Optical tweezers, QPD back focal plane interferometry vs imaging

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Discussion Overview

The discussion centers around the comparison of imaging techniques in optical trapping setups, specifically focusing on the use of back focal plane interferometry (BFPI) versus traditional imaging methods. Participants explore the implications of these techniques for applications at the cell and vesicle level, including potential advantages and data processing considerations.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant describes their setup using a 10x infinity objective and a 40mm lens for imaging onto a quadrant photodiode (QPD), expressing uncertainty about the advantages of BFPI for their specific application.
  • Another participant asks for clarification on the acronym 'BFPI' and requests a reference for it.
  • A participant provides a definition of BFPI and links to a resource, indicating that it involves imaging the back focal plane of the condenser lens to capture interference patterns.
  • It is noted that the advantage of BFPI is the ability to measure sub-resolution motion of particles through interferometry, which may not be achievable with standard imaging techniques.

Areas of Agreement / Disagreement

Participants express differing levels of understanding regarding BFPI and its application, indicating that the discussion remains unresolved on the specific advantages and data processing changes associated with this method compared to traditional imaging.

Contextual Notes

There are limitations in the discussion regarding the precise definitions of terms and the assumptions underlying the advantages of BFPI, as well as the specifics of data processing methods used in conjunction with these techniques.

donroy81
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Hello, I use a 10x infinity objective as a condenser in a optical trap setup. The collimated forward scattered light is then focused with a 40mm lens onto a QPD. This is the imaging techqnique. There is also BFPI, and I am not clear on this method. My understanding is that I need to image the back focal plane of the 10x infinity objective by inserting another lens. Then use the 40mm lens to image onto the QPD. For cell/vesicle level work ( not single molecules) what advantage does this bring? More importantly, does the data processing change? I use the power spectrum method to calibrate.
 
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What does 'BFPI' stand for, and can you provide a reference for it?
 
Hello,It stands for < a href="http://biopt.ub.edu/force-detection/back-focal-plane-interferometry"> Back focal plane interferometry </a>.
 
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Oh, ok- the back focal plane (technically, it's actually the exit pupil) of the condenser lens is where the interference pattern is; the relay lens images the back pupil plane onto a detector. The advantage is that sub-resolution motion of the particle can easily be measured with interferometry.
 

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