In situ axion generation and detection in laser-plasma wakefield interaction

Abstract

We propose a laser-plasma wakefield interaction based scheme for in situ axion generation and detection through the Primakoff process. Strong electromagnetic fields ($\gtrsim 10^{11}$\,V/m) in the wakefield can enhance axion production rates by 2 orders of magnitude compared to conventional light-shining-through-a-wall experiments. By replacing the axion generation stage with laser-wakefield interaction, the axion-photon coupling constraints can achieve the level of $\gagg \sim 10^{-10}\,\text{GeV}^{-1}$ for axion mass less than 0.1\,meV. Besides, the generated axions can convert back into photons in the background fields, leading to axion-regenerated electromagnetic fields (AREM) with unique polarization, frequency, and transverse modes. This provides a new promising way to search axions by detecting the filtered AREM fields from the background laser and plasma fields.

Figures (5)

• Figure 1: Typical results of axion generation and conversion through laser-wakefield interactions. Different fields with the plasma wakefield are shown: (a) the laser electric field $E_{0, y}$, (b) the axion field $\phi$, (c) the AREM $E_{1, y}$, and (d) the AREM $E_{1, z}$. The electric fields are normalized to the characteristic field $E_\gamma$ at the laser frequency.
• Figure 2: Frequency and LG decomposition of different field components: (a) $E_{0,y}$, (b)$E_{0,z}$, (c) $E_{1,y}$, and (d) $E_{1,z}$. The red lines show the frequency spectra. The slice images show the LG decomposition of the corresponding frequency components.
• Figure 3: The dephasing distances of the axion and AREM. The dashed lines indicate the dephasing distances in a laser driven wakefield bubble, while the solid lines indicate those in a cleaner wakefield bubble driven by an electron beam.
• Figure 4: (a) Axion conversion ratio in this work and ALPS-II experiment, defined as the ratio of the axion energy to the initial laser energy: $P_a =\int \mathcal{H}_a \,\mathrm{d} V / \int \mathcal{H}_\gamma \,\mathrm{d} V$, where $\mathcal{H}_a = \frac{1}{2}\left[(\partial_t\phi)^2 + (\nabla\phi)^2 + m_a^2\phi^2\right]$ and $\mathcal{H}_\gamma = \frac{1}{2}\left(\bm E_0^2+\bm B_0^2\right)$ are the energy densities of the axion field and the laser field, respectively. (b) The signal-to-noise ratio for the unfiltered fields ($E_{1,y}/ E_{0,y}$) and the filtered fields by selecting different polarization, frequency and spatial mode ($E_{1,z,2\omega_0, l=1} / E_{0,z,2\omega_0,l=1}$). The results are calculated using an electron beam as wakefield driver with beam energy 40 GeV, duration 2 $\mu$m, radius 7 $\mu$m, and peak density $6\times10^{20}$ cm$^{-3}$ to drive a clearer and stronger wakefield bubble. The laser inside the wake has the same parameters as before.
• Figure 5: The axion-photon coupling constraint that can be achieved in this work. The solid lines show the constraints from the ALPS-I experiments AxionLimits, while the dashed lines show the constraints from this work and ALPS-II. The green shaded region indicates the detection region for $\chi$ within $(1,\, 10)$.