Phuong,  Web site of Rakic gives you the refractive index of Nickel interpolated at 515nm as n=1.7388 and k=3.0832, the copy of which is attached.         Shigeo

Oh, I already found the data on this website, I also found some mistake in my question. I want to look for the extinction coefficient of Zinc  at 515 nm. I donot know why this website only update the data from 1230 nm for Zinc?

Anyway, thank you so much for reminding me

Prepare a series of standard solutions.Take the absorbance and from the slope get the molar extinction coefficient.