Optical cavity enhanced frequency comb spectroscopy

Abstract

Exemplary devices, methods, and systems are provided for determining characteristics of a target gas in a fluid sample. In some embodiments, the example apparatus includes a frequency comb illumination source configured to emit pulsed light having a plurality of frequency comb wavelengths. The device also includes an optical cavity containing the fluid sample and exhibiting a plurality of cavity resonance modes. A frequency comb wavelength of the plurality of frequency comb wavelengths associated with the frequency comb illumination source is configured to align with a cavity resonance mode of the plurality of cavity resonance modes. A characteristic of the fluid sample is determined based on one or more optical characteristics of transmitted light passing through the fluid sample within the optical cavity.

Description

Technical Field

[0001] Embodiments of the present disclosure relate generally to frequency comb spectroscopy, and more particularly to enhancing frequency comb spectroscopy using an optical cavity. Background Art

[0002] Applicants have recognized the many technical challenges and difficulties associated with determining the gas composition in a sample fluid. Through applied effort, ingenuity, and innovation, Applicants have solved the problems associated with detecting target gases in a sample fluid by developing solutions embodied in the present disclosure, which are described in detail below. Summary of the invention

[0003] Various embodiments are directed to an exemplary apparatus, method, and system for determining a property associated with a composition of a fluid sample. In some embodiments, an exemplary apparatus may include a frequency comb illumination source configured to emit pulsed light including a plurality of frequency comb wavelengths; and an optical cavity including a plurality of cavity resonance modes, wherein a fluid sample is disposed within the optical cavity. In some embodiments, a frequency comb wavelength in the plurality of frequency comb wavelengths is configured to align with a cavity resonance mode in the plurality of cavity resonance modes, and a property of the fluid sample is determined based on one or more optical properties of transmitted light of the fluid sample within the optical cavity.

[0004] In some embodiments, the device also includes a photodetector positioned to receive the transmitted light, wherein the photodetector is configured to generate an electrical signal proportional to the amplitude of the transmitted light.

[0005] In some embodiments, the apparatus further includes a controller electrically connected to the photodetector, wherein the controller is configured to determine a characteristic of the fluid sample based at least in part on the electrical signal received from the photodetector.

[0006] In some embodiments, the controller determines the absorption signature based at least in part on an amplitude of the transmitted light at a subset of frequency comb wavelengths in the plurality of frequency comb wavelengths.

[0007] In some embodiments, a property of a fluid sample is determined based at least in part on an absorption signature.

[0008] In some embodiments, the characteristic of the fluid sample is the concentration of the target gas.

[0009] In some embodiments, the frequency comb illumination source is configured to emit pulsed light at a pulse repetition rate.

[0010] In some embodiments, the pulse repetition rate of the frequency comb illumination source is matched to the free spectral range of the optical cavity or a multiple thereof.

[0011] In some embodiments, the frequency comb illumination source is a dual frequency comb spectral illumination source.

[0012] In some embodiments, the optical cavity includes two or more mirror elements.

[0013] In some embodiments, the physical properties of the optical cavity are tuned to modify the plurality of cavity resonance modes such that one or more comb wavelengths resonate within the optical cavity.

[0014] In some embodiments, the physical property of the optical cavity is at least one of a reflectivity of the two or more mirror elements, a refractive index of a component within the optical cavity, and an optical cavity length of transmitted light within the optical cavity.

[0015] An exemplary method for determining a property of a target gas in a fluid sample is also provided. In some embodiments, the method includes causing a frequency comb illumination source to emit pulsed light including a plurality of frequency comb wavelengths, wherein the pulsed light is directed to an optical cavity including a plurality of cavity resonance modes, and wherein the fluid sample is disposed within the optical cavity. In some embodiments, the method also includes adjusting at least one of a physical property of the optical cavity and a physical property of the pulsed light to align a frequency comb wavelength among the plurality of frequency comb wavelengths with a cavity resonance mode among the plurality of cavity resonance modes. In some embodiments, the method also includes receiving an electrical signal proportional to the amplitude of the transmitted light from a photodetector positioned to receive the transmitted light, wherein the transmitted light passes through the fluid sample within the optical cavity. In some embodiments, the method also includes determining a property of the fluid sample based on the electrical signal.

[0016] In some embodiments, the method further includes determining the absorption signature based at least in part on an amplitude of the transmitted light at a subset of the frequency comb wavelengths in the plurality of frequency comb wavelengths.

[0017] In some embodiments, the method further includes determining a characteristic of the fluid sample based at least in part on the absorption signature.

[0018] In some embodiments, the characteristic of the fluid sample is the concentration of the target gas.

[0019] In some embodiments, the frequency comb illumination source is configured to emit pulsed light at a pulse repetition rate, and the pulse repetition rate of the frequency comb illumination source is matched to a free spectral range of the optical cavity or a multiple thereof.

[0020] In some embodiments, the frequency comb illumination source is a dual frequency comb spectral illumination source.

[0021] In some embodiments, the method further comprises adjusting physical properties of the optical cavity to modify the plurality of cavity resonance modes such that one or more comb wavelengths resonate within the optical cavity.

[0022] An exemplary system for determining the concentration of a target gas in a fluid sample is also provided. In some embodiments, the system includes a fluid sample inlet configured to receive a fluid sample into a fluid sample chamber. The exemplary system also includes an optical cavity including a plurality of cavity resonance modes, wherein a portion of the fluid sample chamber is within the optical cavity. The exemplary system also includes a frequency comb illumination source configured to emit pulsed light including a plurality of frequency comb wavelengths. The exemplary system also includes a photodetector positioned to receive transmitted light through the portion of the fluid sample chamber in the optical cavity, wherein the photodetector is configured to generate an electrical signal proportional to the amplitude of the transmitted light. The exemplary system also includes a controller electrically connected to the photodetector, wherein a frequency comb wavelength in the plurality of frequency comb wavelengths is configured to align with a cavity resonance mode in the plurality of cavity resonance modes, and wherein the controller is configured to determine the concentration of the target gas in the fluid sample based on the electrical signal received from the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Reference will now be made to the drawings. In certain embodiments described herein, components illustrated in the drawings may or may not be present. Some embodiments may include fewer (or more) components than those shown in the drawings according to exemplary embodiments of the present disclosure.

[0024] Figure 1 An exemplary block diagram of an exemplary optical cavity enhanced frequency comb spectrometer according to an exemplary embodiment of the present disclosure is shown.

[0025] Figure 2 An exemplary block diagram of an exemplary optical cavity enhanced frequency comb spectrometer including a controller according to an exemplary embodiment of the present disclosure is shown.

