# Multiple-Diffraction Subtractive Double Monochromator with High Resolution and Low Stray Light
## 6 Conclusions  
In summary, this study developed a subtractive dispersion mount comprising two symmetrical multiple-diffraction monochromators (FM and SM) connected by a resolution slit for spectroscopic analysis. The FM increases the resolution through multiple diffractions, while the SM eliminates stray light owing to dispersion subtraction. Taking these two \begin{table}
\begin{tabular}{c c c c} \hline  & **Multiplexed Grating** & **Triple Dispersion** & **Multiple-Diffraction** \\  & **Spectrometer** & **Spectrometer** & **Subtractive** \\  & & & **Double Monochromator** \\ \hline Times of diffraction & 2 & 3 & 2 \(\times\) 2 \\ Spectral resolution & 57 pm & 36 pm & 18.8 pm \\ Wavelength range & 1250 to 1650 nm & 1250 to 1650 nm & 1250 to 1650 nm \\ OSNR & 55 dB & 30 dB & 69.17 dB \\ \hline \end{tabular}
\end{table} 
Table 1: A comparison between present and previous multi-diffraction dispersions. \begin{table}
\begin{tabular}{c c c c} \hline  & & & **Multiple-Diffraction** \\  & **Commercial Instrument 1** & **Commercial Instrument 2** & **Subtractive** \\  & & & **Double Monochromator** \\ \hline Spectral resolution & 20 pm & 60 pm & 18.8 pm \\ Wavelength range & 600 to 1700 nm & 600 to 1700 nm & 1250 to 1650 nm \\ OSNR & 73 dB & NaN & 69.17 dB \\ \hline \end{tabular}
\end{table} 
Table 2: Key performance of proposed vs. leading commercial spectral analysis instruments. diffractions as examples, we designed a double-diffraction subtractive double monochromator with a volume of 176 mm \(\times\) 168 mm \(\times\) 87 mm. It was experimentally verified that the multiple diffractions in the FM increased the spectral resolution and that the symmetric FM and SM significantly suppressed the stray light. The spectral resolution was 18.8 pm, and the OSNR attained was approximately 70 dB. Despite these achievements, the current work has limitations. The achieved resolution, while high, is constrained by the practical limit on diffraction times implemented in this initial prototype. Furthermore, the spectral operating range is currently limited by the achievable grating scan angle within the compact design. Next, we will address these limitations by further enhancing the resolution through increasing diffraction times and expanding the grating scan angle to broaden the spectral operating range. The proposed spectrometer mount demonstrates significant potential and can serve as a valuable tool for accurate optical spectral analyses in many domains. Conceptualization, Y.Z. and K.C. ; methodology, Z.W. ; software, Z.W. and K.C. ; validation, Z.W., K.C. and D.C.; formal analysis, Y.Z. ; investigation, Z.W. ; resources, T.C. ; data curation, D.C.; writing--original draft preparation, Z.W. ; writing--review and editing, Y.Z. ; visualization, Z.W. ; supervision, H.Y. ; project administration, T.C. ; funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Scientific Instrument and Equipment Development Project of China, grant number 2014 YQ510403. Not applicable. The original contributions presented in this study are included in this article; further inquiries can be directed to the corresponding author. We hereby extend our sincere gratitude to the Optical Society of America for their Premium Language Editing service, which conducted a thorough review of linguistic and grammatical accuracy, significantly enhancing the readability and logical coherence of the manuscript. Author [PERSON] and [PERSON] were employed by the company Tianjin Deviser Photoelectric Technology. The remaining authors declare that the re-search was con-ducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The following abbreviations are used in this manuscript: