(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(10) International Publication Number
`
`WO 2014/143276 A2
`
`KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, No, NZ,
`OM, PA, PE, PG, PH, PL, PT, QA, R0, RS, RU, Rw, SA,
`sc, SD, SE, SG, SK, SL, SM, ST, sv, SY, TH, TJ, TM,
`TN, TR, TT, Tz, UA, UG, US, UZ, vc, VN, ZA, ZM,
`zw.
`
`Designated States (unless otherwise indicated, for every
`land 9' regional protection available): ARIPO (BW, GH,
`GM, KE, LR, Ls, MW, Mz, NA, RW, SD, SL, sz, TZ,
`UG, ZM, ZW), Eurasian (AIM, AZ, BY, KG, KZ, RU, TJ,
`TM), European (AL, AT, BE, BG, CH, CY, cz, DE, DK,
`EE, Es, FI, FR, GB, GR, rm, HU, IE, IS, rr, LT, LU, Lv,
`MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM
`TR), OAPI (BF, BJ, CF, CG, CL CNL GA. GN, GQ, GW,
`KM, ML, MR, NE, SN, TD, TG).
`
`:
`&
`
`9—
`
`/
`WIPOIPCT
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`(43) International Publication Date
`18 September 2014 (18.09.2014)
`
`(51) International Patent Classification: Not classified
`
`(21) International Application Number:
`
`PCT/USZOI3/075767
`
`(22) International Filing Date:
`
`17 December 2013 (1712.201 3)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`(84)
`
`English
`
`(30) Priority Data:
`61/747,485
`
`3 l Decunber 2012 (31 12.2012)
`
`US
`
`(71) Applicant: OMNI MEDSCI, INC. [US/US]; 1718 New-
`port Creek Drive, Ann Arbor, Michigan 48103 (US).
`
`(72) Inventor: ISLAl“, Mohamed N.; 1718 Newport Creek
`Drive, Ann Arbor, Michigan 48103 (Us).
`
`Declarations under Rule 4.17:
`
`as to applicant's entitlement to applyfor and be granted a
`patent (Rule 4.1 709))
`
`(74) Agents: BIR, David S. et al; Brooks Kushman RC, 1000 —
`Town Cents, Twenty-Second Floor, Southfield, Michigan
`48075 (US).
`
`_
`
`(81) Designated States (unless otherwise indicated, for every
`kind 4' national protection available): AE, AG, AL, AM,
`Ao, AT, AU, AZ, BA, BB, BG, BH, BN, BR, Bw, BY,
`BZ, CA, CH, CL, CN, CO, CR CU, cz, DE, DK DM,
`DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT,
`HN,HR,HU,lD,IL,IN,IR,IS,JP,KE,KG,KN,KP,KR,
`
`as to the applicant's entitlement to claim thepriority 4' the
`earlier application (Rule 41 7(I-fi))
`Published:
`
`without international search report and to be republished
`upon receiptf that report (Rule 48.2(g))
`
`(54) Title: SHORT-WAVE INFRARED SUPER-CONTINUUM LASERS FOR NATURAL GAS LEAK DETECTION, EXPLOR-
`ATION, AND OTHER ACTIVE REMOTE SENSING APPLICATIONS
`
`FIGURE 1GB
`
`",6!
`
`
`
`
`
`zen/143276A2|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
`
`(57) Abstract: A syst- and method for using near-infrared or short-wave inflated (SWIR) light sources between approximately
`1.4-1.8 microns, 2—25 microns, 1.4—2.4 microns, 1-1 .8 microns for active remote sensing or hypu—spectral
`imaging for detection of
`natural gas leaks or exploration sense the presence ofhydro—carbon gases such as methane and ethane. Most hydro-carbons (gases,
`liquids and solids) exhibit spectral features in the SWIR, which may also coincide with atmospheric transmission windows (e_g,, ap-
`proximately 1.4—1.8 microns or 2—25 microns). Active remote sensing or hyper-spectral
`imaging systuns may include a fiber-based
`super-continuum laser and a detection system and may reside on an airmail, vehicle, handheld, or stationary platform Super-con -
`o tinunm sources may emit light in the near—inflated or SWlR s. An imaging spectrometer or a gas—filter correlation radiometer may be
`used to identify substances or materials such as oil spills, geology and mineralogy, vegetation, greenhouse gases, construction mater-
`ials, plastics, explosives, fertilizers, paints, or drugs.
