Research Highlights

Though microscopes have been in use for centuries, there is still much that we cannot see at the smallest length scales. Current microscopies range from the simple optical microscopes used in high school science classes, to x-ray microscopes that can image through visibly-opaque objects, to electron microscopes that use electrons instead of light to capture images of vaccines and viruses. However, there is a great need to see beyond the static structure of an object—to be able capture a nano- or biosystem functioning in real time, or to visualize the magnetic field on nanometer scales. A team of researchers from the STROBE Center have been working together to overcome these challenges. STROBE is an NSF Science and Technology Center led by JILA Fellow Margaret Murnane. The large and multidisciplinary collaboration included Chen-Ting Liao and the Kapteyn-Murnane group from JILA, the Miao and Osher groups from University of California Los Angeles, Ezio Iacocca from University of Colorado, Colorado Springs, David Shapiro and collaborators at Lawrence Berkley National Laboratory, and the Badding and Crespi groups from Pennsylvania State University. They developed and implemented a new method to use x-ray beams to capture the 3D magnetic texture in a material with very high 10-nanometer spatial resolution for the first time. They published their new technique and new scientific findings in Nature Nanotechnology.

Lasers have not only fascinated scientists for decades, but they have also become an integral part of many electronic devices. To create scientific-grade lasers, physicists try to control the temporal, spatial, phase, and polarization properties of the laser beam’s pulse to be able to manipulate it. One of these properties is called the orbital angular momentum (OAM), and its phase, or shape, swirls as the doughnut-shaped laser beam travels through space. There are two types of OAM, spatial (S-OAM) and spatial-temporal (ST-OAM). S-OAM describes the angular momentum of the laser beam that is parallel to the light source's propagation direction. In contrast, ST-OAM has angular momentum that moves in a motion perpendicular to the light source’s  propagation direction, which creates a time component to the momentum  [1, 2].  Because of these differences, ST-OAM is more difficult to study due to this time component. According to senior scientist Dr. Chen-Ting Liao: “The problem is that ST-OAM is very difficult to see or measure. And if we can't see or measure this easily, there's no way we can fully understand and optimize it, let alone use it for potential future applications.” To try to overcome this difficulty, a collaboration led by Dr. Liao and other researchers, including JILA Fellows Margaret Murnane and Henry Kapteyn, worked out a method to image and better analyze ST-OAM beams. Their work was subsequently published in ACS Photonics and featured on the cover [3].

More than 400 years later, scientists are in the midst of an equally-important revolution. They’re diving into a previously-hidden realm—far wilder than anything van Leeuwenhoek, known as the “father of microbiology,” could have imagined. Some researchers, like physicists Margaret Murnane and Henry Kapteyn, are exploring this world of even tinier things with microscopes that are many times more precise than the Dutch scientist’s. Others, like Jun Ye, are using lasers to cool clouds of atoms to just a millionth of a degree above absolute zero with the goal of collecting better measurements of natural phenomena. 

Physicists develop some of the most cutting-edge technologies, including new types of lasers, microscopes, and telescopes. Using lasers, physicists can learn more about quantum interactions in materials and molecules by taking snapshots of the fastest processes, and many other things. While lasers have been used for decades, their applications in technology continue to evolve. One such application is to generate and control x-ray laser light sources, which produce much shorter wavelengths than visible light. This is important because progress in developing x-ray lasers with practical applications had essentially stalled for over 50 years. Fortunately, researchers are beginning to change this by using new approaches. In a paper published in Science Advances, a JILA team, including JILA Fellows Margaret Murnane, and Henry Kapteyn, manipulated laser beam shapes to better control properties of x-ray light.

Last week, U.S. Rep. Joe Neguse got a first-hand look at the future of ultrafast lasers, record-setting clocks, and quantum computers on the CU Boulder campus. Neguse visited the university Thursday to tour facilities at JILA, a research partnership between CU Boulder and the National Institute of Standards and Technology (NIST).

The second quantum revolution is underway, a period marked by significant advances in quantum technology, and huge discoveries within quantum science. From tech giants like Google and IBM, who build their own quantum computers, to quantum network startups like Aliro Quantum, companies are eager to profit from this revolution. However, doing so takes a new type of workforce, one trained in quantum physics and quantum technology. The skillset required for this occupation is unique, and few universities expose students to real-world quantum technology. 

Two new papers from the Murnane and Kapteyn group are changing the way heat transport is viewed on a nanoscale, and explain the group’s surprising finding that nanoscale heat transport can be far more efficient than originally thought. One of these papers, published in the Proceedings of the National Academy of Sciences (PNAS), explains heat transport for the tiniest of hotspots, with sizes <100 nm. The other, published in American Chemical Society Nano (ACS Nano), presents a theory that is applicable to larger arrays of hotspots. Both papers postulate theories that can fully explain the surprising data collected by the team of researchers, showing that heat transport on scale lengths relevant to a wide range of nanotechnologies is more efficient than originally thought.

