Sub-cycle pulse revealed with carrier-envelope phase control of soliton self-compression in anti-resonant hollow-core fiber.

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.

[Possibilities of monotherapy with Prostatex in patients with chronic abacterial prostatitis].

AIM: To study the efficiency of the treatment of patients with chronic abacterial prostatitis using the drug Prostatex. MATERIALS AND METHODS: A total of 72 patients aged 22 to 43 years with chronic abacterial prostatitis were included in the study. All patients received Prostatex in the form of suppositories 10 mg QD within 20 days. The duration of the follow-up was 1 month. RESULTS: By the third visit from the start of treatment, there were almost no symptoms of the disease, according to the NIH-CPSI and IPSS questionnaires. In 67 (93.1%) patients, the prostate became an elastic, while in 69 (95.8%) men it was painless at palpation. In addition, a decrease in the prostate size, volume of residual urine and an improvement in urine flow rate were seen. CONCLUSION: Our results showed that monotherapy with Prostatex in patients with chronic abacterial prostatitis was effective and had pathogenetic rationale. This drug has a positive effect on the main symptoms of the disease, significantly reduces pain, urination disturbances, helps to reduce the prostate size and the volume of residual urine, improves prostate microcirculation and can be recommended for this category of patients.

High-harmonic-driven inverse Raman scattering.

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.

Coherently enhanced microwave pulses from midinfrared-driven laser plasmas.

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.

Sub-half-cycle field transients from shock-wave-assisted soliton self-compression.

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.

Chirp-controlled high-harmonic and attosecond-pulse generation via coherent-wake plasma emission driven by mid-infrared laser pulses.

Coherent-wake plasma emission induced by ultrashort mid-infrared laser pulses on a solid target is shown to give rise to high-brightness, high-order harmonic radiation, offering a promising source of attosecond pulses and a probe for ultrafast subrelativistic plasma dynamics. With 80-fs, 0.2-TW pulses of 3.9-µm radiation used as a driver, optical harmonics up to the 34th order are detected, with their spectra stretching from the mid-infrared region to the extreme ultraviolet region. The harmonic spectrum is found to be highly sensitive to the chirp of the driver. Particle-in-cell analysis of this effect suggests, in agreement with the generic scenario of coherent-wake emission, that optical harmonics are radiated as trains of extremely short, attosecond ultraviolet pulses with a pulse-to-pulse interval varying over the pulse train. A positive chirp of the driver pulse can partially compensate for this variation in the interpulse separation, allowing harmonics of the highest orders to be generated in the plasma emission spectrum.

Anomalous and near-zero group-velocity dispersion in the sub-THz and mm-band atmospheric windows.

Analysis of the complex refractive index of atmospheric air reveals remarkably broad and continuous regions of anomalous and near-zero group-velocity dispersion in the subterahertz (sub-THz) and millimeter-band atmospheric windows. One such broadband dispersion anomaly is shown to occur in the high-frequency wing of the 60-GHz band of molecular oxygen. Adjacent to this dispersion anomaly is a broadband atmospheric transparency region within which the group-velocity dispersion is unusually weak, enabling distortion-free long-distance transmission of broadband millimeter-wave field waveforms, as well as broadband remote sensing in the millimeter band. Although broad regions of anomalous and near-zero dispersion also exist in the sub-THz range, their utility for long-distance transmission and remote sensing is limited because of strong atmospheric absorption.

Chirp-controlled filamentation and formation of light bullets in the mid-IR.

Formation of light bullets-tightly localized in space and time light packets, retaining their spatiotemporal shape during propagation-is, for the first time, experimentally observed and investigated in a new regime of mid-infrared filamentation in ambient air. It is suggested that the light bullets generated in ambient air by multi-mJ, positively chirped 3.9-µm pulses originate from a dynamic interplay between the anomalous dispersion in the vicinity of CO2 resonance and positive chirp, both intrinsic, carried by the driver pulse, and accumulated, originating from nonlinear propagation in air. By adjusting the initial chirp of the driving pulses, one can control the spatial beam profile, energy losses, and spectral-temporal dynamics of filamenting pulses and deliver sub-3-cycle mid-IR pulses in high-quality beam on a remote target.

High-order harmonic generation from a solid-surface plasma by relativistic-intensity sub-100-fs mid-infrared pulses.

