EIT locking of a semiconductor diode laser: significant improvement over Doppler locking

We report a precise frequency locking technique using electromagnetically induced transparency in an atomic vapour cell for a semiconductor diode laser. The sub natural line-width of EIT (Electromagnetically induced transparency) allows improvement in the stability of the laser diode under the locked condition. D₂ transition of ⁸⁵Rb atom is used for this experiment. Frequency stability of the laser under the locked condition is of the order of 426 kHz which provides nearly 80 times better stability than the Doppler locked condition.