The soft X-ray region below 200 eV is important for investigating chemical and biological phenomena since it covers K-edges of Li and B and L-edges of Si, P, S and Cl. In this study, the argon gas window is proposed as a new soft X-ray transmission window in the low-energy region. High-order X-rays are removed by the absorption of the Ar L-edge (240 eV), and first-order X-rays become the major contribution of transmitted soft X-rays in the low-energy region. The XAS measurements confirmed that the argon gas window is effective for soft X-ray transmission in the low-energy region from 60 to 240 eV.
