We study the optical properties of $CuGaSe_2$ and $CuGaSe_2$:Co. The photoacoustic spectra of $CuGaSe_2$ and $CuGaSe_2$:Co are observed in visible region. The spectra of $CuGaSe_2$ and $CuGaSe_2$:Co show the A($\Gamma_7\rightarrow\Gamma_7$) transitions in 1.684 eV and 1.642 eV, respectively and the B($\Gamma_7\rightarrow\Gamma_6$) transitions in 1.746 eV and 1.748 eV, respectively. $CuGaSe_2$ thin films was grown by thermal evaporation. X-ray diffraction patterns of the thin films depend on the temperature of the boat. Reflectance spectrum of $CuGaSe_2$:Co normalized by that of $CuGaSe_2$ show $^4A_2\rightarrow^4T_1(^4F)$ and $^4A_2\rightarrow^4T_1(^4P)$ transitions in 6211 $cm^{-1}$ and 11111$cm^{-1}$. We calculated Dq = 373 $cm^{-1}$ and Racah parameter B = 408$cm^{-1}$.