[0026] Figure 3 An exemplary block diagram of an exemplary controller according to an exemplary embodiment of the present disclosure is shown.

[0027] Figure 4 An exemplary optical cavity according to an exemplary embodiment of the present disclosure is shown.

[0028] Figure 5 A diagram showing exemplary optical cavity resonance modes according to an exemplary embodiment of the present disclosure.

[0029] Figure 6 An exemplary embodiment of an optical cavity enhanced frequency comb spectrometer including a dual frequency comb illumination source according to an exemplary embodiment of the present disclosure is shown.

[0030] Figure 7 An exemplary pulsed light output of a frequency comb illumination source according to an exemplary embodiment of the present disclosure is shown.

[0031] Figure 8 Exemplary absorption characteristics of exemplary target gases according to exemplary embodiments of the present disclosure are shown.

[0032] Fig. 9 A flow chart of an exemplary method for determining a characteristic of a fluid sample according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0033] Exemplary embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the present disclosure are shown. Indeed, the embodiments of the present disclosure may be 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 the disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.

[0034] The terms "electrically connected", "electrically coupled", "electrically coupled", "in communication with", "electronically communicate with", or "connected" in this disclosure refer to two or more elements or components that are connected by wired means and / or wireless means so that signals, voltage / current, data and / or information can be transmitted to one of the components and / or received from one of the components.

[0035] Various exemplary embodiments address technical problems associated with determining the physical composition of a fluid sample (e.g., determining the concentration of a target gas) using spectroscopic methods. As will be appreciated by those skilled in the art to which the present disclosure pertains, there are various exemplary scenarios in which determining the concentration of a target gas and other physical properties associated with the composition of a fluid sample may be beneficial.

[0036] Spectral analysis of a fluid sample can be used to determine one or more components within the fluid sample by illuminating the fluid sample with light of a specific wavelength and monitoring the absorption of the light over the optical path length. Each component (atom or molecule) of the fluid sample has a unique absorption signature that can be used to identify the presence and / or concentration of the component within the fluid sample, or in some embodiments, to identify the absence of a specific target gas (e.g., a leaked toxic gas) in the fluid sample. For example, the concentration of methane or carbon dioxide can be measured by illuminating the fluid sample with light of different wavelengths and analyzing the absorption signatures of the various wavelengths.

[0037] Detecting and / or determining the concentration of a target gas in a sample fluid can have many applications in a variety of industries. The health industry can determine the concentration of various target gases in the patient's exhaled breath. Exhaled breath contains many low-concentration gases that can indicate the patient's metabolic state and other health conditions. For example, elevated levels of acetone in a patient's exhaled breath may be an indicator of improper kidney surgery. In such health applications, it may not be feasible to use equipment with a long free space optical path length. A much smaller configuration may be required to achieve instant analysis and / or laboratory analysis of the patient's exhaled breath. In addition, many industries can determine the concentration of target gases in sample fluids to preemptively detect dangerous conditions. For example, the presence of certain gases may be dangerous to the health of workers and / or create a dangerous working environment.

[0038] Many of these target gases are present in low concentrations (parts per million or parts per billion). Typically, when active illumination spectroscopy is used to detect and determine the concentration of low concentration gases, a long optical path length is required. The optical path is the distance that the emitted light travels between the illumination source and the receiver (such as a receiving photodetector). A long optical path length (e.g., greater than one meter) can produce sufficient absorption of the light emitted from the illumination source to be measured at the receiving photodetector. For some applications, such as atmospheric analysis or leak detection at industrial plants, a long optical path length is readily available and is not a significant limiting factor. However, other applications may require a shorter optical path length, for example, applications in limited spaces, mobile applications, and / or applications near targets of interest. In such applications, the optical path length may not be sufficient to detect low concentrations of target gases.

[0039] Various exemplary embodiments described herein utilize various techniques to determine the characteristics of a fluid sample, utilizing a frequency comb illumination source and an optical cavity to achieve signal enhancement. For example, instead of the pulsed light emitted from the frequency comb illumination source propagating through the free space of a long optical path, the pulsed light of one or more exemplary embodiments described herein is injected into an optical cavity. Non-limiting examples of optical cavities may include Fabry-Perot interferometers, multi-mirror ring cavities, whispering gallery optical cavities, or other similar optical cavities. The reflected light in the optical cavity may pass through the cavity multiple times. The resonant wavelength of the reflected light matched to the resonant mode of the optical cavity can be selectively absorbed by various components of the fluid sample. The approximate number of round trips of the reflected light through the optical cavity acts as a multiplication factor for absorption. Therefore, even when the concentration of the target gas is low (e.g., parts per million or parts per billion), the absorption of various wavelengths of the pulsed light from the frequency comb illumination source can be detected at the receiving photodetector. The presence and / or concentration of the target gas can be determined based on the optical characteristics of the transmitted light received at the receiving photodetector.

[0040] In some embodiments, various aspects of the optical cavity and the transmitted light can be altered so that one or more frequency comb wavelengths generated by the frequency comb illumination source can be aligned with one or more cavity resonance modes of the optical cavity. By aligning one or more frequency comb wavelengths with the optical cavity modes, the frequency comb wavelengths of the pulsed light can be reflected in the optical cavity containing the fluid sample, thereby increasing the total optical path of the transmitted light.

[0041] In some embodiments, alignment of the frequency comb wavelength can be achieved by adjusting one or more physical properties of the pulsed light emitted from the frequency comb illumination source. The physical properties can include pulse repetition rate, frequency of the pulsed light, and other similar properties. In some embodiments, a dual frequency comb illumination source can be used as the frequency comb illumination source. The dual comb frequency illumination source can enable further adjustment of the frequency comb wavelength to align with the cavity resonance mode.

[0042] In some embodiments, the physical properties of the optical cavity can be adjusted to align the frequency comb wavelength with the cavity resonant mode. For example, the physical layout of the mirror elements of the optical cavity can be adjusted. In addition, the reflectivity of the mirror elements and / or the refractive index of one or more components within the optical cavity can be adjusted to tune the cavity resonant mode of the optical cavity. In addition, the length or distance between the mirror elements can be adjusted to facilitate the alignment of the frequency comb wavelength with the cavity resonant mode.

[0043] As a result of the exemplary embodiments described herein, and in some examples, the effectiveness of target gas detection devices using active illumination spectroscopy can be greatly improved. Additionally, the concepts described herein can enable detection of low concentration levels of target gases within limited physical space constraints.

