# Resolution formula for Second Harmonic generation microscopy

**URL:** <https://forum.microlist.org/t/resolution-formula-for-second-harmonic-generation-microscopy/1366>\
**Category:** Theory\
**Created:** [April 9, 2021, 9:34am UTC](https://forum.microlist.org/t/resolution-formula-for-second-harmonic-generation-microscopy/1366 "2021-04-09T09:34:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Bobafotz](https://avatars.discourse-cdn.com/v4/letter/b/dbc845/32.png) [@Bobafotz](https://forum.microlist.org/u/Bobafotz)\
**Post date:** [April 9, 2021, 9:34am UTC](https://forum.microlist.org/t/resolution-formula-for-second-harmonic-generation-microscopy/1366/1 "2021-04-09T09:34:59Z")

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Hello everyone,

I would like to calculate the optimal pixel-size to meet the Nyquist-Shannon criterion for SHG microscopy but I can’t find the formula anywhere. Do you guys have anything related to it ?  
We collect the signal with an epi configuration, does it change anything to its calculation ?

Thank you for your kind help

Julien

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**Author:** ![jasonkirk](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.microlist.org/jasonkirk/32/668_2.png) [@jasonkirk](https://forum.microlist.org/u/jasonkirk)\
**Post date:** [April 14, 2021, 2:49pm UTC](https://forum.microlist.org/t/resolution-formula-for-second-harmonic-generation-microscopy/1366/2 "2021-04-14T14:49:13Z")

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Hi Julien,

Since SHG requires emission collection at 1/2 the incident wavelength of excitation - we routinely use this wavelength to calculate sampling. So if you are using 900nm from your TiS laser for excitation - you can use 450nm to determine resolution using Rayleigh (0.61\*lambda/NA). Then set your pixel size to 2.5-3x smaller than Rayleigh.

Hope this helps!

-Jason

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**Author:** ![Bobafotz](https://avatars.discourse-cdn.com/v4/letter/b/dbc845/32.png) [@Bobafotz](https://forum.microlist.org/u/Bobafotz)\
**Post date:** [April 26, 2021, 9:16am UTC](https://forum.microlist.org/t/resolution-formula-for-second-harmonic-generation-microscopy/1366/3 "2021-04-26T09:16:15Z")

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Hi Jason,

Thank you very much for your input, and sorry for the delay in my answer.  
It was my assumption as well to use the resolution formula of confocal microscopy, but I was wondering if it exists a formula dedicated to this technique and to its specific component.  
Anyway, it wont be less than confocal microscopy, so having a bit of oversampling is not a big deal I guess !

Thank you again !