Laser-assisted nuclear photoeffect

Proton emission from nuclei via the nuclear photoeffect in the combined electromagnetic fields of a $\gamma$-ray photon and an intense laser wave is studied. An $S$-matrix approach to the process is developed by utilizing methods known from the theory of nonperturbative laser-atom interactions. As a specific example, photo-proton ejection from halo nuclei is considered. We show that, due to the presence of the laser field, rich sideband structures arise in the photo-proton energy spectra. Their dependence on the parameters and relative orientation of the photon fields is discussed.

Figure 1

Distributions of the partial cross sections ${\sigma }_n$ for laser-assisted proton emission from ${}^8$B, as a function of the number of absorbed ($n>0$) or emitted ($n<0$) laser photons. The circularly polarized laser field has a frequency of ${\omega }_0=2$ keV. Its intensity amounts to (a) $I=4.0\times {10}^{21}$ W/cm${}^2$, (b) $I=1.0\times {10}^{23}$ W/cm${}^2$, and (c) $I=2.5\times {10}^{24}$ W/cm${}^2$, respectively. The $\gamma$-ray photon has an energy of ${\omega }_{\gamma }=3$ MeV; its polarization vector lies in the polarization plane of the laser.

Figure 2

Same as Fig. 1, but for a laser frequency of ${\omega }_0=100$ eV at intensity $I=6.25\times {10}^{21}$ W/cm${}^2$.

Figure 3

(a) Same as Fig. 1, but for laser frequency ${\omega }_0=200$ eV and laser intensity $I=6.25\times {10}^{21}$ W/cm${}^2$; (b) Same as (a) but the laser field is polarized in the $x$-$y$ plane (i.e., perpendicularly to the polarization direction of the $\gamma$ photon).