Humphrey Maris
Professor:
Physics
Phone: +1 401 863 2185
Phone 2: +1 401 863 3857
humphrey_maris@brown.edu
Professor Maris has a number of research interests, including: studies of superfluid hydrodynamics using magnetically-levitated helium drops; development of new detectors for solar neutrinos; quantum nucleation of bubbles in liquid helium at negative pressure; tests of quantum measurement theory using electrons in liquid helium; and ultrafast optical studies of solids including picosecond ultrasonic measurements on thin films and nanostructures.
Biography
Professor Maris came to Brown in 1965 after two years as a postdoctoral research associate at Case Institute of Technology. He is a 1960 graduate of Imperial College, London, where he also received the Ph.D. in 1963, before coming to the United States. In 1972 and 1973 he was a visiting professor at the University of East Anglia in England and at Chalmers Institute of Technology in Goteborg, Sweden. He has carried out research at the Max Planck Institute in Grenoble, University of Tokyo, University of Paris, Centro Atomico Bariloche in Argentina, Institute for Physical Problems in Moscow, and the University of Hokkaido. He is a Professor of Research at École Normale Supérieure in Paris. In 1991 he was appointed the George Chace Professor of Natural Science at Brown.
Interests
In a project funded by the National Science Foundation, the behavior of electrons in liquid helium is being studied. When an electron is injected into helium, it forces open a spherical cavity with a diameter of 40 Angstroms from which helium atoms are excluded. The size of this cavity is such as to minimize the sum of the zero-point energy of the electron, the surface energy and the energy associated with any externally-applied pressure. If the electron is excited to a higher quantum state, the size and shape of the cavity changes. Recently, these excited state bubbles have been detected and their properties studied. When the electron is optically excited to the higher energy state, the surface of the bubble begins to move very rapidly. As a result of this violent motion, it is possible that the bubble breaks into two parts.
By application of a negative pressure to an electron bubble it is possible to make the bubble explode. The bubble can then grow large enough to be recorded with a video camera. Currently experiments are underway in which an electron bubble is repeatedly exploded using a sound wave. Through the use of this novel technique, it is possible to make a movie showing the motion of a single electron.
With NASA support, an apparatus has been developed that can be used to levitate drops of liquid helium. A drop is placed in a strong magnetic field (16 Tesla) with a strength that decreases with height. Because helium is weakly diamagnetic, this provides an upward force on the drop that can be made sufficiently large to balance gravity. Drops of diameter up to 1cm can be levitated in this way. Over one hundred years ago Lord Rayleigh predicted that a liquid drop would become unstable if the electric charge on it exceeds a critical value. This instability will be studied and the change in shape of the drop with time after the instability is reached will be recorded.
New techniques have been developed in our laboratory at Brown that make it possible to perform ultrasonic experiments at very high frequency. Femtosecond light pulses are used to generate and to detect short sound pulses. The Fourier spectrum of these sound pulses extends up to 1 Terahertz. Brown University has licensed the technology that has been developed to an established metrology company, and they have produced a commercial version of the equipment. This has become a standard technique for the measurement of the thickness of opaque films in semiconductor chips and is now in use by all of the leading chip fabricators world-wide.
Awards
UK Science Research Council Fellowship, 1972
Japanese Society for Promotion of Science Senior Fellowship, 1982
Senior Alexander Von Humboldt Award,1989
Japanese Society for Promotion of Science Senior Fellowship, 2003
Affiliations
Fellow of the American Physical Society.
Associate Editor, Journal of Low Temperature Physics.
Divisional Associate Editor of Physical Review Letters.
Funded Research
National Science Foundation "Nucleation Processes in Liquid Helium", Grants DMR-0305115 (6/1/03-5/31/06) and DMR-0605355 (6/1/06-5/31/09).
National Aeronautics and Space Administration (NASA) "Coalescence of Superfluid Helium Drops in a Microgravity Environment" NAGW NAG3-2925 (4/1/05-3/31/06).
Rudolph Technologies, "Support for a Graduate Student in Picosecond Ultrasonics"
Zygo Corporation, "Proposal for Development of a High Resolution Scanning Probe Opto-Acoustic Microscope", (11/15/05-11/14/08).
Total external funding for current year is $673,000.
Web Links
- Humphrey Maris
- A look into the lab: exploding electron bubbles
- Brown physicist proposes that electron may be split in two