High-order harmonic generation (HHG) in plasmas induced by ultrashort, relativistic-intensity laser pulses on solid surfaces can provide an efficient source of attosecond pulses and opens routes toward new regimes of laser-matter interactions, x-ray generation, laser particle acceleration, and relativistic nonlinear optics. However, field intensities in the range of Irel∼1019 W/cm2 are typically needed to achieve the relativistic regime of HHG in experiments with near-infrared laser pulses. Here, we show that, in the mid-infrared range, due to the λ-2 scaling of Irel with the driver wavelength λ, relativistic HHG can be observed at much lower levels of laser field intensities. High-peak-power 80-fs, 3.9-µm pulses are focused in our experiments on a solid surface to provide field intensities in the range of 1017 W/cm2. Remarkably, this level of field intensities, considered as low by the standards of relativistic optics in the near infrared, is shown to be sufficient for generation of high-order harmonics with signature properties of relativistic HHG-beam directionality, spectra with extended plateaus, and a high HHG yield sustained for both p- and s-polarized driver fields.

Filamentation of mid-IR pulses in ambient air in the vicinity of molecular resonances.

Properties of filaments ignited by multi-millijoule, 90 fs mid-infrared pulses centered at 3.9 µm are examined experimentally by monitoring plasma density, losses, spectral dynamics and beam profile evolution at different focusing strengths. By changing from strong (f=0.25 m) to loose (f=7 m) focusing, we observe a shift from plasma-assisted filamentation to filaments with low plasma density. In the latter case, filamentation manifests itself by beam self-symmetrization and spatial self-channeling. Spectral dynamics in the case of loose focusing is dominated by the nonlinear Raman frequency downshift, which leads to the overlap with the CO2 resonance in the vicinity of 4.2 µm. The dynamic CO2 absorption in the case of 3.9 µm filaments with their low plasma content is the main mechanism of energy losses and, either alone or together with other nonlinear processes, contributes to the arrest of intensity.

Ultrafast mid-infrared spectrochronography of dispersion near molecular absorption bands.

Quantitative characterization of dispersion near molecular resonances is difficult both conceptually and technically, as it requires systematic measurements of rapidly varying dispersion profiles across the edges of molecular absorption bands. Here, we show that this challenge can be confronted with an ultrafast spectrochronography technique that combines time-resolved four-wave mixing and cross-correlation frequency-resolved optical gating. We demonstrate that, with the spectrum of an ultrashort mid-infrared laser probe stretching across the edge of a molecular absorption band, the Wigner chronocyclic maps of such a probe reveal universal signatures of anomalous dispersion and help quantify such dispersion anomalies.

Long-wavelength infrared solitons in air.

Dispersion and optical nonlinearity of atmospheric air in the long-wavelength infrared (LWIR) range are shown to enable unique soliton dynamics in freely propagating laser beams. Analysis of spatiotemporal LWIR waveform evolution in air reveals soliton self-compression scenarios whereby ultrashort LWIR subterawatt pulses can be compressed to single-cycle terawatt field waveforms.

The generalized Sellmeier equation for air.

We present a compact, uniform generalized Sellmeier-equation (GSE) description of air refraction and its dispersion that remains highly accurate within an ultrabroad spectral range from the ultraviolet to the long-wavelength infrared. While the standard Sellmeier equation (SSE) for atmospheric air is not intended for the description of air refractivity in the mid-infrared and long-wavelength infrared, failing beyond, roughly 2.5 µm, our generalization of this equation is shown to agree remarkably well with full-scale air-refractivity calculations involving over half a million atmospheric absorption lines, providing a highly accurate description of air refractivity in the range of wavelengths from 0.3 to 13 µm. With its validity range being substantially broader than the applicability range of the SSE and its accuracy being at least an order of magnitude higher than the accuracy that the SSE can provide even within its validity range, the GSE-based approach offers a powerful analytical tool for the rapidly progressing mid- and long-wavelength-infrared optics of the atmosphere.

Mapping anomalous dispersion of air with ultrashort mid-infrared pulses.

