Applied Physics is a graduate department in the School and Sciences. It is one of three elements — Applied Physics, of Humanities  Physics, and  the Stanford Linear Accelerator Center — in the broader physics community at Stanford. The Department emphasizes fundamental research in areas of potential technological importance and in areas of science where a physics point of view is particularly effective. The Department also has a tradition of inventing new tools for science and new devices for technology. Present activities include research in accelerator physics, atomic and molecular physics, biophysics, condensed matter and materials physics, nanoscience and technology, photonics, quantum information, synchrotron radiation and ultrafast science.

  Because of the broad range of techniques and intellectual points of view that are relevant to contemporary applied physics, the course work and research in the Department are designed to bring the student into contact with activity in several disciplines related to physics, such as engineering, materials science, biology and chemistry. The program of graduate training is designed to prepare graduates for professional leadership careers in science and technology, either in academia or in industrial environments. Students may enter the Department with the intention of obtaining either a MS or a PhD or both degrees.

The activities of the Department reflect a spectrum of interests ranging from pure science to engineering and include several interdisciplinary programs. Student research is supervised by faculty in the Department of Applied Physics, by affiliated faculty, and by members of other departments.

Accelerator Physics

Astrophysics

Atomic and Molecular Physics

Biophysics

Condensed Matter and Materials Physics

Nanoscience and Nanotechnology

Photonics

Quantum Information Science

Synchrotron Radiation

Ultrafast Science

Other Research Opportunities

Accelerator Physics. Accelerator physics research explores the physics and technologies of particle accelerators and beams. The objectives include understanding and improving accelerator performance, developing new technologies, and exploring novel accelerators driven by lasers and based on plasmas. This research encompasses non-linear dynamics, computer simulation and modeling, high speed data acquisition and processing, photonics, plasma physics and other areas of applied physics. The context for the research often comes from other branches of science where accelerators have a central role. These range from particle physics to studies of atoms, molecules, and condensed matter using x-rays and neutrons. Accelerator physics research is carried out at the Ginzton Laboratory and at the Stanford Linear Accelerator Center (SLAC).

High current particle accelerators exhibit complex dynamics which can lead to unstable oscillatory beam motion limiting the accelerator intensity and performance. Feedback control of instabilities incorporates the physics of dynamic systems, modern control theory and high speed wideband signal processing electronics. The research to control unstable particle beams requires experimental measurements, development of simulation models and tools, special technologies in RF/Microwave instrumentation, microwave power sources and technology expertise in high-speed signal processing. The interdisciplinary nature of the work offers numerous research opportunities to develop wideband detectors with picosecond time resolution and apply electro-optic and digital signal processing for beam instrumentation and new control methods for accelerator stability and performance.

Laser driven dielectric accelerators have the promise of combining high accelerating gradient with compact scale. The research into laser driven structures is based on the rapid progress in near-IR lasers where 1) phase locking at a small fraction of an optical wavelength has been demonstrated and recognized recently with a Nobel Prize, 2) lasers with high energy efficiency from wall-plug power to laser light are available commercially, and 3) novel materials and fabrication techniques are active areas of inquiry in industry and academia. This research program combines laser development with the design, fabrication and testing of laser driven accelerators with a relativistic electron beam.

Plasmas have been shown to sustain accelerating gradients two to three orders of magnitude greater than achieved in conventional metallic accelerator structures. This research is aimed at realizing this exceptional performance in practical accelerators by experimentally studying the interaction between particle beams and plasmas using high energy electron and positron beams at SLAC. Innovative beam instrumentation is a key component of these experiments, which measure gradient, energy gain, beam transport, particle production in plasmas, etc.

 Atomic and Molecular Physics. Atomic and Molecular Physics research at Stanford spans ultrafast science, quantum information science, degenerate quantum gases, and precision measurement. For research descriptions, see links to individual group web pages for participating faculty.

