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Single crystals of 0.7 at% Er:YVO 4 co-doped with varied concentrations of Yb (1.5, 3.0 and 8.0 at%) were grown by optical floating zone technique. The absorption spectra of the grown crystal are characterized by the prominent absorption at 985 nm due to Yb ion and multiple absorption due to Er ions. The overall characteristic absorption for π-polarization (E||c) is stronger than that for σ-polarization (E┴c) due to alignment of dipole moments along c-direction. The line strength of all the transitions of Er ions decreases as the doping concentration of Yb increases. Judd Ofelt parameter Ω 2 , which strongly depends on the environment of ligand, decreases with increasing Yb concentration in the lattice. The value of spectroscopic quality factor was found to be nearly invariant (~ 1.80) with respect to the Yb doping concentration but better than that for Er doped YVO 4 (~1.31) [1] . The radiative lifetime and emission cross-section of 4 I 13/2 → 4 I 15/2 transition of Er ions was also found to be independent of Yb doping concentration. This is one of the biggest advantages of Yb co-dopant as a good sensitizer in the Er:YVO 4 as it results in high population density in upper level of Er ions making it. The emission cross-section of 4 I 13/2 → 4 I 15/2 line for excitation at 985 nm is ~ 2.33 × 10 −20 cm 2 . Further, the values of emission cross-section for both the excitation at 808 nm (Er absorption line) and 985 nm (Yb absorption line) were found nearly same. [ABSTRACT FROM AUTHOR]

Undoped and Nd (0.2, 0.6, 0.8, 1.0, 1.2 and 1.6 at%)-doped GdVO4 single crystals have been grown by optical floating zone technique. XRD analysis reveals small lattice expansion especially along c axis on Nd doping. It has been observed that the extra-ordinary refractive index (RI) of undoped GdVO4 crystals is higher than the doped GdVO4 single crystals up to 1.0 at% Nd doping, beyond which it surpasses the value of the undoped crystal. This is due to the competing effect of lattice elongation and decrease in electron density on Nd doping. The increase in RI with Nd doping is attributed to macroscopic polarization effects. Moreover, the extra-ordinary refractive index (ne) only increases on increasing Nd concentration, whereas ordinary refractive index (no) remains unaffected within the measurement limits. The temperature-dependent RI measurements depicted a positive thermo-optic coefficient (TOC) for RI and birefringence, which is ~ 10−5/°C and is independent of doping concentration. TOC for ne is higher than no, which has been explained on the basis of anisotropic thermal expansion. An important set of relations between TOC and wavelength (532–1551 nm) has been established which is useful for estimating TOC in the temperature range of 30–150 °C. [ABSTRACT FROM AUTHOR]

Single crystals of Cr-co-doped 0.7 at.% Nd:YVO4 were grown using the optical floating zone method with varied Cr doping concentrations (0.7, 1.0, 1.4 and 2.0 at.%) in different oxygen partial pressures. The lattice parameters are unaffected by Cr doping. Further, the effect of the doping concentration and the growth atmosphere on the optical absorption, particularly for the 2A1→2B2 transition, which is due to the pentavalent state of Cr ion, has been investigated under two orthogonally polarized lights (i.e., E ⊥ [001]) and E ǁ [001]). This transition is important as it results in saturable absorption that is used for self-Q-switching of laser output. The observation suggests that the concentration of the desired pentavalent Cr increases to 1.4 and 2.0 at.% Cr as the oxygen partial pressure in the growth ambience increases, whereas for 0.7 and 1.0 at.% of Cr, the increase in the oxygen partial pressure results in an adverse effect. This finding suggests that on the basis of the concentration of Cr5+ required in Nd:YVO4 to attain the desired level of saturable absorption, the growth ambience should be chosen judiciously so that it is in line with the result presented here. [ABSTRACT FROM AUTHOR]

Single crystals of YVO 4 with different doping concentrations of Yb (1.5, 3.0, 8.0, and 15.0 at. %) and with good crystalline quality (FWHM ∼43-55 arc sec of rocking curve) were grown by the optical floating zone technique. Refractive index measurements were carried out at four wavelengths as a function of temperature. The measurements show that as the doping concentration of Yb is increased, the refractive index varies marginally for n e whereas there is a significant change in the value of n o . The thermo-optic coefficient (dn/dT) was found to be positive with a value ∼10 -5 /°C, which is 1 order higher than that for the undoped YVO 4 crystal. The thermo-optic coefficient is higher for n e compared to that of n o . Also, a set of relations describing the wavelength dependence of the thermo-optic coefficient were established that are useful for calculating the thermo-optic coefficient at any temperature in the range 30°C-150°C and at any wavelength in the range 532-1551 nm.