Randolf Pohl

Randolf Pohl
Johannes Gutenberg-Universität Mainz | JGU · Institute of Physics

Dr. sc. nat.

About

141
Publications
24,048
Reads
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5,344
Citations
Additional affiliations
May 2016 - present
Johannes Gutenberg-Universität Mainz
Position
  • Professor
November 2010 - February 2011
Ludwig-Maximilians-University of Munich
Position
  • Professor (temprorary)
April 2005 - present
Max-Planck-Institut für Quantenoptik
Position
  • Independent Research Group Leader

Publications

Publications (141)
Preprint
Full-text available
Muonic atom spectroscopy -- the measurement of the x rays emitted during the formation process of a muonic atom -- has a long standing history in probing the shape and size of nuclei. In fact, almost all stable elements have been subject to muonic atom spectroscopy measurements and the absolute charge radii extracted from these measurements typical...
Article
The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen ( \mu μ p) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with 2\times10^{-4} 2 × 10 − 4 relative accuracy. In the proposed experiment, the \mu μ p atom undergoes a laser exc...
Article
In Sec. 6 (polarization monitor) of our recent publication [Opt. Express29(5), 7024 (2021)10.1364/OE.417455], we assumed a small value of δ. This is however incorrect. The correct approximation for small β leads to the updated Eqs. (10)-(11), resulting in a corrected Fig. 12.
Article
Full-text available
The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon Induced X-ray Emission (MI...
Preprint
Full-text available
The toolbox for material characterization has never been richer than today. Great progress with all kinds of particles and interaction methods provide access to nearly all properties of an object under study. However, a tomographic analysis of the subsurface region remains still a challenge today. In this regard, the Muon-Induced X-ray Emission (MI...
Preprint
Full-text available
The CREMA collaboration is pursuing a measurement of the ground-state hyperfine splitting (HFS) in muonic hydrogen ($\mu$p) with 1 ppm accuracy by means of pulsed laser spectroscopy to determine the two-photon-exchange contribution with $2\times10^{-4}$ relative accuracy. In the proposed experiment, the $\mu$p atom which undergoes a laser excitatio...
Article
Full-text available
The energy levels of hydrogen-like atomic systems are shifted slightly by the complex structure of the nucleus, in particular by the finite size of the nucleus. These energy shifts are vastly magnified in muonic atoms and ions, i.e. the hydrogen-like systems formed by a negative muon and a nucleus. By measuring the 2S-2P energy splitting in muonic...
Article
Full-text available
A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03360-2.
Article
We present an improved active fiber-based retroreflector (AFR) providing high-quality wavefront-retracing anti-parallel laser beams in the near UV. We use our improved AFR for first-order Doppler-shift suppression in precision spectroscopy of atomic hydrogen, but our setup can be adapted to other applications where wavefront-retracing beams with de...
Article
Full-text available
The energy levels of hydrogen-like atomic systems can be calculated with great precision. Starting from their quantum mechanical solution, they have been refined over the years to include the electron spin, the relativistic and quantum field effects, and tiny energy shifts related to the complex structure of the nucleus. These energy shifts caused...
Article
Testing physics using the hydrogen atom Discrepancy between the proton radius determined from hydrogen and muonic hydrogen spectroscopy data, the so-called “proton radius puzzle,” has been a focus of the physics community for more than a decade now. Using two-photon ultraviolet frequency comb spectroscopy below 1 kilohertz, Grinin et al. report a h...
Article
Full-text available
The hyperfine splitting of the 5g→4f transitions in muonic Re185,187 has been measured using high resolution high purity germanium detectors and compared to state-of-the-art atomic theoretical predictions. The spectroscopic quadrupole moment has been extracted using modern fitting procedures and compared to the values available in literature obtain...
Preprint
Full-text available
The hyperfine splitting of the 5g -> 4f transitions in muonic 185,187-Re has been measured using high resolution HPGe detectors and compared to state-of-the-art atomic theoretical predictions. The spectroscopic quadrupole moment has been extracted using modern fitting procedures and compared to the values available in literature obtained from muoni...
Article
Full-text available
This study investigates the stability to tilts (misalignments) of Fourier-based multipass amplifiers, i.e., amplifiers where a Fourier transform is used to transport the beam from pass to pass. Here, the stability properties of these amplifiers to misalignments (tilts) of their optical components have been investigated. For this purpose, a method t...
