The plasma density gradient plays a critical role in laser plasma instabilities within laser inertial confinement fusion and laser plasma acceleration. Currently, measurement techniques for plasma density gradients primarily involve calculating the gradient from measured plasma density distributions, making it challenging to achieve direct and precise measurements of the density gradient. Here, we propose a transient direct measurement method for plasma density gradients based on variations in the pulse duration of a femtosecond probe laser. By exploiting the reflection of laser light at critical plasma density and measuring the change in the reflected laser pulse duration, the plasma density gradient can be directly determined. This approach offers advantages including femtosecond-level temporal resolution and capability for in-situ measurements.

Plasma density,Femtosecond lasers,Pulse duration,Corona plasma