`
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`WO 2014/143276
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`PCT/U52013/075767
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`SHORT-WAVE INFRARED SUPER-CONTINUUM LASERS FOR NATURAL GAS LEAK
`
`DETECTION, EHLORATION, AND OTHER ACTIVE REMOTE SENSING APPLICATIONS
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`
`[0001]
`
`This application claims the benefit of US. provisional application Serial No.
`
`61/747,485 filed December 31, 2012, the disclosure of which is hereby incorporated by reference in
`
`its entirety.
`
`[0002]
`
`This application is related to US. provisional application Serial No. 61,747,472 filed
`
`December 31, 2012; US. provisional application Serial Nos. 61/747,477 filed December 31, 2012;
`
`Serial No. 61/747,481 filed December 31, 2012; Serial No. 61/747,487 filed December 31, 2012;
`
`Serial No. 61/747,492 filed December 31, 2012; Serial No. 61/747,553 filed December 31, 2012;
`
`and Serial No. 61/754,698 filed January 21, 2013, the disclosures of which are hereby incorporated
`
`in their entirety by reference herein.
`
`[0003]
`
`This
`
`application is being filed concurrently with International Application
`
`entitled Near-Infrared Lasers For Non—Invasive Monitoring Of Glucose, Ketones,
`
`HBAlC, And Other Blood Constituents
`
`(OMNIOlOlPCT);
`
`International Application
`
`entitled Short-Wave Infrared Super—Continuum Lasers For Early Detection Of
`
`Dental Caries (Attorney Docket No. OMN10102PCT); US. Application
`
`entitled
`
`Focused Near—Infrared Lasers For Non—Invasive Vasectomy And Other Thermal Coagulation Or
`
`Occlusion Procedures (Attorney Docket No. OMN10103PUSP); US. Application
`
`entitled Short-Wave Infrared Super-Continuum Lasers For Detecting Counterfeit Or Illicit Drugs
`
`And Pharmaceutical Process Control (Attorney Docket No. OMNIOIOSPUSP); US. Application
`
`entitled Non-Invasive Treatment Of Varicose Veins (Attorney Docket No.
`
`OMN10106PUSP); and US. Application
`
`entitled Near—Infrared Super-Continuum
`
`Lasers For Early Detection Of Breast And Other Cancers (Attorney Docket No. OMNI0107PUSP),
`
`the disclosures ofwhich are hereby incorporated in their entirety by reference herein.
`
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`TECHNICAL FIELD
`
`[0004]
`
`This disclosure relates to lasers and light sources for natural gas leak detection,
`
`natural gas exploration, and other active remote sensing or hyper-spectral
`
`imaging applications
`
`including systems and methods for using near-infrared or short-wave infrared light sources for
`
`remote detection ofnatural gas and other active remote sensing applications.
`
`BACKGROUND AND SUlVIMARY
`
`[0005]
`
`Remote sensing or hyper-spectral imaging often uses the sun for illumination, and the
`
`short-wave infrared (SWIR) windows of about 1.5-1.8 microns and about 2-2.5 microns may be
`
`attractive because the atmosphere transmits in these wavelength ranges. Although the sun can be a
`
`bright and stable light source, its illumination may be affected by the time—of-day variations in the
`
`sun angle as well as weather conditions. For example, the sun may be advantageously used for
`
`applications such as hyper—spectral imaging only between about 9am to 3pm, and it may be diflicult
`
`to use the sun during cloudy days or during inclement weather.
