Proceedings of the John Hall Symposium

The following sections are included:

• CONTENTS

• PHOTOS

• DR. JOHN L. HALL BIOGRAPHY

It really seems not so long ago that I applied to be an National Research Council (NRC) postdoc at the National Bureau of Standards (NBS) in Washington, D.C. Lindy and I had our first child by then and it clearly was going to be necessary to leave the security of the physics graduate life at Carnegie Tech by finalizing my research degree with advisor R. T. Schumacher and preparing for the next professional opportunity. Optical pumping was at the frontier, and I proposed to do an optical pumping experiment with Pete Bender at the NBS in downtown Washington, D.C. The NRC filing date was in the early winter. Little did I know that just at the previous year's end that Ali Javan, Bill Bennett, and Don Herriott had gotten the first gas laser action in a Helium-Neon discharge: the light that changed most of physics as we then knew it. By the time I began at NBS, the gas laser had joined its more powerful cousin, the pulsed ruby laser, as the hottest field of research. That same summer, optical harmonic generation in quartz was reported by Peter Franken's group, although the "blemish" of an extra line in the spectrogram was edited out by the publication team at Physical Review Letters. "Misteakes" can still happen…

Good morning. On behalf of the National Institute of Standards and Technology (NIST), one-half of the long and successful partnership known as JILA, I am pleased to welcome you all to this very special John Hall Symposium…

Boulder Laboratories of NIST (formerly NBS) together with JILA and the University of Colorado have been one of the most important world centers of high precision spectroscopy, and acting as the world center of time and length standards. By investigating the history of such prominent activities, we see that J.L. Hall, for whose honor the present symposium has been organized, has been leading the research activity in the center of active groups, and also that the basis and the direction of the activities were founded in early 1960's by his leadership.

Jan, whose 70th birthday and scientific contributions we celebrate today, was a founding (charter) member of the Joint Institute for Laboratory Astrophysics (now JILA). He came in July of 1961 as a National Research Council Postdoctoral Fellow to the National Bureau of Standards (jointing the Atomic Physics Division) in Washington. A year later he came to Boulder with the contingency from that Division who constituted the bulk of the Federal Government's scientific staff contribution to the Joint Institute. Midway during Jan's first year at JILA he was made a regular NBS employee…

When invited to participate in this Symposium for John Hall ("Jan" to his friends) I was enthusiastic to come, but not sure what I should talk about. Eventually it seemed the best thing might just be to recount how I first came to meet Jan, the exciting time we spent working together on a new technique for stabilizing lasers to cavities, and some of the things that have developed from this and some of his other work…

For many years physicists have been facing up to the exacting experimental challenge of searching for gravitational waves. Predicted by General Relativity to be produced by the acceleration of mass, but considered by early relativists to be transformable away at the speed of thought, gravitational waves have remained an enigma since 1917. Jan Hall to the present has not become a formal member of any of the gravitational wave projects worldwide and yet without his unflagging enthusiasm, his experimental ability and his enthusiasm at helping younger researchers in the field, it is unlikely that the present generation of long baseline detectors such as LIGO, VIRGO, GEO 600 and TAMA 300 could have come about.

Dear John, First of all, please accept my most sincere and kind wishes on your wonderful holiday - your 70 birthday…

The progress of high resolution and accurate spectroscopic studies using a trapped and laser cooled single ion at the National Research Council of Canada (NRC) is described. Summaries of the work are presented in the context of the important conceptual and research support provided by Dr. John L. Hall. Results including sub-100 Hz spectroscopy of the Sr+ single ion transition, absolute frequency measurement of the centre frequency via chain and optical frequency comb technology, and use of the ion reference for the precision determination of other frequencies such as the 633-nm I2/HeNe operating frequency are described.

John Hall has been a friend, colleague, and mentor to me and my family over the past twenty years. He has profoundly influenced and enabled my career by way of the wonderful scientific ideas and technical tools that he has so generously shared with me, and indeed, an extended scientific community around the world. More importantly, he has taught me and several generations of scientists completely different ways to think, both with regard to the substance and the culture of science. In this contribution in celebration of his seventieth birthday, I give a brief sketch of my association with John Hall.

Since the early 1970's, the Bureau International des Poids et Mesures (BIPM) has pursued activities in the field of optical frequency standards trying continuously to improve them, and gain increasing understanding of their limitations. All this is in support of the worldwide implementation of the metre by arranging international comparisons, technology transfer and technical support, and to serve as a forum for scientists working with similar standards in National Metrological Institutes all over the world. Part of the BIPM's role is to maintain close cooperation with a large number of national metrological laboratories. In particular, the group of J. L. Hall in JILA has interacted frequently with the BIPM. Several members of the BIPM staff have spent time in JILA to benefit from the high level of research in this institute and its warm and friendly atmosphere…

