Spectroscopic and laser properties of Er:LuSGG crystal for high-power ∼2.8 µm mid-infrared laser.

We demonstrate a novel Er:LuSGG active gain medium emitting laser wavelength at 2795 nm for the first time. The Er:LuSGG crystal is grown successfully by the Czochralski method with high crystalline and optical quality. The spectra properties, including absorption and fluorescence emission cross-section are presented in contrast with similar Er-doped garnet crystals. The fluorescence lifetimes of the upper (4I11/2) and lower (4I13/2) laser levels are 1.75 and 4.64 ms, respectively. Under 973 nm laser diode pumping, a maximum output power of 789 mW in continuous-wave mode, corresponding to optical-to-optical efficiency of 20.2% and slope efficiency of 24.4%, is achieved with high laser beam quality. The results show that the Er:LuSGG is a promising MIR laser material operated at 2.8 µm.

2.7 µm dual-wavelength laser performance of LD end-pumped Er:YAP crystal.

We demonstrate a laser diode (LD) end-pumped Er:YAP laser with dual-wavelength outputs of 2710 and 2728 nm. The maximum average powers of 739 and 738 mW are achieved in the continuous wave (CW) and pulse modes, which corresponds to optical-to-optical efficiencies of 10.1% and 12.3%, and the slope efficiencies of 12.1% and 13.8%, respectively. In addition, a comparison of laser performance on differently sized crystals indicates that the 1 × 1 × 5 mm3 Er:YAP crystal has a best cooling efficiency. This helps to decrease the thermal lensing effect, which contributes to improving laser efficiency and beam quality.

Laser performance of a 966 nm LD side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 µm.

We demonstrate a 966 nm laser diode (LD) side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 µm under a high repetition rate. The lifetimes of the upper level I11/24 and lower level I13/24 are 0.66 and 0.85 ms, respectively. The laser performance under different repetition rates and pulse widths is experimentally studied with the optimal cavity structure. A maximum output power of 8.86 W is achieved at 125 Hz and 200 µs pulse widths, corresponding to the slope efficiency of 14.8% and electrical-to-optical efficiency of 7.7%. With increasing frequency from 50 to 200 Hz, the slope efficiency varies from 24.7% to 11.7% operated at a 125 µs pulse width. Moreover, the Mx2/My2 factors of 7.52/7.59 and Θx/Θy far-field divergences of 16.1/16.5 mrad are also measured. The results indicate that a high-performance 2.79 µm laser could be realized on the Er,Pr:GYSGG radiation resistant crystal by deactivation and LD side-pumping.

Thermal analysis and laser performance of a GYSGG/Cr,Er,Pr:GYSGG composite laser crystal operated at 2.79 µm.

We demonstrate the thermal analysis and laser performance of a GYSGG/Cr,Er,Pr:GYSGG composite crystal. The lifetime ratio of lower and upper levels of Er3+ in Cr,Er,Pr:GYSGG crystal is further reduced due to the optimized doping concentrations. The thermal effect of composite crystal is lower than that of Cr,Er,Pr:GYSGG crystal. A maximum pulse energy 342.8 mJ operated at 5 Hz and 2.79 µm is obtained on the composite crystal, corresponding to electrical-to-optical efficiency of 0.86% and slope efficiency of 1.08%. Under the same condition, these values on the Cr,Er,Pr:GYSGG crystal are only 315.8 mJ, 0.79% and 1.04%, respectively. Moreover, the composite crystal has also a relative high laser beam quality, exhibiting obvious advantage in reducing thermal effects and improving laser performances.

Growth, spectroscopy, and laser performance of a 2.79 µm Cr,Er,Pr:GYSGG radiation-resistant crystal.

