Another paper accepted, but in record time

In a recent post, I mentioned a paper that took about 4 years to get published. In contrast, we did some work that took about 3 months to complete, and today, the manuscript was accepted for publication in JOSA B.

The topic:

Testing the diffusion hypothesis as a mechanism of self-healing in Disperse orange 11 doped in PMMA

This is an important piece of work that get's us one step closer to understanding self healing in dye-doped polymers, a phenomena that was discovered in our lab a decade ago. The first comment I always get when introducing our work at scientific meetings is that the laser is heating the material, causing the dye molecules to diffuse away from the beam. When the laser is turned off, the dye molecules diffuse back. So, rather than the molecules breaking apart and then reassembling themselves, they are just moving out then into the beam - a much less sexy phenomena.

The report of one of the reviewers summarizes our results best:

This manuscript describes a combined experimental and theoretical study on the recovery of absorption in dye-doped polymer samples exposed to high light intensities. There are several possible mechanisms for such a self-healing effect and it is of significant interest to understand which one(s) contribute. The paper presents a set of experimental data on the dynamics and spatial profile of the optical properties of the damage region. It then presents a thorough and detailed model of what is expected if diffusion of undamaged dye molecules into the damaged region is responsible for all or part of the recovery. The difference between the broadened profile of the concentration predicted by the diffusion model and the constant profile shape observed experimentally is persuasive in demonstrating that diffusion is not a significant contributor to the self-healing. The manuscript is well-presented, thorough, and sound. It warrants publication in JOSA B.

Congratulations to Shiva and Nathan for a job well done!

A silver lining

We have been on the east coast visiting with family in the Philadelphia area. What should have been a fun time has for me been colored with sadness and anxiety. First, there is the issue of what to do with my 95-year-old father.

He is highly independent, living on his own, cooking for himself, and competently driving a car. In fact, in the summer, he and his buddies (all younger than him) routinely drive to Cape May - a Victorian beach town - for a day of walking on the beach and eating out.

He is so energetic that he volunteers twice a week to work at the senior lunch, collecting the $1.50 cost of the meal, and making sure that the books are balanced. He even helps deliver food to the eighty-year-olds who need walkers.

Ten years ago, we decided to build an addition to our home so that my father could move in with us. He refused. I don't blame him. He has friends and activities to keep him busy. He routinely takes part in activities at the Ukrainian Church and the Ukrainian Center in the Fox Chase area of north of Philly. Pullman, on the other hand, has for all practical purposes zero Ukrainians for him to befriend. Though we are here for him, work is a large part of our days, so he would be bored to death without our company. In Philly, he is an active part of his micro-community.

My father is concerned that his driver's license will not be renewed, making his present lifestyle impossible. We are also concerned that as he gets older, he will be less able to take care of himself. Our agonizing decision comes down to a choice between him continuing to live alone with the chance that he may injure himself, but otherwise have a happy life; or, moving him to Pullman, and dooming him to certain misery. In my mind, both choices are far from ideal.

Our concerns were renewed a few days ago when my father fell (when alone in his apartment) as a result of a dizzy spell. He was bruised but otherwise seemed unharmed. However, it was painful for him to walk, and his nurse (who visits him occasionally at home for blood tests), recommended that he get an X-ray to make sure that he did not fracture his hip. Fortunately, we had made plans to have lunch with good friends of ours from Yardley. After lunch, John - an orthopedic surgeon, and Camille - a physical therapist, checked my fathers injuries and felt that they were not serious, but ordered X-rays just in case. We went to a local hospital in an expedited process - care of our friends. He was indeed not badly injured

This whole process reminded us of my father's precarious situation and the decisions that would have to be made. Unfortunately, every option, other than the status quo, is unacceptable to my father. No senior living homes, no roommates, no moving to Pullman, etc. So for now, we are trying to find ways to make his life simpler in his present living arrangements.

In the meantime, we have been driving extensively to get between my fathers place, and the various in-laws. As a result, I have been feeling depressed and anxious about not having time to work, not to mention my motion sickness. Yesterday afternoon, after arriving at my sister-in-law's vacation home in Delaware, I finally sat down at my computer to work, only to come down with a migraine headache moments later. My symptoms put me out of commission for the rest of the evening.

This morning, I awoke feeling physically well, but mentally exhausted with thoughts of the piles of work that has accumulated. As I was working, I got two pieces of good news within a few minutes of each other.

First, I was notified that my NSF proposal on sum rules has been recommended for funding. However, there are several questions that I first need to address before approval. This will be my first priority, so my other work will need to wait. Hope my graduate students understand my inaccessibility during this period of time.