Biophysics. Biophysics research in the Department of Applied Physics involves a range of topics that includes single molecule studies of individual proteins and nucleic acids, biomolecular structural studies conducted at the Stanford Synchrotron Radiation Laboratory, simulations of biomolecular dynamics, in vivo optical imaging studies of the mammalian brain, computational and theoretical studies of neuronal networks, and development of new techniques for microgenomics, among others. A variety of techniques are emphasized, such as optical tweezers, single molecule fluorescence, small angle X-ray scattering, two-photon fluorescence excitation, and methods for linear amplification of nucleic acid sequences. Further, Applied Physics students pursuing biophysics research have available many opportunities afforded by the forty-one laboratories affiliated with the Stanford Biophysics Program and the Stanford Bio-X Program.

The behavior of single motor proteins and nucleic acid-based enzymes including RNA polymerase can be studied using a variety of techniques including optical tweezers, optical interferometry, and fluorescence resonance energy transfer (FRET). A main goal of such research is to elucidate the mechanisms by which individual enzymes produce movements, enzymatic activity, and the replication of genetic information. Other studies investigate protein and RNA structure, dynamics, and folding kinetics at the scale of individual molecules.

Ultrashort pulsed lasers can be used to excite nonlinear optical processes, including two-photon excited fluorescence and second harmonic generation, in biological tissues. Such processes form the basis for laser-scanning imaging techniques that can be used to explore neuronal dynamics, not only in live cells but also in the living mammalian brain. When used in conjunction with fiber- and micro-optics, one can perform minimally invasive, cellular level imaging in deep areas of the live brain, in both anesthetized and freely moving subjects. Further, there are emerging clinical applications of such imaging techniques.

Using a combination of computational, theoretical, and experimental approaches such as small angle x-ray scattering (see Stanford Synchrotron Radiation Laboratory) the structure and dynamics of protein complexes can be explored towards understanding both the physical principles governing protein behavior and the role of protein dynamics in cellular function. A major challenge here is that molecular dynamics simulations work on a femtosecond time scale while functional changes in proteins are on a millisecond time scale.

The application of integrated photonic and microfluidic techniques to the study of biological molecules is allowing large-scale data collection at an unprecedented scale and pace. As such integrated devices become increasingly miniaturized; new applications are emerging in both basic and applied research, such as in genomics and protein crystallography.

 Condensed Matter and Materials Physics. Condensed matter and materials physics involves the making, physical study and theoretical understanding of materials for the advance of science and applications as appropriate. The CMMP community at Stanford is large. The center of gravity of this activity is in Applied Physics and is housed in the Geballe Laboratory for Advanced Materials, which is an independent laboratory under the Dean of Research with faculty from Applied Physics, Physics and Materials Science and Engineering. The full range of opportunities includes activities in the Ginzton Laboratory, the Center for Integrated Systems, the ClarkCenter, SLAC, and the Departments of Biology, Chemistry, Chemical Engineering, Electrical Engineering, Materials Science and Engineering, and Physics.

Currently, the CMMP research in Applied Physics includes the discovery of new materials with novel physical properties, the growth of materials as models systems, the physical study of materials with a wide range of approaches (including scanning probes and synchrotron radiation as well as more traditional approaches) and the quantum theory and statistical mechanics of materials. Active research areas presently include highly-correlated electronic systems, superconductivity and its applications, magnetism and spintronics, and nanostructures and mesoscopic quantum physics.

Nanoscience and Nanotechnology.  Many traditional disciplines of science and engineering are making dramatic strides by studying and capitalizing on the properties of materials at length scales ranging from 1 to 1000 nanometers. Nanoscale Science and Engineering is characterized not only by its great technological potential but also by its fascinating scientific challenges. If we try to extend our understanding down from the macroscopic, we find that nanoscale systems do not behave like larger systems. They are too small to be characterized by the rules developed in various disciplines to describe macroscopic systems: disorder and statistics become more important, and quantum mechanics and fluctuations often play a large role.  If we try to extend our understanding up from the atomic, we also find that nanoscale systems do not behave like smaller systems. The two-body problem can be solved by students in freshman mechanics, and the three-body problem is somewhat harder: the 1,000,000-body system challenges even our impressive modern computational capabilities and theoretical understanding.

