High index of refraction via quantum interference in a three-level system of Er³⁺-doped yttrium aluminium garnet crystal

A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er³⁺-doped yttrium aluminium garnet (YAG) crystal, which is achieved for a probe field between the excited state ⁴I_13/2 and ground state ⁴I_15/2 by adjusting a strong coherent driving field between the upper excited state ⁴I_11/2 and ⁴I_15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er³⁺ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.