In the laser ablation process, the recoil of the plume induces a momentum change to the target, which can be quantified in terms of the employed laser pulse energy by the so-called momentum coupling coefficient . This figure of merit is rather sensitive to laser parameters. Basically, three regimes exist: (1) Below the threshold fluence , no momentum coupling occurs; (2) beyond the ablation threshold, an optimum fluence exists where the impulse coupling coefficient exhibits its peak value. In the range from to , the so-called vaporization regime, rapidly increases; and (3) around , plasma ignition commences, which marks the beginning of the transition regime where plasma shielding of the target becomes more and more important. Correspondingly, at fluences roughly 1 order of magnitude above , full plume ionization indicates the onset of the plasma regime. Hence, due to plasma shielding, slowly decreases for fluences higher than .