[0044] Reference now Figure 1 , an exemplary optical cavity enhanced frequency comb spectrometer 100 is provided. Figure 1 As depicted, exemplary optical cavity enhanced frequency comb spectrometer 100 includes an optical cavity 104 configured to receive pulsed light 108 from a frequency comb illumination source 102. Pulsed light 108 is reflected within optical cavity 104 as reflected light 110. An unabsorbed portion of the light exits optical cavity 104 as transmitted light 112 and is received by photodetector 106.

[0045] like Figure 1 As depicted, an exemplary optical cavity enhanced frequency comb spectrometer 100 includes a frequency comb illumination source 102. The frequency comb illumination source 102 is any illumination source configured to generate pulsed light 108 at a plurality of frequency comb wavelengths that are uniformly spaced according to a pulse repetition rate of the frequency comb illumination source 102. The frequency comb illumination source 102 may include periodic modulation of a continuous wave laser, four wave mixing in a nonlinear medium, stabilization of a pulse train generated by a mode locked laser, or other similar mechanisms that generate the uniformly spaced pulsed light 108.

[0046] like Figure 1 As further depicted in FIG. 1 , pulsed light 108 is generated by a frequency comb illumination source 102. Pulsed light 108 is any infrared, visible, or ultraviolet collection of photons emitted by the frequency comb illumination source 102 at a uniform pulse repetition rate. The pulse repetition rate is the time between individual pulses emitted by the frequency comb illumination source 102. Pulsed light 108 includes a number of optical properties, including an amplitude of the pulsed light 108, a frequency of the pulsed light 108, a polarization of the pulsed light 108, a phase of the pulsed light 108, and other similar optical properties.

[0047] like Figure 1 As depicted, pulsed light 108 is directed toward an optical cavity 104 by a frequency comb illumination source 102. Optical cavity 104 is any arrangement of mirror elements that form a resonant cavity for light waves. Pulsed light 108 enters optical cavity 104 by passing through one or more reflective elements of optical cavity 104. Optical cavity 104 is configured to circulate and / or reflect light (e.g., reflected light 110) within a confined area (e.g., a fluid sample chamber). In some embodiments, the optical cavity 104 configuration may include a Fabry-Perot interferometer, a confocal Fabry-Perot interferometer, a ring cavity, a whispering gallery mode cavity, or another similar optical cavity configuration.

[0048] The optical cavity 104 exhibits one or more cavity resonance modes. The reflected light 110 confined in the optical cavity 104 may be reflected multiple times in the reflector element. Certain frequencies of the pulsed light 108 will be maintained by the optical cavity 104, while other frequencies of the pulsed light 108 experience destructive interference. The frequencies of the light maintained by the optical cavity 104 represent the cavity resonance modes. The resonance modes of the optical cavity 104 may depend on some physical properties of the optical cavity 104. For example, the optical properties of the reflector element may affect the resonance modes of the optical cavity 104. These optical properties may include the reflectivity of the reflector element, the refractive index of the components within the optical cavity 104, and other similar properties. The resonance modes of the optical cavity 104 may also depend on the physical layout of the optical cavity 104. The physical layout may include the shape, spacing, and number of the reflector elements. The physical layout may also include the optical path length, or the length that the reflected light 110 travels within the optical cavity 104. The optical properties of the reflector element and the physical layout of the optical cavity 104 may be adjusted to change the cavity resonance modes of the optical cavity 104.

[0049] A portion of the reflected light 110 can exit the optical cavity 104 as transmitted light 112 toward the photodetector 106. In some embodiments, the optical properties of the transmitted light 112 can be changed compared to the pulsed light 108. The optical properties of the transmitted light 112 can include amplitude, frequency, polarization, phase, and other similar optical properties of the transmitted light. For example, in some embodiments, the reflected light 110 can be reflected, refracted, distorted, absorbed, or otherwise changed when reflected in the optical cavity 104. The optical cavity enhanced frequency comb spectrometer 100 can determine certain properties of the fluid sample contained in the optical cavity 104 based on the changes in the optical properties of the transmitted light 112.

[0050] like Figure 1 As further depicted in , the exemplary optical cavity enhanced frequency comb spectrometer 100 includes a photodetector 106. The photodetector 106 can be any collection of one or more photodiodes, integrated circuits, devices, sensors, photosensitive diodes, or other structures that generate an electrical signal proportional to the intensity of light received at the photodetector 106. For example, the electrical signal output by the photodetector 106 can increase as the number of photons per second that strike the photodetector 106 increases. In such embodiments, the current output from the photodetector 106 can be used to determine the intensity or amplitude of the light (e.g., the transmitted light 112) that strikes the photodetector 106. In some embodiments, the photodetector 106 can be a photosensitive semiconductor diode that generates electron-hole pairs at a pn junction when a photon of sufficient energy strikes the photodetector 106.

[0051] Reference now Figure 2 , an exemplary optical cavity enhanced frequency comb spectrometer 200 is provided. Figure 2 As depicted, an exemplary optical cavity enhanced frequency comb spectrometer 200 includes an optical cavity 204 configured to receive pulsed light 208 from a frequency comb illumination source 202. The pulsed light 208 is reflected within the optical cavity 204 as reflected light 210. The unabsorbed portion of the light exits the optical cavity 204 as transmitted light 212 and is received by a photodetector 206. Figure 2 As further depicted in , an exemplary optical cavity enhanced frequency comb spectrometer 200 includes a controller 220 electrically connected to a frequency comb illumination source 202 , an optical cavity 204 , and a photodetector 206 .

[0052] like Figure 2 As shown, the exemplary optical cavity enhanced frequency comb spectrometer 200 includes a controller 220. The controller 220 is any computing device electrically connected to the frequency comb illumination source 202, the optical cavity 204, and the photodetector 206 and configured to transmit and receive control / status messages.

[0053] The control / status messages exchanged with the frequency comb illumination source 202 may include electrical signals configured to control the frequency and / or wavelength of the pulsed light 208 generated by the frequency comb illumination source 202. The command messages may also control the pulse repetition rate of the frequency comb illumination source 202. By controlling the pulse repetition rate of the frequency comb illumination source 202, the spacing between the multiple frequency comb wavelengths may be adjusted. The controller 220 may adjust the frequency comb wavelength of the frequency comb illumination source 202 to align the frequency comb wavelength with the cavity resonance mode of the optical cavity 204. Figure 7 Adjusting the frequency comb wavelength of the frequency comb illumination source 202 is further discussed.

