In The Lab

After finally turning 18, I was able to enter and work in the optics lab. The lab, however, was not completely set up. None of the optical tables were operational, and equipment still hadn’t arrived. Throughout the rest of that week, I continued my research on cyanotoxins and microspheres.

The monday of the next week, we decided we would float the optical table. The several hundred pound table would be lifted from it’s legs with pressures between 50 and 80 psi. Floating the optical table prevents external forces such as vibrations from machinery and walking from affecting the optical system. We set up a system of pressure controllers and air filters to lift the table. After adjusting the individual pressures of the legs, we were able to get the table flat relative to the ground.IMG_2420

Two days later, we began to build our CO2 laser system. We used 6 mirrors, three of which were coated with zinc selenide to efficiently reflect infrared light, 2 pinhole positioners to precisely position both the visible light and CO2 lasers, a lense to focus the beam, a beam splitter and a flat top laser beam shaper to evenly distribute the wave’s energy. We used uv sensitive paper to see the laser as we adjusted the mirrors and lenses. The process took two days of tedious and meticulous work to get the beams accurately through the system. We then focused the microscope by melting a glass slide with the CO2 laser and adjusting the microscopes position until we found the spot where the laser hit the glass.

Once the system was completed, we decided to test it by producing microspheres from optical an optical fiber’s core. After some trial and error, we ended up shooting the laser for 1 second at about 3 watts to produce a small microsphere. We currently cannot calculate the quality (Q) factor of the sphere, but it was not large enough to be useful as a biosensor.IMG_2424

Now you are probably wondering what a Q factor is and what it’s purpose is (or not it’s up to you). Well, a Q factor for microresonators is numerical value describing resonators’ ability to maintain light with minimal decay. The longer it takes for light to decay, the better the resonator is at storing the light, the higher the quality factor. Finding this value is surprisingly simple. By finding the resonance wavelength of the microsphere and gathering data regarding the transmission of wavelengths close to but not the same as the resonance wavelengths, we can generate a lorentzian curve. The function can is used to determine the Full Width at half Minimum (FWHM), and then calculate the Q factor.

Lorentzian
Example graph

 

The lab is almost finished, but until we receive the flow controller to manage the hydrogen, we find Q factors and produce microspheres.

Sources:

Example Graph: http://imagebank.osa.org/getImage.xqy?img=OG0kcC5sYXJnZSxvZS0xNi05LTYyODUtZzAwMg

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3 thoughts on “In The Lab

  1. Awesome setup, Jared. When you say you used a laser to make microspheres did you melt pieces off of a larger piece of optical fiber? Will there be a way to reliably create spheres will adequate Q factor or do you have to rely on trial and error?

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    1. When we produce the microspheres, we only melt the tip of the optical fiber enough so that surface tension creates a sphere on the fiber. The sphere is not separate from the fiber making it easier to work with. While we cannot produce the exact same sphere every time, we have been achieve Q factors in the 10^7 region consistently and are still improving the technique. If you’re interested, here’s a video and procedure describing the basic processes for microspheres and microtoroids. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3471275/). While I specifically am not producing microtoroids, they are another resonator with high potential in the production of lab-on-a-chip, biosensors field, and are being worked with in our lab.

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      1. If you are interested in either the math or concepts behind the science of optical biosensing, I could send you some papers related to topics such as coupling and microresonators

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