`
`In one embodiment, the hyper-
`
`spectral sensors measure the reflected solar signal at hundreds (e.g., 100 to 200*) contiguous and
`
`narrow wavelength bands (e.g.. bandwidth between 5nm and IOnm). Hyper-spectral images may
`
`provide spectral
`
`information to identify and distinguish between spectrally similar materials,
`
`providing the ability to make proper distinctions among materials with only subtle signature
`
`differences.
`
`In the SWIR wavelength range, numerous gases,
`
`liquids and solids have unique
`
`chemical signatures, particularly materials comprising hydro-carbon bonds, 0-H bonds, N—H bonds,
`
`etc. Therefore, spectroscopy in the SWIR may be attractive for stand-off or remote sensing of
`
`materials based on their chemical signature, which may complement other imaging information.
`
`[0006]
`
`A SWIR super-continumn (SC) source may be able to replace at least in part the sun
`
`as an illumination source for active remote sensing, spectroscopy, or hyper-spectral imaging.
`
`In one
`
`embodiment, reflected light spectroscopy may be implemented using the SWIR light source, where
`
`the spectral reflectance can be the ratio of reflected energy to incident energy as a function of
`
`wavelength. Reflectance varies with wavelength for most materials because energy at certain
`
`wavelengths may be scattered or absorbed to different degrees. Using a SWIR light source may
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`permit 24/7 detection of solids, liquids, or gases based on their chemical signatures. As an example,
`
`natural gas leak detection and exploration may require the detection of methane and ethane, whose
`
`primary constituents include hydro-carbons.
`
`In the SWIR, for instance, methane and ethane exhibit
`
`various overtone and combination bands for vibrational and rotational resonances of hydro-carbons.
`
`In one embodiment, diffuse reflection spectroscopy or absorption spectroscopy may be used to
`
`detect the presence of natural gas. The detection system may include a gas filter correlation
`
`radiometer, in a particular embodiment. Also, one embodiment of the SWIR light source may be an
`
`all-fiber
`
`integrated SWIR SC source, which leverages
`
`the mature technologies
`
`from the
`
`telecommunications and fiber optics industry. Beyond natural gas, active remote sensing in the
`
`SWIR may also be used to identify other materials such as vegetation, greenhouse gases or
`
`environmental pollutants, soils and rocks, plastics,
`
`illicit drugs, counterfeit drugs, firearms and
`
`explosives, paints, and various building materials.
`
`[0007]
`
`In one embodiment, a measurement system includes a light source configured to
`
`generate an output optical beam comprising one or more semiconductor sources configured to
`
`generate an input beam, one or more optical amplifiers configured to receive at least a portion of the
`
`input beam and to deliver an intermediate beam to an output end of the one or more optical
`
`amplifiers, and one or more optical fibers configured to receive at least a portion of the intermediate
`
`beam and to deliver at least the portion of the intermediate beam to a distal end of the one or more
`
`optical fibers to form a first optical beam. A nonlinear element is configured to receive at least a
`
`portion of the first optical beam and to broaden a spectrum associated with the at least a portion of
`
`the first optical beam to at least 10m through a nonlinear effect in the nonlinear element to form the
`
`output optical beam with an output beam broadened spectrum, wherein at least a portion of the
`
`output beam broadened
`
`spectrum comprises
`
`a
`
`short-wave
`
`infrared wavelength between
`
`approximately 1400 nanometers and approximately 2500 nanometers, and wherein at least a portion
`
`of the one of more fibers is a fused silica fiber with a core diameter less than approximately 400
`
`microns. A measurement apparatus is configured to receive a received portion of the output optical
`
`beam and to deliver a delivered portion of the output optical beam to a sample, wherein the delivered
`
`portion of the output optical beam is configured to generate a spectroscopy output beam from the
`
`sample. A receiver is configured to receive at least a portion of the spectroscopy output beam
`
`having a bandwidth of at least 10 nanometers and to process the portion of the spectroscopy output
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`beam to generate an output signal, and wherein the light source and the receiver are remote from the
`
`sample, and wherein the output signal is based on a chemical composition of the sample.
