YAG Rod Research Articles

A high-power high-stability Q-switched green laser with intracavity frequency doubling using a diode-pumped composite ceramic Nd:YAG laser

We successfully obtain a high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight plano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By using a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.

Design of a high brightness solar-pumped laser by light-guides

To improve solar-pumped laser output performance, a compact fused silica light-guide assembly is combined with a 2V-shaped cavity to achieve uniform pumping along a Nd:YAG rod. Based on both refractive and total internal reflection principles, the light-guide assembly provides an effective approach in both guiding and redistributing the highly concentrated solar radiation. A near Gaussian profile focal spot of a 1.5m diameter parabolic mirror is transformed into an intense rectangular light column, uniformly distributed along the 2D-CPC output end of the assembly, avoiding the generation of hot pump spots within the laser rod. By trapping the pump light within the 2V-shaped cavity, efficient multi-pass absorption is achieved. Optimum pumping parameters and solar laser output powers are found through ZEMAX© non-sequential ray-tracing and LASCAD© laser cavity analysis. The solar laser output performances of both single-crystal and core-doped Nd:YAG rods are compared. Laser beam brightness figure of merit B=9.0×10−1W is calculated, which is 310% more than the most recent record. About 16.4W/m2 collection efficiency is also numerically predicted.

Efficient depolarization-loss-compensation of solid state lasers using only a Glan-Taylor polarizer

A novel scheme for reducing the depolarization loss resulting from thermally induced stress birefringence of a free running flash-lamp pumped single Nd: YAG rod is reported here and measured under resonator configuration with the use of a Glan-Taylor polarizer only. The depolarization loss has been systematically investigated and compared with the quarter wave-plate scheme. The Glan-Taylor polarizer is given two rotations with respect to two perpendicular axes for obtaining Brewster's effect as well as phase retardation inside a stable resonator. This single optical element optimally reduces depolarization loss to ∼18% and performs better than quarter wave-plate in combination with a polarizer. Using Jones-vector formulation, we analyzed the effect of tilting of Glan-Taylor polarizer and accounted the measured data of depolarization loss.

120 watt continuous wave solar-pumped laser with a liquid light-guide lens and an Nd:YAG rod

We propose a simple and efficient pumping approach for a high-power solar-pumped laser by using a liquid light-guide lens (LLGL) and a hybrid pumping cavity. A 2×2 m Fresnel lens is used as a primary concentrator to collect natural sunlight; 120 W cw laser power and a 4.3% total slope efficiency are achieved with a 6-mm diameter Nd:YAG rod within a 14-mm diameter LLGL. The corresponded collection efficiency is 30.0 W/m(2), which is 1.5 times larger than the previous record. This result is unexpectedly better than that of Cr:Nd:YAG ceramics. It is because the scattering coefficient of Cr:Nd:YAG ceramics is 0.004cm(1), which is 2 times larger than that of the Nd:YAG crystal, although both have similar saturation gains.

Study on LD-Pumped Yb:YAG Rod Laser

The physical properties and characteristics of absorption and emission spectra of Yb: YAG crystal are analyzed in this paper. From the rate equation of quasi-three-level system ,We derive the rate equations of diode-pumped continuous work-end-pumped solid state laser and a theoretical analysis and optimization design for continuous LD end-pumped lasers are given.

Improvement of the linearly polarized output power in Nd:YAG laser with [100]-cut rod

Thermal depolarization caused by birefringence is a major factor that limits the output power of linearly polarized Nd:YAG laser. This paper theoretically analyzes the thermal depolarization of [111]- and [100]-cut Nd:YAG rods and output power of two diode-pumped Nd:YAG rods are compared experimentally. 3×80 mm sized [111]- and [100]- cut rods with doping concentration of 1.1±0.1at.% are used. With a pump power of 180 W, the ratio of linearly polarized output power versus unpolarized output power obtained with the [111]- and [100]- cut rods are 19% and 43% respectively, with a difference of 24%. The experiment demonstrates that in comparison with conventional [111]- cut Nd:YAG rod, [100]- cut Nd:YAG rod can improve the linearly polarized output power obviously. The thermal depolarization depends on the polarization direction for the [100]- cut Nd:YAG rod, and the linearly polarized output power can be improved by suitably modification of the polarization direction of linearly polarized laser to minimize thermal depolarization.

High-power near diffraction-limited 1 064-nm Nd:YAG rod laser and second harmonic generation by intracavity-frequency-doubling

We present a near diffraction-limited 1 064-nm Nd:YAG rod laser with output power of 82.3W(M2 \approx 1.38). The power fluctuation over two hours is better than \pm 1.1%. Pulsed 1 064-nm laser with an average power of 66.6 W and pulse width of 46 ns are achieved when the laser is Q-switched at a repetition rate of 10 kHz. The short pulse duration stems from the short cavity as well as the high-gain laser modules. Using intracavity-frequency-doubling, a 35.0-W near diffraction-limited 532-nm green laser (M2 \approx 1.32) is achieved with a pulse width of 43 ns.

Efficient 1645 nm continuous-wave and Q‑switched Er:YAG laser pumped by 1532 nm narrow-band laser diode

Energy transfer upconversion induced thermal effects are mainly responsible for the low efficiency of laser diode pumped Er:YAG lasers. The current work adopts Er:YAG rods with 0.25% Er(3+) doping concentration, instead of the commonly used rods with 0.5% Er(3+) doping concentration. Results show that the thermal effect is greatly alleviated. A continuous-wave output of 10.2 W is obtained using 31 W incident pump power. Optical-optical efficiency is approximately 33%. Slope efficiency, with respect to the absorbed pump power, is as high as 83%, which is close to the quantum efficiency. In a Q-switched operation, 7 mJ pulses with a pulse width of ~65 ns are obtained at 100 Hz PRF.

Highly efficient solar-pumped Nd:YAG laser

The recent progress in solar-pumped laser with Fresnel lens and Cr:Nd:YAG ceramic medium has revitalized solar laser researches, revealing a promising future for renewable reduction of magnesium from magnesium oxide. Here we show a big advance in solar laser collection efficiency by utilizing an economical Fresnel lens and a most widely used Nd:YAG single-crystal rod. The incoming solar radiation from the sun is focused by a 0.9 m diameter Fresnel lens. A dielectric totally internally reflecting secondary concentrator is employed to couple the concentrated solar radiation from the focal zone to a 4 mm diameter Nd:YAG rod within a conical pumping cavity. 12.3 W cw laser power is produced, corresponding to 19.3 W/m(2) collection efficiency, which is 2.9 times larger than the previous results with Nd:YAG single-crystal medium. Record-high slope efficiency of 3.9% is also registered. Laser beam quality is considerably improved by pumping a 3 mm diameter Nd:YAG rod.

60 W yellow laser at 561 nm by intracavity frequency doubling of a diode-pumped Q-switched Nd:YAG laser

A high-power yellow laser was achieved by intracavity frequency doubling of a diode-pumped Nd:YAG rod laser. A solid etalon was inserted into the resonator to implement efficient operation of the low-gain single line at 1123 nm transition. By using a LBO crystal inside the cavity as the frequency doubler, the maximum output power of the 561 nm yellow laser was obtained to be as high as 60.3 W with a pulse repetition frequency of 6 kHz, corresponding to an optical-to-optical conversion efficiency of about 6.1%. The output power fluctuation of the yellow laser was measured to be better than 3% in half an hour.

Lensing effects in Q-switched unstable laser cavities with side-pumped Nd:YAG and ruby crystal rods

We present a comprehensive numerical model that accounts for non-uniform pumping and a related thermal and electronic lensing effects in Q-switched unstable laser cavities. We study the influence of these effects on the output beam profile in Nd:YAG and ruby laser systems with side-pumped crystal rods. We also constructed both lasers to experimentally validate the numerical results and found very good agreement. The results show that both types of lensing effects are particularly detrimental in ruby, while they are insignificant in Nd:YAG.

Passively mode-locked radially polarized laser based on ceramic Nd:YAG rod

A mode-locked radially polarized laser based on a ceramic Nd:YAG rod that was transversely pumped by LD bars. The maximum output power of 10.6 W was achieved with the frequency of 45 MHz, the average pulse width of 75 ps Abstract: By using a semiconductor saturable absorber mirror, we demonstrated the generation of and the beam quality of M2 = 2.11.

101 W of average green beam from diode-side-pumped Nd:YAG/LBO-based system in a relay imaged cavity

Studies on intracavity frequency doubling of acousto-optically Q-switched Nd:YAG rod laser using 18 mm long type-II phase-matched LBO crystal in a relay-imaged cavity is reported. A single pump head comprised of Nd:YAG rod, diffusive reflectors and linear array laser diode bars is used. 101 W of average green power at a total diode pumping power of 700 W is obtained corresponding to 14.4% optical-to-optical conversion efficiency. The pulse repetition rate is 30 kHz with an individual pulse duration of 200 ns.

Efficient and high-power green beam generation by frequency doubling of acousto-optic Q-switched diode-side pumped Nd:YAG rod laser in a coupled cavity

A 52-W green laser at 532 nm by extra-cavity second-harmonic generation in a coupled-cavity configuration is demonstrated. The fundamental laser is a diode-side-pumped acousto-optic (AO) Q-switched Nd:YAG rod laser producing 84 W of average power at 1064 nm at 8 kHz repetition rate. Type-II phase-matched polished KTP crystal is used as the nonlinear crystal for second-harmonic generation. The individual green pulse width is 50 ns and the fundamental to second harmonic conversion efficiency is 61.8%.

Review of the formula of thermal focal length in side-pumped laser rods

The expressions of focal length in side-pumped rod lasers are studied. Good agreement is obtained between simulation and experiments reported previously, using Koechner's theory. The results reveal that underestimation of thermal lens accrues from overestimating the material's thermal conduction and without considering the nonuniform heat deposit. In the case of Nd:YAG rods, temperature-dependent variation of the refractive index constitutes the major contribution of thermal lensing, whereas the temperature- and stress-dependent variations of the refractive index make the major contributions of thermal lensing for Nd:Glass rod lasers.