[0054] The control / status messages exchanged with the optical cavity 204 may include electrical signals configured to control the position, spacing, and / or angle of the mirror elements. In some embodiments, one or more mirror elements of the optical cavity 204 may be adjusted via the control messages. By controlling the mirror elements of the optical cavity 204, the cavity resonant mode may be changed. The controller 220 may adjust the physical properties of the optical cavity 204 to align the cavity resonant mode with the frequency comb wavelength of the frequency comb illumination source 202. Adjusting the cavity resonant mode of the optical cavity 204 will be related to the frequency comb wavelength of the frequency comb illumination source 202. Figure 5 Further discussion.

[0055] Control / status messages exchanged with the photodetector 206 may include receiving an electrical signal representing the intensity of the transmitted light 212 received at the photodetector 206. In addition, the controller 220 may be configured to control parameters of the photodetector 206, such as sampling rate, spectral responsivity, response time, and other similar parameters. The controller 220 may determine optical properties of the transmitted light 212, such as the frequency and intensity of the received transmitted light 212, based on the received electrical signal. The optical properties may be used to determine the presence, absence, and / or concentration of one or more gases within the optical cavity 204. For example, the controller 220 may determine an absorption signature based on the intensity of the transmitted light 212 received at the photodetector 206, and utilize the absorption signature to determine the composition of the fluid sample in the optical cavity 204. Figure 8 Utilizing absorption signatures to determine the composition of the fluid sample in the optical cavity 204 is further discussed.

[0056] Controller 220 may be embodied by one or more computing systems, such as Figure 3 The device 300 shown. The device 300 includes a processor 302, an input / output circuit 304, a data storage medium 306, a communication circuit 308, a frequency comb illumination circuit 310, an optical cavity circuit 312, and a photodetector circuit 314. In some embodiments, the device 300 is configured to use one or more of the group of circuits 302, 304, 306, 308, 310, 312, and / or 314 to perform the operations described herein.

[0057] Although these components are described with respect to functional limitations, it should be understood that specific implementations necessarily include the use of specific computing hardware. It should also be understood that in some embodiments, certain components described herein include similar or common hardware. For example, two circuit groups can each utilize the use of the same processor, network interface, storage medium, etc. to perform their associated functions, such that each circuit group does not require duplicate hardware. Therefore, it should be understood that the use of the term "circuit" as used herein with respect to components of the apparatus described herein includes specific hardware configured to perform the functions associated with the specific circuits described herein.

[0058] In particular, the term "circuit" should be broadly understood to include hardware, and in some embodiments, software for configuring hardware. For example, in some embodiments, a "circuit" includes processing circuits, storage media, network interfaces, input / output devices, etc. Alternatively or additionally, in some embodiments, other elements of the device 300 provide or supplement the functionality of other specific circuit groups. For example, in some embodiments, the processor 302 provides processing functionality to any of the circuit groups, the data storage medium 306 provides storage functionality to any of the circuit groups, the communication circuit 308 provides network interface functionality to any of the circuit groups, etc.

[0059] In some embodiments, the processor 302 (and / or a co-processor or any other processing circuit assisting the processor or otherwise associated with the processor) communicates with the data storage medium 306 via a bus for transferring information between components of the device 300. In some embodiments, for example, the data storage medium 306 is non-transitory and may include, for example, one or more volatile memories and / or non-volatile memories. In other words, for example, in some embodiments, the data storage medium 306 includes or embodies an electronic storage device (e.g., a computer-readable storage medium). In some embodiments, the data storage medium 306 is configured to store information, data, content, applications, instructions, etc. for enabling the device 300 to perform various functions according to the exemplary embodiments of the present disclosure.

[0060] Processor 302 can be embodied in a number of different ways. For example, in some exemplary embodiments, processor 302 includes one or more processing devices that are configured to execute independently. Additionally or alternatively, in some embodiments, processor 302 includes one or more processors that are configured in series via a bus to enable independent execution of instructions, pipelines, and / or multithreading. The use of the terms "processor" and "processing circuit" should be understood to include a single-core processor, a multi-core processor, a plurality of processors within device 300, and / or one or more remote processors or "cloud" processors outside device 300.

[0061] In an exemplary embodiment, the processor 302 is configured to execute instructions stored in the data storage medium 306 or otherwise accessible to the processor. Alternatively or additionally, in some embodiments, the processor 302 is configured to execute hard-coded functionality. Therefore, whether configured by hardware methods or software methods, or by a combination thereof, the processor 302 represents an entity (e.g., physically embodied in circuit form) capable of performing operations according to embodiments of the present disclosure while being configured accordingly. Alternatively or additionally, as another example, in some exemplary embodiments, when the processor 302 is embodied as an executor of software instructions, the instructions specifically configure the processor 302 to perform the algorithms embodied in the specific operations described herein when executing such instructions.

[0062] In some embodiments, device 300 includes input / output circuit 304, which provides output to the user, and in some embodiments, receives the indication of user input. In some embodiments, input / output circuit 304 communicates with processor 302 to provide such functionality. Input / output circuit 304 may include one or more user interfaces (e.g., user interface), and in some embodiments includes display, which includes an interface presented as a web user interface, application user interface, user equipment or back-end system etc. Processor 302 and / or the input / output circuit 304 including processor may be configured to control one or more functions of one or more user interface elements by computer program instructions (e.g., software and / or firmware) stored in a processor-accessible memory (e.g., data storage medium 306 etc.). In some embodiments, input / output circuit 304 includes or utilizes user-oriented applications to provide input / output functionality to client devices and / or other displays associated with a user.

[0063] In some embodiments, the device 300 includes a communication circuit 308. The communication circuit 308 includes any component, such as a device or circuit embodied in hardware or a combination of hardware and software, which is configured to receive and / or send data from / to a network and / or any other device, circuit or module that communicates with the device 300. In this regard, for example, in some embodiments, the communication circuit 308 includes a network interface for implementing communication with a wired or wireless communication network. Additionally or alternatively, in some embodiments, the communication circuit 308 includes one or more network interface cards, antennas, buses, switches, routers, modems, and any other device that supports hardware, firmware and / or software, or is suitable for implementing communication via one or more communication networks. Additionally or alternatively, the communication circuit 308 includes a circuit for interacting with an antenna and / or other hardware or software to transmit a signal via an antenna or process the reception of a signal received via an antenna. In some embodiments, the communication circuit 308 enables data to be sent to and / or received from a client device that communicates with the device 300.

[0064] The frequency comb illumination circuitry 310 includes hardware, software, firmware, and / or combinations thereof that support various functionality associated with configuring a frequency comb illumination source (e.g., frequency comb illumination source 102, frequency comb illumination source 202). For example, in some embodiments, the frequency comb illumination circuitry 310 includes hardware, software, firmware, and / or combinations thereof to send and receive control / status messages for adjusting a plurality of frequency comb wavelengths of a frequency comb illumination source.

