The result is visually (near) identical to the single-mode case due to the van-Hove-type singularity in the 1D DOS, depicted in the dashed curve. Fig. presents k/k 0 for many Q j DOF coupled to many modes inside a 2D FP cavity, using Eq. 8 with α = 0.7, and the k 2D VSC expression in Eq. 22, with the parameter D = 3.33 µm, which is a typical value estimated from the VSC experiments . The numerical integration in Eq. 22 is evaluated using trapezoidal integration, with the numerical details provided in Supplementary Note 9. One can see that the resonance peak is still sharply centered around ω c = ω Q , where ω c is the normal incidence frequency in a 2D FP cavity. Compared to the single mode or 1D case (Fig. ), the k/k 0 distribution is slightly red-shifted, and the resonance peak is asymmetric as it tails toward the lower energy regions (ω c < ω 0 ), which is a prediction form the current theory k 2D VSC (Eq. 22). In recent VSC experiments by Simpkins , it does seem that the ω c < ω 0 side has a longer tail than the ω c > ω 0 side of the action spectrum (see Fig. of Ref. 10). However, this seemingly asymmetrical rate constant profile in Ref. 10 could be caused by a lack of experimental data points for a blue-tuned cavity (ω c > ω 0 ) due to the experimental difficulty of obtaining such measurements. More experimental data are required to test this trend.