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Autobiography of Prof. John C. Wright have always wanted to be a spectroscopist. My first memory is the first day of kindergarten. When I did not return home, my mother went looking for me and found me, swirling the colors of an oil film in a mud puddle. The colors that captured my attention so long ago still entrance me today. I grew up in a blue-collar neighborhood in Endwell, New York. All the boys in my neighborhood had chemistry sets, the old-fashioned kind that actually had interesting chemicals. We made rockets powered by gun powder, launched hydrogenfilled balloons with appropriate fuses, and went out at night to look at the stars and planets with Perry Williamson’s telescope. However, we also did the same things that all kids do: I enjoyed the Wiffle ball tournaments and touch football games in the street. My youth was tempered by the death of my father in 1944 when his C-47 crashed in England on a resupply mission. My mother remarried and moved to be near her parents. I took advantage of my nearby grandparents because they had two sets of books. One was an encyclopedia and the other was a series that covered every science. I intended to read them all from A to Z. Unfortunately, I never got past Anthropology. My Mom was my biggest fan. She told me on many occasions, “You can do anything you want to do.” She bought books, such as My Friend the Atom, and provided subscriptions to Sky and Telescope and Science Digest. My stepfather built a chemistry lab in our basement from chicken wire and installed a lock to prevent my four younger brothers and sisters from entering. This safe haven fostered my love of chemistry and my chemical intuition. Although I enjoyed science at home, I did not excel in school. That changed in sixth grade when Miss Sentessi’s passion for science ignited my love of learning. One of my most memorable influences came from reading an article entitled “The Fundamental Particles of Physics” by Arthur Snell in the June 1957 issue of Sky and Telescope. The article was above and beyond my comprehension, but I really wanted to understand it. I knew then I would become a physicist. After graduation from ninth grade, my grandfather drove me to Florida for the summer. I begged him to stop at North Carolina State University because they had a nuclear reactor. We found two graduate students, who agreed to show us the reactor. When we finished, I asked, “What is the most important thing for me to learn if I want to become a scientist?” The answer, “Learn how to write”, was not what I expected or wanted to hear. Although I hated writing, I vowed to pay more attention in English class. I am thankful for their sound advice since it has become clear that they were quite right. The launch of Sputnik in 1957 led to an unprecedented commitment to science education in schools throughout the United States. I was selected to participate in a special program for 25 gifted students at Union-Endicott High School, and I flourished. I had a group of friends who shared my excitement for science, and we had great science teachers. My chemistry teacher, Dr. Kazlauskas, was at the top of the list. Dr. K. gave
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me and Ron Gados free-rein in the chemistry lab after school. We had a great time, particularly when we were exploring the properties of compounds at the opposite corners of the electromotive series. Our free-rein ended with an experiment that filled the fume hood with thick, black smoke and flames that shot through the hood’s small openings. Dr. K. was livid, of course, and despite my insistence that my sub-five-foot frame would be the better choice, he made the six-foot Ron Gados fit himself into the hood to clean the inside window until it was transparent again. Despite the disastrous outcome to our experiment, we were not hurt, and we did not lose our favored status with Dr. K. Although chemistry was great, my real love remained physics. I was looking forward to my senior year when I would take a physics course with Dr. Moore. I immediately lost my enthusiasm when I opened the textbook and saw steam shovels. I closed the book and never opened it again. Instead, I found my mother’s physics textbook from college and studied physics on my own. I became enthralled by the beauty of physics and its interconnections with mathematics. The insights I received from studying on my own reinforced my intuitive understanding of how the world worked and instilled a passion for science. Despite my dangerous record for after-school lab work, Dr. Moore gave me free-rein of the physics lab, where I could indulge my curiosity. I remember fondly a board containing a vacuum tube with current and volt meters at every point in the circuit and pots that allowed complete control of the current and potentials. I played with that board until I really understood vacuum tubes. The hands-on learning that occurred after school directed my own teaching strategies for creating a learning environment where students can enjoy