Secondly, while reading through the email from NSF, my email dinged with a message that a third paper was accepted in our series of papers on Nathan's work on photo mechanical liquid crystal elastomers. An excerpt of comments from each reviewer follows.

REVIEWER 1

The manuscript provides an in-depth model and related discussion on the deformation mechanism of azo containing liquid crystal elastomer upon a light trigger. The authors incorporated in the model heat effects as related to absorption and diffusion during and after exposure in the absorption band of the azo compound. To my opinion this was the first time that it was described so extensively rather than mentioning that heat effects might also play role next to the photo-isomerization reaction. For this reason it is my opinion that the paper should be published in the Journal of the Optical Society of America...

REVIEWER 2
In the manuscript “Modeling the mechanisms of the photomechanical response of a nematic liquid crystal elastomer”, authors have done the modeling to explain the plausible mechanisms involved in photomechanical response of nematic liquid crystal elastomer. In the previous report: N. J. Dawson et al., J. Opt. Soc. Am. B 28, 1916 (2011), authors have reported the experimental determination of mechanisms of photomechanical effects in a nematic liquid crystal elastomer in a particular device geometry. More interestingly, in the present report the models have been initially proposed and then used to compare with experimental results and to evaluate related material parameters. Undoubtedly, the theoretical modeling, comparison with experimental results and related explanations are up to the mark. Moreover, the report does not only demonstrate the fundamental mechanisms but also provide the platform for design of optical devices based on photomechanical effect and hence seems to be greatly useful for liquid crystal community as well as other related fields.
On the basis of the originality and novelty of the work presented in this report, I feel that it would be really of worth to keep this article in JOSA B. Therefore, I recommend it for the publication in JOSA B.

I have to run!

An intellectual creation that exceeds its creator

A few posts back, I discussed Monte Carlo studies that shed light on many unexplained observations. For those of you interested in seeing a preprint, it can be found on the physics archives at: http://lanl.arxiv.org/PS_cache/arxiv/pdf/1101/1101.1041v1.pdf. The manuscript is now under review at the Journal of the Optical Society of America B.

I am still excited by our observations because of the breadth of understanding that has resulted. While this paper may not be appreciated by a large number of people, it is certainly on my list of top 5 papers that I have published over my career. Ironically, while my most highly-cited papers report solid science that has been useful to many other researchers, I prefer to judge my work on the degree to which it opens my mind; and, the awe/wonder that it elicits. Ideas that paint the universe with the broadest of brushes are king. This recent work is an intellectual creation that, like a brilliant child, has grown beyond its creators. I marvel at all that it continues to teach us as well as its ability to inspire new lines of research.

The abstract and conclusion says it all:

ABSTRACT: Studies aimed at understanding the global properties of the hyperpolarizabilities have focused on identifying universal properties when the hyperpolarizabilities are at the fundamental limit. These studies have taken two complimentary approaches: (1) Monte Carlo techniques that statistically probe the full parameter space of the Schrodinger Equation using the sum rules as a constraint; and, (2) numerical optimization studies of the first and second hyperpolarizability where models of the scalar and vector potentials are parameterized and the optimized parameters determined, from which universal properties are investigated. Here, we employ an energy spectrum constraint on the Monte Carlo method to bridge the divide between these two approaches. The results suggest an explanation for the origin of the factor of 20-30 gap between the best molecules and the fundamental limits and establishes the basis for the three-level ansatz.

CONCLUSION

Classifying Monte Carlo simulations using an energy spectrum function resolves several long-standing questions. First, our work shows the centrality of energy spacing in determining the intrinsic nonlinear response. While a broad range of transition moments are observed in atoms and molecules, the energy spacing - as characterized by the energy parameter, E, varies little between systems. Indeed, the importance of the energy parameter in attaining larger hyperpolarizabilities has been demonstrated in several experimental studies.[6, 37]

...

Monte Carlo calculation using the energy classification scheme have bridged the divide between Monte Carlo simulations and potential energy optimization studies. The power of the Monte-Carlo technique lies in the fact that all possible Hilbert spaces are probed, leading to very broad and fundamental relationships. Using energy classifications allows the parameter space to be reduced to subsets that describe atoms and molecules. Future refinements may lead to more specific design guidelines for making improved molecules for a variety of applications. The potential for discovering new fundamental science with this approach is of equal importance.

