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<p><b>Cavity ring-down spectroscopy</b> (<b>CRDS</b>) is a highly sensitive <a href="/wiki/Spectroscopy" title="Spectroscopy">optical spectroscopic</a> technique that enables measurement of absolute <a href="/wiki/Optical_extinction" class="mw-redirect" title="Optical extinction">optical extinction</a> by samples that <a href="/wiki/Scattering" title="Scattering">scatter</a> and <a href="/wiki/Absorption_(electromagnetic_radiation)" title="Absorption (electromagnetic radiation)">absorb</a> light. It has been widely used to study gaseous samples which absorb light at specific <a href="/wiki/Wavelength" title="Wavelength">wavelengths</a>, and in turn to determine <a href="/wiki/Mole_fraction" title="Mole fraction">mole fractions</a> down to the <a href="/wiki/Parts_per_trillion" class="mw-redirect" title="Parts per trillion">parts per trillion</a> level. The technique is also known as <b>cavity ring-down laser absorption spectroscopy</b> (<b>CRLAS</b>). </p><p>A typical CRDS setup consists of a <a href="/wiki/Laser" title="Laser">laser</a> that is used to illuminate a high-finesse <a href="/wiki/Optical_cavity" title="Optical cavity">optical cavity</a>, which in its simplest form consists of two highly reflective <a href="/wiki/Mirror" title="Mirror">mirrors</a>. When the laser is in <a href="/wiki/Resonance" title="Resonance">resonance</a> with a cavity <a href="/wiki/Normal_mode" title="Normal mode">mode</a>, <a href="/wiki/Intensity_(physics)" title="Intensity (physics)">intensity</a> builds up in the cavity due to <a href="/wiki/Constructive_interference" class="mw-redirect" title="Constructive interference">constructive interference</a>. The laser is then turned off in order to allow the measurement of the exponentially decaying light intensity leaking from the cavity. During this decay, light is reflected back and forth thousands of times between the mirrors giving an effective path length for the extinction on the order of a few kilometers. </p><p>If a light-absorbing material is now placed in the cavity, the <a href="/wiki/Mean_lifetime" class="mw-redirect" title="Mean lifetime">mean lifetime</a> decreases as fewer bounces through the medium are required before the light is fully absorbed, or absorbed to some fraction of its initial intensity. A CRDS setup measures how long it takes for the light to decay to 1/<i>e</i> of its initial intensity, and this "ringdown time" can be used to calculate the concentration of the absorbing substance in the gas mixture in the cavity. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Detailed_description">Detailed description</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cavity_ring-down_spectroscopy&action=edit&section=1" title="Edit section: Detailed description"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Cavity ring-down spectroscopy is a form of <a href="/wiki/Laser_absorption_spectroscopy" class="mw-redirect" title="Laser absorption spectroscopy">laser absorption spectroscopy</a>. In CRDS, a laser pulse is trapped in a highly reflective (typically R > 99.9%) <a href="/wiki/Optical_cavity" title="Optical cavity">detection cavity</a>. The intensity of the trapped pulse will decrease by a fixed percentage during each round trip within the cell due to <a href="/wiki/Absorption_(optics)" class="mw-redirect" title="Absorption (optics)">absorption</a>, scattering by the medium within the cell, and reflectivity losses. The intensity of light within the cavity is then determined as an <a href="/wiki/Exponential_function" title="Exponential function">exponential function</a> of time. