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The polarized absorption and emission spectra have been measured for the Tm3+ doped NaY(MoO4)2 crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters Ω t eff (t = 2, 4, 6) are 11.67 ×10−20, 2.21 × 10−20, 1.74 × 10−20 cm2, respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm3+ doped laser crystals, Tm3+:NaY(MoO4)2 crystal has potential as a promising laser crystal.

Large crystals of pure and Y b 3+ doped NaY (MoO 4 ) 2 have been grown using the Czochralski method. The major problem with these crystals is that they are black in colour, causeing total absorption in the visible range, this was resolved by annealing and the nature of the colour defect was discussed. Measurements such as DTA, thermal expansion in different crystallographic directions, and refractive index as a function of wavelength were investigated. The broad absorption band at about 980 nm and high value of the absorption cross-section are obtained for the Y b 3+ doped crystal. The results show that Y b 3+ :NaY (MoO 4 ) 2 crystal has potential as a promising laser crystal.

This paper reports crystal growth and optical characteristics of dysprosium (Dy3+) and erbium (Er3+) doped mid-infrared laser crystal temary-potassium-lead-chloride (KPb2Cl5). Two transparent crystals with good optical quality have been grown successfully by using the Bridgman technique, the largest crystal size reaches up to 010x60mm(2). Measurements of X-ray diffraction (XRD) and absorption spectra were carried out. Based on Judd-Ofelt theory, the intensity parameters Omega(t)(t=2,4,6), the experimental and theoretical oscillator strengths have been obtained. The intensity parameters Omega(t)(t=2,4,6) of Er3+ :KPb2Cl5 were calculated to be Omega(2)=5.10 x 10(-20) cm(2), Omega(4)=1.25 x 10(-20) cm(2), Omega(6)=0. 83 x 10(-20) cm(2), and the values for D Y3+ :KPb2Cl5 were calculated to be Omega(2)=6.26 x 10(-1) cm(2), Omega(4)=2.45 x 10(-20) cm(2), Omega(6)=0.04 x 10(-20) cm(2) respectively.

The Dy3+-doped NaY(MoO4)2 single crystals were grown successfully by the Czochralski technique. The main spectroscopic properties (absorption, luminescence, decay curve) of Dy3+-doped NaY(MoO4)(2) have been determined for both the sigma and pi polarizations. By using the Judd-Ofelt theory, the measured room temperature absorption spectra were applied to determine the intensity parameters, spontaneous transition probabilities, branching ratios, and radiative lifetimes of Dy3+ transitions. The results show that the Dy3+-doped Nay(MoO4)(2) crystal may realize the yellow laser operation. (C) 2006 Elsevier B.V. All rights reserved.

In this paper, we present the broadband optical amplification in bismuth-doped germanate glass, at the second telecommunication window when excited with 808 nm and 980 nm laser diodes, respectively. The amplification range is from 1272 nm to 1348 nm wavelength, which is within the O-band of silica fiber communication. This bismuth-doped glass can be used as ultra broadband amplification material for wavelength-division-multiplexing (WDM) at the second telecommunication window.

Yb3+ doped SrWO4 crystal has been grown by the Czochralski method. Polarized absorption and emission spectra together with fluorescent decay curve were measured at room temperature. The stimulated emission cross sections of the potential laser transitions were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula. The potential laser gain versus wavelength for the F-2(5/2) ->-> F-2(7/2) transition was also estimated and discussed. This material is a potential candidate for a 1.0 mu m laser media. (C) 2006 Elsevier B.V. All rights reserved.

Ho3+-doped SrWO4 crystal was grown by the Czochralski method. The polarized absorption and emission spectra together with the fluorescent decay curve were measured at room temperature. The intensity parameters, radiative lifetimes and branching ratios were calculated based on the Judd-Ofelt theory. The stimulated emission cross-sections of the potential laser transitions were determined using the reciprocity method.

Tin doped NaBi(WO4)(2) of good optical quality with sizes of about 20 min x 20 mm x 40 mm was grown successfully by the Czochralski technique. The absorption spectra for both sigma- and pi-polarizations were recorded at room temperature. Based upon these data, the oscillator strengths and radiative transition rates were evaluated. The sigma- and pi-polarized emission spectra together with the fluorescence decay curve were also obtained. The emission cross-section of the potential laser transition at 1460 nm was determined to be 1.49 x 10(-19) cm(2). The results show that Tm3+:NaBi(WO4)(2) crystal is a promising laser material. (c) 2006 Elsevier B.V. All rights reserved.

