The present disclosure provides a balloon system for mitigating solar radiation. The balloon system reflects solar radiation away from the earth. The balloon system includes at least one balloon having an outer surface for reflecting solar radiation. An orbital launching system launches the balloon to a set orbital location at which the balloon can orbit around earth in a path of solar radiation from the sun toward earth. At the set orbital location, the earth's gravitational force and solar pressure imparted on the balloon counterbalance the sun's gravitational force on the balloon. The set orbital location is spaced apart from a Lagrange stability point L1 in a direction toward the sun and away from the earth.

A reflective member having transflective and substantially opaque regions is disclosed. The transflective region may serve as a sensor opening region. When viewing the member from a first direction, the difference between a total light reflectance of the member at the substantially opaque region and at the sensor opening region is less than five percent. Additionally, when viewing the member from the first direction, the difference between a color reflectance of the member at the substantially opaque region and at the sensor opening region is less than 5 delta C* units. A sensor disposed in a second direction of the sensor opening region of the member is operable to receive light through the member at the sensor opening region. The second direction is opposite the first direction.

A multilayer thin film that reflects an omnidirectional structural color including a multilayer stack. The multilayer stack includes a reflector layer; a selective absorber layer extending over the reflector layer; an absorbing layer extending over the first layer; and a dielectric layer extending over the second layer. The multilayer thin film reflects a single narrow band of visible light when exposed to broadband electromagnetic radiation, the single narrow band of visible light having a center wavelength greater than 550 nm, and a visible full width at half maximum (FWHM) width of less than 200 nm. A color shift of the reflected single narrow band of visible light is less than 50 nm when the multilayer stack is exposed to broadband electromagnetic radiation and viewed from angles between 0 and 45 degrees relative to a direction normal to an outer surface of the multilayer thin film.

A highly reflective mirror for use in the wavelength range of 0.300 μm to 15 μm includes a substrate, a first interface layer, a reflective layer, a second interface layer, a plurality of tuning layers including a combination of a low index material and a high index material wherein the high index material is HfO.sub.2, and a protective layer. The highly reflective mirror has a reflectivity of at least 90% over the wavelength range of 335 nm to 1000 nm at an angle of incidence (AOI) of 45°.

A micromechanical mirror structure includes a mirror element designed to reflect an incident light radiation and a protective structure arranged over the mirror element to provide mechanical protection for the mirror element and to increase the reflectivity of the mirror element with respect to the incident light radiation. The protective structure has a first protective layer and a second protective layer which are stacked on the mirror element. The second protective layer is arranged on the first protective layer and the first protective layer is arranged on the mirror element. The layers include a respective dielectric material and having respective refractive indexes that jointly increase the reflectivity of the mirror element in a range of wavelengths of interest.

A high-efficiency, multiwavelength beam-expander optical system that employs dielectric-enhanced mirrors is disclosed. Each mirror includes a reflective multilayer coating formed from alternating layers of HfO.sub.2 and SiO.sub.2 that define, in order from the substrate surface, at least first and second sections, wherein the HfO.sub.2/SiO.sub.2 layer thicknesses are generally constant within a given section and get smaller section by section moving outward from the substrate surface. The first and second sections are respectively configured to optimally reflect different operating wavelengths so that the beam-expander optical system has an optical transmission of greater than 95% at the different operating wavelengths.

An omnidirectional multilayer thin film is provided. The multilayer thin film includes a multilayer stack having a first layer of a first material and a second layer of a second material, the second layer extending across the first layer. The multilayer stack reflects a narrow band of electromagnetic radiation having a full width at half maximum (FWHM) of less than 300 nanometers (nm) and a color of less than 50 nm when the multilayer stack is exposed to broadband electromagnetic radiation and viewed from angles between 0 and 45 degrees. In some instances, the multilayer stack has a total thickness of less than 2 microns (μm). Preferably, the multilayer thin film has a total thickness of less than 1.5 μm and more preferably less than 1.0 μm.

A reflective optical element, in particular for a DUV or VUV operating wavelength range, includes a substrate, a dielectric layer system and a metallic coating between the substrate and the dielectric layer system. The dielectric layer system (26) includes a layer (L) of material having a lower refractive index n1 at the operating wavelength, a layer (H) of material having a higher refractive index n2 at the operating wavelength and a layer (M) of material having a refractive index n3 at the operating wavelength, where n1<n3<n2. The layer (M) is arranged at at least one transition from a layer (L) to a layer (H) and/or from a layer (H) to a layer (L). The dielectric layer system has a four-layer sequence of (LMHM)m or (HMLM)m, where m is equal to the number of four-layer sequences in the dielectric layer system.

A solid-state thermochromic device and method for producing the device, the device including: a stack successively including, from a rear face to a front face exposed to solar radiation: a) a solid substrate of an inorganic material resistant up to a temperature of 550° C.; b) an infrared-reflective layer of an electronically conductive material; c) electronically insulating interface layers; d) an electronically insulating inorganic dielectric layer transparent to infrared radiation, of cerium oxide CeO2, with a thickness between 400 and 900 nm; e) electronically insulating interface layers; f) a layer of an infrared-active thermochromic material, an n-doped VO.sub.2 vanadium oxide, and crystallized in a monoclinic or rutile phase, with a thickness between 30 and 50 nm; and g) a solar-protective coating, transparent to infrared radiation.

A reflecting element includes a first reflecting film to reflect light and a second reflecting film configured to increase a reflectivity of the first reflecting film. The second reflecting film includes a layer of high-refractive-index material and a layer of low-refractive-index material with a refractive index lower than the layer of high-refractive-index material. The layer of low-refractive-index material is a top layer of the second reflecting film.