The magneto‐optical ceramics of terbium oxide doped with different rare earth elements (REE) REE:Tb2O3 (REE—Y3+, Lu3+, Sc3+, Ce3+, Dy3+, Ho3+, Yb3+, Nd3+) are successfully fabricated by hot pressing ...using powders obtained by the self‐propagating high‐temperature synthesis (SHS) method. The prepared REE:Tb2O3 ceramics have good optical quality and magneto‐optical properties. The in‐line transmittance of Tb2O3 ceramics doped with REE except Sc3+ is close to undoped terbium oxide, especially in the long‐wavelength region. The Verdet constant of the REE:Tb2O3 samples considered at 633 nm is about 3.3 and 2.6 times higher in absolute value than that of the commercial terbium–gallium garnet (TGG) single crystal and terbium–aluminum garnet (TAG) ceramics, respectively. It is noted that REE (except Yb3+ and Nd3+) doping only slightly increases the Verdet constant of pure Tb2O3 (when the content of terbium ions in the optical element is taken into consideration in the calculation). The dilution of the Tb2O3 matrix with REE in relatively high concentrations leads to a decrease in the absolute value of the Verdet constant.
Rare earth elements in terbium oxide ceramics increase its Verdet constant, normalized to the concentration of terbium ions. However, the Verdet constant absolute value decreases due to the dilution of the Tb2O3 matrix with rare earth elements. Thus, pure terbium oxide has a record Verdet value among the studied materials.
Faraday isolators for high average power lasers operating at room temperature are surveyed. Three devices on 001 oriented TGG crystals with the most known optical schemes are considered: traditional ...scheme, and schemes with compensation of thermally induced depolarization inside magnetic field and outside magnetic field. We report a unique 30-mm-aperture Faraday isolator with thermally induced depolarization compensation inside magnetic field. It provides 33.5-dB isolation ratio at 1.5-kW average laser power.
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·T1·m−1 at 1070 nm, which is higher than that of commercial Tb3Ga5O12 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.
A cycle of works on manufacturing and studying laser and magnetooptical ceramics with a focus on their thermo-optical characteristics performed by the research team is analyzed. Original results that ...have not been published before such as measurements of the Verdet constant in the Zr:TAG, Re:MgAl2O4, and ZnAl2O4 ceramics are also presented.
Faraday isolator with composite terbium gallium garnet TGG/sapphire magneto-optical elements that were produced by the surface-activated direct bonding method was created. Thermally induced ...depolarization and thermal lens for composite elements were investigated experimentally and numerically. The resulting structures operated successfully at a high radiation power, providing an isolation ratio exceeding the classical single element made of TGG by 5 dB and amounted to 34 dB at a laser power of 700 W. The maximum operating power at which the isolation ratio was higher than 30 dB was estimated to be over 2 kW, which is almost 3 times more than in the case of a single TGG.
Magnetoactive materials are of considerable current interest, primarily for applications in nonreciprocal Faraday devices used for polarization control, optical isolation, optical switching, and ...modulation. The need for such devices is growing with laser power enhancement. They reduce risk of self-excitation of the amplifiers and optical elements damage and are a handy tool for organizing multipass schemes. However, at high average power of radiation these devices are subject to thermally induced effects that impair their operability and lead to increased losses and to the formation of phase distortions in the transmitted radiation. One of the methods to reduce thermally induced effects is to use in Faraday devices new magnetoactive materials with better thermo-optical properties. This paper is devoted to the study of thermo-optical and magneto-optical characteristics of a unique magnetoactive material-a terbium scandium aluminum garnet (TSAG) crystal. The TSAG has an extraordinary value of optical anisotropy parameter ξ, a Verdet constant 25% higher than the traditionally used terbium gallium garnet crystal and the highest magneto-optical figure-of-merit known in magnetoactive materials at the moment.
Thermally induced distortions of laser radiation caused by the photoelastic effect during high-power beam propagation through optical elements cut along the optical axis of uniaxial crystals have ...been investigated. Thermo-optical characteristics for uniaxial crystals of all three syngony types have been introduced: the optical anisotropy parameter ξ defining the distribution of the axes of thermally induced birefringence over the cross section of the optical element, and the thermo-optical constants Q and P specifying the value of thermally induced depolarization and thermal lens strength, respectively. The introduced thermo-optical characteristics may be used as applicability criteria of various uniaxial crystals for work with high-power laser radiation. The optical anisotropy parameter ξ of trigonal and hexagonal crystals has been found to be equal to unity by virtue of the isotropy of their piezo-optical properties in a plane perpendicular to the optical axis. We have analyzed by way of example thermally induced polarization distortions in a tetragonal DKDP crystal and in a trigonal CeF 3 crystal. The distributions and dependences observed in experiment fully agree with the theoretical considerations.
A Faraday isolator system with external compensation of thermally induced birefringence was investigated for the case when optical components of the Faraday isolator and the compensator are made of ...different materials. Simultaneous reduction of thermally induced depolarization and thermal lens in the Faraday isolator based on a TGG crystal was demonstrated experimentally for the first time using an Sm:CaF
2
crystal. A method of compensating thermally induced birefringence without reciprocal polarization rotator was described theoretically and demonstrated in experiments for the first time. It was used as a basis for a new scheme of Faraday isolator with external compensation of thermally induced birefringence.
Samples of TAG ceramics doped with Ce and Pr ions (0, 0.5, 1, 1.5, 2 at.% concentrations) and with Ho ions (0.5 at.%) were studied. The wavelength dependence of the Verdet constant of each sample in ...the 405 nm - 1064 nm range was measured, and analytical approximation was found. The obtained value of the Verdet constant of the studied TAG ceramics did not depend on the dopant concentration and type in the studied range of concentrations. The dependence of thermally induced depolarization on laser radiation power was investigated, and the magneto - optical figure of merit was estimated for each studied sample. It was demonstrated that doping of ceramics can provide a substantial reduction of the magneto-optical figure of merit. The obtained results will be useful for creating Faraday isolators and rotators based on TAG ceramics.
A magneto-active terbium containing cubic zirconia crystal is an attractive material for creating Faraday isolators thanks to a high value of its Verdet constant and low absorption coefficient. The ...optical anisotropy parameter of this crystal which shows the distribution of orientations of the axes of thermally induced birefringence in a thermally loaded optical element has negative value. It means that there exists a dedicated orientation of crystallographic axes, at which the axes of thermally induced birefringence are arranged in the one direction and thermally induced depolarization may be reduced substantially. For assessing potential of this crystal for high-power applications we have investigated its temperature dependence of the Verdet constant that proved to correspond to the paramagnetic behavior. Thermo-optical characteristics are also of principal importance when operating with high-power laser radiation. We present results of measurements of thermo-optical characteristics Q and P which determines values of polarization and phase distortions of passing laser radiation. Measured values can be used to determine the characteristics of Faraday isolators based terbium containing cubic zirconia crystals in various implementations of their optical schemes for various parameters of laser radiation.
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