The polarized absorption, emission spectra and the fluorescence decay curve of Er3+ ions in the anisotropic NaY(MoO4)2 crystal were investigated at room temperature, and spectral parameters have been calculated from the absorption data based on the Judd–Ofelt theory. The experimental oscillator strengths for the transitions from the ground state to excited states were compared with the theoretical oscillator strengths calculated from the Judd–Ofelt theory. The emission cross-section and gain cross-section for the π- and σ-spectrum were determined for the 4H13/2 → 4H15/2 transition of special interest for laser application.

The polarized absorption and emission spectra of Pr3+ ions in NaY(MoO4)2 single crystal were investigated. The standard and modified Judd–Ofelt theory have been applied to the measured optical absorption intensities to determine the spectroscopic parameters, including the Judd–Oflet intensity parameters Ωt (t=2,4,6), the radiative transition rates, branching ratios, and emission cross-sections for various excited levels of Pr3+ ions. In samples with Pr3+ ions concentration of 2.00×1020 cm-3, the excitation of the 1D2 manifold decays non-radiatively by the electric dipole–dipole transfer between Pr3+ neighbors. The good spectroscopic properties show the possible application of the Pr3+ doped NaY(MoO4)2 crystal as a solid-state laser.

Yb3+:GdAl3(BO3)4 (hereafter Yb3+:GAB) crystals with large sizes and good optical quality have been grown by the top-seed solution growth (TSSG) method. The polarized absorption and emission spectra have been investigated at room temperature. For the σ-polarization, the intensities of both absorption and emission spectra are stronger than those for the π-polarization, the σ-absorption cross section of Yb3+ in GAB being 3.43×10-20 cm2 at 977 nm, and the σ-emission cross section being 0.98×10-20 cm2 at 1045 nm. The fluorescence lifetime of the 2 F 5/2→2 F 7/2 transition was measured to be 800 μs in the 5% doped sample used for our laser experiments, 993 μs in a 10% doped sample and 569 μs in a 0.5% doped sample. The laser parameters were estimated as: βmin=0.022, Isat=10.4 kW/cm2 and Imin=0.23 kW/cm2. About 0.4 W laseroutput at the wavelength of 1043 nm was achieved when the Yb3+:GAB crystal was pumped by a 974 nm laser diode, with 27.4% slope efficiency.

Ca3Gd2(BO3)4:Nd3+ crystals of high optical quality with a size up to 20 × 50 mm were grown by the Czochralski method. The absorption spectra of the crystal in three mutually perpendicular arbitrary directions were measured. Based on Judd–Ofelt and TPM methods, the intensity parameters Ω t (t = 2, 4, 6), the experimental and theoretical oscillator strengths, the radiative transition rates, radiative lifetime and fluorescent branching ratios of Nd3+ from 4F3/2 to 4IJ, were obtained. The fluorescence spectrum and decay curve under excitation at 808 nm were also measured. The stimulated emission cross-section and radiative quantum efficiency were also calculated.

The absorption and fluorescence spectra of Nd3+:Gd0.2Y0.766Al3(BO3)4 crystal have been measured. Basing on Judd–Ofelt and TPM theory, intensity parameters Ω t (t=2,4,6), radiative lifetime, experimental and theory oscillation strength, fluorescence branching ratios and stimulated emission cross-sections were obtained and related to the laser action of this crystal. A laser output of 48 mW at 1060 nm and of 78 mW at 1300 nm with the optical to optical efficiency of 20% and of 9.75% respectively were obtained under a Ti–sapphire laser pumping. Meanwhile, a laser output of 26.7 mW at 532 nm with an optical to optical efficiency of 10.68% was obtained when it was pumped by a AlGaAs diode laser.

The Ca 3 Gd 2 (BO 3 ) 4 :Yb 3+ crystal with a size up to ∅ 20 mm×50 mm was grown by the Czochralski method. The absorption and emission spectra were measured. There is a broad absorption band ranging from 850 to 1000 nm in the absorption spectrum. A broad emission spectrum from 930 to 1100 nm was exhibited from 895 nm wavelength pumping. This crystal is promising as a tunable infrared laser crystal.

The Ca3Y2(BO3)4:Er3+ crystal with a size up to ϕ 20 mm×30 mm was grown by the Czochralski method. The absorption spectrum was measured and its absorption peaks were assigned to the corresponding transitions between the Er3+ energy levels. A broad emission spectrum from 1429.4 to 1662.8 nm was exhibited from 530 nm wavelength pumping. This crystal is promising as a tunable infrared laser crystal.

