Broadband resonant cavity spectroscopy gas cell

Abstract

The present disclosure provides a spectroscopic gas cell comprising: a cylindrical body defining a chamber for receiving a gas to be analyzed; an inlet for adding gas to the chamber; an outlet for removing gas from the chamber; a fiber input port closing a first end of the cylindrical body and adapted to connect to a first fiber ferrule to input laser light into the chamber; a fiber output port closing a second end of the cylindrical body and adapted to connect to a second fiber ferrule; a first off-axis ellipsoidal reflector positioned within the input port to reflect laser light from the first ferrule into the chamber; and a second off-axis ellipsoidal reflector positioned within the output port to reflect laser light from the chamber towards the second ferrule.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Indian Patent Application No. 202511003019, filed on January 13, 2025, entitled “INTEGRATED BROADBAND RESONANTCAVITY ENHANCED SPECTROSCOPY GAS SENSING”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a spectral gas sensing system, and more specifically to a broadband resonant cavity-enhanced spectral gas cell. Background Technology

[0004] Spectroscopic gas sensing systems are widely used for detecting and analyzing various gases in industrial, environmental, and safety applications. These systems typically employ lasers to interact with gas molecules, where specific wavelengths are absorbed by the target gas according to its molecular structure. The absorption characteristics provide spectral features that enable the identification and quantification of gas concentrations.

[0005] Cavity-enhanced spectroscopy represents an advanced approach that increases the effective optical path length by confining the laser within a highly precise optical cavity. In such systems, the laser undergoes multiple reflections between highly reflective mirrors, effectively extending the interaction distance between light and gas molecules by several kilometers beyond the physical cavity length. This enhancement significantly improves sensitivity, enabling the detection of trace gas concentrations at the parts per million or parts per billion level.

[0006] Conventional resonant cavity systems face limitations when attempting operation across a wide wavelength range. Many gas sensing applications require the detection of multiple gas species, each with different absorption wavelengths. Traditional optical coupling systems rely on refractive lens assemblies to focus diverging light from the optical fiber into the resonant cavity. However, these lens-based systems suffer from chromatic aberration, where different wavelengths are focused at different locations, thus limiting effective operation to a narrow spectral band or a single wavelength.

[0007] Chromatic aberration becomes particularly problematic in broadband applications where multiple wavelengths must be coupled simultaneously into a resonant cavity with high efficiency. Achromatic lens designs can partially address this issue for a limited number of wavelengths, but they cannot provide the broadband performance required for integrated multi-gas detection systems. This limitation often necessitates multiple independent sensors or frequent recalibration and refocusing when switching between different target gases.

[0008] The inventors have identified numerous areas for improvement in the prior art and methods, which are the subject of the embodiments described herein. Through effort, ingenuity, and innovation, many of these deficiencies, challenges, and problems have been addressed by developing solutions included in the embodiments of this disclosure, some examples of which are described in detail herein. Summary of the Invention

[0009] This invention is provided to introduce a series of concepts in a simplified form, which are further described in the detailed embodiments below. This invention is not intended to identify key or essential features of the claimed subject matter, nor is it intended to aid in determining the scope of the claimed subject matter.

[0010] The various implementation schemes described herein relate to spectral gas cells, as well as systems and methods for gas spectroscopy.

[0011] According to one aspect of this disclosure, a spectroscopic gas cell is provided. The spectroscopic gas cell includes a cylindrical body defining a chamber for receiving a gas to be analyzed. The spectroscopic gas cell includes an inlet through which the gas to be analyzed is added to the chamber. The spectroscopic gas cell includes an outlet through which the gas to be analyzed is removed from the chamber. The spectroscopic gas cell includes an optical fiber input port attached to and closing a first end of the cylindrical body, and adapted to selectively connect to a first optical fiber sleeve to input laser light into the chamber. The spectroscopic gas cell includes an optical fiber output port attached to and closing a second end of the cylindrical body, and adapted to selectively connect to a second optical fiber sleeve. The spectroscopic gas cell includes a first off-axis ellipsoidal reflector positioned within the optical fiber input port and positioned to reflect laser light from the first optical fiber sleeve into the chamber. The spectral gas cell includes a second off-axis ellipsoidal reflector positioned within the fiber optic output port and configured to reflect laser light from the chamber toward a second fiber optic sleeve to output laser light from the chamber.

[0012] According to other aspects of this disclosure, the gas cell may include one or more of the following features: Each of the first and second off-axis ellipsoidal reflectors may include aluminum. Each of the first and second off-axis ellipsoidal reflectors may include silver-coated aluminum. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of about two millimeters and a quadratic constant of about 0.9. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of 1.967 millimeters and a quadratic constant of 0.936. The first off-axis ellipsoidal reflector may be adapted to reflect the laser such that the waist of the laser is positioned approximately midway between the first and second off-axis ellipsoidal reflectors. Each of the fiber optic input port and fiber optic output port may have five degrees of freedom of adjustment.

[0013] According to another aspect of this disclosure, a system for gas spectroscopy is provided. The system includes a laser emitter for emitting laser light. The system includes a first optical fiber cable having a first end connected to the laser emitter and a second end connected to a first optical fiber sheath. The system includes a laser receiver for receiving laser light. The system includes a second optical fiber cable having a first end connected to a second optical fiber sheath and a second end connected to the laser receiver. The system includes a spectral gas cell comprising: a cylindrical body defining a chamber for receiving a gas to be analyzed; an inlet through which the gas to be analyzed is added to the chamber; an outlet through which the gas to be analyzed is removed from the chamber; an optical fiber input port attached to and closing a first end of the cylindrical body and connected to a first optical fiber sleeve to input emitted laser light into the chamber; an optical fiber output port attached to and closing a second end of the cylindrical body and connected to a second optical fiber sleeve; a first off-axis ellipsoidal reflector positioned within the optical fiber input port and configured to reflect laser light from the first optical fiber sleeve into the chamber; and a second off-axis ellipsoidal reflector positioned within the optical fiber output port and configured to reflect the laser light from the chamber toward the second optical fiber sleeve to output the laser light from the chamber.

