Theodor Haensch

Theodor Haensch
Nobel Laureate
Ludwig-Maximilians-University of Munich | LMU · Faculty of Physics

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916
Publications
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Publications

Publications (916)
Article
Full-text available
Mid-infrared high-resolution spectroscopy has proven an invaluable tool for the study of the structure and dynamics of molecules in the gas phase. The advent of frequency combs advances the frontiers of precise molecular spectroscopy. Here we demonstrate, in the important 3-µm spectral region of the fundamental CH stretch in molecules, dual-comb sp...
Article
Full-text available
A laser frequency comb is a broad spectrum composed of equidistant narrow lines. Initially invented for frequency metrology, such combs enable new approaches to spectroscopy over broad spectral bandwidths, of particular relevance to molecules. The performance of existing spectrometers — such as crossed dispersers employing, for example, virtual ima...
Preprint
We demonstrate single-photon time-domain interference in a new realm. We observe interferences in the photon counting statistics with two separate mode-locked femtosecond lasers of slightly different repetition frequencies, each emitting a comb of evenly spaced spectral lines over a wide spectral span. We exploit the interference pattern for spectr...
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
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
Our ability to generate new distributions of light has been remarkably enhanced in recent years. At the most fundamental level, these light patterns are obtained by ingeniously combining different electromagnetic modes. Interestingly, the modal superposition occurs in the spatial, temporal as well as spatio-temporal domain. This generalized concept...
Conference Paper
A dual-comb interferometer using electro-optic modulators and nonlinear frequency conversion enables linear absorption spectroscopy in the 390-nm region at the single-photon level. Photon-counting instrumentation alleviates the use of high-power lasers.
Conference Paper
Near-infrared and visible frequency combs, combined with fast CMOS cameras and multi-heterodyne read-out, open up new opportunities for lens-less imaging, three-dimensional metrology and scan-free wavefront reconstruction.
Article
Full-text available
Holography ¹ has always held special appeal as it is able to record and display spatial information in three dimensions 2–10 . Here we show how to augment the capabilities of digital holography 11,12 by using a large number of narrow laser lines at precisely defined optical frequencies simultaneously. Using an interferometer based on two frequency...
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...
Conference Paper
Dual-comb spectroscopy with frequency modulation and synchronous lock-in detection over the entire spectral bandwidth of the combs is demonstrated with absorption and dispersion spectra of C2H2 in the 1.5 μm region.
Article
Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the impl...
Preprint
Full-text available
Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the impl...
Preprint
Full-text available
Holography has always held special appeal, for it is able to record and display spatial information in three dimensions. Here, we show how to augment the capabilities of digital holography by using a large number of narrow laser lines at precisely-defined optical frequencies simultaneously. Using an interferometer based on two frequency combs of sl...
Preprint
Our ability to generate new distributions of light has been remarkably enhanced in recent years. At the most fundamental level, these light patterns are obtained by ingeniously combining different electromagnetic modes. Interestingly, the modal superposition occurs in the spatial, temporal as well as spatio-temporal domain. This generalized concept...
Article
Full-text available
A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03360-2.
Preprint
Full-text available
We describe a simple method for measuring the residual fast phase noise of a cavity-stabilized laser using the cavity as a reference. The method is based on generating a beat note between the laser output and the strongly filtered light transmitted through the cavity. The beat note can be directly analyzed without requiring further calibration of s...
Preprint
Full-text available
We investigate the motional resonances of dual-species Coulomb crystals comprised of $^9$Be$^+$ and $^{24}$Mg$^+$ ions held in a 4-rod linear Paul trap. Our experimental data and simulations show that the secular motion of such mixed crystals has rich dynamics. Their secular spectra can differ significantly from those of pure ion crystals. We propo...
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...
Conference Paper
The many evenly-spaced lines of a frequency comb are harnessed for a new approach digital holography, using dual-comb interferometry. A “movie” of recorded holograms enables 3- dimensional hyperspectral imaging with high spatial and spectral resolution.
Conference Paper
Fundamental and technical noise sources in III-V-on-silicon mode-locked lasers are investigated and minimized. Their frequency stability is optimized to make them suited to applications such as dual-comb spectroscopy or dual-comb LIDAR.
Conference Paper
A dual-comb interferometer with two semiconductor lasers on silicon photonic chips enables an optical resolution of 1 GHz, over a 0.7-THz span. The spectrometer di- rectly and unambiguously samples near-infrared rovibrational transitions without spectral interleaving.
