Self-Frequency Doubled Green NdxY1-xCa4O(BO3)3 Laser

Abstract

Nd-doped yttrium calcium oxyborate, NdxY1-xCa4O(BO3)3 (NYCOB), was grown using pulling from the melt, with large sizes and good optical quality as well as different Nd3+-ion densities of 0 to 10 at% in the lattice structure. These crystals belong to the monoclinic system with point group m, conforming space group Cm. The unit cell constants were a = 0.8076(7), b = 1.6020(10), and c = 0.3527(2) nm for a Nd3+ content of 8 at%, with β = 101.23°, and z = 2. The measured absorption of the NYCOB was compared to Judd-Ofelt (JO) theory. When applied, the JO theory of parity-forbidden electric-dipole transitions of rare earth ions on non-centrosymmetric sites demonstrates good agreement. The polarized absorption coefficients at 811 nm were calculated as αX = 1.59, αY = 1.75, and αZ = 2.02 1/cm, respectively. The valence–conduction band gap is about 5.39 eV. The fitted intensity parameters Ωt (t = 2, 4, and 6) were 3.51 × 10—20, 7.82 × 10—20, and 3.79 × 10—20 cm2, with a root-mean square deviation of 6.30 × 10—21 cm2. The emission properties of the excited 4F3/2 state with the level lifetime of 216.67 μs were studied, which exhibit the two pass bands of laser for possible applications in practice. The self-frequency doubling tests are interesting. A very low threshold power of 2 mW for a sample with average Nd3+ content of 7 at%, length of 6 mm, and phase matching angles of θ = 64.5° and φ = 35.5° have been measured. The measured output power of green light was 19.4 mW accompanied with a conversion efficiency of 3.7%.