We report on the depletion and power ampli cation of the driving laser pulse in a strongly-driven
laser wake eld accelerator. Simultaneous measurement of the transmitted pulse energy and temporal
shape indicate an increase in peak power from 187
11 TW to a maximum of 318
12 TW after
13 mm of propagation in plasma density of 0
:
9
10
18
cm
3
. The power ampli cation is correlated
with the injection and acceleration of electrons in the non-linear wake eld. This process is modeled
by including localized redshift and subsequent group delay dispersion at the laser pulse front.