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What is the principle of operation for a phased array spectrophotometer for coherent and incoherent visible light? I read this recent article about: http://www.laserfocusworld.com/articles/print/volume-51/issue-10/features/lidar-lidar-nears-ubiquity-as-miniature-systems-proliferate.html.

Frank
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  • Phased-array won't work for incoherent light. – WhatRoughBeast Mar 20 '16 at 23:08
  • @WhatRoughBeast, Why won't Phased-array work for incoherent light? We need to detect and discriminate coherent and incoherent visible light to protect pilot's vision and preserve a large field of view. Thank you. – Frank Mar 21 '16 at 00:09
  • Because a phased array only works on signals with the same reference phase; in other words, coherent emitters. Incoherent light by definition does not have a specified phase, and therefore cannot be manipulated by changing its phase. And just because you need to do something does not make it possible. – WhatRoughBeast Mar 21 '16 at 03:53
  • There's some nice write ups on this for the DARPA ACT program. They are making phased arrays, and the white papers are a good way to get you started. – b degnan Mar 21 '16 at 13:19
  • @b degnan, Thank you for your comment. Do the DARPA ACT white papers address how to design a hybrid spectrophotometer for coherent and incoherent light? – Frank Mar 21 '16 at 14:37
  • @WhatRoughBeast, Thank you for your explanation, Has anyone constructed a hybrid spectrophotometer for coherent and incoherent light? – Frank Mar 22 '16 at 03:50

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There is not, at least in terms of the linked article, any such thing as "a phased array spectrophotometer", for coherent or incoherent light. The article refers to the SWEEPER, a very agile LIDAR, as benefiting from miniaturization in the same way other instruments, including spectrometers, have done.

Apparently you have the idea that combining the beam-steering capabilities of the SWEEPER with a spectrometer would allow detection of a laser being shined at a pilot's eye, allowing protective action to be taken. I presume that you are attempting to address the increasing problem of commercial aircraft getting painted by yo-yos with laser pointers.

There is no difference in spectrometer design between coherent and incoherent sources, so the concept of a "hybrid" makes no sense.

Using a phased-array to steer the input of a spectrometer so as to analyze an incoming light source also makes no sense. It's necessary to analyze an entire field of view in order to determine where to point the spectrometer, and if you can identify a source point as needing analysis it's too late - the pilot is already being painted.

WhatRoughBeast
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  • What do you suggest as a way to tune the center of the optical notch filter response function to the incoming laser pointer wavelength so as to prevent the pilot from being already pointed? Thank you. – Frank Mar 22 '16 at 05:38