Spectral noise reduction and temporal coherence control using a phase unsynchronized wave synthesizing method

Highly accurate spectrometry requires spectral noise reduction. In this paper, we propose a phase unsynchronized wave synthesizing (PuwS) method that provides different optical path lengths for different wave elements obtained from the division of a wavefront and synthesizes the respective wave elements to have the same propagation direction. PuwS achieves spectral noise reduction and contributes to temporal coherence control. To confirm these properties observed in experimental data, we propose a series of analytical models based on a traditional wave train model. According to the analytical model, PuwS generates an ensemble average effect that prevents spectral noise and decreases the visibility of the spectral fringe pattern. The experimental data show that the spectral noise is reduced when the total number of wave elements increases. PuwS is found to drastically change the measured spectral profile of a silk sample, achieving highly accurate spectrometry. The data also show that a combination of PuwS and an appropriate diffuser decreases the spectral visibility regarding the temporal coherence more effectively than a conventional method using one or more diffusers.