Abstract-Waveform nonlinear optics aims to study and control the nonlinear interactions of matter with extremely short optical waveforms custom-tailored within a single cycle of light. Different technological routes to generate such multimillijoule sub-opticalcycle waveforms are currently pursued, opening up unprecedented opportunities in attoscience and strong-field physics. Here, we discuss the experimental schemes, introduce the technological challenges, and present our experimental results on high-energy sub-cycle optical waveform synthesis based on (1) parametric amplification and (2) induced-phase modulation in a two-color-driven gas-filled hollow-core fiber compressor. More specifically, for (1), we demonstrate a carrier-envelope-phase (CEP)-stable, multimillijoule three-channel parametric waveform synthesizer generating a >2-octave-wide spectrum (0.52-2.4 μm). After two amplification stages, the combined 125-μJ output supports 1.9-fs FWHM waveforms; energy scaling to >2 mJ is achieved after three amplification stages. FROG pulse characterization of all three second-stage outputs demonstrates the feasibility to recompress all three channels simultaneously close to the Fourier limit and shows the flexibility of our intricate dispersion management scheme for different Manuscript received January 23, 2015; revised April 16, 2015; accepted April 21, 2015. This work was supported by the Center for Free-Electron Laser Science at DESY, the excellence cluster "The Hamburg Centre for Ultrafast Imaging-Structure, Dynamics and Control of Matter at the Atomic Scale" of the Deutsche Forschungsgemeinschaft, the ERC-Synergy grant AXSIS under Grant 609920, and by JRA-INREX from LASERLAB-EUROPE under Grant 284464, ECS Seventh Framework Programme. The work of C. Manzoni was supported by MIUR FIRB under Grant RBFR12SW0J. experimental situations. For (2), we generate CEP-stable 1.7-mJ waveforms covering 365-930 nm (measured at 1% of the peak intensity) obtained from induced-phase modulation in a two-colordriven gas-filled hollow-core fiber. Using custom-designed doublechirped mirrors and a UV spatial light modulator will permit compression close to the 0.9-fs FWHM transform limit. These novel sources will become versatile tools for controlling strong-field interactions in matter and for attosecond pump-probe spectroscopy using VIS/IR and XUV/soft-X-ray pulses.Index Terms-Ultrabroadband sources, parametric oscillators and amplifiers, gas-filled hollow-core fiber pulse compression, pulse synthesis, waveform nonlinear optics.
Attosecond science promises to reveal the most fundamental electronic dynamics occurring in matter and it can develop further by meeting two linked technological goals related to high-order harmonic sources: improved spectral tunability (allowing selectivity in addressing electronic transitions) and higher photon flux (permitting to measure low cross-section processes). New developments come through parametric waveform synthesis, which provides control over the shape of field transients, enabling the creation of highly-tunable isolated attosecond pulses via high-harmonic generation. Here we demonstrate that the first goal is fulfilled since central energy, spectral bandwidth/shape and temporal duration of isolated attosecond pulses can be controlled by shaping the laser waveform via two key parameters: the relative-phase between two halves of the multi-octave spanning spectrum, and the overall carrier-envelope phase. These results not only promise to expand the experimental possibilities in attosecond science, but also demonstrate coherent strong-field control of free-electron trajectories using tailored optical waveforms.
We study the effect of pump-seed timing fluctuations on the carrier-envelope phase (CEP) of signal and idler pulses emerging from an OP(CP)A. A simple analytical model is derived in order to provide an intuitive explanation of the origin of CEP fluctuations, while split-step simulations are performed to cover a broad range of different seeding schemes. Finally, we compare the simulation results with real observations of the CEP of idler pulses generated by an OPA. The quantitative model presented provides a key tool for designing the next generation of low-noise CEP-stable OP(CP)A-based sources. good levels of stability [7,8]. However, in order to reach high pulse energies, OP(CP)A systems have grown in size and complexity, entailing an increase in the timing jitter among the different amplification stages.In this Letter, we intend to clarify the influence of pumpseed timing fluctuations on the CEP of both signal and idler pulses emerging from an OP(CP)A. We analyze two of the most significant schemes: generation of a CEP-stable idler and amplification of a broadband stretched signal successively compressed.We start by considering the system of three coupled equations [9], which describes parametric amplification along the propagation direction, within the approximation of monochromatic plane waves and perfect phase matching. The parametric amplification process is maximized when the generalized phase Φ ϕ p − ϕ s − ϕ i is equal to π∕2 [10], in other words ϕ i ϕ p − ϕ s − π∕2. It is worth noting that the phase ϕ k (k p; s; i), represents the absolute phase (AP) of each wave, that is, the phase with respect to the lab reference frame and not the CEP of the corresponding pulses. To analytically determine the CEP of the signal and idler pulses generated in an OPA, it would be necessary to solve the aforementioned coupled equation system while considering the time dependency of the amplitude envelope of each pulse and the effect of dispersion. Unfortunately, no analytic solutions have been found in this case. However, within certain limits, it is still possible to describe analytically the effect of the pump-seed timing fluctuations on the CEP of signal and idler.Consider a white-light (WL) seeded OPA or any other parametric amplifier where the seed has been produced starting from a portion of the pump pulse via a coherent process, i.e., the seed pulse has inherited the AP from the pump pulse. During the spectral broadening, an additional term is added to the phase of the seed, but we will not consider it because such phase term has no dependence on timing fluctuations but rather on intensity fluctuations, whose effects on CEP goes beyond the scope of this paper. For small pump-seed relative arrival time fluctuations ΔT compared with the pump pulse Full control of the electric field of an ultrashort laser pulse is necessary to precisely control light-matter interaction processes happening on femtosecond (fs) and attosecond (as) time scales [1][2][3]. To describe the time-dependence of the electric field of a laser pu...
