An apparatus for laser absorption spectroscopy comprising: a radiation source; a detector; and a sample cell comprising: at least one opening for receiving a beam from the radiation source into an inner volume (104, 114) of the sample cell and for allowing the beam to exit the sample cell to contact the detector; inner surfaces (202,404,452) of an outer wall of the sample cell at least partially defining the inner volume (104, 114)into which a beam of radiation from the source is received, the inner surfaces (202,404,452) defining a boundary of the inner volume; at least one reflective surface at each of two opposing ends in the inner volume; a first insert that reduces an excess gas volume within the inner volume through which the beam does not pass, wherein the first insert is sized and positioned at a location intermediate the reflective surfaces, the first insert reducing a clearance distance, defined as the closest approach between the beam and an innermost surface in the sample cell, whereby gas flows through the inner volume (104, 114) at locations within the inner volume through which the beam passes as well as through locations through which the beam does not pass; wherein the first insert is disposed adjacent to the inner surfaces and the sample cell comprises a second insert within the inner volume and wherein the second insert is sized and positioned at a location intermediate the reflective surfaces, the second insert further reducing the clearance distance in cooperation with the first insert so that the excess gas volume in the sample cell, through which the beam does not pass is minimized. a radiation source; a detector; and a sample cell comprising: at least one opening for receiving a beam from the radiation source into an inner volume (104, 114) of the sample cell and for allowing the beam to exit the sample cell to contact the detector; inner surfaces (202,404,452) of an outer wall of the sample cell at least partially defining the inner volume (104, 114)into which a beam of radiation from the source is received, the inner surfaces (202,404,452) defining a boundary of the inner volume; at least one reflective surface at each of two opposing ends in the inner volume; a first insert that reduces an excess gas volume within the inner volume through which the beam does not pass, wherein the first insert is sized and positioned at a location intermediate the reflective surfaces, the first insert reducing a clearance distance, defined as the closest approach between the beam and an innermost surface in the sample cell, whereby gas flows through the inner volume (104, 114) at locations within the inner volume through which the beam passes as well as through locations through which the beam does not pass; wherein the first insert is disposed adjacent to the inner surfaces and the sample cell comprises a second insert within the inner volume and wherein the second insert is sized and positioned at a location intermediate the reflective surfaces, the second insert further reducing the clearance distance in cooperation with the first insert so that the excess gas volume in the sample cell, through which the beam does not pass is minimized. at least one opening for receiving a beam from the radiation source into an inner volume (104, 114) of the sample cell and for allowing the beam to exit the sample cell to contact the detector; inner surfaces (202,404,452) of an outer wall of the sample cell at least partially defining the inner volume (104, 114)into which a beam of radiation from the source is received, the inner surfaces (202,404,452) defining a boundary of the inner volume; at least one reflective surface at each of two opposing ends in the inner volume; a first insert that reduces an excess gas volume within the inner volume through which the beam does not pass, wherein the first insert is sized and positioned at a location intermediate the reflective surfaces, the first insert reducing a clearance distance, defined as the closest approach between the beam and an innermost surface in the sample cell, whereby gas flows through the inner volume (104, 114) at locations within the inner volume through which the beam passes as well as through locations through which the beam does not pass; wherein the first insert is disposed adjacent to the inner surfaces and the sample cell comprises a second insert within the inner volume and wherein the second insert is sized and positioned at a location intermediate the reflective surfaces, the second insert further reducing the clearance distance in cooperation with the first insert so that the excess gas volume in the sample cell, through which the beam does not pass is minimized.