[0014] According to other aspects of this disclosure, the system may include one or more of the following features: Each of the first and second off-axis ellipsoidal reflectors may include aluminum. Each of the first and second off-axis ellipsoidal reflectors may include silver-coated aluminum. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of about two millimeters and a quadratic constant of about 0.9. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of 1.967 millimeters and a quadratic constant of 0.936. The first off-axis ellipsoidal reflector may be adapted to reflect the laser such that the waist of the laser is positioned approximately midway between the first and second off-axis ellipsoidal reflectors. Each of the fiber optic input port and fiber optic output port may have five degrees of freedom of adjustment.

[0015] According to another aspect of this disclosure, a method for gas spectroscopy is provided. The method includes providing a spectral gas cell comprising: a cylindrical body defining a chamber for receiving a gas to be analyzed; an inlet through which the gas to be analyzed is added to the chamber; an outlet through which the gas to be analyzed is removed from the chamber; an optical fiber input port attached to and closing a first end of the cylindrical body; an optical fiber output port attached to and closing a second end of the cylindrical body; a first off-axis ellipsoidal reflector positioned within the optical fiber input port; and a second off-axis ellipsoidal reflector positioned within the optical fiber output port. The method includes connecting a laser transmitter to the optical fiber input port via a first optical fiber cable having a first end connected to the laser transmitter and a second end connected to a first optical fiber sleeve. The method also includes connecting a laser receiver to the optical fiber output port via a second optical fiber cable having a first end connected to a second optical fiber sleeve and a second end connected to the laser receiver. The method includes emitting a broadband laser from a laser emitter, such that the emitted laser enters an optical fiber input port via a first optical fiber sleeve. The emitted laser entering the optical fiber input port is reflected into a cavity by a first off-axis ellipsoidal reflector. The laser reflected into the cavity by the first off-axis ellipsoidal reflector is reflected from a second off-axis ellipsoidal reflector toward a second optical fiber sleeve to output laser light from the cavity.

[0016] According to other aspects of this disclosure, the method may include one or more of the following features: Each of the first and second off-axis ellipsoidal reflectors may comprise silver-coated aluminum. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of approximately two millimeters and a quadratic constant of approximately 0.9. Each of the first and second off-axis ellipsoidal reflectors may have a radius of curvature of 1.967 millimeters and a quadratic constant of 0.936. The first off-axis ellipsoidal reflector may be adapted to reflect the laser such that the waist of the laser is positioned approximately midway between the first and second off-axis ellipsoidal reflectors. The method may also include adjusting the position of the fiber optic input port and / or fiber optic output port.

[0017] The foregoing general description of the exemplary embodiments and the following detailed description are merely exemplary aspects of the teachings of this disclosure and are not restrictive. Attached Figure Description

[0018] The description of the exemplary embodiments is read in conjunction with the accompanying drawings. It should be understood that, for the sake of simplicity and clarity, the elements illustrated in the figures are not necessarily drawn to scale unless otherwise described. For example, unless otherwise described, the dimensions of some elements are exaggerated relative to others. Embodiments with the teachings of this disclosure are shown and described in conjunction with the accompanying drawings presented herein.

[0019] Figure 1 An isometric view of a spectral gas cell according to various aspects of this disclosure is illustrated.

[0020] Figure 2 Examples of various aspects according to this disclosure are illustrated. Figure 1 A cross-sectional view of the spectral gas cell.

[0021] Figure 3 Examples of various aspects according to this disclosure are illustrated. Figure 1 A partial isometric view of the spectral gas cell.

[0022] Figure 4 Examples of adjustable components according to various aspects of this disclosure are illustrated. Figure 1 An isometric view of the decomposition of the spectral gas cell.

[0023] Figure 5A An isometric view of an off-axis ellipsoidal reflector according to various aspects of this disclosure is shown.

[0024] Figure 5B Examples of various aspects according to this disclosure are illustrated. Figure 5A A cross-sectional view of an off-axis ellipsoidal reflector.

[0025] Figure 6A block diagram illustrating a control device for a spectral gas cell system according to various aspects of this disclosure is shown. Detailed Implementation

[0026] Some embodiments of this disclosure will be described more fully below with reference to the accompanying drawings, which illustrate some, but not all, embodiments of this disclosure. In fact, these disclosures are embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will meet applicable legal requirements. Similar reference numerals always refer to similar elements.

[0027] As used herein, terms such as “front,” “rear,” “top,” “bottom,” “left,” “right,” etc., in the examples provided below, are used for illustrative purposes to describe the relative positions of certain parts or portions of parts. Furthermore, as will be apparent to those skilled in the art based on this disclosure, the terms “substantially” and “approximately” indicate that the referenced element or associated description is accurate within applicable engineering tolerances.

[0028] As used herein, the term “comprising” means including but not limited to, and should be interpreted in the manner in which it is typically used in the patent context. The use of broader terms such as “comprising,” “including,” and “having” should be understood to provide support for narrower terms such as “consisting of,” “substantially composed of,” and “substantially constituted by.”

[0029] The phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally mean that the specific feature, structure, or characteristic following the phrase is included in at least one embodiment of this disclosure, and is included in more than one embodiment of this disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

[0030] Phrases such as “in one example,” “according to one example,” “in some examples,” etc. generally mean that the particular feature, structure, or characteristic following the phrase is included in at least one example of this disclosure, and is included in more than one example of this disclosure (importantly, such phrases do not necessarily refer to the same example).

