Many studies on ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ doped with various dopants have been conducted to explore the relationship between charge density waves (CDWs) and superconductivity. Among them, only Cr-doped ${\mathrm{CsV}}_3{\mathrm{Sb}}_5\left[\mathrm{Cs}{\left({\mathrm{V}}_{1-x}\mathrm{C}{\mathrm{r}}_x\right)}_3\mathrm{S}{\mathrm{b}}_5\right]$ exhibits a simultaneous weakening of the CDW and superconductivity as the doping concentration increases. In this study, we investigated two Cr-doped ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ samples with doping levels of $x$ = 0.024 and 0.057 using optical spectroscopy with a focus on the CDW phase. By combining the experimental results with first-principles calculations, we found that the low-energy interband transitions were tuned by the saddle point at the $M$ point and were significantly enhanced by Cr doping. Furthermore, from a two-Drude-Lorentz model analysis, selective spectral weight transfer, previously observed in the pristine ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ compound, was confirmed to exist in the Cr-doped samples and systematically changed with Cr doping. We observed that the spectral weight of the narrow Drude component decreased as the Cr doping increased, suggesting a reduction in superconductivity. We extracted the CDW gaps of the two Cr-doped samples and found that the CDW order was suppressed more rapidly with Cr doping than expected based solely on the transition temperature. We expect that our results will provide insights into understanding the simultaneous weakening of both the CDW and superconductivity in Cr-doped ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$.

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• Charge density waves
• Density of states
• Electrical conductivity
• Optical conductivity