Fig. 1. Structure and parameters of thin films. (a) Diagram of the thin-film structure; (b) optical constants of the materials; (c) melting points and deposition rates.

Fig. 2. Color distribution and electric field regulation. (a) The color of the thin films and reflectance at the central wavelength (λ₀ = 1064 nm) vary by changing the optical thickness of dielectrics. (b)–(c) The electric field intensity distribution changes with the thickness of each dielectric in the same total optical thickness. (d) The maximum and Al layer surface electric field intensity of each film.

Fig. 3. Characterizations on color saturation control. (a)–(c) Saturation of structure γ (n = 1) varies by changing the thickness of the Nb layer; (d)–(f) saturation of structure γ (n = 2) varies by changing the thickness of the Nb layer.

Fig. 4. Preparation of different samples. (a) Samples on Al foil and BK7 substrates; (b) chromaticity coordinates of samples; (c) measurement and design spectra of S₁; (d) measurement and design spectra of S₃; electric field distributions of (e) S₁ and (f) S₃ at the wavelength of 1064 nm.

Fig. 5. Schematic diagram of a laser testing device.

Fig. 6. Laser irradiation test results. (a) Test curve of laser irradiation on single-layer Al; (b) test curve of laser irradiation on S₁; (c) single-layer Al micrograph of the front after irradiation; (d) S₁ micrograph of the front after irradiation; (e) single-layer Al micrograph of the back after irradiation; (f) S₁ micrograph of the back after irradiation.

Fig. 7. Series of SEM images. (a) Surface morphology of S₁ exhibiting crack damage; (b) surface morphology of S₁ exhibiting an ablative hole. (c) Surface morphology of S₁ exhibiting a trace of irradiation under an unbroken test. (d) Cross section of 100 nm single-layer Al; (e) cross section of S₃; (f) cross section of S₃ irradiated with the highest power density laser for 60 s.

Fig. 8. Verification and application of thin films with symmetrical structure. (a) Schematic diagram of symmetrical S₁ structure on the base; (b) front side and back side spectra of symmetrical S₁; (c) colors of front side and back side. (d) cross section of symmetrical S₁; (e) collection of S₁ microreflectors; (f) coating spraying effect.