Comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO4/Nd:GdVO4 and YVO4/Nd:YVO4 crystals under direct pumping

The comparison on performance of passively Q-switched laser properties of continuous-grown composite GdVO(4)/Nd:GdVO(4) and YVO(4)/Nd:YVO(4) crystals under direct pumping to the emitting level was demonstrated. A Cr(4+):YAG crystal was used as saturable absorber. At an incident pump power of 10 W, the average output power, the pulse width, the repetition rate, the pulse energy, and the peak power for a GdVO(4)/Nd:GdVO(4) laser were 1.22 W, 48.1 ns, 121 kHz, 10.1 μJ, and 209.6 W, respectively. And for a YVO(4)/Nd:YVO(4) laser under the same conditions, these output characteristics were 1.26 W, 44.9 ns, 218 kHz, 5.8 μJ, and 128.7 W, respectively.     

Optical properties of a single mode planar waveguide in Nd:YVO4 fabricated by multienergy He ion implantation

We fabricated a single-mode planar waveguide in z-cut Nd:YVO(4) by multienergy He ion implantation in total fluence of 4.5×10(16) ions/cm(2) at room temperature and investigated optical properties of Nd:YVO(4) before and after He ion implantation by measuring transmission, confocal microluminescence, and confocal Raman spectra. Absorption bands and the photoluminescence features of the bulk Nd:YVO(4) crystal have been preserved after He ion implantation. In Raman spectra, most of the peak positions and peak widths had no obvious change before and after He ion implantation. The guiding mode and near-field image in the waveguide were measured by the prism coupling method and end-face coupling method, respectively. We investigated the damage behavior of a Nd:YVO(4) waveguide after implantation, annealing treatment by the Rutherford backscattering/channeling technique. The minimum yield of the virgin z-cut Nd:YVO(4) was 1.98%, which increased to 4.73% after He ion implantation and decreased to 3.20% after annealing at 600 K for 30 minutes.     

Multipass pumped Nd-based thin-disk lasers: continuous-wave laser operation at 1.06 and 0.9 microm with intracavity frequency doubling

The laser performances of the 1.06 microm (4)F(3/2) --> (4)I(11/2) four-level transition and of the 0.9 microm (4)F(3/2) --> I(9/2)4 quasi-three-level transition were investigated using multipass pumped Nd-based media in thin-disk geometry. When pumping at 0.81 microm into the (4)F(5/2) level, continuous-wave laser operation was obtained with powers in excess of 10 W at 1.06 microm, in the multiwatt region at 0.91 microm in Nd:YVO(4) and Nd:GdVO(4), and at 0.95 microm in Nd:YAG. Intracavity frequency-doubled Nd:YVO(4) thin-disk lasers with output powers of 6.4 W at 532 nm and of 1.6 W at 457 nm were realized at this pumping wavelength. The pumping at 0.88 microm, which is directed into the (4)F(3/2) emitting level, was also employed, and Nd:YVO(4) and Nd:GdVO(4) thin-disk lasers with ~9 W output power at 1.06 microm and visible laser radiation at 0.53 microm with output power in excess of 4 W were realized. Frequency-doubled Nd:vanadate thin-disk lasers with deep blue emission at 0.46 microm were obtained under pumping directly into the (4)F(3/2) emitting level.     

Semianalytical thermal analysis on a Nd:YVO(4) crystal

Based on analytical theory of anisotropy, distributions of thermal distortion and temperature field within a diode-end-pumped rectangular Nd:YVO(4) laser crystal are investigated. A thermal model that matches the actual working state of the laser crystal is established by analyzing the working characteristics of the Nd:YVO(4) laser crystal. A novel method, to the best of our knowledge, is adopted to solve the heat conduction equation of the anisotropic medium. General solutions of the temperature field, thermal strain field, and thermal distortion field of the Nd:YVO(4) crystal are obtained. The effect of anisotropic thermal parameters on the thermal strain field of the Nd:YVO(4) laser crystal is also analyzed quantitatively. Research results show that a maximum temperature rise of 244.9 degrees C and a maximum thermal distortion of 1.99 mum can be obtained in the center of the pump face when the Nd:YVO(4) laser crystal doped with 0.5 at. % Nd(3+) is diode end pumped in the center of the front end face with 15 W output power. This method can be applied to other thermal analyses of laser crystals and offers a theoretical basis to solve thermal problems effectively in the laser system.     