The absorption spectra of Tm3+:KGd(WO4)2 crystal in three mutually perpendicular arbitrary directions at room temperature were measured. Based on Judd–Ofelt theory and TPM method, the intensity parameters Ω t (t=2,4,6) , the radiative lifetimes, the experimental and theoretical oscillation strengths, and the fluorescence branching ratios were obtained. The broad emission spectrum from 1650 to 2000 nm was obtained under 800 nm excitation. Also, the fluorescence spectra at 455 and 665 nm were measured under 360 nm excitation. Their stimulated emission cross-sections were also calculated.

We report for the first time the spectroscopy and the laser operation of GdAl 3 (BO 3 ) 4 : Nd 3+ (NGAB) near 1338 nm corresponding to the 4 F 3/2 → 4 I 13/2 channel. Their features have been found favorable for self-frequency doubling in order to generate a red radiation at 669 nm and more generally for self-frequency conversions. The emission cross-section in σ-polarization was estimated to be 5.5×10 −20 cm 2 . We demonstrated self-frequency doubling despite of non-optimal experimental conditions.

Under short-pulsed longitudinal pumping at 600 nm we obtained intracavity stimulated Raman scattering frequency self-conversion of the 1352.5 nm laser line in KGd(WO4)2:Nd3+. The wavelength which was produced is eye-safe at 1539.5 nm and the conversion efficiency was 1.26% with uncoated faces of the 3 cm long crystal.

A diode pumped intracavity frequency-doubled Nd: YVO4 laser emitting at 671 nm with a type-II noncritical phase-matched LBO crystal is reported. A maximum output power at 671 nm of 404 mW was obtained under an incident pump power of 5.16 W, with an optical-to-optical conversion efficiency up to 7.8%. The output power fluctuates less than 5% while the temperature change of the LBO crystal is maintained at ± 0.5 °C at the phase-matched temperature.

Bulk crystals of 4-aminobenzophenone (ABP) were grown from organic solution. The crystal structure was determined by X-ray analysis. The refractive indices were determined by the method of prism minimum deviation. Some effective nonlinear-optical coefficients d eff were measured. A blue second-harmonic emission with wavelengths of 433 and 460 nm were observed during laser diode pumping.

Studies of the linear and nonlinear optical properties of KBBF crystal were carried out. The Sellmeier's equations, which are accurate from 1.4 μm to about 180 nm, are reported. KBBF crystal has been found to be phase matchable for second harmonic generation down to 180 nm and to possess a phase-matching retrace behavior, which just occurred in the commercial laser region.

We demonstrate the simultaneous generation of the three basal red–green–blue colors from a lone GdAl3(BO3)4:Nd3+ bi-functional laser and optical nonlinear crystal. The laser works in a dual-wavelength operation in the two 4F3/2→4I11/2 (near 1062 nm) and 4F3/2→4I13/2 (near 1338 nm) channels, under a fixed wavelength pumping (at 744.7 nm) and with a fixed crystal orientation. Red and green results from self-frequency doubling of the two laser channels, blue results of self-sum frequency mixing of the pump and the 1338 nm laser.

We combine inside a single noncentrosymmetric laser crystal, GdAl3(BO3)4:Nd3+, a stimulated emission and two second-order nonlinearities in cascade. The first one self-doubles the 1062.8 nm Nd3+ laser emission corresponding to the 4F3/2→4I11/2 channel, despite the fact that it is not phase-matched. The second one can be phase-matched or not and mixes the laser wave and its second harmonic (SH) in order to produce the third harmonic (TH) at 354.3 nm.

13C separation at a laboratory scaled-up level by the13C-selective InfraRed MultiPhoton Dissociation (IRMPD) of CHClF2 in the presence of Br2 has been investigated in a flow reactor. With a complete scaled-up system including a flow reactor, an industrially reliable TEA CO2 laser with longer pulse duration and a product-separation set-up for13C separation, it has been attempted to optimize the parameters suitable for large-scale production of the carbon isotope. The optimization of13C separation parameters, such as laser fluence, laser frequency and the partial pressure of CHClF2 and Br2 was tested under static conditions. By irradiation with longer pulses, a lower optimum pressure for a high13C-production rate was determined. Furthermore, the separation process was scaled in the flow system to examine the13C-production rates,13C atomic fractions in the CBr2F2 products and13C depletions in the CHClF2 reactants at different flow rates and laser repetition frequencies. The data obtained from the flow tests demonstrated a 40 mg/h production rate for CBr2F2 at 65%13C by using a 40 W (4 J, 10 Hz) laser beam focused with a lens of 120 cm focal length. If the reliable TEA CO2 laser is operated with 100 W (10 J, 10 Hz) output, the production rate of CBr2F2 for13C at 60% of 200 mg/h can be attained. The measurements of the spatial profile of the focused laser beam imply a 2 g/h production rate for the 60%13C product for an incident power of 200 W (20 J, 10 Hz).

