⇦Chinese Physics Letters, 2023, Vol. 40, No. 11, Article code 113101 Generation of Ultrafast Attosecond Magnetic Field from Ne Dimer in Circularly Polarized Laser Pulses Shujuan Yan (闫淑娟), Qingyun Xu (徐清芸), Xinyu Hao (郝欣宇), Ying Guo (郭颖), and Jing Guo (郭静)* Affiliations Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China Received 13 August 2023; accepted manuscript online 28 September 2023; published online 18 October 2023 *Corresponding author. Email: gjing@jlu.edu.cn Citation Text: Yan S J, Xu Q Y, Hao X Y et al. 2023 Chin. Phys. Lett. 40 113101    Abstract By numerically solving time-dependent Schrödinger equations, we investigate the generation of electron currents, ultrafast magnetic fields and photoelectron momentum distributions (PMD) when circularly polarized laser pulses interact with a Ne dimer in the charge migration (CM) process. By adjusting the laser wavelength, we consider two cases: (i) coherent resonance excitation ($\lambda=76$ nm) and (ii) direct ionization ($\lambda=38$ nm). The results show that the current and magnetic field generated by the Ne dimer under resonance excitation are stronger than under direct ionization. This phenomenon is due to the quantum interference between the initial state $2p\sigma_{\rm g}$ and the excited state $3s\sigma_{\rm g}$ under resonance excitation, so the CM efficiency of the dimer can be improved and the strength of the PMD under different ionization conditions is opposite to the strength of the electron current and induced magnetic field. In addition, we also find that both $2p\pi_{\rm g}$ and $2p\pi_{\rm u}$ have coherent resonance excitation with $3s\sigma_{\rm g}$ state and generate periodic oscillating currents for the Ne dimer. The study of the dynamics of the Ne dimer under different ionization conditions lays a foundation for research of ultrafast magnetism in complex molecular systems.
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 DOI:10.1088/0256-307X/40/11/113101 © 2023 Chinese Physics Society Article Text In recent years, with the rapid development of laser technology, researchers have been committed to studying microscopic phenomena inside molecules at attosecond timescales.[1-5] When the ultrafast intense laser field interacts with molecules, a series of nonlinear phenomena will occur, such as high-order harmonics,[6] non-ordered double ionization,[7] and above-threshold ionization.[8] Attosecond laser pulses can be achieved by higher-order harmonics, which can be obtained using femtosecond $10^{-15}$ s lasers interacting with inert gases,[9,10] resulting in ultra-short laser pulses of 43 as in Ref. [11]. In the past, the study of internal molecular electron dynamics at attosecond timescales was mainly limited to linearly polarized laser pulses.[12] Recently, it was found that circularly polarized (CP) pulses can produce CP coherent short-wavelength harmonics.[13,14] CP pulses have attracted wide attention and become a powerful tool for studying internal microstructures of atoms and molecules. Many studies have shown that when a laser pulse acts on a molecule, the electrons in the molecule are excited and ionized to produce an electric current, which induces a magnetic field.[15-18] In the study of current and magnetic field, the ultrafast charge migration (CM) process caused by the coherent superposition of multiple electron states has attracted extensive attention in the fields of photophysics and photochemistry.