• Technical Conference:  16 – 20 September 2018
  • Science & Industry Showcase:  18 – 19 September 2018

Far from a Bohr (100 Years Even)

Ok, right off the bat, sorry for the pun. Anyone could probably see it coming, but I couldn’t help myself. Frontiers in Optics/Laser Science 2013 opened in great style with the Symposium on the 100th Anniversary of the Bohr Atom. What does Bohr’s atom have to do with optics and lasers? Well, as anyone in the field could guess, quite a lot actually (where can’t photonics be applied?).
The symposium opened with a great introduction by Charles Clark of NIST. Dr. Clark gave an overview of Neils Bohr’s seminal work, focusing on how his nearly parenthetical comment on applying quantization to the mechanical model of the angular momentum of atomic electrons provided a tremendous leap forward in the development of quantum mechanics. Although since proven to be an inadequate model, the elegance of Bohr’s idea is in its simplicity and yet remarkable 

See caption below
The Bohr model of an atom with c negatively charged electron orbiting a positively charged nucleus in discrete orbitals. The quantization leads to very particular spectral emission lines with dark gaps between (image from Wikipedia).

Chris Greene of JILA, University of Colorado at Boulder followed by discussing Rydberg electrons. As Dr. Greene describes, even before Bohr came up with his quantized orbital model of the atom, Johannes Rydberg developed an empirical model for atomic emission. Since that time, ever increasing refinements have been made to the understanding of atomic and molecular transitions, accounting for more and more complexities, including molecular vibration and rotation effects. Admittedly, quite a bit was over my head, but I was certainly impressed by the progress that has been made, and continues to be made, over the last 50 years (and his talk certainly piqued my interest in learning some of this unfamiliar physics).
The focus then shifted to performing quantum interference experiments on massive (orders of magnitude larger than an AMU) molecules with a lecture provided by Nadine Dörre of University of Vienna, Austria. The essential problem lies in the fact that as a molecule or particle becomes more massive, its size can actually be many orders of magnitude larger than its de Broglie wavelength. This calls for novel interferometry experiments to be able to resolve the wavelength. Rather than using far-field interference patterns, Dr. Dörre described how near-field interferometry, in the form of Talbot length measurements, can be used to resolve wavelength. Moreover, by using a Talbot configuration but in the time domain, one can circumvent issues presented by measurement dependence on particle velocity. She demonstrated that by using such techniques, remarkably short wavelengths can be measured from very massive molecules.
Finally, Masaki Hori of the Max Planck Institute for Quantum Optics presented on the measurement of antiproton mass using two-photon spectroscopy. The foundation of the method seems to be the creation of an “exotic atom” in which an electron from a helium atom is replaced by an antiproton. The antiproton in helium has the remarkable property that its wavefunction does not overlap with the atomic nucleus, meaning it takes a long time to annihilate (microseconds, plenty of time for good measurements). Then the trick is to overcome Doppler broadening which obscures the transition under investigation. This is where two photon spectroscopy, with two counter-propagating laser beams at different wavelengths, comes in. The result is a measurement that demonstrates that, according to today’s measurements, the masses of the proton and antiproton agree to a precision of 7x10-10.
Well, that wraps up my first of several entries for this week at Frontiers in Optics. The last thing I’d like to mention is that there was an excellent welcome reception as well, so I hope all who could make it enjoyed the good food, drink, and company! I’m looking forward to a great week at the conference and sharing it in these entries! Until tomorrow… 
Disclaimer: Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government and MIT Lincoln Laboratory.

Posted: 10/7/2013 7:33:36 AM by By Dom Siriani | with 0 comments

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