Self-frequency Doubling Laser Research Articles

Actively Q-switched self-frequency-doubled Yb:YCOB green laser with output power of a dozen watts.

A diode laser (LD) end-pumped acousto-optic Q-switched self-frequency-doubled (SFD) Yb:YCa4O(BO3)3 (Yb:YCOB) pulsed green laser was realized for the first time (to our knowledge), with a maximum average output power of 11.6 W and an optical conversion efficiency of 30.0% from the LD to SFD lasers. The wavelength of the SFD lasers was controlled to be 507 nm for improving quantum efficiency up to 96% and reducing thermal effects. The repetition rates ranged from 20 to 500 kHz, and the maximum pulse energy was 312.0 µJ with a peak power of 4.78 kW at a repetition rate of 20 kHz. This work represents the highest output power in the SFD pulsed lasers and provides an efficient and compact way to generate high-power pulsed green lasers that should have important applications in many aspects, such as ultraviolet (UV) laser generation, laser display, and medical, military, and scientific research.

>10 kW peak power self-frequency doubling laser

A passively Q-switched self-frequency doubling (SFD) green laser based on quasi-continuous diode-pumped and Nd:Ca3TaGa3Si2O14 crystal was developed for the first time with Cr4+:Y3Al5O12 as the saturation absorber. The output wavelength was 533 nm and the maximum average output power was 57 mW, corresponding to single pulse energy, pulse duration, and peak power of 190 μJ, 14.35 ns, and 13.24 kW, respectively. To our knowledge, this is the best result of diode-pumped, pulsed SFD lasers to date. Its compact components and low cost provide a better way to obtain an all-solid-state, miniaturized green laser with high peak power.

High-power continuous-wave self-frequency-doubled monolithic laser.

We report a high-power self-frequency-doubled (SFD) Yb:YCa4O(BO3)3 laser by employing a simple and high-integration monolithic configuration with an oscillator length of 6 mm. By reducing the reabsorption and increasing the quantum efficiency, the continuous-wave output power of 21.6 W was obtained with an optical conversion efficiency of 19.0% at the wavelength of about 510 nm. To our knowledge, the results represent the highest output power of a SFD laser. We believe that the high-power SFD laser with a highly compact structure will have broad and promising application prospects in laser display, medical treatment, spectral analysis, scientific research, and other fields.

Watt-level self-frequency-doubling laser at 540 nm of Nd:LCB crystal by utilizing the energy level splitting

We demonstrated the output power improvement of a self-frequency-doubling (SFD) green laser in Nd3+-doped La2CaB10O19 (Nd:LCB) crystal. The spectra were measured and calculated by the Judd-Ofelt theory [1,2], which provide the design guides for the SFD lasers. Taking advantage of energy level splitting of Nd3+ ions, the output power of 1.7 W SFD green laser was realized with a monolithic configuration at the wavelength of 540 nm because of avoiding the intrinsic absorption of Nd3+ ions, which represent the highest output power in the Nd:LCB crystal. This work not only develops a promising SFD laser crystal, but also provides an effective way for the improvement of the SFD laser output power.

Bifunctional Nd:CaSrNb2O7 crystal: A potential self-frequency-doubling laser material candidate

One of the convenient methods to obtain green laser is by self-frequency-doubling (SFD) technique, the key is the SFD laser crystal. In this article, a bulk single crystal of 3.34 at.% Nd:CaSrNb2O7 was successfully grown by Czochralski method at about 1481 °C. Its spectral and thermal properties were investigated. There is a broad and strong absorption band at around 804 nm, which is very suitable for AlGaAs laser diode pumping. The polarized emission spectra show large emission cross-sections and full width at half maximum at around 1068 nm, and the fluorescence lifetime is 202 μs? Moreover, the fluorescence quantum efficiency reaches to 98.6%. The long lifetime, large emission cross-section, and high fluorescence quantum efficiency of Nd:CaSrNb2O7 crystal indicate that it is easy to achieve laser oscillation. The second harmonic generation intensity of 3.34 at.% Nd:CaSrNb2O7 crystal is about 3 times that of KH2PO4, and phase matching can be realized in this crystal. All these results show that Nd:CaSrNb2O7 is a good bifunctional crystal, which possesses laser and nonlinear optical functions simultaneously, and also demonstrate that it is a promising SFD material.