[0065] The optical cavity circuitry 312 includes hardware, software, firmware, and / or combinations thereof that support various functionality associated with configuring an optical cavity (e.g., optical cavity 104, optical cavity 204). For example, in some embodiments, the optical cavity circuitry 312 includes hardware, software, firmware, and / or combinations thereof that are used to send and receive control / status messages that control the physical characteristics of the optical cavity.

[0066] The photodetector circuit 314 includes hardware, software, firmware, and / or combinations thereof that support various functionality associated with configuring a photodetector (e.g., photodetector 106, photodetector 206). For example, in some embodiments, the photodetector circuit 314 includes hardware, software, firmware, and / or combinations thereof that are used to send and receive control / status messages that control the operation of the photodetector. Additionally, the photodetector circuit 314 includes hardware, software, firmware, and / or combinations thereof that are used to receive from the photodetector an electrical signal representing the intensity of transmitted light (e.g., transmitted light 112, transmitted light 212) received at the photodetector.

[0067] Additionally or alternatively, in some embodiments, one or more of the circuit groups 302 to 314 are combinable. Additionally or alternatively, in some embodiments, one or more of the circuit groups performs some or all of the functionality associated with another component. For example, in some embodiments, one or more of the circuit groups 302 to 314 are combined into a single module embodied in hardware, software, firmware, and / or a combination thereof. Similarly, in some embodiments, one or more of the circuit groups (e.g., frequency comb illumination circuit 310, optical cavity circuit 312, and / or photodetector circuit 314) are combined so that processor 302 individually performs one or more of the operations described above with respect to each of these circuits.

[0068] Reference now Figure 4 , an exemplary embodiment of the optical cavity 404 is provided. Figure 4 As depicted, the exemplary optical cavity 404 includes a first confocal mirror element 444 and a second confocal mirror element 446 separated by an optical cavity length 440 and defining a confined area 448. A fluid sample 442 is dispensed within the confined area 448 such that reflected light 410 entering the cavity from the generated pulsed light 408 interacts with the fluid sample 442 within the optical cavity 404. Transmitted light 412 exits the optical cavity 404 through the partially reflecting mirror element 446 to be received by a photodetector.

[0069] like Figure 4 As depicted, the exemplary optical cavity 404 includes a pair of mirror elements 444, 446. The mirror elements 444, 446 are any reflective elements or partially reflective elements that enable light to circulate within a confined region 448 of the optical cavity 404. Although the mirror elements depicted are arranged in a confocal Fabry-Perot interferometer arrangement, the mirror elements may be arranged in any optical cavity configuration that causes the reflected light 410 to pass through the confined region 448 multiple times before exiting the optical cavity 404. For example, the mirror elements 444, 446 may be arranged in a Fabry-Perot interferometer configuration, a confocal Fabry-Perot interferometer configuration, a ring cavity, a whispering gallery circular cavity, or other similar optical cavity configuration. The mirror elements 444, 446 also include at least a portion of a partially reflective mirror through which the reflected light 410 may pass as transmitted light 412.

[0070] like Figure 4 As further depicted in FIG. 4 , the mirror elements 444, 446 are separated by an optical cavity length 440. The optical cavity length 440 may be inversely proportional to the free spectral range of the cavity resonant mode, as described with respect to Figure 5As further described. Optical cavity length 440 may also define the optical path length of reflected light 410. The optical path length is the total distance that the reflected light travels in confined region 448 of optical cavity 404. The optical path length is generally related to the specific configuration and characteristics of the optical cavity, and is closely related to the sophistication and quality of the optical cavity. As a non-limiting example, in some embodiments, the optical path length may be characterized by the following equation:

[0071]

[0072] Where OPL is the optical path length, L is the optical cavity length, and R is the mirror reflectivity.

[0073] Thus, in a case where the optical cavity length is 50 cm and the reflectance of the mirror is 0.99, the optical path length will be 5000 cm. The optical path length in one of the cavity resonance modes is 100 times greater than the optical cavity length alone. This increase in optical cavity length can be achieved in confined spaces (e.g., 50 cm) and results in increased accuracy in detecting low concentrations of gas, which is usually only available with larger optical cavity lengths. Figure 5 As depicted, in a confocal Fabry-Perot interferometer configuration, the radius of the confocal mirror elements 444 , 446 is equal to the optical cavity length 440 .

[0074] In some embodiments, the mirror elements 444, 446 can be adjustable. Adjusting the mirror elements 444, 446 can increase the optical cavity length 440 and / or the optical path length. Adjusting the mirror elements 444, 446 can additionally change the cavity resonance mode of the optical cavity 404. In some embodiments, a controller (e.g., controller 220) can adjust the mirror elements 444, 446 to align the cavity resonance mode with the frequency comb wavelength during operation of the optical cavity enhanced frequency comb spectrometer.

[0075] like Figure 4 As further depicted in FIG. 4 , the optical cavity 404 includes a confined area 448 in which the fluid sample 442 is distributed. The confined area 448 is any space between the reflector elements (e.g., reflector elements 444, 446) through which the reflected light 410 passes when it is reflected in the optical cavity. In some embodiments, a fluid sample chamber may be positioned in the confined area 448 of the optical cavity 404. The fluid sample chamber may be configured to contain the fluid sample 442. In some embodiments, the fluid sample chamber may control the inflow and outflow of the fluid sample 442. For example, the fluid sample chamber may include a fluid sample inlet configured to receive the fluid sample from an external source, and a fluid sample outlet configured to release the fluid sample from the fluid sample chamber.

[0076] like Figure 4As further depicted in FIG. 4 , a fluid sample 442 is dispensed in a confined region 448 of the optical cavity 404. The fluid sample 442 is any liquid or gas dispensed within the confined region 448 of the optical cavity 404, and certain characteristics of the fluid sample 442 are to be determined. An optical cavity enhanced frequency comb spectrometer (e.g., optical cavity enhanced frequency comb spectrometer 100, optical cavity enhanced frequency comb spectrometer 200) can be configured to identify and analyze gases or molecules contained within the fluid sample 442. For example, the optical cavity enhanced frequency comb spectrometer can be configured to determine the concentration of water vapor (H2O) in the fluid sample 442, and / or the optical cavity enhanced frequency comb spectrometer can be configured to determine the presence of methane (CH4) in the fluid sample 442.