The angular acceptance and the spectral acceptance about the retracing point of phase-matching angles for type I second-harmonic generation in LiB3O5 (LBO) crystal have been measured. The exact wavelength in retracing point is found to be 1.303 μm, and the spectral acceptance bandwidth and angular acceptance width are about 115 nm-cm and 11mrad-cm respectively. A possible application of LBO crystal in direct frequency doubling of femtosecond laser pulse has been predicted with theory.

Generation of tunable vacuum ultraviolet radiation down to 187.7 nm has been achieved by means of type-I sum-frequency mixing with the outputs of the fifth harmonic of a Nd:YAG laser and on optical parametric oscillator (OPO) pumped by the second harmonic of the same Nd:YAG laser in a LiB3O5 crystal. A peak power as high as 67 kW with an average power of 2 mW is obtained at 191.4 nm. Furthermore, a suitable modification has been made on the Sellmeier's equations of the crystal so that the equations can be basically used in wide range from vacuum ultraviolet to infrared.

We present second-harmonic generation characteristics of LiB(3)O(5) (LBO) crystal with different phase-matching lengths and comparison with those of beta-BaB(2)O(4) crystal. A computer program of the numerical interaction method was adopted to make the theoretical calculation of second-harmonic generation conversion efficiencies of LBO with different phase-matching lengths and power densities of the fundamental beam of a Nd:YAG laser, and the calculated result was compared with the experimental one. It is seen from the calculated and experimental results that for certain power densities of the fundamental laser beam, so long as the length of the LBO crystal is selected appropriately, a high energy conversion efficiency could be obtained. For example, an optimal external energy conversion efficiency of LBO crystal of more than 70% has been attained for several 100-MW/cm(2) fundamental laser beams. Experiments also showed that the crystal could be used under high power densities without any damage to the surface and the interior.

Highly efficient generation of UV radiation at 355 nm has been achieved in a LiB(3)O(5) crystal through the frequency mixing of the fundamental and second-harmonic radiation of a Nd:YAG laser. An energy conversion efficiency of 60% has been obtained under the experimental conditions described here. Thus the usefulness of LiB(3)O(5) for frequency-conversion applications is demonstrated.

We exploited Nd(3+) laser emission at 1061.9 nm ((4)F(3/2)?(4)I(11/2) channel) in a self-chi((2)) active GdAl(3)(BO(3))(4):Nd(3+) laser crystal. UV radiation was obtained from a 1.8% yield from self-sum-frequency mixing: 1/pump + 1/1061.9 = 1/UV, during pumping in the Nd(3+) (4)G(5/2)-(2)G(7/2) levels near 588 nm. The UV tunability had a range of 378-382 nm. We have demonstrated, for the first time to our knowledge, generation of coherent IR radiation from a self-difference-frequency mixing laser: 1/pump - 1/1061.9 = 1/IR. We got a 0.5% yield and tunability in the 1305-1365-nm range.

With a type-I noncritically phase-matched LiB3O5 crystal as the intracavity frequency doubler in a diode pumped Nd:YVO4 laser, 440 mW of 671 nm light was obtained at 5.5 W of incident pump power, the optical-optical conversion efficiency being 8.0%.

TmAl3(BO3)4 crystallizes in the trigonal system R32 (No. 155) with a = b = 9.2741(13) A, c = 7.218(3) A, alpha = beta = 90 degrees , gamma = 120 degrees , V = 537.7(2) A(3), D(c) = 4.494 g cm(-3), and Z = 3. The absorption spectrum of this crystal was recorded at room temperature. The Judd-Ofelt (J-O) theory was applied to the absorption intensities of TmAl(3)(BO3)4 to obtain the three J-O parameters: Omega(2) = 2.40 x 10(-20) cm(2), Omega(4) = 0.48 x 10(-20) cm(2), and Omega(6) = 1.09 x 10(-20) cm(2). The radiative probabilities, radiative lifetimes, and branching ratios of TmAl3(BO3)4 were calculated. The absorption and emission cross sections, together with the potential laser gain near 1.9 microm, were investigated. The potential laser gain curves indicate that the tunability range is about 200 nm.

