Research History - Dr. Oliver A. Hemmers

In November of 1986, I joined the group of Professor Uwe E. Becker at the Technical University of Berlin, Germany for my graduate and PhD studies in the field of atomic and molecular spectrometry. The research is based on the reaction between vacuum ultra-violet (vuv) light or x-rays with atoms or molecules, one of the most common form of interaction in our universe. Light is absorbed by the atoms or molecules and then electrons are emitted based on energy and momentum conservation laws. Electron emission intensities and their angular distributions are not only dependent on photon energy and photon momentum but also on the electronic subshell the electron is coming from and all other electronic subshells in the atom or molecule. This highly complicated dependence of electron emission has been of great interest in the atomic and molecular physics community for over 40 years. When molecules lose the electrons that build the bond between their atoms, the molecules fragment into mostly positively charged ionic particles that also have been studied to better understand the ionization and fragmentation dynamics during and after photoionization. My PhD thesis was on correlation effects in small molecules (nitrogen, carbon monoxide and carbon dioxide) studying the differential cross section behaviors of various electronic shells over wide ranges of photon energies. The special light (vuv and x-rays) necessary for these types of experiments are produced at facilities called Synchrotron Light Sources. These light sources house large storage rings in which electrons (or positrons) circle with almost the speed of light. On the curved sections and special straight sections of those storage rings the electrons (or positrons) emit the most intense beams of ultraviolet and soft-x-ray radiation in the world. The light then travels along beamlines to the experimental endstations. At this time there are about 50 of such light sources available worldwide for a large variety of research projects in biology, medicine, materials sciences, surface and condensed matter physics, chemistry and others.

In April 1994, I joined the group of Professor Dennis W. Lindle at the University of Nevada, Las Vegas as a post-doctoral scholar and provided for 1.5 years my own salary through a successful application to the German Research Society (DFG). In 1998 I became an Assistant Research Professor at UNLV. My task was the design, development and construction of an electron time-of-flight (TOF) endstation for angular resolved spectrometry. The idea was not only to build the best electron TOF analyzers and detectors but also build enough of them to cover all angles necessary to measure angular distributions that have never been measured before. Once the new endstation with 5 analyzers was ready for commissioning we shipped it to a then brand new national facility - the Advanced Light Source (ALS) at the Department of Energy supported Lawrence Berkeley National Laboratory (LBL), located in Berkeley, CA. The ALS is a storage ring of 67 m diameter and one of the brightest and finest light sources in the world. I will shortly describe how successful we have been to gain access to beamtime at the ALS. The ALS receives currently over 1500 research proposals every year that undergo a strict peer-review selection process to determine the allotted times the researchers receive for their experiments. Only 50% of the submitted proposals receive a time-slot. Over the last couple of years the proposals submitted by our group for the electron-TOF endstation have ranked in the top ten out of 1500, surely a sign of outstanding research. Our research program has reported numerous never-before observed fundamental phenomena that have reshaped the field of electron and ion spectroscopy. Recently, for example, we have been focusing on the breakdown of two fundamental approximations in atomic and molecular photoionization, the 'dipole approximation' and the 'independent particle approximation.' Until our studies were published, these approximations were thought to be excellent in the x-ray photoionization range. Our research proved otherwise. And as a result, two new fields of inquiry were initiated in which much is being published at present by a variety of researchers all over the world. The new fields of study not only affect the atomic and molecular research community, but also the surface science, plasma, and condensed matter research communities. The fundamental nature of my research results will likely require a 'rewriting' of atomic and molecular phenomena discussed in physics and physical chemistry textbooks. I have actively pursued national and international collaborations with experimentalists and theoreticians and I am well known worldwide as an expert in my field of research. In addition, students (undergraduate and graduate) and post-doctoral scholars have benefited through participation in research activities in a multinational research environment by conducting experiments at the ALS and other x-ray user facilities, both national and abroad.

I have published almost 40 papers in refereed journals, with quite a large share in Physical Review Letters. Another measure of the importance of a research program, and how it is seen by the peer group, is the success in outside funding. Our group has been very successful with the two major agencies that fund this area, the National Science Foundation and the Department of Energy.


My CV as of April 2002 in PDF-format

Cover letter of Paul Herzog with information about letters of recommendation in PDF-format

Sample Letters in PDF-format: 01, 02, 03, 04, 05, 06, 07, 08, 09