FAST ELECTROCHROMIC SWITCHING FOR OPTICAL HARDENING APPLICATIONS

A PROGRAM TO DEVELOP ELECTROCHROMIC DEVICES CAPABLE OF FAST TRANSMISSIVE TO REFLECTIVE OPTICAL SWITCHING IS PROPOSED. THESE DEVICES WOULD BE USED FOR OPTICAL HARDENING IN THE WAVELENGTH RANGE FROM 0.615 MICROMWTERS. OPTICAL SWITCHING ELEMENTS BASED ON SINGLE CRYSTAL LAYERS OR EPITAXIAL FILMS OF THE METAL DICHALOCOGENIDES ZRS(2) AND HF(2) WOULD BE DEVELOPED. WE PROPOSE TO INTERCALATE SINGLE CRYSTALS OF ZRS(2) AND HFS(2) WITH LII. UNDER THE APPLICATION OF AN EXTERNALLYAPPLIED CURRENT PULSE, THE LII WILL UNDERGO A REDUCTION/OXIDATION REACTION THAT CONTRIBUTES A FREE-ELECTRON TO THE CONDUCTION BAND OF THE HOST CRYSTAL. THE PROPOSED DEVICES WOULD HAVE A VARIABLE FREEELECTRON DENSITY THAT COULD BE CONTROLLED BETWEEN <10(16) TO 10(22) -E/CUBIC CENTIMETERS. THE LARGE VARIATION OF FREE-ELECTRON DENSITY ALLOWS THE WAVELENGTH AND DEGREE OF SPECULAR REFLECTANCE TO BE MODULATED. OPTICAL SWITCHING WOULD BE ACHIEVED IN A 3-LAYER DEVICE COMPRISED OF THE OPTICALLY ACTIVE ELEMENT (ZRS(2)/LII OR HFS(2)/LII AND TWO TRANSPARENT ELECTRODES. A MODEST CURRENT PULSE (<200 MA/SQUARE CENTIMETERS) WOULD BE USED TO SWITCH THE DEVICE FROM TRANSMITTING TO REFLECTING. BY HAVING THE LII REDUCTION/OXIDATION CENTERS HOMOGENEOUSLY DISTRIBUTED IN THE VAN DER WALLS' GAPS OF THE ZRS(2)/LII AND HFS(2)/LII CRYSTLS, THE OPTICAL SWITCHING SHOULD BE EXTREMELY RAPID. THE GOAL OF THE PROPOSED RESEARCH IS TO DEVELOP OPTICAL HARDENING DEVICES THAT UNDERGO REVERSIBLE TRANSMISSIVE TO REFLECTIVE SWITCHING IN <10 TO THE MINUS SIX POWER SECONDS.