Broadband light absorbers are attractive for their applications in photodetection and thermal detectors. Metal-black coatings have been experimentally proven to have broadband light absorption characteristic. A large area and broadband gold-black coating was fabricated by a low-cost but effective sputtering process. The gold-black films exhibited reduced reflection of 4.81%, 2.48% and 1.93% for sputtering pressure of 50, 65 and 80 Pa in 300-800 nm spectral range, and their size reached 4- inches. A three-dimensional nanocone-like array model was proposed for the gold-black films. Then, the nanocone array of this model was embedded with many gold nanoparticles due to the rough surface of the gold-black films. The results indicated this proposed model of nanocone-like array embedded with nanoparticles can be a good tool to design broadband gold-black absorbers.
KEYWORDS: Signal to noise ratio, Infrared radiation, Signal detection, Interference (communication), Oscillators, Signal processing, Phase measurement, Sensors, Modulation, Reflectivity
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.
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