Article
Context. The general theory of relativity predicts the redshift of spectral lines in the solar photosphere as a consequence of the gravitational potential of the Sun. This effect can be measured from a solar disk-integrated flux spectrum of the Sun’s reflected light on Solar System bodies. Aims. The laser frequency comb (LFC) calibration system att...
Article
Full-text available
Significance Dual-comb spectroscopy has emerged a powerful technique of Fourier transform spectroscopy without moving parts. Broad spectra can be acquired with a single photodetector in any spectral range where laser frequency combs are available. Because the technique is multiplex, systematic effects are minimized and a great consistency of the sp...
Preprint
The General Theory of Relativity predicts the redshift of spectral lines in the solar photosphere, as a consequence of the gravitational potential of the Sun. This effect can be measured from a solar disk-integrated flux spectrum of the Sun's reflected light on solar system bodies. The laser frequency comb (LFC) calibration system attached to the H...
Conference Paper
Imaging absorption spectroscopy with laser frequency combs simultaneously measures 64 spectra at 250-MHz resolution over a span of 4 nm, within 3 seconds. At 1000 s averaging,the high signal-to-noise ratio reaches 250 per pixel.
Conference Paper
Dual-comb spectroscopy of Doppler-broadened rovibrational transitions of ethylene is performed in the 3-µm region with resolved comb lines and self-referencing of the fiber combs, leading to line-position measurements with an average uncertainty of 2.3 MHz.
Conference Paper
A single electro-optic modulator enables near-infrared dual-comb spectroscopy over a span of 40 GHz with a 150-kHz refresh rate and a 50-s coherence time. The signal-to-noise ratio is 950 at 100-MHz resolution and 100-ms measurement.
Conference Paper
Using photon-counting technology, dual-comb spectroscopy with resolved comb lines is performed at a power level of a few picowatts. The low power, >10 ^ 7 times weaker than most previous implementations, opens up applications to precision spectroscopy.
Preprint
Full-text available
Frequency combs, spectra of evenly-spaced narrow phase-coherent laser lines, have revolutionized precision measurements. On-chip frequency comb generators hold much promise for fully-integrated instruments of time and frequency metrology. While outstanding developments are being reported with Kerr, quantum cascade and microring electro-optic combs,...
Article
Full-text available
Laser frequency combs (LFCs) are well on their way to becoming the next-generation calibration sources for precision astronomical spectroscopy1,2,3,4,5,6. This development is considered key in the hunt for low-mass rocky exoplanets around solar-type stars whose discovery with the radial-velocity method requires cm s–1 Doppler precision⁷. In order t...
Conference Paper
An integrated III-V-on-silicon mode-locked laser enables the first on-chip comb generator of 1.0-GHz line-spacing for direct interrogation of gas-phase narrow rovibrational transitions in molecules. Its flat-top spectrum empowers real-time multiplexed spectroscopy without any scanning elements.
Conference Paper
Mid-infrared self-referenced spectra with resolved comb lines of 100-MHz spacing span up to 8 THz. Schemes for direct mid-infrared and up-conversion detections lead to signal-to-noise ratio higher than 4000 at 1000-s averaging time.
Conference Paper
We demonstrate dual-comb interferometry and spectroscopy with a III-V-on-silicon passively mode-locked laser of 1-GHz repetition rate and 1-THz span. We heterodyne the on-chip device with an electro-optic modulator comb for initial assessment.
Preprint
We devise a new detection technique for mid-infrared multi-heterodyne spectroscopy. As an experimental implementation, mid-infrared light interrogates a gas sample in the 3-$\mu$m region of the fundamental CH, OH, NH stretch in molecules and detection is performed in the near-infrared telecommunication region. Spectra showing 18000 resolved comb li...
Preprint
Full-text available
Laser frequency combs (LFCs) are well on their way to becoming the next-generation calibration sources for precision astronomical spectroscopy. This development is considered key in the hunt for low-mass rocky exoplanets around solar-type stars whose discovery with the radial-velocity method requires cm/s Doppler precision. In order to prove such p...
Article
Full-text available
Precision measurements represent a cornerstone in fundamental science. The capability of observing and quantifying subtle phenomena and events allows new discoveries and it confirms or confutes the theories describing our understanding of nature. The optical frequency comb, providing hundreds of thousands of phase-locked and evenly spaced laser lin...