[0031] If the specification states that a component or feature "may," "can," "should," "will," "preferably," "possibly," "usually," "optionally," "for example," "as an example," "in some examples," "often," or "may" (or other such language) be included or have that feature, then the specific component or feature is not necessarily included or has that feature. Such components or features are optionally included in some examples or excluded.

[0032] The terms “example” or “exemplary” as used herein mean “used as an example, instance, or illustration.” Any specific implementation described herein as an “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other specific implementations.

[0033] The terms “electrically coupled,” “electrically coupled,” “communicating with,” “electronically communicating with,” or “connection” in this disclosure mean that two or more elements or components are connected by wired and / or wireless means such that signals, voltages / currents, data, and / or information are transmitted to and / or received from these elements or components.

[0034] The term "component" can refer to an article of writing, device, or apparatus that may include one or more surfaces, portions, layers, and / or elements. For example, an example component may include one or more substrates providing one or more underlying layers for the component, and may include one or more elements that may form a portion on top of the substrate and / or one or more elements that may be disposed on top of the substrate. In this disclosure, the term "element" can refer to an article of writing, device, or apparatus that can provide one or more functions.

[0035] Cavity-enhanced spectroscopy offers a technique for extending the effective optical path length within compact gas sensing devices. In conventional spectroscopic gas detection, the sensitivity of the measurement depends on the interaction path length between the laser and gas molecules. A resonant cavity allows the laser to bounce multiple times between highly reflective mirrors, resulting in an effective optical path length several orders of magnitude longer than the physical size of the cavity. For example, a resonant cavity with a physical size of approximately 75 millimeters can achieve an effective optical path length exceeding 1000 meters through multiple reflections.

[0036] Traditional resonant cavity systems face limitations when attempting broadband operation across multiple wavelengths. Conventional fiber-coupled systems typically employ refractive lens assemblies to focus and collimate the laser between the fiber and the resonant cavity. These lens-based systems suffer from chromatic aberration, where different wavelengths of light are focused at different locations. This chromatic aberration limits the system to operation at a single wavelength, or at most a few discrete wavelengths that can be matched using a combination of achromatic lenses. Such limitations necessitate multiple independent sensors to detect different gas species, each optimized for a specific wavelength.

[0037] These limitations can be overcome by using reflective optics instead of refractive lens systems. Reflective optics, such as ellipsoidal reflective surfaces with a metallic coating, handle essentially all wavelengths without introducing chromatic aberration. This approach enables broadband operation across a wide range of wavelengths within a single device. Due to the reflective optics design, the system achieves chromatic aberration-free broadband operation over a wide wavelength range.

[0038] Systems for gas spectroscopy can provide enhanced sensitivity for trace gas detection applications. These systems can be designed for low-concentration and difficult-to-detect multi-gas detection applications, replacing conventional designs that require multiple sensors. Such applications may include the detection of toxic gases at concentration levels of parts per million (PPM) or parts per billion (PPB), where weak absorption coefficients necessitate extended optical path lengths to achieve sufficient sensitivity.

[0039] Gas spectroscopy methods utilize the broadband capabilities of reflective optical systems to analyze multiple gas species sequentially or simultaneously. This approach enables the detection of a wide variety of target gases without requiring reconfiguration of the optical system or replacement of wavelength-specific components. It reduces system complexity and cost while expanding the range of detectable gases within a single instrument.

[0040] refer to Figure 1 The spectral gas cell 100 can be configured for broadband cavity-enhanced spectroscopic applications. The spectral gas cell 100 includes a cylindrical body 102 that defines a chamber for receiving the gas to be analyzed. The cylindrical body 102 forms the main structural element of the spectral gas cell 100 and provides mechanical support for optical and gas handling components.

[0041] The spectroscopic gas cell 100 may include a gas inlet 106 positioned on a cylindrical body 102. The gas inlet 106 serves as an inlet through which the gas to be analyzed is added to the chamber defined by the cylindrical body 102. The spectroscopic gas cell 100 may also include a gas outlet 110 positioned on the cylindrical body 102. The gas outlet 110 serves as an outlet through which the gas to be analyzed is removed from the chamber. The gas inlet 106 and the gas outlet 110 enable controlled introduction and removal of gas samples for spectroscopic analysis.

[0042] The spectral gas cell 100 may include an optical fiber input port 114 positioned at one end of a cylindrical body 102. The optical fiber input port 114 may be attached to and may close the first end of the cylindrical body 102. The optical fiber input port 114 may be adapted to selectively connect to a first optical fiber sleeve to input laser light into the chamber. In some cases, the optical fiber input port 114 may provide an interface for coupling laser light from an external source into the spectral gas cell 100.

[0043] The spectral gas cell 100 may further include an optical fiber output port 116 positioned at opposite ends of the cylindrical body 102. The optical fiber output port 116 may be attached to a second end of the cylindrical body 102 and may close the second end of the cylindrical body. The optical fiber output port 116 may be adapted to selectively connect to a second optical fiber sleeve. The optical fiber output port 116 may enable the collection of laser light that has passed through the chamber and interacted with the gas sample.

[0044] like Figure 1 As shown, a first fiber optic cable 118 can be connected to a fiber optic input port 114. The first fiber optic cable 118 may have a first end connected to a laser emitter and a second end connected to a first fiber optic sleeve 120. The first fiber optic sleeve 120 provides an interface for coupling laser light from the first fiber optic cable 118 through the fiber optic input port 114 into the spectral gas cell 100. In some cases, the first fiber optic sleeve 120 may be configured to cooperate with the fiber optic input port 114 to establish optical communication between the first fiber optic cable 118 and a chamber within the cylindrical body 102.

