  We investigate the recoil heating phenomenon experienced by a dielectric
spherical particle when it interacts with a linearly polarized plane wave
within the Rayleigh regime. We derive the fluctuating force acted upon the
particle arising from the fluctuations of the electromagnetic fields. Our
derivations reveal that the spectral density of the fluctuating force along the
propagation direction is $7\hbar \omega_0 P_{\mathrm{scat}}/5c^2$. Meanwhile,
along the direction of the electric and magnetic fields, it is $\hbar \omega_0
P_{\mathrm{scat}}/5c^2$ and $2\hbar \omega_0 P_{\mathrm{scat}}/5c^2$,
respectively. Here, $P_{\mathrm{scat}}$ denotes the power scattered by the
particle, $\hbar\omega_0$ represents the energy of a photon, and $c$ is the
speed of light. Recoil heating imposes fundamental limitations in levitated
optomechanics, constraining the minimum temperatures achievable in cooling
processes, the coherence time of the system, and the sensitivity of force
measurements.