[19-23] For example, it has been found that linear and CP ultraviolet laser pulses resonating with degenerate $\pi$-orbits in aromatic molecules can generate electron ring currents and thus the magnetic fields are much stronger than traditional static magnetic fields.[24-26] In H$_{2}^{+}$, it has been found that the generation of an ultrafast magnetic field in the molecular center can be controlled by adjusting the laser parameters and the molecular orientation.[27-29] In addition, when a linearly polarized laser pulse is applied to the current-carrying state 2$p^+$ of the Ne atom, it is found that a spatially oscillating magnetic field of up to 47 T is generated in the center of the Ne atom.[30] Moreover, magnetic fields can be controlled experimentally by adjusting the spatial distribution of electron currents in semiconductors.[31] Although there have been many studies on oscillating magnetic fields generated by atoms and diatomic molecules, research of electron dynamics in the Ne dimer is still unclear and needs further developments. In this work, by numerically solving the time-dependent Schrödinger equation, we study the time-evolving electron current, ultrafast magnetic field, and photoelectron momentum distribution (PMD) of the Ne dimer in a specific excited state by a CP laser pulse. We consider two cases of (i) coherent resonance excitation ($\lambda=76$ nm) and (ii) direct ionization ($\lambda=38$ nm), and find that the currents, magnetic field and PMD generated by the Ne dimer all follow the same rules in both cases. In this study, we adopt a two-dimensional (planar) model of molecular plane laser polarization, and the corresponding two-dimensional time-dependent Schrödinger equation (TDSE) of the Ne dimer is \begin{align} {i}\frac{\partial\psi({\boldsymbol r},t)}{\partial t}=\Big[-\frac{1}{2}\nabla_{\boldsymbol r}^2+V_{\scriptscriptstyle{\rm C}}({\boldsymbol r})+V_{\scriptscriptstyle{\rm L}}({\boldsymbol r})\Big]\psi({\boldsymbol r},t), \tag {1} \end{align} where $-\frac{1}{2}\nabla_{\boldsymbol r}^2$ is the kinetic energy term, and the Ne dimer is arranged along the $x$-axis. For the Ne dimer, the Coulomb soft-core potential can be expressed as[32] \begin{align} V_{\scriptscriptstyle{\rm C}}({\boldsymbol r})=-\sum\limits_{\alpha=1}^{2}\frac{Z_{\infty}+(Z_0-Z_{\infty})\exp(-\frac{|{\boldsymbol r}-{\boldsymbol R}_{\alpha}|^2}{b^2})}{\sqrt{|{\boldsymbol r}-{\boldsymbol R}_\alpha|^2+a}}, \tag {2} \end{align} where ${\boldsymbol r}=(x,y)$ indicates the electron coordinate in the $(x,y)$ plane, ${\boldsymbol R}_{\alpha}$ denotes the $\alpha$ nucleus at the fixed coordinate $(x,y)$, and $Z_{\infty}=0.5$, $Z_{0}=10$ are the effective nuclear charge and bare charge.[32] For the Ne dimer, the molecular orbital configuration of the ground state is $(1s\sigma_{\rm g})^2(1s\sigma_{\rm u})^2(2s\sigma_{\rm g})^2(2s\sigma_{\rm u})^2(2p\sigma_{\rm g})^2(2p\pi_{\rm u})^4(2p\pi_{\rm g})^4$ $(2p\sigma_{\rm u})^2$, and we choose the soft-core parameter to avoid the singularity of a function. In the $2p\sigma_{\rm g}$ orbital, the soft-core parameter $a=1.2$ and effective charge shielding parameter $b=0.815$, when balanced internuclear distance $|{\boldsymbol R}|=|{\boldsymbol R}_1-{\boldsymbol R}_2|=5.86\,{\rm a.u.}=3.1$ Å and the ionization potential energy of the ground state $I_p=0.747$ a.u.