`
`[0008]
`
`In another embodiment, a measurement system includes a light source configured to
`
`generate an output optical beam comprising a plurality of semiconductor sources configured to
`
`generate an input optical beam, a multiplexer configured to receive at least a portion of the input
`
`optical beam and to form an intermediate optical beam, and one or more fibers configured to receive
`
`at least a portion of the intermediate optical beam and to form the output optical beam, wherein the
`
`output optical beam comprises one or more optical wavelengths. A measurement apparatus is
`
`configured to receive a received portion of the output optical beam and to deliver a delivered portion
`
`of the output optical beam to a sample, wherein the delivered portion of the output optical beam is
`
`configured to generate a spectroscopy output beam from the sample. A receiver is configured to
`
`receive at
`
`least a portion of the spectroscopy output beam and to process the portion of the
`
`spectroscopy output beam to generate an output signal, wherein the light source and the receiver are
`
`remote from the sample, and wherein the output signal is based on a chemical composition of the
`
`sample.
`
`[0009]
`
`In yet another embodiment, a method of measuring includes generating an output
`
`optical beam comprising generating an input optical beam from a plurality of semiconductor sources,
`
`multiplexing at least a portion of the input optical beam and forming an intermediate optical beam,
`
`and guiding at least a portion of the intermediate optical beam and forming the output optical beam,
`
`wherein the output optical beam comprises one or more optical wavelengths. The method may also
`
`include receiving a received portion of the output optical beam and delivering a delivered portion of
`
`the output optical beam to a sample located remotely from the generated output optical beam, and
`
`generating a spectroscopy output beam having a bandwidth of at least 10 nanometers from the
`
`sample, wherein the spectroscopy output beam comprises spectral features of hydrocarbons or
`
`organic compounds. The method may ftuther include receiving at least a portion of the spectroscopy
`
`output beam and processing the portion of the spectroscopy output beam and generating an output
`
`signal, wherein the output signal is based on a chemical composition of the sample.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0010]
`
`For a more complete understanding of the present disclosure, and for further features
`
`and advantages thereof. reference is now made to the following description taken in conjunction
`
`with the accompanying drawings, in which:
`
`[0011]
`
`FIGURE 1 illustrates wavelength bands for different chemical compounds over the
`
`SWIR wavelength range of approximately 1400nm to 2500nm. Also indicated are whether the
`
`bands are overtone or combination bands.
`
`[0012]
`
`FIGURE 2 shows the absorption spectra for (a) methane and (b) ethane.
`
`[0013]
`
`FIGURE 3 illustrates the reflectance spectra for some members of the alkane family
`
`plus paraffin.
`
`[0014]
`
`FIGURE 4A depicts that micro-seepages may result from the vertical movement of
`
`hydro-carbons from their respective reservoirs to the surface.
`
`It is assumed that the rock column,
`
`including the seal rock, comprises interconnected fiactures or micro -fracture systems.
`
`[0015]
`
`FIGURE 4B illustrates that surface alterations may occur because leaking hydro-
`
`carbons set up near-surface oxidation and/or reduction zones that favor the development of a diverse
`
`array of chemical and mineralogical changes.
`
`[0016]
`
`FIGURE 5A shows the reflectance spectra for locations with natural gas fields (501)
`
`and locations without natural gas fields (502).
`
`[0017]
`
`FIGURE 5B illustrates spectra from field tests over regions with natural gas, which
`
`show two spectral features:
`
`one near 1.725 microns and another doublet between about 2.311
`
`microns and 2.36 microns.
`
`[0018]
`
`FIGURE 6 shows the reflectance spectra of a sample of oil emulsion fiom the Gulf of
`
`Mexico 2010 oil spill (different thicknesses of oil).
`
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`[0019]
`
`FIGURE 7 illustrates the reflectance spectra of some representative minerals that may
`
`be major components of rocks and soils.
