AN IMPROVED SAMPLE HOLDER

The present invention is directed to a sample holder for use in molecular absorption spectroscopy. The sample holder comprises a first surface having a first predetermined geometry. and a second surface having a second predetermined geometry. The first surface is opposite the second surface. The sample holder is configured to hold a measurement sample between the first surface and the second surface such that a distance between the first surface and the second surface defines an optical pathlength of the sample holder. The predetermined geometries of the first surface and the second surface provides a continuously variable cross-section across the sample holder so as to provide a continuous range of optical pathlengths.