{"id":82,"date":"2017-01-11T18:08:54","date_gmt":"2017-01-11T17:08:54","guid":{"rendered":"http:\/\/frantzmartinache.eu\/?p=82"},"modified":"2017-01-11T18:11:58","modified_gmt":"2017-01-11T17:11:58","slug":"coherence-length","status":"publish","type":"post","link":"https:\/\/frantzmartinache.eu\/index.php\/2017\/01\/11\/coherence-length\/","title":{"rendered":"Coherence length"},"content":{"rendered":"<h1>Coherence length and bandwitdh<\/h1>\n<p>A finite spectral bandwidth results in some spectral decorrelation of the electric field emanating from a source: even with a true point source, you will only observe the interference phenomenon (mutual coherence of the field) over a finite range of optical path difference (OPD) that is constrained by the coherence length.<\/p>\n<p align=\"center\">Coherence length: \u039b<sub>0<\/sub> = \u03bb\u00b2\/\u0394\u03bb<\/p>\n<p>An purely monochromatic and phase-calibrated signal like the one coming out of a very good laser would exhibit an infinite coherence length, represented by the green curve plotted below.<\/p>\n<p>Change the bandpass of the filter (here expressed as 1\/R=\u0394\u03bb\/\u03bb) to see its effect on the coherence length (the blue curve).<\/p>\n<p>For a given bandpass (say 0.05 and 0.1), how many fringes can you make out in the fringe packet? How do the two quantities (bandpass, number of fringes) relate to each other?<\/p>\n<div style=\"text-align: center;\"><canvas id=\"canvas\" width=\"600\" height=\"250\"><\/canvas><\/p>\n<p><script type=\"text\/javascript\" src=\"\/scripts\/coherence_length.js\"><\/script><br \/>\n<br \/>Bandpass<input id=\"DNU\" size=\"5\" type=\"text\" value=\"0.1\" \/><br \/>\n<br \/><input style=\"width: 400px;\" max=\"0.5\" min=\"0.001\" step=\"0.001\" type=\"range\" onchange=\"setDNU(this.value)\" oninput=\"setDNU(this.value)\"\/><\/div>\n<p>This tool was developed as a part of the on-line course <a href=\"http:\/\/www.fun-mooc.fr\/courses\/oca\/27001\/Trimestre_1_2015\/about\">Eagle Eye Astronomy<\/a>, hosted on the <a href=\"http:\/\/www.fun-mooc.fr\/\">France Universit\u00e9 Num\u00e9rique<\/a> website.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Coherence length and bandwitdh A finite spectral bandwidth results in some spectral decorrelation of the electric field emanating from a source: even with a true point source, you will only observe the interference phenomenon (mutual coherence of the field) over a finite range of optical path difference (OPD) that is constrained by the coherence length. &hellip; <a href=\"https:\/\/frantzmartinache.eu\/index.php\/2017\/01\/11\/coherence-length\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Coherence length<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,4],"tags":[],"_links":{"self":[{"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/posts\/82"}],"collection":[{"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/comments?post=82"}],"version-history":[{"count":12,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/posts\/82\/revisions"}],"predecessor-version":[{"id":94,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/posts\/82\/revisions\/94"}],"wp:attachment":[{"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/media?parent=82"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/categories?post=82"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/frantzmartinache.eu\/index.php\/wp-json\/wp\/v2\/tags?post=82"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}