The present invention provides a system for measuring concentrations of trace gases in gas mixtures using an absorption spectroscopy method. The system comprising: a resonant optical cavity containing a gas mixture, a continuous-wave external cavity laser, a detector system for measuring an absorption of laser light by the gas in the resonant optical cavity, wherein the ratio of the round-trip length of the external cavity laser to the round-trip length of the resonant optical cavity or its inverse value is between N0.2 and N+0.2, where N is a positive integer number.

Systems and methods for measuring the isotope ratio of one or more gaseous oxides produced during combustion of drugs, pharmaceuticals, or medicines aiming to detect counterfeit drugs, pharmaceuticals, or medicines based on comparison of the isotopic composition of the tested drugs, pharmaceuticals, or medicines with the isotopic composition of the authentic products.

The present invention provides systems and methods for measuring the isotope ratios of one or more trace gases based on optical absorption spectroscopy methods. The system includes an optical cavity containing a gas. The system also includes a laser optically coupled with the optical cavity, and a detector system for measuring absorption of laser light by the gas in the cavity.

The present invention provides a system for measuring concentrations of trace gases in gas mixtures using an absorption spectroscopy method. The system comprising: a resonant optical cavity containing a gas mixture, a continuous-wave external cavity laser, a detector system for measuring an absorption of laser light by the gas in the resonant optical cavity, wherein the ratio of the round-trip length of the external cavity laser to the round-trip length of the resonant optical cavity or its inverse value is between N0.2 and N+0.2, where N is a positive integer number.

Various techniques are provided for increasing contrast of gas features in a scene. In one example, a method includes receiving a captured infrared image comprising a gas feature and a scene feature. The captured infrared image comprises a first range of pixel values associated with a first temperature range of the gas feature and the scene feature. The method also includes applying a spatial filter to the captured infrared image to provide a spatially filtered infrared image retaining the gas feature and removing the scene feature. The spatially filtered infrared image comprises a second range of pixel values associated with a second temperature range of the gas feature without the additional scene feature to exhibit increased gas contrast over the captured infrared image. Additional methods and systems are also provided.

The present invention provides systems and methods for measuring the isotope ratios of one or more trace gases based on optical absorption spectroscopy methods. The system includes an optical cavity containing a gas. The system also includes a laser optically coupled with the optical cavity, and a detector system for measuring absorption of laser light by the gas in the cavity.

The present invention provides a system for measuring concentrations of trace gases in gas mixtures using an absorption spectroscopy method. The system comprising: a resonant optical cavity containing a gas mixture, a continuous-wave external cavity laser, a detector system for measuring an absorption of laser light by the gas in the resonant optical cavity, wherein the ratio of the round-trip length of the external cavity laser to the round-trip length of the resonant optical cavity or its inverse value is between N0.2 and N+0.2, where N is a positive integer number.

The present invention provides a system for measuring concentrations of trace gases in gas mixtures using an absorption spectroscopy method. The system comprising: a resonant optical cavity containing a gas mixture, a continuous-wave external cavity laser, a detector system for measuring an absorption of laser light by the gas in the resonant optical cavity, wherein the ratio of the round-trip length of the external cavity laser to the round-trip length of the resonant optical cavity or its inverse value is between N0.2 and N+0.2, where N is a positive integer number.

The present invention provides a system for measuring concentrations of trace gases in gas mixtures using the absorption spectroscopy method. The system comprising an optical cell containing a gas mixture, a continuous-wave tunable laser, a detector system for measuring an absorption of laser light by the gas in the optical cell, and a processor to conduct an absorption spectroscopy analysis of the gas mixture based on light intensity measured by the detector system at one or more laser frequencies.

The present invention provides a system for measuring concentrations of trace gases in gas mixtures using the absorption spectroscopy method. The system comprising: a resonant optical cavity, a continuous-wave stepwise tunable external cavity laser having a DFB laser as a gain media; a detector system for measuring an 5 absorption of laser light by the gas in the resonant optical cavity, wherein the roundtrip optical cavity length of the external cavity laser are the roundtrip optical cavity length of the resonant cavity are close.