similar experiences. My self-study also paid off when I got the first perfect score in the history of U-E High School on the New York State Regents physics examination. After I finished my junior year, my aunt took my cousin and me on a tour of midwest colleges. We visited Dennison, Oberlin, Kenyon, and some other colleges that I do not remember because I was having more than enough fun with my cousin. I was not ready to think about college. Senior year brought more seriousness to my college thoughts, and after conversations with Dr. K. and Dr. Moore, my college choices narrowed down to Cornell and Union College. I eliminated the former after I discovered that college life at Cornell involved crossing a suspension bridge over a 400-foot gorge. I initially tried to pursue a joint degree in chemistry and physics at Union College, but that idea died after discovering that organic chemistry demanded the memorization of named reactions. I do not memorize. Physics was definitely going to be my life. My role model at Union was C. D. Swartz, a gifted physicist who taught me the power of thinking carefully, logically, and fundamentally about everything. He also pointed me toward graduate school at The Johns Hopkins University Special Issue: Prof. John C. Wright Festschrift Published: July 25, 2013 5839
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Of course, I enjoyed other aspects of life at The Johns Hopkins University. I was an end on the Rowland Ghosts football team. Rowland was JHU’s most famous physicist. He invented diffraction gratings, and yes, these gratings had lots of ghosts. Even more importantly, my football teammate, Steve Shapiro, connected me with my future wife, Carol. Steve leaned over before a quantum mechanics class and asked if I wanted to meet a cute girl. Of course, I said, “Yes”, and Steve wrote Carol’s telephone number in my quantum mechanics notebook. Unfortunately, I left the notebook on the football practice field that afternoon, but fortunately, it was still there the next morning. I called Carol that evening, and as the old saying goes, the rest is history. Two events influenced my choice of postdoctoral positions. The first was reading the title of Arthur Schawlow’s talk at the Chicago APS meeting, “Is Spectroscopy Dead?” Although I did not see the talk, I am sure he concluded that the discovery of lasers brought new life to the field. Still, the title did not inspire confidence in spectroscopy’s future in physics. Shortly after seeing this title, I found out that Frank Fong at Purdue was looking for a postdoctoral student to join his group in the Chemistry Department. Spectroscopy was a forefront science in chemistry, and Frank had DARPA money and a laser to develop Bloembergen’s proposed 10-μm infrared quantum counter. The idea was exciting and I went to Purdue. Fong was a very creative, energetic, and ambitious physical chemist, who wanted to win a Nobel Prize. He had me read “The Double Helix” so I knew how to win. Frank had a large research group, but he also needed some expertise in spectroscopy. My two years at Purdue were scientifically invaluable, particularly because I gained first-hand experience with one of the first cw-dye lasers ever made and some of the first minicomputers. The dye laser had severe problems with “burning” of the inner windows of the dye cell, which forced me to gain expertise with the intricacies of dye lasers. I would have invented the “jet-stream” dye laser except we abandoned it for a better idea, the spinning dye cell. I was also strongly influenced by the presence of Fred Lytle who joined the department two years before my arrival. Fred had more enthusiasm for lasers and science than anyone I had met and his drive for achieving “femtosecond and femtomole” limits was inspiring. The raw enthusiasm in his lectures and talks was also inspiring. I once tried to imitate him in my class but quickly recognized that he could not be imitated, at least not by me. My experience with the minicomputer was also valuable. It gave me intimate familiarity with the machine language programming that I needed to integrate minicomputers into my research. In addition, the environment in Fong’s group fostered my ability to see the bigger picture and develop my own research ideas. The most valuable contribution, however, was Fong’s mentoring on how to gain “flair”, a quality that is valuable for a faculty member and a quality that Fong possessed in abundance. When Fong accepted an offer to move to Northwestern, I decided to search for my own faculty position. I applied for positions at Harvard and Wisconsin. My Harvard interview came first. My lunch with the physical chemistry faculty and the hospitality of my host, Bill Klemperer, were experiences I shall not forget. Harvard was great, but they said that, if I became a faculty member, I would not be tenured but that I would have six years to work with the best graduate students in the world. That did not sound very tempting but I was also not given the choice. My next interview was with the University of Wisconsin.
