The properties of a pure semiconductor GaP crystal were studied aimed to evaluate its applicability for the development of Faraday rotators for high-power radiation in the near-and mid-infrared (IR) ranges. The dispersion dependence of the Verdet constant was measured in the 560-1940 nm wavelength range. Thermally induced polarization and phase distortions arising in a GaP crystal sample heated with the radiation at the wavelengths of 1075 nm and 1940 nm were studied. The obtained experimental data were used to determine the magnetooptical figure of merit of the studied sample at these wavelengths, as well as to estimate the maximum operating power of Faraday isolators. For a wavelength of 1940 nm, the maximum operating power of the isolator is estimated to be 85 W, indicating the potential of using the GaP crystal in the mid-IR range. At a wavelength of 1075 nm, it is also possible to implement isolators for high-power radiation, but the main competitive advantage at this wavelength is a high value of the Verdet constant, which can be beneficial when using magnetic systems with highly uniform field or with a field profile that suppresses polarization distortions. The studies of the thermal lens showed that the piezo-optical contribution to the observed effect can significantly compensate for the contribution of the temperature dependence of the refractive index. This balance of thermo-optical characteristics is advantageous when working with high-power laser radiation, as it reduces the magnitude of thermally induced phase distortions.

The magneto-optical and thermo-optical characteristics of high-purity germanium crystals of different isotopic compositions were studied to assess the applicability of this material as a magnetoactive medium for Faraday isolators for high-power radiation in the mid-IR range. An increase in the Verdet constant with increasing atomic mass of the isotope was observed in experiments. The physical mechanisms arising from the quantum theory of the Faraday effect associated with interband transitions, which can explain this dependence, are discussed. No isotopic variations in the thermo-optical characteristics that determine the maximum operating power of Faraday isolators of conventional design were observed. The results of measurements at a wavelength of 1940 nm demonstrated the possibility of constructing a Faraday isolator with one magneto-optical element at an operating power over 100 W and an isolator with compensation of thermally induced depolarization using a reciprocal rotator at an operating power surpassing 200 W. The prospects of using Ge crystals for developing Faraday isolators for longer wavelength radiation were discussed. The use of radiation with wavelengths greater than or similar to 2 mu m opens up broad opportunities for increasing the operating power of isolators based on various schemes and for creating broadband isolators.

A new architecture of a MOPA laser system with a 4-channel Yb:YAG single-rod amplifier was proposed and brought to life. An average power of 20 W at a pulse energy of 17 mJ was achieved at the system output. A tiled-aperture coherent beam combining with 57% power in the central lobe was demonstrated. A digital controller with feedback enabled efficient suppression of phase fluctuations in channels that were mainly concentrated in the bandwidth up to 10 Hz. The relative standard deviation of residual fluctuations was similar to 1%. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

The study of the thermo-optical properties of a unique terbium oxide crystal was conducted. The key piezo-optical anisotropy parameter, ξ , which determines the prospects for using the material in isolators with high average power (more than 1 kW), was measured. It has been shown that the record-high value of the Verdet constant and the newly revealed negative value of ξ , equal to −0.11, make Tb 2 O 3 single crystals highly promising for use in high-power Faraday isolators.

A laser amplifier based on an active element in the shape of a Yb:YAG slab is developed. It combines the propagation of an amplified elliptical beam without internal reflections, the use of high-brightness diode pump channel combining, and a heat sink made of silicon carbide. Its laser characteristics and factors limiting the output pulse energy are studied. It is shown that the application of an active element with gradient doping ensures stable operation of the laser head at pump powers of ∼0.5 kW. The use of signal radiation diverging along one axis compensates for the effect of reducing the output cross section of the amplified beam; as a result, a gain of G = 4 is ensured with a beam quality factor M2 < 1.4.

We developed Yb:YAG thin slab scalable laser amplifier and investigated numerically and experimentally the main problems limiting its average and peak power: overheating, surface breakdown and pump power scaling. We have shown that using composite gradient doped slab with compensation of beam area compression effect allows to use pump power to 1000 W with maximum output energy of 50 mJ with a M2<1.5.

Broadband amplification of laser radiation in a combination of Yb:YLF and Yb:YAG crystals was demonstrated. It was shown that, with the input spectrum width of 20 nm, the width at the output spectrum can reach 17 nm. A thermal lens induced in the Yb:YAG crystal is partially compensated by the lens in the Yb:YLF crystal due to the different signs of the partial derivative n /partial derivative T coefficients of the crystals. The thermal lens in the Yb:YLF crystal in the thin and thick ("long -the -side pumped") rod geometries was studied theoretically and experimentally. An analytical model of thermally induced phase distortions in uniaxial crystals caused by the piezo-optical effect was developed for the thin -rod geometry. (c) 2024 Optica Publishing Group

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass $M>70$ $M_\odot$) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities $0 < e \leq 0.3$ at $0.33$ Gpc$^{-3}$ yr$^{-1}$ at 90\% confidence level.

