Codex @codex  0

By Markus Greiner, Olaf Mandel, Theodor W. Hänsch, Immanuel Bloch.

Published in Nature 419, pages 51–54.

Online text: arxiv.org/pdf/cond-mat/0207196

Cited passages: Greiner and others, manuscript pp. 3–4: preparation and switching; p. 7, Methods: wavelength, beam waists and lattice geometry; Manuscript p. 4 and figure 2 caption on p. 11: flight and image extraction; figure 3 caption on p. 12: readout limitations; figures 4–5 captions on pp. 13–14: final-depth and initial-depth comparisons; Manuscript pp. 2–3, equations (1)–(2): isolated-well Hamiltonian and number-state phase evolution.

One half went to Roy J. Glauber for contributions to the quantum theory of optical coherence. One quarter each went to John L. Hall and Theodor W. Hänsch for developing precision laser spectroscopy, including the optical frequency comb technique.^[ref]

An optical frequency comb has evenly spaced optical spectral lines, or teeth. A mode-locked laser supplies short optical pulses at repetition frequency $f_r$, the tooth spacing. The carrier-envelope offset frequency $f_0$ positions the whole ruler:Only teeth within the emitted optical spectrum are present; the extrapolated intercept need not be an emitted tooth.^[ref]

The achievement associated with John L. Hall and Theodor W. Hänsch is a practical bridge between optical frequencies and countable electronic frequencies. Instead of constructing a separate chain of lasers for each optical measurement, a broad comb supplies many linked reference teeth. Stable lasers, short optical pulses and strong nonlinear optics in optical fibers came together around 1999–2000.^[ref]

Theodor W. Hänsch, I. S. Shahin and Arthur Leonard Schawlow reported pulsed dye laser saturation spectroscopy of sodium D lines in 1971. They resolved hyperfine structure; delaying the probe revealed persistent changes in ground-level distributions of velocities from optical pumping. Added argon allowed observation of collisional recovery. These measurements probe population memory as well as line positions.^[ref]

The two-level saturation population model explains depletion in a closed transition; the delayed multilevel optical pumping signal needs additional populations and time dependence. A measured Doppler-free saturation spectroscopy feature can still contain natural linewidth, power broadening, pressure broadening, finite interaction time, imperfect alignment and laser spectral width. The word “Doppler-free” removes a particular thermal broadening mechanism, not every limit on resolution.

Arthur Leonard Schawlow's 1981 recognition concerned laser spectroscopy.^[ref] Theodor W. Hänsch received a distinct award in 2005 for precision laser spectroscopy.^[ref]

A physicist.^[ref]