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Reports: ND654059-ND6: Understanding the role of quantum coherence in molecular energy transfer using three-dimensional coherent spectroscopy

Steven T. Cundiff, PhD, University of Michigan

During the last year, the PI moved his laboratory from University of Colorado to University of Michigan. This required disassembling the apparatus and rebuilding it, a non-trivial and extended task. Since the apparatus had to be disassembled, we took the opportunity, and down time while it was in transit, to have one of the translation stages repaired. One of the limit switches had failed so it would "crash" at the end of its range. The repair tooks several months including the time to ship it to the vendor and back.

Once the system was installed at University of Michigan, we spent time trying to solve long standing stability issues with the light source, an optical parametric oscillator pumped by a regenerative amplifier. The biggest issue was beam point stability. Drifts in the beam pointing are very deleterious for the experiment because it causes the overlap of the beams on the sample to change with time. Efforts to remedy this problem with simple improvements in alignment failed to produce satisfactory results. Ultimately we gave up on that route and purchased a commercially availabe position for actively stabilizing beam position and pointing. This investment solved the problem.

With the beam point problems solved, we began running the system. We discovered additional problems. The liquid crystal phase modulators used to phase cycling did not seem to respondning properly, this turned out to be an issue of the measurement, but delayed progress by about a month. The another artifact turned out to be due to the shutter on the CCD camera "quivering", the reasons for this behavior are unclear, however we've found a work around to force it to stay open. Finally, we spent a significant amount of time rewriting the complex software running the apparatus, which was the result of accretion of changes made by several generations of post-docs and graduate students. The software is now significantly more stable.

The next effect of all of these problems and improvements is that only at the very end of the grant period did we begin producing 2D spectra again. We have not tried producing 3D spectra yet, so did not have a chance to return to the proposed work.

We plan to continue in this direction and will acknoweldge the PRF in any future publications that leverage the support that has gone into improving and perfecting the expeimental apparatus.