Resonance ionisation of Ga atoms

Saturation of the photoionisation of Ga atoms by resonance ionisation is demonstrated. The photoionisation cross section of the excited 4s 2 (1S) 3/2 state is measured to be 3 × 10 −18 cm 2 . Saturation (100% ionisation) of a given samnple is achieved at power levels of the order of 100 MW/cm 2 .