Article
Full-text available
High‐resolution laser spectroscopy serves the purpose of determining the energy difference between states of atoms and molecules with the best possible accuracy. Therefore, one may face the problem of finding the center of a symmetric line within a small fraction of the line width, or one needs to extract the energy difference from an asymmetric li...
Preprint
Full-text available
We present a multi-pass amplifier which passively compensates for distortions of the spherical phase front occurring in the active medium. The design is based on the Fourier transform propagation which makes the output beam parameters insensitive to variation of thermal lens effects in the active medium. The realized system allows for 20 reflection...
Preprint
Full-text available
The stability properties of Fourier-based multipass amplifier to misalignments (tilts) of its optical components has been investigated. For this purpose, a method to quantify the sensitivity to tilts based on the amplifier small signal gain has been elaborated and compared with measurements. To improve on the tilt stability by more than an order of...
Conference Paper
Full-text available
Testing theories means to compare precise measurements with theoretical predictions. I will describe where we stand with quantum electrodynamics by verifying calculations of energy levels in atomic hydrogen.
Article
We present an architecture for a multipass amplifier based on a succession of optical Fourier transforms and short propagations that shows a superior stability for variations of the thermal lens compared to state-of-the-art 4f -based amplifiers. We found that the proposed multipass amplifier is robust to variations of the active medium dioptric pow...
Article
Full-text available
Precision spectroscopy of light muonic atoms provides unique information about the atomic and nuclear structure of these systems and thus represents a way to access fundamental interactions, properties and constants. One application comprises the determination of absolute nuclear charge radii with unprecedented accuracy from measurements of the 2S...
Preprint
Full-text available
We present a novel architecture for a multi-pass amplifier based on a succession of optical Fourier transforms and short propagations that shows a superior stability for variations of the thermal lens compared to state-of-the-art 4f-based amplifiers. We found that the proposed multi-pass amplifier is robust to variations of the active medium dioptr...
Article
Full-text available
An up to date review of the theoretical contributions to the $2S\rightarrow{}2P$ Lamb shift and the fine structure of the $2P$-state in the $(\mu^4\mathrm{He})^+$ ion is given. This summary will serve as the basis for the extraction of the alpha particle charge radius from the muonic helium Lamb shift measurements at the Paul Scherrer Institute Swi...
Preprint
Full-text available
Precision spectroscopy of light muonic atoms provides unique information about the atomic and nuclear structure of these systems and thus represents a way to access fundamental interactions, properties and constants. One application comprises the determination of absolute nuclear charge radii with unprecedented accuracy from measurements of the 2S$...
Conference Paper
Full-text available
The core of the “proton radius puzzle” is the discrepancy of four standard deviations between the proton root mean square charge radii (rp) determined from regular hydrogen (H), and the muonic hydrogen atom (μp). We have measured the 2S-4P transition frequency in H, utilizing a cryogenic beam of H and directly demonstrate that quantum interference...
Article
The double response of a large area avalanche photodiode, a planar RMD model S1315, to 6-keV x-rays was investigated as a function of APD biasing voltage and for different operating temperatures. Our data are consistent with the interpretation that the dissimilar APD response is due to x-ray interactions in the different APD-layer structures; inter...
Article
Full-text available
Muonic atoms have been used to extract the most accurate nuclear charge radii based on the detection of X-rays from the muonic cascades. Most stable and a few unstable isotopes have been investigated with muonic atom spectroscopy techniques. A new research project recently started at the Paul Scherrer Institut aims to extend the highresolution muon...
Article
Full-text available
Spatial hole burning prevents single-frequency operation of thin-disk lasers when the thin disk is used as a folding mirror. We present an evaluation of the saturation effects in the disk for disks acting as end-mirrors and as folding-mirrors explaining one of the main obstacles towards single-frequency operation. It is shown that a twisted-mode sc...
Article
Full-text available
The present knowledge of Lamb shift, fine-, and hyperfine structure of the 2S and 2P states in muonic helium-3 ions is reviewed in anticipation of the results of a first measurement of several $\mathrm{2S\rightarrow2P}$ transition frequencies in the muonic helium-3 ion, $\mathrm{\mu^3He^+}$. This ion is the bound state of a single negative muon $\m...
Article
Full-text available
Laser spectroscopy of the Lamb shift (2S-2P energy difference) in light muonic atoms or ions, in which one negative muon $\mu^-$ is bound to a nucleus, has been performed. The measurements yield significantly improved values of the root-mean-square charge radii of the nuclei, owing to the large muon mass, which results in a vastly increased muon wa...
