Cold mirrors

Heat- and light-separation coatings (also known as hot and cold mirrors) are important applications that separate the hot (infrared) from the cold (visible) radiation. The principle is shown schematically inFig. 16.2. The transmittance of a cold mirror is shown in Fig. 16.3a. This mirror is coated with a dielectric film reflecting more than 90% of the... 

Hot- and cold-mirror CVD coatings are used in projectors to maintain the film gate at low temperature and avoid damaging the film. They are also used increasingly in tungsten-halogen lamps. 

These changes in temperature represent a macroscopic proof that microscopic processes do occur. Indeed, it is difficult to envisage a transfer of energy between the gas particles with the cold mirror without these microscopic interactions. 

Example of a cold mirror reflector. (Courtesy of Horde UV America.)... 

Cold mirror A reflector that is coated by a dichroic material that absorbs or passes wavelengths in the infrared region while reflecting those in the UV range. 

Dichroic reflector A reflector having reduced reflectance to long wavelengths (IR radiation) also called "cold mirror."... 

Similar principles can be used for designing selective absorbers, where the goal is absorb as much of the solar spectrum as possible and convert that absorbed energy into heat, or thermal energy. Conversely, reflective materials can be designed to select only visible (cold mirror) or infrared (hot mirrors) to isolate and direct selected portions of the solar spectrum for various applications. 

Fig. 9.4 Time evolution of PEC water splitting on a Ir02/Ta0N electrode under visible light (of wavelength longer than 420 nm) illumination using a 300 W Xe lamp (Cermax equipped with a cold mirror CM2, a cut-oflf filter Hoya L42) at 0.8 V versus Pt in an aqueous 0.1 M Na2S04 electrolyte at 288 K. Stoichiometric H2 02 (2 1) gas production was observed. Adapted from Ref. [10]...

When a cold mirror is used the main product is the diarsine. It seems that methylene radicals also react with arsenic mirrors though in this case the products have not been identified (35). Phenylarsines are produced when phenyllithium or phenylmagnesium bromide react with arsenic 36), when phenyldiazonium chloride is decomposed by chalk in the presence of arsenic (37), and when tetraphenyltin is heated with arsenic 37a). These reactions are also believed to involve free radicals. 

A reflective surface can be specular (mirror-like, glossy) or diffuse. Fig. 2.34. The retroreflective surfaces return the beam in the direction the incident light came from. Regardless of the type of reflectivity, most of the radiation is returned from the illuminated surface toward the radiation source. This radiation can be practically unchanged or can be shifted in liequency spectrum, either toward higher or toward lower frequencies ( hot and cold mirrors). 

In addition to reflective, colored, and AR coatings, more recent optical applications include contrast enhancement filters [15,21], cold mirrors [15-21], patternable thick films for diffraction gratings [41] and optical memory disks [41,42], and ferroelectric films [38-40,58-67] (PLZT, KNbOj, or LiNbOs) for optoelectronic and integrated optics applications [38-40],... 

Cold mirror (optics) A thin film structure that reflects shorter wavelengths (typically visible) while transmitting longer wavelengths (IR). See also Heat mirror. 

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