Ronald Holzwarth

• Dr.
• Managing Director at Menlo Systems GmbH

To compare the increasing number of optical frequency standards, highly stable optical signals have to be transferred over continental distances. We demonstrate optical-frequency transfer over a 1840-km underground optical fiber link using a single-span stabilization. The low inherent noise introduced by the fiber allows us to reach short term inst...

The best spectrographs are limited in stability by their calibration light source. Laser frequency combs are the ideal calibrators for astronomical spectrographs. They emit a spectrum of lines that are equally spaced in frequency and that are as accurate and stable as the atomic clock relative to which the comb is stabilized. Absolute calibration p...

The mid-infrared spectral range (lambda 2–20 mm) is of particular importance as many molecules exhibit strong vibrational fingerprints in this region. Optical frequency combs—broadband optical sources consisting of equally spaced and mutually coherent sharp lines—are creating new opportunities for advanced spectroscopy. Here we demonstrate a novel...

Airborne and spaceborne integral-path differential absorption (IPDA) lidar has the potential to deliver column measurements of the major greenhouse gases influenced by human activity with the high accuracy that is required to significantly reduce the uncertainties in our estimations of surface fluxes of methane and carbon dioxide by inverse modelli...

We report on the first deployment of a ytterbium (Yb) transportable optical lattice clock (TOLC), commercially shipping the clock 3000 km from Boulder, Colorado, to Washington DC. The system, composed of a rigidly mounted optical reference cavity, an atomic physics package, and an optical frequency comb, fully realizes an independent frequency stan...

We report on the first deployment of a ytterbium (Yb) transportable optical lattice clock (TOLC), commercially shipping the clock 3,000 km from Boulder, Colorado to Washington DC. The system, composed of a rigidly mounted optical reference cavity, atomic physics package, and an optical frequency comb, fully realizes an independent frequency standar...

We report on the implementation of quantum entanglement distribution and quantum state teleportation over a 14.4 km urban dark-fiber link, which is partially underground, partially overhead, and patched in several stations. We characterize the link for its use as a quantum channel and realize its active polarization stabilization. Using a type-II c...

We have measured the geopotential difference between two locations separated by 457 km by comparison of two optical lattice clocks via an interferometric fiber link, utilizing the gravitational redshift of the clock transition frequency. The 87 Sr clocks have been compared side-by-side before and after one of the clocks was moved to the remote loca...

Controlled charge flows are fundamental to many areas of science and technology, serving as carriers of energy and information, as probes of material properties and dynamics¹ and as a means of revealing2,3 or even inducing4,5 broken symmetries. Emerging methods for light-based current control5–16 offer particularly promising routes beyond the speed...

We present a system composed of an Er:laser-based ultra-low-noise frequency comb seeding a custom-designed photonic-crystal fiber with 2nJ pulse energies. A super-continuum is obtained spanning from 650nm to 2 µ m. System qualifications will be presented.

We present a transportable clockwork system capable of porting the optical spectral purity down to the microwave domain at the level of a few parts in 10 ⁻¹⁹ .

THz time-domain spectrometers are finding increasing applications in cutting-edge science and demanding industry environments. We present an industrialized THz spectrometer with enhanced high-power performance, and unprecedented flexibility for easy integration and turn-key operation.

The precise time and frequency transmissions based on optical fibre have evolved recently. The time and frequency transfer methods by GSSN are becoming gradually obsolete, definitely providing lower measurements than we can do. Yet, we do struggle with the best effotrt to enable clock comparison, and to utilize the experience with the fibre. An opt...

We demonstrate a stabilization scheme for dissipative Kerr solitons in SiN-resonators achieving high comb stability and long-term operation. Measuring 10Hz level absolute Kerr comb line stability (at 1 second) close to the pump, resulting in kHz level stability in the spectral domain of NIR astronomical spectrographs.

A radiation tolerant Erbium doped fiber comb has been demonstrated. Signals of the comb's fundamental frequencies did not degrade after Gamma radiation with an accumulated dose of 1 kGy, comparable to a decade of operation in a Mid-Earth Orbit.

We report a latest generation of the laser frequency comb (LFC) for astronomy. The new features include all fibercoupled, alignment-free filter cavities; specially designed photonic crystal fiber for spectral broadening; reflective spectral flattening systems. All the features ensure the long-term stability of the whole LFC system. The LFC is desig...

Advanced radiation tolerant Erbium doped fibers have been developed surviving an accumulated dose of 1 kGy∗. Femtosecond fiber lasers and amplifiers manufactured from such fibers have been packaged and irradiated under active operation to test for accelerated ageing with dose rates up to 10 mGy/s using a Cobalt 60 source. The laser output power deg...

