YAG Rod Laser Research Articles

Polymer Composite Cladding for Selective Frequency Filtration: An Experimental and Modeling Study

Laser selective frequency filtering is currently performed using expensive, heavy, and bulky (millimeters in thickness) ceramic composite claddings around the laser rod, which limits the miniaturization and transportability of the laser. The cladding absorbs undesired spontaneous emissions and reflects the desired wavelength of the "pump" diode. As an improved alternative for the cladding on, say, a diode-pumped solid-state Nd:YAG laser rod, we investigate a spray-coated polymer composite cladding (micrometers in thickness). The polymer composite cladding is easier to process and lighter and has a much smaller volume vs. traditional ceramic composite claddings. The approach is demonstrated on spray-coated glass slides, where cubic samaria (Sm2O3) particles are used as the filler in the polymer composite cladding. The rationale for using samaria as the filler in the composite is its absorption near the laser spontaneous emission wavelength (i.e., 1064 nm) and high reflectivity at the incident pump wavelength (i.e., 808 nm). The addition of a second polymer composite layer loaded with alumina particles enables reduction of the samaria composite layer thickness. The Kubelka-Munk model is shown to successfully predict the experimentally measured optical performance of single and bilayer claddings, making it a reliable design tool for multilayer claddings.

Numerical investigation into the Nd doped YAG rod grooving impact on the sunlight-pumped-laser performance

This paper presents a numerical analysis of the impact of grooving the Nd doped YAG rod on the sunlight-pumped lasers performance. The study analyzes laser systems that utilize side-exciting and end-side-exciting approaches to activate both grooved and non-grooved Nd doped YAG laser rods. The effects of the rod surface groove on the performance of the sunlight-pumped-lasers are thoroughly examined using ZEMAX© and LASCAD© software. To excite the grooved and non-grooved Nd doped YAG rods alternately, a ring-array sunlight flux concentrator is employed. Moreover, in the side-exciting technique, the head of the laser system contains a rectangular light guide of an extremely transparent glass made from fusing silica and an excitation cavity with a V-shaped configuration, housing the Nd doped YAG rod. This exciting method with a grooved laser rod resulted in a 13.70% increase in laser power and a 28.20% reduction in stress intensity compared to the non-grooved rod. In the end-side-exciting technique, the head of the laser system comprises an aspheric lens made of a fused silica glass and a conical-shaped excitation cavity, accommodating the Nd doped YAG rod. Results indicate that using grooved laser rod in this exciting system did not lead to an amelioration in output laser power. However, this technique enhanced the stress intensity by a reduction of 35.03%.

Enhancement of Laser-Induced Damage Threshold of Nd:YAG Laser Rods through Improved Polishing Processes

Enhancement of Laser-Induced Damage Threshold of Nd:YAG Laser Rods through Improved Polishing Processes

Fresnel Lens Solar-Pumped Laser with Four Rods and Beam Merging Technique for Uniform and Stable Emission under Tracking Error Influence

Significant numerical improvements in Fresnel lens Nd:YAG solar laser collection efficiency, laser quality factors and tracking error compensation capacity by two Fresnel lenses as primary solar concentrators are reported here. A Nd:YAG four-rod side-pumping configuration was investigated. The four-rod side-pumping scheme consisted of two large aspherical lenses and four semi-cylindrical pump cavities, where the Nd:YAG laser rods were placed, enabling an efficient solar pumping of the laser crystals. A 104.4 W continuous-wave multimode solar laser power was achieved, corresponding to 29.7 W/m2 collection efficiency, which is 1.68 times that of the most efficient experimental Nd:YAG side-pumped solar laser scheme with heliostat–parabolic mirror systems. End-side-pumped configuration has led to the most efficient multimode solar lasers, but it may cause more prejudicial thermal effects, poor beam quality factors and a lack of access to both rod end-faces to optimize the resonant cavity parameters. In the present work, an eight-folding-mirror laser beam merging technique was applied, aiming to attain one laser emission from the four laser rods that consist of the four-rod side-pumping scheme with a higher brightness figure of merit. A 79.8 W multimode laser output power was achieved with this arrangement, corresponding to 22.7 W/m2. The brightness figure of merit was 0.14 W, being 1.6, 21.9 and 15.7 times that of previous experimental Nd:YAG solar lasers pumped by Fresnel lenses. A significant advance in tracking error tolerance was also numerically attained, leading to a 1.5 times enhancement in tracking error width at 10% laser power loss (TEW10%) compared to previous experimental results.

