This paper focuses on the influence upon the structure of the wake-field and the production of hot electrons due to a finite-width laser of high intensity and ultra-short duration propagation through an underdense plasma. Under the action of lognitudinal and transverse pondermotive forces, the plasma density forms a horseshoe cavity which acts as a moving convex to make the laser pulse self-focusing. The wake wave front curvature increases with time until a transverse wav e breaking occurs which depresses the wave breaking limit of the electrostatic f ield. The decrease of transverse wave breaking pushes more electrons into the ac celerating phase region to be trapped by wake wave and decreases the maximum ele ctronic kinetic energy.