Abstract: An absorption spectroscopy instrument is provided with a re-injection mirror to greatly increase the optical power coupled into an optical cavity, comprised of two or more mirrors, for the purpose of increasing the quality of absorption and extinction measurements made in the cavity. Light reflected from the first cavity mirror upon which a light beam is incident, can be efficiently collected and back reflected onto the same mirror, effectively producing a plurality of optical injections into the cavity. The instrument can be used for off-axis cavity ringdown spectroscopy, off-axis integrated cavity output spectroscopy, or other cavity-based spectroscopy applications.

Abstract: The disclosure describes an absorption spectroscopy method for sensing hydrogen gas in a sample atmosphere and an associated hydrogen sensor. A light beam, having a wavelength corresponding to a vibrational transition of hydrogen molecules from a ground vibration state to any excited rotational vibration state via a quadrupole interaction, is introduced into an optical cavity adapted to receive a sample atmosphere to be tested for the presence of hydrogen gas. The light is introduced into the cavity in an off-axis alignment to systematically eliminate cavity resonances, while preserving the absorption signal amplifying properties of such cavities. Hydrogen absorption is measured is terms of cavity output, as in the ICOS technique.

Abstract: The disclosure describes an absorption spectroscopy method for sensing hydrogen gas in a sample atmosphere and an associated hydrogen sensor. A light beam, having a wavelength corresponding to a vibrational transition of hydrogen molecules from a ground vibration state to any excited rotational vibration state via a quadrupole interaction, is introduced into an optical cavity adapted to receive a sample atmosphere to be tested for the presence of hydrogen gas. The light is introduced into the cavity in an off-axis alignment to systematically eliminate cavity resonances, while preserving the absorption signal amplifying properties of such cavities. Hydrogen absorption is measured is terms of cavity output, as in the ICOS technique.

Abstract: An integrated-cavity output spectroscopy (ICOS) instrument adapted for measuring liquid samples has a low-scatter flow cell arrangement passing through a stable optical cavity defined by an arrangement of two or more mirrors. The flow cell provides a sample volume within the cavity of at most one microliter at any given time. The optical cavity has an effective cavity length of at most one centimeter and mirror radii of curvature for the stable cavity arrangement are much longer than the cavity length. A light beam with stable characteristics is introduced into the cavity, passes through the liquid sample cell multiple times, and a detector measures a portion of the light from the cavity. The light measurement is analyzed to determine absorption by the liquid sample, and related information.

Abstract: This patent describes a new method and apparatus which allows optical cavities to be used simply and effectively as absorption cells for the purpose of performing sensitive absorption spectroscopy. This method introduces a continuous-wave light beam into the cavity using an off-axis cavity alignment geometry to systematically eliminate the resonances commonly associated with optical cavities, while preserving the absorption signal amplifying properties of such cavities. This reduces the complexity of the apparatus considerably compared with other optical cavity-based absorption methods when applied in conjunction with either cavity ringdown spectroscopy or integrated cavity output spectroscopy. This method can also be used to characterize other optical loss processes occurring within the cavity such as scattering or total extinction coefficients, and to determine the losses due to the cavity mirrors themselves (reflectometry).

Abstract: Chemically specific fiber and waveguide sensors are formed in a fiber optic or optical waveguide material in which injected light is trapped within a Bragg grating optical cavity. The Bragg cavity effectively traps the light for long times, corresponding to effective path lengths equal to hundreds or thousands of meters in the fiber or waveguide medium. The Bragg grating optical cavity is surrounded by a cladding of chemically sensitive material whose optical properties change when exposed to specific chemicals or classes of chemicals. The change in the optical properties of the cladding results in a change in the light trapping characteristics of the fiber or waveguide. Changes in optical transmission of the fiber optic or waveguide sensor can then be related to the concentration of specific chemicals or classes of chemicals in the environment surrounding the sensor.