Efficient, multiwatt, continuous-wave laser operation on the (4)F((3/2))-(4)I((9/2)) transitions of Nd:YVO(4) and Nd:YAG

Reabsorption cross section of Nd3+-doped quasi-three-level lasers

The ⁴F_3/2 → ⁴I_9/2 laser transition of Nd³⁺-doped crystals emitting at 900 nm is a standard quasi-three-level laser system. The reabsorption effect is one of the factors that restricts laser output power. Based on rate equations, a theoretical model considering the reabsorption effect for continuous-wave Nd³⁺-doped quasi-three-level lasers is established. The simulation results indicate that the reabsorption effect should be restrained to improve laser characteristics, which are mainly influenced by the Nd³⁺-doping concentration, laser medium length, pumping beam divergence angle and output mirror transmissivity. The optimal experimental results illustrate the availability of a theoretical model that considers the reabsorption effect. To quantitatively evaluate the reabsorption effect of a Nd³⁺-doped laser medium, a reabsorption cross section is proposed for the first time to the best of our knowledge. Comparing the experimental results and theoretical calculation results, the reabsorption cross section is estimated for a 912-nm Nd:GdVO₄ laser, 914-nm Nd:YVO₄ laser and 946-nm Nd:YAG laser.

Pure-three-level Yb:GdCOB CW laser at 976 nm

We present what is, to the best of our knowledge, the first pure-three-level Yb:Ca₄GdO(BO₃)₃ (Yb:GdCOB) laser emitting at 976 nm based on the F_5/22-F2_7/2 transition, generally used for a quasi-three-level emission at 1032 nm. A maximum power of 782 mW at 976 nm has been achieved in continuous-wave (CW) operation pumped by a quasi-three-level Nd:SrLaAlO₄ laser emitting at 902 nm. Moreover, a self-frequency-doubling CW blue laser has also been demonstrated with a maximum power of 133 mW at 488 nm.

Efficient 914-nm Nd:YVO₄ laser under double-end polarized pumping

We report herein the enhancement of output power and optical efficiency of a quasi-three-level Nd:YVO₄ laser through a double-end polarized pumping scheme, which improves the usually insufficient pump absorption of the short laser gain medium with low doping concentration, and meanwhile alleviates the influence of thermal effect. 17.7 W laser output at 914 nm is obtained under the launched 808-nm pump of 53.0 W, corresponding to an optical efficiency of 33.4%.

Broadband-tunable CW laser operation of Pr(3+):LiYF(4) around 900 nm

We present here the first broadband-tunable CW laser operation of a Pr(3+)-doped LiYF(4) crystal in the 900-nm spectral range after pumping with an optically pumped semiconductor laser at 479 nm. It is confirmed that the entire emission band can be assigned to the same set of thermalized emitting levels (I(6)1,P3(0,1)). It is also demonstrated that laser performance could be improved up to laser slope efficiencies of about 33% with threshold absorbed pump powers not exceeding 100 mW.

Analysis of Si+-implanted Nd:YVO4 crystal: the relation between lattice damage and waveguide formation

We report the lattice damage and annealing properties of the 500 keV Si+ ions implanted Nd:YVO4 crystal with different doses. The Rutherford backscattering spectrometry/channeling technique was used to analyze the damage profiles of ion-implanted samples. A series of post-implant annealing was performed at temperatures from 250 °C to 400 °C to investigate the relation between lattice damage profile and the waveguide formation. Implantations at doses of more than 5×10(14) ions/cm2 can result in high damage ratio in the near-surface region and the lattice structure cannot be restored even after annealing at 400 °C. Such seriously damaged lattice is relatively stable and contributes to the waveguide structure. Convergence of the refractive index at the surface region after ion implantation is believed mainly due to the elastic collisions with the target atoms caused by nuclear energy loss.

Quasi-three-level neodymium-doped yttrium aluminum garnet laser emitting at 885 nm

We present a diode-pumped quasi-three-level neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 885 nm, based on the 4F3/2-4I9/2 transition, generally used for a 946 nm emission. Combined with polarization components (Nd:YAG), the electro-optical crystal KH2PO4 (KDP) formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an incident pump power of 9.2 W, a 714 mW continuous-wave (CW) output at 885 nm was achieved, and the optical-to-optical efficiency was 7.8%. With an adjustable voltage applied to the KDP crystal, the laser wavelength could be tuned from 885 nm to 884 nm. A simultaneous dual-wavelength Nd:YAG laser at 885 nm and 884 nm was also realized by adjusting the free spectral range of the Lyot filter. To our knowledge, it is the first study that has realized the tuning between the 884 and 885 nm lines and the simultaneous dual-wavelength CW laser operation at 885 nm and 884 nm.

