Measurement of the particle number density in a pulsed flow gas cell with a second-harmonic interferometer

A high-sensitivity high-speed second-harmonic interferometer is used to monitor the particle number density inside a pulsed flow gas cell designed for laser wakefield acceleration. The interferometer can precisely follow the particle density temporal evolution therefore offering a practical way to control in real-time the target density during laser-plasma interaction. The presented results are relevant for the evaluation of density diagnostic tools for flow gas cells used as laser-plasma acceleration stages.