We demonstrate the growth, spectroscopy, and laser performance of a 2.79 µm Cr,Er,Pr:GYSGG radiation-resistant crystal. The lifetimes for the upper laser level (4)I(11/2) and lower laser level (4)I(13/2) are 0.59 and 0.84 ms, respectively, which are due to the doping of the Pr(3+) ions. A maximum pulse energy of 278 mJ operated at 10 Hz and 2.79 µm is obtained when pumped with a flash lamp, which corresponds to the electrical-to-optical efficiency of 0.6% and a slope efficiency of 0.7%. A maximum average power of 2.9 W at 60 Hz is achieved, which corresponds to the electrical-to-optical efficiency of 0.4% and slope efficiency of 0.8%. Compared with a Cr,Er:YSGG crystal, the Cr,Er,Pr:GYSGG crystal can be operated at a higher pulse repetition rate. These results suggest that doping deactivator Pr(3+) ions can effectively decrease the lower laser level lifetime and improve the laser repetition rate. Therefore, the application fields and range of the Cr,Er,Pr:GYSGG laser can be extended greatly due to its properties of radiation resistance and high repetition frequency.

Performances of a diode end-pumped GYSGG/Er,Pr:GYSGG composite laser crystal operated at 2.79 µm.

We demonstrate a comparative investigation on Er,Pr:GYSGG and GYSGG/Er,Pr:GYSGG composite crystals at 2.79 µm. Simulating results show the highest temperatures are 369 K and 318 K, respectively. A maximum output power of 825 mW with slope efficiency of 19.2% and maximum laser energy of 3.65 mJ with slope efficiency of 22.7% are obtained in the GYSGG/Er,Pr:GYSGG composite crystal, which have an obvious improvement than those of Er,Pr:GYSGG crystal. The thermal focal lengths are respectively 41 and 62 mm when the pump power is 2.5 W. All these results indicate that the GYSGG/Er,Pr:GYSGG composite crystal has great advantages in reducing the influence of thermal effects and improving laser performances.

Spectroscopic properties and diode end-pumped 2.79 µm laser performance of Er,Pr:GYSGG crystal.

We demonstrate a 968 nm diode end-pumped Er,Pr:GYSGG (Gd1.17Y1.83Sc2Ga3O12) laser at 2.79 µm operated in the pulse and continuous-wave (CW) modes. The lifetimes for the upper laser level 4I11/ 2 and lower level 4I13/2 are 0.52 and 0.60 ms, respectively. The laser produces 284 mW of power in the CW mode, corresponding to the optical-to-optical efficiency of 14.8% and slope efficiency of 17.4%. The maximum laser energy achieved is 2.4 mJ at a repetition rate of 50 Hz and pulse duration of 0.5 ms, corresponding to a peak power of 4.8 W and slope efficiency of 18.3%. These results suggest that doping deactivator Pr3+ ions can effectively decrease the lower-level lifetime and improve the laser efficiency.

2.79 µm high peak power LGS electro-optically Q-switched Cr,Er:YSGG laser.

A flash lamp pumped Cr,Er:YSGG laser utilizing a langasite (LGS) crystal as an electro-optic Q-switch is proposed and demonstrated. It is proved that a LGS crystal with relatively high damage threshold can be used as the electro-optic Q-switch at 2.79 µm, and 216 mJ pulse energy with 14.36 ns pulse width is achieved. Its corresponding peak power of pulse can reach 15 MW, to our knowledge the best result at a 2.79 µm wavelength.

Spectroscopic, diode-pumped laser properties and gamma irradiation effect on Yb, Er, Ho:GYSGG crystals.

We demonstrate a diode end-pumped Yb, Er, Ho:Gd(1.17)Y(1.83)Sc(2)Ga(3)O(12) (GYSGG) laser operated at 2.79 µm in continuous-wave mode. Spectral analysis shows that Yb(3+) and Ho(3+) act as sensitizer and deactivator ions, respectively. Pumping with a 967 nm laser diode produces the maximum output power of 411 mW, corresponding to optical-optical conversion and slope efficiencies of 11.6% and 13.1%, respectively. The minimum laser threshold is only 81 mW because of Ho(3+) doping. The laser properties are only slightly influenced by 100 mrad gamma irradiation. The Yb, Er, Ho:GYSGG crystal possesses excellent radiation resistance and is a potential laser gain medium in radiant environments.