17.9 W continuous-wave self-frequency-doubled Nd:GdCOB laser

We demonstrated the output power scaling of a self-frequency-doubled (SFD) laser with N d : G d C a 4 O ( B O 3 ) 3 (Nd:GdCOB) crystal by employing a partially end-pumped slab structure and optimized laser-diode (LD) pump wavelength. Associated with the theoretical calculation about the thermal distribution in the SFD Nd:GdCOB crystal, the maximum SFD output power was achieved to be 17.91 W at the wavelength of 545.5 nm, which represents the highest output power in SFD lasers, and the optical conversion efficiency from the LD to SFD laser power reached up to 20%. Since the wavelength at 545.5 nm is located at the eye-sensitive spectral region and the SFD lasers have the advantages in the compact structure, the demonstrated SFD laser should have promising applications in some regimes such as laser display, medical, military, and scientific research.

Power scaling of the self-frequency-doubled quasi-two-level Yb:YCOB laser with a 30% slope efficiency.

The lab-on-chip integration of photonic devices has been attracting increasing attention recently. Multifunctional materials provide natural platforms for the desirable performance by the coupling of different functionalities. The insufficient coupling efficiency of the laser and nonlinear processes in self-frequency-doubled (SFD) lasers is the limiting factor for the output power and further practical applications. Here we demonstrate a SFD Yb3+-doped calcium yttrium oxoborate (Yb:YCOB) crystal laser with an unprecedented slope efficiency of 30% and output power of 6.2W at 513nm. The successful realization of this laser operating in a quasi-two-level configuration is based on enhanced coupling of the laser and frequency-doubling processes using a monolithic configuration, benefiting from an ultimately small laser quantum defect, the anisotropic gain cross sections, and the high effective nonlinearity of the monoclinic YCOB outside the principal planes. Solid-state lasers in the spectral range around 510nm are scarce, and the results not only present a significant advancement in the field of SFD lasers, but also pave the way for future applications of such green lasers, especially in areas such as medical treatment, daily life, and scientific investigations.

1 kW Peak Power Self-Frequency-Doubling Microchip Laser

With Nd:CTGS crystal as self-frequency-doubling (SFD) medium, and Cr4+:YAG crystal as passively Q-switcher, a pulsed microchip green laser was demonstrated. The maximum average output power was 69 mW, and the corresponding pulse duration, repetition rate, single pulse energy, and peak power were 7.12 ns, 8.83 kHz, 7.81 μ J, and 1.01 kW, respectively. As we have known, they are the best results of diode pumped, pulsed SFD laser, and the simple structure, miniaturization, as well as low cost are very favorable for large-scale production and application.

Passively Q-switched self-frequency doubling Nd3+:ReCa4O(BO3)3 (Re = Y, Gd) lasers with tin diselenide as a saturable absorber

With tin diselenide (SnSe2) film as a saturable absorber (SA), the passively Q-switched self-frequency doubling (SFD) lasers were realized in Nd3+:ReCa4O(BO3)3 (Re = Y, Gd) crystals. For Nd:YCa4O(BO3)3 crystal, the maximum average output power at 532 nm was 19.6 mW, and the corresponding pulse repetition frequency, pulse duration, single pulse energy, and peak power were 17.6 kHz, 91.9 ns, 1.1 μJ, and 12.1 W, respectively. For Nd:GdCa4O(BO3)3 crystal, these values were 14.5 mW, 22.1 kHz, 48.7 ns, 0.66 μJ, and 13.5 W.

Diode-pumped passively Q-switched self-frequency-doubled Nd:CNGS laser.

With Cr4+:YAG as a saturable absorber, a passively Q-switched self-frequency-doubled (SFD) laser based on a trigonal Nd:Ca3NbGa3Si2O14 (Nd:CNGS) silicate crystal was demonstrated for the first time. The maximum average output power at 532 nm was 16.2 mW, and the corresponding pulse repetition frequency, single pulse energy, pulse duration and peak power were 2.25 kHz, 7.2 μJ, 13.7 ns, 0.53 kW, respectively. We also present a rate-equation model of such a passively Q-switched SFD laser showing a good agreement with the experiment. Nd:CNGS is a promising pulse SFD material for miniature all-solid-state visible light sources.

Tunable second harmonic generation from a Kerr-lens mode-locked Yb:YCa4O(BO3)3 femtosecond laser**Project supported by the National Major Scientific Instruments Development Project of China (Grant No. 2012YQ120047), the National Natural Science Foundation of China (Grant No. 61205130), and the Doctor Fund from Southwest University, China (Grant No. SWU110645).