Article
Full-text available
The discrepancy between the size of the proton extracted from the spectroscopy of muonic hydrogen and the value obtained by averaging previous results for “regular” hydrogen has puzzled physicists for the past 7 years. Now, Beyer et al. shed light on this puzzle (see the Perspective by Vassen). The authors obtained the size of the proton using very...
Preprint
Full-text available
High-precision measurements of the proton radius from laser spectroscopy of muonic hydrogen demonstrated up to six standard deviations smaller values than obtained from electron-proton scattering and hydrogen spectroscopy. The status of this discrepancy, which is known as the "proton radius puzzle" will be discussed in this paper, complemented with...
Article
Full-text available
We give a pedagogical description of the method to extract the charge radii and Rydberg constant from laser spectroscopy in regular hydrogen (H) and deuterium (D) atoms, that is part of the CODATA least-squares adjustment (LSA) of the fundamental physical constants. We give a deuteron charge radius rd from D spectroscopy alone of 2.1415(45) fm. Thi...
Article
Seit einigen Jahren gibt es eine dramatische Diskrepanz bei der Bestimmung der Größe des Protons. Während Elektron-Proton-Streuung und Laserspektroskopie von atomarem Wasserstoff einen Ladungsradius von 0,88 fm liefern, ergab unsere Messung im exotischen myonischen Wasserstoff nur 0,84 fm – 7 Standardabweichungen kleiner als der Mittelwert aller bi...
Article
Laser spectroscopy of muonic hydrogen atoms, μp, has revealed a proton root-mean-square (rms) charge radius rE that is an order of magnitude more accurate than the CODATA world average from elastic electron-proton scattering and precision spectroscopy of regular (electronic) hydrogen. Interestingly, though, the value of rE from μp is 4%, or 7 combi...
Article
The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ–. We measu...
Article
The deuteron is the simplest compound nucleus, composed of one proton and one neutron. Deuteron properties such as the root-mean-square charge radius rd and the polarizability serve as important benchmarks for understanding the nuclear forces and structure. Muonic deuterium μd is the exotic atom formed by a deuteron and a negative muon μ–. We measu...
Article
Full-text available
We present a fundamental obstacle in power scaling of thin-disk lasers related to self-driven growth of misalignment due to thermal lens effects. This self-driven growth arises from the changes of the optical phase difference at the disk caused by the excursion of the laser eigen-mode from the optical axis. We found a criterion based on a simplifie...
Article
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 requi...
Conference Paper
We report the first laser spectroscopy of muonic deuterium. At the Paul Scherrer Institute, we have measured the frequency of the 2S-2P Lamb shift in muonic deuterium. As in the case of the muonic hydrogen, the observed lines are shifted from the theoretical predictions. Thanks to improved new QED and nuclear structure calculations, an accurate det...
Article
Full-text available
We identify a systematic present in two-photon direct frequency comb spectroscopy (DFCS) which is a result of chirped laser pulses and is a manifestation of the first-order Doppler effect. We carefully analyze this systematic and propose methods for its mitigation within the context of our measurement of the hydrogen 1S−3S transition. We also repor...
Article
Full-text available
We investigate the quantum interference shifts between energetically close states, where the state structure is observed by laser spectroscopy. We report a compact and analytical expression that models the quantum interference induced shift for any admixture of circular polarization of the incident laser and angle of observation. An experimental sc...
Article
Full-text available
Precision measurements of transition frequencies in atomic hydrogen provide important input for a number of fundamental applications, such as stringent tests of QED and the extraction of fundamental constants. Here we report on precision spectroscopy of the 2S–4P transition in atomic hydrogen with a reproducibility of a few parts in 10 12 . Utilizi...
Article
Full-text available
Novel thin-disk laser pump layouts are proposed yielding an increased number of passes for a given pump module size and pump source quality. These novel layouts result from a general scheme which bases on merging two simpler pump optics arrangements. Some peculiar examples can be realized by adapting standard commercially available pump optics simp...
Article
Full-text available
In the context of the Lamb shift measurement in muonic helium we developed a thin-disk laser composed of a Q-switched oscillator and a multi-pass amplifier delivering pulses of 150 mJ at a pulse duration of 100 ns. Its peculiar requirements are stochastic trigger and short delay time (< 500 ns) between trigger and optical output. The concept of the...
Article
Full-text available
We review the status of the proton charge radius puzzle. Emphasis is given to the various experiments initiated to resolve the conflict between the muonic hydrogen results and the results from scattering and regular hydrogen spectroscopy.