It is proposed to use a new diamond–silicon carbide (DSC) composite “skeleton” as a heatsink material for Yb:YAG thin-disk lasers. The main advantage of the DSC “skeleton” over a conventional diamond is a possibility to manufacture parts of almost any size and shape, which allows optimizing heat removal parameters and achieving better mechanical and thermophysical properties. Temperature distribution, phase distortions, and lasing in the active elements on heatsinks made of DSK “skeleton” and diamond are compared theoretically and experimentally.

Magnetars are neutron stars with exceptionally strong dipole magnetic fields which are observed to display a range of x-ray flaring behavior, but the flaring mechanism is not well understood. The third observing run of Advanced LIGO and Virgo extended from April 1, 2019 to March 27, 2020, and contained x-ray flares from known magnetar SGR 1935+2154, as well as the newly-discovered magnetar, Swift J1818-1607. We search for gravitational waves coincident with these magnetar flares with minimally modeled, coherent searches which specifically target both short-duration gravitational waves produced by excited f-modes in the magnetar's core, as well as long-duration gravitational waves motivated by the Quasi-Periodic Oscillations observed in the tails of giant flares. In this paper, we report on the methods and sensitivity estimates of these searches, and the astrophysical implications.

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for $U(1)_{B-L}$ gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the $U(1)_{B-L}$ gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM.

Gravitational lensing by massive objects along the line of sight to the source causes distortions to gravitational wave (GW) signals; such distortions may reveal information about fundamental physics, cosmology, and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO-Virgo network. We search for repeated signals from strong lensing by (1) performing targeted searches for subthreshold signals, (2) calculating the degree of overlap among the intrinsic parameters and sky location of pairs of signals, (3) comparing the similarities of the spectrograms among pairs of signals, and (4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by (1) frequency-independent phase shifts in strongly lensed images, and (2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the nondetection of GW lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects.

The results of the ion source of the neutron generator upgrade, which makes it possible to operate in a CW mode, are presented. A magnetic trap consisting of permanent magnets (NdFeB) was developed. A 3-electrode extraction system equipped with a magnetic lens was used to extract the deuterium ion beam. Calculations are made for the formation of a deuterium ion beam with a current over 500 mA and an energy of 100 keV with practically no losses in the extraction system. Keywords: extraction system, magnetic trap, neutron generator, ion beam.

Tb3Al5O12(TAG) ceramics with high optical quality were fabricated successfully by a solid-state reaction method combined with hot isostatic pressing (HIP) post-treatment. The microstructure, optical transmittance, Verdet constant, and thermo-optical properties were investigated. The obtained TAG ceramics showed a dense microstructure, and the in-line transmittance reached 82.8% at 1070 nm after laser-grade polishing. The Verdet constant of TAG ceramics was measured to be 50.9 rad center dot T-1 center dot m(-1) at 1070 nm, which is higher than that of commercial Tb3Al5O12 crystals. The Faraday isolator based on TAG ceramics can provide an isolation ratio of 30 dB with a laser power of more than 1 kW. With excellent optical quality, high Verdet constant, and maximum working power, TAG transparent ceramics are promising for applications of kilowatt-level Faraday isolators.

The scheme for amplification of 4 beams in single-rod Yb:YAG amplifier and their coherent combining using a tiled aperture scheme is proposed and demonstrated experimentally. This approach will allow scaling average and peak power.

Thermal lens in zinc selenide (ZnSe), cadmium selenide (CdSe) and zinc sulfphide (ZnS) magnetooptical media was investigated by phase-shifting interferometry. It was shown that the thermal lens in ZnSe is 10 times weaker and in ZnS and CdSe are 2 and 16 times higher than in popular magnetooptical terbium gallium garnet crystal. The focal shift and thermo-optical characteristics and of magneto-optical figure of merit were determined. The obtained values of absorption coefficient 1.1x10(-4) cm(-1) allowed determining a record, 4 kW maximum operating power of a ZnSe Faraday isolator.

We created and measured properties (the Verdet constant, absorption coefficient, thermooptical constants Q and P relevant to thermally induced depolarization and thermal lens effect) of promising magneto-optical Terbium-Aluminium Garnet (TAG) and Terbium-Hafnium Pyrochlore (THP) ceramics. It is shown that TAG ceramics made by solid-state reaction sintering has smallest absorption coefficient and could work as magnetooptical element in Faraday Isolator (FI) with a kW-class laser power providing 30 dB isolation ratio. So, TAG based Faraday rotators can be successfully used in laser system with high average and peak power.

As a promising magneto-optical (MO) material applied in Faraday isolators, magneto-optical ceramics possess excellent comprehensive properties and have attracted much attention these years. Herein, we review the fabrication and properties of magneto-optical ceramics including garnet, sesquioxide, and A(2)B(2)O(7) ceramics. Some of the ceramics have been proved to possess applicable performance, while further studies are still needed for most of the magneto-optical ceramics. Aiming at the application for isolators, the research status, existing problems, and development trends of magneto-optical ceramics are shown and discussed in this review.

A unique compact Faraday isolator has been developed, based on a single-stage magnetic system, operating at wavelengths up to ∼800 nm and providing an isolation coefficient of more than 50 dB. The device was created thanks to the development of a new approach to optimizing permanent magnet systems.