We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond (fs) laser with a self-frequency doubling Yb:YCa4O(BO3)3 crystal. Sub-40 fs laser pulses were directly generated from the oscillator without extracavity compression. The central wavelength was tunable from 1039 nm to 1049 nm with a typical bandwidth of 35 nm and an average output power of 53 mW. For the first time, a self-frequency doubled second harmonic green laser with tunable range from 519 nm to 525 nm was observed.

β′-Yb3+:Gd2(MoO4)3 crystal – A promising self-frequency doubling laser material

A β′-Yb3+:Gd2 (MoO4)3 crystal with dimensions of 22×22×25mm3 was grown successfully by the Czochralski method. Its relative efficiency of second harmonic generation was measured by Kurtz power method, the intensity is about 3 times as large as that of KH2PO4 crystal. The thermal expansion coefficients of the crystal are 14.7×10−6K−1, 13.5×10−6K−1 and −20.1×10−6K−1 along a-, b- and c-axes, respectively. The thermal conductivity along the c-axis is 1.44W/mK at room temperature. The absorption cross section at 977nm is 0.48×10−20cm2 with full width at half maximum of 20nm. The emission cross section at 1030nm is 1.13×10−20cm2. The fluorescence lifetime is 722μs. The results indicate that β′-Yb:Gd2(MoO4)3 crystal is a promising candidate of self-frequency doubling laser material.

Observation of Self-Frequency Doubling in Diode-Pumped Mode-Locked Nd-Doped La3Ga5SiO14 Laser

A diode-pumped passively mode-locked Nd-doped La3Ga5SiO14 (Nd:LGS) laser is realized by using a semiconductor saturable absorber mirror. With the pump power of 2 W, we obtain a 532 nm self-frequency doubling (SFD) laser together with a 10.9 ps fundamental laser at the repetition rate of 173.7 MHz. To the best of our knowledge, it is the first time for self-frequency doubling in the diode-pumped mode-locked Nd:LGS laser. Benefited from the diode lasers and its self-frequency doubling property, Nd:LGS could be a potential candidate for compact, stable and cheap ultrafast green laser sources.

Color Centers in Ca4GdO(BO3)3Single Crystals Irradiated by Gamma Quanta

A great interest in non-linear optical materials used for frequency conversion and for self-frequency doubling lasers has been observed in the last years. Recently, Nd-doped YAl3(BO3)4, LiNbO3, Li2B4O7 and LiB3O5 have been reported as very e cient non-linear optical crystals for achieving self-frequency doubling in the green part of the spectrum [1 3]. Undoped single crystals of gadolinium calcium oxoborate (Ca4GdO(BO3)3; GdCOB) are piezoelectronics elements and optical planar waveguides [4], while crystals doped with rare-earth ions (Nd, Yb, Eu, Er, Tm) are new and promising laser materials. By combining the non-linear properties of the GdCOB matrix and the laser emission due to Nd ions, it is possible to high-e cient generate directly by self-frequency doubling of green (at 530.5 nm) and blue (at 468 nm) laser light [5]. The main advantage of GdCOB, comparing with other borates is large transparent range (32

High output power of differently cut Nd:MgO:LiTaO3 CW lasers

A high-quality Nd3+ and Mg2+ co-doped LiTaO3 (Nd:MgO:LT) crystal was grown by the Czochralski method. The polarized absorption spectra and fluorescence spectra were studied, and the absorption cross section was calculated by Judd–Ofelt (J–O) theory. The laser performance with different sample cuts of the crystal was investigated for the first time, and it was found that Nd:MgO:LT crystal with different cutting directions (a and c) exhibits different laser properties. By optimizing a partial reflectivity mirror in the laser experimental setting, a high continuous wave output power of 3.58 W was obtained at 1092 and 1076 nm with an optical-to-optical conversion efficiency of 22.78% and slope efficiency of 26.06%. The results indicate that Nd:MgO:LT crystal is a promising candidate for the manufacture of Nd3+ doped periodically poled MgO:LiTaO3 crystal (Nd:PPMgOLT), which should have considerable applications in self-frequency doubling and optical parametric oscillation laser devices.