Note: self Q-switched Nd:YVO4 laser at 914 nm

By exploiting the saturable nature of re-absorption loss under the quasi-three-level laser transition self Q-switching operation in Nd:YVO(4) laser at 914 nm is demonstrated. The stable self-pulsing operation was observed with Nd:YVO(4) crystal with doping concentration of 0.3 at.%. At an incident pump power of 30 W around 600 mW of average power was obtained. Individual pulse energy and FWHM pulse duration were experimentally measured to be 10 μJ and 460 ns, respectively. The performance of the laser was analyzed with the help of a rate equation model. The simulation results show good agreement with the experiment.

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.

1073 nm continuous-wave Nd:YVO₄ laser with Type I phase-matching LiB₃O₅

Continuous output from a Nd:YVO₄ crystal around 1073 nm was studied. The output of 1064 nm was suppressed with a Type I phase-matching LiB₃O₅ (LBO) crystal rotated by 45°. With a pump power of 4.5 W, a 300 mW continuous output at 1073 nm was achieved for what we believe is the first time, and the optical-to-optical efficiency was 7%. With an adjustable LBO crystal, the wavelength is tunable from 1073.2 to 1073.5 nm. Even simultaneous output of 1066 and 1073 nm was realized by adjusting the LBO crystal. The experiments proved related theoretical analysis.

Experimental study of the generation of a blue laser by intracavity frequency doubling of a cw Nd:GdVO4 laser with lithium borate

Efficient cw intracavity frequency doubling of a diode end-pumped Nd:GdVO4 laser that operates in the 4F(3/2) --> 4I(9/2) transition at 912 nm is demonstrated. A 15 mm long lithium borate crystal, cut for critical type I phase matching at room temperature, was used for second harmonic generation of the fundamental laser. A maximum output power of 14.8 W in the deep blue spectral range at 456 nm was achieved at an incident pump power of 40 W. In 2 h we achieved an optical-to-optical conversion efficiency of 37% with a better than 2.57% power stability.

Diode-pumped Nd:YVO(4)/Yb:S-FAP laser emitting at 985 and 492.5 nm

For the first time, to the best of our knowledge, Yb:S-FAP crystals have been intracavity pumped by a Nd:YVO(4) laser at 914 nm. This original pumping scheme allows efficient laser action on the three-level transition at 985 nm with 1.4 W output power. Second-harmonic generation is also presented with a total output power of 120 mW at 492.5 nm.

Analytical solution of the heat equation in a longitudinally pumped cubic solid-state laser

Knowledge about the temperature distribution inside solid-state laser crystals is essential for calculation of thermal phase shift, thermal lensing, thermally induced birefringence, and heat-induced crystal bending. Solutions for the temperature distribution for the case of steady-state heat loading have appeared in the literature only for simple cylindrical crystal shapes and are usually based on numerical techniques. For the first time, to our knowledge, a full analytical solution of the heat equation for an anisotropic cubic cross-section solid-state crystal is presented. The crystal is assumed to be longitudinally pumped by a Gaussian pump profile. The pump power attenuation along the crystal and the real cooling mechanisms, such as convection, are considered in detail. A comparison between our analytical solutions and its numerical counterparts shows excellent agreement when just a few terms are employed in the series solutions.

Continuous-wave, 15.2 W diode-end-pumped Nd:YAG laser operating at 946 nm

A high-power continuous-wave (cw) Nd:YAG laser operating at 946 nm by utilizing a quasi-three-level transition is reported. The laser consists of a composite Nd:YAG rod end pumped by a fiber-coupled diode laser and a simple plane-concave cavity. At an incident pump power of 40.2 W, a maximum cw output of 15.2 W at 946 nm is obtained, achieving a slope efficiency of 45%. To the best of our knowledge, this is the highest output at 946 nm ever generated by diode-pumped Nd:YAG lasers. In addition, at an incident pump power of 15.2 W, a 1.25 W blue output at 473 nm is achieved with a simple compact three-element cavity and a type-I lithium triborate (LiB(3)O(5)) crystal as a frequency doubler.

Highly efficient, 0.84 slope efficiency, 901 nm, quasi-two-level laser emission of Nd in strontium lanthanum aluminate

The possibility of using direct pumping into the emitting level of the Nd3+ ion in magnesium-compensated strontium lanthanum aluminate (Sr(1-x)La(x-y)Nd(y)Mg(x)Al(12-x)O19) to improve 900 nm 4F(3/2) --> 4I(9/2) laser emission is discussed. Selection of the composition parameters x and y for optimization of laser emission and reduction of heat generation is based on the spectroscopic and crystal growth characteristics. Pumping in the 865.5 nm absorption band 4I(9/2)(Z1) --> 4F(3/2)(R1) transforms the laser process into a quasi-two-level scheme of very low (below 4%) quantum defects. A very high slope efficiency (over 84%) for 901 nm continuous-wave laser emission is demonstrated with Ti:sapphire laser pumping in this band for a crystal with x = 0.4 and y = 0.05.