[Microstructure study on bismuth triborate crystal and its melt at high temperature by Raman spectroscopy].

Temperature dependent Raman spectra of BiB3 O6 crystal and its melt were recorded and the microstructure of BiB3 O6 melt was predicted. Multiple theoretical methods including quantum chemistry ab initio calculation and DFT (Density Function Theory) methods were applied to simulate the BiB3 O6 crystal and melt structure and Raman spectra. It was demonstrated that B-O triangles and Bi lattice in the crystal reveal little affected in structure while B-O tetrahedra shows severe distortion with increasing temperature, especially B-O tetrahedra disappears after being completely melt. The microstructure of BiB3 O6 melt consists of six-member ring, [B6 O12](6-), which varies in bond lengths and angles individually. Cation Bi behaves to balance the charge of anion cluster, and the oxygen coordination number of cation Bi is 3, different from the crystal situation in which cation Bi is coordinated with 6 oxygens.

Efficient diode-end-pumped dual-wavelength Nd, Gd:YSGG laser.

We demonstrate a dual-wavelength laser based on a new laser material-Nd, Gd:YSGG, or Nd:GYSGG for short-for the first time to our knowledge. Besides its attractive properties such as antiradiation, high segregation coefficient, etc., this kind of laser crystal also shows excellent laser performance. For continuous-wave operation, the maximum output power is 10.1 W with the absorbed power of 18.45 W at 808 nm, corresponding to the slope efficiency of nearly 60%. The maximum single pulse energy and peak power reach 277 µJ and 4.6 kW (60 ns) when the absorbed pump power is 11.4 W for acousto-optic Q-switched operation.

[Raman spectra analysis of Nd : YAG single crystal and its nano-powder].

In the present paper, the authors measured the Raman spectra of YAG/Nd : YAG single crystal, Nd : YAG precursor and the powder sintered at different temperatures. The bands of these Raman spectra were assigned and analyzed. The results show that there is a structure transformation process in the course of sintering Nd : YAG precursor. The powder sintered at 700 degrees C was amorphous and it is of AlO4 tetrahedron structure. With the increase in sintering temperatures, the Raman spectra varied mainly in two respects. One is the decrease in FWHM with the increase in the bands intensity; the other is the bands shift. These should be due to the increase in the order degree of the interface component. Additionally, the difference in the lattice vibration modes between the powders sintered at 800 degrees C and the Nd : YAG single crystal powder was caused by the contribution of the interface component.

[Raman spectroscopy studies on the aqueous solutions of sodium formate and lithium formate].

The structures of the aqueous solutions of sodium formate and lithium formate are studied according to the growth conditions of the crystals under different supersaturations and temperatures by Raman spectroscopy. The effects of temperature, concentration, supersaturation and cation on the structures of solutions and the structure difference between lithium formate solution and lithium formate monohydrate crystal are analyzed. The result shows that the concentration, temperature and supersaturation effect the structures of the solutions slightly and the cation effects the frequency of the bands greatly.

[Judd-Ofelt spectral theory].

In this article, the development and application of Judd-Ofelt spectral theory(J-O theory) was reviewed briefly. J-O theory was used to analyze the absorption and emission spectra of rare earth ions in solids, and compute their transition probabilities, line strengths, energy lifetimes, emission cross sections, and so on. When J-mixing was considered in J-O theory, the theoretical and experimental results were more consistent. The spectra of Pr3+ can be analyzed relatively accurately with modified J-O theory. The spectral properties of anisotropic crystal can be analyzed from the unpolarized-light transmission spectrum of a quadratic sample without special-orientation processing. The overlapped absorption bands can be treated as one band approximatively. The J-O parameters can also be calculated with fluorescence lifetimes.

[Structure analysis on growth solid-liquid boundary layer of BSO crystal at real time].