We present experimental studies of long-distance transmission of ultrashort mid-infrared laser pulses through atmospheric air, probing air dispersion in the 3.6-4.2-µm wavelength range. Atmospheric air is still highly transparent to electromagnetic radiation in this spectral region, making it interesting for long-distance signal transmission. However, unlike most of the high-transmission regions in gas media, the group-velocity dispersion, as we show in this work, is anomalous at these wavelengths due to the nearby asymmetric-stretch rovibrational band of atmospheric carbon dioxide. The spectrograms of ultrashort mid-infrared laser pulses transmitted over a distance of 60 m in our experiments provide a map of air dispersion in this wavelength range, revealing clear signatures of anomalous dispersion, with anomalous group delays as long as 1.8 ps detected across the bandwidth covered by 80-fs laser pulses.

Power-scalable subcycle pulses from laser filaments.

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/Pcr of the peak power of an ultrashort laser pulse, P, to the critical power of self-focusing, Pcr, 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/Pcr. 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 Pcr.

Modeling high-peak-power few-cycle field waveform generation by optical parametric amplification in the long-wavelength infrared.

Extended coupled-wave analysis of optical parametric chirped-pulse amplification (OPCPA) reveals regimes whereby high-peak-power few-cycle pulses can be generated in the long-wavelength infrared (LWIR) spectral range. Broadband OPCPA in suitable nonlinear crystals pumped at around 2 µm and seeded either through the signal or the idler input is shown to enable the generation of high-power field waveforms with pulse widths shorter than two field cycles within the entire LWIR range.

Solid-State Source of Subcycle Pulses in the Midinfrared.

We demonstrate a robust, all-solid-state approach for the generation of microjoule subcycle pulses in the midinfrared through a cascade of carefully optimized parametric-amplification, difference-frequency-generation, spectral-broadening, and chirp-compensation stages. This method of subcycle waveform generation becomes possible due to an unusual, ionization-assisted solid-state pulse self-compression dynamics, where highly efficient spectral broadening is enabled by ultrabroadband four-wave parametric amplification phase matched near the zero-group-velocity wavelength of the material.

X-SEA-F-SPIDER characterization of over octave spanning pulses in the infrared range.

We show a practical implementation of a pulse characterization method for sub-cycle pulse measurements in the infrared spectral range based on spectral shearing interferometry. We employ spatially-encoded arrangement filter-based spectral phase interferometry for direct electric field reconstruction with external ancila pulses (X-SEA-F-SPIDER). We show merits and limitations of the setup and an in-depth comparison to another widely used temporal characterization technique - Second-Harmonic Generation Frequency Resolved Optical Gating (SHG-FROG). The X-SEA-F-SPIDER implementation presented in this paper allows measurement of sub-cycle pulses with over one octave wide spectrum spanning the 900-2400 nm range without adding any extra dispersion due to the pulse characterization apparatus.

Angle-resolved multioctave supercontinua from mid-infrared laser filaments.

Angle-resolved spectral analysis of a multioctave high-energy supercontinuum output of mid-infrared laser filaments is shown to provide a powerful tool for understanding intricate physical scenarios behind laser-induced filamentation in the mid-infrared. The ellipticity of the mid-infrared driver beam breaks the axial symmetry of filamentation dynamics, offering a probe for a truly (3+1)-dimensional spatiotemporal evolution of mid-IR pulses in the filamentation regime. With optical harmonics up to the 15th order contributing to supercontinuum generation in such filaments alongside Kerr-type and ionization-induced nonlinearities, the output supercontinuum spectra span over five octaves from the mid-ultraviolet deep into the mid-infrared. Full (3+1)-dimensional field evolution analysis is needed for an adequate understanding of this regime of laser filamentation. Supercomputer simulations implementing such analysis articulate the critical importance of angle-resolved measurements for both descriptive and predictive power of filamentation modeling. Strong enhancement of ionization-induced blueshift is shown to offer new approaches in filamentation-assisted pulse compression, enabling the generation of high-power few- and single-cycle pulses in the mid-infrared.

Mid-infrared-to-mid-ultraviolet supercontinuum enhanced by third-to-fifteenth odd harmonics.

A high-energy supercontinuum spanning 4.7 octaves, from 250 to 6500 nm, is generated using a 0.3-TW, 3.9-µm output of a mid-infrared optical parametric chirped-pulse amplifier as a driver inducing a laser filament in the air. The high-frequency wing of the supercontinuum spectrum is enhanced by odd-order optical harmonics of the mid-infrared driver. Optical harmonics up to the 15th order are observed in supercontinuum spectra as overlapping, yet well-resolved peaks broadened, as verified by numerical modeling, due to spatially nonuniform ionization-induced blue shift.