A miniaturized photoreactor based on a hollow-core metal cladding waveguide

We present a novel reactor based on the ultrahigh order modes in a hollow-core metal cladding waveguide (HCMW). Aqueous Fe2+/Fe3+ salt solutions in the hollow-core act as the HCMW guiding layer. Light power is induced into the guiding layer using the free-space coupling technique. A series of enhanced power points, considered to be optical trapping points, are formed because of the excitation of the ultrahigh-order modes. It is demonstrated that, at these optical trapping points, crystalline magnetite γ-Fe2O3 is synthesized after the deionized water is photolyzed into OH−. The magneto-optical effect of this γ-Fe2O3 is explored for potential applications.