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Weit uber werbende Auftritte hinaus ist die Grundung einer Privatklinik eine interessante Moglichkeit, neue Betatigungsfelder zu erschliesen. Hierbei sind weitreichende Gestaltungsoptionen hinsichtlich der Rechtsform und des Grunderkreises moglich. So kann etwa die zulassige Einbindung von Investoren neue Chancen bieten. Auch im Hinblick auf die Frage der Liquidation der durchgefuhrten Behandlungen eroffnen sich neue Wege. Die Abrechnung von zuvor mit der Privatklinik vereinbarten Pauschalhonoraren ist unter Beachtung gewisser Voraussetzungen nach vorliegender Auffassung moglich. Eine Bindung an die Gebuhrenordnung fur Arzte (GOA) in diesem Fall also nicht zwingend. So ermoglichen die Grundung und der Betrieb einer Privatklinik auf verschiedenen Ebenen neue und interessante Handlungsoptionen.

Ultralow phase-noise mode-locked lasers are crucial for real-world applications. We present two accomplishments: (1) short-term FF CEP stabilization of a SESAM mode-locked Er:Yb:glass laser at 1.55 um with timing jitter below 3 as (1-3 MHz) and (2) a hybrid solution adding a FB technique addressing slowly varying sources of interference to the FF system that demonstrates 75 hours of stabilization with a minimally detrimental effect amounting to a timing jitter of 11 as.

OSA continuum 4(6), 1889 - 1896 (2021). doi:10.1364/OSAC.424340, We present a comparison of two low-noise carrier-envelope offset (CEO) frequency stabilization methods studied using an ytterbium (Yb) fiber laser oscillator based on a nonlinear amplifying loop mirror. We first investigate the phase locking performance achieved with cross-gain modulation (XGM) via injection of an auxiliary low-power continuous-wave (CW) laser into the fiber gain medium. Amplification of the injected CW laser light cross-modulates the gain of the oscillator, resulting in an intra-cavity power modulation, thus providing control of the CEO frequency. The XGM method is then compared with the conventional pump-current modulation scheme. Both stabilization methods provide similar locking performances with sub-200-mrad of integrated residual carrier-envelope-phase (CEP) noise (10 Hz to 1 MHz), suitable for high-resolution comb spectroscopy applications., Published by OSA, Washington, DC

We develop an Arrival Time Monitor (ATM) achieving high sensitivity for soft X-ray pulses in low-fluence conditions. The ATM cross-correlates ultrashort X-ray with 800nm laser pulses using a new multi-layer target designed and grown in-house to achieve optimal sensitivity.

A major design goal for femtosecond fiber lasers is to increase the output power but not at the cost of increasing the noise level or narrowing the bandwidth. Here, we perform a computational study to optimize the cavity design of a femtosecond fiber laser that is passively modelocked with a semiconductor saturable absorbing mirror (SESAM). We use dynamical methods that are more than a thousand times faster than standard evolutionary methods. We show that we can obtain higher pulse energies and hence higher output powers by simultaneously increasing the output coupling ratio, the gain, and the anomalous group delay dispersion. We can obtain output pulses that are from 5 to 15 times the energy of the pulse in the current experimental design with no penalty in the noise level or bandwidth.

We present carrier-envelope phase stabilization of an Er:Yb:glass laser at 1.55 pm via the feed-forward method with 2.9 as (1 Hz - 3 MHz) timing jitter and continuous stabilization over 24 hours.

We present the new drive laser system for the photo-injector of the LCLS-II XFEL at SLAC, including the first commissioning results and challenges encountered due to high power, high repetition rate ultraviolet laser operation.

We present a flexible figure-9 Yb: fiber-laser and investigate the impact of intra-cavity group delay dispersion on amplitude/phase noise. We show that the free-running carrier-envelope-offset frequency short-term linewidth can range from several MHz to

We demonstrate the first frequency comb laser absorption spectroscopy in an industrial environment. Recent advancements in robust frequency comb design enabled installation of the sensor in an operating power plant, where we simultaneously measured temperature, H 2 O and CO 2 concentration in the exhaust of a 16 MW stationary gas turbine. The frequency comb laser spectrometer probed 16,000 individual wavelengths of light spaced by 0.007 cm −1 (0.0014 nm) near 1440 nm, spanning 279 absorption features of H 2 O and 43 features of CO 2 . Fits to the measured absorption spectra yield simultaneous temperature, H 2 O and CO 2 concentrations with between 10 and 60 second time resolution. Measurements over a 5 hour period tracked variations in the exhaust consistent with various changes to the gas turbine operation. Much larger wavelength ranges (200+ nm) and different time resolutions are possible depending on the desired precision by changing various settings on the same spectrometer. Overall, this work demonstrates the potential for frequency comb laser absorption spectroscopy in industrial combustion environments.