`
`[0020]
`
`FIGURE 8 shows the reflectance spectra of different
`
`types of green vegetation
`
`compared with dry, yellowed grass.
`
`[0021]
`
`FIGURE 9 illustrates the atmospheric absorption and scattering of greenhouse gases
`
`at different wavelengths.
`
`[0022]
`
`FIGURE 10 overlays the reflectance for different building materials from the ASTER
`
`spectra library.
`
`[0023]
`
`FIGURE 11 shows the absorbance for two common plastics, polyethylene and
`
`polystyrene.
`
`[0024]
`
`FIGURE 12 shows the experimental set-up for a reflection-spectroscopy based stand-
`
`off detection system.
`
`[0025]
`
`FIGURE 13 illustrates the chemical structure and molecular
`
`formula for various
`
`explosives, along with the absorbance spectra obtained using a super-continuum source.
`
`[0026]
`
`FIGURE 14A shows the reflection spectra for gypsum, pine wood, ammonium nitrate
`
`and urea.
`
`[0027]
`
`FIGURE 14B illustrates the reflection spectra for three commercial automotive paints
`
`and military grade CARC paint (chemical agent resistant coating) (reflectance in this case are in
`
`arbitrary units).
`
`[0028]
`
`FIGURE 15 shows the mid-wave infiared and long—wave infrared absorption spectra
`
`for various illicit drugs.
`
`It is expected that overtone and combination bands should be evident in the
`
`SWIR and near-infrared wavelength bands.
`
`[0029]
`
`FIGURE 16A is a schematic diagram of the basic
`
`elements of an imaging
`
`spectrometer.
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`[0030]
`
`FIGURE 16B illustrates one example of a typical
`
`imaging spectrometer used in
`
`hyper—spectral imaging systems.
`
`[0031]
`
`FIGURE 17 shows one example of a gas-filter correlation radiometer, which is a
`
`detection system that uses a sample of the gas of interest as a spectral filter for the gas.
`
`[0032]
`
`FIGURE 18 exemplifies a dual-beam experimental set-up that may be used to
`
`subtract out (or at least minimize the adverse effects of) light source fluctuations.
`
`[0033]
`
`FIGURE 19 illustrates a block diagram or building blocks for constructing high
`
`power laser diode assemblies.
`
`[0034]
`
`FIGURE 20 shows a platform architecture for different wavelength ranges for an all-
`
`fiber-integrated, high powered, super-continuum light source.
`
`[0035]
`
`FIGURE 21 illustrates one preferred embodiment for a short-wave infrared super-
`
`continuum light source.
`
`[0036]
`
`FIGURE 22 shows the output spectrum from the SWIR SC laser of FIGURE 2 1 when
`
`about 10m length of fiber for SC generation is used. This fiber is a single-mode, non-dispersion
`
`shifted fiber that is optimized for operation near 1550mn.
`
`[0037]
`
`FIGURE 23 illustrates high power SWIR-SC lasers that may generate light between
`
`approximately 1.4-1.8 microns (top) or approximately 2-2.5 microns (bottom).
`
`DETAILED DESCRIPTION OF EXAIVIPLE EMBODIMENTS
`
`[0038]
`
`As required, detailed embodiments of the present disclosure are described herein;
`
`however,
`
`it
`
`is to be understood that the disclosed embodiments are merely exemplary of the
`
`disclosure that may be embodied in various and alternative forms. The figures are not necessarily to
`
`scale; some features may be exaggerated or minimized to show details of particular components.
`
`Therefore, specific structural and flmctional details disclosed herein are not to be interpreted as
`
`limiting, but merely as a representative basis for teaching one skilled in the art to variously employ
`
`the present disclosure.
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`[0039]
`
`One advantage of optical systems is that they can perform non-contact, stand-off or
`
`remote sensing distance spectroscopy of various materials. For remote sensing particularly, it may
`
`also be necessary to operate in atmospheric transmission windows. For example, two windows in
`
`the SWIR that
`
`transmit
`
`through the atmosphere are approximately 1.4-1.8 microns and 2-2.5
`
`microns.
