“…Again, we use 1 to approximate (1 ) to obtain the integral of the above equation with respect to as (32) From (24), the first two terms on the right-hand side of (32) become where has been used. From (5), (6), and (9), we have Hence, in (32) and (32) becomes The first term in the previous equation describes the desired phase evolution of the ponderomotive potential while the second term represents a small correction. The latter describes detailed features of electron trajectory that are not included in the simplified relationship of 1 .…”