Optical tweezers, QPD back focal plane interferometry vs imaging

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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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Andy Resnick
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What does 'BFPI' stand for, and can you provide a reference for it?
 
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Hello,It stands for < a href="http://biopt.ub.edu/force-detection/back-focal-plane-interferometry"> [Broken] Back focal plane interferometry </a>.
 
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Andy Resnick
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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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