[0045] The second fiber optic cable 122 can be connected to the fiber optic output port 116. The second fiber optic cable 122 may have a first end connected to a second fiber optic sleeve 124 and a second end connected to a laser receiver. The second fiber optic sleeve 124 provides an interface for coupling laser light from the spectral gas cell 100 through the fiber optic output port 116 into the second fiber optic cable 122. The second fiber optic sleeve 124 can be configured to cooperate with the fiber optic output port 116 to collect laser light that has passed through the chamber.

[0046] The configuration of the fiber optic input port 114 and fiber optic output port 116 at opposite ends of the cylindrical body 102 establishes an optical path through the spectral gas cell 100. This arrangement allows the laser to enter through the first fiber optic sleeve 120, interact with the gas sample within the chamber through multiple reflections between two high-precision mirrors, and exit through the second fiber optic sleeve 124 for subsequent analysis. Compared to free-space optical configurations, the fiber-coupled method offers advantages in system flexibility and alignment stability.

[0047] refer to Figure 2 The spectral gas cell 100 may include a resonant cavity 104 extending longitudinally through the interior of a cylindrical body 102. The resonant cavity 104 may be defined by the internal dimensions of the cylindrical body 102 and may provide a chamber in which the laser 126 can interact with a gas sample introduced through a gas inlet 106 and removed through a gas outlet 110. The resonant cavity 104 may be configured as a cavity-enhanced spectral system with high-precision mirrors to achieve an equivalent sensing path length exceeding 7500 meters within a physical cavity length of approximately 75 mm.

[0048] like Figure 2 As shown, a first off-axis ellipsoidal reflector 130a can be positioned within the fiber optic input port 114. The first off-axis ellipsoidal reflector 130a can be positioned adjacent to the first fiber optic sleeve 120 and can be configured to receive laser light 126 emitted from the first fiber optic sleeve 120. The first off-axis ellipsoidal reflector 130a can be positioned to reflect the laser light 126 from the first fiber optic sleeve 120 into the resonant cavity 104. In some cases, the first off-axis ellipsoidal reflector 130a can receive the diverging laser light 126 emitted from the end of the first fiber optic sleeve 120 and can redirect the diverging laser light 126 into a focused beam directed toward the center of the resonant cavity 104.

[0049] The spectral gas cell 100 may further include a second off-axis ellipsoidal reflector 130b positioned within the fiber optic output port 116. The second off-axis ellipsoidal reflector 130b may be positioned adjacent to the second fiber optic sleeve 124 and configured to receive laser light 126 that has traveled through the resonant cavity 104. The second off-axis ellipsoidal reflector 130b may be positioned to reflect the laser light 126 from the resonant cavity 104 toward the second fiber optic sleeve 124 to output the laser light 126 from the resonant cavity 104. The second off-axis ellipsoidal reflector 130b may collect laser light 126 exiting the resonant cavity 104 and may focus the laser light 126 into the second fiber optic sleeve 124 for transmission via the second fiber optic cable 122.

[0050] Off-axis ellipsoidal reflectors 130a and 130b may have two focal points that image the laser Gaussian beam waist from one to the other without aberrations, enabling aberration-free coupling across the entire wavelength range. The first off-axis ellipsoidal reflector 130a can position one focal point at the end of the first fiber optic sleeve 120 and guide the laser 126 to a second focal point located within the resonant cavity 104. Similarly, the second off-axis ellipsoidal reflector 130b can receive the laser 126 from the focal point within the resonant cavity 104 and redirect the laser 126 to a focal point at the end of the second fiber optic sleeve 124. This dual-focal configuration provides perfect laser beam mode matching between the fiber and the resonant cavity for maximum coupling efficiency.

[0051] Figure 2The illustrated optical path shows how the laser 126 travels from the first fiber optic sleeve 120, is reflected by the first off-axis ellipsoidal reflector 130a, passes through the resonant cavity 104, is reflected by the second off-axis ellipsoidal reflector 130b, and enters the second fiber optic sleeve 124. Within the resonant cavity 104, the laser 126 undergoes multiple reflections between highly reflective mirrors, creating an extended interaction path with gas molecules present in the cavity. This resonant cavity enhancement mechanism enables the detection of trace gas concentrations through multiple reflections and an extended light-gas interaction distance exceeding 1000 meters within the compact physical dimensions of the spectral gas cell 100.

[0052] Using off-axis ellipsoidal reflectors 130a and 130b instead of a refractive lens system provides aberration-free focusing and collimation of the laser 126 across a wide range of wavelengths. This reflective optics approach enables broadband spectral gas sensing within the resonant cavity 104, allowing the spectral gas cell 100 to analyze multiple gas species without requiring wavelength-specific optical components or system reconfiguration.

[0053] refer to Figure 5A and Figure 5B The first off-axis ellipsoidal reflector 130a may include detailed structural features capable of achieving broadband chromatic aberration-free operation. Although Figure 5A and Figure 5B The first off-axis ellipsoidal reflector 130a is illustrated in detail, but it should be understood that the second off-axis ellipsoidal reflector 130b is the same as the first off-axis ellipsoidal reflector 130a.

[0054] like Figure 5A As shown, the first off-axis ellipsoidal reflector 130a may include an off-axis ellipsoidal reflector body 132 having a generally cylindrical shape. The off-axis ellipsoidal reflector body 132 may provide mechanical structures for mounting and positioning the reflective surface within the fiber optic input port 114. The off-axis ellipsoidal reflector body 132 may include an off-axis ellipsoidal reflector orientation notch 136 formed on one side of the cylindrical surface. The off-axis ellipsoidal reflector orientation notch 136 may provide mechanical features for alignment and orientation during assembly of the spectral gas cell 100.