Dual-comb spectroscopy systems based on two pulse trains emitted from a single laser cavity benefit from passive mutual coherence between the two pulse trains, which leads to common-mode noise cancellation in the down converted radio-frequency (RF)-comb [1]. Due to their robustness, single cavity dual-color/dual-comb fiber lasers are promising candidates for such spectroscopy systems [2,3]. Here, we present a novel method to generate two pulse trains out of a single fiber laser cavity based on mechanical spectral filtering, which offers two key features: dynamical adjustment of the spectral separation between the two pulse trains and tuning of the difference in repetition rates. After demonstrating the concept in a 23-MHz nonlinear polarization evolution (NPE) mode-locked ytterbium (Yb) laser [4], we have now for the first time implemented this concept in a nonlinear amplified loop mirror (NALM) mode-locked all-polarization maintaining (PM) Yb:fiber laser operating at a repetition rate of 77 MHz, thus improving both the stability as well as the non-aliasing dual-comb bandwidth. The laser contains a free-space arm with a transmission grating compressor, in which the spectral components of the intra-cavity light are spatially dispersed (Fig.1(a)). By introducing a small beam block into the grating compressor, we split the spectrum into two separate regions. We show that these two spectral regions can be independently mode-locked, thus creating two pulse trains with slightly different repetition rates (Fig.1(b-d)). Due to the spatial distribution of the spectral components, we can vary the width of the spectral cut between the two spectra by rotating the beam block (Fig. 1(b), blue curves). Furthermore, adjusting the grating spacing (and thus the amount of dispersion) allows us to tune the difference in the repetition rate Δf rep from 1–6 kHz (Fig. 1(e)). After spectral separation at the cavity output, the pulse centered around 1030 nm is amplified and broadened in a nonlinear fiber to create a spectral overlap with the 1060 nm-pulse (Fig. 1(f)). The overlapping spectrum is bandpass-filtered around 1055 nm and sent onto a photodiode (PD). An oscilloscope trace of the PD output shows interferograms (Fig. 1(f), inset) occurring with a periodicity of 1/Δf rep , which correspond to the Fourier-transform of the down-converted RF comb that is generated by the beating of both optical combs.

We demonstrate the generation of a tunable single-cavity dual-comb out of an all-polarization-maintaining ytterbium fiber laser via spectral subdivision. The feasibility of spectroscopy measurements is demonstrated by measuring the transmission of a 5-mm thick etalon.

Few-cycle pulsed laser technology highlights the need for control and stabilization of the carrier-envelope phase (CEP) for applications requiring shot-to-shot timing and phase consistency. This general requirement has been achieved successfully in a number of free space and fiber lasers via feedback and feed-forward methods. Expanding upon existing results, we demonstrate CEP stabilization through the feed-forward method applied to a SESAM mode-locked Er:Yb:glass laser at 1.55 um with a measured ultralow timing jitter of 2.9 as (1 Hz - 3 MHz) and long-term stabilization over a duration of eight hours. Single-digit attosecond stabilization at telecom wavelengths opens a new direction in applications requiring ultra-stable frequency and time precision such as high-resolution spectroscopy and fiber timing networks., Comment: 4 pages, 4 figures, submitted to Optics Letters

Optical frequency combs have revolutionized optical frequency metrology and are being actively investigated in a number of applications outside of pure optical frequency metrology. For reasons of cost, robustness, performance, and flexibility, the erbium fiber laser frequency comb has emerged as the most commonly used frequency comb system and many different designs of erbium fiber frequency combs have been demonstrated. We review the different approaches taken in the design of erbium fiber frequency combs, including the major building blocks of the underlying mode-locked laser, amplifier, supercontinuum generation and actuators for stabilization of the frequency comb.

We design and realize an arrival time diagnostic for ultrashort X-ray pulses achieving unprecedented high sensitivity in the soft X-ray regime via cross-correlation with a ≈1550 nm optical laser. An interferometric detection scheme is combined with a multi-layer sample design to greatly improve the sensitivity of the measurement. We achieve up to 275% of relative signal change when exposed to 1.6 mJ/cm2 of soft X-rays at 530 eV, more than a hundred-fold improvement in sensitivity as compared to previously reported techniques. The resolution of the arrival time measurement is estimated to around 2.8 fs (rms). The demonstrated X-ray arrival time monitor paves the way for sub-10 fs-level timing jitter at high repetition rate X-ray facilities.

With the progress in the development of optical frequency standards grows the demand for the dissemination of stable optical frequencies. To date, optical fiber links constitute the most promising medium to bridge large geographical distances while still maintaining a high degree of frequency stability and accuracy. We investigated the transfer of an optical frequency along different fiber links during the past years and achieved a fractional instability and uncertainty at a level lower than 10 − 19 using fiber links with lengths of up to almost 2000 km. We give an overview of different techniques and methods that can be used in combination with optical fiber links to achieve a stable frequency transfer. The results of different fiber links are summarized and an outlook of future links is given.

Using aluminum-nitride photonic-chip waveguides, we generate optical-frequency-comb supercontinuum spanning from 500 nm to 4000 nm with a 0.8 nJ seed pulse, and show that the spectrum can be tailored by changing the waveguide geometry. Since aluminum nitride exhibits both quadratic and cubic nonlinearities, the spectra feature simultaneous contributions from numerous nonlinear mechanisms: supercontinuum generation, difference-frequency generation, second-harmonic generation, and third-harmonic generation. As one application of integrating multiple nonlinear processes, we measure and stabilize the carrier-envelope-offset frequency of a laser comb by direct photodetection of the output light. Additionally, we generate ~0.3 mW in the 3000 nm to 4000 nm region, which is potentially useful for molecular spectroscopy. The combination of broadband light generation from the visible through the mid-infrared, combined with simplified self-referencing, provides a path towards robust comb systems for spectroscopy and metrology in the field., 8 pages, 5 figures

We utilize silicon-nitride waveguides to self-reference a telecom-wavelength fiber frequency comb through supercontinuum generation, using 11.3 mW of optical power incident on the chip. This is approximately ten times lower than conventional approaches using nonlinear fibers and is enabled by low-loss (

The power efficiency of femtosecond fiber lasers with semiconductor saturable absorbers is limited by the wake instability. We computationally optimize the output power and efficiency by increasing the output coupling ratio and gain fiber length.

Optics express 27(20), 28062 - (2019). doi:10.1364/OE.27.028062, We demonstrate dual-comb generation from an all-polarization-maintaining dual-color ytterbium (Yb) fiber laser. Two pulse trains with center wavelengths at 1030 nm and 1060 nm respectively are generated within the same laser cavity with a repetition rate around 77 MHz. Dual-color operation is induced using a tunable mechanical spectral filter, which cuts the gain spectrum into two spectral regions that can be independently mode-locked. Spectral overlap of the two pulse trains is achieved outside the laser cavity by amplifying the 1030-nm pulses and broadening them in a nonlinear fiber. Spatially overlapping the two arms on a simple photodiode then generates a down-converted radio frequency comb. The difference in repetition rates between the two pulse trains and hence the line spacing of the down-converted comb can easily be tuned in this setup. This feature allows for a flexible adjustment of the tradeoff between non-aliasing bandwidth vs. measurement time in spectroscopy applications. Furthermore, we show that by fine-tuning the center-wavelengths of the two pulse trains, we are able to shift the down-converted frequency comb along the radio-frequency axis. The usability of this dual-comb setup is demonstrated by measuring the transmission of two different etalons while the laser is completely free-running, Published by Soc., Washington, DC

We demonstrate frequency comb based, robust, long-term conversion of optical frequency standards to an optical timescale that outputs a 1 pulse per second (PPS) optical time signal at a defined reference plane. This level of robustness is essential for time standards based on optical clocks.

We computationally study wake modes in a fiber comb laser with a slow saturable absorber. We show that these modes will lead to the experimentally-observed sidebands, and we predict the laser's stable operating regime.

We develop a system to convert the high frequency accuracy of optical clocks to an optical timescale that outputs a 1 pulse per second (PPS) optical time signal at a defined reference plane.