[32,33] In Eq. (1), $V_{\scriptscriptstyle{\rm L}}({\boldsymbol r})={\boldsymbol r}\cdot {\boldsymbol E}(t)$ is the interaction between the laser field and dimer. In this work, the laser pulse can be indicated as \begin{align} {\boldsymbol E}(t)=\frac{E_0}{\sqrt{2}}f(t)[\cos(\omega t)\hat{\boldsymbol e}_x+\sin(\omega t)\hat{\boldsymbol e}_{y}], \tag {3} \end{align} where $\hat{\boldsymbol e}_x$ and $\hat{\boldsymbol e}_y$ are polarization vectors of the laser pulse, $\omega$ is the carrier frequency of the laser pulse, $E_0=0.053$ a.u. is total laser pulse field strength, and the laser intensity $I_0=1.0\times10^{14}$ W/cm$^{2}$. The total duration is $T_{\rm total}=10\tau$, where $T_{\rm total}=T_1+T_2$, $T_1=7\tau$ represents the duration that the laser pulse with field intensity $I_0$ acts on the Ne dimer and $T_2=3\tau$ is the duration of the wave function propagation without field after the end of the laser pulse. Here, $\tau=\frac{2\pi}{\omega}$ is an optical period of a laser pulse, and carrier envelope $f(t)=\sin^2(\pi t/T_1)$. In order to eliminate the influence of electrostatic field and carrier envelope phase, we guarantee $\int E(t)\,{d}{t}=0$. We solve the 2D TDSE (1) numerically by combining the split operator method and the fast Fourier transform (FFT),[34,35] \begin{align} \psi({\boldsymbol r},t+\Delta{t})=\,& e^{-{i}(\frac{p^2}{4})\Delta{t}} e^{-{i}[V_{\scriptscriptstyle{\rm C}}({\boldsymbol r})-V_{\scriptscriptstyle{\rm L}}({\boldsymbol r},t)]\Delta t}\notag\\ &\cdot e^{-{i}(\frac{p^2}{4})\Delta t}\psi({\boldsymbol r},t)+O (\Delta t)^3, \tag {4} \end{align} where the time step $\Delta t=0.05$ a.u., the space grid points are $1024\times1024$, they have the same step size in the $x$ and the $y$ directions $\Delta x=\Delta y=0.4$ a.u., the variation range of the grid points is $-204.8$ a.u. to $204.8$ a.u. and the total spatial length is $409.6$ a.u. In order to avoid non-physical effects caused by the reflection of the wave packet from the boundary, the wave function cos$^{(1/8)}$ is multiplied by the absorption function for each time step in our computation and the absorption range is from $|x,y|=150$ a.u. to $|x,y|=204.8$ a.u. The time-dependent wave function $\psi({\boldsymbol r},t)$ consists of the ionized and unionized parts. The ionized part can be written as $[1-M(r)]\psi({\boldsymbol r},t)$, where $r=\sqrt{x^2+y^2}$, and \begin{align} M(r)=\begin{cases} 1,& r\le {{r}_{\rm b}}, \\ \exp [-\beta (r-{r_{\rm b}})],& r>{{r}_{\rm b}}, \\ \end{cases} \tag {5} \end{align} with $\beta$=1 and $r_{\rm b}=30$ being the boundary between the ionized and nonionized electron wave functions. The PMD can be obtained by taking the FFT of the ionized electron wave function, and the photoelectron angular distribution (PAD) can be obtained by angle statistics of the PMD. In the length gauge, the time-dependent electronic current can be written as \begin{align} j({\boldsymbol r},t)=-\frac{i}{2}[\psi({\boldsymbol r},t)\nabla_{\boldsymbol r}\psi^*({\boldsymbol r},t)-\psi^*({\boldsymbol r},t)\nabla_{\boldsymbol r}\psi({\boldsymbol r},t)], \tag {6} \end{align} where $\nabla_{\boldsymbol r}=\frac{\partial}{\partial x}{\boldsymbol i}+\frac{\partial}{\partial y}{\boldsymbol j}$, and $\psi({\boldsymbol r},t)$ is the wave function obtained from Eq. (1). Ultrafast magnetic field can be obtained through the classical Jefimenko equation[36] \begin{align} B({\boldsymbol r},t)=\,&-\frac{\mu_0}{4\pi}\int\Big[\frac{j({\boldsymbol r}',t_r)}{|{\boldsymbol r}-{\boldsymbol r}'|^3}+\frac{1}{|{\boldsymbol r}-{\boldsymbol r}'|^2c}\frac{\partial j({\boldsymbol r}',t_r)}{\partial{t}}\Big]\notag\\ &\times({\boldsymbol r}-{\boldsymbol r}')\,{d}^3{\boldsymbol r}', \tag {7} \end{align} where $t_r=t-\frac{r}{c}$ is the delay time, $c$ is the velocity of light in vacuum, and $\mu_0=4\pi\times10^{-7}\rm{NA}^{-2}(6.692\times10^{-4}$ a.u.).