Growth, structural, optical and thermal properties of Yb-doped and Yb–Mg codoped LiNbO3 single crystals

Yb–Mg codoped LiNbO3 (LN) crystals have many applications in self-frequency doubling lasers. However, the great difficulty associated with growing this crystal is one of the obstacles for its application. In this work, Yb-, Mg-doped and Yb–Mg codoped (MgYb0.8 and MgYb1.2) single crystals were successfully grown by the Czochralski method from the congruent melt. Some basic physical properties have been measured to provide reliable reference for application of the crystals. Compared to its value in a singly doped crystal, the effective segregation coefficient of the Yb3+ ion in codoped crystals clearly decreases. When doping Yb into Mg-doped LN, the absorption edge of the crystal shifts to longer wavelengths, while the refractive index stays nearly the same. Yb3+ doping apparently decreases the Curie temperature Tc. The thermal conductivity of Yb–Mg codoped LiNbO3 was found to be identical to that of Mg-doped LN and greater than that of congruent LN (CLN), which is a benefit for laser applications. The occupation sites of the Yb3+ ions are discussed, and the distinct raised growth ridges observed are attributed to the change in the lattice structure due to Yb–Mg co-doping.

Generation of Crystal-Structure Transverse Patterns via a Self-Frequency-Doubling Laser

Two-dimensional (2D) visible crystal-structure patterns analogous to the quantum harmonic oscillator (QHO) have been experimentally observed in the near- and far-fields of a self-frequency-doubling (SFD) microchip laser. Different with the fundamental modes, the localization of the SFD light is changed with the propagation. Calculation based on Hermite-Gaussian (HG) functions and second harmonic generation theory reproduces well the patterns both in the near- and far-field which correspond to the intensity distribution in coordinate and momentum spaces, respectively. Considering the analogy of wave functions of the transverse HG mode and 2D harmonic oscillator, we propose that the simple monolithic SFD lasers can be used for developing of new materials and devices and testing 2D quantum mechanical theories.

Nd:MgO:LiTaO3 crystal for self-doubling laser applications: growth, structure, thermal and laser properties

Nd3+ and Mg2+ co-doped LiTaO3 (Nd:MgO:LT) crystal has great potential for applications in self-frequency doubling (SFD) lasers, and self-optical parametric oscillation (SOPO) infrared lasers. However, a related high performance laser device has not yet been realized. No reliable data on the basic physical properties of Nd:MgO:LT have been obtained, because of the lack of high quality Nd:MgO:LT crystals available due to the great difficulty in growing this crystal. In this paper, by optimizing the growth parameters and the thermal field by means of simulation, a high quality Nd3+ and Mg2+ co-doped LiTaO3 crystal was grown by a modified Czochralski method. A comprehensive characterization of the crystal, including structure, composition, thermal properties, and CW laser performance, was performed. The experimental results indicate that Nd:MgO:LT is a monocrystal with strong anisotropic physical properties. The anisotropic thermal expansion was confirmed by observing the lattice parameter variation via temperature-dependent XRD analysis. Some important physical property data, such as thermal diffusivity, thermal conductivity and specific heat of the Nd:MgO:LT single crystal are reported for the first time, and should be of great utility for the application of this crystal. A CW laser output power of 3.58 W with an optical-to-optical conversion efficiency of 11.55, and a slope efficiency of 13.78%, was achieved with an incident pump power of 31 W, which is the highest laser output reported for this kind of crystal. It is demonstrated that single crystal Nd:MgO:LT will have important applications in SFD and SOPO lasers.

Growth, structure and optical properties of a nonlinear optical crystal α-LaBMoO6

An α-LaBMoO6 crystal with dimensions of ϕ 20 × 30 mm3 has been successfully grown by a modified Czochralski method. The grown crystal belongs to the low temperature phase and crystallizes in the monoclinic system with space group P21. Its crystal structure features a three-dimensional network composed of one-dimensional LaO7, BO2 and MoO4 chains along the b-axis interconnected via corner- and edge-sharing. Corner-sharing BO3 triangles are linked together forming novel zigzag chains along the b-axis. It is found that the α-LaBMoO6 crystal has a SHG effect which is 1.8 times as large as that of KDP crystal. α-LaBMoO6 crystal exhibits high transparency in the range of 350–1100 nm. The absorption edge of the crystal in the UV range is at 340 nm. Therefore, the α-LaBMoO6 crystal could be considered as a potential nonlinear optical crystal and self-frequency doubling laser crystal material.

Efficient high-power self-frequency-doubling Nd:GdCOB laser at 545 and 530 nm

We report an efficient high-power self-frequency-doubling (SFD) Nd:GdCOB laser. The maximum output power is 3.01 W at a wavelength of 545 nm with an optical efficiency of 20.7%, which, to our knowledge, is the highest SFD laser output power and efficiency yet obtained. By optimizing the configuration and cut orientation of the Nd:GdCOB crystals, a SFD laser at a wavelength of about 530 nm was achieved with a maximum output power of 1.32 W. We propose that these SFD lasers will have promise in applications such as laser displays, medical treatment, spectroscopic analysis, etc.