{ "id": "epmz62tge3", "slug": "infrared-spectroscopic-ellipsometry", "title": "Infrared spectroscopic ellipsometry", "updated": "2026-10-15", "topic_path": [ { "id": "physical", "label": "Physical world and mathematics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical" }, { "id": "physical.physics", "label": "Physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics" }, { "id": "physical.physics.matter-and-radiation", "label": "Matter and radiation physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics.matter-and-radiation" }, { "id": "physical.physics.matter-and-radiation.condensed-matter", "label": "Condensed matter physics", "api_url": "https://www.edgepedia.org/api/v1/topics/physical.physics.matter-and-radiation.condensed-matter" } ], "geo": [ { "id": "geo.nongeo.t1946.physical.physics.matter-and-radiation.condensed-matter", "label": "Non-geographic · 1946 to 2000: Condensed matter physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.physical.physics.matter-and-radiation.condensed-matter", "path": [ { "id": "geo.nongeo", "label": "Non-geographic", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo" }, { "id": "geo.nongeo.t1946", "label": "Non-geographic · 1946 to 2000", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946" }, { "id": "geo.nongeo.t1946.physical", "label": "Physical world and mathematics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.physical" }, { "id": "geo.nongeo.t1946.physical.physics", "label": "Physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.physical.physics" }, { "id": "geo.nongeo.t1946.physical.physics.matter-and-radiation", "label": "Matter and radiation physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.physical.physics.matter-and-radiation" }, { "id": "geo.nongeo.t1946.physical.physics.matter-and-radiation.condensed-matter", "label": "Condensed matter physics", "api_url": "https://www.edgepedia.org/api/v1/geo/geo.nongeo.t1946.physical.physics.matter-and-radiation.condensed-matter" } ] } ], "excerpt": "Infrared spectroscopic ellipsometry is a contactless, nondestructive optical technique measuring how infrared light's polarization changes on reflection, yielding dielectric functions, phonon properties, and free-carrier data.", "snippet": "Infrared spectroscopic ellipsometry is a contactless, nondestructive optical technique measuring how infrared light's polarization changes on reflection, yielding dielectric functions, phonon properties, and free-carrier data.", "node": "physical.physics.matter-and-radiation.condensed-matter", "markdown": "# Infrared spectroscopic ellipsometry\n\nInfrared spectroscopic ellipsometry is an optical characterization technique that measures how the polarization of infrared light changes upon reflection from or transmission through a material, in order to determine its dielectric function, vibrational (phonon) properties, and free-carrier properties without reference standards. Operating mainly in the mid-infrared from about 2.5 µm to 16.0 µm (4000–625 cm⁻¹), the fingerprint range of many molecular vibrations and phonons,[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry) it is a contactless, nondestructive probe of free-carrier and crystal-structure properties of semiconductor heterostructures.[2](https://www.sciencedirect.com/science/article/abs/pii/S0924203101001977) Its parameters are absolute, self-referenced values that require no reference sample.[3](https://beta.iopscience.iop.org/article/10.1088/1361-648X/ab8523)\n\n| Key fact | Value |\n| --- | --- |\n| Spectral range (typical commercial MIR) | 2.5–16.0 µm (4000–625 cm⁻¹); extended instruments reach 1.7–30 µm (333–5900 cm⁻¹)[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry) • [4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf) |\n| Measured quantities | tan Ψ (relative amplitude ratio) and Δ (relative phase difference) of p and s reflection coefficients[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry) |\n| Output | Complex dielectric function, phonon frequencies, static dielectric constants, free-carrier concentration, mobility, effective mass[2](https://www.sciencedirect.com/science/article/abs/pii/S0924203101001977) |\n| Thin-film sensitivity | 5 nm Nylon film on Au demonstrated; submonolayer sensitivity reported[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub) |\n| Angle of incidence | Typically about 70° for semiconductors, chosen near the Brewster angle; automated ranges of 32°–90° exist[6](https://link.springer.com/article/10.1007/s11051-009-9662-6) • [4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf) |\n| Fastest time resolution | 10 µs at a single wavelength, 100 ms or less for full spectra (quantum-cascade-laser ellipsometry)[7](https://www.degruyterbrill.com/document/doi/10.1515/aot-2022-0013/html) |\n\n## How it works\n\nEllipsometry measures the change in polarization state of light interacting with a sample. The fundamental quantity is\n\n\\[ \\rho = \\tan \\Psi \\, e^{i\\Delta} = \\frac{R_{P}}{R_{S}}, \\]\n\nthe ratio of the complex Fresnel reflection coefficients for p- and s-polarized light, where tan Ψ is the relative amplitude ratio and \\( \\Delta = \\delta_{1} - \\delta_{2} \\) is the phase shift upon reflection.