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Fig. 1. (a) Schematic drawing of ultrafast magnetic field $B({\boldsymbol r},t)$ propagating along the $z$ axis. The electron current is produced in the $(x,y)$ plane. (b) With CP pulse interaction with the Ne dimer, the schematic diagram of two ionized cases of (i) coherent resonance excitation ($\lambda=76$ nm, $\omega=0.6$ a.u.) and (ii) direct ionization($\lambda=38$ nm, $\omega=1.2$ a.u.). (c) Initial electron density distribution of the Ne dimer.
In our computation, we study the electron current, ultrafast magnetic field and PMD generated by CP laser pulses acting on a Ne dimer. We consider two cases: (i) Coherent resonance excitation: For the Ne dimer, in $2p\sigma_{\rm g}$–$3s\sigma_{\rm g}$ coherent resonance excitation between electronic states occurs and the energy range between the two states is $-Ip_{\rm e}-(-Ip_{\rm A'})=0.6$ a.u. ($Ip_{\rm e'}$ is excited state energy, $Ip_{\rm A'}$ is initial state energy). When a CP laser pulse of carrier frequency $\omega=0.6$ a.u. $(\lambda=76$ nm) acts on the Ne dimer, a resonance excitation process occurs in the dimer.[37] (ii) Direct ionization: Direct ionization occurs when a laser pulse of $\omega=1.2$ a.u. ($\lambda=38$ nm) is applied to the Ne dimer, and electrons jump directly from the initial state ($2p\sigma_{\rm g}$) to the continuum state. Figure 1(b) shows a schematic diagram of these two ionization conditions. For the Ne dimer, we study the coherent resonance from $2p\sigma_{\rm g}$ ($\psi_{\rm A'}({\boldsymbol r})$ with energy $-Ip_{\rm A'}= -0.747$ a.u.) to $3s\sigma_{\rm g}$ ($\psi_{\rm e}({\boldsymbol r})$ with energy $-Ip_{\rm e}=-0.14$ a.u.) and direct ionization from $2p\sigma_{\rm g}$ to continuum state. In order to satisfy these two ionization conditions, we select CP laser pulses of wavelength $\lambda=76$ nm [$\omega=\Delta E=-Ip_{\rm e}-(-Ip_{\rm A'})=0.6$ a.u.] and $\lambda=38$ nm ($\omega=1.2$ a.u.), respectively. For case (i) of resonance excitation, due to the coherent superposition between the two electron states $(2p\sigma_{\rm g}$–$3s\sigma_{\rm g})$, strong charge resonance excitation occurs inside the dimer. The wave function after coherent superposition can be expressed as \begin{align} \psi_0({\boldsymbol r},t)=C_{\rm A'}\psi_{\rm A'}({\boldsymbol r}) e^{-{i}{Ip}_{\rm A'}t}+C_{\rm e}\psi_{\rm e}({\boldsymbol r}) e^{-{i}Ip_{\rm e}t}, \tag {8} \end{align} where $C_{\rm A'}$ and $C_{\rm e}$ are occupancy coefficients, $\psi_{\rm A'/e}({\boldsymbol r})$ and $Ip_{\rm A'/e}$ are the wave functions and energies of the initial and excited states, respectively. Thus, the expression for the electron density as a function of the time can be written as \begin{align} \!A({\boldsymbol r},t)=|\psi_0({\boldsymbol r},t)|^2=A^{\scriptscriptstyle{\rm A'}}({\boldsymbol r})+A^{\rm e}({\boldsymbol r})+A^{\scriptscriptstyle{(\rm A',e)}}({\boldsymbol r},t), \tag {9} \end{align} and $A^{\scriptscriptstyle{\rm A'}}({\boldsymbol r})=|C_{\rm A'}\psi_{\rm A'}({\boldsymbol