[0055] The longitudinal axis 138 of the off-axis ellipsoidal reflector extends through the center of the off-axis ellipsoidal reflector body 132, thereby defining the primary mechanical axis of the reflector component. The off-axis ellipsoidal reflector body 132 terminates at an off-axis ellipsoidal reflector end 139, which defines an axial boundary of the component. The cylindrical geometry of the off-axis ellipsoidal reflector body 132 facilitates integration with the fiber optic input port 114, while the off-axis ellipsoidal reflector orientation notch 136 ensures proper rotational alignment of the reflective surface relative to the optical path.

[0056] refer to Figure 5B The first off-axis ellipsoidal reflector 130a may include a concave ellipsoidal reflecting surface 134 formed at one end of the off-axis ellipsoidal reflector body 132. The concave ellipsoidal reflecting surface 134 may have an ellipsoidal curvature configured to focus and redirect the laser 126. The concave ellipsoidal reflecting surface 134 may be positioned such that laser 126 entering at one focal point can be reflected and focused to a second focal point within the resonant cavity 104.

[0057] like Figure 5B As further shown, the ellipsoidal axis 140 may be offset from the off-axis longitudinal axis 138 by approximately 2 mm, thereby defining the "off-axis" characteristic of the first off-axis ellipsoidal reflector 130a. The focal point 142 may be located along the ellipsoidal axis 140, corresponding to one of the two focal points of the ellipsoidal surface geometry. This off-axis configuration allows the first off-axis ellipsoidal reflector 130a to redirect the laser 126 from the first fiber optic sleeve 120 at an angle while maintaining precise focusing characteristics.

[0058] The first off-axis ellipsoidal reflector 130a and the second off-axis ellipsoidal reflector 130b may comprise aluminum. In some cases, the first off-axis ellipsoidal reflector 130a and the second off-axis ellipsoidal reflector 130b may comprise silver-coated aluminum. The aluminum construction provides structural stability and thermal properties suitable for spectral applications, while the silver coating provides high reflectivity across a wide wavelength range. The metallic reflective surfaces can handle all wavelengths substantially equally without introducing chromatic aberration, thereby enabling broadband operation of the spectral gas cell 100.

[0059] The first off-axis ellipsoidal reflector 130a and the second off-axis ellipsoidal reflector 130b may have a radius of curvature of approximately two millimeters and a quadratic constant of approximately 0.9. In some cases, the first off-axis ellipsoidal reflector 130a and the second off-axis ellipsoidal reflector 130b may have a radius of curvature of 1.967 millimeters and a quadratic constant of 0.936. The values ​​of the radius of curvature and the quadratic constant define the mathematical form of the ellipsoidal surface, thereby determining the focusing properties and optical performance of the reflector. The quadratic constant describes the deviation from sphericity, where the ellipsoidal surface geometry provides bifocal characteristics for aberration-free imaging.

[0060] refer to Figure 3 The exploded isometric view illustrates the spectral gas cell 100, illustrating the spatial relationships between its main components. This exploded view shows how the various components can be arranged along a common axis and how they can be assembled to form the assembled spectral gas cell 100. A cylindrical body 102 serves as a central structural element around which other components can be positioned during assembly.

[0061] refer to Figure 4 A detailed exploded isometric view illustrates the spectral gas cell 100, showcasing the arrangement and relationships of components and five-degree-of-freedom adjustment mechanisms within the resonant cavity system. This exploded view demonstrates how various optical, mechanical, and gas handling components can be assembled to form an integrated spectral gas cell 100 with precise alignment capabilities. Due to the similarity between the fiber optic output port 116 and the fiber optic input port 114, Figure 4 Details of the fiber optic output port 116 are omitted.

[0062] The spectral gas cell 100 may include a first reflector 144 and a second reflector 148, which may form resonant cavity mirrors within a cylindrical body 102. The first reflector 144 and the second reflector 148 may be dielectric-coated mirrors with a broadband reflectivity greater than 99.999%. In some cases, the first reflector 144 and the second reflector 148 may achieve a fineness greater than 300,000 to obtain an enhancement factor greater than 100,000. The high reflectivity and fineness characteristics of the first reflector 144 and the second reflector 148 enable the resonant cavity 104 to achieve an equivalent gas sensing path length of 7.5 km through multiple reflections of the laser 126 within the compact physical dimensions of the spectral gas cell 100.

[0063] like Figure 4 As shown, the mirror back ring 146 provides support for the first mirror 144 within the assembly. A piezoelectric spacer 150 and a piezoelectric ring actuator 152 can be positioned between the second mirror 148 and the cylindrical body 102. The piezoelectric ring actuator 152 can enable precise adjustment of the mirror spacing to maintain resonant conditions within the resonant cavity 104. In some cases, the piezoelectric ring actuator 152 can precisely lock the resonant free spectral range (FSR) to the comb laser source for resonance locking. The piezoelectric ring actuator 152 provides nanometer-scale control of the cavity length to accommodate different wavelengths and maintain optimal resonant conditions across a wide wavelength range.

[0064] The spectroscopic gas cell 100 may include a gas inlet gasket 108 positioned at a gas inlet 106 and a gas outlet gasket 112 positioned at a gas outlet 110. The gas inlet gasket 108 and the gas outlet gasket 112 provide sealed interfaces for the gas handling system, enabling controlled introduction and removal of gas samples while maintaining the integrity of the resonant cavity 104. The gaskets prevent gas leakage and ensure that the gas sample remains contained within the resonant cavity 104 during spectroscopic analysis.

[0065] like Figure 4As further shown, the fiber optic input port 114 may include a fiber optic input port cap 154 ​​that secures the alignment components in place. The first fiber optic cable 118 can be connected to the PC / APC connector 156 via a first fiber optic sleeve 120. The PC / APC connector 156 provides a standardized interface for fiber optic connections and may incorporate angled polishing to minimize back reflections that could interfere with the laser source. This angled connector configuration prevents unwanted reflections from the fiber endface from traveling back into the laser source, which could complicate or damage the laser system.