`
`In general,
`
`the near-infrared region of the electromagnetic spectrum covers between
`
`approximately 0.7 microns (700nm) to about 2.5 microns (2500nm). However,
`
`it may also be
`
`advantageous to use just the short-wave infrared between approximately 1.4 microns (1400m) and
`
`about 2.5 microns (2500nm). One reason for preferring the SWIR over the entire NIR may be to
`
`operate in the so-called "eye safe" window, which corresponds to wavelengths longer than about
`
`1400nm. Therefore, for the remainder of the disclosure the SWIR will be used for illustrative
`
`purposes. However, it should be clear that the discussion that follows could also apply to using the
`
`NIR wavelength range, or other wavelength bands.
`
`[0040]
`
`In particular, wavelengths in the eye safe window may not transmit down to the retina
`
`of the eye, and therefore, these wavelengths may be less likely to create permanent eye damage from
`
`inadvertent exposure. The near-infrared wavelengths have the potential to be dangerous, because the
`
`eye cannot see the wavelengths (as it can in the visible), yet they can penetrate and cause damage to
`
`the eye. Even if a practitioner is not looking directly at the laser beam, the practitioner's eyes may
`
`receive stray light from a reflection or scattering from some surface. Hence, it can always be a good
`
`practice to use eye protection when working around lasers. Since wavelengths longer than about
`
`1400nm are substantially not transmitted to the retina or substantially absorbed in the retina, this
`
`wavelength range is known as the eye safe window. For wavelengths longer than 1400nm, in
`
`general only the cornea of the eye may receive or absorb the light radiation.
`
`[0041]
`
`The SWIR wavelength range may be particularly valuable for identifying materials
`
`based on their chemical composition because the wavelength range comprises overtones and
`
`combination bands for numerous chemical bonds. As an example, FIGURE 1 illustrates some of the
`
`wavelength bands for different chemical compositions. In 100 is plotted wavelength ranges in the
`
`SWIR (between 1400 and 2500nm) for different chemical compounds that have vibrational or
`
`rotational resonances, along with whether the bands are overtone or combination bands. Numerous
`
`hydro—carbons are represented, along with oxygen-hydrogen and carbon—oxygen bonds. Thus, gases,
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`liquids and solids that comprise these chemical compounds may exhibit spectral features in the
`
`SWIR wavelength range.
`
`In a particular embodiment, the spectra of organic compounds may be
`
`dominated by the C—H stretch. The C-H stretch flmdamental occurs near 3.4 microns, the first
`
`overtone is near 1.7 microns, and a combination band occurs near 2.3 microns.
`
`[0042]
`
`One embodiment of remote sensing that is used to identify and classify various
`
`materials is so-called "hyper-spectral imaging." Hyper-spectral sensors may collect information as a
`
`set of images, where each image represents a range of wavelengths over a spectral band. Hyper-
`
`spectral imaging may deal with imaging narrow spectral bands over an approximately continuous
`
`spectral range. As an example, in hyper-spectral imaging the sun may be used as the illumination
`
`source, and the daytime illumination may comprise direct solar illumination as well as scattered
`
`solar (skylight), which is caused by the presence of the atmosphere. However, the sun illumination
`
`changes with time of day, clouds or inclement weather may block the sun light, and the sun light is
`
`not accessible in the night time. Therefore, it would be advantageous to have a broadband light
`
`source covering the SWIR that may be used in place of the sun to identify or classify materials in
`
`remote sensing or stand-off detection applications.
`
`[0043]
`
`As used throughout this document, the term "couple" and or "coupled" refers to any
`
`direct or indirect communication between two or more elements, whether or not those elements are
`
`physically connected to one another. As used throughout this disclosure, the term "spectroscopy"
`
`means that a tissue or sample is inspected by comparing different features, such as wavelength (or
`
`frequency), spatial location, transmission, absorption, reflectivity, scattering, refractive index, or
`
`opacity.
