Comparison and application of wavelet transform and Kalman filtering for denoising in δCO measurement by tunable diode laser absorption spectroscopy at 2.008 µm: retraction.

The referenced article [Opt. Express25, A896 (2017)] has been retracted.

Comparison and application of wavelet transform and Kalman filtering for denoising in δCO measurement by tunable diode laser absorption spectroscopy at 2.008 µm.

We propose to use the wavelet transform and Kalman filter methods for processing noise in δCO measurement using laser absorption spectroscopy at 2.008 µm and they have been shown to be useful tool for reducing the intrinsic noise of the optical system. Through the performance comparison and analysis of these two denoising techniques for the intrinsic noise reduction of optical system, it can be found that the Kalman filter is a more suitable approach for the extraction of gas isotope measurement signal from a contaminated signal.

[Development of a photoacoustic spectroscopy system for the measurement of absorption coefficient of atmospheric aerosols].

In the present paper, the authors focus on the effect of the resonance frequency shift due to the changes in temperature and humidity on the PA signal, present several methods to control the noise derived form gas flow and vibration from the sampling pump. Based on the efforts mentioned above, a detection limit of 1.4 x 10(-8) W x cm(-1) x Hz(-1/2) was achieved for the measurement of atmospheric aerosols absorption coefficient.

[Low temperature properties of T shape photoacoustic cell and applications].

A homemade low-temperature T shape photoacoustic system (PAS) in the range from 0 to - 100 degrees C is well established. The mode distribution, the temperature dependence of the resonant frequency, Q-factor and the sensitivity of the PAS were investigated. The measurement of the carbon dioxide in the range from 0 to -100 degrees C showed that the system can be used in trace gas detection under low-temperature.

[New method for wave-plate orientation determination based on the shape of the modulated spectrum].

A new method for the determination of fast axis of wave-plate is introduced. Based on the principle of electro-optic phase compensation in the wave-plate phase measuring method, the relation between the polarization extinction system out-put signal and the modulating signal can be acquired through the composition of frequency fixed alternating voltage modulation signal. Through the analysis of this process with Jones matrix, the out-put signal was usually found to be the composition of fundamental frequency and second harmonic frequency, the composition signal reflects the axis information as well as the phase information of the wave-plate, and this phenomenon has never been noticed before.