Fig. 1. Each harmonic signal. (a) Odd harmonic signal; (b) even harmonic signals

Fig. 2. Equivalent model of PIN photodiode

Fig. 3. I-I_L response relationship with different R_d values. (a) R_d=10 kΩ; (b) R_d=100 kΩ; (c) R_d=1 MΩ

Fig. 4. Schematic diagram of photoelectric detection circuit. (a) Cross resistance amplification circuit; (b) negative feedback amplification circuit; (c) BW filtering circuit

Fig. 5. Photoelectric detection circuit simulation results. (a) Output signals of each stage of amplification circuit; (b) frequency response characteristic of gain and phase

Fig. 6. Structural diagram of ammonia laser telemetry system

Fig. 7. Dark current noise signal. (a) HSPDC noise; (b) TLB PDC noise

Fig. 8. System output signals when telemetry distance changes. (a) HSPDC output signal; (b) TLB PDC output signal

Fig. 9. Curves of the second harmonic peak-to-peak value and standard deviation changing with distance

Fig. 10. Variation in signal peak-to-peak value with frequency

Fig. 11. System output second harmonic waveforms. (a) Gas concentration 0.2%; (b) gas concentration 1%; (c) gas concentration 2%

Fig. 12. System concentration response characteristic curves when modulation signal is 1 kHz and 3 kHz