The bulk crystals of 4-aminobenzophenone were grown from organic solution. The refractive indices and nonlinear-optical coefficients deff were measured and were reported. Blue second harmonic emission with wavelength of 433 and 460 nm was observed as pumped by a laser diode, second-harmonic generation and a conversion efficiency of 2.5×10−5 was obtained at 866 nm.

The nonlinear optical crystal KBe2BO3F2 has been used to produce vacuum ultraviolet second‐harmonic generation with an output range of 200–184.7 nm. The Sellmeier equation further indicates that this new crystal can generate the sixth harmonic from Nd‐based laser systems.

The Ca3Y2(BO3)4:Tm3+ crystal with the size up to ∅ 15 mm ×35 mm was grown by the Czochralsky method. The absorption spectrum was measured and its absorption peaks were assigned to the corresponding transitions between the Tm3+ energy levels. A broad emission spectrum ranging from 1332.6 to 1429.1 nm was exhibited from 800 nm wavelength pumping. This crystal is promising as a tunable infrared laser crystal.

The retracing behavior of the phase‐matching angle (RBPA) in optical parametric generation (OPG) based on a LiB3O5 (LBO) crystal and pumped at 532 nm by a frequency doubled, passive‐active mode‐locked Nd:YAG laser is investigated. Two pairs of radiations, which are simultaneously generated in the OPG, are observed and the spectral radiant power of the four tunable beams are obtained, showing good agreement with the theoretical calculation results. Together with the parametric process, two kinds of frequency‐mixing waves are produced and this novel multiwavelength interaction phenomenon is analyzed.

POWERFUL, tunable ultraviolet laser sources, required for many spectroscopic applications, rely on the frequency-doubling of lasers in the visible range. Such second-harmonic generation (SHG) depends on the development of nonlinear optical (NLO) materials with high SHG coefficients, a wide transparent region in the ultraviolet, and moderate birefringence. Few such materials are available; those most widely used at present are the inorganic crystals β-BaB2O4 (BBO)1 and LiB3O5 (LBO)2. These crystals are effective for SHG only down to wavelengths of 205 nm (ref. 3), because of a limited ultraviolet-transparent range in the former case and birefringence problems in the latter. We have developed previously4 a new inorganic NLO crystal, KBe2BO3F2 (KBBF), which avoids both of these problems to a large degree. But it is hard to grow large crystals of KBBF because of weak binding between its layered structural units. We have now developed an improved material by rational design: Sr2Be2B2O7 (SBBO), which shares (and in fact slightly improves on) all of the favourable NLO properties of KBBF and is easy to grow as large (so far up to 7 × 7 × 3 mm) crystals of high optical quality. The large SHG coefficients and wide range of ultraviolet transparency make this material a promising candidate for frequency doubling into the ultraviolet.

The study on broadband infrared parametric amplification in a lithium triborate (LBO) crystal is reported. By using optical parametric amplification in LBO, the picosecond (ps) infrared (IR) laser pulse with a bandwidth of 165 nm has been generated. The energy of broadband laser pulse train is 9.4 μJ, and the pulse duration is 20 ps.

A second‐harmonic generation of a Q‐switched Nd:YAG laser at λ=530 nm was focused into the polished beta barium metaborate crystals, and the scattering light was collected by a motor‐driven camera at 90° direction. This arrangement allows direct and nondestructive detection of microdefects in bulk crystals. Dislocation lines decorated by impurity atoms could be seen by a laser beam illuminating with the power intensity of about 0.5 MW/cm2, while microinclusions of about 1–5 μm in size could be observed with much lower laser intensity.

Forty 4,4′-disubstituted benzylidene-aniline derivatives were synthesized, and their second harmonic generation (SHG) efficiency was measured by the Kurtz powder technique. The effect of the electronic property and the positions of the substituents as well as the crystallization media on the powder SHG efficiency was studied.