[0077] The characteristics of the fluid sample 442 include any measurement results corresponding to the composition of the gas that includes the fluid sample 442. For example, the characteristics of the fluid sample 442 can be the concentration of a specific gas in the fluid sample 442, such as water vapor (H2O), carbon dioxide (CO2), oxygen (O2), methane (CH4), or any other gas. Other characteristics may include the presence of a specific gas, such as a toxic, hazardous, or flammable gas. In some embodiments, the characteristics of the fluid sample 442 can include the absence of a specific target gas (e.g., a leaking toxic gas) in the fluid sample 442 or the absence of a specific target gas in some embodiments.

[0078] Reference now Figure 5 , a graph 550 is provided depicting exemplary cavity resonance modes 552a, 552b, 552c of an exemplary optical cavity (e.g., optical cavity 104, 204, 404) separated by a free spectral range 554. Figure 5 As depicted, the x-axis 556 of graph 550 represents the frequency of pulsed light (eg, pulsed light 108, 208, 408) entering the optical cavity, and the y-axis 558 represents the intensity of reflected light within the optical cavity.

[0079] like Figure 5 As depicted in FIG. 550 , an exemplary optical cavity includes a plurality of cavity resonance modes 552a, 552b, 552c. Cavity resonance modes 552a, 552b, 552c are any frequencies of light reflected in a confined region (e.g., confined region 448) of an optical cavity such that reflected light (e.g., reflected light 110, 210, 410) within the confined region (e.g., confined region 448) causes the reflected light to remain within the confined region of the optical cavity due to constructive interference, and the intensity of the reflected light experiences a local maximum with respect to a frequency range. The cavity resonance modes 552a, 552b, 552c of the optical cavity are equally spaced according to a free spectral range 554. The free spectral range 554 represents the frequency difference between subsequent cavity resonance modes 552a, 552b, 552c.

[0080] As described herein, the frequencies of the cavity resonant modes 552a, 552b, 552c can be affected by the physical properties of the optical cavity and / or the optical properties of the transmitted light. For example, the reflectivity of the reflector element, the refractive index of the components within the optical cavity, the arrangement of the reflector element, the optical path length of the reflected light, and other physical properties can be adjusted to change the position and intensity of the cavity resonant modes 552a, 552b, 552c. For example, in some embodiments, the free spectral range 554 that defines the spacing between the cavity resonant modes 552a, 552b, 552c can be defined by the following equation:

[0081]

[0082] where Δλ FSR is the distance in wavelength between the cavity resonance modes 552a, 552b, 552c, λ is the wavelength of the pulsed light, n is the refractive index, and L is the optical path length. Thus, as the optical path length L increases, the distance between the cavity resonance modes 552a, 552b, 552c becomes smaller. As the distance between the cavity resonance modes 552a, 552b, 552c becomes smaller, more frequencies of pulsed light can be emitted into the optical cavity and provide useful feedback related to a fluid sample (e.g., a fluid sample) within a confined region of the optical cavity. Smaller spacing between the cavity resonance modes 552a, 552b, 552c also provides greater resolution when determining the absorption characteristics of the fluid sample.

[0083] Reference now Figure 6 , an exemplary optical cavity enhanced frequency comb spectrometer 600 is provided. Figure 6 As depicted, an exemplary optical cavity enhanced frequency comb spectrometer 600 includes a frequency comb illumination source 602 that includes a first frequency comb 660a and a second frequency comb 660b. Transmitted light from the frequency combs 660a, 660b is combined using a cube beam splitter 662 to form a pulsed light 608 signal directed toward an optical cavity 604. The pulsed light 608 propagates within the confined space of the optical cavity 604 as reflected light 610, interacting with a fluid sample 642. At least a portion of the reflected light 610 exits the optical cavity 604 as transmitted light 612 that is received by a photodetector.

[0084] like Figure 6As depicted, a frequency comb illumination source 602 includes a dual frequency illumination source having a first frequency comb 660a and a second frequency comb 660b. The dual frequency comb illumination source utilizes two frequency combs 660a, 660b, each emitting light pulses at a different pulse repetition rate, and thereby generating a frequency comb that differs by an offset related to the frequency difference between the two pulse repetition rates. The light pulses emitted from the two frequency combs 660a, 660b are combined using a cubic beam splitter 662 configured to combine the two optical signals. The result is a single pulsed light 608 signal guided at the optical cavity 604. Although in Figure 6 602 , but the frequency comb illumination source 602 may be any source configured to generate pulsed light 608 at multiple frequency comb wavelengths evenly spaced apart based on the pulse repetition rate of one or more frequency comb illumination sources. Figure 7 The frequency comb generated by frequency comb illumination source 602 is described in more detail.

[0085] Reference now Figure 7 , a time domain diagram 770 and a frequency domain diagram 772 of an exemplary pulse signal (e.g., pulsed light 108, 208, 408, 608) are provided. Figure 7 As shown, the time domain plot 770 includes a plurality of short optical pulses 776 separated in time by a pulse repetition rate 774. The frequency domain plot 772 depicts a correlated frequency comb 778 generated by the plurality of optical pulses.

[0086] like Figure 7 As depicted, a frequency comb illumination source (e.g., frequency comb illumination source 102, 202, 602) generates a plurality of light pulses 706 at a pulse repetition rate 774. In some embodiments, the frequency comb illumination source can utilize a mode-locked laser to generate short light pulses 776. For example, the frequency comb illumination source can include a laser resonator configured to circulate a single light pulse within the laser resonator. The light pulses can contact an output coupler at regular intervals (e.g., pulse repetition rate 774), and output a light pulse 776 whenever the output coupler is contacted. Thus, as depicted in time domain graph 770, light pulses 776 are generated according to the pulse repetition rate 774.

[0087] like Figure 7As further depicted in the frequency domain graph 772 of , the plurality of light pulses 706 generated at a pulse repetition rate 774 correspond to a plurality of frequency combs 778. Each frequency comb 778 is separated in the frequency domain by the pulse repetition rate 774. The frequencies corresponding to each frequency comb 778 are associated with different wavelengths of light, or in other words, with frequency comb wavelengths. Thus, the pulsed light includes a plurality of frequency comb wavelengths. Upon entering a confined region within an optical cavity, each of the plurality of frequency comb 778 wavelengths may interact differently with the gases, substances, and molecules contained in the fluid sample. For example, some wavelengths of light may be absorbed, refracted, and / or reflected, while other wavelengths of light pass through uninhibited. Based on the absorption level of each of the plurality of frequency comb wavelengths passing through the optical cavity, an absorption feature specific to the fluid sample may be determined.

[0088] Reference now Figure 8 , an exemplary absorption characteristic graph 880 is provided. The depicted absorption characteristic graph 880 indicates the relationship between the absorption percentage (depicted on the y-axis 886) and the wavelength of the light (depicted on the x-axis 888). Figure 8 As shown, the absorption signature graph includes three target gas absorption signatures 882a - 882c and an exemplary fluid sample absorption signature 884 .

