January 16, 2019
by Abhijit Marar
Update with 200 nm beads:
We were able to eliminate the twin image problem encountered the previous time. We placed the curved mirror on a linear piezo-electric translational stage and that helped us perform the phase stepping required to eliminate the twin image problem. Figures 1a, 1b and 1c show the different holograms of 200 nm dark red (660/680) fluorescent microspheres at phases 0o, 120o and 240o respectively.
Update with 100 nm beads:
We have also been able to image 100 nm red fluorescent microsphere (580/605) using the interferometric setup. This is our first step towards imaging smaller fluorescent emitters. Our next step will be to try and look at 40 nm beads or the quantum dots that have been provided to us by Dr. Winter’s lab. Figure 2a is a hologram of 100 nm fluorescent microsphere imaged at an exposure time of 10 ms and Figure 2b shows the hologram imaged at 50 ms.
Update on the interferometric setup (Dual diffractive lenses):
In addition to understanding the sources of noise in our system, we are also working towards optimizing the size of the hologram to improve the strength of the signal. By using two spherical waves instead of one spherical and one plane wave, it is possible to control the size of the hologram and find the optimal size. We want to reduce the size of the hologram such that the signal rises above the background but at the same it should also be possible to sample the finest concentric ring using the detector. To understand such a configuration, we have setup the previous system using the SLM alongside the interferometric system. Our goal now will be to find the optimal focal lengths of the mirrors required to satisfy the conditions mentioned previously. We are also trying to calculate the axial range we will be able to access using the optimal parameters. Figures 3a and 3b show holograms captured with different parameters using the new setup consisting of dual diffractive lenses.