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle I(t)=I_{0}\exp \left(-t/\tau \right)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>I</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> <mo>=</mo> <msub> <mi>I</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mi>exp</mi> <mo>⁡</mo> <mrow> <mo>(</mo> <mrow> <mo>−</mo> <mi>t</mi> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mi>τ</mi> </mrow> <mo>)</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle I(t)=I_{0}\exp \left(-t/\tau \right)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/405d8914c17697b42771d3276f5400380a9b67e0" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:19.757ex; height:2.843ex;" alt="{\displaystyle I(t)=I_{0}\exp \left(-t/\tau \right)}"></span></dd></dl> <p>The principle of operation is based on the measurement of a decay rate rather than an absolute <a href="/wiki/Absorbance" title="Absorbance">absorbance</a>. This is one reason for the increased sensitivity over traditional absorption spectroscopy, as the technique is then immune to shot-to-shot laser fluctuations. The decay constant, τ, which is the time taken for the intensity of light to fall to 1/e of the initial intensity, is called the ring-down time and is dependent on the loss mechanism(s) within the cavity. For an empty cavity, the decay constant is dependent on mirror loss and various optical phenomena like scattering and refraction: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \tau _{0}={\frac {n}{c}}\cdot {\frac {l}{1-R+X}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>n</mi> <mi>c</mi> </mfrac> </mrow> <mo>⋅</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>l</mi> <mrow> <mn>1</mn> <mo>−</mo> <mi>R</mi> <mo>+</mo> <mi>X</mi> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \tau _{0}={\frac {n}{c}}\cdot {\frac {l}{1-R+X}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/7df06c88626c8a2b6cf1a1a9f141b1b66657445c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:20.502ex; height:5.509ex;" alt="{\displaystyle \tau _{0}={\frac {n}{c}}\cdot {\frac {l}{1-R+X}}}"></span></dd></dl> <p>where <i>n</i> is the <a href="/wiki/Index_of_refraction" class="mw-redirect" title="Index of refraction">index of refraction</a> within the cavity, <i>c</i> is the <a href="/wiki/Speed_of_light" title="Speed of light">speed of light</a> in vacuum, <i>l</i> is the cavity length, <i>R</i> is the mirror reflectivity, and <i>X</i> takes into account other miscellaneous optical losses. This equation uses the approximation that ln(1+<i>x</i>) ≈ <i>x</i> for <i>x</i> close to zero, which is the case under cavity ring-down conditions. Often, the miscellaneous losses are factored into an effective mirror loss for simplicity. An absorbing species in the cavity will increase losses according to the <a href="/wiki/Beer-Lambert_law" class="mw-redirect" title="Beer-Lambert law">Beer-Lambert law</a>. Assuming the sample fills the entire cavity, </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \tau ={\frac {n}{c}}\cdot {\frac {l}{1-R+X+\alpha l}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>τ</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>n</mi> <mi>c</mi> </mfrac> </mrow> <mo>⋅</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>l</mi> <mrow> <mn>1</mn> <mo>−</mo> <mi>R</mi> <mo>+</mo> <mi>X</mi> <mo>+</mo> <mi>α</mi> <mi>l</mi> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \tau ={\frac {n}{c}}\cdot {\frac {l}{1-R+X+\alpha l}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/6f7724b2896b1706b68f0485fe4b3cb10af7bf35" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:24.655ex; height:5.676ex;" alt="{\displaystyle \tau ={\frac {n}{c}}\cdot {\frac {l}{1-R+X+\alpha l}}}"></span></dd></dl> <p>where α is the absorption coefficient for a specific analyte concentration at the cavity's resonance wavelength. The decadic absorbance, <i>A</i>, due to the analyte can be determined from both ring-down times. </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle A={\frac {n}{c}}\cdot {\frac {l}{2.303}}\cdot \left({\frac {1}{\tau }}-{\frac {1}{\tau _{0}}}\right)}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>A</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>n</mi> <mi>c</mi> </mfrac> </mrow> <mo>⋅</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>l</mi> <mn>2.303</mn> </mfrac> </mrow> <mo>⋅</mo> <mrow> <mo>(</mo> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <mi>τ</mi> </mfrac> </mrow> <mo>−</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <msub> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> </mfrac> </mrow> </mrow> <mo>)</mo> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle A={\frac {n}{c}}\cdot {\frac {l}{2.303}}\cdot \left({\frac {1}{\tau }}-{\frac {1}{\tau _{0}}}\right)}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/81c26e826e0e3ad5f53fafc1cdc7dce950c66e97" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.505ex; width:27.77ex; height:6.176ex;" alt="{\displaystyle A={\frac {n}{c}}\cdot {\frac {l}{2.303}}\cdot \left({\frac {1}{\tau }}-{\frac {1}{\tau _{0}}}\right)}"></span></dd></dl> <p>Alternatively, the <a href="/wiki/Molar_absorptivity" class="mw-redirect" title="Molar absorptivity">molar absorptivity</a>, ε, and analyte concentration, <i>C</i>, can be determined from the ratio of both ring-down times. If <i>X</i> can be neglected, one obtains </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {\tau _{0}}{\tau }}=1+{\frac {\alpha l}{1-R}}=1+{\frac {2.303\epsilon lC}{(1-R)}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>τ</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>0</mn> </mrow> </msub> <mi>τ</mi> </mfrac> </mrow> <mo>=</mo> <mn>1</mn> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>α</mi> <mi>l</mi> </mrow> <mrow> <mn>1</mn> <mo>−</mo> <mi>R</mi> </mrow> </mfrac> </mrow> <mo>=</mo> <mn>1</mn> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2.303</mn> <mi>ϵ</mi> <mi>l</mi> <mi>C</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>−</mo> <mi>R</mi> <mo stretchy="false">)</mo> </mrow> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {\tau _{0}}{\tau }}=1+{\frac {\alpha l}{1-R}}=1+{\frac {2.303\epsilon lC}{(1-R)}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2f62211871f541b9fd4fef05af36bcb1e17fee65" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:33.249ex; height:6.176ex;" alt="{\displaystyle {\frac {\tau _{0}}{\tau }}=1+{\frac {\alpha l}{1-R}}=1+{\frac {2.303\epsilon lC}{(1-R)}}}"></span></dd></dl> <p>When a ratio of species' concentrations is the analytical objective, as for example in carbon-13 to carbon-12 measurements in carbon dioxide, the ratio of ring-down times measured for the same sample at the relevant absorption frequencies can be used directly with extreme accuracy and precision. </p> <div class="mw-heading mw-heading2"><h2 id="Advantages_of_CRDS">Advantages of CRDS</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cavity_ring-down_spectroscopy&action=edit&section=2" title="Edit section: Advantages of CRDS"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are two main advantages to CRDS over other absorption methods: </p><p>First, it is not affected by fluctuations in the laser intensity. In most absorption measurements, the light source must be assumed to remain steady between blank (no <a href="/wiki/Analyte" title="Analyte">analyte</a>), standard (known amount of analyte), and sample (unknown amount of analyte). Any drift (change in the light source) between measurements will introduce errors. In CRDS, the ringdown time does not depend on the intensity of the laser, so fluctuations of this type are not a problem. Independency from laser intensity makes CRDS needless to any calibration and comparison with standards.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>Second, it is very sensitive due to its long pathlength. In absorption measurements, the smallest amount that can be detected is proportional to the length that the light travels through a sample. Since the light reflects many times between the mirrors, it ends up traveling long distances. For example, a laser pulse making 500 round trips through a 1-meter cavity will effectively have traveled through 1 kilometer of sample. </p><p>Thus, the advantages include: </p> <ul><li>High sensitivity due to the multipass nature (i.e. long pathlength) of the detection cell.</li> <li>Immunity to shot variations in laser intensity due to the measurement of a rate constant.