Al-based metallic glasses with relatively high glass-forming ability have been studied using fluctuation electron microscopy (FEM). These glasses exhibited well-defined glass transition and remained fully amorphous throughout the FEM experiments. Peaks were observed in the normalized intensity variance curves, evolving with sample composition and thermal history, while diffraction patterns remained identical. Specifically, minor alloying of Co into the Al85Ni5Y10 glass improved its medium-range homogeneity. This is in accord with, and partly explains, the increase in the glass-forming ability. After annealing of Al85Ni5Y8Co2 below its glass transition temperature, FEM suggests structural homogenization or intensified medium-range fluctuations, depending on the annealing temperature. Such dissolution versus growth of quenched-in heterogeneity accompanying structural relaxation was not detectable using other techniques.

The spectroscopic properties of GdAl3(BO3)4:Tm3+ single crystal for the Tm3+ transition near 1.9μm are presented. The absorption cross section, the emission cross section, and the potential laser gain near 1.9μm are investigated for both σ and π polarizations. The broad absorption band at about 797nm and high value of the above cross section are promising features for obtaining a laser diode pumped Tm3+ laser. The maximum emission cross sections are 1.29×10−20 and 6.60×10−20cm2 at 1.85μm for the σ and π polarizations, respectively. The potential laser gain curves indicate that more than 200nm tunability range is expected for this material.

Er3+:SrWO4 crystal of good optical quality was grown by Czochralski technique method. Polarized absorption and emission spectra of Er3+ ions in SrWO4 crystal have been investigated. The Judd-Ofelt (JO) theory was applied to the polarized absorption spectra of Er3+:SrWO4 to obtain the three JO parameters: Ω2=7.41×10−20cm2, Ω4=0.25×10−20cm2, and Ω6=1.71×10−20cm2. The radiative probabilities, radiative lifetimes, and branch ratios of Er3+:SrWO4 were calculated. The stimulated emission cross sections of the potential laser transitions at 1535nm were determined using the reciprocity method and the Fuchtbauer-Ladenberg formula, and the potential laser gain versus wavelength for the I13∕24→I15∕24 transition has been estimated and discussed.

We have demonstrated two self-frequency conversions from the bifunctional laser and optical nonlinear GdAl3(BO3)4:Nd3+ crystal. For the first one, the laser operated in a dual-wavelength mode in the F3∕24→I11∕24 (at 1062nm) and F3∕24→I13∕24 (at 1338nm) channels, under a fixed wavelength pumping (at 747.7nm) and with a fixed crystal orientation (28.5°). Then the self-sum frequency mixing 1∕1062+1∕1338→1∕592 process occurred, leading to a weak yellow beam at 592nm. In the second self-frequency conversion, the Nd3+:GdAl3(BO3)4 laser operated in a single wavelength mode at 1062nm. Then the self-difference frequency mixing process 1∕λP−1∕1062=1∕λI occurred at a 29.9° phase matching angle. The idler wavelength λI was tunable in the 2450–2600nm range, due to the tunability of the λP pump wavelength. The highest yield was 0.12%. New Sellmeier formulas valid at least up to 2600nm have been established.

We present the absorption and emission spectroscopy of GdAl3(BO3)4:Nd3+ as functions of the σ and π polarizations. From the Judd–Ofelt analysis extended to anisotropic crystals, we have determined the parameters Ω2σ=1.455×10-20 cm2,Ω4σ=1.175×10-20 cm2,Ω6σ=2.043×10-20 cm2,Ω2π=0.208×10-20 cm2,Ω4π=0.326×10-20 cm2, and Ω6π=1.257×10-20 cm2. The radiative lifetime of the 4F3/2 level is 293 µs. The σ-polarized stimulated emission cross section was measured to be 3.0×10-19 cm2 at the laser wavelength of 1061.9 nm. No excited-state absorption was found at this wavelength. Green generation by self-frequency doubling was obtained with a yield of 4.3%. Blue generation tuneable in the 436-nm to 443-nm range was obtained with a yield of 7.3% from self-sum frequency mixing.

The new nonlinear optical crystal K2Al2B2O7 is discovered with the molecular engineering approach on the basis of anionic group theory. An optically perfect single crystal with space group P321, free of moisture and hygroscopy, is readily grown by the top-seeding flux method. Its transparence range covers 180 to 3600 nm. The refractive indices are measured with the minimum-deviation method, based on which the Sellmeier equation is obtained. The measured nonlinear optical coefficient d11 is 0.45 pm/V. The moderate walk-off angle and angular bandwidth, together with the high optical homogeneity, make it a promising candidate for the fourth- and the fifth-harmonic generation of a Nd:YAG laser.