r})|^2$, $A^{\rm e}({\boldsymbol r})=|C_{\rm e}\psi_{\rm e}({\boldsymbol r})|^2$, $A^{\scriptscriptstyle{(\rm A',e)}}({\boldsymbol r},t)$ is the interference term, which can be written as \begin{align} \!A^{\scriptscriptstyle{(\rm A',e)}}({\boldsymbol r},t)\propto|C_{\rm A'}(t)C_{\rm e}(t)||\psi_{\rm A'}({\boldsymbol r})\psi_{\rm e}({\boldsymbol r})|\cos(\Delta Et), \tag {10} \end{align} where $\Delta E=-Ip_{\rm e}-(-Ip_{\rm A'})=0.6$ a.u. It can be seen from Eq. (11) that the interference term $A^{\scriptscriptstyle{(\rm A',e)}}({\boldsymbol r},t)$ is proportional to time $t$, and the attosecond coherent CM process in the system is described. The period of coherent electron migration is $\Delta\tau=\frac{2\pi}{\Delta E}=T_0=10.472\,{\rm a.u.}=253.4$ as. Figure 2(a) depicts the electron density distribution $A({\boldsymbol r},t)$ and electron current changes of the Ne dimer under coherent resonance excitation at four different times. It can be seen that as time increases, the electron density migrates between the two protons. At $t=4\tau$, electron charge moves to the left, at $t=4.25\tau$, the charge moves to the right and, at this point, the $A({\boldsymbol r},t)$ intensity increases. At $4.5\tau$, the charge still moves to the right, but the electron density intensity is reduced. Lastly, when $t=4.75\tau$, the intramolecular charge moves to the left and the charge density increases. According to the laws of evolution in these four moments, when $t=5\tau$, the charge is still moving to the left, at this time the density of $A({\boldsymbol r},t)$ is the same as that at $t=4\tau$. Therefore, CM changes periodically over an optical period. Now let us consider the case (ii) of direct ionization. Figure 2(b) shows the distribution of electron density $A({\boldsymbol r},t)$ and electron current at four different times when a CP laser with $\lambda=38$ nm is applied to a Ne dimer. At $t=4\tau$, $4.25\tau$, $4.5\tau$, and $4.75\tau$, the electron current density rotates clockwise within dimer, at this time the efficiency of the CM process is low. The reason for this phenomenon is that, in the case of direct ionization, the electron absorbs a photon and directly transitions to the continuum state, and the electron with relatively small kinetic energy moves in the $y$ direction due to the non-zero drift velocity in the $y$ direction.[38] In addition, in the case of direct ionization, there is no coherent electron wave packet.
cpl-40-11-113101-fig2.png
Fig. 2. Electronic dynamics in the CM process when the equilibrium nuclear distance $R=5.86\,{\rm a.u.}=3.1$ Å and the initial excited state is $2p\sigma_{\rm g}$ of the Ne dimer in coherent resonance excitation and direct ionization conditions. Electron density distribution and electron current density distribution at four moments under (a) coherent resonance excitation ($\lambda=76$ nm, $\omega=0.6$ a.u.) and (b) direct ionization ($\lambda=38$ nm, $\omega=1.2$ a.u.). The white arrow indicates the direction of the electron current.
