Restoration Method for Rotating Fourier Transform Ultraviolet Raman Spectrum Based on the Reusable Feature Sequence

The rotating Fourier transform ultraviolet Raman spectrometer (RFTURS) is capable of obtaining spectra with high signal to noise ratio (SNR) and high stability. However, the optical path difference (OPD) is nonlinear to the angle of the rotating mirror, especially in the UV band, this brings a great challenge to the accurate restoration of Raman spectrum. To overcome the challenge, this article proposes a method of restoration for RFTURS based on the reusable feature sequence. First, a motor reducer with a high reduction ratio is used to increase the OPD resolution. Second, OPD is divided into a vector with a large and equal interval. Then, the indices of the sampling points whose OPD is closest to the member of the vector is extracted as feature sequence. Finally, the signal is downsampled by the sequence, and the spectrum is restored by fast Fourier transform (FFT). The proposed method does not need another bulky and expensive ultraviolet laser compared with the reference laser method. Compared with the nonuniform FFT (NUFFT) and resampling method, it costs lower program runtime as well as obtain excellent SNR and spectral resolution (SR) since the sequence can be repeatedly used for signals generated by the same optical system. The method was tested with a simulated signal and the measured signal. The results show that the proposed method saves at least 61.8% in processing simulated signals and at least 84.5% in processing measured signals.