[8](http://pages.charlotte.edu/glenn-boreman/wp-content/uploads/sites/146/2014/06/Folks_PSSc_5_2008.pdf) From ρ the optical constants are constrained: the complex refractive index \\( N = n + ik \\) relates to the complex dielectric function \\( \\varepsilon = \\varepsilon_{1} + i\\varepsilon_{2} \\) via \\( N = \\sqrt{\\varepsilon} \\),[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry) and equivalently \\( \\varepsilon = (n + ik)^{2} \\) can be obtained through Ψ and Δ with no need for Kramers–Kronig transforms.[6](https://link.springer.com/article/10.1007/s11051-009-9662-6) Direct inversion of ρ is only possible for simple samples, such as a homogeneous, isotropic, semi-infinite material at a known angle of incidence; for films and multilayers the optical constants are retrieved by fitting a layer-stack model.\n\nThis differs from ordinary IR reflectance or absorbance in two ways. First, an intensity measurement records one number per wavelength and needs a reference beam or background spectrum; ellipsometry records two self-referenced parameters per wavelength and is hardly affected by light-source instabilities, atmospheric absorption, or ambient unpolarized stray light.[3](https://beta.iopscience.iop.org/article/10.1088/1361-648X/ab8523) Second, because phase as well as amplitude is measured, both n and k are determined directly over the measured range without extrapolating data as a Kramers–Kronig analysis would.[4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf)\n\n## How it is done\n\nSources are typically a globar, synchrotron radiation, or a tunable quantum cascade laser (QCL); FT-IR spectrometers are the usual spectral engine, though infrared grating spectrometers are also used.[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry)\n\nThe angle of incidence is chosen carefully depending on the Brewster angle of the materials; about 70° is typical for semiconductors, and commercial instruments offer automated angles from 32° to 90° with unambiguous Δ from 0° to 360°.[6](https://link.springer.com/article/10.1007/s11051-009-9662-6) • [4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf)\n\nExtraction of sample properties is an indirect process: a theoretical model of the layer stack, typically the thickness and refractive index of each layer plus the substrate, is adjusted until calculated spectra match the measured ones.[9](https://journals.sagepub.com/doi/10.1366/12-06883) Fit quality is judged with a figure of merit, most popularly based on the mean square root of the differences between measured and calculated data; Mueller-matrix instruments instead minimize the error-weighted reduced \\( \\chi^{2} \\) over all normalized matrix elements using Levenberg–Marquardt regression.[9](https://journals.sagepub.com/doi/10.1366/12-06883) • [10](https://www.helmholtz-berlin.de/pubbin/oai_publication?ID=102335&VT=1)\n\n## Origin\n\nThe first spectroscopic IR ellipsometers were based on grating monochromators with rotating polarizer/analyzer (RAE) or photoelastic modulator (PME) configurations, and their sensitivity was limited by the weak detected signal intensity.[11](https://doi.org/10.1063/1.1143953)\n\nThe FTIR-based form of the technique was reported by more than one group in 1989. F. Ferrieu described in Review of Scientific Instruments (1989) a prototype infrared spectroscopic ellipsometer using a Fourier transform PC-based infrared spectrometer, with applications to bulk substrates, thick layered materials, and determination of the dielectric function of layered materials such as silicon oxide and silicon nitride.[12](https://doi.org/10.1063/1.1140554) The same year, J.L. Stehle and colleagues described in MRS Proceedings a variable-angle FT-IR ellipsometer covering 600 to 6600 cm⁻¹, which extended the spectral range and capabilities of spectroscopic ellipsometry into the infrared and could record ellipsometric data together with vibrational absorption bands as a layer fingerprint.[13](https://doi.org/10.1557/proc-171-349) In 1993, A. Canillas, E. Pascual, and B. Drévillon reported in Review of Scientific Instruments a phase-modulated FTIR ellipsometer combining a 37 kHz photoelastic modulator with FTIR spectroscopy below 1 kHz, achieving a full spectrum from 900 to 4000 cm⁻¹ in 2 s for real-time kinetic studies.[11](https://doi.org/10.1063/1.1143953) Arnulf Röseler later described the combination of a photometric ellipsometer with a [Fourier transform](https://www.edgepedia.org/fourier-transform) spectrometer in the book chapter \"Spectroscopic Infrared Ellipsometry\" (Elsevier, 2005).