Abstract
We present an active fiber-based retroreflector providing high quality phase-retracing anti-parallel Gaussian laser beams for precision spectroscopy of Doppler sensitive transitions. Our design is well-suited for a number of applications where implementing optical cavities is technically challenging and corner cubes fail to match the demanded requirements, most importantly retracing wavefronts and preservation of the laser polarization. To illustrate the performance of the system, we use it for spectroscopy of the 2S-4P transition in atomic hydrogen and demonstrate an average suppression of the first order Doppler shift to 4 parts in 106 of the full collinear shift. This high degree of cancellation combined with our cryogenic source of hydrogen atoms in the metastable 2S state is sufficient to enable determinations of the Rydberg constant and the proton charge radius with competitive uncertainties. Advantages over the usual Doppler cancellation based on corner cube type retroreflectors are discussed as well as an alternative method using a high finesse cavity.
Highlights
The Doppler effect can be a major obstacle in laser spectroscopy
The first order Doppler shift of an individual atom moving at a velocity v in a plane wave described by a wave vector k = 2π/λ is given by
We find that residual uncompensated Doppler shifts are on average reduced to less than 4 parts in 106 of the full collinear shift in our setup which will be used for precision spectroscopy of the 2S-4P one-photon transition in atomic hydrogen at
Summary
W. Hänsch, “Low phase noise diode laser oscillator for 1S-2S spectroscopy in atomic hydrogen,” Opt. Lett. W. Hänsch, “Subhertz linewidth diode lasers by stabilization to vibrationally and thermally compensated ultralow-expansion glass Fabry-Perot cavities,” Phys. “Precision Spectroscopy on atomic hydrogen” (PhD thesis, Ludwig-Maximilians-Universität München, 2011). W. Hänsch, “Precision measurement of the hydrogen 1S-2S frequency via a 920-km fiber link,” Phys. Atom - Photon Interactions: Basic Process and Appilcations (Wiley-VCH Verlag GmbH, 2004). “Frequency shift in saturation spectroscopy induced by mechanical effects of light,” Phys. B. Newell, “CODATA recommended values of the fundamental physical constants: 2010,” Rev. Mod.
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