Article
Full-text available
Quantum interference between energetically close states is theoretically investigated, with the state structure being observed via laser spectroscopy. In this work, we focus on hyperfine states of selected hydrogenic muonic isotopes, and on how quantum interference affects the measured Lamb shift. The process of photon excitation and subsequent pho...
Conference Paper
Full-text available
A precision measurement of the 2S-4P transition in atomic hydrogen, when combined with the precisely known 1S-2S transition frequency\footnote{C. G. Parthey et al., PRL 107, 203001 (2011)}, can be used to determine the value of the r.m.s. proton charge radius r p . We report on our progress towards an absolute frequency measurement, using a cryogen...
Conference Paper
Precision spectroscopy of atomic hydrogen has long been successfully used to provide stringent tests on fundamental theories and precisely determine physical constants. The current limit originates from the uncertainty in the value of the proton r.m.s. charge radius r p . Moreover, the value of r p extracted from laser spectroscopy of muonic hydrog...
Article
The present knowledge of Lamb shift, fine- and hyperfine structure of the $\mathrm{2S}$ and $\mathrm{2P}$ states in muonic deuterium is reviewed in anticipation of the results of a first measurement of several $\mathrm{2S-2P}$ transition frequencies in muonic deuterium ({\mu}d). A term-by-term comparison of all available sources reveals reliable va...
Article
Full-text available
Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work we report on a fitting technique used to account for different detector responses resulting from photo absorption in the various APD layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2, and corr...
Conference Paper
Full-text available
Laser spectroscopy of muonic atoms, where a nucleus is orbited by one negative muon, is a novel tool for tests of quantum electrodynamics and the Standard Model, determination of fundamental physical constants, and for nuclear physics.
Article
Full-text available
Reach-through avalanche photodiodes (RT-APDs) from Hamamatsu Photonics, with different active areas, $5 times 5$ and $3 times 5$ mm$^2$, were investigated to evaluate their suitability for the muonic helium Lamb shift experiment. The gain has been determined as a function of voltage and temperature for both prototypes. As expected, it increases wit...
Article
Full-text available
A multipass laser cavity is presented which can be used to illuminate an elongated volume from a transverse direction. The illuminated volume can also have a very large transverse cross section. Convenient access to the illuminated volume is granted. The multipass cavity is very robust against misalignment, and no active stabilization is needed. Th...
Article
Full-text available
The recent measurement of the Lamb shift in muonic hydrogen resulted in a tenfold improved value of the rms charge radius of the proton. The value is, however, 7 standard deviations discrepant from the world average of this quantitiy which is obtained from elastic electron-proton scattering and precision spectroscopy of hydrogen and deuterium. New...
Article
Two experiments have come up with two wildly different values for the proton's radius. What's going on?
Article
Full-text available
Precise determinations of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state...
Article
Full-text available
Radiative deexcitation (RD) of the metastable 2S state of muonic hydrogen and deuterium atoms has been observed. In muonic hydrogen, we improve the precision on lifetime and population (formation probability) values for the short-lived mup(2S) component and give an upper limit for RD of long-lived mup(2S) atoms. In muonic deuterium at 1 hPa, 3.1 +-...
Article
Precision spectroscopy of the 2S − 4P_1/2 and 2S − 4P_3/2 transitions in atomic hydrogen is performed with a reproducibility of a few parts in 10^12. A cryogenic beam of metastable 2S atoms is obtained by optical excitation, avoiding excessive heating of electron impact excitation used in all previous experiments of this kind. Despite the low tempe...
Article
Muonic hydrogen (μp) is a very sensitive probe of the proton structure. Laser spectroscopy of two 2S-2P transitions in μp was used to determine both the Lamb shift and the hyperfine splitting of the 2S state in μp. The rms charge radius of the proton, fm, was extracted from the Lamb shift. The Zemach radius of the proton, fm, was obtained from the...
Article
Full-text available
Radiative deexcitation (RD) of the metastable 2S state of muonic protium and deuterium atoms has been observed. In muonic protium, we improve the precision on lifetime and population (formation probability) values for the short-lived {\mu}p(2S) component, and give an upper limit for RD of long-lived {\mu}p(2S) atoms. In muonic deuterium at 1 hPa, 3...
Article
Die Frage nach der Größe des Protons rückte vor einiger Zeit erneut in das Interesse von Physikern, als eine von uns gemachte Messung einen um 4 % signifikant kleineren Wert erhielt, als bis dahin angenommen. Die Ursache dieser viel diskutierten Diskrepanz ist nach wie vor unklar. Eine weitere Messung unserer Gruppe bestätigt nun den damals gefunde...