A method for measuring the group refractive index and dispersion of dielectrics using a pump-probe scheme demonstrated with a ZnSe crystal. In this approach, an intense, ultrashort pump pulse causes ionization of the crystal, leading to scattering and absorption effects on the subsequent broadband probe pulse, which experiences dispersive broadening as it propagates through the crystal. By adjusting the time delay between the pump and probe pulses, we can effectively control the spectrum transmitted through the crystal, enabling the retrieval of both the group refractive index and dispersion characteristics.

A universal technique is developed for the detection of high harmonics generated by relativistic and subrelativistic laser pulses irradiating a solid target. Features in the spectra of harmonics generated by a parametric mid-IR laser system and near-IR laser system based on chirped pulse amplification were analyzed. Experimental spectra of harmonics in the range up to 35 nm were recorded. They can be used as a source of coherent radiation in the extreme UV region.

The generation of spectral components sensitive to the carrier-envelope phase of a laser pulse in a thin zinc selenide film has been experimentally demonstrated and confirmed by a numerical simulation. A pump–probe scheme has been implemented so that a pump pulse with a duration of about 1.5 field cycles, a central wavelength of 1.7 μm, and a stabilized carrier-envelope phase induces photoionization in a thin zinc selenide film. The probe pulse is scattered by the plasma, generating new phase-sensitive spectral components at the edges of its spectrum. The theoretical analysis has confirmed plasma nonlinearity as a mechanism for generating these components. The observed effect can be used to characterize the carrier-envelope phase of ultrashort pulses during the generation of high-order harmonics and sequences of attosecond pulses.

The paper presents a technique for broadband two-dimensional infrared spectroscopy with signal detection in visible range by nonlinear chirped-pulse upconversion. This approach helps to avoid direct measurement of the mid-infrared signal that requires cryogenic technology, and instead uses low-cost high-sensitivity multichannel silicon linear arrays. This leads to a reduction by two orders of magnitude of the measurement time of a single two-dimensional spectrum, which makes it possible to observe the fast dynamics of complex molecular compounds. The use of a quasi-phase-cycling achieved by sub-cycle delay modulation suppresses scattering background by almost two orders of magnitude and increases the measurement speed twice compared to optical chopping. Numerical simulation using the density matrix formalism and analysis of its evolution based on the solution of the Bloch–Redfield equation effectively reproduces the features of the two-dimensional infrared spectrum of inorganic octacarbonyl dicobalt compound.

Terahertz pulse generation from multiterawatt laser surface plasma near thick solid targets and thin foils has been studied. Pulses with energies up to 7 μJ were detected in the spectral region <3 THz in the direction of specular reflection from the surface of the CaF 2 target. The dependence of the terahertz pulse energy $${{W}_{{{\text{THz}}}}}$$ on the laser pulse intensity $$I_{L}^{\alpha }$$ can be approximated by the power function $${{W}_{{{\text{THz}}}}} \sim I_{L}^{\alpha }$$ . For a fixed laser pulse duration and variable energy the power index lies in the range $$\alpha \approx 1.5{-} 2.8$$ , while for a fixed energy and variable duration $$\alpha \approx 1$$ .

В работе продемонстрировано влияние фазы несущей относительно огибающей на спектр суперконтинуума и характеристики предельно коротких импульсов, формируемых в результате нелинейно-оптического преобразования импульсов накачки в заполненном аргоном полом антирезонансном волноводе. Экспериментальный и теоретический анализ показывает, что в результате солитонной самокомпрессии излучения накачки с начальной центральной длиной волны около 2 мкм формируется импульс длительностью порядка одного оптического периода, спектр которого уширяется в область 400-800 нм, где наблюдается интерференция с генерируемой этим же импульсом широкополосной третьей гармоникой. Интерференционная картина оказывается чувствительной к изменению фазы несущей относительно огибающей лазерного импульса. Анализ интерференционной картины дает информацию о разности спектральных фаз солитона и третьей гармоники в спектральном диапазоне с шириной больше октавы, а также позволяет контролировать длительность формируемых в процессе солитонной самокомпрессии импульсов.

The influence of the carrier–envelope phase on the spectrum of the supercontinuum and on the characteristics of ultrashort pulses, which are formed by the nonlinear optical transformation of pump pulses in an argon-filled antiresonant hollow waveguide has been demonstrated. The experimental and theoretical analysis has shown that the soliton self-compression of pump radiation with a central wavelength of about 2 μm forms a pulse with a duration of nearly one optical cycle and with a spectrum broadened to the region of 400‒800 nm, where interference with the broadband third harmonic generated by the same pulse is observed. The interference pattern is sensitive to the carrier–envelope phase of the laser pulse. The analysis of the interference pattern provides information on the difference of the spectral phases of the soliton and third harmonic in the spectral range wider than an octave and allows one to control the duration of pulses formed in the process of soliton self-compression.

The influence of the carrier-envelope phase (CEP) of a pump pulse on the multioctave supercontinuum (SC) generation in a gas-filled anti-resonant hollow-core fiber (AR HCF) by soliton self-compression (SSC) has been explored. We have shown an octave-wide third harmonic generation (THG) in the visible-to-near-infrared range during the pulse compression down to a sub-cycle duration. The CEP of a multi-cycle pump pulse provides control of interference between the third harmonic (TH) and the SC that indicates the coherent synthesis of a sub-cycle pulse with a duration of about 0.4 optical cycles and a peak power of more than 2 GW at the fiber output.

Electric-current transients driven by high-peak-power midinfrared laser pulses are shown to provide a source of broadband current, wide-angle microwave-terahertz radiation, whose spectral, spatial, and polarization properties can be adequately understood from a perspective of impulsively driven antenna radiation. When suitably tailored, such laser-driven antennas are shown to generate bright microwave-terahertz pulses with energies in the range of tens of microjoules and ultrawide-angle radiation patterns extending to obtuse angles well beyond the broadside plane, with a considerable radiation flux detected at angles 0 > 125 degrees relative to the direction of the driver beam. Polarization of microwave radiation from laser-driven plasmas is shown to bear clear signatures of the symmetry of transient plasma currents, providing a sensitive probe for ultrafast laser-plasma interactions.

A method of direct measurement of the light field has been implemented. It allows one to reveal features of the time structure of single-cycle pulses formed through soliton self-compression of near and mid-infrared pulses. Broadband anomalous dispersion necessary for the soliton transformation of near and mid-infrared pulses is ensured by the structure of a waveguide system optimized in the class of hollow photonic-crystal waveguides with an antiresonance shell. The structure of the field of pulses formed under these conditions is characterized by the presence of the central most intense half-cycle whose reproducibility from pulse to pulse is ensured by the stability of the field phase with respect to the envelope.

We demonstrate a multicompartment, power-scalable beam-line design in which sub-40-fs, terawatt field waveforms are tailored in space and time for downstream pulse compression to few-cycle pulse widths attained right at the site where the intense laser field interacts with a target. An accurate field-waveform characterization performed at multiple locations along the beam path shows that, despite all the complexity of their upstream nonlinear electrodynamics, field waveforms shorter than three field cycles can be delivered to a laser–matter interaction site in such a system, enabling a vast class of ultrafast strong-field laser–matter interaction studies.

By exploiting stimulated Raman scattering in long nitrogen-filled capillary fibers, we demonstrate continuous tunability of Yb laser systems over the 1.0-1.7 µm range, with conversion efficiency up to 82%, and an up to 10-fold pulse compression.

Polarization- and angle-resolved analysis of microwave-to-terahertz (mu Wv/THz) radiation from gas-phase plasmas induced by ultrashort mid-infrared laser pulses reveals a complex vectorial electrodynamic picture of mu Wv/THz generation by a diverse manifold of laser-driven plasma currents and provides a powerful tool to distinguish between currents of different spatial symmetries as sources of mu Wv/THz radiation. In experiments with a single-color mid-IR driver, the spatial mode of mu Wv/THz radiation is found to retain a remarkably uniform, conical-emission structure across its entire spectral span, with angular dispersion and a spatial mode profile as dictated by Cherenkov-type phase matching. This spatial mode structure is consistent with its polarization properties of mu Wv/THz radiation, indicating the dominant role of radiation by ponderomotively driven longitudinal currents. In experiments with a two-color laser driver, the spatial-polarization mode structure of mu Wv/THz radiation is found to change across its spectrum and as a function of the gas pressure, revealing mixed symmetries of underlying electric currents and indicating the shifting roles of transverse and longitudinal currents as mechanisms behind mu Wv/THz generation.

Ultrafast nonlinear dynamics driven by high-peak-power ultrashort mid-infrared (mid-IR) pulses gives rise to ultrabroadband radiation whose spectrum spans over multiple decades, stretching from the terahertz (THz) to the microwave range. We show that, despite its enormous, multidecade bandwidth, an accurate spectral and spatial-mode characterization of this radiation is possible via a suitable combination of mutually complementary signal-analysis methods borrowed from ultrafast optics, radioelectronics, THz photonics, and microwave engineering. This analysis reveals intense subgigahertz radiation emitted as a part of mid-IR-driven supercontinuum generation and shows that microwave-to-THz field waveforms can almost reach the diffraction limit in their beam focusability, yielding field strengths above ≈3 MV/cm.

Ultrafast ionization of a gas medium driven by ultrashort midinfrared laser pulses provides a source of bright ultrabroadband radiation whose spectrum spans across the entire microwave band, reaching for the sub-gigahertz range. We combine multiple, mutually complementary detection techniques to provide an accurate polarization-resolved characterization of this broadband output as a function of the gas pressure. At low gas pressures, the lowest-frequency part of this output is found to exhibit a drastic enhancement as this field builds up its coherence, developing a well-resolved emission cone, dominated by a radial radiation energy flux. This behavior of the intensity, coherence, and polarization of the microwave output is shown to be consistent with Cherenkov-type radiation by ponderomotively driven plasma currents.

Spectral analysis of high-order harmonics generated by ultrashort mid-infrared pulses in molecular nitrogen reveals well-resolved signatures of inverse Raman scattering, showing up near the frequencies of prominent vibrational transitions of nitrogen molecules. When tuned on a resonance with the v'=0→v''=0 pathway within the B3Πg→C3Πu second positive system of molecular nitrogen, the eleventh harmonic of a 3.9 µm, 80 fs driver is shown to acquire a distinctive antisymmetric spectral profile with red-shifted bright and blue-shifted dark features as indicators of stimulated Raman gain and loss. This high-harmonic setting extends the inverse Raman effect to a vast class of strong-field light-matter interaction scenarios.