QuasAr2-mOrange2 is a genetically encoded voltage indicator that acts as a fluorescent reporter for membrane voltage with improved sensitivity. It consists of the 'QuasAr2' voltage-sensitive sequence fused to the mOrange2 fluorescent protein. QuasAr2 is a mutated form of the Halorubrum sodomense Archaerhodopsin-3 (aop3) gene (UniProtKB:P96787) that contains the amino acid replacements P60S, T80S, D95Q, D106H and F161V relative to the wild-type aop3 sequence. QuasAr2 does not generate a photocurrent, and thus does not generate membrane hyperpolarization (PMID:24952910).