The good, the bad, and the nasty

Just a few minutes ago I was preparing my lectures for my graduate mechanics class. As I often do, I was once again distracted, thumbing through the latter pages of the textbook - marveling at the simple beauty of physics. Even classical physics is rich with phenomena, yet it is unified by simple ideas from the calculus of variations. I yearn to savor the physics that lies before me, but awaken to reality with every ping alerting me to a new email. Sadly, life is filled with trivial tasks that keep me from my passions.

The last few days brought some good and bad news. As I had anticipated, Nathans' revised manuscript was accepted for publication. And, Shoresh's and Mark's JOSA B paper, which I had previously reported as being highlighted on the Optical Society of America's website, was the second most downloaded JOSA B paper in September 2010. See http://www.opticsinfobase.org/josab/abstract.cfm?uri=josab-27-9-1849 for a free download of the paper.

The paper that I had submitted to the Journal of Chemical Computation and Theory with David Watkins, over which I waged a full out battle with the referees, was finally rejected. I had expected this outcome from the outset, but thought it worth a try. My intention was to expose a new audience to our work, but apparently, this was not to be. Below is the strongest criticism of our paper.

"Professor Kuzyk seems strongly taken with his own work but is not sufficiently mindful of the work by others. Perhaps the most egregious example deals with the issue of neglecting the effect of vibronic interactions on the static first hyperpolarizability. As justification he cites two of his own papers, but totally misses the extensive literature in this field showing that the vibronic effect cannot be ignored. There are, in fact, many instances where the vibronic term is comparable to, or larger than, the pure electronic contribution. Hence, the maximum value he uses (derived only by considering electrons) could easily be breached without invoking any exotic systems."

The reviewer is referring to the fact that I cited one of our papers that shows that vibronic states do not contribute substantially to the hyperpolarizability. Undoubtedly, in heated debates, the parties involved often speak past each other. To do my part, I am once again plowing through this literature to understand the issue. However, I find it is a bit annoying that the reviewer did not point out an error in our logic, but rather made sweeping statements. My guess is that it is certainly possible for real molecules to have vibronic contributions that are large compared with electronic excitations; but, I believe that when a quantum system is designed to have a hyperpolarizability near the fundamental limit, the vibronic contribution will never be as large. And since we are always concerned with the physics of a system near the limits, I believe that we are correct.

It is interesting that the reviewer states that the limit could easily be breached in the presence of vibronic states. Since the best molecules ever measured fall a factor of 30 short of the limit, I do not believe that the reviewer's confidence is justified.

Though this exchange with the reviewer was one of the nastier ones I have experienced, I find it all to be trivial in the larger scheme of things. Happiness is most abundant when I am absorbed in Physics. At some point, I will rewrite this manuscript, taking into account these comments, and will see how our results mesh with the body of scientific understanding. I take solace in the fact that people are reading our papers. I see this review not as a devastating blow, but as an opportunity for new investigations. The last 6 years of my research on fundamental limits were ignited by a comment that was published on my 2000 PRL paper. In the process of accumulating evidence to show the criticisms wrong, I made many discoveries and gained deep insights. These kinds of experiences should not be seen as defeat, but as an invigorating start to a new chapter of research.

Monte Carlo simulation appears on the Spotlight on Optics section of OpticsInfoBase.org

Our paper on Monte Carlo simulations of the second hyperpolarizability has just appeared in the Journal of the Optical Society of America B. The paper was selected to be highlighted on Spotlight on Optics. An excerpt from the summary follows:

Spotlight summary: The paper of Shafei et al. belongs to a series of papers initiated a decade ago by M.G. Kuzyk, oriented toward a theoretical analysis of fundamental limits and the optimization of attainable first- and second-order off-resonant electronic nonlinear hyperpolarizabilities, which describe a molecule’s response—its nonlinear polarization—to optical fields. Nonlinear hyperpolarizabilities are expressed in terms of infinite series. In the absence of a small parameter, the optimization of hyperpolarizabilities and the search for universal features constitute a challenge, which requires, first of all, a deep physical intuition.

In earlier papers, Kuzyk et al. calculated the fundamental limits for nonlinear hyperpolarizabilities using the three-state ansatz, which states that when a hyperpolarizability is near the fundamental limit, the system can be described by a three-level model. To this end they have used sum rules—one of standard approaches in quantum theories—that put constraints on infinite sets of energy levels and transition moments.

Surprisingly, experimental studies and earlier theoretical approaches have revealed a large gap between attainable values of the first and second hyperpolarizabilities and predicted fundamental limits. This casted doubt on the validity of the three-state ansatz...see more