Efficient pumping scheme for neodymium-doped materials by direct excitation of the upper lasing level

An efficient pumping scheme that involves direct excitation of the upper lasing level of the Nd(3+) ion is demonstrated experimentally. The results obtained for direct upper laser level pumping of Nd:YAG R2 (869 nm) and Nd:YVO(4) (880 nm) were compared with traditional ~808-nm pump band excitation. A tunable cw Ti:sapphire laser was used as the pump source. In Nd:YAG, the oscillator slope efficiency increased by 10% and the threshold decreased by 11%. In Nd:YVO(4), the slope efficiency increased by 5% and the threshold decreased by 11%. These results agree with theory. The increase in optical efficiency indicates that laser material thermal loading can be substantially reduced.     

Nd3+:Y0.5Gd0.5VO4晶体生长和基本特性

Nd^3 :Y0.5Gd0.5VO4晶体作为一种新的激光材料，可以用中频感应加热提拉法生长。X射线粉末衍射分析表明它的结构与Nd^3 :YVO4晶体结构相同，它的晶格常数介于YVO4和NdVO4晶格常数之间。用ICP光谱法测定晶体中Nd^3 含量为0．8at％，分凝系数为0．8，与Nd^3 :GdVO4晶体中Nd^3 的分凝系数0．78相当；用称重法测定其密度为5．00g／cm^3；用稳态纵向热流法测出其室温热导率为12．5W／mK。实验表明Nd^3 :Y0.5Gd0.5VO4晶体有希望作为高功率ID泵浦激光晶体材料。     

Noise characteristics of a Nd:YVO(4) laser pumped by laser diode modulated at high frequency

We report, for the first time to our knowledge, on the noise characteristics of a Nd:YVO(4) laser pumped by a laser diode modulated at high frequency. We have investigated noise characteristics of a Nd:YVO(4) laser pumped by a laser diode that is oscillating in a stable multilongitudinal mode because of modulation by a high-frequency (several hundred megahertz) current. As a result, low-noise operations of -130 dB/Hz above frequencies of 1 MHz have been achieved. This noise level is comparable to the level obtained when pumping a Nd:YVO(4) laser with a laser diode that is oscillating in a single longitudinal mode. However, a noise peak corresponding to relaxation oscillations of the Nd:YVO(4) laser has appeared around a frequency of several hundred kilohertz.     

Periodic pulse oscillation in an intracavity-doubled Nd:YVO(4) laser

We report periodic pulse oscillation in an intracavity-doubled Nd:YVO(4) laser. The pulse oscillation is caused by alternate oscillation between two modes. We investigated improvement of green-light power with the pulse oscillation in a Nd:YVO(4) laser. The pulse oscillation gave a factor of approximately 2 higher average green-light power than that for cw oscillation at the same pumping power.     

Compact and Efficient 3.2-W Diode-Pumped Nd:YVO(4)/KTP Green Laser

We demonstrate a simple way to achieve single-frequency operation by using fiber-coupled diode-pumped Nd:YVO(4)/KTP green lasers in a short standing-wave linear cavity. A single-mode output with 3.2-W green power was generated with a 12.6-W pump power corresponding to a conversion efficiency of 25.4%. The single-mode operation was obtained through the combined action of the anisotropic emission cross section of Nd:YVO(4) and the KTP crystal acting as a birefringent filter.     

Tunable green laser source based on frequency mixing of pump and laser radiation from a Nd:YVO4 crystal operating at 1342 nm with an intracavity KTP crystal

We report on cw tunable green laser light generation from a Nd:YVO4 laser operating at 1342 nm. Visible radiation was produced by a frequency mixing of pump and laser radiation inside an intracavity KTP crystal. When Nd:YVO4 was diode pumped, green laser was tunable from 503 to 505 nm. The green tuning range increases up to 22 nm when a Ti:sapphire laser is used as the pump source. In nonoptimal conditions, and for a pump power of 650 mW, green power was above 3 mW and close to 0.1 mW for Ti:sapphire and diode pumping, respectively.     

High-powered green light generation by intracavity frequency doubling using grating feedback optics

Grating feedback optics is shown to contribute to narrowing the spectral bandwidth of a multilongitudinal-mode laser diode to less than 0.2 nm and tuning the lasing wavelength to the peak absorption wavelength of Nd:YVO(4). A continuous green light of 31 mW was efficiently generated by intracavity frequency doubling of the Nd:YVO(4) laser with a KTiOPO(4) crystal. A relative intensity noise of less than -140 dB/Hz was obtained in the frequency region greater than 2 MHz. The noise characteristics of generated green light are discussed as compared with the case of using a single-longitudinal-mode laser diode as the pumping source.     

Compact and efficient Nd:YVO 4 laser that generates a tunable single-frequency green output

We demonstrate 250 mW of single-frequency 532-nm output from a simple intracavity-doubled Nd:YVO(4) laser, pumped with 1.2 W from a fiber-coupled diode laser. The laser can be frequency chirped smoothly over ~17 GHz while maintaining a single-frequency green output of greater than 200 mW. A short Fabry-Perot cavity is used, and single-frequency operation is enforced by means of a birefringent filter that utilizes the birefringence of both the KTP doubling crystal and the Nd:YVO(4) laser crystal with polarization-dependent loss from a glass Brewster plate combined with polarization-dependent gain from the laser crystal.     

Growth of YLF:Yb:Tm:Nd for optical applications

The focus of this study is the behavior of Tm, Yb and Nd ions in the LiYF₄ (YLF) crystal. One YLF crystal was successfully grown by the Czochralski method; it was doped with 20 mol% Yb, 1.3 mol% Nd and 0.05 mol% Tm. The segregation coefficients of the dopants and lattice parameters were determined. The spectroscopic properties of samples with different amounts of Nd were obtained from absorption and emission studies.     

Characterization and laser performance of a new material: 2 at. % Nd:YAG grown by the Czochralski method

We report on the optical quality and laser performance of Czochralski-grown 2-at. %-doped Nd:YAG. Using a diode pumped laser in an end pumped configuration, we compare the laser performance of this material with the performance of 1-at. %-doped Nd:YAG and 0.7-at. %-doped Nd:YVO4 crystals. Experimental results show the superior performance of 2-at. % Nd:YAG over Nd:YVO4. With a pump power of 25.7 W, a maximum output power of 12.3 W with a slope efficiency of 57% and an optical-to-optical efficiency of 48% were achieved.     

Spectroscopic and lasing properties of a diode pumpable Nd:GdF3 crystal

A Nd:GdF₃ single crystal is investigated in terms of absorption and emission properties. It is found that the absorption spectrum around 796 nm has a bandwidth broader than in Nd:YAG or Nd:YLF. As a matter of fact, the absorption band is well fitted to the emission of AlGaAs pump diodes. In the 1050 to 1070 nm region, the emission spectrum is strongly polarized and high peaks are observed at 1051 and 1064 nm. Room-temperature laser emission was achieved under Ti:sapphire pumping for different orientations of the Nd:GdF₃ crystal. An optical efficiency of 25% with a 33% slope efficiency was measured. Then Nd:GdF₃ could be a serious candidate for microlaser applications compared to standard materials like Nd:YVO₄.     

All-solid-state, high-power, deep-UV laser system based on cascaded sum-frequency mixing in CsLiB6O10 crystals

We report on an efficient use of CsLiB(6)O(10) (CLBO) crystals employed for an all-solid-state deep-UV laser system operated at 5 kHz. We obtained greater than 3 W of UV radiation around 242 nm by mixing the 349-nm third harmonic of a Nd:YLF laser with the tunable output from a Ti:sapphire laser in a CLBO crystal. This UV radiation was subsequently mixed with the residual 1047-nm output from the Nd:YLF laser in a second CLBO crystal. The system produced 1.5 W of deep-UV radiation at 196.3 nm, which is, to our knowledge, the highest deep-UV power below 200 nm generated in a nonlinear optical crystal. Additionally, the bandwidth of both outputs was estimated to be less than 200 MHz.     