[14](https://doi.org/10.1016/b978-081551499-2.50013-7)\n\n## Variants\n\n**Mueller-matrix ellipsometry** measures the full 4 × 4 polarization transfer matrix, capturing amplitude ratios, phase differences, and depolarization, and thereby probing dielectric properties, structure, composition, optical anisotropy, and molecular orientation. An infrared Mueller-matrix ellipsometer operating in reflection at incidence angles between 45° and 90°, coupling an FT-IR spectrometer with a globar source, provides high sensitivity for nanometer-thin films at sensitivities up to \\( 10^{-4} \\) in normalized matrix elements.[10](https://www.helmholtz-berlin.de/pubbin/oai_publication?ID=102335&VT=1)\n\n**Far-infrared and synchrotron extensions** push below the MIR range. A far-IR ellipsometer at a synchrotron beamline measures rotating-analyzer and full Mueller-matrix spectra using rotating retarders and wire-grid polarizers over about 20–4000 cm⁻¹, with a sample stage allowing temperatures between 4.2 and 450 K; a single Mueller-matrix measurement can distinguish magnetic and electric dipoles such as magnons and phonons without modeling arguments.[15](https://www.osti.gov/biblio/22105411)\n\n**Generalized and magneto-optic ellipsometry** handles anisotropic materials. Generalized ellipsometry was implemented for infrared applications including solutions for arbitrarily anisotropic and helically symmetric media, and the first complete measurement of the magneto-optic free-charge-carrier dielectric function tensor at infrared wavelengths was presented as an optical \"inert\" mass scale for free carriers in layered structures.[16](http://ellipsometry.unl.edu/people/schubert/HabTOC.pdf)\n\n**Laser ellipsometry** replaces the broadband source with a QCL or HeNe laser; a multiple-angle rotating-analyzer mapping ellipsometer with a tunable QCL achieved time resolutions down to 80 ms.[1](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry)\n\n## Applications\n\nAnalysis of IR ellipsometry data from 2 to 33 µm can precisely determine thin-film dielectric functions without numerical Kramers–Kronig analysis, providing phonon mode frequencies and broadening parameters, static dielectric constants, and free-carrier parameters, even for films with thicknesses only a fraction of the probing wavelength; alloy composition, film strain, and crystal quality of heterostructure constituents can also be derived.[2](https://www.sciencedirect.com/science/article/abs/pii/S0924203101001977)\n\nFree-carrier absorption at IR wavelengths in metals, heavily doped semiconductors, and transparent conducting oxides is modeled with a Drude oscillator function, which provides information about the material conductivity; carrier depth profiles generated from nondestructive IR ellipsometry compare well with those from destructive SIMS and SRP measurements.[4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf) Free-carrier absorption in the IR also distinguishes doping concentrations, characterizing epitaxial Si layers invisible to visible-range ellipsometry.[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub)\n\nSensitivity to very thin films is a defining strength: IR ellipsometry has demonstrated sensitivity to a 5 nm thick [Nylon](https://www.edgepedia.org/nylon) film on Au and submonolayer sensitivity.[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub) In-situ mid-IR ellipsometry of polymer processing benefits from the method's immunity to source instabilities, atmospheric absorption, and stray light, enabling absolute measurements without reference measurements.[17](https://pmc.ncbi.nlm.nih.gov/articles/PMC8747145/)\n\n## Limitations and alternatives\n\nIR ellipsometry is affected by nonideal sources, polarizers, compensators, and detectors, and its progress has depended on improved optical designs, calibration, and correction procedures.[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub) Reflection from a bare, uncoated isotropic substrate is uncommon in practice because surface oxidation or roughness on most substrates forces model-based regression.[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub) FTIR-based instruments are limited in temporal resolution by the interferometric measurement principle and by the time needed to move or rotate optical elements such as polarizers and phase manipulators.[7](https://www.degruyterbrill.com/document/doi/10.1515/aot-2022-0013/html)\n\nAgainst alternatives: intensity-based FTIR reflection or absorbance is less sensitive to film thickness, though it retains chemical sensitivity;[4](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf) IR ellipsometry measures ρ, the ratio of complex p and s reflection coefficients, and is more detailed than RAIRS (reflection-absorption IR spectroscopy);[3](https://beta.iopscience.iop.org/article/10.1088/1361-648X/ab8523) and visible–NIR ellipsometry cannot see free-carrier absorption in epitaxial Si layers, which the IR range resolves.