`
`In one embodiment, "spectroscopy" may mean that the wavelength of the light source is
`
`varied, and the transmission, absorption or reflectivity of the tissue or sample is measured as a
`
`fimction of wavelength.
`
`In another embodimen , "spectroscopy" may mean that the wavelength
`
`dependence of the transmission, absorption or reflectivity is compared between different spatial
`
`locations on a tissue or sample. As an illustration, the "spectroscopy" may be performed by varying
`
`the wavelength of the light source, or by using a broadband light source and analyzing the signal
`
`using a spectrometer, wavemeter, or optical spectrum analyzer.
`
`[0044]
`
`As used throughout this document, the term "fiber laser" refers to a laser or oscillator
`
`that has as an output light or an optical beam, wherein at least a part of the laser comprises an optical
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`fiber. For instance, the fiber in the "fiber laser" may comprise one of or a combination of a single
`
`mode fiber, 3 multi-mode fiber, a mid-infiared fiber, a photonic crystal fiber, a doped fiber, a gain
`
`fiber, or, more generally, an approximately cylindrically shaped waveguide or light-pipe.
`
`In one
`
`embodiment, the gain fiber may be doped with rare earth material, such as ytterbium, erbium, and/or
`
`thulium.
`
`In another embodiment,
`
`the mid-infrared fiber may comprise one or a combination of
`
`fluoride fiber, ZBLAN fiber, chalcogenide fiber, tellurite fiber, or germanium doped fiber.
`
`In yet
`
`another embodiment,
`
`the single mode fiber may include standard single-mode fiber, dispersion
`
`shifted fiber, non-zero dispersion shifted fiber, high-nonlinearity fiber, and small core size fibers.
`
`[0045]
`
`As used throughout
`
`this disclosure,
`
`the term "pump laser" refers to a laser or
`
`oscillator that has as an output light or an optical beam, wherein the output light or optical beam is
`
`coupled to a gain medium to excite the gain medium, which in turn may amplify another input
`
`optical signal or beam.
`
`In one particular example, the gain medium may be a doped fiber, such as a
`
`fiber doped with ytterbium, erbium and/or thulium.
`
`In one embodiment, the "pump laser" may be a
`
`fiber laser, a solid state laser, a laser involving a nonlinear crystal, an optical parametric oscillator, a
`
`semiconductor laser, or a plurality of semiconductor lasers that may be multiplexed together.
`
`In
`
`another embodiment, the "pump laser" may be coupled to the gain medium by using a fiber coupler,
`
`a dichroic mirror, a multiplexer, a wavelength division multiplexer, a grating, or a fused fiber
`
`coupler.
`
`[0046]
`
`As used throughout
`
`this
`
`document,
`
`the
`
`term "super-continuum"
`
`and or
`
`"supercontinuum" and or "SC" refers to a broadband light beam or output that comprises a plurality
`
`of wavelengths.
`
`In a particular example, the plurality of wavelengths may be adjacent to one-
`
`another, so that the spectrum of the light beam or output appears as a continuous band when
`
`measured with a spectrometer.
`
`In one embodiment, the broadband light beam may have a bandwidth
`
`of at
`
`least
`
`lOnm.
`
`In another embodiment,
`
`the "super-continuum" may be generated through
`
`nonlinear optical
`
`interactions in a medium, such as an optical fiber or nonlinear crystal.
`
`For
`
`example,
`
`the "super-continuum" may be generated through one or a combination of nonlinear
`
`activities such as four-wave mixing, parametric amplification,
`
`the Raman effect, modulational
`
`instability, and self-phase modulation.
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`[0047]
`
`As used throughout this disclosure, the terms "optical ligh " and or "optical beam"
`
`and or "light beam" refer to photons or light transmitted to a particular location in space. The
`
`"optical light" and or "optical beam" and or "light beam" may be modulated or unmodulated, which
`
`also means that they may or may not contain information.
