One of the essential ingredients in existing polar gap models (e.g. Ruderman & Sutherland 1975; Arons & Scharlemann 1979, hereafter AS) is a pair cascade above polar caps. In these models, pair cascade is initiated by curvature photons radiated by primary particles and produced pairs screen out the electric field, forming a pair-production-limited acceleration zone (called the polar gap). For pulsars with strong magnetic fields (B ≳ 1012 G) and hot polar caps, resonant inverse Compton scattering (RICS) can be important (e.g. Dermer 1990; Sturner 1995, and references therein). The gap height is significantly reduced by the RICS effect (Luo 1996), and this may reduce the energetics of the polar gap as the maximum energy of primary particles is constrained by the gap height. The minimum temperature for RICS to be important is (Luo 1996)