[5](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub)\n\nMachine learning is entering the analysis workflow, which traditionally relies on model-based fitting.[18](https://www.mdpi.com/2073-4352/16/5/311)\n\n## References\n\n1. [Infrared mapping spectroscopic ellipsometry (Spectroscopy Europe/World)](https://www.spectroscopyeurope.com/index%2ephp/article/infrared-mapping-spectroscopic-ellipsometry)\n2. [Infrared spectroscopic ellipsometry, a new tool for characterization of semiconductor heterostructures (Kasic, Schubert, Einfeldt, Hommel, Vibrational Spectroscopy 29, 121–124, 2002)](https://www.sciencedirect.com/science/article/abs/pii/S0924203101001977)\n3. [Sensing and structure analysis by in situ IR spectroscopy: from mL flow cells to microfluidic applications](https://beta.iopscience.iop.org/article/10.1088/1361-648X/ab8523)\n4. [IR-VASE brochure (J.A. Woollam)](https://www.jawoollam.com/download/pdfs/ir-vase-brochure.pdf)\n5. [Progress in spectroscopic ellipsometry: Applications from vacuum ultraviolet to infrared (review)](https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1009&context=electricalengineeringfacpub)\n6. [Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale](https://link.springer.com/article/10.1007/s11051-009-9662-6)\n7. [Mid-infrared laser ellipsometry: a new era beyond FTIR](https://www.degruyterbrill.com/document/doi/10.1515/aot-2022-0013/html)\n8. [REPRINT (Folks, Phys. Status Solidi C, 2008)](http://pages.charlotte.edu/glenn-boreman/wp-content/uploads/sites/146/2014/06/Folks_PSSc_5_2008.pdf)\n9. [Application of Spectroscopic Ellipsometry and Mueller Ellipsometry to Optical Characterization](https://journals.sagepub.com/doi/10.1366/12-06883)\n10. [Ultrasensitive broadband infrared 4 × 4 Mueller-matrix ellipsometry for studies of depolarizing and anisotropic thin films](https://www.helmholtz-berlin.de/pubbin/oai_publication?ID=102335&VT=1)\n11. [A. Canillas, E. Pascual, B. Drévillon (1993). Phase-modulated ellipsometer using a Fourier transform infrared spectrometer for real time applications. Review of Scientific Instruments.](https://doi.org/10.1063/1.1143953)\n12. [F. Ferrieu (1989). Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: Some applications in thin-film characterization. Review of Scientific Instruments.](https://doi.org/10.1063/1.1140554)\n13. [J.L. Stehle and colleagues (1989). A Mew Variable Angle Ft, ir Ellipsometer. MRS Proceedings.](https://doi.org/10.1557/proc-171-349)\n14. [Arnulf Röseler (2005). Spectroscopic Infrared Ellipsometry. Elsevier eBooks.](https://doi.org/10.1016/b978-081551499-2.50013-7)\n15. [Synchrotron radiation-based far-infrared spectroscopic ellipsometer with full Mueller-matrix capability](https://www.osti.gov/biblio/22105411)\n16. [Infrared Ellipsometry on III-V semiconductor layer structures (Schubert habilitation, table of contents)](http://ellipsometry.unl.edu/people/schubert/HabTOC.pdf)\n17. [Towards Real-Time In-Situ Mid-Infrared Spectroscopic Ellipsometry in Polymer Processing](https://pmc.ncbi.nlm.nih.gov/articles/PMC8747145/)\n18. [Artificial Intelligence in Ellipsometry: Methods, Challenges, and Opportunities](https://www.mdpi.com/2073-4352/16/5/311)\n\n---\n*Topic: Encyclopedia › Physical world and mathematics › Physics › Matter and radiation physics › Condensed matter physics*\n\n*Initially written Sep 29, 2026 · Edited: Oct 15, 2026*\n\n*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*\n\nLicense: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license\n", "same_as": [ "http://ellipsometry.unl.edu/people/schubert/HabTOC.pdf" ], "url": "https://www.edgepedia.org/infrared-spectroscopic-ellipsometry", "markdown_url": "https://www.edgepedia.org/infrared-spectroscopic-ellipsometry.md", "license": { "name": "Edgepedia Community License 1.0", "url": "https://www.edgepedia.org/edgepedia/license", "summary": "Free with credit, commercial use included. AI training is open to everyone. For other uses, organizations over USD 100M in revenue or 100M monthly users license separately.", "spdx": "LicenseRef-Edgepedia-Community-1.0" }, "credit": "\"Infrared spectroscopic ellipsometry\", Edgepedia (EdgeChat), https://www.edgepedia.org/infrared-spectroscopic-ellipsometry. Edgepedia Community License 1.0.", "credit_md": "\"[Infrared spectroscopic ellipsometry](https://www.edgepedia.org/infrared-spectroscopic-ellipsometry)\", Edgepedia (EdgeChat), [https://www.edgepedia.org/infrared-spectroscopic-ellipsometry](https://www.edgepedia.org/infrared-spectroscopic-ellipsometry). [Edgepedia Community License 1.0](https://www.edgepedia.org/edgepedia/license).", "credit_html": "\"Infrared spectroscopic ellipsometry\", Edgepedia (EdgeChat), https://www.edgepedia.org/infrared-spectroscopic-ellipsometry. Edgepedia Community License 1.0.", "speakable": "Infrared spectroscopic ellipsometry is a contactless, nondestructive optical technique measuring how infrared light's polarization changes on reflection, yielding dielectric functions, phonon properties, and free-carrier data." }