Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Coherent emission of light by thermal sources


A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently1,2 that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100 nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle—the so-called Wolf effect3,4. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Image of the grating obtained by atomic force microscopy.
Figure 2: Polar plot of the emissivity of the grating depicted in Fig. 1 at λ = 11.36 µm and for p-polarization.
Figure 3: Emissivity of a SiC grating in p-polarization.
Figure 4: Comparison between measured and calculated spectral reflectivities of a SiC grating at room temperature.
Figure 5: Dispersion relation wavevector, ω(k), of surface-phonon polaritons.


  1. Shchegrov, A., Joulain, K., Carminati, R. & Greffet, J. J. Near-field spectral effects due to electromagnetic surface excitations. Phys. Rev. Lett. 85, 1548–1551 (2000).

    ADS  CAS  Article  Google Scholar 

  2. Carminati, R. & Greffet, J. J. Near-field effects in spatial coherence of thermal sources. Phys. Rev. Lett. 82, 1660–1663 (1999).

    ADS  CAS  Article  Google Scholar 

  3. Wolf, E. Non-cosmological red-shifts of spectral lines. Nature 326, 363–365 (1987).

    ADS  Article  Google Scholar 

  4. Wolf, E. & James, D. F. Correlation-induced spectral changes. Rep. Prog. Phys. 59, 771–818 (1996).

    ADS  CAS  Article  Google Scholar 

  5. Morris, G. M. & Faklis, D. Effects of source correlation on the spectrum of light. Opt. Commun. 62, 5–11 (1987).

    ADS  CAS  Article  Google Scholar 

  6. Le Gall, J., Olivier, M. & Greffet, J. J. Experimental and theoretical study of reflection and coherent thermal emission by a Sic grating supporting a surface photon polariton. Phys. Rev. B 55, 10105–10114 (1997).

    ADS  CAS  Article  Google Scholar 

  7. Hesketh, P. J., Zemel, J. N. & Gebhart, B. Organ pipe radiant modes of periodic micromachined silicon surfaces. Nature 325, 549–551 (1986).

    ADS  Article  Google Scholar 

  8. Mandel, L. & Wolf, E. Optical Coherence and Quantum Optics. Sec. 5.3 (Cambridge Univ. Press, New York, 1995).

    Book  Google Scholar 

  9. Greffet, J. J. & Nieto-Vesperinas, M. Field theory for the generalized bidirectional reflectivity: derivation of Helmholtz's reciprocity principle and Kirchhoff's law. J. Opt. Soc. Am. A 10, 2735–2744 (1998).

    ADS  MathSciNet  Article  Google Scholar 

  10. Zhizhin, G. N., Vinogradov, E. A., Moskalova, M. A. & Yakovlev, V. A. Applications of surface polaritons for vibrational spectroscopic studies of thin and very thin films. Appl. Spectrosc. Rev. 18, 171–263 (1982).

    ADS  CAS  Article  Google Scholar 

  11. Mulet, J. P., Joulain, K., Carminati, R. & Greffet, J. J. Nanoscale radiative heat transfer between a small particle and a plane surface. Appl. Phys. Lett. 78, 2931–2933 (2001).

    ADS  CAS  Article  Google Scholar 

  12. Whale, M. D. in Proc. Conf. on ‘Heat Transfer and Transport Phenomena in Microscale’ (ed. Celata, G. P.) 339–346 (Begell House, New York, 2000).

    Google Scholar 

Download references

Author information

Authors and Affiliations


Corresponding author

Correspondence to Jean-Jacques Greffet.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Greffet, JJ., Carminati, R., Joulain, K. et al. Coherent emission of light by thermal sources. Nature 416, 61–64 (2002).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing