Cross-relaxation and spectral broadening of gain for Nd/Cr:YAG ceramic lasers with white-light pump source under high-temperature operation

Spectral broadening of the fluorescence of a Nd/Cr:YAG ceramic at the 1064 nm lasing wavelength was observed, and the amplification properties at a high temperature were investigated by considering cross-relaxation. These ceramics are promising for use as a solid-laser material pumped with solar or lamp light. It has been found that whenever the temperature of a laser medium is high and a spectral shift occurs, a high small-signal gain remains owing to the broad spectral band and the cross-relaxation. This optical property is remarkably different from that of a Nd:YAG laser. For a conventional Nd:YAG laser, the bandwidth at 1064 nm is 0.45 nm, and a reduction in small-signal gain occurs at a temperature of 373 K because the spectral peak shift is 0.005 nm/K. However, for the Nd/Cr:YAG ceramic, the bandwidths are 1.2 and 1.9 nm in the case of 0.1% Cr ion doping and 3% Cr ion doping, respectively, owing to the existence of excited Cr ions and the shortening of the effective Nd ion coherence time. It is prospected that the laser medium can be used at a high temperature of 600 K.     

High repetition rate laser pulses amplified by Nd/Cr:YAG ceramic amplifier under CW arc-lamp-light pumping

Laser pulses with high repetitive rate generated from a Q-switch microchip Nd:YAG oscillator were amplified by Active mirror composed of Nd/Cr:YAG ceramic pumped by CW arc-lamp. The laser pulses were amplified, and saturation of averaged output laser power was observed. Repetitive ratio of injected laser pulses was changed from 20 to 100 kHz. Averaged output laser power and gain were measured, and gain coefficient and power-extraction efficiency were evaluated. Output laser power was calculated and compared to experimentally measured one, and the calculated results are consistent with the experimental ones. For amplification of laser pulses with high repetitive ratio, this laser material can realize very high laser gain with low pumping power density and high optical-optical conversion efficiency under CW-lamp-light pumping.     

Dual-polarization electro-optical Q-switched ceramic laser

A dual-polarization electro-optical Q-switched Nd:YAG ceramic laser was studied. By selecting the appropriate size of calcite crystals, the dual-polarization Q-switched pulse was achieved by characteristics of calcite crystal. Experimental results show that compared with the traditional single-polarization electro-optical Q-switched laser, insertion loss is reduced, dynamic to static ratio is greatly improved, thermally induced birefringence of electro-optical Q-switched Nd:YAG ceramic laser is effective compensated. The output power of 19 W and the pulse width of 13 ns are obtained at the repetition rate of 1 kHz and pumped power of 144 W. The dynamic to static ratio is 71%. The results formed the basis for the further development of the high power and high efficiency ceramic red laser.     

Temperature characteristics of small signal gain for Nd/Cr:YAG ceramic lasers

Thermal dependence on the small signal gain of Nd/Cr:YAG (yttrium aluminum garnet) ceramics was observed experimentally. Usually, Nd:YAG crystal and ceramics have remarkable gain reduction when optical pumping is performed and the temperature of the laser media is upped to 373 K. A CW laser light generated in a 1064 nm Nd:YAG laser oscillator was amplified by Nd/Cr:YAG ceramic amplifier, and the output power was measured at non-saturation level. Laser small signal gain of the ceramic disk was kept to 470 K. This property was remarkably different from one of Nd:YAG crystals or ceramics. The peak shift of the fluorescence was observed experimentally when the temperature is high.     

Side-pumped continuous-wave Cr:Nd:YAG ceramic solar laser

To clarify the advantages of Cr:Nd:YAG ceramics rods in solar-pumped lasers, a fused silica light guide with rectangular cross-section is coupled to a compound V-shaped cavity within which a 7 mm diameter 0.1 at.% Cr:1.0 at.% Nd:YAG ceramic rod is uniformly pumped. The highly concentrated solar radiation at the focal spot of a 2 m diameter stationary parabolic mirror is transformed into a uniform pump radiation by the light guide. Efficient pump light absorption is achieved by pumping uniformly the ceramic rod within the V-shaped cavity. Optimum pumping parameters and solar laser output powers are found through ZEMAX^© non-sequential ray-tracing and LASCAD^© laser cavity analysis codes. 33.6 W continuous-wave laser power is measured, corresponding to 1.32 times enhancement over our previous results with a 4 mm diameter Nd:YAG single-crystal rod. High slope efficiency of 2.6 % is also registered. The solar laser output performances of both the ceramic and the single-crystal rods are finally compared, revealing the relative advantage of the Cr:Nd:YAG rod in conversion efficiency. Low scattering coefficient of 0.0018 cm^?1 is deduced for the ceramic rod. Heat load is considered as a key factor affecting the ceramic laser output performance.     