In order to observe more clearly the difference between the internal electron dynamics of the Ne dimer in the cases of coherent resonance and direct ionization, we integrate the time-varying current $j_x(t)$ on the $x$-axis as $j_x(t)=\int_{-\infty}^{+\infty}j(0,y,t)\cdot \,{d}y$, where \begin{align} {\boldsymbol j}({\boldsymbol r},t)=j_x({\boldsymbol r},t)\hat{\boldsymbol e}_x+j_y({\boldsymbol r},t)\hat{\boldsymbol e}_y, \tag {11} \end{align} and $\hat{\boldsymbol e}_x$ and $\hat{\boldsymbol e}_y$ are unit vectors in the $x$ and $y$ directions. As can be seen from Fig. 3(a), the current under resonance excitation is stronger than that under direct ionization, and the maximum current under resonance excitation reaches 0.003 a.u., while the maximum current under direct ionization is 0.001 a.u. This indicates that direct ionization is not conducive to inducing strong current, which is also consistent with the CM efficiency shown in Fig. 2. This is due to the fact that, in direct ionization, the electron absorbs the photon and directly transitions to the continuum state, and the ionization rate is reduced. When the laser pulse is turned off ($t>7\tau$), in the case of resonance excitation, the oscillating current is still generated due to the presence of coherent electron wave packets, while in the case of direct ionization, no current is generated. Ultrafast magnetic fields can be induced by electric currents inside dimer. As shown in Fig. 3(b), it can be seen that the ultrafast magnetic field takes $\tau$ as the oscillation period, and the induced magnetic field intensity rule is consistent with the current. Under resonance excitation, the maximum magnetic field strength is 0.3 T, and under direct ionization, the maximum magnetic field strength is 0.14 T. When the laser pulse is turned off ($t>7\tau$), a periodic oscillating magnetic field is still generated under resonance excitation. This shows that the generation of an ultrafast magnetic field is dependent on electron currents, and the yield of the ultrafast magnetic field can be controlled by adjusting the parameters of the laser pulse.
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Fig. 3. Electron current $j(t)$ and induced magnetic field $B(r,t)$ of the Ne dimer as functions of time in coherent resonance excitation and direct ionization. (a) Electron current as a function of time at $r=0$. (b) Induced ultrafast magnetic field at $r=-R/2$. O.C.: optical cycle.
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Fig. 4. (a) PMD and PAD of the Ne dimer under resonant excitation; (b) PMD and PAD of the Ne dimer under direct ionization; (c) PAD prediction of the Ne dimer using two-center interference in Eq. (14).
We also study the PMD and PAD of the Ne dimer at the end of the pulse. It is found that the momentum of the photoelectron shows a 6-lobe structure in both cases, and the intensity of the PMD under direct ionization is stronger than that under resonant excitation. The reason is that when $T=10\tau$, in the case of direct ionization the ionized electrons are all fixed in the continuum state [Fig. 4(b) shows the distribution of all ionized electrons], and in the case of resonance excitation the ionized electrons mainly resonate between $2p\sigma_{\rm g}$ and $3s\sigma_{\rm g}$, and fewer photoelectrons can be observed. Therefore, the intensity of the PMD in the case of direct ionization is stronger than that of resonance excitation, which is consistent with the results shown in Fig. 3. After the laser pulse is turned off $(t>7\tau)$, the photoelectrons are concentrated in the continuum state under direct ionization, without the CM process, and the current and magnetic field are equal to 0. However, under resonance excitation, the photoelectrons move between the two states, and the CM efficiency is high, so current and induced magnetic field oscillating with the period are generated. We analyze the structure of the Ne dimer: Ne dimer is composed of two Ne atoms and there is a weak interaction between two Ne atoms so the wave function