror dew point meters