Flexural Plane Distortion Measurement Technique

My engineering PI has asked me to find a way to measure flexural distortion of a cell culture. The overall magnitude of it is very small, so the conventional way (i.e., a brute force way) of physically measuring the distortion with a ruler is not valid here. 

Based on the following available preliminary knowledge about the culture which I have obtained from a brief conversation with my PI, I laid out a plan to develop a whole new way of measuring lattice distortion.

1. The cell culture is transparent.
2. The cell dish on which the culture is to be placed is also transparent.

Since the culture as well as the dish permits the passage of electromagnetic waves, why not exploit this optical property to measure flexural distortion? I carefully think of the following scenario.

1. Obtain a high power laser source (>50mW)
2. Obtain two linear diffraction gratings
3. Place them in the path of the beam
4. Superimpose them with the grating orientations aligned orthogonal to each other.
5. Project the resulting "lattice" of beams on to the transparent dish+culture geometry.
6. Analyze the resulting pattern on the other side of the dish+culture.
7. Compare and observe the "shifts" in the beam locations with the controlled group.
8. Calculate curvature based on known refractive indices.

I purchased one green laser diode rated at 50mW, one cooling fan to provide convective cooling to the diode, soldering board, power source, and finally diffraction gratings rated at 500 lines/inch. Total cost? All less than 50 dollar. My first objective is to prove that the above idea is feasible in real settings. So building a prototype to verify the concept has to be on the way.


This picture shows a quickly built prototype laser system in action. I rubberband-tied the diode with the 12W fan together. Power is supplied by my sprint HTC Hero cell phone battery. The fan is rated at 12VDC but I am only supplying 3.7V since it is already enough to provide sufficient convective cooling (I didn't calculate the convective heat transfer rate, but if it is necessary, one has to use the good old "forced convection formula with constant heat flux assumption on a cylindrical geometry"). Once the diode is set to emit the beam, I collimated it and prepared for the diffraction gratings.


The next picture shows the beams diffracted away by two orthogonally aligned linear diffraction gratings. The culture is not shown here yet since I am yet to have access to it. How do I test it then? One of the quickest way to do this is to use my eyeglasses. The rough curvature of my eyeglasses lenses calculated from the image should roughly corresponds to the theoretical curvature of the lenses based on my eye prescription which I have successfully confirmed within 10% accuracy using refractive index of acrylic glass. The result is perfectly acceptable considering how rough everything has been setup to achieve this result!

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