Lucian Gheorghe

Second-harmonic generations of blue light in nonlinear optical crystals of Gd 1−x Lu x Ca 4 O(BO 3 ) 3 and Gd 1−x Sc x Ca 4 O(BO 3 ) 3 through noncritical phase matching

Nonlinear optical borate crystals of Gd1−xSCxCa4O(BO3)3 and Gd1−xLuxCa4O(BO3)3 have been grown and characterized. By changing the composition of these crystals, their optical birefringence can be controlled to obtain second-harmonic generations (SHG) in the ranges of 790-824 nm along the Y axis and 920-963 nm along the Z axis through noncritical phase matching (NCPM). The refractive indices of grown crystals were measured with a minimum-deviation technique. The experimental results of NCPM conditions for SHG are in good agreement with the theoretical predictions.

First measurement of the nonlinear coefficient for Gd(1-X)Lu(X)Ca(4)O(BO(3))(3) and Gd(1-X)Sc(X)Ca(4)O(BO(3))(3) crystals.

The effective nonlinear coefficient and temperature acceptance bandwidth of three Lu and Sc co-doped GdCa(4)O(BO(3))(3) type nonlinear crystals were measured. NCPM for SHG in to the blue-UV spectral region can be obtained by controlling the co-dopant concentration. Measurements were based on intra-cavity SHG of a CW Ti:Sapphire laser, and the effective nonlinear coefficients were found to be in the range of 0.5 to 0.6 pm/V for the three crystals used. The FWHM temperature acceptance bandwidth was measured to be more than 35 degrees C using a 6 mm long Gd(0.871)Lu(0.129)Ca(4)O(BO(3))(3) crystal. A maximum of 115 mW at 407.3 nm in a single direction was measured using a 6.5 mm long Gd0.96Sc0.04Ca(4)O(BO(3))(3) crystal.

Spectroscopy and energy transfer characteristics of Nd3+ in CNGG

The garnets with disordered structure such as calcium niobium gallium garnet (CNGG) doped with Nd3+ are interesting materials for diode pumping. Spectroscopic investigations on Nd3+:CNGG have revealed a multisite structure and this is reflected in laser emission characteristics. The purpose of this paper is to present several new spectral aspects, a modeling for the main nonequivalent centers, energy transfer characteristics and an attempt to connect the laser characteristics to centers structure. Samples were grown by Czochralski method with Nd3+ from 0.1 to 5 at.% and the high resolution spectral and decay measurements were performed at 10 K. Similar considerations were made in the case of Nd3+ doped in calcium lithium niobium gallium garnet (CLNGG).

New nonlinear Gd1-xRxCa4O(BO3)3 (R = Lu, Sc) crystals for 400-nm blue-violet light generation by type-I noncritical phase-matching frequency doubling processes

Single crystals of Gd1-xRxCa4O(BO3)3 (R3+ = Sc3+ or Lu3+) with large size and good quality have been grown by Czochralski method. The optical birefringence of Gd1-xScxCa4O(BO3)3 and Gd1-xLuxCa4O(BO3)3 crystals can be controlled by changing the compositional parameter x. The chemical compositions of the grown crystals were determined and X-ray diffraction measurements have been carried out to characterize the structural changes with compositional parameter x. According to our assumptions, the obtained results demonstrate that two of the grown crystals convert the near-infrared radiation of 800nm into blue-violet light (400nm) by type-I noncritical phase-matching (NCPM) second-harmonic generation (SHG) processes along Y axis.

1W of 902 nm Laser Emission of Neodymium Doped Strontium and Lanthanum Aluminate (Nd:ASL), under Fiber Coupled Diode Laser Pumping Source

We present a 792 nm fiber coupled laser diode pump Nd:ASL crystals Sr1-xLax-yNdyMgxAl12-xO19(x = 0.3; y = 0.05). The best results lead to 1W of 902 nm output laser with two Nd:ASL crystals concentration.

Growth and noncritical phase matching second harmonic generation of Gd 1-x R x Ca 4 O(BO 3 ) 3 (R = Sc or Lu) nonlinear crystals

Single crystals of Gd1-xRxCa4O(BO3)3 (R3+ = Sc3+ or Lu3+) with large size and good quality have been grown by Czochralski method. By changing the compositional parameter x of Gd1-xScxCa4O(BO3)3 and Gd1-xLuxCa4O(BO3)3 crystals, their optical birefringence can be controlled in order to achieve non critical phase matching (NCPM) in the ranges of 792-824nm along Y axis and 922-963nm along Z axis, during second harmonic generations (SHG). The chemical compositions of the grown crystals were determined and X-ray diffraction measurements have been carried out to characterize the structural changes with compositional parameter x. The solubility limits of R3+ ions in the Gd4Ca4O(BO3)3 crystals were also determined. Nonlinear optical properties of these new biaxial borate crystals are reported. Experimental determinations of doubled frequencies in NCPM conditions are in good agreement with theoretical predictions.

Crystal Growth of Gd1-xRxCa4O(BO3)3 (R = Sc or Lu) for Non Critical Phase Matched (NCPM) Second Harmonic Generation (SHG) at 800 nm

We have grown Gd1-xScxCa4O(BO3)3 (x = 0.10) and Gd1-xLuxCa4O(BO3)3 (x = 0.07, 0.13) nonlinear crystals and succeeded in generating a SHG of Ti:sapphire laser at almost 800 nm under non critical phase matching conditions.

Spectral and structural studies of GdCOB and YCOB crystals

The structural data obtained from of high resolution optical spectroscopic investigations on Nd3+, Eu3+ and Yb3+ ions in rare earth calcium oxoborate crystals RCOB, mainly GdCOB and YCOB, but also EuCOB, are compared with those obtained from other studies such as X-ray diffraction or differential thermal analysis. The dependence of non-equivalent center intensities and on R3+ (dopants) ionic radii is in qualitative accord with X-ray diffraction data. The glassy like behavior of 4F3/2 Nd3+ emission under selective excitation, as well as the shift of one line of 5Do → 7F1 Eu3+ emission are explained in terms of cationic structural disorder of RCOB crystals.

Growth and spectral characteristics of Nd3+ in calcium lithium niobium gallium garnet (CLNGG) crystals

Laser crystals with disordered structure present a series of advantages for diode pumping or short pulse generation as compared with ordered crystal. Such a system proved to be calcium lithium niobium gallium garnet (CLNGG) doped with Nd3+. The papers present the growth and x-ray analysis of specially doped CLNGG. Very few spectroscopic data on this system have been previously published. The paper present low temperature absorption spectra, site selective excitation and lifetime measurements of Nd3+ in CLNGG. At least four distinct nonequivalent centers are observed, the spectral lines for every center presenting a disordered Gaussian shape. based on structural, spectral static and emission dynamics data an attempt of modeling the structure of these centers is proposed.