As mentioned earlier, OM structures are formed by the combination of different optical forces. Therefore, for a specific type of particle, the structural arrangement will be mostly dictated by the properties of the light used (wavelength, polarization, power density, area irradiated…). We expect the position of the trapping laser relative to the interface to directly impact the arrangement and crystallinity of the optical matter formed. Henceforth, we used the FRAME to investigate this effect. By focusing the laser at different Z depths (-1.5 µm, -2.5 µm, and -3.5 µm), we were able to study how the relative position of the laser focus to the interface influenced the 3D structure of the optical matter.From the backscattered intensity profile at the focal spot, we determined the beam waist radius (w0) to be approximately 1.8 µm, with a power density (I0) of 19.6 MW/cm². The beam waist diameter at Z-depths of -1.5 µm, -2.5 µm, and -3.5 µm was calculated as 2.13 µm, 2.66 µm, and 3.15 µm, respectively, with corresponding power densities of 14 MW/cm², 8.97 MW/cm², and 6.41 MW/cm² (Figure ). For details, see Section S3.