Disk-type Nd/Cr:YAG ceramic lasers pumped by arc-metal-halide-lamp

We observed the lasing of highly sensitized Nd/Cr:YAG ceramic disks that use artificial solar radiation pumping. The disk material can be used for high power multi-stage amplifiers pumped by lamplight or sunlight because of its scalability and ability to handle high power densities. A maximum output power of 86 mW was experimentally obtained, and this value correlated well with the calculated results. A small signal gain of 1.9 was obtained, and the estimated stored energy was 0.6 J/cm³, which is three or four times higher than that from a Nd:YAG medium.     

A kilowatt level diode-side-pumped QCW Nd:YAG ceramic laser

We demonstrate a kilowatt level Quasi-continuous-wave (QCW) diode-side-pumped Nd:YAG ceramic laser at 1064 nm. The laser system adopts a master oscillator power amplifier scheme (MOPA). The master oscillator contains two diode-pumped laser modules. Under the pump power of 2000 W, an output power of 686 W was obtained. After amplified by an identical ceramic laser module, a maximum output power of 1020 W was obtained under a total incident pump power of 3433 W, corresponding to an optical-optical conversion efficiency of 29.7%. At the maximal output power, the repetition frequency was measured to be 1 kHz and the pulse width was 114 μs. To the best of our knowledge, this is the first time to realize QCW side-pumped Nd:YAG ceramic laser system with output power above 1 kW.     

678 nm RTP electro-optical Q-switched ceramic laser

The RTP electro-optical Q-switched ceramic laser at the wavelength of 678 nm with narrow pulse width is studied. We used the laser diode arrays side-pumped Nd:YAG ceramic crystal with 1.1 at% Nd doping and dimensions of Φ3 mm × 50 mm, designed folding cavity parameters, and discussed the variation of the beam radius in the ceramic crystal and frequency doubling crystal with the thermal focal length of ceramic crystal or KTP crystal. By using double RTP crystals as electro-optic Q-switch and KTP crystal type II phase matching for intracavity frequency-doubling, a narrow pulse width electro-optical Q-switched Nd:YAG ceramic laser was obtained. The output energy of 0.9 mJ and the pulse width of 41.6 ns at 678 nm are obtained at the repetition rate of 1000 Hz and pumped power of 144 W. The results formed the basis for the further development of the high power and high efficiency ceramic red laser.     

端面抽运Nd∶YAG陶瓷1.83 μm激光

报道了基于Nd∶YAG透明陶瓷4F3/2-4I15/2跃迁实现1.83 m激光输出的研究。采用简单紧凑的平凹腔结构,结合对腔镜镀膜参数的设计,控制其他能级跃迁谱线对应波长激光的透射损耗来抑制较强能级跃迁对应的激光振荡。在入射抽运功率14.6 W的808 nm波长半导体激光端面抽运Nd∶YAG透明陶瓷,获得了0.65 W的1.83 m激光输出,斜率效率5.8%。可见Nd∶YAG透明陶瓷可望成为获得1.8 m波段激光直接输出的激光介质。     

108 W Nd: YAG ceramic laser with birefringence compensation resonator

The quartz rotator's effective birefringence compensation for ceramic Nd:YAG rods has been first demonstrated. Furthermore, a high output power continuous-wave laser is presented based on an optimized resonator made up of four Nd:YAG ceramic rods. By an appropriate design of the resonator, an output power of 108 W at 1064 nm is obtained. The corresponding optical-to-optical conversion efficiency is 16.8% and the slope efficiency is 28.1%. Meanwhile, the numerical analysis for output power is detailed.     

High conversion efficiency solar laser pumping by a light-guide/2D-CPC cavity

A simple and efficient light-guide/2D-CPC solar pumping approach is proposed. A fused silica light-guide assembly is used to transmit 6 kW concentrated solar power from the focal spot of a large parabolic mirror to the entrance aperture of a 2D-CPC pump cavity, where a long and thin Nd:YAG rod is efficiently pumped. Numerical calculations are made for different light-guides, 2D-CPC cavities and laser rods. The laser output power is investigated through finite element analysis. With 4 mm diameter rod, the maximum calculated laser power of 75.8 W is obtained, corresponding to the conversion efficiency of more than 11 W/m². The tracking error dependent laser power losses are lower than 4%. A small scale prototype was constructed and tested, reaching 8.1 W/m² conversion efficiency.     

532 nm laser based on V-type doubly resonant intra-cavity frequency-doubling

LD side-pumped dual interconnected V-type quasi-continuous wave green laser has been demonstrated. The two Nd:YAG modules were placed in a plane-concave V-type resonator and a plane-concave straight cavity formed two stable operation beam of the 1064-nm fundamental frequency laser. Through acousto-optic Q-switched and frequency doubling crystal, two double-frequency laser beams arrived at the folded flat mirror, which were unidirectional output by the folded flat mirror at the end. As the pumped current was 50 A, the 532 nm green laser maximum average output power of 206 W at a repetition of 22.4 kHz was achieved with a pulse width of 201 ns and the largest single pulse energy of 9.2 mJ, corresponding to a peak power of 45.8 kW and a double frequency efficiency of 60.2%.     

Liquid-cooled ceramic Nd:YAG split-disk amplifier for high-average-power laser

A liquid-cooled ceramic Nd:YAG split-disk laser amplifier has been designed for a high-average-power laser system. The maximum average output power of 17.1 W (1.71 J at 10 Hz) and the beam size of far-field pattern with 1.5 times diffraction limit was obtained. The combination of liquid cooling for disk laser material and wavefront compensation with a phase conjugation mirror was demonstrated. The wavefront degradation by liquid cooling was observed and measured with Michelson interferometer and far-field patterns.     

Quasi-three-level Nd:YAG laser under diode pumping directly into the emitting level

We present theoretical and experimental investigations on ground-state direct pumping at 869 nm into the emitting level ⁴F_3/2 of end-pumped quasi-three-level Nd:YAG lasers operating at 946 nm. We have demonstrated, what we believe is for the first time, a Nd:YAG laser at 946 nm directly pumped by diodes and obtained 1.6 W of output power.     

The first-stokes pulse generation in Nd:KGW intracavity driven by a diode-pumped passively Q-switched Nd:YAG/Cr<Superscript>4+</Superscript>:YAG laser

The operation of an all solid-state pulsed Nd:KGW Raman laser pumped by compact passively Q-switched Nd:YAG/Cr:YAG laser is demonstrated. The first-Stokes radiation of stimulated Nd:KGW Raman scattering at the 1178 nm is generated. The average output power of 336 mW at Stokes wavelength was obtained under the laser diode pump power of 5.74 W. The corresponding optical efficiency from the diode light to the Raman output is 9.85%. The pulse width of 1.65 ns and a pulse repetition rate of 10 kHz were also obtained.     

The study of green laser performances by using composite crystals of different initial transmissions

This paper reported a passively Q-switched green laser of LD pumped linear cavity structure by using Nd:YAG/Cr⁴⁺:YAG composite crystal and the type II phase matching KTP crystal. The dependence of average output power, pulse width and pulse repetition rate on pump power at different initial transmissions of Cr⁴⁺:YAG were measured and analyzed. With Cr⁴⁺:YAG of 80% initial transmission, under pump power of 13.97 W, the output average power is up to 681 mW, with pulse width of 200 ns and pulse repetition rate of 9.1 kHz. The laser operates in a fundamental mode.     

Diode-pumped passively Q-switched Nd:LuVO4 laser at 916 nm

We demonstrate a passively Q-switched Nd:LuVO₄ laser at 916 nm by using a Nd, Cr:YAG crystal as the saturable absorber. As we know, it is the first time to realize the laser with a simple linear resonator. When the incident pump power increased from 14.6 W to 23.7 W, the pulse width of the Q-switched laser decreased from 24 ns to 21 ns. The pulse width was insensitive to the incident pump power in the experiment. The average output power of 288 mW with repetition rate of 39 kHz was obtained at an incident pump power of 22.5 W, with the optical-to-optical efficiency and slope efficiency 1.3% and 3.6%, respectively.     

600-W lamp pumped CW Nd:YAG laser

A lamp pumped CW Nd:YAG laser is presented in this paper for the requirement of industrial application. The main factors, which affect output power and beam quality of high power solid-state laser module, are theoretically analyzed. Total electro-optics efficiency of lamp pumped Nd:YAG crystal as high as 4.0% is obtained, and output power is higher than 647 W with beam parameter product 22 mm·mrad.     

Simultaneous dual-wavelength laser operation at 1342 and 946 nm in two laser crystals and their sum-frequency mixing

A sum-frequency yellow-green laser at 554.9 nm is reported by this paper, 946 nm wavelength is obtained from ⁴F_3/2-⁴I_9/2 transition in Nd:YAG and 1342 nm wavelength is obtained from ⁴F_3/2-⁴I_13/2 transition in Nd:YVO₄. Using a doubly folded-cavity type-II critical phase matching KTP crystal intra cavity to make 946 nm laser from Nd:YAG and 1342 nm laser from Nd:YVO₄ frequency summed, with incident pumped power of 30 W in Nd:YAG and 20 W in Nd:YVO₄, TEM₀₀ mode yellow-green laser at 554.9 nm at 1.15 W is obtained and its M² factor is less than 1.22. The experimental results show that the Nd:YAG and Nd:YVO₄ crystals intra-cavity sum-frequency mixing is an effective method for yellow-green laser and it can be applied to other two laser crystals to obtain more all-solid-state lasers with different wavelengths.     

Efficient tunable Yb:YAG ceramic laser

A high-power efficient ceramic Yb:YAG laser was demonstrated at a room temperature of 20 °C with an Yb concentration of 9.8 at.%, a gain medium of 1 mm, a pumping power of 13.8 W, an output coupler of T = 10%, and a cavity length of 20 mm. A 6.8 W cw output power was obtained with a slope efficiency of 72%. The ceramic Yb:YAG laser exhibited a continuous tunability in the spectral range of 63.5 nm from 1020.1 to 1083.6 nm for T = 1% at a maximum output power of 1.6 W. To the best of our knowledge, this is the first study of the tunability of ceramic Yb:YAG lasers, except crystal Yb:YAG studies.