Compact LD side-pumped Nd:YAG oscillator at 100 Hz without water-cooling

A high-repetition-frequency side-pumped electro-optical (E-O) Q-switched Nd:YAG laser without water cooling is reported. A 100 Hz laser module without water-cooling was designed and the related parameters of crystal are simulated. The crystal is annularly pumped in both ends and is conductively cooled in the middle. The heat generated by crystal and laser diode is dissipated by thermoelectric cooler (TEC), fins and fan. The 1064 nm maximum output energy is 68 mJ with a pulse width of 31 ns and a repetition rate of 100 Hz. The optical–optical conversion efficiency is 10.6%. To the best of our knowledge, this is the first report of 100 Hz repetition rate operation for a E-O Q-switched Nd:YAG rod laser without water-cooling.

Fabrication of engineered dopant profiles in Er/Lu:YAG transparent laser ceramics via additive manufacturing

Transparent ceramic Er:YAG laser rods were fabricated via the direct ink write (DIW) method with engineered doping profiles featuring an Er-doped core with endcaps and core-clad structures. Laser rods up to 11 cm in length were produced which required development of a scalable process. To achieve this, multiple improvements were implemented, including printing the rods horizontally on a substrate, rather than vertically, eliminating the need for an external support structure and using a sacrificial drying layer to mitigate warping and defects. Highly transparent rods were achieved with optical scatter levels as low as 0.5%/cm (at 543 nm). A small refractive index difference of 5.7 ppm was measured at the interface between the Er-doped core and the Lu-doped endcaps and cladding. These results demonstrate DIW as a straightforward method for making good optical quality laser rods with engineered doping profiles to improve laser performance.

Most efficient simultaneous solar laser emissions from three Ce:Nd:YAG rods within a single pump cavity

We report here, to the best of our knowledge, the most efficient simultaneous emissions of three continuous-wave 1064 nm solar laser beams. A fused silica aspheric lens was used to couple the concentrated solar radiation from the focal zone of a 0.4 m 2 effective collection area primary parabolic mirror into three 2.5 mm diameter, 25 mm length 0.1 at.% Ce:1.1 at.% Nd:YAG laser rods within a single conical pump cavity. For 356 W incoming solar power, 16.5 W continuous-wave total multimode solar laser power was measured, corresponding to 4.64% solar-to-laser conversion efficiency, 41.25 W/m 2 collection efficiency, and 7.64% slope efficiency, which are 1.24, 1.27, and 1.11 times, respectively, higher than previous records by pumping a single 4.5 mm diameter, 35 mm length 0.1 at.%Cr:1.0 at.%Nd:YAG ceramic laser rod. The three-rod Ce:Nd:YAG solar laser also provided 2.13, 2.25 and 1.50 times enhancements in solar-to-laser conversion efficiency, collection efficiency, and slope efficiency, respectively, as compared to previous records by pumping three 3.0 mm diameter, 25 mm length 1.0 at.% Nd:YAG rods within the same single conical pump cavity. • Most efficient simultaneous emissions of three 1064 nm solar laser beams. • 4.64% solar power-to-laser power conversion efficiency attained. • 41.25 W/m 2 solar laser collection efficiency achieved. • 7.64% solar laser slope efficiency was calculated.