The micro Raman spectra of solid-liquid boundary layer, the melts and crystal side, were measured at real time, concerning BSO crystal grown with zone-melting method. The structure characters in boundary layer, melts and crystal were analyzed. The process, of which the growth unit structure changed while they transited from melts through boundary layer to crystal lattice, was analyzed. The results show that, there exists Bi3O4 and [SiO4] bonding structure in the melts of BSO crystal. While in the solid-liquid boundary layer, the Bi3O4 molecular units converge into [BiO7] octahedron monomer of polymer in form, the monomer or the polymer converge with the [SiO4] structure units, then all these converged structure enter into crystal lattice sites.

[Calculation of spectroscopic parameters of highly doped Er3+ in lithium niobate].

A highly doped Er3+: LiNbO3 (concentration 6 mol%) crystal was grown successfully by Czochralski method. The crystal is higher than that of the lowly doped Er3+ in LiNbO3 crystal, which is helpful to improve absorption coefficient of the grown the pumping efficiency. The absorption spectra at two unpolarized directions (X and Z) and two polarized directions (E parallel Z, E perpendicular Z) were measured. Using the Judd-Ofelt theory, and according to the measured absorption spectra, the intensity parameters omegalambda of Er3+ were fitted. The results of root-mean square (r. m. s) deviation show that the error of polarized fitting is less than that of unpolarized one. Thus fluorescence transition probabilities (Ajj), radioactive lifetime (tau), fluorescence branching ratio (beta), and integrated emission cross section (sigmap) were calculated and accepted according to the polarized results, and were also discussed and compared with the ones reported in the literature.

[High temperature Raman spectra and structure character study of BSO crystal].

The structure character of BSO crystal at room temperature was generalized. The main Raman shifts of lattice vibration at room temperature were interpreted. The Raman spectra of BSO crystal were measured in a temperature range from 293 K to 1123 K with high temperature Raman spectroscopy and time-resolved detection techniques. Temperature-dependence character of the Raman spectra of the crystal was investigated. The vibration mode of the longest bond Bi-O(1) in crystal shifts from 542 cm(-1) to 512 cm(-1) with the temperature increasing from room temperature to 1123 K. It can be attributed to the fact that oxygen atoms are electrostatic bond to Bi atoms. The intensity of 88 cm(-1) modes, which belongs to combination mode of bending and stretching in Bi3O4 unit, changes not so noticeably as other modes, and even the 58 cm(-1) mode of Bi atoms motions in crystal lattice decreases rapidly when the temperature is higher than 873 K, which indicates that the framework structure of the crystal is broken down at high temperature, while the Bi3O4 unit still exists.

[Crystal growth and spectral parameter computation of Yb:YAG].

In this article, a good-quality crystal Yb:YAG was grown by pull method, and its absorption spectrum of 200-3000 nm was measured at room temperature. Its absorption of 200-300 nm is from the host YAG, and there exists only the characteristic absorption of Yb3+ in the range of 390-3000 nm. Judd-Ofelt theory computation indicates that the absorption and emission oscillator strengths of electric dipole of (24 at%) Yb:YAG are 3.58 x 10(-6) and 4.77 x 10(-6), respectively, and the absorption and emission transition probabilities are 879 and 1171/s respectively. As for magnetic dipole, the absorption and emission oscillator strengths are 3.32 x 10(-7) and 4.43 x 10(-7) respectively, and the absorption and emission transition probabilities are 82 and 109/s respectively. The lifetime of the energy level2 F(5/2) is 781 micros.

[Raman spectra study of tellurium dioxide (TeO2) crystal].

The room temperature and high temperature Raman spectra of solid/melt growth boundary layers of TeO2 grown from melt were measured by high-temperature laser-micro-Raman spectrum. By analyzing, vibrational modes of the room temperature Raman spectra peaks of TeO2 crystal from band 200-800 cm-1 were confirmed, the expansion and frequency shift of each peak of the high temperature Raman spectra were interpreted and the possible structure group of the melt was proposed. So, certain foundation for studying the growth theory of functional crystal materials was provided.