For laser science, one major goal is to achieve full control over the spatial, temporal and polarization properties of light, and to learn how to precisely manipulate these properties.  A  property of light is called the Orbital Angular Momentum (OAM), that depends on the spatial distribution of the phase (or crests) of a doughnut-shaped light beam. More recently, a new variant of OAM was discovered - called the spatial-temporal OAM (ST-OAM), with much more elusive properties, since the phase/crests of light evolve both temporally and spatially. In a collaboration led by senior scientist Dr. Chen-Ting Liao, working with graduate student Guan Gui and Nathan Brooks and JILA Fellows Margaret Murnane and Henry Kapteyn, the team explored how such beams change after propagating through nonlinear crystals that can change their color. The team published theri results in Nature Photonics. 

Electronics keep shrinking. As they shrink the properties of the materials that make them change too. 

In a new study from the Kapteyn-Murnane Group, ultrafast laser pulses can precisely cut through and manipulate the interaction between electrons and phonons in tantalum diselenide, changing its properties.

Researchers at JILA and the University of Salamanca have found a new property of light, one that creates a whirling vortex that can speed itself up. 

By using ultrafast lasers to measure the temperature of electrons, JILA researchers have discovered a never-before-seen state in an otherwise standard semiconductor. This research is the most recent demonstration of a new technique, called ultrafast electron calorimetry, which uses light to manipulate well-known materials in new ways.

The hardest problems are never solved by one person. They are solved by teams; or in the case of science, collaborations. It took a collaboration of 17 researchers, including four JILA fellows and another six JILA affiliates, just a little over five years to achieve robust polarization control over isolated attosecond (one billionth of a billionth of a second) pulses of extreme-ultraviolet light. 

Magnets hold cards to your fridge, and store data in your computer. They can power speakers, and produce detailed medical images. And yet, despite millennia of use, and centuries of study, magnetism is still far from fully understood.

The Kapteyn-Murnane group has come up with a novel way to use fast bursts of extreme ultraviolet light to capture how strongly electrons interact with each other in materials. This research is important for figuring out how quickly materials can change their state from insulating to conducting, or from magnetic to nonmagnetic. In the future such fast switching may lead to faster and more efficient nanoelectronics.

Dennis Gardner and his coworkers in the Kapteyn-Murnane group accomplished two major breakthroughs in imaging tiny structures much too small to be seen with visible light microscopes: (1) for the first time in the extreme ultraviolet (EUV) or soft X-ray region, they achieved a resolution smaller than the wavelength of the light; and (2) for the first time, they obtained high resolution quantitative imaging of near periodic tiny objects (structures with repetitive features).

The Kapteyn/Murnane group has measured how long it takes an electron born into an excited state inside a piece of nickel to escape from its birthplace. The electron’s escape is related to the structure of the metal. The escape is the fastest material process that has been measured before in the laboratory––on a time scale of a few hundred attoseconds, or 10^-18 s. This groundbreaking experiment was reported online in Scienceon June 2, 2016. Also in Science on July 1, 2016, Uwe Bovensiepen and Manuel Ligges offered important insights into the unusual significance of this work. 

Cong Chen and his colleagues in the Kapteyn/Murnane group have generated one of the most complex coherent light fields ever produced using attosecond (10-18 s) pulses of circularly polarized extreme ultraviolet (EUV) light. (The circularly polarized EUV light is shown as rotating blue sphere on the left of the picture. The complex coherent light field is illustrated with the teal, lilac, and purple structures along the driving laser beam (wide red line).

Imagine laser-like x-ray beams that can “see” through materials––all the way into the heart of atoms. Or, envision an exquisitely controlled four-dimensional x-ray microscope that can capture electron motions or watch chemical reactions as they happen. Such exquisite imaging may soon be possible with laser-like x-rays produced on a laboratory optical table. These possibilities have opened up because of new research from the Kapteyn/Murnane group.

The Kapteyn/Murnane group, with Visiting Fellow Charles Durfee, has figured out how to use visible lasers to control x-ray light! The new method not only preserves the beautiful coherence of laser light, but also makes an array of perfect x-ray laser beams with controlled direction and polarization. Such pulses may soon be used for observing chemical reactions or investigating the electronic motions inside atoms. They are also well suited for studying magnetic materials and chiral molecules like proteins or DNA that come in left- and right-handed versions.