Passively mode-locked lasers with semiconductor saturable absorption mirrors are attractive comb sources due to their simplicity, excellent self-starting properties, and their environmental robustness. These lasers, however, can have an increased noise level and wake mode instabilities. Here, we investigate the wake mode dynamics in detail using a combination of evolutionary and dynamical methods. We describe the mode-locked pulse generation from noise when a stable pulse exists and the evolution of the wake mode instability when no stable pulse exists. We then calculate the dynamical spectrum of the mode-locked pulse, and we show that it has six discrete eigenmodes, two of which correspond to wake modes. The wake modes are unstable when the wake mode eigenvalues have a positive real part. We also show that even when the laser is stable, the wake modes lead to experimentally observed sidebands.

We transferred an optical frequency along a 1840km fiber link and achieved an instability of 3x10^-15 at 1s with 4x10^-19 after 100s. The transferred frequency shows no systematic offset within an uncertainty of 3x10^-19. Detailed analysis revealed a t^-2 response in the modified Allan deviation.

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.

We demonstrate optical frequency transfer over an 1840 km underground optical fiber link using a single-span stabilization. To compensate for more than 420 dB of optical attenuation of the light we use twenty Erbium doped fiber amplifiers along the entire link and two additional fiber Brillouin amplifiers. The good passive stability of our fiber link allows us to reach short term instabilities expressed as the modified Allan deviation of 3 × 10-15 for a gate time τ of 1 s reaching 4 × 10-19 in just 100 s. By comparing the sent and transferred frequencies we find no systematic offset within the statistical uncertainty of about 3 × 10-19. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a τ-2 slope in the modified Allan deviation.

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.

Synchronize Watches Time standards based on the energy-level transitions of atoms and ions provide the most accurate and precise methods of time keeping. Measurements made in one laboratory and in another must be done with clocks that have been synchronized and calibrated to ensure that the same measurement is being made. Such clocks, however, are not particularly mobile and are housed in national metrology labs. Predehl et al. (p. 441; see the Perspective by Warrington ) linked two optical clocks separated by over 900 kilometers using optical fiber to show that the clocks can be synchronized, with the clocks showing a frequency stability better than 3.7 × 10 −19 . Such long-distance synchronization should allow for tests of fundamental physics, such as general relativity and quantum electrodynamics.

When comparing independent simultaneous measurements of the same, non-constant frequency, synchronization errors between the frequency counter's gate time intervals lead to an apparent frequency deviation between the measurements. Here we present a technique that allows for a remote measurement of the counters' synchronization offset with sub-microsecond accuracy using a phase-stabilized fiber link.

Optical frequency transmission via phase-stabilized telecommunication fiber is currently the most precise technique available for disseminating frequencies. We summarize some key advances, results and applications for fiber networks spanning up to 1000 km.

In this chapter we describe, how ZIMPLis used as an algebraic modeling language for mixed-integer linear programs (MIPs) at the INFORM GmbH (Aachen, Germany). We firstly give an overview of ZIMPL, thereby motivating the choice of ZIMPL for modeling a production planning problem. Besides depicting the role of ZIMPLduring the development and training process of optimization software at INFORM, we show explicitly how a basic model of a production planning problem, the MLCLSP, can be modeled with ZIMPL, thereby demonstrating its ease-of-use and some of its features.

We aim at distributing the most precise frequency references provided by optical clocks, both from specialized labs to end users, and between specialized labs for comparing optical clocks. Transmitting an optical carrier over standard telecom fibre, we have transported frequency information over up to 900 km distance, with fidelity close to theoretical limits and reaching a precision of a few parts in 1018.

In this article a set of guidelines for the design of genetic operators and the representation of the phenotype space is proposed. These guidelines should help to systematize the design of problem-specific evolutionary algorithms. Hence, they should be particularly beneficial for the design of genetic programming systems.

Optical frequency transfer via a 920 km fiber link has been investigated. Active noise compensation enables the transfer of a stable optical frequency with a stability of 3.8 × 10−14 at 1 s reaching 4 × 10−18 after 104 s and an accuracy of 3.6 × 10−19.

We demonstrate a low-noise carrier-envelope-offset frequency stabilized all-PM Yb:fiber oscillator. Two different stabilization methods lead to sub 200 mrad integrated fo phase noise (10 Hz to 1 MHz), suitable for comb spectroscopy applications. © 2019 The Author(s)

We reference high-precision spectroscopy on atomic hydrogen measured with an uncertainty of 4×10−15 to a remote Cs-fountain clock using a 920 km actively noise-compensated fiber link.