The embodiments of the present invention are directed to addressing the complexity, sample geometry, and even pressure feedback issues associated with mechanical-only mechanisms. In particular, by utilizing one or more bellows capsules in an attenuated total internal reflection (ATR) instrument as a pressure vessel that can expand, contract, and tilt in all directions, the mechanisms disclosed herein can substantially apply uniform pressure to an interposed sample surface to include non-orthogonal sample surfaces, and thus conform to any sample geometry within such instruments. The result of the novel arrangements described herein is to provide a user with a convenient and simple interface for operating the interrogating ATR optical instrument.