Fig. 1. Hydrogen telemetry TDLAS system

Fig. 2. Light source module

Fig. 3. Diagram of laser radiation transmission model of non-cooperative target surface

Fig. 4. Module design of open optical path

Fig. 5. Data detection module

Fig. 6. Output frequency

Fig. 7. Centre frequency

Fig. 8. Absorbance ln(I₀/I_t)

Fig. 9. Detector received light intensity I_t

Fig. 10. Second harmonic signal

Fig. 11. Backward reflected laser power on surface of common non-cooperative targets at different detection distances

Fig. 12. Relations of light intensity received by detector and F number (changing diameters of pupil)

Fig. 13. Relations of light intensity received by detector and F number (changing focal length)

Fig. 14. Second harmonic signals at different scanning amplitudes

Fig. 15. Second harmonic signals at different scanning frequencies

Fig. 16. Optimized laser-echo incident power for different materials at different detection distances

Fig. 17. Second harmonic signals at different concentrations