[0066] The spectral gas cell 100 may incorporate a five-degree-of-freedom adjustment system capable of precise alignment of optical components. An alignment spacer 158 may surround the first off-axis ellipsoidal reflector 130a and provide an adjustment mechanism for precise optical alignment. The alignment spacer 158 may accommodate two pairs of rollers for translation along the X and Y directions and rotation about the X and Y axes. Specifically, the alignment spacer 158 may incorporate an X-axis roller 160 and a Y-axis roller 162, which are capable of translational movement in the X and Y directions, respectively.

[0067] The five-degree-of-freedom adjustment system may include an X-direction translation set screw 164 and a Y-direction translation set screw 166, which control the translational positioning of optical components. The X-direction translation set screw 164 adjusts the position of the fiber optic input port 114 along the X-axis, while the Y-direction translation set screw 166 adjusts its position along the Y-axis. These translational adjustments enable precise alignment of the laser beam with the resonant optical path within the resonant cavity 104.

[0068] The adjustment system may also include X and Y axis rotating cap screws 168, which are adjustable for rotational orientation about the X and Y axes. The X and Y axis rotating cap screws 168 can achieve angular adjustment to align the laser beam with the resonant centerline. The rotational adjustment provided by the X and Y axis rotating cap screws 168 can be combined with translational adjustment to achieve optimal beam alignment within the resonant cavity 104.

[0069] The fiber focusing cap screw 170 adjusts the axial position of the first fiber optic sleeve 120 to control the focusing characteristics of the laser 126. The fiber focusing cap screw 170 allows adjustment of the fiber end distance to position the Gaussian beam waist at the center of the resonant cavity 104. In some cases, the first off-axis ellipsoidal reflector 130a can be adapted to reflect the laser 126, such that the waist of the laser 126 can be positioned approximately midway between the first off-axis ellipsoidal reflector 130a and the second off-axis ellipsoidal reflector 130b. The fiber focusing cap screw 170 allows for fine adjustments to the beam waist position to achieve optimal mode matching between the fiber and the resonant cavity 104.

[0070] By combining the X-direction translation set screw 164, the Y-direction translation set screw 166, the X and Y axis rotation cap screw 168, and the fiber focusing cap screw 170, the fiber input port 114 and the fiber output port 116 can each have five degrees of freedom of adjustment. These five degrees of freedom of adjustment can include X and Y direction translation, X and Y axis tilting, and fiber end focusing adjustment. The five degrees of freedom of adjustment capability allows the laser beam to be perfectly mode-matched and aligned with the resonant cavity optical axis with the highest coupling efficiency and across a wide broadband wavelength range.

[0071] Figure 4 The integrated design shown demonstrates how resonant cavity mirrors, piezoelectric actuation systems, gas handling components, and five-degree-of-freedom adjustment mechanisms can be assembled to form a compact and precisely controllable spectral gas cell 100. The combination of off-axis ellipsoidal reflectors, high-precision mirrors, precise piezoelectric control, and multi-axis adjustment capabilities enables the spectral gas cell 100 to achieve broadband resonant cavity-enhanced spectroscopy, which offers optimal performance across a wide range of wavelengths and gas species.

[0072] refer to Figure 6 The control device 600 can be configured as a component to operate and coordinate the spectral gas sensing system. The control device 600 may include a processing circuit 602, which can serve as a central computing element for controlling system operation and analyzing spectral data. The processing circuit 602 can be configured to execute control algorithms, process measurement signals, and coordinate the timing of laser emission and detection operations.

[0073] The control device 600 may also include a memory circuit 604 that stores data and instructions for operating the control device 600. The memory circuit 604 may retain calibration parameters, spectral reference data, measurement results, and software instructions executable by the processing circuit 602. In some cases, the memory circuit 604 may store algorithms for analyzing spectral signals and determining gas concentrations based on absorption measurements.

[0074] like Figure 6As shown, the control device 600 may include an input / output circuit 606 that facilitates interaction with external devices and user interfaces. The input / output circuit 606 enables data exchange between the control device 600 and external systems, allowing for the configuration of measurement parameters, retrieval of measurement results, and monitoring of system status. The input / output circuit 606 provides an interface for connection to a display device, data storage system, or network connection for remote monitoring and control.

[0075] The control device 600 may also include a communication circuit 608, which enables data transmission and reception with other system components. The communication circuit 608 can be connected to the processing circuit 602, the memory circuit 604, and the input / output circuit 606, thereby enabling coordinated data exchange and system control functions. The communication circuit 608 facilitates communication protocols for controlling the laser source, receiving detector signals, and coordinating measurement sequences.

[0076] Continue to refer to Figure 6 The control device 600 can be operatively connected to the laser emitter 610 and the laser receiver 612. The laser emitter 610 generates a laser beam that can be directed into the spectral gas cell 100 via a first fiber optic cable 118 and a first fiber optic sleeve 120. In some cases, the laser emitter 610 can be configured to emit broadband laser light across multiple wavelengths to enable the detection of various gas species within a single measurement system. The laser emitter 610 can be controlled by the control device 600 via communication circuitry 608 to coordinate emission timing, wavelength selection, and power levels.

[0077] Laser receiver 612 can detect the laser light output from spectral gas cell 100 via second fiber optic sleeve 124 and second fiber optic cable 122. Laser receiver 612 can convert the optical signal into an electrical signal, which can be processed by control device 600 to determine the spectral characteristics of the gas sample. In some cases, laser receiver 612 can be configured to detect broadband optical signals across the same wavelength range as laser emitter 610, thereby enabling comprehensive spectral analysis of multiple gas species.

[0078] The communication circuit 608 can communicate with both the laser emitter 610 and the laser receiver 612 to coordinate system operation. The communication circuit 608 can send control signals to the laser emitter 610 to initiate a laser emission sequence and can receive measurement signals from the laser receiver 612 for subsequent processing. This bidirectional communication capability allows the control device 600 to synchronize laser emission and detection operations to achieve optimal measurement accuracy.