My initial advisor at JHU was J. Alvin Bearden, who gave me the following wise advice, “Young physicists are enamored with mathematics, but most important physics emerges from the laboratory.” He also told me that “There are really only about 50 things you need to know in physics. Everything else follows logically.” I think it is actually fewer than 50. We certainly learned mathematics in graduate school since the physics curriculum required four semesters of graduate courses from the math department but I looked forward to the research. I selected Warren Moos as my major professor. Since Moos was a postdoctoral student in Arthur Schawlow’s laboratories just after lasers were invented, he participated in the earliest laser experiments. Moos was a great choice because he gave me almost complete freedom. His instructions for my thesis topic were succinct: “See if you can expand on Gary Prinz’s spectroscopic studies of exchange couplings in NdCl3 single crystals.” The intellectual excitement in the group came from Les Reisberg’s presence. Les was energetic, dynamic, and intellectually confident and a good mentor for me. His animated arguments with Moos led to questions about who was smarter. I was surprised and shocked because I had never argued with a professor, at least not obnoxiously. I thought the best way to expand on the Prinz study was to find materials with large magnetic moments and short distances between the cations. After searching the literature, I decided that the DyPO4, DyAsO4, and DyVO4 crystal family was the most promising. After learning how to grow DyPO4 crystals, I placed them in liquid helium and measured their high resolution absorption spectrum with a 21-foot, Paschenmounted spectrometer, the pride of the JHU Physics Department. The Paschen was a large, circular room with a grating, an entrance slit, and a curved brass rail on which we mounted photographic plates. Sure enough, the plates showed a five-line structure, exactly what would be expected from having all possible spin orientations on the four nearest-neighbor Dy3+ ions. Even better, the lines collapsed to one line when the crystal ordered antiferromagnetically at 3.4 K. I proudly took the plates to Moos, whose first reaction was “I think you have found your thesis.” The next task was to resurrect the 1.8-m prototype of Bill Fastie’s Fastie−Ebert spectrometer. It was made from a large sewer pipe and sat abandoned in the dark corners of the lab. Although it was ugly, it was a magnificent instrument. It had curved proving ring slits that opened by placing a weight on them, a very fast f#, and an echelle grating that provided a 450,000 resolution in 10th order. I used it to make photometric measurements of the temperature and magnetic field dependence of the magnetic ordering. I also established a collaboration with Jack Colwell and Billy Mangum at the National Bureau of Standards to make heat capacity and magnetic susceptibility measurements that would complement the optical measurements. The collaboration resulted in my first Physical Review Letter, which reported that DyPO4 was the world’s best Ising antiferromagnet with a spin of 15/2. I then turned to DyAsO4 and DyVO4, which turned out to be totally different. Although they had almost the same crystal structure and would order magnetically, their spins were oriented perpendicular to the optical axis. Even more strikingly, their ordering was defined by a cooperative Jahn−Teller distortion that was induced by the magnetic ordering. It is amazing to me that I now have a Nd:YVO4 laser. Altogether, my thesis resulted in five research papers. 5840
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and fluorescence spectra into their individual spectral components. Site-selective laser spectroscopy formed the basis for the first half of my research program. It led directly to an extensive research program in solid-state defect chemistry. Point defects like vacancies, interstitials, and electrons play the same role in solid-state chemistry as protons and hydroxyls play in solution chemistry. Site-selective spectroscopy could follow the dynamics of different defects as we changed dopants and dopant concentrations, temperature, annealing atmospheres, and pressure. In addition, defect clustering created an ideal environment for studying energy transfer processes. Since ion clusters have well-defined ion−ion separations, ensemble averaging over separation distances becomes irrelevant because the dynamics can be measured directly. This simple idea formed the basis for a second research program in energy transfer. Processes now called exciton fission, multiexciton generation, three-body energy transfer, and up-conversion were efficient, and their mechanisms were easily measured in our experiments. This work later formed the basis for up-conversion lasers. A third program focused on combining the selectivity of siteselective spectroscopy with the detection limits achievable with lasers. Lanthanide, actinide, and transition metals could be measured at sub-parts-per-trillion detection limits. They could also be used as probes of nonfluorescent ions because these ions could change the crystal field splitting and act as a fingerprint of their presence. This sensitivity to environment formed the basis for a fourth program to