Nanoscale Science and Engineering is not an intellectual discipline in the traditional sense. It is a set of tools and cross-disciplinary questions. The nanoscale is a natural intellectual frontier in a number of disciplines, including biology, materials science and engineering, medicine, chemical engineering, and device physics, as well as the present areas of strength of the Stanford Applied Physics Department, namely condensed matter physics, biology, and photonics. Many if not most Applied Physicists do at least some nanoscale research. Stanford is also fortunate to have excellent facilities in nano, including SSRL, SNF, and SNL. Stanford’s Nanoscale Science and EngineeringCenter, called the Center for Probing the Nanoscale, includes many Applied Physics faculty and is housed in the Geballe Laboratory for Advanced Materials.

The field of mesoscopic physics in closely related to nanoscale science. “Mesoscopic” literally means something that is on the border between the macroscopic world of ordinary human perception and the microscopic, or atomic, scale. Mesoscopic objects, like macroscopic objects, are large enough that they are made of many atoms; but, like microscopic objects, they are small enough that fluctuations and quantum mechanics are important. Contemporary mesoscopic physics is the study of electronic, magnetic, photonic, and mechanical objects that are sufficiently small that quantum mechanics is important for their description.

Quantum Information Science. Quantum information science is a rapidly growing field with broad spectra covering from the foundation of quantum mechanics to the implementation of various quantum algorithms. The Department of Applied Physics is the home department for research on quantum information science at Stanford. The quantum information systems under intensive current research include quantum cryptography, quantum metrology, quantum repeater, quantum simulation, quantum computation and quantum authentication. Both theoretical and experimental studies have been actively performed in the respective sub-areas.

Professor Martin Fejer’s group is working on PPLN waveguide devices for single photon frequency conversion and parametric entangled photon generation. Professor Steve Harris’ group is working on the twin photon generation from atomic ensemble in the EIT regime. Professor Mark Kasevich’s group is working on precision measurements and quantum metrology with cold neutral atoms and optical lattice. Professor Jelena Vuckovic of Electrical Engineering is working with many Applied Physics students in the area of photonic crystal network devices for photonic quantum information systems. Professor Yoshihisa Yamamoto’s group is working on the experimental implementation of various quantum communication systems based on solid state devices. His effort includes quantum key distribution system experiments, deterministic single photon sources based on semiconductor quantum dots, quantum repeaters based on cavity QED nodes and coherent state bus, quantum computation based on electron spins and ultrafast optical pulses and quantum simulation of Hubbard models using surface acoustic waves.

Synchrotron Radiation. Research utilizing extremely intense vacuum ultraviolet, soft x-ray and x-ray radiation is carried out at the Stanford Synchrotron Radiation Laboratory (SSRL), and in the near future the Linac Coherence Light Source (LCLS), the x-ray free electron laser. At SSRL, 24 experimental stations provide beams whose spectra are continuous and whose intensities are approximately seven orders of magnitude greater than those of more classical sources. The principal areas of experimental research are vacuum ultraviolet and soft x-ray studies of atoms, molecules, and solids, x-ray studies of condensed matter, and structural molecular biology studies utilizing x-rays. At LCLS, six experimental stations, when completed, will be the world’s first x-ray free electron laser when it becomes operational in 2009.  Pulses of x-ray laser light from LCLS will be many orders of magnitude brighter and several orders of magnitude shorter than what can be produced by any other x-ray source available now or in the near future. These characteristics will enable frontier new science areas in atomic and molecular physics and condensed matter sciences ranging from materials to biology.

Vacuum Ultraviolet (VUV) and Soft X-Ray Studies. Research utilizing the VUV and soft x-ray radiation includes: (a) the determination of electronic states in metals, semiconductors, magnetic systems, superconductors and other interesting materials; (b) properties of ultra-thin layers and small clusters; (c) kinetic processes in a variety of materials; (d) spectral microscopy; and, (e) dynamic processes in quantum solids. The primary experimental tools involve angle-resolved photoemission spectroscopy, soft x-ray spectroscopy and scattering techniques using SSRL and LCLS in the future. Research in Shen's group also utilizes laboratory facilities, including laser based time and spin resolved spectroscopies, microwave microscopy, Auger nano-probe, focus ion beam techniques.

X-Ray Studies of Condensed Matter. Research utilizing x-rays for studies of condensed matter include the following areas: (a) structures of amorphous materials, catalysts and environmentally interesting systems; (b) structures of and phase transitions in surfaces and thin surface layers; (c) kinetics of structural changes in materials; (d) chemical reactivities in the gas phase; (e) nuclear resonant scattering; (f) fundamental x-ray scattering and absorption physics; (g) high-resolution studies of magneto-structural phenomena in strongly correlated electron systems; and (h) magnetic x-ray scattering.

