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Methods for long-distance time and frequency transfer over optical fibres 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 fibre network for precise time and frequency reference dissemination.

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 spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for ultra-broadband and flat-envelope mid-IR frequency combs. Our mid-IR dual-comb spectrometer has an instantaneous bandwidth covering the functional group region from 2800 – 3600 c m − 1 , comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, sub-Doppler spectral resolution, and a high speed. In addition to the traditional functional groups, their isotopologues are also resolved in this supercontinuum-based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signaling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.

We report on a Er:fiber-based optical frequency comb transferring the stability of ultra-stable lasers from 194THz to 429THz. Sub-Hz level transfer to a fiber-delivered 698.44nm output port for future Strontium QPN-limited lattice clocks is demonstrated

We report on a transportable photonic microwave synthesizer comprising an ultrastable laser and a ultra-low noise frequency comb. The last acts as a frequency divider, transferring the spectral purity from the optical to microwave domain.

A Tm-doped fiber chirped-pulse amplifier delivers 60 W average power at 100 MHz pulse-repetition rate and

The advent of long-term stable ultra-low noise (ULN) frequency combs opens new prospects for precision measurements. We characterize the stability of such ULN combs and present dual-comb precision spectroscopy of molecules and cavities.

We report on a Er:fiber-based optical frequency comb transferring the stability of ultrastable lasers from 194THz to 429THz. Sub-mHz level transfer to a fiber-delivered 698.44nm output port for future Strontium QPN-limited lattice clocks is demonstrated.

The Optical Frequency Comb (OFC) represents a cornerstone of precision metrology, because it provides a clockwork to down-convert hundreds of THz of optical frequency standards to the countable and traceable radio frequency (RF) domain. In particular, for a future redefinition of the Coordinated Universal Time by an optical atomic transition [1], it will be an essential ingredient. Nowadays, narrowband optical transitions show relative stability and accuracy on the level of 10−18 [2, 3] and the comb has to keep pace in order not to add noise or instability. While there are schemes to mix out noise related to the comb by appropriate RF techniques, modern ultra-low noise frequency combs may advantageously be used with much reduced complexity.

We report on an ultra-low noise optical frequency comb simultaneously stabilized at its carrier-envelope offset frequency and one optical mode, using a novel electro-optic group-velocity shifter with a fix-point in the optical domain with nanosecond response time.

We report on an all-PM mode locked 2-μm central wavelength fiber laser oscillator based on Thulium/Holmium codoped gain fiber supporting femtosecond pulses at MHz-repetition rate.

We demonstrate a sub-100-fs, 5.2-micrometer parametric amplifier driven by a ps 2.1-micrometer Ho:YAG chirped-pulse amplifier and its application to high harmonic generation. We also present a novel approach for further pulse compression.

110-fs, 5.3-μm parametric amplifier driven by a ps 2.1-μm Ho:YAG chirped-pulse amplifier is demonstrated. It offers an all-in-one solution for seeding, pumping, and CEP-stabilization of few-cycle pulses in ZnGeP 2 and similar mid-IR crystals.

A compact all-polarization maintaining 2.05 μm fiber laser system emitting femtosecond pulses at 1-MW peak power is studied and applied to dielectric laser acceleration of non-relativistic electrons obtaining acceleration gradients up to ∼ 50 MeV/m.

A method for analyzing the statistical nature of laser noise is demonstrated. By application to CEP noise characteristics, the method is shown to enable discriminating between deterministic technical and stochastic quantum noise contributions.

A novel broadband 6-um parametric amplifier driven by a fs 2.1-um Ho:YAG chirped-pulse amplifier is demonstrated. It offers an all-in-one solution for seeding, pumping, and CEP-stabilization of few-cycle pulses in ZnGeP2 and similar mid-IR crystals.

We have optically compared two fiber-based frequency combs with ultra-high stability. The resulting beat frequency shows integrated phase noise below 100 mrad (100Hz to 2MHz) and an overlapping Allan deviation of 1×10−16 at 1s, dropping below 1×10−18 at 500s.

Laser frequency combs have found their way from laboratory spectroscopy into astronomy to serve as calibrators for spectrographs. Boosting the precision available in astronomical spectroscopy, this might pave the way to many new discoveries. In this tutorial we give an overview on this recent development.

We report a novel source for mid-IR nonlinear spectroscopy in the molecular fingerprint spectral range based on a white-light-seeded ZnGeP2 OPA tunable in the 3-4.2 µm (signal) and 4.2-7 µm (idler) range and pumped by a 1-ps 2090-nm Ho:YAG laser.

We have locked fceo and frep of an all-PM 250 MHz Er:fiber femtosecond frequency comb with a bandwidth exceeding 1 MHz. This results in record-low integrated phase noise of 68 mrad and 55 mrad respectively.

We have developed compact ultrafast laser sources for a wide variety of applications, including quality control and optical frequency combs for precision measurements. Fields ranging from astronomical observatories to spaceflights, optical clocks or long distance links are served with this technology.

We report on an oscillator seeded all-PM fiber based 2.05 µm CPA system emitting 371 fs pulses at 1 MHz and 1 MW peak power without the need of LMA amplifier or complex temporal management.

We demonstrate the generation of broadband, visible astronomical frequency combs with flattened spectral envelopes. The flat-top region of the spectrum ranges from about 450 to 730 nm, at mode spacings of 18 and 25 GHz.

A novel class of high energy ultrafast OPCPA system at 7 μm, pumped by an optically synchronized and Tm:fiber pumped 2 μm picosecond Ho:YLF CPA system, delivers mJ-level pulses supporting a sub-4 optical cycle duration.

We report on a compact coherent All-PM fiber laser amplifier system at around 2.03 mm running at 100 MHz delivering broadband pulses at 290 mW average power and pulse duration down to 128 fs.

We measured relative envelope jitter of two fiber comb lasers, each with one comb line phase locked to a CW optical phase reference. Integrated jitter is 0.9fs RMS from 10Hz to 2MHz.

We report on an all-PM fiber oscillator-CPA system at 2.08 µm running at 7 MHz pulse repetition rate with 10 nJ pulse energy and 390 fs pulse duration behind external compression.

We characterize a GPS carrier-phase link with 450 km baseline, using a long-distance phase-stabilized optical fiber link. Active hydrogen masers at both ends are compared via both links simultaneously. This allows us to assess the instability and accuracy of the GPS link with sub-10^-15 resolution.

Optical frequency transfer via a 1840 km fiber link has been investigated. Twenty fiber amplifiers and two fiber Brillouin amplifiers are needed to compensate for 420 dB of loss. Active noise compensation reduces the instability to 2.7 × 10−15 at 1 s with 4 × 10−19 after 100 s and an accuracy of a few parts in 1019.

We present OSCAT laser systems as a general tool for pump and probe experiments. The current development offers unlimited temporal scanning range using the intracavity motor and a rapid scan mode with a range of 100 ps.

Harmonics up to order 21 generated in Xe are coupled out of a 78-MHz enhancement cavity with a fused silica Brewster plate. An irreversible degradation of the plate, accelerated by the generated harmonics, is observed.

We discuss promising high-field applications of a CEP-stable parametric wave synthesizer producing three-color phase-locked tunable frequency pulses. The asymmetric waveform reproducibility is confirmed in the measurements of ATI and THz transients.

We demonstrate high-gain broadband amplification in Yb:CaF2 crystal pumped with a bright source based on an ultra-large-core PCF-rod. 3-fold single-pass gain was obtained in a 10-mm Yb:CaF2, which significantly outperforms any cw-diode-pumped scheme.

We report on high-power, ultrafast enhancement cavity designs with enlarged laser spots on the mirrors. Together with a novel seeding Yb-fiber based CPA, MW-level intra-cavity average powers with sub-ps pulse durations come into reach.

Directional electron generation asymmetry is measured using incommensurate-frequency multicolor pulses that are carrier-envelope-phase-locked. The demonstrated Yb-laser-pumped OPA technology produces a shot-to-shot-stable femtosecond field combining three carrier frequencies that can be set to an arbitrary ratio.

We demonstrate direct full-octave spanning frequency comb generation via four-wave mixing in continuous wave laser pumped microresonators for the first time. The generated comb lines are fully tunable over more than one free spectral range.

An Yb-fiber frequency comb was developed and employed to calibrate an astronomical spectrograph. The repeatability was photon noise limited at 300kHz. Absolute accuracy was improved by a factor of 20 compared to traditional calibration sources.

Using only a short piece of gain fiber, a 570 MHz Yb-fiber oscillator was set up and mode-locked via NPE, assisted by spectral filtering. Tuning the filter enables changing both center wavelength or optical bandwidth.

We use low finesse Fabry-Perot cavities in series to generate frequency combs with large mode spacing by simultaneously maintaining high spectral bandwidth. The attenuation of laser modes closest to the pass band exceeds 70 dB relative to the modes centered within the pass band for a 5 GHz Fabry-Perot filtering a 250 MHz frequency comb.

We present a simple method that enables fast, broadband spectroscopy at sub-Megahertz resolution over ≫4 THz bandwidth using a mode-hop-free tunable diode laser and a frequency comb. This scheme is utilized to measure microresonator dispersion.

In order to compare optical frequency standards over large distances PTB and MPQ are establishing an optical fiber link of more than 900 km length. We report the intermediate results of this project.

Frequency Combs are optimized for larger mode spacing by mode filtering, or with Kerr combs generated in micro toroids. New applications include precision calibration of astronomical spectrometers or the synchronisation of atomic clocks over large distances.

We show that optical sidebands generated via optical-parametric-oscillations in an on-chip microcavity are equidistant thus overcoming intrinsic cavity dispersion. This leads to generation of optical-frequency combs at input powers

It is shown that the cascaded optical sidebands generated via optical parametric oscillations in a monolithic microcavity are equidistant and lead to the generation of femtosecond pulses in time domain.

We present low temperature grown InGaAs multiple-quantum well structures which are successfully applied as transmitters and receivers in THz time domain systems. Operation at telecom wavelengths of 1.55µm with a femtosecond fiber laser is demonstrated.

It is shown that the cascaded optical sidebands generated via optical parametric oscillations in a monolithic microcavity are equidistant down to a resolution bandwidth limited level of 2 kHz. (Nonlinear Optics: Materials, Fundamentals and Applications, 2007) Article not available.

The evolution of the carrier-envelope phase was fully electronically controlled in a train of sub-6-fs pulses and characterized for a train of sub-5-fs pulses. Optical waveform synthesis will soon enable the control of strong field nonlinear interactions on a time scale shorter than the optical cycle.

6-fs, 1-MW laser pulses have been produced at the full repetition rate of a mode-locked laser upon simultaneous synthesization of phase-locked laser modes over the spectral range extending from 500 nm to 1100 nm, opening the door to the measurement and stabilization of the absolute phase of few-cycle light pulses by use time- and frequency-domain techniques, respectively.