We introduce a simple all-inline variation of a balanced optical cross-correlator (BOC) that allows to measure the arrival time difference (ATD), over the full Nyquist bandwidth, with increased common-mode rejection and long-term stability. An FPGA-based signal processing unit allows for real-time signal normalization and enables locking to any setpoint with an unprecedented accuracy of 0.07 % within an increased ATD range of more than 400 fs, resulting in attosecond resolution locking. The setup precision is verified with an out-of-loop measurement to be less than 80 as residual jitter paving the way for highly demanding applications such as parametric waveform synthesizers.
Abstract:We present longitudinal-phase stability measurements between separate supercontinua generated in different bulk materials. The remarkably low relative phase jitter of few attoseconds allows multiple-white-light seeding schemes for flexible and ultrabroadband optical parametric waveform synthesizers. The current quest for optical parametric waveform synthesizers emitting intense electric-field transients E(t) customsculpted on a sub-optical-cycle time scale is fuelled by numerous intriguing applications in strong-field physics and attoscience [1]. Such OP(CP)A-based synthesizers [2,3] are often seeded by an ultrabroad white-light supercontinuum (WL) generated in bulk materials. Although seeding of multi-channel parametric waveform synthesizers by a single, multi-octave WL (ideally passively CEP-stabilized [4]) is possible and already demonstrated [2], such single-WL seeding schemes impose extreme challenges on the synthesizer design: (i) the generation of a WL filament stable over its full bandwidth is far from trivial and, most critically, (ii) precise dispersion control, that permits final recompression to sub-cycle pulse durations (<2 fs), requires very complex dispersion management schemes [2]. Implementing separate WLs, potentially even driven at different wavelengths, and created in different bulk materials, would thus add new degrees of freedom in the dispersion optimization and allow for unprecedented many-octave spectral coverage of such synthesizers. The immediate question arises: can sub-optical-cycle parametric waveform synthesizers in principle be seeded by separate bulk white-light supercontinua at all?Since its first observation by Alfano and Shapiro in 1970 [5], WL generated by ultrashort laser pulses in bulk materials has attracted scientists' attention due to the created ultrabroadband spectra [6]. Importantly, the pioneering experiment of Bellini and Hänsch demonstrating phase coherence between two WL continua with 'negligible random phase jitter' also paved the way for optical frequency metrology based on femtosecond frequency combs [7]. WL generation via filamentation in bulk materials results from very complex highly nonlinear propagation [8], leading to its sensitive dependence on a number of parameters, both of the material and of the laser pulse used. Recently, also the influence of higher-order Kerr effect (HOKE) [9] has controversially been discussed. Therefore, the precise predictive power of numerical investigations concerning fine details of the spectral phase, CEP jitter and timing jitter [10] (resulting from amplitude-to-phase noise conversion) is at present unclear.In this study, we experimentally determine a lower limit for the temporal coherence of WLs generated in separate few-mm-long bulk materials using 150-fs high-energy laser pulses from a cryogenic Ti:sapphire chirped-pulse amplifier. Note, single-WL seeding of synthesizers has the obvious advantage that the different spectral regions of The phase of the fringes of each spectrum is plotted as red curve. Initially ...
The quest for ever‐shorter optical pulses has been ongoing for over half a century. Although few‐cycle pulses have been generated for nearly 40 years, pulse lengths below the single‐cycle limit have remained an elusive goal for a long time. For this purpose, optical waveform synthesizers, generating high‐energy, high‐average‐power pulses via coherent combination of multiple pulses covering different spectral regions, have been recently developed. They allow unprecedented control over the generated optical waveforms, spanning an extremely broad spectral range from ultraviolet to infrared. Such control allows for steering strong‐field interactions with increased degrees of freedom. When driving high‐harmonic generation, tailored waveforms can produce bright attosecond pulse trains and even isolated attosecond pulses with tunable spectra up to the soft X‐ray range. In this paper recent progress on parametric and hollow‐core fiber waveform synthesizers is discussed. Newly developed seeding schemes; absolute, relative, and spectral phase measurement; and control techniques suitable for synthesizers are described. The progress on serial and parallel waveform synthesis based on Ti:sapphire and Ytterbium laser systems and their latest applications in high‐harmonic generation in gaseous and solid media, attosecond science, and laser wakefield acceleration is discussed.
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