An anesthetic and respiratory gas monitoring apparatus adapted to (i) identify a target anesthetic or respiratory gas species and (ii) determine a concentration of the identified target anesthetic or respiratory gas species, the apparatus comprising: a multi-spectral mosaic filter and lens array that comprises a two-dimensional array of paired lens structures and long wave infrared band-pass filter elements configured to receive a broadband infrared energy beam and to focus and spectrally filter the received broadband IR energy beam into a plurality of focused and spectrally filtered IR beams, the mosaic filter and lens array further having at least one of (i) a patterned thermally reflective metal layer overlying a first surface at least between adjacent lens structures of the paired lens structures and long wave IR band-pass filter elements and (ii) a patterned thermally reflective metal layer overlying a second surface at least between adjacent filter elements of the paired lens structures and long wave IR band-pass filter elements; a composite thermal sensing focal plane array that comprises a plurality of individual thermal sensing focal plane arrays with integrated read out integrated circuits, wherein each of the individual thermal sensing focal plane arrays is provided for and spaced a distance from a respective paired lens structure and filter element (14,16) of the mosaic filter and lens array, the multi-spectral mosaic filter and lens array and the composite thermal sensing focal plane array being arranged such that each of the plurality of focused and spectrally filtered IR beams is directed onto a respective surface of an individual thermal sensing focal plane array and having a focused spot size less than a total surface area of the respective surface, with a remaining unexposed area of the respective surface outside the focused spot being thermally dark and used for dark baseline subtraction, wherein, responsive to receiving the focused and spectrally filtered IR beams, each respective integrated read out integrated circuit (ROIC) of a corresponding individual thermal sensing focal plane array outputs a respective sensed channel data; and a signal processor operatively coupled to receive the sensed channel data outputs of each respective integrated read out integrated circuit (ROIC) of a corresponding individual thermal sensing focal plane array, wherein the signal processor is adapted to generate an output signal indicative of at least one of an identification and a concentration of a target gas selected from the group consisting of one or more anesthetic and respiratory gas species, based on an oversampling of an absorption signal on at least one or more of (i) a frame by frame basis and (ii) an image stacking basis of the sensed channel data outputs, with dark baseline subtraction. a multi-spectral mosaic filter and lens array that comprises a two-dimensional array of paired lens structures and long wave infrared band-pass filter elements configured to receive a broadband infrared energy beam and to focus and spectrally filter the received broadband IR energy beam into a plurality of focused and spectrally filtered IR beams, the mosaic filter and lens array further having at least one of (i) a patterned thermally reflective metal layer overlying a first surface at least between adjacent lens structures of the paired lens structures and long wave IR band-pass filter elements and (ii) a patterned thermally reflective metal layer overlying a second surface at least between adjacent filter elements of the paired lens structures and long wave IR band-pass filter elements; a composite thermal sensing focal plane array that comprises a plurality of individual thermal sensing focal plane arrays with integrated read out integrated circuits, wherein each of the individual thermal sensing focal plane arrays is provided for and spaced a distance from a respective paired lens structure and filter element (14,16) of the mosaic filter and lens array, the multi-spectral mosaic filter and lens array and the composite thermal sensing focal plane array being arranged such that each of the plurality of focused and spectrally filtered IR beams is directed onto a respective surface of an individual thermal sensing focal plane array and having a focused spot size less than a total surface area of the respective surface, with a remaining unexposed area of the respective surface outside the focused spot being thermally dark and used for dark baseline subtraction, wherein, responsive to receiving the focused and spectrally filtered IR beams, each respective integrated read out integrated circuit (ROIC) of a corresponding individual thermal sensing focal plane array outputs a respective sensed channel data; and a signal processor operatively coupled to receive the sensed channel data outputs of each respective integrated read out integrated circuit (ROIC) of a corresponding individual thermal sensing focal plane array, wherein the signal processor is adapted to generate an output signal indicative of at least one of an identification and a concentration of a target gas selected from the group consisting of one or more anesthetic and respiratory gas species, based on an oversampling of an absorption signal on at least one or more of (i) a frame by frame basis and (ii) an image stacking basis of the sensed channel data outputs, with dark baseline subtraction.