Optical rectification

<h2 id="explanation">Explanation</h2>
<p>Optical rectification can be intuitively explained in terms of the symmetry properties of the non-linear medium: in the presence of a preferred internal direction, the polarization will not reverse its sign at the same time as the driving field. If the latter is represented by a sinusoidal wave, then an average DC polarization will be generated.
</p><p>Optical rectification is analogous to the <a href="/facts/Rectifier/me8XDxND">electric rectification effect</a> produced by <a href="/facts/Diode/JyaoyGnk">diodes</a>, wherein an AC signal can be converted ("rectified") to DC. However, it is <i>not</i> the same thing. A diode can turn a sinusoidal electric field into a DC current, while optical rectification can turn a sinusoidal electric field into a DC polarization, but not a DC current. On the other hand, a <i>changing</i> polarization is a kind of current. Therefore, if the incident light is getting more and more intense, optical rectification causes a DC current, while if the light is getting less and less intense, optical rectification causes a DC current in the opposite direction. But again, if the light intensity is constant, optical rectification cannot cause a DC current.
</p><p>When the applied electric field is delivered by a <a href="/facts/Femtosecond/vaVXTVyR">femtosecond</a>-<a href="/facts/Pulsed_laser/PIcW85dx">pulse-width</a> <a href="/facts/Laser/jk6PTvvT">laser</a>, the spectral bandwidth associated with such short pulses is very large. The mixing of different frequency components produces a beating polarization, which results in the emission of electromagnetic waves in the <a href="/facts/Terahertz_radiation/729QecPK">terahertz</a> region. The EOR effect is somewhat similar to a classical electrodynamic emission of radiation by an accelerating/decelerating charge, except that here the charges are in a bound dipole form and the THz generation depends on the second order susceptibility of the nonlinear optical medium. A popular material for generating radiation in the 0.5–3 THz range (0.1 mm wavelength) is <a href="/facts/Zinc_telluride/09dzJv8U">zinc telluride</a>.
</p><p>Optical rectification also occurs on <a href="/facts/Metal/pqQVs8QU">metal</a> surfaces by similar effect as <a href="/facts/Surface_second_harmonic_generation/y6cBdhTR">surface second harmonic generation</a>. The effect is however influenced e. g. by nonequilibrium electron excitation and generally it manifests in a more complicated way.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>Similar to other nonlinear optical processes, optical rectification is also reported to become enhanced when <a href="/facts/Surface_plasmons/6H6a2fYC">surface plasmons</a> are excited on a metal surface.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h2 id="applications">Applications</h2>
<p>Together with carrier acceleration in semiconductors and polymers, optical rectification is one of the main mechanisms for the generation of terahertz radiation using lasers.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> This is different from other processes of terahertz generation such as <a href="/facts/Polaritonics/F15We24k">polaritonics</a> where a polar <a href="/facts/Lattice_vibration/tflWW6vw">lattice vibration</a> is thought to generate the <a href="/facts/Terahertz_radiation/729QecPK">terahertz radiation</a>.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Terahertz_time-domain_spectroscopy/yLXAY1lW">Terahertz time-domain spectroscopy</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Rice et al., "Terahertz optical rectification from <110> zinc-blende crystals," Appl. Phys. Lett. 64, 1324 (1994), doi:10.1063/1.111922 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Bass et al., "Optical rectification," Phys. Rev. Lett. 9, 446 (1962), doi:10.1103/PhysRevLett.9.446 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Kadlec, F., Kuzel, P., Coutaz, J. L., "Study of terahertz radiation generated by optical rectification on thin gold films," Optics Letters, 30, 1402 (2005), doi:10.1364/OL.30.001402 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>G. Ramakrishnan, N. Kumar, P. C. M. Planken, D. Tanaka, and K. Kajikawa, "Surface plasmon-enhanced terahertz emission from a hemicyanine self-assembled monolayer," Opt. Express, 20, 4067-4073 (2012), doi:10.1364/OE.20.004067 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Tonouchi, M, "Cutting-edge terahertz technology," Nature Photonics 1, 97 (2007), doi:10.1038/nphoton.2007.3 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
</ol>

Optical rectification open-in-new

Optical rectification