We present a rack-mounted ultra-low-noise laser system for Sr lattice clocks, with spectral purity transfer stability of 4×10 ⁻¹⁸ @1s and 2×10 ⁻¹⁹ @100s. We realize a system stability of 5×10 ⁻¹⁶ @1s, representing state-of-the-art performance for rack-mounted commercial systems.

We present a compact, radiation tolerant, space frequency comb that is scheduled for an in-orbit-demonstration in low-earth-orbit with a launch in 2024.

Long-distance time and frequency transfer methods based on optical fibre links attractive both for very high-performance applications and also for many industrial and societal applications, and they complement and offer an alternative to radio- and satellite-based methods.

We report on a transportable and easy-to-operate optical clock utilizing the ²S1/2 - ²D3/2 transition of a single trapped ¹⁷¹Yb⁺ ion at 436 nm. Developed within a pilot project for quantum technology in Germany lead by industry, the clock is set up in two 19″ racks. In this way, transportation can easily be realized, and the large degree of automat...

Frequency combs downconvert absolute optical frequency references and thereby can significantly advance time and frequency precision in satellite-based navigation systems, fundamental science, earth observation, and many other spaceborne applications. We have developed a compact and vacuum compatible double comb system, thereby minimizing volume, m...

We present a fully phase-locked comb-disciplined-laser system, conceived to operate the Matter-wave Atomic Gradiometer Interferometric Sensor (MAGIS-100). Via phase-locking to the comb, four ECDLs and a Ti:Sapphire laser inherit the stability of an ultra-stable laser.

Long-distance time and frequency transfer methods based on optical fibre links have evolved rapidly in recent years, demonstrating excellent performance for frequency transfer and considerable promise for accurate time transfer. CLONETS-DS is a European Union-funded research and innovation action intended to facilitate the vision of a sustainable,...

Long-distance precise time and ultra-stable frequency transfer methods based on optical fibre have evolved rapidly in recent years, demonstrating excellent performance. CLONETS-DS is a European Union-funded research and innovation action intended to facilitate the vision of a sustainable, pan-European fibre network for time and frequency disseminat...

Aims. We study the 2D spectral line profile of the High Accuracy Radial Velocity Planet Searcher (HARPS), measuring its variation with position across the detector and with changing line intensity. The characterization of the line profile and its variations are important for achieving the precision of the wavelength scales of 10 ⁻¹⁰ or 3.0 cm s ⁻¹...

Aims. We study the 2D spectral line profile of HARPS (High Accuracy Radial Velocity Planet Searcher), measuring its variation with position across the detector and with changing line intensity. The characterization of the line profile and its variations are important for achieving the precision of the wavelength scales of 10^{-10} or 3.0 cm/s neces...

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...

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...

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical processes, and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectro...

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...

The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radial velocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial velocity measurement precisio...

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...

Frequency comb synthesized microwaves have been so far realized with tabletop systems, operated in well-controlled environments. Here, we demonstrate state-of-the-art ultrastable microwave synthesis with a compact rack-mountable apparatus. We present absolute phase noise characterization of a 12 GHz signal using an ultrastable laser at $\sim{194}\;...

We report the measurement of the frequency noise power spectral density (PSD) of a Terahertz (THz) molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL), and emitting 1 mW at 1.1THz in continuous wave. This is achieved by beating the ML frequency with the 1080th harmonic of the repetition rate of a 1560 nm frequency comb (...

Optical frequency measurements are among the most precise tools available to science. With the rapid advances in optical clocks now achieving a low 10⁻¹⁷ stability at 1 s and averaging down to the 10⁻¹⁹ level in a few hundred seconds, real-time sensing of subtle phenomena becomes essential. To render possible such measurements, we introduce real-ti...

We present DFG frequency comb systems operating between 3 and 5 pm based on femtosecond Er- and Yb-fiber laser-amplifier systems, providing an average power of up to 250 mW and 31 pW per comb mode with 1.5 Hz optical linewidths in the mid-IR.

A micro-integrated laser module has been developed for the deployment in a compact, transportable ¹⁷¹ Yb ⁺ optical clock. With this laser module, the clock laser system demonstrated a Modified Allan Deviation of less than 1.5×10 ⁻¹⁵ for 1 s ≤ 100 s when compared against a superior reference laser. © 2020 The Author(s)

We report the development of a field-deployable frequency comb operated as clockwork for transportable Sr-clocks. While referencing it at ~194.4THz, we characterize spectral lines at ~214.6THz. Prospects on complete Sr-lattice laser systems will be outlined.