Since the advent of the laser in the early 1960s, and subsequent stabilization of the frequency of the 633 nm and 3.39 um He-Ne lasers by means of sub-Doppler spectroscopy of iodine and methane in absorption cells, an increasingly wide international programme to establish optical frequency standards has been undertaken. The aims of this research have been to provide improved primary and secondary standards of length and time, and sources for precision spectroscopy to undertake ever more accurate tests of physics and fundamental constants. Throughout these last four decades, Jan Hall has contributed a pivotal role to development of high precision spectroscopic techniques in the optical / infra-red regions, and his insight has greatly facilitated the transfer of microwave standards techniques into the optical region, with a corresponding vast increase in resolution. We now stand with cold atom and ion optical standards on a par with the best microwave fountains, and the potential for an optical redefinition of the SI second. In addition we have a significant range of stabilized laser secondary standards covering the visible through to the mid infra-red, and a high precision comb technology capable of interlinking all these standards. Jan has been instrumental in demonstrating the basic concepts from which this huge expansion of optical technique has evolved…

Dear Jan, Many French researchers are very grateful to you for the time they spent and all they learned with you in Boulder, and of course, some of them were invited to give talks in your honour, but they were not able to attend the symposium on these dates. They asked me to tell you how much they do regret not being here to share with you this very special time. But I can tell you that all of us share all we heard today with respect to your generosity, kindness, etc. I am speaking of people like Jean-Marie Chartier, Christian Borde, Alain Brillet, Christophe Salomon, Christian Chardonnet, Raymond Felder, Olivier Pfister and many more who spent weeks or months from time to time in your world renowned laboratory…

I feel truly honored to have been asked to introduce Lindy Hall, whom I have known and admired for almost 40 years. Most educated women of our generation felt we had to choose: we could have families, or we could team with our husbands, or we could have our own, full-time careers. But Lindy wouldn't settle for that. Lindy knew she could have it all. And she had the drive, the talent, the creativity and, above all, the energy to pull it off…

It is a pleasure and privilege to add some words to this collection of writings. I think that I can claim to have known Jan longest of anyone in the world science culture, as we met in February, 1956 at Carnegie Institute of Technology in Pittsburgh, Pennsylvania. As a senior in physics, he was already taking advanced classes in that Department, so his decision that spring to transition into graduate school at CIT was an easy and natural one. The next five years were a golden time of fun and learning for us both. In our respective programs, there was a good mix of technical and humanistic specialties to study and lots of opportunities for practical application and problem solving. As we and others in our core group of students married and started families, a community of colleagues and friends developed with shared interests and interactions…

There are three permanent problems lying in the basement of all optical devices and measurements: Sensitivity, Resolution, Accuracy/Fidelity. The distinguishing successes and real progress in the other fields of science are not gradual but undergo jumps based on some new ideas, unexpected predictions or experimental demonstrations. Typically, after appearing more or less "raw" pioneer idea the work of many people is necessary for practical development and converting it to "everyday working" units or methods. And for effective "reorientation" of colleagues (scientists, engineers, metrologists,…) into a new road the idea should be sounded/demonstrated clearly. Further, the people determining a high-tech progress could be divided in two non equal parts: one – who just can say, and other – who are mostly able to realize. John L. Hall happily combines both talents: ability to predict of new horizons and their clear realization – he is a great inventor and great practician…

The deformations of the lineshapes of the saturated absorption signal produced by optical pumping, by light pressure on atoms and by the coherent population trapping are discussed.

Laser stabilization methods learned by the authors from Jan Hall are applied to control a nondegenerate optical parametric oscillator above threshold in order to generate frequency-stable quantum twin beams. These beams are used to test quantum noise reduction in interferometric measurements and heterodyne polarimetry is demonstrated at 4.8 dB below the shot noise limit.

In a frequency mixing experiment in Jan's lab, where one of us (SS) was visiting during 1989-90, a linearly polarized Ar-ion beam was accidentally directed onto a crossed polarizer. At the output of the polarizer we saw a four lobe pattern although the incident beam had the lowest order Hermite-Gaussian beam profile [HG₀₀]. We attributed it to a small mixture of HG₁₁ mode in the laser output and moved on. A few years later, when this phenomenon was encountered in a different context, a careful examination revealed the secret side of a gaussian beam - Maxwell's equations require linearly polarized laser beams to have a small mixture of cross-polarization component [Erikson and Singh, Phys Rev. E 49, 5778]. This effect is described here.

Electro-optic control and locking techniques are key ingredients of today's quantum optics experiments. We present an example of the superb technology pioneered by Jan Hall and how it has contributed to optical quantum information and communication.

This note should be easy, but I find it difficult: easy in that by any measure, Jan Hall is not only an extraordinarily good scientist, but also an exemplary teacher, who has generously, openly & consistently shared his ideas with all of us—difficult because this short summary cannot begin to reveal Jan's unique insight and his many utterly clever solutions that have borne us all well, much less, to adequately convey my gratitude for all that he has taught me…

Since a few years, we have started the spectroscopic analysis of Extremely Thin Cell (ETC) of dilute vapor. The anisotropy intrinsic to such cells justifies the partial or total elimination of Doppler broadening [1-5] under normal incidence, owing to the enhanced transient response of the atoms with the longest free paths from wall-to-wall. One of our present purposes is to develop an effective method for the evaluation of the atom-surface interaction. This communication focuses on sensitivity issues – a long-time concern of Jan Hall [6] – in this peculiar type of spectroscopy. With these small and often submicrometric slices of vapor, the most uncommon features are the relatively small number of interacting atoms, and the fact that essential results are already obtained in the frame of linear spectroscopy.