[0079] Processing circuit 602 processes the signal received from laser receiver 612 to determine the characteristics of the gas sample within resonant cavity 104. Processing circuit 602 analyzes the intensity, wavelength dependence, and time characteristics of the detected optical signal to calculate gas concentration, identify gas species, and evaluate measurement quality. In some cases, processing circuit 602 can determine the gas concentration based on measured optical absorption and the known effective path length within resonant cavity 104.

[0080] The control device 600 coordinates the operation of the laser emitter 610 and monitors the output detected by the laser receiver 612 to perform spectral analysis of the gas sample. The control device 600 can execute a measurement sequence that may involve scanning the laser wavelength across a wide bandwidth, controlling the piezoelectric ring actuator 152 to maintain resonant conditions, and analyzing the resulting absorption spectrum to identify and quantify the types of gases present in the resonant cavity 104. This integrated control method enables automated operation of the spectral gas sensing system with minimal user intervention while maintaining high measurement accuracy and repeatability.

[0081] During operation of the spectroscopic gas sensing system, components can interact in a coordinated sequence to perform broadband spectroscopic analysis of a gas sample. A laser emitter generates a broadband laser beam, which can be transmitted through a first fiber optic cable to a first fiber optic sleeve. Due to the numerical aperture characteristics of the fiber, the laser beam can exit from the end of the first fiber optic sleeve as a diverging beam.

[0082] The diverging laser beam encounters a first off-axis ellipsoidal reflector, which collects the diverging light and redirects it toward the resonant cavity. The ellipsoidal geometry of the first off-axis ellipsoidal reflector focuses the laser beam to form a beam waist at the center of the resonant cavity, where the light interacts with gas molecules present in the cavity. The off-axis configuration allows the reflector to redirect the light at an angle while maintaining precise focusing characteristics across a wide wavelength range.

[0083] Within the resonant cavity, the laser undergoes multiple reflections between the first and second mirrors. Each reflection extends the effective optical path length, allowing the laser to interact with gas molecules over distances potentially exceeding the physical dimensions of the cavity by several orders of magnitude. The high reflectivity of dielectric-coated mirrors can enable hundreds of thousands of reflections, resulting in effective path lengths approaching several kilometers within a compact cavity structure.

[0084] When a laser beam crosses the resonant cavity multiple times, the gas molecules present in the cavity absorb light of specific wavelengths according to their molecular absorption characteristics. This absorption reduces the laser intensity at wavelengths corresponding to the absorption lines of the gas species present in the sample. The magnitude of absorption depends on the gas concentration, the absorption cross-section of the gas molecules, and the effective path length achieved through multiple reflections within the resonant cavity.

[0085] The laser light exiting the resonant cavity can be collected by a second off-axis ellipsoidal reflector, which redirects the light toward the second fiber optic sleeve. The second off-axis ellipsoidal reflector focuses the light from the beam waist position within the resonant cavity onto the end of the second fiber optic sleeve. The ellipsoidal geometry provides efficient coupling of the light into the second fiber optic cable, which then transmits the light to a laser receiver for detection and analysis.

[0086] A laser receiver converts optical signals into electrical signals, which are then processed by control equipment to determine the spectral characteristics of a gas sample. The processing circuitry analyzes wavelength-correlated absorption to identify the gas species and calculates the gas concentration based on the measured absorption and the known effective path length within the resonant cavity.

[0087] Compared to conventional refractive lens systems, this reflective optics design offers several advantages. By eliminating chromatic aberration through the use of a metallic reflective surface, broadband operation across a wide range of wavelengths can be achieved without the focusing errors inherent in refractive lenses. This chromatic aberration-free performance allows the system to analyze multiple gas species sequentially or simultaneously without requiring wavelength-specific optics or system reconfiguration.

[0088] This broadband capability enables the detection of multiple gas species without the need for multiple sensors, thereby reducing system complexity and cost while extending the range of gases detectable within a single instrument. Conventional systems may require separate sensors optimized for different wavelength ranges, each with its own optics and calibration requirements. This broadband reflective optics approach eliminates these limitations by providing consistent optical performance across the entire wavelength range of interest.

[0089] Although various embodiments based on the principles disclosed herein have been shown and described above, modifications can be made by those skilled in the art without departing from the teachings of this disclosure. The embodiments described herein are representative only and not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of this disclosure. Alternative embodiments resulting from the merging, integration, and / or omission of features of the embodiments are also within the scope of this disclosure. Therefore, the scope of protection is not limited by the description set forth above, but is defined by the following claims, which include all equivalents of the subject matter of the claims. Each claim is incorporated into the specification as further disclosure, and the claims are embodiments of this disclosure. Furthermore, any of the foregoing advantages and features may relate to specific embodiments, but the application of such published claims should not be limited to methods and structures that achieve any or all of the above advantages or have any or all of the above features.

[0090] Furthermore, the chapter titles used in this article are intended to correspond with 37 CFR. The recommendations in 1.77 are consistent with or provide organizational clues. These headings should not limit or characterize the disclosure set forth in any of the claims published in this disclosure. For example, the description of the technology in “Background Art” should not be interpreted as an admission that a certain technology is prior art to any disclosure in this disclosure. Nor should “Summary of the Invention” be considered a limiting characterization of the disclosure set forth in the published claims. Furthermore, any reference in this disclosure to the singular forms “Disclosure” or “Simplification” should not be used to prove that there is only one novel point in this disclosure. Multiple embodiments of this disclosure may be set forth according to the limitations of the multiple claims published in this disclosure, and such claims accordingly define the disclosure protected by them and its equivalents. In all cases, the scope of these claims should be considered in accordance with the advantages of the claims themselves, and should not be limited by the headings set forth herein.

