Long-wave Infrared Imaging Systems Research Articles

Fabrication of Plastic Optics from Chalcogenide Hybrid Inorganic/Organic Polymers for Infrared Thermal Imaging

AbstractThe development of infrared (IR) plastic optics for infrared thermal imaging, particularly, in the long‐wave IR (LWIR) spectrum (7–14 µm) is an area of growing technological interest due to the potential advantages associated with plastic optics (e.g., moldability and low cost). The development of a new class of optical polymers, chalcogenide‐based inorganic/organic hybrid polymers (CHIPs) derived from the inverse vulcanization of elemental sulfur, has enabled significant improvements in IR transparency due to reduction of IR absorbing organic comonomer units. The vast majority of effort has focused on new chalcogenide hybrid polymer synthesis and optical property improvements (e.g., refractive index, Abbe number, and LWIR transmission); however, fabrication and IR imaging methodology to prepare optical components has not been demonstrated, which remains critical to develop viable IR plastic optics. A new methodology is reported to fabricate optical components and evaluate LWIR imaging performance of this emerging class of optical polymers. New diffractive flat optics with a Fresnel lens design for these materials have been developed, along with a basic LWIR imaging system to evaluate CHIPs for LWIR imaging. This system‐based approach enables correspondence of copolymer structure‐property correlations with LWIR imaging performance, along with demonstration of room temperature LWIR imaging.

Performance evaluation of common-aperture visible and long-wave infrared imaging system based on a comprehensive resolution

Abstract In this article, a new method based on a comprehensive resolution is proposed to evaluate the performance of a common-aperture visible and long-wave infrared (LWIR) imaging system. The influence of the comprehensive resolution on target recognition range is analyzed. Under the condition of common-aperture and a combination of four comprehensive resolutions, the main factors affecting the ratio of target recognition range between the visible imaging system and the LWIR imaging system are discussed. Combined with the constraints of the optical system and the detector, the impact of the comprehensive resolution on the target recognition range is analyzed. The ratio of the target recognition range of the two imaging systems is modeled using the comprehensive resolution of the visible imaging system. The experimental system is built and the experimental results are acquired. The predictive results and experimental results show that when the comprehensive resolution of the visible light imaging system increases, the target recognition ranges of the visible light imaging system and the LWIR imaging system increase, as well as the ratio of the target recognition ranges of the two systems increases.

Simulation for multiwavelength large-aperture all-silicon metalenses in long-wave infrared

Long-wave infrared imaging systems are widely used in the field of environmental monitoring and imaging guidance. As the core components, the long-wave infrared lenses suffer the conditions of less available materials, difficult processing, large volume and mass. Metalens composed of sub-wavelength structures is one of the most potential candidates to achieve a lightweight and planar optical imaging systems. Meanwhile, it is essential to obtain large-aperture infrared lenses with high power and high resolution. However, it is difficult to use the finite-difference time-domain method to simulate a large-aperture metalens with the diameter of 201 mm due to the large amount of computational memory and computational time required. Here, to solve the mentioned problem, we firstly propose a simulation method for designing a large-aperture metalens, which combines the finite-difference time-domain algorithm and diffraction integration. The finite-difference time-domain algorithm is used to simulate the meta-atom’s transmitted complex amplitude and the one-dimensional simplification of the diffraction integral is to calculate the focused field distributions of the designed metalens. Furthermore, the meta-atom spatial multiplexing is applied to design the all-silicon metalenses with the aperture of 201 mm to realize dual-wavelength (10 and 11 μm) achromatic focusing, super anomalous dispersion focusing and super normal dispersion focusing. The designed metalenses are numerically confirmed, which reveal the feasibility of all-silicon sub-wavelength structures to accomplish the multiwavelength dispersion control. The designed all-silicon metalenses have the advantage of lightweight and compact. The proposed method is effective for the development of large-aperture imaging systems in the long-wave infrared.

Gas Leak-Detection and Measurement Systems: Prospects and Future Trends

The article presents the findings of main recent research and development works conducted for gas leak detection and measurement. Higher emphasis are considered for 2-D arrays sensors because of the wider coverage area they can handle in real-time, especially if they are carried within moving vehicles such as drones, helicopters, and satellites. This includes long-wave infrared (LWIR)- and medium-wave infrared (MWIR)-imaging systems. In spite of their success to accurately detect, localize, and even quantify leaks, under certain conditions, LWIR and MWIR imaging systems still face several challenges. This prevented them to continuously operate in all environmental conditions and within a reasonable long period of time. Thus, the article also presents other alternative technologies which can potentially complement or substitute LWIR and MWIR techniques. This includes photoacoustic, temperature profiling, and short-wave infrared (SWIR)-based techniques. The article can be a useful resource to help deciding which of these techniques can be used for a particular gas leak-detection application.

微偏振片阵列型长波红外成像系统定标方法

微偏振片阵列型长波红外成像系统定标方法

Measuring radiant emissions from entire prescribed fires with ground, airborne and satellite sensors – RxCADRE 2012

Characterising radiation from wildland fires is an important focus of fire science because radiation relates directly to the combustion process and can be measured across a wide range of spatial extents and resolutions. As part of a more comprehensive set of measurements collected during the 2012 Prescribed Fire Combustion and Atmospheric Dynamics Research (RxCADRE) field campaign, we used ground, airborne and spaceborne sensors to measure fire radiative power (FRP) from whole fires, applying different methods to small (2 ha) and large (>100 ha) burn blocks. For small blocks (n = 6), FRP estimated from an obliquely oriented long-wave infrared (LWIR) camera mounted on a boom lift were compared with FRP derived from combined data from tower-mounted radiometers and remotely piloted aircraft systems (RPAS). For large burn blocks (n = 3), satellite FRP measurements from the Moderate-resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors were compared with near-coincident FRP measurements derived from a LWIR imaging system aboard a piloted aircraft. We describe measurements and consider their strengths and weaknesses. Until quantitative sensors exist for small RPAS, their use in fire research will remain limited. For oblique, airborne and satellite sensors, further FRP measurement development is needed along with greater replication of coincident measurements, which we show to be feasible.