A broadband circularly polarized metasurface antenna with low radar cross-section (RCS) is proposed. Four metasurface elements are arranged orthogonally in a 2×2 array and fed with a 90° phase difference to achieve circular polarization radiation. Each metasurface element is a non-uniform sub-array of 4×4 metallic patches. Attributed to the non-uniform property of the metasurface element, two characteristic modes with different resonant frequencies but with similar surface current distributions are formed. By optimizing the geometric parameters of the non-uniform element, the two modes are merged with each other, resulting in bandwidth (BW) broadening of the proposed antenna. Simulated and measured results show that the designed antenna has a −10-dB impedance BW of 49.60%, 3-dB axial ratio BW of 33.13%, and peak gain of 13.17 dBic. Moreover, the RCS reduction is higher than 6 dB in the entire operation frequency band. Additionally, the antenna has a low profile of 0.08λ (λ is the free-space wavelength at an operation frequency of 8.25 GHz).

Optical absorption and emission intensities are investigated for ${\mathrm{Nd}}^{3+}$ ions in a $\alpha -{\mathrm{Nd}}^{3+}{:\mathrm{L}\mathrm{a}\mathrm{S}\mathrm{c}}_3{(\mathrm{B}\mathrm{O}}_3{)}_4$ crystal. Oscillator strengths of transition were measured from absorption spectra recorded at 300 K. Corresponding oscillator strengths for transition between the J manifold were calculated using the Judd-Ofelt theory. Phenomenological intensity parameters were derived from a least-squares-fitting procedure. The root-mean-square deviation of observed and calculated oscillator strengths was ±8.1%. The intensity parameters were also used to calculate the radiative transition probabilities and branching ratios from a level of ${}^4{\mathrm{F}}_{3/2},$ which fluoresce in a $\alpha -{\mathrm{Nd}}^{3+}{:\mathrm{L}\mathrm{a}\mathrm{S}\mathrm{c}}_3{(\mathrm{B}\mathrm{O}}_3{)}_4$ crystal. The stimulated emission cross sections ${\sigma }_p$ were calculated. It was concluded that $\alpha -{\mathrm{Nd}}^{3+}{:\mathrm{L}\mathrm{a}\mathrm{S}\mathrm{c}}_3{(\mathrm{B}\mathrm{O}}_3{)}_4$ crystal is a laser material with high-emission intensity.

The compound β-LaSc₃(BO₃)₄ crystallizes in the rhombohedral with space group R32 and cell parameters a=9.819(3), c=7.987(1) Å, Z=3, V=666.5(3) ų, Dc=3.80 g/cm³, λ(MoKα)=0.71067 Å, F(000)=708, final R=0.053. R_W=0.072 for 512 observed reflection with I≥3σ(I). The La atoms, Sc atoms and B atoms occupy trigonal prisms, octahedra and planar triangle of oxygen, respectively. The isolated LaO₆ trigonal prisms alternate along the c-axis with BO₃ triangle (B(1)) that are perpendicular to the c-axis. La³⁺ ions join by means of La-O-Sc(B)-O-La with the distance between La³⁺ ions being 6.263 Å. This structural characteristic will result in a weaker interaction between Nd³⁺ ions and a lower fluorescence concentration quenching effect.

Cr³⁺ ion doped MgWO₄ crystal with dimensions of 3 × 3 × 20 mm³ has been grown for the first time. The Cr³⁺:MgWO₄ crystal showed strong absorption in the visible range and strong emission in the near-infrared range. The absorption and emission cross section of this crystal are 8.86 × 10⁻²⁰ cm² and 41 × 10⁻²⁰ cm² at 740 nm and 993.6 nm, respectively. Energy transfer procedure between Cr³⁺ ion and the defect center in the host crystal has been demonstrated. The crystal field, electron-vibration coupling and energy levels of the Cr³⁺:MgWO₄ crystal are discussed.

An Nd³⁺ -doped Li₃Ba₂Y₃(WO₄)₈ crystal with dimensions up to 32 × 20 × 14 mm³ has been grown by the TSSG method. The Li₃Ba₂Y₃(WO₄)₈ crystal crystallizes in the monoclinic system with the space group C2/c. The unit cell parameters are a = 5.181(2) Å, b = 12.677(7) Å, c = 19.161(10) Å, β = 92.237(13)° and Z = 2. The Li₃Ba₂Y₃(WO₄)₈ crystal has a high structure disorder. The spectral properties of Nd³⁺ -doped Li₃Ba₂Y₃(WO₄)₈ crystal exhibited broad absorption and emission bands, which are caused by the disordered structure of the Li₃Ba₂Y₃(WO₄)₈ crystal. Therefore, it may be regarded as a laser host material for diode laser pumping.

In order to obtain new, more efficient laser materials for diode laser-pumped lasers, the laser host materials with broad absorption bands are very important. This paper reports the structure and spectral properties of Nd³⁺ : KBaGd(MoO₄)₃ crystal. KBaGd(MoO₄)₃ crystallizes in the monoclinic system with space groupC2/c. The structure analysis shows that KBaGd(MoO₄)₃ crystal has a disordered structure. The investigation of the spectral properties of Nd³⁺ : KBaGd(MoO₄)₃ crystals shows that it exhibits broad absorption and emission bands, which are caused by the disordered structure of the KBaGd(MoO₄)₃ crystal. The broad absorption band is very suitable for diode laser pumping. To sum up the spectral properties of Nd³⁺ : KBaGd(MoO₄)₃ crystal, it may be regarded as a potential solid-state laser material for diode laser pumping.