Extremely high-intensity laser interactions with fundamental quantum systems

The field of laser-matter interaction traditionally deals with the response of atoms, molecules, and plasmas to an external light wave. However, the recent sustained technological progress is opening up the possibility of employing intense laser radiation to trigger or substantially influence physical processes beyond atomic-physics energy scales. Available optical laser intensities exceeding ${10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ can push the fundamental light-electron interaction to the extreme limit where radiation-reaction effects dominate the electron dynamics, can shed light on the structure of the quantum vacuum, and can trigger the creation of particles such as electrons, muons, and pions and their corresponding antiparticles. Also, novel sources of intense coherent high-energy photons and laser-based particle colliders can pave the way to nuclear quantum optics and may even allow for the potential discovery of new particles beyond the standard model. These are the main topics of this article, which is devoted to a review of recent investigations on high-energy processes within the realm of relativistic quantum dynamics, quantum electrodynamics, and nuclear and particle physics, occurring in extremely intense laser fields.

Figure 1

Summary of the four pillars of ELI. A power value of $10(\times 2)\mathrm{PW}$ indicates the availability of two laser systems each with 10-PW power. From 147.

Figure 2

Comparison among the peak brilliances of the three facilities FLASH, LCLS, and European XFEL as a function of the laser-photon energy. An envisaged peak brilliance of $5\times {10}^{33}\mathrm{photons}/(\mathrm{s}{\mathrm{mrad}}^2{\mathrm{mm}}^{2}0.1\%\mathrm{bandwidth})$ at a photon energy of 12.4 keV for the SACLA facility is reported in 142. See also 142.

Figure 3

Free wave-packet evolution in a plane-wave field. The solid gray line indicates the center-of-mass trajectory, coinciding essentially with the classical trajectory, and the laser pulse travels from left to right. The blue regions indicate the copropagating self-adaptive numerical grid. Time and space coordinates are given in atomic units, with $1\mathrm{a}.\mathrm{u}.=24$ as and $1\mathrm{a}.\mathrm{u}.=0.05\mathrm{nm}$, respectively. From 31.

Figure 4

The total ${\mathrm{Rb}}^{10+}$ (black lines) and ${\mathrm{Rb}}^{11+}$ (red lines) ion populations in a gaseous target as a function of the peak intensity of a linearly polarized laser field with a wavelength of $0.8\mu \mathrm{m}$ and with a pulse duration of 5 fs. The solid lines display two-electron inelastic tunneling, the dashed lines one-electron inelastic tunneling, and the dash-dotted lines the results via the PPT theory. Adapted from 260.

Figure 5

(a) Experimental photoelectron spectra for argon at $I_0=1.2\times {10}^{19}\mathrm{W}/{\mathrm{cm}}^2$ and at an angle of 62° from the laser propagation direction. Analytical results are shown for all photoelectrons (solid line) and for the $L$ shell (dashed line). The angular distributions are at electron energies of (b) 60 keV, (c) 400 keV, and (d) 770 keV. From 98.

Figure 6

Dipole (left) and nondipole (right) probability densities of the Kramers-Henneberger wave function in the $x\mathrm{\text{−}}z$ plane for a $x$-polarized, 10-cycle sin-like pulse propagating in the positive $z$ direction (upward), with $E_0=1.5\times {10}^{11}\mathrm{V}/\mathrm{cm}$ and ${\omega }_0=54\mathrm{eV}$. The snapshots are taken at $t=0$, $t=T_0/2$, and $t=1.8T_0$ from top to bottom. The length of the horizontal line corresponds to about $50a_B\approx 2.7\mathrm{nm}$, with $a_B={\lambda }_C/\alpha \approx 5.3\times {10}^{-9}\mathrm{cm}$ being the Bohr radius. Note that the scale is logarithmic with four contours per decade. From 159.

Figure 7

The HHG setup with two counterpropagating APTs. After ionization by laser pulse 1, the ejected electron is driven in the same pulse (light blue), propagates freely after pulse 1 has left (gray dashed), and is driven back to the ion by laser pulse 2 (dark blue). From 258.

