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Intense light pulses in the visible and adjacent spectral ranges with their energy mostly confined to a half wave cycle—optical attosecond pulses—are synthesized and used to measure the time it takes electrons to respond to light. Sub-femtosecond control of bound electrons A fundamental speed limit for controlling matter through the electromagnetic force of light arises from the time it takes bound electrons to respond. Experiments have shown that this response is not instantaneous, but the lack of sufficiently fast probes has prevented direct measurements. Eleftherios Goulielmakis and colleagues have now produced intense light pulses in the visible and nearby spectral ranges and with energy largely confined to a half wave cycle, and show that these so-called optical attosecond pulses can control and measure the dynamics of bound electrons in krypton atoms. Proof-of-principle measurements establish the value of optical attosecond pulses for probing and manipulating bound electrons in atoms, molecules or solids, and suggest they may also find use in light-based nonlinear photonics operating on sub-femtosecond time scales and petahertz rates. The time it takes a bound electron to respond to the electromagnetic force of light sets a fundamental speed limit on the dynamic control of matter and electromagnetic signal processing. Time-integrated measurements of the nonlinear refractive index 1 of matter indicate that the nonlinear response of bound electrons to optical fields is not instantaneous; however, a complete spectral characterization of the nonlinear susceptibility tensors 2 —which is essential to deduce the temporal response of a medium to arbitrary driving forces using spectral measurements—has not yet been achieved. With the establishment of attosecond chronoscopy 3 , 4 , 5 , the impulsive response of positive-energy electrons to electromagnetic fields has been explored through ionization of atoms 6 and solids 7 by an extreme-ultraviolet attosecond pulse 8 or by strong near-infrared fields 9 , 10 , 11 . However, none of the attosecond studies carried out so far have provided direct access to the nonlinear response of bound electrons. Here we demonstrate that intense optical attosecond pulses synthesized in the visible and nearby spectral ranges allow sub-femtosecond control and metrology of bound-electron dynamics. Vacuum ultraviolet spectra emanating from krypton atoms, exposed to intense waveform-controlled optical attosecond pulses, reveal a finite nonlinear response time of bound electrons of up to 115 attoseconds, which is sensitive to and controllable by the super-octave optical field. Our study could enable new spectroscopies of bound electrons in atomic, molecular or lattice potentials of solids 12 , as well as light-based electronics operating on sub-femtosecond timescales and at petahertz rates 13 , 14 , 15 .

Thermal activation of transient receptor potential (TRP) cation channels is one of the most striking examples of temperature-controlled processes in cell biology. As the evidence indicating the fundamental role of such processes in thermosensation builds at a fast pace, adequately accurate tools that would allow heat receptor logic behind thermosensation to be examined on a single-cell level are in great demand. Here, we demonstrate a specifically designed fiber-optic probe that enables thermal activation with simultaneous online thermometry of individual cells expressing genetically encoded TRP channels. This probe integrates a fiber-optic tract for the delivery of laser light with a two-wire microwave transmission line. A diamond microcrystal fixed on the fiber tip is heated by laser radiation transmitted through the fiber, providing a local heating of a cell culture, enabling a well-controlled TRP-assisted thermal activation of cells. Online local temperature measurements are performed by using the temperature-dependent frequency shift of optically detected magnetic resonance, induced by coupling the microwave field, delivered by the microwave transmission line, to nitrogen—vacancy centers in the diamond microcrystal. Activation of TRP channels is verified by using genetically encoded fluorescence indicators, visualizing an increase in the calcium flow through activated TRP channels.

We show that a broadly accepted criterion of laser-induced breakdown in solids, defining the laser-breakdown threshold in terms of the laser fluence or laser intensity needed to generate a certain fraction of the critical electron density rc within the laser pulse, fails in the case of high-intensity few-cycle laser pulses. Such laser pulses can give rise to subcycle oscillations of electron density ρ with peak ρ values well above ρ c even when the total energy of the laser pulse is too low to induce a laser damage of material. The central idea of our approach is that, instead of the ρ  =  ρ c ratio, the laser-breakdown threshold connects to the total laser energy coupled to the electron subsystem and subsequently transferred to the crystal lattice. With this approach, as we show in this work, predictions of the physical model start to converge to the available experimental data.

Arrays of submicron air holes are shown to modify the properties of guided modes in optical fibers, enabling a fine tuning of fiber dispersion, nonlinearity, and gain. We demonstrate fiber dispersion nanomanagement solutions that provide ultra-flattened group-velocity dispersion profiles and control the fiber nonlinearity and gain.

We identify an unusual regime of ultrafast nonlinear dynamics in which an optical shock wave couples to soliton self-compression, steepening the tail of the pulse, thus yielding self-compressing soliton transients as short as the field sub-half-cycle. We demonstrate that this extreme pulse self-compression scenario can help generate sub-half-cycle mid-infrared pulses in a broad class of anomalously dispersive optical waveguide systems.

The signal-to-noise contrast of the optical readout in broadband Raman quantum memories is analyzed as a function of the pulse widths and phase properties of tailored optical field waveforms used to write in and read out broadband photon wave packets. Based on this analysis, we quantify the tradeoff between the readout contrast and the speed of such memories. Off-resonance coherent four-wave mixing is shown to provide a source of noise photons, lowering the readout contrast in broadband Raman quantum memories. This noise cannot be suppressed by phase matching, but can be radically reduced with a suitable polarization arrangement and proper field-waveform tailoring.

Compression of optical pulses to ultrashort pulse widths using methods of nonlinear optics is a well-established technology of modern laser science. Extending these methods to pulses with high peak powers, which become available due to the rapid progress of laser technologies, is, however, limited by the universal physical principles. With the ratio P / P cr of the peak power of an ultrashort laser pulse, P , to the critical power of self-focusing, P cr , playing the role of the fundamental number-of-particles integral of motion of the nonlinear Schrödinger equation, keeping this ratio constant is a key principle for the power scaling of laser-induced filamentation. Here, we show, however, that, despite all the complexity of the underlying nonlinear physics, filamentation-assisted self-compression of ultrashort laser pulses in the regime of anomalous dispersion can be scaled within a broad range of peak powers against the principle of constant P / P cr . We identify filamentation self-compression scaling strategies whereby subcycle field waveforms with almost constant pulse widths can be generated without a dramatic degradation of beam quality within a broad range of peak powers, varying from just a few to hundreds of P cr .

The influence of the structure of holey-fiber cladding on the spectral broadening of femtosecond laser pulses is experimentally studied. These experiments demonstrate that the spectral broadening of 70-fs pulses of 800-nm Ti:sapphire laser radiation transmitted through 2- and 3-μm-pitch holey fibers can be enhanced by a factor of about 1.5 by increasing the air-filling fraction of the fiber cladding from 16 up to 65%.

Broadband and supercontinuum pulses with a linear chirp define a linear transform, mapping the difference between the instantaneous frequencies of pump pulses onto the delay time between these pulses. This delay between the pump pulses can be then mapped onto the spatial coordinate with the use of a broad-beam wave-mixing or pump–probe geometry. The new possibilities offered by these mappings for four-wave-mixing techniques are discussed. The spectral and temporal resolution of chirped-pulse wave-mixing and pump–probe techniques are examined. Single-shot multidimensional wave-mixing techniques using broadband and supercontinuum chirped pulses are discussed.