[0091] Furthermore, without departing from the scope of this disclosure, the systems, subsystems, apparatuses, technologies, and methods described and illustrated in various embodiments in a discrete or separate manner can be combined or integrated with other systems, modules, technologies, or methods. Other devices or components shown or discussed as coupled or communicating with each other may be indirectly coupled through an intermediate device or component, whether electrically, mechanically, or otherwise. Other examples of variations, substitutions, and modifications that can be identified by those skilled in the art without departing from the scope of this disclosure are also provided.

[0092] Those skilled in the art to which these embodiments pertain will recognize numerous modifications and other embodiments of the disclosure set forth herein, which benefit from the teachings presented in the foregoing description and associated drawings. Although the drawings show only certain components of the apparatuses and systems described herein, various other components may be used in conjunction with the components and structures disclosed herein. Therefore, it should be understood that this disclosure is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. For example, various elements or components may be combined, rearranged, or integrated into another system, or certain features may be omitted or not implemented. Furthermore, the steps in any of the methods described above may not necessarily occur in the order depicted in the drawings, and in some cases, one or more of the depicted steps may occur substantially simultaneously, or additional steps may be involved. Although specific terms are used herein, they are used only in a general and descriptive sense and not for limiting purposes.

Claims

1. A spectroscopic gas cell, the spectroscopic gas cell comprising: A cylindrical body defining a chamber for receiving the gas to be analyzed; The gas to be analyzed is added to the chamber via the inlet; The gas to be analyzed is removed from the chamber via the outlet. An optical fiber input port is attached to and closes the first end of the cylindrical body, and is adapted to selectively connect to a first optical fiber sleeve to input laser light into the chamber. An optical fiber output port is attached to and closes the second end of the cylindrical body, and is adapted to selectively connect to a second optical fiber sleeve. A first off-axis ellipsoidal reflector is positioned within the fiber optic input port and is configured to reflect laser light from the first fiber optic sleeve into the cavity. and A second off-axis ellipsoidal reflector is positioned within the fiber optic output port and is configured to reflect the laser from the chamber toward the second fiber optic sleeve to output the laser from the chamber.

2. The gas pool of claim 1, wherein each of the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector comprises silver-coated aluminum.

3. The gas pool according to claim 1, wherein each of the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector has a radius of curvature of about two millimeters and a quadratic curve constant of about 0.

9.

4. The gas cell of claim 1, wherein the first off-axis ellipsoidal reflector is adapted to reflect the laser such that the waist of the laser is positioned approximately midway between the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector.

5. The gas cell according to claim 1, wherein each of the optical fiber input port and the optical fiber output port has five degrees of freedom of adjustment.

6. A system for gas spectroscopy, the system comprising: Laser emitter for emitting laser light A first optical fiber cable, the first optical fiber cable having a first end connected to the laser transmitter and a second end connected to a first optical fiber sleeve; A laser receiver for receiving the laser; The second optical fiber cable has a first end connected to the second optical fiber sleeve and a second end connected to the laser receiver; and A spectroscopic gas cell, the spectroscopic gas cell comprising: A cylindrical body defining a chamber for receiving the gas to be analyzed; The gas to be analyzed is added to the chamber via the inlet; The gas to be analyzed is removed from the chamber via the outlet. An optical fiber input port is attached to and closes the first end of the cylindrical body, and is connected to the first optical fiber sleeve to input the emitted laser into the chamber. An optical fiber output port is attached to the second end of the cylindrical body and closes the second end of the cylindrical body, and is connected to the second optical fiber sleeve; A first off-axis ellipsoidal reflector, positioned within the fiber optic input port and configured to reflect laser light from the first fiber optic sleeve into the cavity; and A second off-axis ellipsoidal reflector is positioned within the fiber optic output port and is configured to reflect the laser from the chamber toward the second fiber optic sleeve to output the laser from the chamber.

7. The system of claim 6, wherein each of the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector comprises silver-coated aluminum.

8. The system of claim 6, wherein each of the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector has a radius of curvature of about two millimeters and a quadratic curve constant of about 0.

9.

9. The system of claim 6, wherein the first off-axis ellipsoidal reflector is adapted to reflect the laser such that the waist of the laser is positioned approximately midway between the first off-axis ellipsoidal reflector and the second off-axis ellipsoidal reflector.

10. A method for gas spectroscopy, the method comprising: A spectral gas cell is provided, the spectral gas cell comprising: A cylindrical body defining a chamber for receiving the gas to be analyzed; The gas to be analyzed is added to the chamber via the inlet; The gas to be analyzed is removed from the chamber via the outlet. An optical fiber input port is attached to the first end of the cylindrical body and closes the first end of the cylindrical body. An optical fiber output port is attached to the second end of the cylindrical body and closes the second end of the cylindrical body. A first off-axis ellipsoidal reflector is positioned within the fiber optic input port; and A second off-axis ellipsoidal reflector is positioned within the fiber optic output port; The laser transmitter is connected to the optical fiber input port via a first optical fiber cable, the first optical fiber cable having a first end connected to the laser transmitter and a second end connected to a first optical fiber sleeve; The laser receiver is connected to the fiber optic output port via a second fiber optic cable, the second fiber optic cable having a first end connected to a second fiber optic sleeve and a second end connected to the laser receiver; and Broadband laser light is emitted from the laser emitter, and the emitted laser light enters the optical fiber input port through the first optical fiber sleeve; The laser emitted into the fiber optic input port is reflected into the cavity by the first off-axis ellipsoidal reflector; and The laser light reflected into the cavity by the first off-axis ellipsoidal reflector is reflected from the second off-axis ellipsoidal reflector toward the second fiber optic sleeve to output the laser light from the cavity.

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