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Spectroscopy and laser operation of Ho:CaYAlO4

Single crystals of Ho-doped CaYAlO4 crystals with 1.0% and 0.5% holmium concentration have been grown by Czochralski technique in N2 atmosphere. Due to the randomly distributing of Ca2+ and Y3+ ions in the crystal structure, the doped Ho3+ ions show a broad absorption and fluorescence bands. So it can be efficiently utilized to obtain ultrafast pulse generation in time range of pico- or even femtoseconds. Moreover, Ho:CYA laser was operated pumped by Tm:fiber laser, and the maximum output laser power of 2.38 W for 1.0% Ho:CaYAlO4 was obtained.

Effect of substitution of lutetium by gadolinium on emission characteristics of (Lu x Gd 1-x ) 2 SiO 5 : Sm 3+ single crystals

Single crystals of (LuxGd1-x)2SiO5:Sm (0.5 at%) with x = 0.19 (81% Gd3+) and x = 0.11 (89% Gd3+) belonging respectively to the C2/c and P21/c space groups were grown by the Czochralski method under nitrogen atmosphere. Detailed investigation of their spectroscopic properties were performed with the aim of understanding the effect of structural modification on emission characteristics of incorporated Sm3+ ions with a special attention directed to a laser potential associated with yellow emission line. It was inferred from low temperature optical spectra that almost all emission intensity in the host with C2/c symmetry comes from one of two available Sm3+ sites, whereas two Sm3+ sites contribute to emission in the host with P21/c symmetry. Excitation spectra of Sm3+ emission recorded in the VUV-UV region between 100 nm and 350 nm made it possible to locate the energy of CT transition at about 6.11 eV and to assess the low energy limit for the 4f5→ 4f45d1 transitions of Sm3+ to about 6.81 eV. It implies that in the two systems studied these energies are advantageously high thereby preventing the contribution of intense allowed transitions to an adverse excited state absorption of both blue pump radiation and yellow emission. Experiments of optical amplification of yellow emission were performed employing a pump-and-probe technique in order to verify this implication. It was found that for a LGSO:Sm3+ crystal having the C2/c symmetry an increase of the pump power density from 20 mJ/cm2 to 50 mJ/cm2 at a constant power probe density of 150 μW/cm2 brings about a positive gain growing from about 0.25 to 2 [cm−1]. In the same conditions a maximum gain value of 1 cm−1 was measured for LGSO:Sm3+ crystal having the P21/c symmetry. It was concluded that the former system is promising for the design of all-solid-state yellow lasers.

Optical properties of crystals doped with Sm3+ or Dy3+ relevant to potential InGaN/GaN laser diode-pumped visible laser operation: A comparative study

Results of detailed spectroscopic investigation of Sm3+ and Dy3+ ions incorporated in crystal structures of Yal YAl3(BO3)4, LiNbO3, Gd3Ga5O12, Gd2SiO5, Lu2SiO5 and (Gd, Lu)2SiO5 are reported and discussed. The impact of the hosts on transition intensities and excited state relaxation dynamics of incorporated luminescent ions was examined. Distribution of luminescence intensity among spectral bands in terms of luminescence branching ratios was evaluated based on numerical integration of luminescence bands. Intensities of UV and blue absorption bands potentially useful for optical pumping were determined quantitatively in units of absorption cross section. The most intense luminescence bands related to potential laser transitions 4G5/2 → 6H7/2 of Sm3+ around 600 nm and 4F9/2 → 6H13/2 of Dy3+ around 580 nm were calibrated in units of emission cross section. Evaluated peak values of emission cross section range from 0.43 × 10−20 cm2 for Sm3+ in (Gd, Lu)2SiO5 to 1.17 × 10−20 cm2 for Sm3+ in LiNbO3. Those for dysprosium-doped crystals range from 0.63 × 10−20 cm2 for LiNbO3:Dy3+ to 2.0 × 10−20 cm2 for Yal YAl3(BO3)4:Dy3+. It follows from these considerations that samarium-doped crystals show promise for laser application owing to the combination of a strong absorption that matches radiation of commercial laser diodes emitting near 405 nm and long luminescence lifetime. Major shortcoming of dysprosium-doped crystals results from a weak intensity of absorption bands available for optical pumping near 450 nm and 385 nm combined with relatively strong self-quenching of luminescence.