Abstract: A method and apparatus for detecting the moisture or filler content of dielectric material is disclosed which utilizes a submillimeter laser source of radiation scanned across the face of the material. A plurality of detectors, placed on the side of the material opposite the laser, supplies the material transmittance information to a microcomputer for calculating the moisture or filler content of the material. When thin dielectric materials and/or continuous scanning are utilized the submillimeter laser is pumped by a single CW (continuous wave) CO.sub.2 laser and when thicker dielectrics are measured with discrete pulses the submillimeter laser is pumped by a single TEA (Transversely Excited Atmospheric) CO.sub.2 laser. Depending on the transmission properties of the environment in which the apparatus operates, either the submillimeter laser beam or the infrared pump laser beam can be transmitted through the medium surrounding the apparatus in order to minimize pre-measurement attenuation of the beam.

Abstract: A system for detecting simultaneously the moisture content and basis weight of paper is disclosed utilizing a submillimeter laser source of radiation of two different wavelengths which is subsequently scanned across the face of the paper. A plurality of detectors placed on the side of the paper opposite the laser supplies the transmittance information for each of the wavelengths to a microcomputer which in turn calculates the moisture content and the basis weight of the material. The two different wavelengths of submillimeter radiation are produced by either a pair of submillimeter lasers pumped by a continuous wave CO.sub.2 laser or by a single submillimeter laser pumped by a waveguide type continuous wave CO.sub.2 laser whose output is controlled by a piezoelectric crystal tuned resonator in order to provide the required two separate wavelengths alternating in time which are output in the single beam of the submillimeter laser.

Abstract: A method and a device for measuring the fibre orientation anisotropy in a fibrous structure such as a sheet of paper or a textile. According to this method, a linearly polarized, far infrared laser beam is directed towards one side of the fibrous structure whose fibre orientation anisotropy is to be measured. The incident energy of the laser beam is measured before this beam traverses the fibrous structure, and its transmitted energy is measured on the other side of the fibrous structure. The transmission coefficient T of the laser beam is determined in at least two different orientations of the polarization plane of the beam with respect to the fibrous structure, this coefficient T being the ratio of the transmitted-to-incident energies. This coefficient T varies exponentially with the basis weight of the fibrous structure and the ratio .alpha.