The time it takes to switch on and off electric current determines the rate at which signals can be processed and sampled in modern information technology. Field-effect transistors are able to control currents at frequencies of the order of or higher than 100 gigahertz, but electric interconnects may hamper progress towards reaching the terahertz (10(12) hertz) range. All-optical injection of currents through interfering photoexcitation pathways or photoconductive switching of terahertz transients has made it possible to control electric current on a subpicosecond timescale in semiconductors. Insulators have been deemed unsuitable for both methods, because of the need for either ultraviolet light or strong fields, which induce slow damage or ultrafast breakdown, respectively. Here we report the feasibility of electric signal manipulation in a dielectric. A few-cycle optical waveform reversibly increases--free from breakdown--the a.c. conductivity of amorphous silicon dioxide (fused silica) by more than 18 orders of magnitude within 1 femtosecond, allowing electric currents to be driven, directed and switched by the instantaneous light field. Our work opens the way to extending electronic signal processing and high-speed metrology into the petahertz (10(15) hertz) domain.

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The electric field of a laser pulse can be described as Here we report the first method permitting absolute CEP detection with a solid-state detector applicable in ambient conditions. Recently, we have shown that the strong electric field of an intense, linearly-polarized, visible/near-infrared (VIS/NIR), few-cycle laser pulse can rapidly increase the (ac) conductivity of a solid insulator, allowing electric currents to be induced and switched with the field of visible light [22]. In these experiments, we exposed amorphous silicon dioxide (bandgap g 9 eV E ≈ ) to a strong, controlled electric field ( ) F t of a few-cycle pulse with a carrier photon energy of ∆ is a consequence of dispersive pulse broadening inside the glass wedges. However, in our experiments P ( ) Q l ∆ was still detectable above the noise level for values of 400 µm l ∆ > , corresponding to a pulse duration of more than 9 fs (FWHM of the time-dependent cycle-averaged intensity). Subsequently, PQ was calibrated with respect to the absolute CEP of the laser pulse via stereo-ATI measurements performed with identical pulses [4]. After the measurement of P ( ) Q l ∆ with the solid-state device, a mirror was inserted into the beam path, deflecting the 5 pulses into a stereo-ATI apparatus located -together with the solid-state detector -in the same vacuum chamber (Fig. 1). Here, the CEP of the incident laser pulse was detected by analyzing the kinetic energy distribution of electrons that are photoemitted from Xe atoms, see Methods Summary. An uncertainty due to a Gouy phase shift in both foci can be neglected since in both experiments, the sample was placed exactly in the region of the highest laser intensity.We set 17 different propagation lengths l ∆ , ranging from 21.5 µm − to 27.5 µm +. For each of them, 500 single-shot stereo-ATI measurements were performed. Because consecutive laser pulses had a CEP-shift of π , which is only required for the accurate detection of P ( ) Q l ∆ , only spectra from odd-numbered pulses were considered for the stereo-ATI measurements. As shown in [4], CEϕ can then be reconstructed by calculating two asymmetry parameters ( , ) X Y by integrating the averaged time-of-flight spectra L,R TOF ( ) n t of the electrons photoemitted from Xe atoms by the intense few-cycle VIS/NIR pulses in two different regions. The parametric plot of ( , ) X Y in Fig. 2(a) was obtained by calculating, for each. The photoelectron spectra L,R TOF ( ) n twere measured with the left (L) and right (R) micro-channel plates (MCPs) of the set-up in Fig. 1 We have compared the results of the solid-state-based phase retrieval with the predictions of two quantum mechanical models. The first model, which was earlier employed in Ref.[24] to describe the ultrafast increase in conductivity of SiO 2 nanojunctions, is based on the nearestneighbor tight-binding approximation. The second model, presented in detail in Ref.[25], describes quantum dynamics in a one-dimensional pseudopotential (see the Methods Summary for details). In both models, the electric fi...

Nonlinear interactions between ultrashort optical waveforms and solids can be used to induce and steer electric currents on femtosecond (fs) timescales, holding promise for electronic signal processing at PHz (10¹⁵  Hz) frequencies [Nature 493, 70 (2013)]. So far, this approach has been limited to insulators, requiring extreme peak electric fields (>1  V/Å) and intensities (>10¹³  W/cm²). Here, we show all-optical generation and control of electric currents in a semiconductor relevant for high-speed and high-power (opto)electronics, gallium nitride (GaN), within an optical cycle and on a timescale shorter than 2 fs, at intensities at least an order of magnitude lower than those required for dielectrics. Our approach opens the door to PHz electronics and metrology, applicable to low-power (non-amplified) laser pulses, and may lead to future applications in semiconductor and (photonic) integrated circuit technologies

At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Our results may blaze a trail to PHz-rate optoelectronics.

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Isolated attosecond pulses (IAPs) produced through laser-driven high-harmonic generation (HHG) hold promise for unprecedented insight into physical, chemical, and biological processes via attosecond x-ray diffraction and spectroscopy with tabletop sources. Efficient scaling of HHG towards x-ray energies, however, has been hampered by ionization-induced plasma generation impeding the coherent buildup of high-harmonic radiation. Recently, it has been shown that these limitations can be overcome in the socalled "overdriven regime" where ionization loss and plasma dispersion strongly modify the driving laser pulse over small distances, albeit without demonstrating IAPs. Here, we report on experiments contrasting the generation of IAPs at 80 eV in argon with neon via attosecond streaking measurements. Comparing our experimental results to numerical simulations, we conclude that IAPs in argon are generated in the overdriven regime. We introduce a simple expression that fully describes the HHG dipole phase-mismatch contribution, specifically the effect of the blueshift of the driving laser. Furthermore, we present a method to numerically calculate the transient HHG phase mismatch, which allows us to demonstrate the accuracy of the introduced phase-mismatch expression. Finally, we perform simulations for different gases and wavelengths and show that including the full HHG dipole phase-mismatch contribution is important for understanding HHG with long-wavelength, few-cycle laser pulses in high-pressure gas targets, which are currently being employed for scaling isolated attosecond pulse generation beyond extreme ultraviolet (XUV) towards soft-x-ray photon energies.

We review theoretical foundations and some recent progress related to the quest of controlling the motion of charge carriers with intense laser pulses and optical waveforms. The tools and techniques of attosecond science enable detailed investigations of a relatively unexplored regime of nondestructive strong-field effects. Such extremely nonlinear effects may be utilized to steer electron motion with precisely controlled optical fields and switch electric currents at a rate that is far beyond the capabilities of conventional electronics. IntroductionIt has long been realized that intense few-cycle laser pulses provide unique conditions for exploring extremely nonlinear phenomena in solids [1,2], the key idea being that a sample can withstand a stronger electric field if the duration of the interaction is shortened. Ultimately, a single-cycle laser pulse provides the best conditions for studying nonperturbative strong-field effects, especially those where the properties of a sample change within a fraction of a laser cycle. The recent rapid development of the tools and techniques of attosecond science [3] not only creates new opportunities for detailed investigations of ultrafast electron dynamics in solids, but it also opens exciting opportunities for controlling electron motion in solids with unprecedented speed and accuracy. Conventional nonlinear phenomena that accompany the interaction of intense laser pulses with solids have already found a vast number of applications in spectroscopy, imaging, laser technology, transmitting and processing information [4]. It can be expected that the less conventional nonpertur-