Structural Molecular Biology. X-rays are used for research in structural molecular biology including: (a) protein structures and functions through diffraction studies in the crystalline state; (b) protein structures through extended x-ray absorption fine structures studies; (c) dynamic fluctuations in biological systems; (d) the nature of membrane and membrane protein interactions; and (e) the structure and function of metal sites in metalloproteins and metalloenzymes.

 Atomic and Molecular Physics and Ultra-Fast Science

Synchrotron Radiation Sources. onsiderable research is also underway in the development of accelerators and devices inserted into the accelerators to produce more intense or brighter synchrotron radiation.

Applied Physics students who wish to carry out research utilizing SSRL may do so in collaboration with either Applied Physics faculty or faculty from the Chemistry, Chemical Engineering, Civil Engineering, Electrical Engineering, Geology, or Materials Science and Engineering Departments.

Ultrafast Science . Research in ultrafast science in Applied Physics takes place in the Ginzton Laboratory, and at the Stanford Photon Ultrafast Laser Science and Engineering Center (PULSE): PULSE is a new independent laboratory at Stanford and also a ResearchCenter at SLAC. It is the home for a wide range of research projects on rapid processes (picosecond scale or faster), in physics, chemistry, biology, and materials science and engineering.

Ultrafast: Femtoscience: Atoms in a molecule or a solid move very quickly. The primary atomic motions involved in vision, or photosynthesis, or melting, all take less than a picosecond. Ultrafast lasers can more than keep up with this, so lasers can act like strobe lights with ultrafast shutter speeds to freeze atomic motion. Much physics and chemistry research is devoted to these kinds of ultrafast observations, in the femtosecond range.

Shorter still: Attoscience: The shortest laser pulses are now less that one thousandth of a picosecond, in the sub-femtosecond range. At these extreme shutter speeds, the laser pulses can begin to capture the motion of electrons within atoms. Such pulses must have sub-optical wavelengths, since the pulse duration is less than a single cycle of visible radiation. This attosecond vacuum ultraviolet coherent radiation has recently been produced through atomic nonlinear processes, and it may soon give us our first images of electrons moving in molecules.

Ultrafast x-rays: The Stanford Linear Accelerator Center will be home to the world’s first x-ray free-electron laser, LCLS, due to begin operations in 2009. This will produce sub-picosecond x-rays that are one billion times brighter than the brightest current sources. As with the most powerful lasers, these x-rays will be focusable to field strengths that exceed the fields that bind electrons in atoms. A wealth of new science is expected from research at LCLS, in atomic physics, condense matter and materials science, ultrafast chemistry, and high energy density science.

Ultrafast control: Ultrafast laser pulses can do more than just detect atomic motion. They can also be used to control basic quantum processes in atoms and molecules. Ultrafast quantum control research uses pulse shaping techniques to create new optical waveforms that can enhance light-induced processes, or even direct photochemical reactions along new paths. The optimal field may not be obvious, but programmable pulse shapers can use clues from the photochemical process itself to evolve new optical field shapes. In this way, the molecule teaches the laser how to perform an atomic-level task.

Faculty: The faculty members in this field can be viewed at the link below. In addition, there are opportunities for ultrafast research in several groups at SLAC and in Chemistry and Materials Science. Further information can be found on the PULSE website.

Other Research Opportunities. There are many interdepartmental or interschool laboratories offering unique opportunities and facilities for research. These include the Edward L. Ginzton Laboratory, the Stanford Synchrotron Radiation Laboratory, the Center for Space Science and Astrophysics, the Center for Integrated Systems, the Geballe Laboratory for Advanced Materials, Stanford Linear Accelerator Center, and the W.W. Hansen Experimental Physics Laboratory. Refer to related departments and research centers in our links page for information on faculty outside of the Applied Physics Department pursuing research in the areas listed.

QueltaNews from StanfordUniversity

 By Vasil Sidorov on April 22, 2009 E-mail: sidorovvasil@gmail.com