incorporate lanthanide ions as probes into proteins, particularly calcium binding proteins, where the lanthanide crystal field splittings could act as a selective fluorescent probe of the calcium-binding sites. We also used it as a probe of guided-wave optical devices and hightemperature superconductors. Despite the success of site-selective spectroscopy, the method was sharply constrained by the need for fluorescence. The key idea of creating multiple vibrational and electronic excitations occurred to me while I was on vacation at Carol’s family cottage in 1978. Since nonlinear interactions would drive the creation of a coherent output signal, fluorescence was no longer needed. Sharp vibrational resonances would provide the selectivity for measuring complex systems, and strong electronic resonances would provide the sensitivity. This idea formed the basis for what became known as Coherent Multidimensional Spectroscopy (CMDS). I was very excited and immediately called my research group to rearrange our nitrogen-laser-pumped dye lasers for nonlinear spectroscopy. When I returned to the lab, we formed three teams running 24h shifts in order to find samples and processes that would demonstrate the feasibility of using multiple resonant enhancements in a nonlinear process. After we had completed the initial explorations, Steve Lee took on the experiments for his Ph.D. thesis, built a dedicated nonlinear system, and became the pioneer of our nonlinear spectroscopy program. We explored the creation of vibrational resonances, using either direct infrared absorption or stimulated Raman scattering to excite vibrational states, and the creation of an output signal, using either another coherent interaction or the excitation of fluorescence. We published the latter in a 1980 Applied Spectroscopy paper. Although the paper was awarded the William F. Meggers Award for the top paper in Applied Spectroscopy, we knew the real success rested on creating
The UW made sure I knew their standards for tenure were very high but were attainable. They gave me an offer and I took it. Before leaving Purdue in 1972, I attended the IEEE Quantum Electronics Conference in Montreal. The special symposium on lasers included the most famous names in the field. Particularly remarkable was Ted Hänsch’s announcement of the high-resolution nitrogen-laser-pumped dye laser and its direct measurement of the Lamb shift in hydrogen, a spectacular achievement. It was immediately clear that the Hänsch dye laser would form the basis for my research program. The symposium ended with a panel discussion. The last question was “What will be the most important application for lasers?” The unequivocal answer was “Chemistry”. When asked why lasers were not used in chemistry, the panel’s unanimous answer was that chemists did not know how to use lasers. That answer confirmed that I had made the right choice. Carol and I moved to Madison in 1972, and I joined the University of Wisconsin’s Department of Chemistry. Although being addressed as “Professor Wright” was a shock, I immediately felt at home. Everyone was accessible, friendly, and helpful. I could even visit the great Joe Hirschfelder, our Medal of Science recipient, and join him for lunch at the Laurel Tavern. Jim Taylor, John Walters, Dennis Evans, and John Schrag gave me great advice and help as I got ready to teach a course I had never taken myselfAnalytical Chemistry. Fortunately, I had a fellow companion in John Schrag, who was also a physicist. He had been hired the year before me, and we were both assigned to teach different sections of the same course. John and I shared the same approach to problems, which was different than that employed by the rest of the analytical division. When we got stuck on a concept, we would visit Dennis Evans, a thoughtful and wise electrochemist. We often noticed a slight shudder when we arrived in his office, probably because our questions were typical of physicists who were just learning chemistry. John Walters emerged as my mentor and role model. He was totally dedicated to both teaching and research, which meant that he worked 80-h weeks. Shortly after my arrival, John asked me to map out my future research program. His request forced me to transform my abstract ideas of the big picture into concrete plans, which turned out to be reasonably accurate. One goal remained abstractthe development of a spectroscopy that involved only laser excitations, no monochromator. I did not know how to accomplish this goal because nonlinear processes were still a foreign idea, but I really wanted to do it. My research program focused on discovering how lasers could be used for chemical measurement, particularly using their narrow spectral line widths to achieve selectivity. The department provided $32,000 to set up my lab. Half went toward purchasing a Molectron 300-kW nitrogen laser. When the laser arrived, I was shocked because, when I removed the cover, it was almost empty. The laser had one long plastic tube with electrodes along the sides, a bunch of capacitors, and some high voltage electronics. Nevertheless, it worked. We built the first of many Hänsch-design dye lasers and published our first paper in 1974, “Selective Laser Excitation of ChargeCompensated Sites in CaF2:Er3+ ”. CaF2:Er3+ has a complicated spectrum because erbium’s charge mismatch created more than 18 different sites. Tuning the laser to specific absorption lines of specific erbium sites creates fluorescence characteristic only of those sites. This strategy formed the basis for site-selective spectroscopy, where one resolves and dissects the absorption 5841