of the dimer can be regarded as the linear superposition of the wave functions of two Ne atoms,[39-41] \begin{align} \psi_{2p}({\boldsymbol r})=\psi_{2p}({\boldsymbol r}-{\boldsymbol R}/2)+\psi_{2p}({\boldsymbol r}+{\boldsymbol R}/2). \tag {12} \end{align} The final photoelectron momentum distributions of the Ne dimer in the $x$ and $y$ directions can be obtained as \begin{align} &A_{\sigma_{\rm g}}^{(x)}\propto\sqrt{2}C^{(x)}\cos(\theta)\cos ({\boldsymbol p}\cdot{\boldsymbol R}/2)\psi_{2p}({\boldsymbol p}),\notag\\ &A_{\sigma_{\rm g}}^{(y)}\propto\sqrt{2}C^{(y)} \sin(\theta)\cos ({\boldsymbol p}\cdot{\boldsymbol R}/2)\psi_{2p}({\boldsymbol p}), \tag {13} \end{align} where ${\boldsymbol p}$ is the electron momentum vector and $\theta$ is the angle between the electron's momentum vector and the $x$ axis. Then the interference term can be written as \begin{align} A_{\sigma_{\rm g}}^{(x,y)}\propto\sqrt{2}\cos^2 ({\boldsymbol p}\cdot{\boldsymbol R}/2)\psi^2_{2p}(|{\boldsymbol p}|). \tag {14} \end{align} From Eq. (14), the distribution of the number of lobes of the Ne dimer PMD can be explained perfectly by using the theory of two-center interference. The results predicted by the model are consistent with those calculated by the TDSE in angle, but not in intensity.
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Fig. 5. Time-dependent electron currents under coherent resonance excitation and direct ionization with $2p\pi_{\rm g}$ (a) and $2p\pi_{\rm u}$ (b) as the initial states, respectively.
In our calculations, we also calculate the time-dependent electron currents in cases (i) and (ii), using the $2p\pi_{\rm g}$ and $2p\pi_{\rm u}$ states as the initial states. According to the calculation results, coherent resonance excitation occurs among $2p\pi_{\rm g}$, $2p\pi_{\rm u}$, and $3s\sigma_{\rm g}$. The induced current intensity of the CP laser pulse with $2p\pi_{\rm g}$ and $2p\pi_{\rm u}$ as the initial state is stronger than that of the CP laser pulse with $2p\sigma_{\rm g}$ as the initial state. Additionally, we also calculate the electron current density generated by the same laser pulse acting on the Ne atom between the 2$p$ and 3$s$ orbital resonance excitation and direct ionization with the 2$p$ orbital as the ground state (Part 1 in the Supplementary Materials), induced current and ultrafast magnetic field (Part 2 in the Supplementary Materials). At the same time, we also found that the induced current intensity generated by the Ne atom is one order of magnitude higher than that of the Ne dimer. In summary, we have studied CP laser pulses of different wavelengths acting on Ne dimer, electron currents generated during the CM process, ultrafast magnetic fields and PMDs. Under the coherent resonance excitation ($\lambda=76$ nm) ($2p\sigma_{\rm g}$–$3s\sigma_{\rm g}$) of the Ne dimer, the electron wave packet has strong coherence and high CM efficiency, so the PMD intensity is weak, a stronger periodic oscillation current is generated and the strong current consequently induces a strong magnetic field. In the case of direct ionization ($\lambda=38$ nm), the CM efficiency is low, and the PMD is stronger, resulting in a weaker electron current and induced magnetic field. The Ne atom resonates between the $2p$ and $3s$ states, the Ne dimer can be regarded as a linear superposition of two Ne atoms since there is a weak interaction between the two atoms in the Ne dimer, and the behavior of the Ne dimer is consistent with that of the Ne atom in electron dynamics. In addition, we find that, for the Ne dimer, there are also resonance excitations between other states, e.g., $2p\pi_{\rm g}$–$3s\sigma_{\rm g}$ and $2p\pi_{\rm u}$–$3s\sigma_{\rm g}$. We expect to generate a strong magnetic field by regulating the wavelength of the laser pulse. Acknowledgments. This work was supported by the National Natural Science Foundation of China (Grant Nos. 12074146 and 11974007), and the Natural Science Foundation of Jilin Province (Grant No. 20220101010JC). 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