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We clarify the claims and errors in the paper "Criterion for NegativeRefraction with Low Optical Losses from a Fundamental Principle of Causality"by Mark Stockman. Contrary to the central assertion in that paper, simpleexamples consistent with the basic inequality which Stockman discovered showthat it is possible to have negative refraction and low loss in an arbitrarilylarge frequency window. Further examination of the paper reveals additionalerrors that invalidate his argument that active materials cannot have low lossand negative refraction in a frequency window. Also, we point out that foractive materials non-analyticity of the electrical permittivity in the upperhalf complex frequency plane does not necessarily imply noncausality, asStockman infers.

Further comments on Mark Stockman's article "Criterion for Negative Refraction with Low Optical Losses from a Fundamental Principle of Causality"