Direct High-Power Laser Acceleration of Ions for Medical Applications

Theoretical investigations show that linearly and radially polarized multiterawatt and petawatt laser beams, focused to subwavelength waist radii, can directly accelerate protons and carbon nuclei, over micron-size distances, to the energies required for hadron cancer therapy. Ions accelerated by radially polarized lasers have generally a more favorable energy spread than those accelerated by linearly polarized lasers of the same intensity.

Figure 1

Schematic geometry of the acceleration scenario. The initial coordinates of the ions are randomly distributed in a cylinder which models the interaction regime of the ion beam and the laser field. The ejected ions then form a beam of circular cross section when the ions are accelerated by radially polarized laser pulses. See text for further details.

Figure 2

Coordinates ($z_f$, $y_f$ of 5000 particles at the end of their trajectories after interaction with linearly polarized light. (a)–(c) are for protons ${}^1\mathrm{H}^{+}$ and (d)–(f) are for carbon nuclei ${}^{12}\mathrm{C}^{6+}$. The parameters are $\lambda =1054\mathrm{nm}$, $w_0=0.5\lambda$. The equations have been integrated over a time interval equivalent to 1000 laser field cycles, approximately amounting to 3.516 ps. For further data, see Table .

Figure 3

Kinetic energy of a typical particle (out of the ensembles of Fig. 2) during interaction with linearly polarized light. In the figure, $T$ is one laser field period.

Figure 4

Same as in Fig. 2, for particles accelerated by radially polarized light. For further data, see Table .

Figure 5

Kinetic energy of a typical particle (out of the ensembles of Fig. 4) during interaction with radially polarized light.