Non Phosphor White LED Light Source for Interferometry

Research output: Chapter in Book/Report/Conference proceedingConference contributionScientificpeer-review

Abstract

Solid state light sources are replacing a tungsten filament based bulbs in Scanning White Light Interferometers. White LEDs generate little heat, feature short switching times, and have long lifetimes. Phosphor-based white LEDs produce a wide spectrum but have two separate peaks which cause interferogram ringing. This makes measuring multi layered structures difficult and may degrade measurement precision even when measuring a single reflecting surface. Most non phosphor white LEDs exhibit a non Gaussian spectrum, but multi-LED based white LEDs can achieve switching times and stability similar to those of single color LEDs. By combining several LEDs and by controlling their input current independently it is possible to create almost an arbitrary spectrum. We designed a new light source by combining a non phosphor white LED (American Opto Plus LED, L-513NPWC- 15D) and single color LEDs. This allowed us to fill the spectral gap between the blue and yellow peaks of the non phosphor white LED. By controlling the input current of the LEDs individually a nearly Gaussian shaped spectrum was achieved. This wide continuous spectrum creates short interferograms (FWHM ~1.4 μm) without side peaks. To demonstrate the properties of this source we measured through a 5 μm thick polymer film. The well localized interference created by the source allows measuring both surfaces of thin films simultaneously. We were able to pulse the source at 5.4 MHz.
Original languageEnglish
Title of host publicationDimensional Optical Metrology and Inspection for Practical Applications : Optical Metrology Methods II
Number of pages8
Volume8133
Place of PublicationSan Diego
PublisherSPIE
Publication dateAug 2011
Pages813309-1 - 813309-8
DOIs
Publication statusPublished - Aug 2011
MoE publication typeA4 Article in conference proceedings
EventDimensional Optical Metrology and Inspection for Practical Applications - San Diego, United States
Duration: 22 Aug 2011 → …

Publication series

NameProceedings of SPIE
PublisherSPIE
Volume8133

Fields of Science

  • 114 Physical sciences
  • Scanning White Light Interferometry
  • Non phosphor LED

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