We demonstrate an approach to dual-comb spectroscopy, based on dispersion engineered and ultra-broadband supercontinuum generation in photonic integrated nonlinear waveguides, and driven by low-noise fiber-laser combs. Both technologies are state-of-the-art and contribute to high-performance mid-infrared spectroscopy.

A robust optical clock was developed, integrated into two mobile 19” rack assemblies and based on the 2S1/2-2D3/2 transition of a single 171Yb+ ion. The system design and a first complete evaluation will be discussed.

We present a fully operational ultra-stable-laser system for cooling, trapping and manipulating Rydberg states in optical tweezer arrays of neutral Sr-atoms. Some CW-lasers are phase-coherently disciplined by an ultra-low-noise comb referenced to a sub-Hz ultra-stable-laser.

We report the development of a complete turn-key 5 × 10-16 ultra-stable laser system for operating neutral strontium atoms for optical lattice clocks or for quantum computing.

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...

The recent demonstration of a terahertz (THz) molecular gas laser pumped by a mid-infrared quantum cascade laser (QCL) has opened up new perspectives for this family of sources, traditionally relying on CO2-laser pumping. A so far open question concerning QCL-pumped THz molecular lasers (MLs) is related to their spectral purity. Indeed, assessing t...

Within the OPUS collaboration, we develop optical frequency references based on spectroscopy of the 1S0→3P1 intercombination line of 88Sr at 689 nm in thermal and laser-cooled strontium beams for operation on sounding rockets. One main objective is to identify suitable experimental setups and core components for a compact and robust strontium beam...

Optical atomic clocks require local oscillators with exceptional optical coherence owing to the challenge of performing spectroscopy on their ultranarrow-linewidth clock transitions. Advances in laser stabilization have thus enabled rapid progress in clock precision. A new class of ultrastable lasers based on cryogenic silicon reference cavities ha...

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical process and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectrosco...

The far-infrared (FIR) is one of the few wavelength ranges where no astronomical data with sub-arcsec resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. Information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, highly excited CO,...

In order to measure the two most important anthropogenic greenhouse gases CO2 and CH4 by means of the integrated path differential absorption (IPDA) lidar technique, stringent requirements with respect to the frequency stability of the transmitter need to be fulfilled In order to measure and optimize the frequency stability of the on-line and off-l...

The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken f...

We build a self-contained optical absolute frequency reference at 1064 nm based on the rovibronic transition R(56)32-0 in molecular iodine and operate this instrument in space on a sounding rocket mission. The frequency reference uses a microintegrated extended cavity diode laser and a quasimonolithic spectroscopy module for modulation transfer spe...

Improvements in atom-light coherence are foundational to progress in quantum information science, quantum optics, and precision metrology. Optical atomic clocks require local oscillators with exceptional optical coherence due to the challenge of performing spectroscopy on their ultra-narrow linewidth clock transitions. Advances in laser stabilizati...

Context. Convective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb. Aims. Precise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understa...

Convective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb. Precise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understanding of the at...

We present the progress towards a transportable photonic microwave synthesizer, porting ultra-high optical stability to a 12 GHz signal. The system is composed of two main sub-units: a 194 THz transportable ultra-stable laser with sub-Hz linewidth and an ultra-low noise optical frequency comb used for dividing such optical frequency to the microwav...

Methods for long-distance time and frequency transfer over optical fibers have demonstrated excellent performances and are evolving rapidly. CLONETS is a European Union-funded coordination and support action intended to facilitate the vision of a sustainable, pan-European optical fiber network for precise time and frequency reference dissemination.

We demonstrate a broadband mid-infrared dual-comb spectroscopy for parallel gas-phase detection in the functional group region from 2800–3600 cm−1, using dispersion engineered silicon nitride dual-core waveguides which produce broadband, intensity-enhanced and coherent mid-infrared frequency combs.

We report on a feed-forward method for compensating phase drifts occurring in multi-branch frequency combs. Tracking the optical phase and compensating the drifts, we demonstrate comb accuracy and stability below 10-19 in less than 100s.

Context. Granular convective motions reach into the lower solar atmosphere, typically causing photospheric spectral lines to exhibit a differential line shift. This Doppler shift to shorter wavelengths is commonly known as convective blueshift. Aims. Spectroscopic high-accuracy measurements provide us with a refined determination of the absolute co...

Granular convective motions reach into the lower solar atmosphere, typically causing photospheric spectral lines to exhibit a differential line shift. This Doppler shift to shorter wavelength is commonly known as convective blueshift. We performed systematic observations of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the...