Optical tweezers, QPD back focal plane interferometry vs imaging

[donroy81]

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.

 

[Andy Resnick]

What does 'BFPI' stand for, and can you provide a reference for it?

 

[donroy81]

Hello,It stands for < a href="http://biopt.ub.edu/force-detection/back-focal-plane-interferometry"> Back focal plane interferometry </a>.

 

[Andy Resnick]

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.

 

[sardar]

I can provide some insight into the use of optical tweezers and the two different techniques, QPD back focal plane interferometry and imaging. Optical tweezers are a powerful tool for manipulating and studying small particles, such as cells or vesicles, at the microscopic level. They use highly focused laser beams to create a trapping force that can hold and move particles in a controlled manner.

In terms of the two techniques you mentioned, QPD back focal plane interferometry (BFPI) and imaging, they both have their advantages and can be used in different scenarios. QPD BFPI involves imaging the back focal plane of the objective lens, which can provide information about the position and motion of the trapped particle. This technique is particularly useful for single molecule studies, as it can provide high sensitivity and resolution.

On the other hand, imaging involves using a camera to capture images of the trapped particles. This technique can provide information about the shape and size of the particles, as well as their position and motion. It is also useful for studying multiple particles at once, such as in cell or vesicle level work.

In terms of data processing, the power spectrum method can be used for both techniques to calibrate and analyze the data. However, the specific data processing steps may differ depending on the technique used and the type of information being studied.

Overall, the choice between QPD BFPI and imaging will depend on the specific research question and goals of the experiment. Both techniques have their advantages and can provide valuable insights into the behavior of trapped particles. I would recommend further research and experimentation to determine which technique is best suited for your particular study.