Self-suspended polyimide (PI) composite films were fabricated. Their diameter and thickness were 2.5 in. and 260 nm, respectively. A high ratio of diameter to thickness of 2.4 × 105 was obtained. The multiwalled carbon nanotubes (MWCNTs) were filled into PI to improve the optical absorption and the photothermal response. By using the N-methyl pyrrolidone solvent for both MWCNTs and poly(amic acid), a homogeneous dispersion of MWCNTs with up to 15% content was obtained. Under the thermal treatment of 300 °C, the composite films were successfully synthesized, which was proved by the measurements of Fourier transform infrared spectrum and x-ray diffraction. Compared with the pure PI film, the optical absorption of the composite films at 532 nm wavelength increased from 10% to 28%. The steady and transient photothermal properties of the composite films were investigated. In the steady state, a temperature rise of 145 °C was obtained under 0.7 W/cm2 illuminating laser power density. The temperature increased by 29 times compared with that of the pure PI film. The corresponding photothermal conversion efficiency improved to 70.8%. In the transient state, the photothermal response time was 7.5 ms, which was only half that of the pure PI film. The excellent photothermal properties of these self-suspended MWCNT/PI composite films highlight their potential applications in micro- and nanoscale devices for photo detection and thermal imaging.

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A radiofrequency (RF)/infrared (IR) beam combiner is used to combine IR signals and RF signals into a common transmission axis. In this study, a dual‐band wide‐angle RF/IR beam combiner with high RF transmission and IR reflection was proposed. Based on the impedance matching principle, the RF/IR beam combiner consisted of a high reflective IR film, an IR substrate, and two RF matching layers. Multi‐objective particle swarm algorithm was applied to optimise the relative permittivity and the thicknesses of the IR substrate and the RF matching layers. A higher than 75% RF transmittance was obtained in both 8–12 GHz and 34–36 GHz bands when the RF incident angle was varied from 30° to 62°. At the same time, the reflectance in 8–12 μm was as high as 96%. It could be used in the hardware‐in‐the‐loop simulation systems to test and evaluate the detecting and tracing performances of the RF/IR dual‐mode guidance devices.