Research Highlights

Fellow Jun Ye’s group is methodically working its way toward the creation of an X-Ray frequency comb. Recently, senior research associate Thomas Schibli, graduate student Dylan Yost, Fellow Jun Ye, and colleagues from IMRA America, Inc. developed a high-performance, ultrastable fiber laser optical frequency comb. At the same time, Yost developed a clever method for getting coherent short-wavelength light out of a femtosecond enhancement cavity used with the fiber laser. These achievements have opened the door to the generation of frequency combs in the extreme ultraviolet (EUV) and soft X-ray regions of the electromagnetic spectrum.

By late 2006, Fellow Jun Ye’s clock team had raised the accuracy of its strontium (Sr)-lattice atomic clock to be just shy of that of the nation’s primary time and frequency standard, the NIST-F1 cesium (Cs) fountain clock. Graduate students Marty Boyd and Andrew Ludlow led the effort to improve the clock’s accuracy.

What sort of experiment could detect the effects of quantum gravity, if it exists? Theories that go beyond the Standard Model of physics include a concept that links quantum interactions with gravity. Physicists would very much like to find evidence of this coupling as these two branches of physics are not yet unified in a single theory that explains everything about our world.

With every breath you take, you breathe out carbon dioxide and roughly 1000 other different molecules. Some of these can signal the early onset of such diseases as asthma, cystic fibrosis, or cancer. Thanks to graduate student Mike Thorpe and his colleagues in Fellow Jun Ye’s group, medical practitioners may one day be able to identify these disease markers with a low-cost, noninvasive breath test. The new laser-based breath test is an offshoot of Thorpe’s research on cavity-enhanced direct optical frequency comb spectroscopy, a molecular fingerprinting technique reported in Science two years ago.

When the Jin and Ye group collaboration wanted to investigate the creation of stable ultracold polar molecules, the researchers initially decided to make ultracold KRb (potassium-rubidium) molecules and then study their collision behavior. Making the molecules required a cloud of incredibly cold K and Rb atoms, the ability to apply a magnetic field of just the right strength to induce a powerful attraction between the different kinds of atoms, and some low-frequency photons.

Researchers from the Ye, Bohn, and Greene groups are busy exploring a cold new world crawling with polar hydroxyl radical (OH) molecules. The JILA experimentalists have already discovered how to cool OH to “lukewarm” temperatures of 30 mK. They’ve precisely measured four OH transition frequencies that will help physicists determine whether the fine structure constant has changed in the past 10 billion years.

In the race to develop the world's best optical atomic clock, accuracy and precision are what count. Accuracy is the degree to which a measurement of time conforms to time's true value. Precision is a gauge of the exactness, or reproducibility, of the measurements. By definition, a high-precision clock must be extremely stable.

"In the right light, in the right time, everything is extraordinary," according to photographer Aaron Rose. He could have just as easily been describing precision optical spectroscopy experiments recently conducted by Research Associates Tanya Zelevinsky and Tetsuya Ido, Graduate Students Martin Boyd and Andrew Ludlow, Fellow Jun Ye and collaborators from Poland's Instytut Fizyki and NIST's Atomic Physics Division.

There's only one way to prove you've invented a better atomic clock: Come out on top of a comparison of your clock with one of the world's best atomic clocks: The NIST-F1 cesium fountain atomic clock, the nation's primary time and frequency standard. NIST-F1 is so accurate it won't gain or lose a second in more than 60 million years.

Science sleuths have a new and powerful method for identifying (and investigating) atoms and molecules, thanks to Graduate Student Mike Thorpe, Research Associate Kevin Moll, Senior Research Associate Jason Jones, Undergraduate Student Assistant Ben Safdi, and Fellow Jun Ye. The new method allows them to study molecular vibrations, rotations, and collisions as well as temperature changes and chemical reactions.

Scientists in Fellow Jun Ye's lab are developing a high-precision optical atomic clock linked to super-narrow optical transitions in ultracold, trapped strontium atoms. However, unless the new clock is portable (it is not) or researchers figure out how to accurately transmit its clock signal over a fiber optic network to NIST, the legendary strontium clock will not be able to help the world keep better time.

Fellow Jan Hall has been working on stabilizing the frequency of lasers since the 1960s. Now, he, JILA Research Associate Mark Notcutt, Long-Sheng Ma (currently at BIPM in France), and Fellow Jun Ye have devised an improved, compact, and less expensive method for stabilizing lasers. The new method is based on a small, vertically mounted optical cavity (shown on the right). Because the cavity is supported exactly in the middle, the top and bottom halves change in length by equal and opposite amounts in response to vibrations.

Jason Jones, Kevin Moll, Mike Thorpe, and Jun Ye have generated the world's first precise frequency comb in the extreme ultraviolet (EUV) using a combination of an ultrafast mode-locked laser and a precision high-finesse optical cavity. The EUV frequency comb consists of regularly spaced sharp lines that extend into the EUV region of the electromagnetic spectrum.

Three years ago Jun Ye decided to apply an old idea for amplifying and stabilizing continuous-wave (cw) lasers to state-of-the-art ultrafast lasers. In 2002, Jason Jones, a postdoctoral fellow with Jun, analyzed whether the build-up cavities used to amplify cw laser outputs could be modified to work with ultrafast, mode-locked lasers. His detailed calculations suggested that it would be possible but technically demanding.

A high-powered JILA collaboration led by JILA Fellows Jun Ye and Chris Greene is making important progress toward developing an ultrastable, high-accuracy optical atomic clock. The new optical clock design will use a variety of laser sources including a femtosecond comb and a diode laser stabilized with an optical cavity, which, in turn, is locked to a narrow energy level transition in ultracold strontium atoms.