Cavity enhanced laser based gas analyzer systems and methods

Inventors

Kachanov, Alexander • Koulikov, Serguei

Assignees

Li Cor Inc

Abstract

Cavity enhanced absorption spectroscopy systems and methods for detecting trace gases using a resonance optical cavity, which contains a gas mixture to be analyzed, and a laser coupled to the cavity by optical feedback. The cavity has any of a variety of configurations with two or more mirrors, including for example a linear cavity, a v-shaped cavity and a ring optical cavity. The cavity will have multiple cavity resonant modes, or a comb of frequencies spaced apart, as determined by the parameters of the cavity, including the length of the cavity, as is well known. Systems and methods herein also allow for optimization of the cavity modes excited during a scan and/or the repetition rate.

Core Innovation

The invention relates to measuring cavity loss of a resonant optical cavity over a range of frequencies by exciting one or a plurality of cavity modes in a controlled manner using a continuous-wave laser responsive to optical feedback light emerging from the cavity. The laser has an adjustable mean optical frequency over the range of frequencies, and the resonant optical cavity includes at least two cavity mirrors with one cavity coupling mirror. The laser light is coupled to the cavity via mode matching optics, and the cavity has a plurality of optical resonance cavity modes with frequencies within the laser frequency range.

A predetermined current profile is applied to the laser to adjust the mean optical frequency and to excite cavity modes in an excitation order responsive to the shape of the applied current profile. The excitation order includes multiple desired cavity modes in a non-consecutive order, and may include excitation of a single desired cavity mode two or more consecutive times. After a cavity mode has been excited, dynamics of intra cavity optical power of light circulating in the cavity are detected.

In some implementations, optical feedback light emerges from a second cavity mirror different than the cavity coupling mirror and is redirected to impinge on the laser, and the phase of the optical feedback is controlled using phase adjustment elements along optical paths between relevant mirrors and the laser. In some variations, cavity isolation from the laser is used while maintaining optical feedback, and detection is based on free-decay cavity ring down dynamics. The detected intra-cavity optical power dynamics are used to support measurement outcomes such as determining gas concentration in the cavity.

Claims Coverage

The independent claims are clm-00001, clm-00013, clm-00015, clm-00024, and clm-00029. Across these independent claims, the core coverage comprises controlled excitation of cavity modes over a frequency range using a continuous-wave, optical-feedback-responsive laser with a current-profile-defined excitation order, together with detection of intra-cavity optical power dynamics after cavity mode excitation, in the context of measuring cavity loss and, in one case, gas analyzer use.

Together, the independent claims cover cavity-mode excitation over a frequency range using an optical-feedback-responsive continuous-wave laser coupled via a cavity coupling mirror, a predetermined current profile that defines an excitation order including non-consecutive cavity mode excitation, and detecting or generating signals representing intra-cavity optical power dynamics after excitation, with additional independent-claim-specific structure such as redirected optical feedback from a second mirror in one instance and gas-analyzer configuration in another.

Stated Advantages

Documented Applications