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stimulated Raman scattering was compromised by much stronger signals from two, cascaded, four-wave mixing processes. We abandoned this approach since it looked hopeless. We then put all our efforts into directly creating the vibrational resonances using infrared excitations. Peter Chen, Jim Hamilton, and Mitch LaBuda took on the challenge of the infrared absorption approach, also in 1986, but it was more difficult because we needed to build a tunable infrared system. The key question confronting the feasibility of this approach was whether the vibrational resonance enhancements could dominate over the nonresonant electronic contributions. Jim and Mitch succeeded in answering this question. They discovered the vibrational resonance enhancements were strong using singly vibrationally enhanced (SIVE) four-wave mixing, but they did not find a sample with coupled resonances in a frequency range that could provide doubly vibrationally enhanced four-wave mixing. The research took on new life when we purchased an Infinity Nd:YAG laser from Coherent and a dual optical parametric amplifier system from Dean Guyer’s company, Laser Vision. When my postdoctoral student, Wei Zhao, saw Dana Dlott’s paper on vibrational relaxation in acetonitrile, he realized that acetonitrile had all of the characteristics for a doubly vibrationally resonant experiment. Wei implemented the experiment on the new system in 1999 and quickly obtained the first demonstration of multiresonant CMDS. He named it Doubly Vibrationally Enhanced Four-Wave Mixing or DOVE FWM. When Wei’s work made it clear that CMDS was going to be a reality, I ended the solid-state chemistry and energytransfer half of my research program so we could concentrate completely on CMDS work. We continued DOVE experiments in order to define the characteristics, capabilities, and range of the methodology, but we also wanted to try other nonlinear processes and extend our methodology from the nanosecond regime to the picosecond regime. In particular, we wanted to explore using three vibrational enhancements. Kent Meyer took the leadership to explore the feasibility of Triply Vibrationally Enhanced (TRIVE) CMDS, and his work established all the basic experimental and theoretical principles for this methodology. Mark Rickard, Nathan Mathew, Kate Kornau, and my postdoctoral student, Andrei Pakoulev, then took the methodology much further by showing how higher excitation intensities could create higher-order processes, up to 12 interactions, that allowed the creation of multiple quantum coherences between high-overtone and combination-band states. The method directly probed the diagonal and offdiagonal parts of the molecular potential-energy surface. They also showed that TRIVE CMDS could identify coherent transfer, whereby one of the states in a coherence evolves coherently to a different state. Nathan Mathew had the insight that, by changing the phase matching, the normal output coherences would become forbidden and that only coherence transfer could create output coherences with allowed transitions. Furthermore, Andrei Pakoulev showed that coherence transfer made it possible to do CMDS with only one excitation frequency. In order to take our research program to the ultrafast regime, I took my sabbatical leave in 1999 with Graham Fleming’s research group at the University of CaliforniaBerkeley. I wanted to gain experience with the nuances of ultrafast spectroscopy, and I wanted to learn how Graham’s group had managed to see six-wave mixing 2D Raman when our experiments showed only cascaded four-wave mixing. Graham
output coherence. All we needed was a sample with three sharp transitions. The key sample was described in a 1982 paper by Decola and Hochstrasser. They showed that pentacene had the sharp electronic, vibrational, and vibronic resonances we needed. It was ideal for demonstrating fully resonant and fully coherent spectroscopy. Dinh Nguyen and Jack Steehler pioneered this effort. They used pentacene as a model system to expand the methodology and demonstrate its experimental capabilities. The methodology included different parametric and nonparametric strategies that we called fully resonant CARS, MENS, MEPS, and CSRS. The different strategies had the same vibrational and electronic resonances but different, although complementary, characteristics and capabilities. These capabilities included all the now well-known characteristics of CMDS: fully coherent pathways, line-narrowing of inhomogeneous broadening, selectivity for specific components in complex samples, and sensitivity to coupling between quantum states. Later, Roger Carlson unified our work. His two volume 1988 Ph.D. thesis did a remarkable job of exploring the full capabilities of these methods and developing the underlying theory required to understand the results. Roger used the fully resonant coherent Raman methods to dissect the absorption and fluorescence spectra of pentacene and