From this observation, we can conclude that beyond t = 60 s, the thermophoretic force is sufficiently small relative to thermal diffusion, indicating that the thermophoretic behavior has reached a steady state. In this way, evaluating the time-evolving thermophoretic force using MSD in Brownian dynamics is possible. However, for forces with spatial distribution, such as the thermophoretic force, the MSD value is highly dependent on the initial positions and distribution of the PSNPs. In particular, in the current system, the MSD value is determined by the ratio of PSNPs positioned within the thermophoretically dominant region (within 20 μm from the center) to those in the Brownian motion-dominated region. Therefore, when evaluating thermophoresis using only MSD, the results are highly dependent on the observation system, making it difficult to directly compare results obtained with different observation systems. To interpret the results in Fig. , which depend on the initial positions of the PSNPs, we here quantitatively calculate the thermophoretic force. Fig. shows the radial distribution of the averaged absolute thermophoretic force ⟨|𝑭 𝑡𝑝ℎ |⟩ and the averaged absolute random force driving Brownian motion ⟨|𝑭 𝐵 |⟩ centered on the laser spot.