Figure 8

Deflection ${\alpha }_{\mathrm{out}}$ of an electron initially counterpropagating with respect to a laser field with an energy of 3 J and a pulse duration of 20 fs, as a function of the impact parameter $b$ for different laser waist radii $w_0$. From 211.

Figure 9

Schematic setup of TWTS with the red lines indicating the laser focal lines. In the notation of 96 $\varphi$ is the angle between the initial electrons’ velocity and the laser’s wave vector and $\alpha$ is the angle between the laser pulse front and the laser propagation direction. Adapted from 96.

Figure 10

Normalized on-axis brightness for different values of the rapidity $\rho ={cosh}^{-1}{\gamma }_0$ at a plasma temperature of 20 keV. See 196 for the meaning of the circles at $\rho =6$. Adapted from 196.

Figure 11

Quantum photon spectra as a function of ${\varpi }^{\prime }=k_{-}^{\prime }/p_{0,-}$ calculated with (solid line) and without (long dashed line) RR and the corresponding classical ones with (short dashed line) and without (dotted line) RR. The error bars in the quantum spectrum with RR stem from numerical uncertainties in multidimensional integrations. The numerical parameters in our notation are ${\epsilon }_0=1\mathrm{GeV}$, ${\omega }_0=1.55\mathrm{eV}$, and $I_0={10}^{23}\mathrm{W}/{\mathrm{cm}}^2$ ($R_Q=1.1$ and ${\chi }_0=1.8$). Adapted from 109.

Figure 12

Vacuum-polarization diagram in an external background electromagnetic field. The thick electron lines indicate electron propagators calculated in the Furry picture, accounting exactly for the presence of the background field.

Figure 13

Cross section of real photon-photon scattering as a function of the energy of the colliding photons in their center-of-momentum system in units of the electron mass. Adapted from 39.

Figure 14

(Color) Schematic three-dimensional setup for laser-assisted photon-photon scattering involving two incoming beams (in blue), an assisting one (in red), and a scattered one (in violet). From 307.

Figure 15

Intensity $I_d$ of the vacuum-scattered wave for a probe beam propagating along the positive $y$ direction and colliding with two strong beams aligned along the $x$ axis. The crosses correspond to coordinates $x_n$ according to the classical prediction $x_n=(n+1/2){\lambda }_{p}d/D$, where $n$ in an integer number, ${\lambda }_p$ is the wavelength of the probe field, $d$ is the distance between the interaction region and the observation screen, and $D$ is the distance between the centers of the two strong beams. The numerical values of the parameters can be found in 246. Adapted from 246.

Figure 16

Feynman diagrams corresponding to processes (i) [(a)], (ii) [(b)], and (iii) [(c)], respectively. The thick solid lines in (a) and (b) indicate Volkov positive- and negative-energy states. The crossed vertex in (b) stands for the Coulomb electromagnetic field. (c) is related to the vacuum current $j_{\mathrm{vac}}^{\mu }(x)$ that one has to determine in order to calculate the $e^{+}\mathrm{\text{−}}{e}^{-}$ pair yield (118). The double line indicates the electron propagator calculated in the Furry picture including exactly the background standing wave.

Figure 17

Transition from the perturbative to the fully nonperturbative regimes of $e^{+}\mathrm{\text{−}}{e}^{-}$ pair creation in electron-laser collisions. The laser-photon energy is 2.4 eV. Adapted from 220.

Figure 18

Number of pairs produced by the x-ray assisted Schwinger mechanism for two different values of the x-ray angular frequency ${\omega }_X$, indicated as $\omega$ in the figure (solid blue and black lines) and the ratio of these catalyzed pairs to those produced by the standard Schwinger mechanism (dashed blue and black lines), both as functions of the optical field strength in units of $F_{\mathrm{cr}}$. Adapted from 129.