[0089] When light (e.g., reflected light 110, 210, 410, 610) passes through a fluid sample (e.g., fluid sample 442, 642), the light reacts differently to the fluid sample depending on the composition of the fluid sample and the wavelength of the light. For example, infrared light exhibiting a wavelength of 6000 nanometers can pass through a fluid sample that primarily includes oxygen and / or carbon dioxide almost unaffected. However, the same light (e.g., having a wavelength of 6000 nanometers) can be almost completely absorbed by a fluid sample that primarily includes water vapor. Therefore, the fluid sample absorption feature 884 can be determined by recording the percentage of light absorbed by a particular fluid sample over a wide wavelength spectrum.

[0090] like Figure 8 As depicted, absorption features 882a-882d are variations in the absorption of a gas or fluid with respect to the wavelength spectrum of light. Figure 8 Absorption features of various sample gases are depicted, such as water vapor absorption feature 882a, carbon dioxide absorption feature 882b, and oxygen absorption feature 882c. An absorption feature 882d of an example fluid sample is further depicted. Absorption features 882a to 882d indicate the percentage of light absorbed at wavelengths ranging from 0.1 microns to 100 microns. The absorption features can be determined by exposing the fluid to light of such a spectrum of wavelengths of light and recording the percentage of light absorbed at each of the wavelengths within the spectrum.

[0091] Once the absorption signature of a particular target gas is determined, the presence, absence, and / or concentration of the target gas can be detected in the sample fluid. By transmitting light including multiple wavelengths across a wide wavelength spectrum and receiving the transmitted light with a photodetector (e.g., photodetector 106, 206, 606), the absorbance of the sample fluid at each wavelength can be determined. The absorption signature can be generated by mapping the absorption percentage of each of the transmitted wavelengths. The absorption signature can be used to determine one or more characteristics of the fluid sample, such as the presence, absence, and / or concentration of the target gas, by comparing the recorded absorption signature with known absorption signatures (e.g., absorption signatures 882a to 882c).

[0092] As described herein, by generating light at multiple frequency comb wavelengths using a frequency comb illumination source, the absorption percentage of multiple frequency comb wavelengths interacting with a fluid sample can be determined simultaneously. In addition, by utilizing an optical cavity, the optical path length of the pulsed light emitted from the frequency comb illumination source can be increased. The increased optical path length enables more accurate detection of low concentrations of target gases within the fluid sample. As further described herein, by aligning one or more of the frequency comb wavelengths with one or more of the cavity resonance modes, the pulsed light aligned with the cavity resonance mode can propagate through the sample fluid with an increased optical path length while providing valuable absorption information across multiple frequency comb wavelengths.

[0093] Reference now Fig. 9 , an exemplary process 990 for determining a characteristic of a target gas in a fluid sample is provided. At block 902, a processor (e.g., controller 220) causes a frequency comb illumination source (e.g., frequency comb illumination source 102, 202, 602) to emit pulsed light (e.g., pulsed light 108, 208, 408, 608) including a plurality of frequency comb wavelengths, wherein the pulsed light is directed to an optical cavity (e.g., optical cavity 104, 204, 404) including a plurality of cavity resonance modes (e.g., cavity resonance modes 552a to 552c), and wherein the fluid sample is disposed within the optical cavity. As described herein, the frequency comb illumination can be configured to generate light at a plurality of frequency comb wavelengths that are evenly separated based on a pulse repetition rate of the frequency comb illumination source. The frequency comb illumination source is positioned such that the pulsed light is configured to enter a confined region of the optical cavity.

[0094] At block 904, the processor adjusts at least one of a physical property of the optical cavity and a physical property of the pulsed light to align a frequency comb wavelength in the plurality of frequency comb wavelengths with a cavity resonance mode in the plurality of cavity resonance modes. As described herein, the physical property of the optical cavity may include a reflectivity of a mirror element, a refractive index of one or more components within the optical cavity, an arrangement of the mirror element, an optical path length of the reflected light, and other similar properties. Each of these physical properties and other properties may have an effect on the frequency of light that undergoes constructive interference in the optical cavity and comprises a plurality of cavity resonance modes of the optical cavity.

[0095] In addition, the physical properties of the pulsed light can be adjusted to change the wavelength of the light including the multiple frequency comb wavelengths generated by the frequency comb illumination source. As described herein, the physical properties of the pulsed light can include the pulse repetition rate, the frequency of the pulsed light, or other similar properties. Adjusting the physical properties (such as the pulse repetition rate) can affect the free spectral range associated with the wavelength of the light generated by the frequency comb illumination source. One or both of the physical properties of the optical cavity and the physical properties of the frequency comb illumination source can be adjusted to align at least one of the frequency comb wavelengths with the cavity resonant mode. In some embodiments, multiple frequency comb wavelengths can be aligned with multiple cavity resonant modes.

[0096] At block 906, a controller receives an electrical signal proportional to the amplitude of the transmitted light from a photodetector (e.g., photodetector 106, 206, 606) positioned to receive transmitted light (e.g., transmitted light 112, transmitted light 212, transmitted light 412, transmitted light 612) that passes through a fluid sample (e.g., fluid sample 442, 642) within an optical cavity. As described herein, pulsed light presenting a frequency comb wavelength aligned with a cavity resonant mode may be reflected within the optical cavity. A fluid sample including one or more target gases is dispensed in a confined area of ​​the optical cavity, such as in a fluid sample chamber. When the reflected light is reflected through the fluid sample, light of different wavelengths is absorbed at different rates depending on the composition of the sample fluid. Light exiting the optical cavity is received at the photodetector. The photodetector is configured to transmit an electrical signal proportional to the amplitude or intensity of the transmitted light to a processor.

[0097] At block 908, the processor determines an absorption feature (e.g., absorption feature 882d) based at least in part on the amplitude of the transmitted light at a subset of the frequency comb wavelengths of the plurality of frequency comb wavelengths. The processor may record the amplitude of the transmitted light associated with one or more frequency comb wavelengths of the plurality of frequency comb wavelengths. In some embodiments, the set of frequency comb wavelengths comprising the absorption feature may be based on key features of the absorption feature of the target gas. In some embodiments, the set of frequency comb wavelengths comprising the absorption feature may be based on alignment of the frequency comb wavelengths with the plurality of cavity resonance modes.