</li> <li>Wide range of use for a given set of mirrors; typically, ±5% of the center wavelength.</li> <li>High throughput, individual ring down events occur on the millisecond time scale.</li> <li>No need for a <a href="/wiki/Fluorophore" title="Fluorophore">fluorophore</a>, which makes it more attractive than <a href="/wiki/Laser-induced_fluorescence" title="Laser-induced fluorescence">laser-induced fluorescence</a> (LIF) or <a href="/wiki/Resonance-enhanced_multiphoton_ionization" title="Resonance-enhanced multiphoton ionization">resonance-enhanced multiphoton ionization</a> (REMPI) for some (e.g. rapidly predissociating) systems.</li> <li>Commercial systems available.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Disadvantages_of_CRDS">Disadvantages of CRDS</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cavity_ring-down_spectroscopy&action=edit&section=3" title="Edit section: Disadvantages of CRDS"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>Spectra cannot be acquired quickly due to the <a href="/wiki/Monochromatic" class="mw-redirect" title="Monochromatic">monochromatic</a> laser source which is used. Having said this, some groups are now beginning to develop the use of broadband <a href="/wiki/LED" class="mw-redirect" title="LED">LED</a> or <a href="/wiki/Supercontinuum" title="Supercontinuum">supercontinuum</a> sources<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> for CRDS, the light of which can then be dispersed by a <a href="/wiki/Diffraction_grating" title="Diffraction grating">grating</a> onto a <a href="/wiki/Charge-coupled_device" title="Charge-coupled device">CCD</a>, or <a href="/wiki/Fourier_transform" title="Fourier transform">Fourier transformed</a> spectrometer (mainly in broadband analogues of CRDS). Perhaps more importantly, the development of CRDS based techniques have now been demonstrated over the range from the near UV to the mid-infrared.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> In addition, the frequency-agile rapid scanning (FARS) CRDS technique has been developed to overcome the mechanical or thermal frequency tuning which typically limits CRDS acquisition rates. The FARS method utilizes an electro-optic modulator to step a probe laser side band to successive cavity modes, eliminating tuning time between data points and allowing for acquisition rates about 2 orders of magnitude faster than traditional thermal tuning.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup></li> <li>Analytes are limited both by the availability of tunable laser light at the appropriate wavelength and also the availability of high reflectance mirrors at those wavelengths.</li> <li>Expense: the requirement for laser systems and high reflectivity mirrors often makes CRDS orders of magnitude more expensive than some alternative spectroscopic techniques.</li></ul> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cavity_ring-down_spectroscopy&action=edit&section=4" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Absorption_spectroscopy" title="Absorption spectroscopy">Absorption spectroscopy</a></li> <li><a href="/wiki/Laser_absorption_spectrometry" title="Laser absorption spectrometry">Laser absorption spectrometry</a></li> <li><a href="/wiki/Noise-immune_cavity-enhanced_optical_heterodyne_molecular_spectroscopy" title="Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy">Noise-Immune Cavity-Enhanced Optical-Heterodyne Molecular Spectroscopy (NICE-OHMS)</a></li> <li><a href="/wiki/TDLAS" class="mw-redirect" title="TDLAS">Tunable Diode Laser Absorption Spectroscopy (TDLAS)</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Cavity_ring-down_spectroscopy&action=edit&section=5" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFSoran_ShadmanCharles_RoseAzer_P._Yalin2016" class="citation journal cs1">Soran Shadman; Charles Rose; Azer P. 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"Cavity ring-down spectroscopy for quantitative absorption measurements". <i>The Journal of Chemical Physics</i>. <b>102</b> (7): 2708–2717. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1995JChPh.102.2708Z">1995JChPh.102.2708Z</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1063%2F1.468647">10.1063/1.468647</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Journal+of+Chemical+Physics&rft.atitle=Cavity+ring-down+spectroscopy+for+quantitative+absorption+measurements&rft.volume=102&rft.issue=7&rft.pages=2708-2717&rft.date=1995-02-15&rft_id=info%3Adoi%2F10.1063%2F1.468647&rft_id=info%3Abibcode%2F1995JChPh.102.2708Z&rft.au=Piotr+Zalicki&rft.au=Richard+N.+Zare&rfr_id=info%3Asid%2Fen.wikipedia.org%3ACavity+ring-down+spectroscopy" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGiel_BerdenRudy_PeetersGerard_Meijer2000" class="citation journal cs1">Giel Berden; Rudy Peeters; Gerard Meijer (2000). <a rel="nofollow" class="external text" href="https://www.differ.nl/node/754">"Cavity ring-down spectroscopy: Experimental schemes and applications"</a>. <i>International Reviews in Physical Chemistry</i>. <b>19</b> (4): 565–607. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2000IRPC...19..565B">2000IRPC...19..565B</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1080%2F014423500750040627">10.1080/014423500750040627</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:98510055">98510055</a>.</cite><span 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title="Fourier-transform infrared spectroscopy">FT-IR</a></li> <li><a href="/wiki/Raman_spectroscopy" title="Raman spectroscopy">Raman</a></li> <li><a href="/wiki/Resonance_Raman_spectroscopy" title="Resonance Raman spectroscopy">Resonance Raman</a></li> <li><a href="/wiki/Rotational_spectroscopy" title="Rotational spectroscopy">Rotational</a></li> <li><a href="/wiki/Rotational%E2%80%93vibrational_spectroscopy" title="Rotational–vibrational spectroscopy">Rotational–vibrational</a></li> <li><a href="/wiki/Molecular_vibration" title="Molecular vibration">Vibrational</a></li> <li><a href="/wiki/Vibrational_circular_dichroism" title="Vibrational circular dichroism">Vibrational circular dichroism</a></li> <li><a href="/wiki/Nuclear_resonance_vibrational_spectroscopy" title="Nuclear resonance vibrational spectroscopy">Nuclear resonance vibrational spectroscopy</a></li> <li><a href="/wiki/Vibrational_spectroscopy_of_linear_molecules" title="Vibrational spectroscopy of linear molecules">Vibrational spectroscopy of linear molecules</a></li> <li><a href="/wiki/Thermal_infrared_spectroscopy" title="Thermal infrared spectroscopy">Thermal infrared spectroscopy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">UV–Vis–NIR "Optical"</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ultraviolet%E2%80%93visible_spectroscopy" title="Ultraviolet–visible spectroscopy">Ultraviolet–visible</a></li> <li><a href="/wiki/Fluorescence_spectroscopy" title="Fluorescence spectroscopy">Fluorescence</a> <ul><li><a href="/wiki/Cold_vapour_atomic_fluorescence_spectroscopy" title="Cold vapour atomic fluorescence spectroscopy">Cold vapour atomic</a></li></ul></li> <li><a href="/wiki/Vibronic_spectroscopy" title="Vibronic spectroscopy">Vibronic</a></li> <li><a href="/wiki/Near-infrared_spectroscopy" title="Near-infrared spectroscopy">Near-infrared</a></li> <li><a href="/wiki/Resonance-enhanced_multiphoton_ionization" title="Resonance-enhanced multiphoton ionization">Resonance-enhanced multiphoton ionization</a> (REMPI)</li> <li><a href="/wiki/Raman_spectroscopy" title="Raman spectroscopy">Raman</a> <ul><li><a href="/wiki/Coherent_anti-Stokes_Raman_spectroscopy" title="Coherent anti-Stokes Raman spectroscopy">Coherent anti-Stokes</a></li></ul></li> <li><a href="/wiki/Raman_optical_activity" title="Raman optical activity">Raman optical activity</a></li> <li><a href="/wiki/Laser-induced_breakdown_spectroscopy" title="Laser-induced breakdown spectroscopy">Laser-induced breakdown</a></li> <li><a href="/wiki/Atomic_spectroscopy" title="Atomic spectroscopy">Atomic</a> <ul><li><a