`
`In one embodiment, the "optical light"
`
`and or "optical beam" and or "light beam" may originate from a fiber, a fiber laser, a laser, a light
`
`emitting diode, a lamp, 3 pump laser, or a light source.
`
`[0048]
`
`As used throughout
`
`this disclosure,
`
`the term "remote sensing" may include the
`
`measuring of properties of an object from a distance, without physically sampling the object, for
`
`example by detection of the interactions of the object with an electromagnetic field.
`
`In one
`
`embodiment,
`
`the electromagnetic field may be in the optical wavelength range,
`
`including the
`
`infrared or SWIR. One particular form of remote sensing may be stand—ofl‘ detection, which may
`
`range from non-contact up to hundreds of meters away, for example.
`
`REMOTE SENSING OF NATURAL GAS LEAKS
`
`[0049]
`
`Natural gas may be a hydro-carbon gas mixture comprising primarily methane, with
`
`other hydro-carbons, carbon dioxide, nitrogen and hydrogen sulfide. Natural gas is important
`
`because it is an important energy source to provide heating and electricity. Moreover, it may also be
`
`used as fuel for vehicles and as a chemical feedstock in the manufacture of plastics and other
`
`commercially important organic chemicals. Although methane is the primary component of natural
`
`gas, to uniquely identify natural gas through spectroscopy requires monitoring of both methane and
`
`ethane. If only methane is used, then areas like cow pastures could be mistaken for natural gas fields
`
`or leaks. More specifically, the typical composition of natural gas is as follows:
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`Raneimole %
`
`87.0-96.0
`
`1.5-5.1
`
`0.1-1.5
`
`0-01-03
`
`001-03
`
`
`
`Trace-0.14
`
`Trace-0.04
`
`Trace-0.06
`
`0.7-5.6
`
`0.01-0.1
`
`Trace-0.02
`
`[0050]
`
`As one example of remote sensing of natural gas, a helicopter or aircraft may be
`
`flown at some elevation. The light source for remote sensing may direct the light beam toward the
`
`ground, and the diffuse reflected light may then be measured using a detection system on the aircraft.
`
`Thus, the helicopter or aircraft may be sampling a column area below it for natural gas, or whatever
`
`the material of interest is.
`
`In yet another embodiment,
`
`the column may sense aerosols of various
`
`sorts, as an example. Various kinds of SWIR light sources will be discussed later in this disclosure.
`
`The detection system may comprise, in one embodiment, a spectrometer followed by one or more
`
`detectors.
`
`In another embodiment,
`
`the detection system may be a dispersive element (examples
`
`include prisms, gratings, or other wavelength separators) followed by one or more detectors or
`
`detector arrays.
`
`In yet another embodiment,
`
`the detection system may comprise a gas-filter
`
`correlation radiometer.
`
`These are merely specific examples of the detection system, but
`
`combinations of these or other detection systems may also be used and are contemplated within the
`
`scope of this disclosure. Also, the use of aircraft is one particular example of a remote sensing
`
`system, but other system configurations may also be used and are included in the scope of this
`
`disclosure. For example, the light source and detection system may be placed in a fixed location,
`
`and for reflection the light source and detectors may be close to one another, while for transmission
`
`the light source and detectors may be at different locations.
`
`In yet another embodiment, the system
`
`could be placed on a vehicle such as an automobile or a truck, or the light source could be placed on
`
`one vehicle, while the detection system is on another vehicle.
`
`If the light source and detection
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`system are compact and lightweight, they might even be carried by a person in the field, either in
`
`their hands or in a backpack.
`
`[0051]
`
`Both methane and ethane are hydro-carbons with unique spectral signatures. For
`
`example, ethane is C2H6, while methane is CH4. Also, methane and ethane have inflated absorption
`
`bands near 1.6 microns, 2.4 microns, 3.3 microns and 7 microns.
`
`It should be noted that the
`
`approximately 7 micron lines cannot be observed generally due to atmospheric absorption.
`
`Although the fimdamental lines near 3.3 microns are stronger absorption features, the light sources
`
`and detectors in the mid-infrared