[0098] At box 910, the processor determines a characteristic of the fluid sample based on the electrical signal. As described herein, the characteristic of the fluid sample may include the presence, absence, and / or concentration of a target gas in the fluid sample. For example, the processor may be configured to detect the presence of methane in the fluid sample. Alternatively, in another example, the processor may be configured to determine the concentration of carbon dioxide in the fluid sample. The processor may utilize the electrical signal and / or the absorption signature to determine a characteristic associated with the composition of the fluid sample. For example, the processor may determine unique aspects of the target gas, such as a specific wavelength at which the absorption of the target gas is abnormally high or low. The processor may then utilize the unique aspects of the absorption signature to determine the presence, absence, and / or concentration of the target gas.

[0099] In some embodiments, the physical properties of the optical cavity and / or the physical properties of the pulsed light can be further adjusted to determine the absorption of the fluid sample over a wider range of wavelengths. For example, the optical cavity can be used to determine the absorption characteristics at one or more frequency comb wavelengths, and then the optical cavity parameters and / or the frequency comb wavelengths can be shifted to probe a new set of wavelengths.

[0100] Those skilled in the art to which the present invention belongs will think of many modifications and other embodiments of the present invention set forth herein, which have the benefit of the teachings presented in the foregoing description and the associated drawings. Although the drawings show only certain components of the apparatus and system described herein, it should be understood that various other components may be used in conjunction with the system. Therefore, it should be understood that the present invention 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. In addition, the steps in the above-described method 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 may involve additional steps. Although specific terms are employed herein, they are used only in a general and descriptive sense, and not for restrictive purposes.

[0101] Although various embodiments according to the principles disclosed herein have been shown and described above, modifications may be made thereto by those skilled in the art without departing from the spirit and teachings of the present disclosure. The embodiments described herein are representative only and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the present disclosure. For example, those skilled in the art will recognize that such principles may be applied to breathalyzers, safety detection systems, atmospheric analysis tools, and the like. Alternative embodiments resulting from merging, integrating, and / or omitting features of the embodiments are also within the scope of the present disclosure. Therefore, the scope of protection is not limited by the above statements.

[0102] Additionally, the section headings used herein are intended to be consistent with the recommendations of 37 CFR 1.77 or to otherwise provide organizational cues. These headings shall not limit or characterize the inventions set forth in any claims that may issue from this disclosure.

[0103] The use of broad terms such as "comprising," "including," and "having" should be understood to provide support for narrower terms such as "consisting of," "consisting essentially of," and "composed essentially of." The use of the terms "optionally," "may," "might," "can," and the like with respect to any element of an embodiment means that the element is not required, or, alternatively, the element is required, both alternatives being within the scope of the embodiment. Additionally, reference to examples is for illustrative purposes only and is not intended to be exclusive.

Claims

1. A device, comprising: a frequency comb illumination source configured to emit pulsed light comprising a plurality of frequency comb wavelengths; and an optical cavity comprising a plurality of cavity resonance modes, wherein a fluid sample is disposed in the optical cavity; wherein a frequency comb wavelength of the plurality of frequency comb wavelengths is configured to be aligned with a cavity resonance mode of the plurality of cavity resonance modes, and Wherein a property of the fluid sample is determined based on one or more optical properties of light transmitted through the fluid sample within the optical cavity.

2. The device according to claim 1, further comprising: a photodetector positioned to receive the transmitted light, wherein the photodetector is configured to generate an electrical signal proportional to the amplitude of the transmitted light; and a controller electrically connected to the photodetector, The controller is configured as follows: determining an absorption signature based at least in part on the amplitude of the transmitted light at a subset of frequency comb wavelengths in the plurality of frequency comb wavelengths, and The characteristic of the fluid sample is determined based at least in part on the electrical signal received from the photodetector and the absorption signature.

3. The apparatus of claim 1, wherein the characteristic of the fluid sample is a concentration of a target gas.

4. The apparatus of claim 1 , wherein the frequency comb illumination source is configured to emit the pulsed light at a pulse repetition rate, and wherein the pulse repetition rate of the frequency comb illumination source matches a free spectral range of the optical cavity or a multiple thereof.

5. The apparatus of claim 1, wherein the frequency comb illumination source is a dual frequency comb spectral illumination source.

6. The apparatus of claim 1 , wherein the optical cavity comprises two or more mirror elements, wherein a physical property of the optical cavity is adjusted to modify the plurality of cavity resonance modes such that one or more comb wavelengths resonate within the optical cavity, and wherein the physical property of the optical cavity is at least one of a reflectivity of the two or more mirror elements, a refractive index of a component within the optical cavity, and an optical cavity length of the transmitted light within the optical cavity.

7. A method for determining a property of a fluid sample, the method comprising: causing a frequency comb illumination source to emit pulsed light including a plurality of frequency comb wavelengths, wherein the pulsed light is guided to an optical cavity comprising a plurality of cavity resonance modes, and wherein the fluid sample is disposed in the optical cavity; adjusting at least one of a physical property of the optical cavity and a physical property of the pulsed light to align a frequency comb wavelength of the plurality of frequency comb wavelengths with a cavity resonant mode of the plurality of cavity resonant modes, receiving an electrical signal proportional to the amplitude of the transmitted light from a photodetector positioned to receive the transmitted light, wherein the transmitted light passes through the fluid sample in the optical cavity; as well as The characteristic of the fluid sample is determined based on the electrical signal.

8. The method according to claim 7, further comprising: determining an absorption signature based at least in part on the amplitude of the transmitted light at a subset of frequency comb wavelengths in the plurality of frequency comb wavelengths; as well as The property of the fluid sample is determined based at least in part on the absorption signature.

9. The method of claim 7, wherein the frequency comb illumination source is configured to emit the pulsed light at a pulse repetition rate, and wherein the pulse repetition rate of the frequency comb illumination source matches a free spectral range of the optical cavity or a multiple thereof.

10. A system for determining the concentration of a target gas in a fluid sample, the system comprising: a fluid sample inlet configured to receive the fluid sample into a fluid sample chamber; an optical cavity comprising a plurality of cavity resonance modes, wherein a portion of the fluid sample chamber is within the optical cavity; a frequency comb illumination source configured to emit pulsed light comprising a plurality of frequency comb wavelengths; a photodetector positioned to receive transmitted light passing through the portion of the fluid sample chamber within the optical cavity, wherein the photodetector is configured to generate an electrical signal proportional to the amplitude of the transmitted light; and a controller electrically connected to the photodetector, wherein a frequency comb wavelength of the plurality of frequency comb wavelengths is configured to be aligned with a cavity resonance mode of the plurality of cavity resonance modes, and Wherein the controller is configured to determine the concentration of the target gas within the fluid sample based on the electrical signal received from the photodetector.

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