Strengthening of poly-crystalline (ceramic) Nd:YAG elements for high-power laser applications

In the last decade, poly-crystalline (ceramic) Nd:YAG components emerged as very promising candidates for high-power lasers, exhibiting some advantages over single-crystal Nd:YAG ones. Such devices are required to endure high thermal stress during operation. In our present work we present experimental results on the strengthening of poly-crystalline YAG and Nd:YAG fine-ground components by chemical etching in hot ortho-phosphoric acid. The strength of poly-crystalline Nd:YAG laser rods was measured inside a laser head by applying the pump power till rod fracture. A factor of ∼3 increase in the fracture longitudinal heat power density for etched poly-crystalline Nd:YAG rods as compared to standard commercial poly-crystalline rods was obtained. This effect is similar to our previous results on single-crystal Nd:YAG laser rods which showed a factor of 3.6–5.0 increase in tensile strength by the same treatment. A modified Weibull analysis was used to assess the fracture probability parameters.

A clinical study of failure in microchannel cooled diodes used in large laser systems

In this paper we investigate the source of failure in commercial, microchannel cooled CW diode bars placed in 12 bar horizontal arrays. The arrays were used to pump Nd:YAG rods in our 10 kW developmental laser. The laser was operated at low duty factor over a period of over 2 years. Experimental evidence indicated that the sudden, catastrophic failure was because of degraded cooling. We used optical microscopes, an X-ray microfocus imager, and a thermal neutron scattering camera to look inside the microcoolers. Our investigations revealed only one possible failure mechanism: cooling flow reduction because of delamination of the Au coating the walls of the microcoolers and the entrapment of Au flakes within the microchannel structures. We observed blisters in the microcoolers under working bars, and flake-like structures in the microcoolers under burnt-out bars (all taken from the laser). We observed no evidence of either massive blockages because of electrochemical deposits, or of corrosion/erosion in the microchannel walls. Integral operation times of the high flow-rate cooling system and of the diodes themselves were too short by one and two orders of magnitude, respectively, to explain the observed failures. Microchannel immersion times in the deionized water were, however, long enough to allow for corrosion of metals that may have been exposed through defects in the Au coatings. Three-dimensional heat flow simulations showed that blockage of multiple microchannels towards the edge of a bar can easily lead to catastrophic temperature increases.

Properties of continuous-wave 1123 nm laser with diode-side-pumped Nd:YAG

Laser properties of diode-side-pumped Nd:YAG laser operating at 1123 nm are demonstrated. A 1.0 at % Nd-doped Nd:YAG rod with a size of O3 × 63 mm2 is used as the active medium. Both radial and tangential thermal focal lengths of this side-pumped Nd:YAG rod are determined under lasing condition. The results show that the bifocusing strength of 1123 nm laser is larger than that of 1164 nm laser, and 1123-nm thermal focal lengths are shorter than those of 1064-nm laser due to higher quantum defect. Laser output performances of 1123 nm in terms of stability, output power and beam quality influenced by pump power at different cavity lengths are also discussed with a convex-piano cavity.

Model of thermally induced wavefront distortion and birefringence in side-pumped Nd-doped YAG and phosphate glass heat capacity rod lasers

We develop an analytic model to describe the dynamic average thermal distortion and phase difference between the two principal polarizations in side-pumped Nd:YAG and Nd:glass heat capacity rod lasers. It can be predicted that the average thermal distortion is proportional to the temperature profile on the cross section from the analytic expression and, therefore, it is feasible to measure the temperature profile by wavefront sensing. In addition, temperature-dependent variation of the refractive index constitutes the major contribution of the thermal lensing for Nd:YAG rod lasers. Temperature- and stress-dependent variation of the refractive index constitute the major contributions of the thermal lensing for Nd:glass rod lasers. In the case of the same pumping and cooling conditions, there are the same orders of depolarization loss for Nd-doped YAG, LG-680, LG-750, LG-760, and LG-770 glass rod lasers.

Parameters effects on the surface morphology and structure of Nd:YAG nanopowders synthesized by co-precipitation method

In recent years, many attempts are made to produce Nd:YAG rods from its nanopowders instead of single crystals because of difficulties and complications of the crystal growth. The quality of new rods is strongly depended on the grain size and agglomeration amount of primary nanopowders. Co-precipitation method is one of the applicable methods to produce Nd:YAG powders with nano sizes; however, with usual co-precipitation method, the grains size are large and the agglomeration amount is high yet. This method contains different steps and parameters that any change of them leads in grains morphological and structural variations. This article’s purpose was to report the effect of different experimental parameters on controlling the quality of the Nd:YAG nanopowders. Some chemical and physical variations on usual co-precipitation method were designed based on particle growth process analysis and performed. By analyzing the result of performed experiments on the grains properties, a modified co-precipitation method could be achieved. This modified method allows the synthesizing of pure YAG powders with smaller grain size and lower agglomeration in comparison with usual co-precipitation technique. It is claimed that this modified method can be applied for a large number of materials produced by the usual co-precipitation technique.