Article
Full-text available
Atomically thin crystals of transition metal dichalcogenides (TMDs) host excitons with strong binding energies and sizable light-matter interactions. Coupled to optical cavities, monolayer TMDs routinely reach the regime of strong light-matter coupling, where excitons and photons admix coherently to form quasiparticles known as polaritons up to roo...
Article
We describe a simple method for measuring the residual fast phase noise of a cavity-stabilized laser using the cavity as a reference. The method is based on generating a beat note between the laser output and the strongly filtered light transmitted through the cavity. The beat note can be directly analyzed without requiring further calibration of s...
Article
Article in open access at https://www.osa-opn.org/home/articles/volume_30/june_2019/features/mid-ir_spectroscopic_sensing/ Pdf version at https://www.osapublishing.org/DirectPDFAccess/C6E34F26-F57D-8334-4B1B0C64E0ED8FB9_413225/opn-30-6-26.pdf
Conference Paper
Automatic interpolation of 25GHz mode spacing in dual EOM comb spectroscopy has been demonstrated. By single shot measurement of 9.3ms, H13C14N absorption spectrum spanning more than 0.8THz with 100MHz resolution could be obtained.
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...
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
Full-text available
We investigate the motional resonances of dual-species Coulomb crystals comprised of ⁹Be⁺ and ²⁴Mg⁺ ions held in a 4-rod linear Paul trap. Our experimental data and simulations show that the secular motion of such mixed crystals has rich dynamics. Their secular spectra can differ significantly from those of pure ion crystals. We propose a simple mo...
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
Mid-infrared high-resolution spectroscopy has proven an invaluable tool for the study of the structure and dynamics of molecules in the gas phase. The advent of frequency combs advances the frontiers of precise molecular spectroscopy. Here we demonstrate, in the important 3-{\mu}m spectral region of the fundamental CH stretch in molecules, dual-com...
Article
Full-text available
We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the sample properties and observe a strong correlation between emission lifetime and brightness, as well as a lifetime reduction for nanocrystals embedded in a polymer film. This is ex...
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$...
Article
Full-text available
Improvements to dual-comb interferometers will benefit precision spectroscopy and sensing, distance metrology, tomography, telecommunications etc. A specific requirement of such interferometers is to enforce mutual coherence between the two combs over the measurement time. With feed-forward relative stabilization of the carrier-enveloppe offset fre...
Article
Full-text available
The quantum Zeno effect (QZE) is not only interesting as a manifestation of the counterintuitive behavior of quantum mechanics, but may also have practical applications. When a spectroscopy laser is applied to target atoms or ions prepared in an initial state, the Rabi flopping of an auxiliary transition sharing one common level can be inhibited. T...
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
Optics Letters article in open access at https://doi.org/10.1364/OL.43.000162 © 2018 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. --------------...
Conference Paper
Multiheterodyne spectroscopy with difference frequency combs demonstrates 130000 resolved comb lines spanning more than 10 THz in the region centered at 90 THz. Signal-to-noise ratios higher than 1300 provide accurate molecular line parameter measurements
Article
Full-text available
Optical frequency combs have revolutionized the measurement of optical frequencies and improved the precision of spectroscopic experiments. Besides their importance as a frequency-measuring ruler, the frequency combs themselves can excite target transitions (direct frequency comb spectroscopy). The direct frequency comb spectroscopy may extend the...
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...
Article
We demonstrate nonlinear pulse compression by multi-pass cell spectral broadening (MPCSB) from 860 fs to 115 fs with compressed pulse energy of 7.5 µJ, average power of 300 W and close to diffraction-limited beam quality. The transmission of the compression unit is >90%. The results show that this recently introduced compression scheme for peak pow...
Conference Paper
Attenuated total reflection spectroscopy with tapered fibers is combined to coherent multi-heterodyne spectroscopy in the near-infrared region. Evanescent sensing is extended to broadband high-resolution spectroscopy in the gas phase at high signal-to-noise ratio.
Article
We theoretically show that an externally driven dipole placed inside a cylindrical hollow waveguide can generate a train of ultrashort and ultrafocused electromagnetic pulses. The waveguide encloses vacuum with perfect electric conducting walls. A dipole driven by a single short pulse, which is properly engineered to exploit the linear spectral fil...
Article
Full-text available
We demonstrate dual-comb spectroscopy based on difference frequency generation of frequency-agile near-infrared frequency combs, produced with the help of electro-optic modulators. The combs have a remarkably flat intensity distribution and their positions and line spacings can be selected freely by simply dialing a knob. We record, in the 3-micron...
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...