Limitation to the accuracy of interferometrically measured electron density profiles of laser-produced plasmas

Using a double pulse ultraviolet holographic interferometer we have investigated the effects of interferometer focusing accuracy on the measured density profiles in an experimental study of plasmas generated by 20-ps duration Neodymium laser pulses on carbon fiber targets. We have found that in accordance with predictions made previously using computer models the critical density region can only be measured accurately in very small spherical plasmas when the interferometer focusing error is less than about 5 μm.