A multi-wavelengths analysis for pulse waveform extraction using laser speckle is conducted. The proposed system consists of three coherent light sources (532nm, 635nm, 850nm). A bench-test composed of a moving skin-like phantom (silicone membrane) is used to compare the results obtained from different wavelengths. The system is able to identify a skin-like phantom vibration frequency, within physiological values, with a minimum error of 0.5mHz for the 635nm and 850nm wavelengths and a minimum error of 1.3mHz for the 532nm light wavelength using a FFT-based algorithm. The phantom velocity profile is estimated with an error ranging from 27% to 9% using a bidimensional correlation coefficient-based algorithm. An in vivo trial is also conducted, using the 532nm and 635nm laser sources. The 850nm light source has not been able to extract the pulse waveform. The heart rate is identified with a minimum error of 0.48 beats per minute for the 532nm light source and a minimal error of 1.15 beats per minute for the 635nm light source. Our work reveals that a laser speckle-based system with a 532nm wavelength is able to give arterial pulse waveform with better results than those given with a 635nm laser. 
Which wavelength is the best for arterial pulse waveform extraction using laser speckle imaging?