{"id":1356,"date":"2010-10-14T18:54:28","date_gmt":"2010-10-14T18:54:28","guid":{"rendered":"http:\/\/www.joswassink.nl\/insight\/?p=1356"},"modified":"2010-10-14T18:54:28","modified_gmt":"2010-10-14T18:54:28","slug":"optical-measuring-tape","status":"publish","type":"post","link":"https:\/\/www.joswassink.nl\/insight\/?p=1356","title":{"rendered":"Optical measuring tape"},"content":{"rendered":"<p><strong> <\/strong><\/p>\n<div id=\"attachment_1358\" style=\"width: 310px\" class=\"wp-caption alignleft\"><strong> <\/strong><strong><a rel=\"attachment wp-att-1358\" href=\"http:\/\/www.joswassink.nl\/insight\/?attachment_id=1358\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1358\" class=\"size-thumbnail wp-image-1358\" title=\"figure_long_arm\" src=\"http:\/\/www.joswassink.nl\/insight\/wp-content\/uploads\/2010\/10\/figure_long_arm1-300x245.jpg\" alt=\"\" width=\"300\" height=\"245\" \/><\/a><\/strong><p id=\"caption-attachment-1358\" class=\"wp-caption-text\">Test set-up in 50 metre long corridor at NMi in Delft.<\/p><\/div>\n<p><strong>Laser distance measuring in air has been brought to its penultimate  level: 100 metres at micrometer accuracy.<\/strong><\/p>\n<p>At first, the task seemed simple enough,\u201d says Dr Nandini  Bhattacharya (Applied Sciences), who co-supervised Dr Moxi Cui&#8217;s PhD  research on distance metrology. Previously Dr Bas Swinkels had developed  laser metrology in the same group with a different kind of laser. A new  &#8216;femtosecond laser&#8217; was expected to perform even better, producing  ultra-short pulses of light (40 microns long) separated by 15  centimetres of nothing. Distance can be measured by splitting the laser  beam: one part is sent down the distance to be measured, gets reflected  and then returns; the other part bounces on a moveable reflector  situated nearby. A pulse counter provides an estimate of (twice) the  distance in multiples of 15 centimetres. Overlaying the pulses from both  arms and bringing them into interference was expected to lower the  precision to the order of the light wavelength (0.4 micron).<!--more--><\/p>\n<p>However,  air plays funny tricks on laser pulses. The pulses that had travelled  100 meters through air were deformed beyond recognition. \u201cTemperature,  pressure and humidity influence the refractive index, which is slightly  different for each of the 18,000 frequencies that constitute the laser  pulse,\u201d Bhattacharya explains.<\/p>\n<p>By calculating the exact influence  of air on the pulses, Cui succeeded in restoring the interference  between the pulses from both arms, thus attaining an accuracy of 1 to 2  micron in measuring a distance of 50 metres. A world record, says his  co-supervisor.<\/p>\n<p>The developed technology might have unexpected  applications. Although laser metrology was developed for the fine  positioning of satellites in space, the knowledge of the refractive  index of air might now also be used for terrestrial laser metrology over  distances of kilometres, or for the optical analysis of breath gases.  Drunk drivers beware.<\/p>\n<p><em>Moxi Cui, &#8216;Distance Metrology in Air  with a Femtosecond Frequency Comb Laser&#8217;, 11 October 2010, PhD  supervisor Prof. Paul Urbach.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Laser distance measuring in air has been brought to its penultimate level: 100 metres at micrometer accuracy.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,6],"tags":[131,256,284],"class_list":["post-1356","post","type-post","status-publish","format-standard","hentry","category-articles","category-delta","tag-distance","tag-laser","tag-metrology"],"_links":{"self":[{"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=\/wp\/v2\/posts\/1356","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1356"}],"version-history":[{"count":0,"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=\/wp\/v2\/posts\/1356\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1356"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1356"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.joswassink.nl\/insight\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1356"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}