Today's Carrier-Envelope Phase (CEP) stabilizations of mode-locked oscillators widely used in attosecond science and frequency metrology rely on octave spanning frequency combs and the detection of beating between the blue end and the frequency doubled red end of the same spectrum. This technique was established by the seminal works of Hänsch and co-workers [1], demonstrating the stabilization of optical frequencies from such a frequency comb by transferring the slippage of the CEP (or carrier-envelope offset frequency) into a detectable radio frequency by f-2f interferometry. The requirement of an octave spanning spectrum means that usually some kind of super-continuum generation is involved, which, in practice often is a fragile scheme since wide band oscillators are very prone to instabilities and noise.

The availability of broadband extreme ultraviolet light sources allows for investigation of electron wave-packets from high lying bound states in atoms [1], [2]. The dynamics of these states can be mapped out in the ionization continuum with an overlapping infrared field, which may also uncover new, light induced, dressed states [3]. Here, we carry out a complete characterization of these electron wave-packets using a small number of attosecond pulses.

Above-threshold ionization spectra from cesium are measured as a function of the carrier-envelope phase (CEP) using laser pulses centered at 3.1  μm wavelength. The directional asymmetry in the energy spectra of backscattered electrons oscillates three times, rather than once, as the CEP is changed from 0 to 2π. Using the improved strong-field approximation, we show that the unusual behavior arises from the interference of few quantum orbits. We discuss the conditions for observing the high-order CEP dependence, and draw an analogy with time-domain holography with electron wave packets.

One of the most widespread and reliable techniques for spectral phase characterization of optical elements is spectrally resolved interferometry (SRI) [1] , [2] , which utilizes a two-arm interferometer illuminated by a broadband light source and a spectrometer to record the generated spectral fringes. The investigated optical element is placed in one arm, and its spectral phase can be extracted by using Fourier-transform (FT) based methods [3] , [4] for instance, which are the most accurate, even when low dispersion values are to be determined. One detriment to this evaluation method, that it requires high spectral resolution. Considering that most of the spectrometers in the mid-infrared (MIR) region have typically a few nm spectral resolution, we propose two alternative methods for measurements in this spectral region.

We present a carrier-envelope phase (CEP)-stable Yb-doped fiber laser system delivering 100 µJ few-cycle pulses at a repetition rate of 100 kHz. The CEP stability of the system when seeded by a carrier-envelope offset-locked oscillator is 360 mrad, as measured pulse-to-pulse with a stereographic above-threshold ionization (stereo-ATI) phase meter. Slow CEP fluctuations have been suppressed by implementing a feedback loop from the phase meter to the pulse picking acousto-optic modulator. To the best of our knowledge, this is the highest CEP stability achieved to date with a fiber-based, high-power few-cycle laser.

We present a CEP-stable Yb:fiber-based laser system delivering 100 μJ few-cycle pulses at the repetition rate of 100 kHz. The reported system is based on a highly scalable in terms of average power and pulse energy concept of a fiber chirped-pulse amplifier (CPA) combined with a hollow-core fiber compression stage. The same concept and similar components are employed by the ELI-ALPS HR1 [1].

We demonstrate the complete reconstruction of the electric field of visible-infrared pulses with energy as low as a few tens of nanojoules. The technique allows for the reconstruction of the instantaneous electric field vector direction and magnitude, thus giving access to the characterisation of pulses with an arbitrary time-dependent polarisation state. The technique combines extreme ultraviolet interferometry with the generation of isolated attosecond pulses.

Nature Photon. 11, 383–389 (2017); published online 29 May 2017; corrected after print 29 June 2017. In the version of this Article originally published, the following sentences were missing from the Acknowledgements: “Financial support by the Alexander von Humboldt Foundation (Project Tirinto) and the Italian Ministry of Research (project FIRB no.

Summary form only given. Today, carrier-envelope-phase (CEP) stable laser pulses have become a versatile tool for a plethora of scientific applications. Many years their generation relied on either optical parametric amplification or the use of titanium-sapphire amplifiers. Although impressive results have been achieved using these technologies [1, 2], their main drawback is the restricted average power (and therewith repetition rate for a given energy) due to thermo-optical limitations. Here we report on another approach, the nonlinear compression of ultrafast ytterbium-based high-power fiber lasers [3]. The first commercially available source employing this technology is the HR1 laser constructed for the ELI-ALPS research facility in Szeged, Hungary. The Extreme Light Infrastructure (ELI) is currently being installed in several European countries aiming to provide unique user facilities with beyond state-of-the-art laser systems. The attosecond facility ELI-ALPS in Szeged, for example, will host several laser systems that will be used for attosecond pulse generation at unprecedented pulse parameters (energy and repetition rate). One of these laser systems is the HR1 (high repetition rate) laser that targets pulse parameters of 1mJ, 6fs pulses at 100kHz repetition rate (100W average power) and with CEP stable operation in its first implementation phase.We will show detailed measurements and characterization of the CPA system as well as the compression unit. General scaling properties of hollow-fiber compressors towards multi-mJ operation at kW-level average powers will be discussed. Furthermore, a detailed discussion on the CEP stabilization of the system will be given and supported by the latest measurement results using a stereo ATI device.

The carrier-envelope phase (CEP) dependence of few-cycle above-threshold ionization (ATI) of Xe is calibrated for use as a reference measurement for determining and controlling the absolute CEP in other interactions. This is achieved by referencing the CEP-dependent ATI measurements of Xe to measurements of atomic H, which are in turn referenced to ab initio calculations for atomic H. This allows for the accurate determination of the absolute CEP dependence of Xe ATI, which enables relatively easy determination of the offset between the relative CEP measured and/or controlled by typical devices and the absolute CEP in the interaction.