href="/wiki/Atomic_emission_spectroscopy" title="Atomic emission spectroscopy">emission</a> <ul><li><a href="/wiki/Glow-discharge_optical_emission_spectroscopy" title="Glow-discharge optical emission spectroscopy">Glow-discharge optical</a></li></ul></li> <li><a href="/wiki/Atomic_absorption_spectroscopy" title="Atomic absorption spectroscopy">absorption</a></li></ul></li> <li><a class="mw-selflink selflink">Cavity ring-down spectroscopy</a></li> <li><a href="/wiki/Saturated_absorption_spectroscopy" title="Saturated absorption spectroscopy">Saturated absorption spectroscopy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">X-ray and Gamma ray</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/X-ray_spectroscopy" title="X-ray spectroscopy">X-ray</a> <ul><li><a href="/wiki/Energy-dispersive_X-ray_spectroscopy" title="Energy-dispersive X-ray spectroscopy">Energy-dispersive</a></li> <li><a href="/wiki/X-ray_emission_spectroscopy" title="X-ray emission spectroscopy">Emission</a></li> <li><a href="/wiki/Extended_X-ray_absorption_fine_structure" title="Extended X-ray absorption fine structure">Extended X-ray absorption fine structure</a></li></ul></li> <li><a href="/wiki/Gamma_spectroscopy" title="Gamma spectroscopy">Gamma</a></li> <li><a href="/wiki/M%C3%B6ssbauer_spectroscopy" title="Mössbauer spectroscopy">Mössbauer</a> <ul><li><a href="/wiki/Conversion_electron_M%C3%B6ssbauer_spectroscopy" title="Conversion electron Mössbauer spectroscopy">Conversion electron</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Electron</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Photoemission_spectroscopy" title="Photoemission spectroscopy">Photoelectron/photoemission</a> <ul><li><a href="/wiki/X-ray_photoelectron_spectroscopy" title="X-ray photoelectron spectroscopy">X-ray</a></li> <li><a href="/wiki/Ultraviolet_photoelectron_spectroscopy" title="Ultraviolet photoelectron spectroscopy">UV</a></li> <li><a href="/wiki/Angle-resolved_photoemission_spectroscopy" title="Angle-resolved photoemission spectroscopy">Angle-resolved</a></li> <li><a href="/wiki/Two-photon_photoelectron_spectroscopy" title="Two-photon photoelectron spectroscopy">Two-photon</a></li></ul></li> <li><a href="/wiki/Auger_electron_spectroscopy" title="Auger electron spectroscopy">Auger</a></li> <li><a href="/wiki/Electron_phenomenological_spectroscopy" title="Electron phenomenological spectroscopy">phenomenological</a></li> <li><a href="/wiki/Electron_paramagnetic_resonance" title="Electron paramagnetic resonance">paramagnetic</a></li> <li><a href="/wiki/Beta_spectroscopy" class="mw-redirect" title="Beta spectroscopy">Beta spectroscopy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Nucleon</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Alpha-particle_spectroscopy" title="Alpha-particle spectroscopy">Alpha</a></li> <li><a href="/wiki/Inelastic_neutron_scattering" class="mw-redirect" title="Inelastic neutron scattering">Inelastic neutron scattering</a> <ul><li><a href="/wiki/Neutron_spin_echo" title="Neutron spin echo">Neutron spin echo</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Radiowave</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Nuclear_magnetic_resonance_spectroscopy" title="Nuclear magnetic resonance spectroscopy">NMR</a> <ul><li><a href="/wiki/Two-dimensional_nuclear_magnetic_resonance_spectroscopy" title="Two-dimensional nuclear magnetic resonance spectroscopy">2D</a></li></ul></li> <li><a href="/wiki/Terahertz_spectroscopy_and_technology" title="Terahertz spectroscopy and technology">Terahertz</a></li> <li><a href="/wiki/Electron_paramagnetic_resonance" title="Electron paramagnetic resonance">ESR/EPR</a></li> <li><a href="/wiki/Ferromagnetic_resonance" title="Ferromagnetic resonance">Ferromagnetic resonance</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Others</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks hlist navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">Data collection, processing</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fourier-transform_spectroscopy" title="Fourier-transform