Full-Optical Background Noise Compensation Method in Photoacoustic Gas Measurement System

This work presents a novel method to effectively mitigate background noise in resonant photoacoustic (PA) gas measurement systems. The method capitalizes on the destructive interference of PA waves generated by two distinct optical sources within a PA cell. Utilizing a unique resonant PA cell and a single microphone along with two light-emitting diodes (LEDs) with different wavelengths, the method is based on adjustment of the intensity and phase of the LED excitation signals to counteract background noise induced during measurements, which inevitably restrict the dynamic range of the useful signal. The proposed method is demonstrated to be straightforward to implement as a stand-alone instrument and offers flexibility in the choice and placement of optical sources. It does not necessitate stringent accuracy in its components, relying instead on the tuning of excitation signal intensity and phase for effective noise reduction. Experimental validation has shown its efficacy in detecting low concentrations of NO2, achieving resolutions below parts per million (ppm) levels and demonstrating high sensitivities (up to about 100 mV/ppm with a resolution of about 120 ppb). Key advantages include its simplicity, making it suitable for deployment beyond laboratory settings, and its cost-effectiveness due to the avoidance of complex mechanical machining and the adoption of low-cost components. The method accommodates various LED types for auxiliary use, provided that they are not tuned to the target gas absorption peak, thus enhancing its adaptability for practical applications.