It was a great pleasure to gather with friends in August 2004 for the symposium honoring Jan Hall and celebrating his 70th birthday, and this book provides a unique opportunity to record some words commemorating Jan's incredible contributions to science and to our lives. At best, my recollections are a faded, myopic snapshot of some events that come to mind after many years of association with Jan. Reflecting on the years that have passed since I first entered Jan's lab, I see that many things have changed, technology has advanced (mostly for the better), the world has evolved in dramatic and significant ways (some good and some not), and I have grown older (but unfortunately not wiser as one might have hoped). Nonetheless, after many years, I find myself still following the path pointed out by Jan's visions and investing most of my productive time and energy working as a scientist trying to get atoms, lasers, electronics, (and the institutional bureaucracy that comes along with them) to work in some kind of harmony…

Together with Jan, the author has established a portable iodine-stabilized Nd:YAG laser at JILA for the purpose of international laser frequency comparison. High-accurate hyperfine constants are obtained from the theoretical fit of the measured hyperfine splittings of molecular iodine. The experience of laser frequency control and measurement at JILA is the foundation of the research activities of the author later in Japan.

In the summer of 1998 we both began NRC postdocs at JILA, sharing an office and working across the hall from each other in the labs of Jan Hall and Steve Cundiff. However, as the coming months were to demonstrate, the barrier of a hallway did not prove to be a significant obstacle to the merging of science and technology from the worlds of the ultrastable and the ultrafast. Those were exciting days at JILA as we were involved in the first optical frequency measurement measurements with octave-spanning frequency combs and the first measurement and stabilization of the carrier-envelope offset frequency for a train of femtosecond laser pulses. Jan was closely involved in all the experiments we performed—helping us to measure and understand the noise sources in the femtosecond lasers and then teaching us the electronics skills to overcome them. And on many nights, he was in the "driver's seat" steering one of his special servos as critical data was collected. Moreover, Jan was a truly inspirational mentor and leader, with an infectious excitement for making great science happen. We owe him a tremendous debt of gratitude for all that he has given to us…

During my graduate career in Jan's lab, I was continually impressed by Jan's fascination with the details of spectral lineshapes. While Jan's influence has affected much of my research, of particular relevance has been his understanding of atomic recoil effects on high resolution spectra, stemming from his seminal work on recoil splitting in saturation spectroscopy. In fact, the importance of recoil effects in high resolution spectroscopy has come full circle in my career; first as a graduate student working with Jan on spectroscopy of laser-cooled sodium, and again more recently in work on optical atomic clocks (a field Jan truly has pioneered), where recoil effects have led to unexpectedly large asymmetries in the clock spectra. As a tribute to Jan, here I discuss both experiments and show how atomic recoil effects can distort the spectra of narrow and broad transitions. Despite seemingly symmetric spectroscopic configurations, these distortions leading to interesting asymmetries, the kinds of which Jan found particularly delicious…

What a splendid idea to have the symposium to celebrate John's 70th birthday. He probably would have been working at JILA in any case on that day! His many contributions to physics and metrology serve to show the young newcomer that metrology can provide a rewarding, fascinating, career of great variety. He reminds us too that a metrologists best work is always just ahead of him or her – rarely is it over.

The issues of scale that arise as robots evolve into devices and systems that are much larger or much smaller than everyday human scale – or both simultaneously – has recently become one of my main research interests. This subject has no obvious connection to the vast body of John L. Hall 's research in metrology or to his pioneering developments in laser photodetachment, the field of my research under his mentorship. What I hope to convey by summarizing my thoughts in this context is the integrative approach to thinking about science that I learned from Jan.

We describe the current status of the Ca optical frequency standard with laser-cooled neutral atoms at PTB. Frequency measurements performed at the Physikalisch-Technische Bundesanstalt (PTB) and the National Institute of Standards and Technology (NIST) make the frequency of the clock transition of ⁴⁰Ca one of the best known optical frequencies with a relative uncertainty of 1.2·10⁻¹⁴.

When I first came to JILA as a graduate student in 1992, Jan greeted me with the words "you are certainly a brave boy, welcome to JILA." In his usually simple and yet subtle manner, Jan had prepared me for many years of hard work, challenge, and excitement ahead. From the first day on, I have been able to share freely with Jan's insightful thoughts and clever tricks. Of equal importance is his encouragement for my independent research activities and imaginations. He passed on his passion and enthusiasm for science and technology to everybody around him. This has been extremely valuable to me during the time when I faced uncertainties and difficult choices. The interaction with Jan not only made it possible for me to complete the stage of Ph.D. studies, but has also prepared me for a life-long endeavor in my scientific career. For this I am forever indebted to Jan.

One of the important applications of coherence-population-trapping (CPT) is the vapor cell atomic frequency standard. The elimination of direct microwave excitation provides the potential of making smaller, simpler and less expensive vapor cell devices, especially for the devices with stringent restrictions on the volume, such as the chip-scale-atomic-clock (CSAC)…