spectroscopy">Fourier-transform spectroscopy</a></li> <li><a href="/wiki/Hyperspectral_imaging" title="Hyperspectral imaging">Hyperspectral imaging</a></li> <li><a href="/wiki/Spectrophotometry" title="Spectrophotometry">Spectrophotometry</a></li> <li><a href="/wiki/Time_stretch_analog-to-digital_converter" class="mw-redirect" title="Time stretch analog-to-digital converter">Time-stretch</a></li> <li><a href="/wiki/Time-resolved_spectroscopy" title="Time-resolved spectroscopy">Time-resolved spectroscopy</a></li> <li><a href="/wiki/Video_spectroscopy" title="Video spectroscopy">Video spectroscopy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Measured phenomena</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Acoustic_resonance_spectroscopy" title="Acoustic resonance spectroscopy">Acoustic resonance spectroscopy</a></li> <li><a href="/wiki/Circular_dichroism" title="Circular dichroism">Circular dichroism spectroscopy</a></li> <li><a href="/wiki/Deep-level_transient_spectroscopy" title="Deep-level transient spectroscopy">Deep-level transient spectroscopy</a></li> <li><a href="/wiki/Dual-polarization_interferometry" title="Dual-polarization interferometry">Dual-polarization interferometry</a></li> <li><a href="/wiki/Hadron_spectroscopy" title="Hadron spectroscopy">Hadron spectroscopy</a></li> <li><a href="/wiki/Inelastic_electron_tunneling_spectroscopy" title="Inelastic electron tunneling spectroscopy">Inelastic electron tunneling spectroscopy</a> <ul><li><a href="/wiki/Scanning_tunneling_spectroscopy" title="Scanning tunneling spectroscopy">Scanning tunneling spectroscopy</a></li></ul></li> <li><a href="/wiki/Photoacoustic_spectroscopy" title="Photoacoustic spectroscopy">Photoacoustic spectroscopy</a></li> <li><a href="/wiki/Photothermal_spectroscopy" title="Photothermal spectroscopy">Photothermal spectroscopy</a></li> <li><a href="/wiki/Pump%E2%80%93probe_spectroscopy" class="mw-redirect" title="Pump–probe spectroscopy">Pump–probe spectroscopy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Applications</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Astronomical_spectroscopy" title="Astronomical spectroscopy">Astronomical spectroscopy</a></li> <li><a href="/wiki/Force_spectroscopy" title="Force spectroscopy">Force spectroscopy</a> (a misnomer)</li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <b><a href="/wiki/Category:Spectroscopy" title="Category:Spectroscopy">Category</a></b></li> <li><span class="noviewer" typeof="mw:File"><span title="Commons page"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/12px-Commons-logo.svg.png" decoding="async" width="12" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/18px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/24px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></span></span> <b><a href="https://commons.wikimedia.org/wiki/Category:Spectroscopy" class="extiw" title="commons:Category:Spectroscopy">Commons</a></b></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Lasers" style="padding:3px"><table class="nowraplinks hlist mw-collapsible mw-collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Lasers" title="Template:Lasers"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Lasers" title="Template talk:Lasers"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Lasers" title="Special:EditPage/Template:Lasers"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Lasers" style="font-size:114%;margin:0 4em"><a href="/wiki/Laser" title="Laser">Lasers</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><a href="/wiki/List_of_laser_articles" title="List of laser articles">List of laser articles</a></li> <li><a href="/wiki/List_of_laser_types" title="List of laser types">List of laser types</a></li> <li><a href="/wiki/List_of_laser_applications" title="List of laser applications">List of laser applications</a></li> <li><a href="/wiki/Laser_acronyms" title="Laser acronyms">Laser acronyms</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Types