Downloaded by INDIANA UNIV PURDUE UNIV AT IN on March 21, 2013 | http://pubs.acs.org Publication Date: April 8, 1999 | doi: 10.1021/bk-1999-0720.pr001
Preface This book deals with cavity-ringdown spectroscopy—a new method for making trace absorption measurements, particularly with gas-phase samples. Traditional absorption measurements involve the determination of two parameters: the incident power of a radiant beam on a sample (P ) and the radiant power of the beam after it has passed through the sample (P, ). As the concentration of the absorbing species decreases, the value of P approaches P , and the detection limit is reached when the magnitudes of the two beams become indistinguishable statistically. By contrast, cavity-ringdown spectroscopy monitors the exponential decay of radiation in an optical cavity. For a given wavelength, the time associated with this exponential decay is related to the absorption coefficient of the gas contained within the cavity; the shorter the decay time, the higher the concentration of the sample. Improvements in the detection limit achieved with cavity-ringdown techniques can be on the order of 10 or more compared to traditional absorption methods. As discussed in the last chapter of this book, techniques related to cavity-ringdown spectroscopy may extend the detection limit even further. The origins of cavity-ringdown spectroscopy can be traced to efforts in the 1980s to develop ways to measure the reflectivity of high reflectivity mirrors by arranging them to form optical cavities, known commercially as cavity lossmeters. In 1988, O'Keefe and Deacon demonstrated that the concept of a cavity lossmeter could be used to make absorption measurements with gas-phase samples. From this and subsequent work, it became clear that cavity-ringdown spectroscopy was capable of routinely measuring absorptions on the order of parts-per-million (ppm) per pass through the cavity. We became interested in the analytical potential of cavity-ringdown spectroscopy after learning about it from two sources. The first source was a seminar presented at Baylor University by David Cedeno, a graduate student working with for Carlos Manzanares. The second source was a series of conversations with Richard Zare, held in March 1996, while he was visiting Baylor University-to present the Gooch-Stephens Lectureship. When we were invited by the program chair of the 1997 Pacific Conference on Chemistry and Spectroscopy to organize a symposium for the meeting, we thought this would be a wonderful opportunity to hold a symposium on cavity-ringdown spectroscopy. While we were organizing the conference symposium, a further thought occurred to us. It was clear, since the advent of cavity-ringdown spectroscopy in the late 1980s, that numerous papers on the topic had been published by research groups from around the world. In spite of the volume of published work, the concept of cavity-ringdown spectroscopy did not appear to be widely known outside a small circle of practitioners. Indeed, when we mentioned the subject of cavity-ringdown spectroscopy at dinner one evening to a former president of the American Chemical Society (ACS) who was visiting Baylor, he replied that he had never heard of the technique. 0
t
Q
3
xi In Cavity-Ringdown Spectroscopy; Busch, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
Downloaded by INDIANA UNIV PURDUE UNIV AT IN on March 21, 2013 | http://pubs.acs.org Publication Date: April 8, 1999 | doi: 10.1021/bk-1999-0720.pr001
Because the basic principles of cavity-ringdown spectroscopy are not widely known, and the published work in this area is scattered among many specialist journals, we realized that a single reference source describing the technique and its applications could be extremely valuable to workers outside the immediate area. Aside from locating articles in the primary literature, another impediment for those wishing to gain an understanding of the technique is obtaining the necessary background in the behavior of optical cavities. For readers who are not familiar with some of the concepts associated with cavity-ringdown spectroscopy, Chapters 2-4 discuss stability criteria and mode formation in optical cavities. Because the participants in the symposium were the primary research groups currently working in the area, the publication of their contributions, preceded by introductory information that set forth the basic principles of the method, seemed a reasonable way to fill the need for a single reference source on cavity-ringdown spectroscopy. Because absorption measurements are widely used in all areas of chemistry, it is anticipated that advances in cavity-ringdown spectroscopy will be of interest to broad segments of the analytical-and physical communities. This will include analytical chemists, spectroscopists, physical chemists doing laser spectroscopy and molecular beam work, combustion scientists, atmospheric chemists, and chemical engineers involved with process measurements—in fact, anyone involved in measuring trace components in gas-phase samples by absorption spectroscopy. Having set forth the origins of this monograph, we would now like to thank those who helped make it possible. We would especially like to thank Michael L. Parsons of the DeVry Institute of Technology, Pomona, California, for inviting us to organize a symposium in the first place. We also thank the staff at ACS, including Cheryl Shanks, Anne Wilson, and Thayer Long, who worked with us on the acquisition and submission of the book. Finally, we especially thank Richard Saykally of the University of California, Berkeley, for the artwork on the cover of the volume. Kenneth W. Busch Department of Chemistry Baylor University Waco, Texas 76798-7348 Marianna A. Busch Department of Chemistry Baylor University Waco, Texas 76798-7348
xii In Cavity-Ringdown Spectroscopy; Busch, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