to identify all of the couplings between the ground vibrational states and the excited vibronic states. He contrasted these measurements with azulene, where two electronic states were accessible. His theoretical work treated all aspects of the four-wave mixing: inhomogeneous broadening in each parametric and nonparametric strategy, higher order mixing and saturation, mode coupling, dephasing induced resonances, coherent interference, population relaxation, and absorption and refractive index effects. His thesis became our group’s nonlinear “Bible”. After establishing the fundamental experimental and theoretical foundations of multiresonant spectroscopy, the research program expanded the range of materials to include other polyaromatic hydrocarbons, porphyrins, conductive polymers, fullerenes, and endohedral fullerenes. Bruce Winker extended the multiresonant methodology to atoms in flames. Not only did this work provide a new way of measuring atomic concentrations, it also provided fundamental insights into the role of dynamic Stark effects on multiresonant nonlinear spectroscopy. Bruce studied a number of different phase matching and resonance structures that had different capabilities and spectra. We also found that it was possible, although complicated, to derive closed-form solutions for the dynamic Stark resonances that modeled the experimental results. This work has proven useful in our current work with higher order processes. Although this work demonstrated the feasibility and capabilities of using fully coherent multiresonant nonlinear processes for multidimensional spectroscopy, it still relied on model systems and cryogenic temperatures. Clearly, we needed to work at room temperature where the vibrational resonances would retain spectral selectivity even as the electronic resonances broadened. Our previous work showed that we could create vibrational resonances either directly by infrared absorption or indirectly by stimulated Raman scattering. Since we already had the dye lasers required for the six-wave mixing process, Joe Ivanecky took on the challenge of the stimulated Raman approach in 1986. The six-wave mixing involved two stimulated Raman transitions and an output Raman transition. Joe discovered that the six-wave mixing process using 5842
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In addition to my research career, my teaching career took on an entirely new aspect in 1991 when I found out that my son’s high school girlfriend would be in my freshman analytical chemistry course. The prospect of having her in class prompted me to change the course structure to emphasize active learning and student collaboration in all aspects of the course. I modified the active learning strategies that John Walters pioneered at St. Olaf and implemented them in my course. When the course was over, I was amazed at the sophistication of the students. Conversations with them were comparable to those with my graduate students. This teaching experiment demonstrated to me that changing the classroom environment and approach could achieve remarkable improvements in student success. After witnessing the power of that experience, I have never returned to a lecture and exam format. The difference in student performance was sufficiently striking that I wanted to disseminate this approach to the other areas of chemistry. First, we needed to have an objective and credible evaluation of whether the active-learning strategies made a difference. Together with my colleagues, Hyuk Yu, Ed Vedejs, Don Gaines, and John Harriman, we designed a twopart strategy to define whether the change in instructional strategy resulted in credible differences in student performance. The first part of the strategy entailed oral examinations of all of the students in two different sections of the same course, one using active learning and one using a lecture format that still engaged the students in class participation. Twenty-five faculty members from outside our department each agreed to examine eight students, four from each section. The eight were chosen from the same octile in their previous chemistry course. The faculty ranked the students from most competent to least competent, using their own definitions of competence. Both faculty and students filled out questionnaires that defined their own perceptions of the oral exam. The second part of the strategy involved a collaboration with Susan Millar’s LEAD (Learning through Evaluation, Assessment, and Dissemination) Center, a campus resource that used the qualitative research strategies of anthropology to identify the nature of the student interactions and learning styles in the two sections. The differences in the perceived competence from both the faculty and student viewpoints were striking. The LEAD study documented that the differences were directly attributable to students learning from each other rather than from the faculty. The results provided an objective confirmation of my personal observations. The details of the active-learning strategy and the assessment were published as separate articles in the Journal of Chemical Education. They formed the foundation for the NSF-funded “New Traditions” program, a consortium of 23 colleges and universities that implemented and disseminated active-teaching methods throughout the chemistry curriculum. I am deeply appreciative of the support of the National Science Foundation and its many program managers over my entire career. It started with Fred Findeis recognizing the promise of laser spectroscopy in chemistry. The NSF’s willingness to fund new ideas has been central to my research and the health of our nation’s science. Without them, my research program would not have been successful. Thank you. The atmosphere and colleagues within my department and university have been wonderful. The collegiality and support I experienced when I joined the department in 1972 has only grown stronger over the years. My career was strongly influenced by my colleagues, John Walters, John Schrag,
