During my summer stay at the University of Leuven in 2006, I was working with my colleagues on interpreting data from new experiments using the intrinsic hyperpolarizability as a guide. That was when we discovered that modulation of conjugation was a new approach for making molecules with larger nonlinearities. It was an exciting time that eventually led to a paper that hit the internet in January 2007.
It caused quite a sensation. The morning that it appeared, I had a pile of emails in my inbox from reporters. My collaborator was even interviewed on Belgian TV. The Inquirer, a British publication, called us boffins (at first I thought it was a derogatory term). CBC News, ScienceBase, Materials World, Nature, and many others also covered the story.
In the midst of all this mayhem, we were working on another project. Who would have guessed that it would be 4 years from the initial idea until the work was finally published. I mentioned this work a while back in a post as being finally done, but as it turns out, it wasn't. We kept on finding mistakes.
While this work will most likely not get as much attention as our paper from 2007, it is perhaps a much better piece of work because it carefully shows how a combination of sum rules and symmetry can be used to reduce a complex problem into a simple one. With all of the complexity removed, it becomes easier to build an understanding of the physics underlying the phenomena that we observe. This is another paper that I rank in my top ten. I predict that this paper will get less citations than my top-40 cited papers, but those statistics are unimportant to me.
The title of the paper is Experimental verification of a self-consistent theory of the first-, second-, and third-order (non)linear optical response, by Javier Perez-Moreno, Sheng-Ting Hung, Mark G. Kuzyk, Juefei Zhou, Shiva K. Ramini, and Koen Clays. It is slated to appear in Physics Review A -- a journal I consider to be top notch. No glitz, no fancy photos, just hard core Physics.
Xavi must have been thrilled when he got the letter:
Dear Dr. Perez-Moreno,
We are pleased to inform you that your manuscript has been accepted
for publication as a Regular Article in Physical Review A.
His email to his coauthors tells it all:
After 3.5 years of revisions, I think we learned a lot about AF455 and octupoles in general, group theory, fluorescence, quantum yields; but, it has paid off. I feel very proud of this paper!
Xavi
I agree!
Showing posts with label University of Leuven. Show all posts
Showing posts with label University of Leuven. Show all posts
Tuesday, August 9, 2011
Friday, August 20, 2010
We finally got it right (we hope)
It's been three years since Juefei Zhou finished his Ph.D. research that culminated in a nice piece of collaborative work with the group of Koen Clays of the University of Leuven in Belgium. The research used a combination of theory and experiments to determine all the parameters needed to predict the full wavelength dependence of the two-photon absorption cross section. The beauty of the approach is that the theory uses the Thomas Kuhn sum rules to significantly reduce the number of parameters required to describe a molecule. This reduced set of parameters was determined from two experiments - a linear absorption spectrum and the measurement of the hyperpolarizability at just one wavelength.
Given that nonlinear-optical quantum calculations are notoriously inaccurate; and, independent measurements (such as first and second hyperpolarizability measurements) often disagree, we were elated that our approach led to a global agreement between all quantities using just one small set of parameters. The only problem was that our theory was wrong. We had made a false assumption. Thus, our manuscript was placed on the back burner.
A year later, in 2009, I spent a summer in Belgium, and used a combination of symmetry arguments and sum rules to show that our equations turned out to be correct, but for very different reasons. As we were applying the final touches to the manuscript when I returned back to Pullman, Xavi found an error. After days of intense debate, we found a way to correct the mistake and submitted a revised manuscript to Physical Review A.
A very sharp reviewer caught what appeared to be a fatal error. Our symmetry arguments were correct, but they implied an additional condition that rendered our approach untenable. For the next 12 months, we were haunted by a model that was wrong yet seemed to fit the data perfectly well.
At the beginning of the summer of 2010, Shengting was getting frustrated with a laser that refused to work properly, and asked for a theoretical project as a diversion. I suggested that he learn group theory and apply it to fixing the model. While Shengting was making good progress in both learning group theory and developing a plan of attack to address our problems, Xavi arrived from Belgium for a six-week stay. During my trip to Budapest, they had found a solution, albeit with a few holes.
A day before I returned, Koen Clays arrived in Pullman, and spent some time discussing the problem with Xavi and Shengting. As a result, they got closer to a solution. When I got back to Pullman (a day late because of a missed connection in Amsterdam), the four of us met to discus the problem and the proposed fix. Xavi acted as the spokesperson and very animatedly described the approach on the blackboard. Within an hour, everything fell into place. Not only did the original mathematical form of the theory turn out to be true, the underlying physics was even more beautiful than we had imagined. This project has led to new ideas that will take us into novel areas of research that we hope will make a closer connection between our theory, which is a bit esoteric, and real molecules.
It was worth the wait. This paper will add a significant new paradigm to the body of knowledge that seeks to more deeply understand the nonlinear-optical response of complex molecules. The path of our research took us through exhilarating highs and unbearable lows. Hopefully, our models are finally right. If not, the self-correcting process of the scientific method will eventually lead us, or someone else, closer to the truth.
Given that nonlinear-optical quantum calculations are notoriously inaccurate; and, independent measurements (such as first and second hyperpolarizability measurements) often disagree, we were elated that our approach led to a global agreement between all quantities using just one small set of parameters. The only problem was that our theory was wrong. We had made a false assumption. Thus, our manuscript was placed on the back burner.
A year later, in 2009, I spent a summer in Belgium, and used a combination of symmetry arguments and sum rules to show that our equations turned out to be correct, but for very different reasons. As we were applying the final touches to the manuscript when I returned back to Pullman, Xavi found an error. After days of intense debate, we found a way to correct the mistake and submitted a revised manuscript to Physical Review A.
A very sharp reviewer caught what appeared to be a fatal error. Our symmetry arguments were correct, but they implied an additional condition that rendered our approach untenable. For the next 12 months, we were haunted by a model that was wrong yet seemed to fit the data perfectly well.
At the beginning of the summer of 2010, Shengting was getting frustrated with a laser that refused to work properly, and asked for a theoretical project as a diversion. I suggested that he learn group theory and apply it to fixing the model. While Shengting was making good progress in both learning group theory and developing a plan of attack to address our problems, Xavi arrived from Belgium for a six-week stay. During my trip to Budapest, they had found a solution, albeit with a few holes.
A day before I returned, Koen Clays arrived in Pullman, and spent some time discussing the problem with Xavi and Shengting. As a result, they got closer to a solution. When I got back to Pullman (a day late because of a missed connection in Amsterdam), the four of us met to discus the problem and the proposed fix. Xavi acted as the spokesperson and very animatedly described the approach on the blackboard. Within an hour, everything fell into place. Not only did the original mathematical form of the theory turn out to be true, the underlying physics was even more beautiful than we had imagined. This project has led to new ideas that will take us into novel areas of research that we hope will make a closer connection between our theory, which is a bit esoteric, and real molecules.
It was worth the wait. This paper will add a significant new paradigm to the body of knowledge that seeks to more deeply understand the nonlinear-optical response of complex molecules. The path of our research took us through exhilarating highs and unbearable lows. Hopefully, our models are finally right. If not, the self-correcting process of the scientific method will eventually lead us, or someone else, closer to the truth.
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