Weak infrared radiation intensity measurement based on extended Duffing oscillator

Measurement of infrared radiation with low intensity in level of 10-6 W / cm2 is difficult. Because both background and the components used in the measurement system will generate infrared radiation, which results in a low signal-to-noise ratio (SNR). Except of using photodetector with high sensitivity, weak signal processing method is crucial. In this paper an infrared radiation intensity measurement setup based on intercomparison method is introduced. A reflective chopper is used to modulate the detected infrared radiation. By using a MCT Detector with Dewar the infrared signal is transferred to electric signal. To process the weak modulated signal with strong noise an extended Duffing oscillator is introduced. Both amplitude and phase of the modulation signal with known frequency is obtained by step-time-delay technique (equivalent to phase shifting in frequency-domain). The measurement error can be maintained below 16.1% even when the SNR is as low as -67 dB. The corresponding received infrared radiation power is only 1.05×10-9 W. The proposed signal processing method shows superior ability and great potential applications compared with commonly used method, such as lock-in amplification.