suggested that I work with David Blank, a new postdoctoral student in Graham’s group. It was a fortunate choice. David was the most talented experimentalist I have met, and he taught me a great deal about ultrafast spectroscopy. We had extensive conversations about cascaded processes, and David soon discovered that their measurements were also compromised by the cascaded processes, which was a disappointment because 2D Raman would have been a great methodology. It would have had the capability to probe a wide variety of vibrational states, and six-wave processes would have opened many new directions. When I returned from sabbatical, we had received our first picosecond laser system with two optical parametric amplifiers from Spectra-Physics, and I needed a student to start work on it. Kent Meyer was a first-year student who did not have much laboratory experience. Although I was reluctant to put him in charge of setting up our system, Kent was so eager that I relented. Kent did not disappoint. He lived in the lab. He rapidly got the system operational despite the fact that he had to design and build the entire optical system, modify the OPAs so they could scan, interface all the delay stages, drivers, micrometer adjustments, and detection electronics, and write the LabView software that integrated and controlled the system. It was a remarkable achievement. When I became the Chairman of the Department of Chemistry, my time with Kent was sharply curtailed. In addition, my group gradually decreased in size until only Kent remained. Even so, Kent’s productivity did not diminish; and the group regrew when my three-year term as Chemistry Chair came to an end. Our application of DOVE and TRIVE CMDS continues. We are pursuing the use of our methods to probe the oxygenevolving complex in photosystem II. Erin Boyle is leading this effort. She has already discovered another member of our multiresonant CMDS family, Triple Sum Frequency (TSF) CMDS. The discovery was unexpected since TSF cannot be phase matched under normal refractive-index dispersion. Nevertheless, it creates very bright signals and is an intriguing new approach. We have also started a new direction in our multiresonant CMDS program, namely, nanostructures. Excitonic states in nanostructures bear many analogies to vibrational CMDS, and the same strategies we had already developed are applicable. In order to test the feasibility, Stephen Block and Lena Yurs used our picosecond laser system and the TRIVE pathways to excite the quantum-confined excitonic peaks in PbSe quantum dots. They obtained beautiful multidimensional spectra. However, the capabilities of multiresonant CMDS are optimized when the excitation pulse temporal width matches the quantum state coherence dephasing times. Such pulses are long enough to excite single quantum states but short enough to resolve the coherent and incoherent dynamics. Research on nanostructures required femtosecond excitation pulses. Schuyler Kain has just finished implementing a dual OPA femtosecond multiresonant CMDS system. It continuously scans the OPA frequencies and time delays so the frequencies cover the range from the infrared to the ultraviolet, while maintaining the spatial overlap within the excitation volume. Since commercial OPA systems are computer controlled, continuous scanning seemed straightforward, which it is not. Despite the challenge, the system is working very well now and is ideal for probing complex nanostructures because its ability to measure fully coherent processes is not constrained to a single excitation frequency. 5843
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James Taylor, and Mary Wirth. My colleagues across the country and across the world have provided the inspiration, guidance, and companionship that make science such a satisfying career. So many other people have helped me over the years that I cannot name all of them here. My students have been uniformly terrific. They make being a professor the best possible job on the planet. I must give special recognition to my first student, David Tallant, who helped me start my career and set the traditions for my future students, and to the late Roger Carlson, who provided the nonlinear background and insights that guided our nonlinear spectroscopy throughout the years. I am forever indebted to all my students. Finally, my wife, Carol, my children, Dawna and David, and my grandchildren, Forest and Eve, have been the anchors that have made my life meaningful and rich. Thank you all!
John C. Wright
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