By Patricia Daukantas
I can’t say it any better than the press release did: “Finally, an optical frequency comb that visibly lives up to its name.”
Researchers in the United States and Germany have collaborated on a 10-GHz frequency comb with spectral coverage from about 470 to 1130 nm. Unlike other combs, a simple grating spectrometer can spatially separate this comb’s “teeth” so that they are visible with the human eye.
OSA Fellow Scott A. Diddams of the U.S. National Institute of Science and Technology (NIST), working with Albrecht Bartels of the University of Konstanz (Germany) and Dirk Heinecke of Konstanz and NIST, published their work in the October 30 issue of Science.
The authors say that the comb’s modes could serve as precise frequency markers for calibration of astronomical spectrographs and for many other spectroscopic uses. As has been noted in this blog in the past, frequency-comb spectroscopy is being explored as an important tool for detecting planets orbiting stars other than the Sun.
Incidentally, this Science article was published on the 68th birthday of OSA Honorary Member Theodor Hänsch, who shared part of the 2005 Nobel Prize in physics with OSA Honorary Member (and longtime NIST scientist) John L. “Jan” Hall for their pioneering work on – you guessed it – frequency combs.
Above: Photographs of four different regions of the new optical frequency comb. The light is filtered through a grating spectrometer and photographed with a digital camera through a microscope. Each visible line or "tooth" is an individual frequency in the comb, which spans the visible spectrum from red to blue. More than 1,500 such photos would need to be lined up to show the entire comb. (Photo credit: S. Diddams/NIST)
Posted by Christina Folz, OPN Managing Editor
This week’s issue of Nature highlights the newest adaptation of the optical frequency comb: an “astro-comb” that astronomers can use to scour the skies for other Earth-like planets. Current methods for detecting planets orbiting distant stars are only capable of finding large planets that have at least five times the mass of the Earth, according to a press release from the Harvard-Smithsonian Center for Astrophysics (CfA).
In order to detect a planet, astronomers typically gauge its effect on the star around which it is orbiting. Using spectrography, they measure how much the star “wobbles”—a phenomenon that is caused by the gravitational pull of the planet on the star; it is a function of the planet’s mass as well as its distance from the star. Because large planets cause the most “wobble,” they are the easiest to find. In addition, planets with tight orbits around their star are easier to detect than those with wide trajectories.
The new astro-comb, which was tested by Chih-Hao Li and his colleagues from the CfA, uses ultrashort, femtosecond pulses of laser light, linked to an atomic clock, to provide an ultra-precise standard against which light from a star can be measured. The adaptation of the optical frequency comb technique is expected to increase the resolution of the current tools by about 100 times, allowing for the detection of smaller planetary masses. According to the press release, a prototype astro-comb will be tested this summer at CfA’s Mount Hopkins Observatory in Arizona, and may be ready to use for a project in the Canary Islands by 2010.
Optical frequency combs revolutionized high-precision optical metrology by enabling scientists to accurately measure much higher frequencies of light than was ever before possible with a single tool. It is this advance for which OSA Honorary Member John L. Hall shared the 2005 Nobel Prize in Physics (with Theodor Hänsch and Roy Glauber). Hall describes his work—and its myriad exciting applications—in this month’s Scientific American magazine.
By Christina Folz
Greetings from San Jose! My trip here for OSA’s 91st annual meeting has been a whirlwind of technical sessions, pubs meetings and receptions. The one sour note for me may have resulted from consuming an ill-advised combination of wine and beer on Monday night, when I hit both the reception to honor 2007 OSA President Joseph Eberly at the Silicon Valley Capitol Club and the student reception at the nearby Tiki lounge. It’s fun to think about how OSA’s student members, many of whom were wearing leis and red T-shirts with the slogan “If this shirt looks blue to you, you’re moving too fast,” may represent the next generation of OSA leadership sipping wine at a president’s reception.
A highlight of the meeting was Monday’s plenary session and awards ceremony, which featured talks from Eli Yablonovitch, a professor of electrical engineering at the University of California, Berkeley, and John L. Hall, a Nobel laureate and OSA honorary member.
OPN recently published profiles of both Yablonovitch and Hall. Going into Monday’s plenary session, I had formed distinct impressions of both based on those articles. When I thought of Yablonovitch, the word that came to mind for me was “prescient.” As the OPN article noted, Yablonovitch has a demonstrated ability to predict upcoming trends in optics and technology.
His talk on Monday reinforced my notions. Yablonovitch discussed how 2-D nanophotonic structures present a tremendous opportunity for the integration of optics with electronics, resulting in the design of photonics into the standard CMOS (complementary metal-oxide-semiconductor) process. Although more research is needed, particularly in the area of developing a light source in silicon, “silicon photonics is on its way,” said Yablonovitch. “The precision of photolithography is mind-boggling at 3-4 nm wavelengths.”
Indeed, Luxtera Inc. has recently announced that it has fabricated an electrical connector that plugs into a network card; it contains all-optics inside the plug. The 40 Gb/s optical active guide is currently being tested by customers and will be in mass production within several months.
When it came time for John Hall’s presentation, I was ready for something unconventional and fun. After all, the first words attributed to Hall in OPN’s profile of him were: “Physics is fun”—the same statement he used in the essay portion of his application to the National Research Council in 1961.
Well, as I learned on Monday, Hall thinks that optical frequency combs—the method for optical frequency measurement for which he won a portion of the 2005 Nobel Prize in Physics—are, in his words, totally fun. Hall’s enthusiasm for his work is palpable and infectious. Unfortunately for me, much of his talk was also way over my head!
Hall is a senior fellow emeritus of the National Institute of Standards and Technology (NIST) and an adjoint fellow of JILA. His work has concentrated on improving the precision and accuracy with which lasers can produce a specific frequency and the stability with which they can hold that frequency. He has helped to develop a broad range of laser applications, including precision spectroscopy for physical and chemical analysis, new tests of fundamental physical laws, and measurement and redefinition of the speed of light.
He is an incredibly humble man— something I noticed about him when we were preparing our profile as well. During his talk, he spent a great deal of time acknowledging and thanking his family and fellow physicists, including Ted Hansch, one of his co-Nobel laureates who came up with the idea for the frequency comb in 1977, Ali Javan, developer of the first He-Ne laser, and Herbert Walther, a renowned scientist and educator who made pioneering contributions to quantum optics.
Speaking of Walther, OSA President Joe Eberly announced at the plenary the establishment of the Herbert Walther award, which will recognize distinguished contributions in quantum optics and atomic physics as well as leadership in the international scientific community. The award, which is jointly sponsored by OSA and the Deutsche Physikalische Gesellschaft, honors the late Walther for his tireless efforts to bring together scientists from all over the world. The first award will be presented in 2009; nominations will be accepted next year.
A final note: This year marks the 90th anniversary of the publication of the first issue of the Journal of the Optical Society of America. We celebrated the occasion at the member reception last evening. Joe Eberly and previous JOSA editor Joseph Goodman thanked the many authors, reviewers, readers, and staff who have played a role in making JOSA—including JOSA A and B and all the other OSA journals—the premier optics publications that they are today. In OPN’s November and December history columns, we will include a list of former JOSA editor David MacAdam’s favorite articles. Meanwhile, check out the JOSA anniversary page on InfoBase to learn more about the history of the journal, download the first issue from 1917, or enjoy free access to the journal’s top cited articles.
Also stay tuned for Pat Daukantas’s January feature article in OPN reporting on the technical findings that came out of FiO.