Figure 19

Probability spectrum of $e^{+}\mathrm{\text{−}}{e}^{-}$ pair production in two counterpropagating laser pulses, with the laser magnetic field included (triangles) and neglected (crosses). In the first case, the labeling (${\ell }_r\mathrm{\text{−}}{\ell }_l$) signifies the number of absorbed photons from the right-left propagating wave; in the second case, the peak labels denote the total photon number ($\ell$). A vanishing initial momentum (i.e., positron momentum) and ${\xi }_0=1$ have been assumed. Adapted from 422.

Figure 20

The number of $e^{+}\mathrm{\text{−}}{e}^{-}$ pairs ($N_{\pm }$) and the number of photons ($N_{\gamma }$) created by an initial single electron in a rotating electric field as a function of the field intensity. The other plotted quantities are described by 36. From 36.

Figure 21

Snapshot of the (a) normalized electron density ${\rho }_e$, of the (b) normalized photon density ${\rho }_{\gamma }$, and of the (c) normalized laser intensity ${\rho }_l$ 25.5 laser periods after the two counterpropagating laser beams collided. The normalized density of positrons is approximately the same as that of the electrons. Also, the intensity of each colliding beam is $I_0=3\times {10}^{24}\mathrm{W}/{\mathrm{cm}}^2$ and the common wavelength is ${\lambda }_0=0.8\mu \mathrm{m}$. Adapted from 370.

Figure 22

Total rates for ${\mu }^{+}\mathrm{\text{−}}{\mu }^{-}$ pair creation by two-photon absorption from an intense XFEL beam (${\omega }_0=12\mathrm{keV}$, $I_0=2.5\times {10}^{22}\mathrm{W}/{\mathrm{cm}}^2$) colliding with various ultrarelativistic nuclei (${\gamma }_n=7000$). The triangles show elastic rates, whereas the squares indicate total ($“\mathrm{\text{elastic}}+\mathrm{\text{inelastic}}”$) rates. The numerical data are connected by fit curves. The dotted line holds for a pointlike nucleus. The production rates are calculated in the rest frame of the nucleus. Adapted from 345.

Figure 23

Number $N_{\gamma }$ of signal photons per nucleus per laser pulse for several isotopes with first excited states below 12.4 keV (squares) and above 12.4 keV (crosses). The results are plotted vs the atomic number $Z$. The considered European XFEL has a pulse duration of 100 fs and an average brilliance of $1.6\times {10}^{25}\mathrm{photons}/(\mathrm{s}{\mathrm{mrad}}^2{\mathrm{mm}}^{2}0.1\%\mathrm{bandwidth})$ (142). Adapted from 384.

Figure 24

HHG spectra emitted from muonic hydrogen (black) and muonic deuterium (red) in a laser field of intensity $I_0\approx {10}^{23}\mathrm{W}/{\mathrm{cm}}^2$ and photon energy ${\omega }_0\approx 60\mathrm{eV}$. “Arb. u.” stands for arbitrary units. From 455.

Figure 25

(a) In conventional $e^{+}\mathrm{\text{−}}{e}^{-}$ colliders bunches of accelerated electrons and positrons are focused to collide head on head incoherently, i.e., the bunches collide head on head but electrons and positrons in the bunch do not. (b) In the recollision-based collider, the electron and positron originating from the same Ps atom may collide head on head coherently (215). From 202.

Figure 26

The coordinate-space distributions of the electron and positron wave packets at the recollision time in focused counterpropagating pulses along the $z$ direction with $w_0=10\mu \mathrm{m}$, ${\lambda }_0=0.8\mu \mathrm{m}$, and with (a), (c) $I_0=4.7\times {10}^{22}\mathrm{W}/{\mathrm{cm}}^2$ and (b), (d) $I_0=1.4\times {10}^{23}\mathrm{W}/{\mathrm{cm}}^2$. The Ps atom is initially located at the origin. Spatial coordinates are given in atomic units, with $1\mathrm{a}.\mathrm{u}.=0.05\mathrm{nm}$. Adapted from 301.