Experimental determination of fractional thermal loading in an operating diode-pumped Nd:YVO4 minilaser at 1064 nm

A practical in situ method is described and used for determination of the fractional thermal-loading parameter eta(h) in an operating diode-pumped Nd:YVO(4) minilaser at 1064 nm. Readily applicable to the thermal characterization of other solid-state media, the method is based on the fact that thermally induced lensing will cause the laser oscillation to be quenched at a critical pump power whose magnitude depends on the cavity configuration, thermo-optical properties of the gain medium, and, in particular, on the value of eta(h). In the experiments described here, a 0.5-mm-long coated Nd:YVO(4) crystal with 3-at. % Nd concentration was used to construct the diode-pumped laser with a flat highly reflecting end mirror and an intracavity lens. For the method to be effective, the resonator was set up close to the edge of the stability range. Above the oscillation threshold, the pump power at which lasing was quenched because of the onset of the thermally induced resonator instability was measured as a function of the intracavity lens position. A numerical model that accounted for absorption saturation and pump-induced thermal lensing was then used to analyze the experimentally measured data with eta(h) as an adjustable parameter. The average best-fit value of eta(h) was determined to be 0.40 with an estimated statistical variation of 8%.     

Study of the mechanical properties of Nd:YVO4 crystal by use of laser interferometry and finite-element analysis

A hybrid method that combines experimental and numerical approaches for determining the material properties of Nd:YVO(4) is reported. In the experimental investigations a laser interferometer is proposed for measuring the physical deformation of lasing materials at the end-pump surface. By matching with the measured end bulging, we have implemented a numerical solution with finite-element analyses to determine the Poisson ratio and Young's modulus of the crystal. The accuracy interval of the evaluated Poisson ratio of 0.33 and Young's modulus of 133 GPa is discussed numerically. Based on the mechanical properties obtained, the end effect is separated from thermal effects, and it shows that the end effect results in an approximate equal thermal lensing effect compared with the index parts for end-pumped Nd:YVO(4) lasers.     

Upconversion and reduced 4F(3/2) upper-state lifetime in intensely pumped Nd:YLF

Nonexponential decay of the 4F(3/2) upper laser state in Nd:YLF was observed with time-resolved fluorescence spectroscopy and small-signal gain probes in low-doped (1.16-at. %) samples when intensely pumped to high population inversions. A rapid initial decay is observed after Q-switched laser pumping, followed by a longer nonexponential decay that is clearly identified as a phase of migration-assisted energy-transfer upconversion (ETU) in the hopping regime. During this phase, a rate-equation treatment is valid and the macroscopic ETU coefficient, alpha2 = (0.98 +/- 0.03) x 10(-16) cm3/s, is directly evaluated from the decay kinetics. The ETU and the migration microparameters are also estimated to be C(da)* approximately 200 x 10(-40) cm6/s and C(dd) approximately 1000 x 10(-40) cm6/s, respectively, and are compared with theoretical values found in the literature. On the basis of these values, rate-equation treatments of intensely pumped Nd:YLF are not strictly valid.     

1053-nm-wavelength selection in a diode-laser-pumped Nd:YLF laser

We report on a Nd:YLF laser that operates at 1053 nm without optical intracavity elements for the suppression of the stronger 1047-nm transition. The Nd:YLF crystal is end pumped by a fiber optically coupled 10-W diode-laser bar. The different thermal-lensing focal lengths of the two main lasing wavelengths in a plane-parallel resonator were used to achieve the selection by tilting the end mirror slightly from its optimum position for maximum output power. With 9.8-W cw diode-laser-pumping power the 1053-nm Nd:YLF laser produces a maximum output power of 1.9 W in cw operation and nearly 1 W of average power at a Q-switch repetition rate of 15 kHz. The highest slope efficiency of 47% achieved in cw operation.