<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>0035-001X</journal-id>
<journal-title><![CDATA[Revista mexicana de física]]></journal-title>
<abbrev-journal-title><![CDATA[Rev. mex. fis.]]></abbrev-journal-title>
<issn>0035-001X</issn>
<publisher>
<publisher-name><![CDATA[Sociedad Mexicana de Física]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0035-001X2003000100014</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[Two-photon absorption]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Perez-Arjona]]></surname>
<given-names><![CDATA[I.]]></given-names>
</name>
<xref ref-type="aff" rid="A01"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Valcárcel]]></surname>
<given-names><![CDATA[G.J. de]]></given-names>
</name>
<xref ref-type="aff" rid="A01"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Roldan]]></surname>
<given-names><![CDATA[Eugenio]]></given-names>
</name>
<xref ref-type="aff" rid="A01"/>
</contrib>
</contrib-group>
<aff id="A01">
<institution><![CDATA[,Universitat de Valencia Departament d'Òptica ]]></institution>
<addr-line><![CDATA[Burjassot Valencia]]></addr-line>
<country>España</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>00</month>
<year>2003</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>00</month>
<year>2003</year>
</pub-date>
<volume>49</volume>
<numero>1</numero>
<fpage>92</fpage>
<lpage>101</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0035-001X2003000100014&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0035-001X2003000100014&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0035-001X2003000100014&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[Two-photon absorption is theoretically analyzed within the semiclassical formalism of radiation-matter interaction. We consider an ensemble of inhomogeneously broadened three-level atoms subjected to the action of two counterpropagating fields of the same frequency. By concentrating in the limit of large detuning in one-photon transitions, we solve perturbatively the Bloch equations in a non-usual way. In this way we derive an analytical expression for the width of the two-photon resonance that makes evident sub-Doppler two-photon spectroscopy. We also derive an analytical expression for the Stark shift of the two-photon resonance.]]></p></abstract>
<abstract abstract-type="short" xml:lang="es"><p><![CDATA[Se analiza teóricamente la absorción de dos fotones dentro del formalismo semiclásico de la interacción entre la radiación y la materia. Consideramos un conjunto, con ensanchamiento inhomogéneo, de átomos de tres niveles sometido a la acción de dos campos contrapropagantes de igual frecuencia. Resolvemos perturbativamente las ecuaciones de Bloch del sistema de una forma no usual concentrándonos en el límite de alta desintonía de las transiciones a un fotón. De esta forma obtenemos una expresión analítica para la anchura de la resonancia a dos fotones en la que se pone de manifiesto la posibilidad de espectroscopía sub-Doppler a dos fotones. También obtenemos una expresión analítica para el desplazamiento Stark de la resonancia a dos fotones.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[Spectroscopy]]></kwd>
<kwd lng="en"><![CDATA[quantum optics]]></kwd>
<kwd lng="en"><![CDATA[two-photon precesses]]></kwd>
<kwd lng="es"><![CDATA[Espectroscopía]]></kwd>
<kwd lng="es"><![CDATA[óptica cuántica]]></kwd>
<kwd lng="es"><![CDATA[procesos a dos fotones]]></kwd>
</kwd-group>
</article-meta>
</front><body><![CDATA[  	    <p align="justify"><font face="verdana" size="4">Ense&ntilde;anza</font></p>      <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="center"><font face="verdana" size="4"><b>Two&#45;photon absorption</b></font></p>      <p align="center"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="center"><font face="verdana" size="2"><b>I. Perez&#45;Arjona, G.J. de Valc&aacute;rcel, and Eugenio Roldan</b></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><i>Departament d'&Ograve;ptica, Universitat de Val&egrave;ncia, Dr. Moliner 50, 46100&#45;Burjassot, Spain.</i></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2">Recibido el 25 de julio de 2002.    ]]></body>
<body><![CDATA[<br> 	Aceptado el 22 de enero de 2003.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Abstract</b></font></p>  	    <p align="justify"><font face="verdana" size="2">Two&#45;photon absorption is theoretically analyzed within the semiclassical formalism of radiation&#45;matter interaction. We consider an ensemble of inhomogeneously broadened three&#45;level atoms subjected to the action of two counterpropagating fields of the same frequency. By concentrating in the limit of large detuning in one&#45;photon transitions, we solve perturbatively the Bloch equations in a non&#45;usual way. In this way we derive an analytical expression for the width of the two&#45;photon resonance that makes evident sub&#45;Doppler two&#45;photon spectroscopy. We also derive an analytical expression for the Stark shift of the two&#45;photon resonance.</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Keywords:</b> Spectroscopy; quantum optics; two&#45;photon precesses.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Resumen</b></font></p>  	    <p align="justify"><font face="verdana" size="2">Se analiza te&oacute;ricamente la absorci&oacute;n de dos fotones dentro del formalismo semicl&aacute;sico de la interacci&oacute;n entre la radiaci&oacute;n y la materia. Consideramos un conjunto, con ensanchamiento inhomog&eacute;neo, de &aacute;tomos de tres niveles sometido a la acci&oacute;n de dos campos contrapropagantes de igual frecuencia. Resolvemos perturbativamente las ecuaciones de Bloch del sistema de una forma no usual concentr&aacute;ndonos en el l&iacute;mite de alta desinton&iacute;a de las transiciones a un fot&oacute;n. De esta forma obtenemos una expresi&oacute;n anal&iacute;tica para la anchura de la resonancia a dos fotones en la que se pone de manifiesto la posibilidad de espectroscop&iacute;a sub&#45;Doppler a dos fotones. Tambi&eacute;n obtenemos una expresi&oacute;n anal&iacute;tica para el desplazamiento Stark de la resonancia a dos fotones.</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Descriptores:</b> Espectroscop&iacute;a; &oacute;ptica cu&aacute;ntica; procesos a dos fotones.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    ]]></body>
<body><![CDATA[<p align="justify"><font face="verdana" size="2">PACS: 42.50.&#45;p; 42.62.Fi.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><a href="../pdf/rmf/v49n1/v49n1a14.pdf" target="_blank">DESCARGAR ART&Iacute;CULO EN FORMATO PDF</a></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>References</b></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">1.&nbsp;M. G&ouml;ppert&#45;Mayer, <i>Ann. 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