JETP Letters最新文献

Recent studies of optical, magneto-optical, and nonlinear optical effects in epitaxial iron garnet films and arrays of ferromagnetic metal nanoparticles on their surface have been reviewed. It has been shown that second and third-harmonic generation microscopy makes it possible to visualize the surface domain structure of garnet. The role of metasurfaces in the formation of the quadratic nonlinear optical response of the composite structure at the micro- and macroscales has been analyzed. The possibility of pinning of domain walls in garnet by metal ferromagnetic metasurfaces deposited over it, as well as the optical visualization of such pinning by means of polarization microscopy and analyzing the diffraction of laser radiation on domains, has been demonstrated.

The storage of single photons generated via nondegenerate spontaneous parametric down-conversion in a cavity with a PPKTP crystal in quantum memory based on an atomic frequency comb in a Eu:YSO crystal is demonstrated. A technique for preparing spectral profiles within the absorption line of a doped crystal that are matched to the spectrum of single-photon radiation is developed. For storage times of 250 and 166 ns, quantum memory efficiencies of 3 and 7% have been obtained with signal-to-noise ratios of 1/4 and 1/2, respectively.

We address the contributions of cross-correlation functions to the resonance fluorescence spectrum of a three-level Ξ-system subjected to resonant bichromatic excitation. These contributions involve the sequential emission of two photons from each of the excited transitions. The cross-correlation functions demonstrate mutual coherence of the emitted frequency separated fields. The contribution to the scattered radiation in the presence of non-stationary processes is also considered. It is shown that the processes contributing to the cross-correlation determine the photon bunching for both excited transitions.

An efficient algorithm for calculating the spectral-angular dependences of the optical reflectivity, transmittance, and absorption coefficients of a photonic crystal layer that contain narrow resonances, such as bound states in the continuum, has been presented. The traditional approach using the Fourier modal method results in direct calculations on a very fine spectral grid to resolve adequately such resonances, which require significant computational resources. The proposed method significantly accelerates the calculations without loss of accuracy. Its key idea is to divide the resonant layer into two non-resonant sublayers. The scattering matrices for these sublayers are calculated only on a coarse spectral grid. The elements of these matrices are then interpolated onto the required fine grid, and the final optical coefficient is calculated on this grid. It has been shown that the developed algorithm achieves a computational speedup of at least four times compared to direct calculations on the fine grid, while maintaining sufficient accuracy in describing the resonant features. This approach opens up possibilities for the rapid and accurate design of composite photonic structures.

Our detailed study of the plasma ejection region in plasma focus facilities has revealed that the source of the ejection is a small region at the top of the converging plasma current sheath, which is activated only after a sharp drop in the current flowing in the sheath. The possible reasons of why this region functions as a “central engine,” similar to that found in young stellar objects, are also discussed.

Stimulated Brillouin scattering and optical breakdown induced by a single pulse in a 30-mm-thick layer of water with emission of the 656.27-nm H_α spectral line have been detected for the first time when a beam of a Nd³⁺:YAG laser (532 nm, 10 ns, 0.4 mJ) was normally incident and focused on the surface with a power several times lower than the critical self-focusing power 1.7 MW in water. At a laser pulse energy of 0.6 mJ, the optical breakdown occurs before the onset of stimulated Brillouin scattering thus blocking it. Experiments with an additional number of samples (acetone, ethanol, toluene, and CCl₄) have revealed the optical breakdown with localization near the surface, which is confirmed by the ejection of a droplet by a shock wave, as well as the generation of a hydrogen line in all samples, except CCl₄, where hydrogen is absent. The synergistic mechanism of nonlinear optical compression of the pulse and beam collapse with the achievement of the water breakdown threshold has been discussed.

The difference-frequency generation of 100-fs Ti:sapphire laser pulses in the wavelength range of 5–10 μm in a BaGa₂GeS₆ nonlinear crystal has been experimentally studied. This crystal has proven to be one of the best for producing extremely short laser pulses in this spectral range. The maximum energy of the laser pulse with a central wavelength of 6 μm and a spectral width of approximately half an octave is 14 μJ. It has been shown experimentally that variation of the laser pulse energy before the filament forming the signal wave does not affect the energy of the difference frequency radiation pulse if the broadening reaches the required frequency shift.

The photonic spin Hall effect in structures with surface plasmon resonance has great potential for various polarization-sensitive applications and devices. A theoretical and experimental study of the photonic spin Hall effect in subwavelength diffraction gratings is carried out. Using polarimetric and optimized weak measurements methods, the photonic spin Hall effect, enhanced by surface plasmon resonance, is demonstrated, which manifests itself in the spatial separation of circularly polarized photons with opposite spin signs when a laser beam is reflected from the grating surface. The effect of the polarization state of the incident laser radiation and the grating material on the angular displacement of the reflected beam is investigated. It is demonstrated that the angular shift can be changed from a spin-independent (Goos–Hanchen shift) to a spin-dependent photonic spin Hall effect when the polarization state of the incident beam changes. It is shown that the polarization states of incident radiation, at which the photon spin Hall effect is observed in nickel and silver gratings, differ significantly.

In this work, the magnon–photon hybridization in a technologically simple system based on an yttrium iron garnet film and a microwave resonator integrated into a microstrip line is numerically simulated for the first time using the ANSYS HFSS package. A characteristic splitting of the resonant frequencies (anticrossing) is demonstrated, indicating the implementation of a strong coupling between magnon and photon modes. A relative frequency splitting on the order of 0.06 is obtained. Furthermore, the influence of the spatial position of the yttrium iron garnet resonator on the parameters of hybrid states is studied, and the possibility of controlling the hybridization frequency by adjusting the resonator parameters is demonstrated. The results show the feasibility of implementing a strong magnon–photon coupling in a simple and easily reproducible microstrip structure and can be used in the design of sensors, tunable microwave filters, and elements of hybrid magnon or quantum systems.

The possibility of controlling the spectrum of high harmonics in the range of 50–200 eV under the excitation of a gas jet by a pair of intense femtosecond near- (1.24 μm) and mid-infrared (4.5 μm) laser pulses has been experimentally demonstrated. It has been established that an increase in the intensity of long-wavelength radiation from ~10⁹ to ~10¹² W/cm² under the peak intensity 10¹⁴ W/cm² of the short-wavelength pulse leads to a transition from a discrete spectrum containing sum and difference frequencies to a quasi-continuous broadband spectrum. This transition has been explained by a change in the regime of influence of the mid-infrared field on the dynamics of the generating electron. The obtained results demonstrate the prospects for generating radiation with the quasi-continuous broadband spectrum up to the soft X-ray region when generating high harmonics by a synthesized laser field.