of lasers</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chemical_laser" title="Chemical laser">Chemical laser</a></li> <li><a href="/wiki/Dye_laser" title="Dye laser">Dye laser</a> <ul><li><a href="/wiki/Bubble_laser" title="Bubble laser">Bubble</a></li> <li><a href="/wiki/Liquid-crystal_laser" title="Liquid-crystal laser">Liquid-crystal</a></li></ul></li> <li><a href="/wiki/Gas_laser" title="Gas laser">Gas laser</a> <ul><li><a href="/wiki/Carbon_dioxide_laser" class="mw-redirect" title="Carbon dioxide laser">Carbon dioxide</a></li> <li><a href="/wiki/Excimer_laser" title="Excimer laser">Excimer</a></li> <li><a href="/wiki/Helium%E2%80%93neon_laser" title="Helium–neon laser">Helium–neon</a></li> <li><a href="/wiki/Ion_laser" title="Ion laser">Ion</a></li> <li><a href="/wiki/Nitrogen_laser" title="Nitrogen laser">Nitrogen</a></li></ul></li> <li><a href="/wiki/Free-electron_laser" title="Free-electron laser">Free-electron laser</a></li> <li><a href="/wiki/Laser_diode" title="Laser diode">Laser diode</a></li> <li><a href="/wiki/Solid-state_laser" title="Solid-state laser">Solid-state laser</a> <ul><li><a href="/wiki/Er:YAG_laser" title="Er:YAG laser">Er:YAG</a></li> <li><a href="/wiki/Nd:YAG_laser" title="Nd:YAG laser">Nd:YAG</a></li> <li><a href="/wiki/Raman_laser" title="Raman laser">Raman</a></li> <li><a href="/wiki/Ruby_laser" title="Ruby laser">Ruby</a></li> <li><a href="/wiki/Ti-sapphire_laser" class="mw-redirect" title="Ti-sapphire laser">Ti-sapphire</a></li></ul></li> <li><a href="/wiki/X-ray_laser" title="X-ray laser">X-ray laser</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Laser_science" title="Laser science">Laser physics</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Active_laser_medium" title="Active laser medium">Active laser medium</a></li> <li><a href="/wiki/Amplified_spontaneous_emission" title="Amplified spontaneous emission">Amplified spontaneous emission</a></li> <li><a href="/wiki/Continuous_wave" title="Continuous wave">Continuous wave</a></li> <li><a href="/wiki/Laser_ablation" title="Laser ablation">Laser ablation</a></li> <li><a href="/wiki/Laser_linewidth" title="Laser linewidth">Laser linewidth</a></li> <li><a href="/wiki/Lasing_threshold" title="Lasing threshold">Lasing threshold</a></li> <li><a href="/wiki/Population_inversion" title="Population inversion">Population inversion</a></li> <li><a href="/wiki/Ultrashort_pulse_laser" title="Ultrashort pulse laser">Ultrashort pulse</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Laser optics</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Beam_expander" title="Beam expander">Beam expander</a></li> <li><a href="/wiki/Beam_homogenizer" title="Beam homogenizer">Beam homogenizer</a></li> <li><a href="/wiki/Chirped_pulse_amplification" title="Chirped pulse amplification">Chirped pulse amplification</a></li> <li><a href="/wiki/Gain-switching" title="Gain-switching">Gain-switching</a></li> <li><a href="/wiki/Gaussian_beam" title="Gaussian beam">Gaussian beam</a></li> <li><a href="/wiki/Injection_seeder" title="Injection seeder">Injection seeder</a></li> <li><a href="/wiki/Laser_beam_profiler" title="Laser beam profiler">Laser beam profiler</a></li> <li><a href="/wiki/M_squared" title="M squared">M squared</a></li> <li><a href="/wiki/Mode_locking" title="Mode locking">Mode locking</a></li> <li><a href="/wiki/Multiple-prism_grating_laser_oscillator" title="Multiple-prism grating laser oscillator">Multiple-prism grating laser oscillator</a></li> <li><a href="/wiki/Optical_amplifier" title="Optical amplifier">Optical amplifier</a></li> <li><a href="/wiki/Optical_cavity" title="Optical cavity">Optical cavity</a></li> <li><a href="/wiki/Optical_isolator" title="Optical isolator">Optical isolator</a></li> <li><a href="/wiki/Output_coupler" title="Output coupler">Output coupler</a></li> <li><a href="/wiki/Q-switching" title="Q-switching">Q-switching</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" 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