High-power efficient diode-pumped Nd:YVO4/LiB3O5 457 nm blue laser with 4.6 W of output power

Continuous-wave 457 blue laser emission at powers as high as 4.6 W is achieved by using a fiber-coupled laser diode array with a power of 30 W to pump 0.1 at. % low-doped bulk Nd:YVO4 crystal, with intracavity frequency doubling in a 15 mm long type I critical phase-matched LiB3O5 (LBO) crystal in a compact three-fold cavity with a length of less than 100 mm. The optical-optical conversion efficiency is greater than 15.3%, and the stability of the output power is better than 3% for an hour.

Diode-pumped passively mode-locked Nd:YVO4 laser at 914 nm

We demonstrate, for the first time, to our knowledge, a diode-pumped passively mode-locked Nd:YVO4 laser, operating on the 4F(3/2)-4I(9/2) transition of the neodymium ion at 914 nm. We obtained 8.8 ps pulses at approximately 914 nm at a repetition rate of 94 MHz, and an averaged output power of 87 mW by using a semiconductor saturable absorber mirror.

Passively mode-locked 914-nm Nd:YVO4 laser

We demonstrate what is to our knowledge the first mode-locked Nd:YVO4 laser operating on the 4F3/2-4I9/2 transition at 914 nm. Using a semiconductor saturable-absorber mirror for passive mode locking, we have obtained 3-ps pulses at a repetition rate of 233.8 MHz. The laser is based on a standard delta cavity and is pumped by a Ti:sapphire laser. We obtained an average output power of 42 mW through one mirror and an accumulated output power of approximately 150 mW (through all cavity mirrors) at a pump power of 1.4 W.

Modeling of energy-transfer upconversion and thermal effects in end-pumped quasi-three-level lasers

An analytical model of cw quasi-three-level lasers that includes the influence of energy-transfer upconversion (ETU) has been developed. The results of the general output modeling were applied to a laser with Gaussian beams, and rigorous numerical calculations have been made to study the influence of ETU on threshold, output power, spatial distribution of population-inversion density, and fractional thermal loading. The model was applied to a laser operating at 946 nm in Nd:YAG, where the dependence of laser-beam size on laser performance was investigated in particular. A simple model for the degradation of laser-beam quality from a transversally varying saturated gain is proposed that is in good agreement with measurements of the laser in a plane-plane cavity.

Noncritically phase-matched second-harmonic generation in cesium lithium borate

Efficient generation of 236-nm light was demonstrated by use of noncritically phase-matched second-harmonic generation in cesium lithium borate. Noncritical phase matching provided approximately 20x the nonlinear drive for second-harmonic generation than beta-barium borate for 236-nm generation. The 236-nm wavelength is the fourth harmonic of a 946-nm Nd:YAG laser. Phase matching was accomplished at a crystal temperature of -15 degrees C.

Efficient operation of a solid-state adaptive laser oscillator

We present the results of a cw diode-pumped Nd:YVO4 laser oscillator based on a self-starting adaptive gain-grating resonator. Adaptive laser operation has been demonstrated with 12-W output for 37 W of diode pumping, producing a TEM00 mode that compensates for thermal aberrations. The issue of the finite aperture of the amplifier is discussed, and a design that incorporates an intracavity lens is used to improve the collection efficiency with severe thermal lensing at high pump powers. The powers of the beams involved in the resonator are compared with theory and are found to be in good agreement. Spectral and temporal behavior of the adaptive laser is investigated, and very interesting behavior is shown, including self-induced temporal modulation dynamics and a switching between a narrowband and a broad bandwidth of operation.

Passively Q-switched quasi-three-level laser and its intracavity frequency doubling

A passively Q-switched quasi-three-level Nd:YAG laser is intracavity frequency doubled to generate a blue laser. The 473-nm blue laser has a peak power of 37 W and a pulse width of 23 ns at a pumping power of 1.6 W. To model this laser numerically, we developed rate equations by taking into consideration both the quasi-three-level nature of the gain medium and the four-level nature of the saturable absorber. Good agreement was achieved between experimental and simulated results for both the fundamental and the second-harmonic output. The reabsorption loss of the gain medium is estimated under pulsed operation.

Efficient Frequency Conversion of a Passively Q-Switched Nd:YAG Laser at 946 nm in Periodically Poled KTiOPO(4)

Efficient continuous-wave and passively Q-switched diode-laser-pumped Nd:YAG lasers at 946 nm are reported together with results on highly efficient frequency doubling. Periodically poled KTiOPO(4) was employed as the nonlinear material because of its high nonlinearity and its resistance to photorefractive damage. In the blue spectral region we measured 76 mW in continuous wave and 285 mW in the Q-switched mode.