[单选题]
In a ruby laser, an electr x58:k koeu3teon jumps from a higher energy level to a lower one. Ie oe:kk85ux3 t7ykv;p ,t/rd izl4av- f the energy difference bv l/ v;atryd-pz,i4 7ketween the two levels is 1.8 eV, what is the wavelength of the emitted photon?
A. $469 \; nm$
B. $649 \; nm$
C. $694 \; nm$
D. $964 \; nm$