Design and Development of a High-Performance LED-Side-Pumped Nd:YAG Rod Laser

We present a design and development of a high-performance light-emitting diode (LED)-side-pumped Nd:YAG rod laser with strong pulse energy, high efficiency, and consistency, very good beam quality, and high uniform pumping intensity in the active area which reduces the effects of thermal gradient significantly. A five-dimensional 810 nm LED array with a full width of 30 nm at half maximum was intended to achieve high coupling efficiency by putting the LED array as close as possible to the side of the Nd:YAG laser rod for overcoming the large pumped divergence. Under 2.25 J pump energy, maximum single pulse energy of 35.86 mJ with duration of 1.24 μs at 1063.68 nm was obtained, equivalent to optical efficiency of 1.59% and a slope efficiency of 2.53%. The laser was set to repeat at a rate of 10 Hz with a beam quality factor of and , as well as with the output power stability of < 4.1% (root mean square) and < 7.3% (peak to peak). To the best of our ability, this is the highest performance for an LED-side-pumped Nd:YAG rod laser oscillator with a 10-mJ-level output ever reported.

Actively Q switched radially polarized Ho:YAG laser with an intra-cavity laser-written S-waveplate.

Nanosecond Q switched pulses and radial polarization are established stand-alone techniques for enhanced laser materials processing applications, but are generally challenging to achieve simultaneously at high average power levels. Here, we demonstrate a 20.6 W radially polarized Ho:YAG rod laser which has been actively Q switched in order to generate 515 μJ, 210 ns pulses at 2097 nm. By utilizing an ultra-low-loss spatially variant birefringent wave plate (S-waveplate) inside the laser cavity, the linearly polarized fundamental mode has been converted to a radially polarized donut-shaped beam with very high conversion efficiency.

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

The generation of a 33.7 W radially polarized output is demonstrated by way of double-pass amplification in a Ho:YAG thin-slab crystal. The amplifier system was seeded with the radially polarized output beam from a continuous-wave 13.2 W, 2.1 µm Ho:YAG rod laser, which exploited gain medium bifocusing and a ring-shaped pump spot to promote preferential lasing on the radially polarized Laguerre–Gaussian mode. By compensating for both the thermally induced stress birefringence in the thin-slab crystal and the Gouy phase shift resulting from astigmatic focusing of the 13.2 W seed, only marginal beam degradation was observed across the 95 W range of pump power into the amplifier.

LED-pumped solid-state lasers with an improved optical pump system

An optical pump system for LED-pumped solid-state lasers is introduced to effectively couple the energy of pump sources to the active medium. The optical system is based on the coupling of optical rays from light-emitting diode sources to laser rod using high reflecting surfaces. Three different configurations with four, five, and six segments have been designed and their geometry is optimized with the 3D Monte-Carlo ray-tracing method to obtain the best performance. Moreover, a geometrical model is developed to describe the general behavior of the pump system. The pump systems have been fabricated and successfully applied to pump 3 mm diameter Ce:Nd:YAG laser rods with available white spectrum LEDs. The performance of the pump system is experimentally compared with the closed-coupled pumping configuration and white spectrum LEDs under equal pump energy and an identical optical resonator. The improved five and six segments pump systems when Epump>350mJ having more than 170 percent higher conversion efficiency than the closed-coupled configuration. Using six segments configuration and 500 mJ optical pump energy, the LED-pumped Ce:Nd:YAG laser oscillator produced laser spikes with a multi-mode beam structure and more than 700 μJ laser energy at 10 Hz repetition rate. A compact, high repetition rate >10 Hz, multi-milli joules LED-pumped solid-state lasers are possible by using the improved optical pump system and infrared LEDs.

Thermal lens effect induced in a Cr,Tm,Ho:YAG laser rod: A comparison between under lasing and non-lasing conditions

In this paper, transient thermal lensing effects in a typical flashlamp-pumped CTH:YAG laser crystal under lasing and non-lasing conditions are studied and compared in a low repetition-rate regime. It is shown that in the lasing regime (for pumping energies higher than 90J) the time-resolved behavior and the strength of the three mode thermal lenses of the rod are different from the non-lasing condition. According to this research, it can be referred that higher-order processes such as excited state absorption of both pump and laser radiation and energy transfer up-conversion may have a more significant contribution to the laser dynamics in the lasing regime. The analysis of the results also shows that the energy transfer between different manifolds in Cr3+, Tm3+, and Ho3+ ions may depend on coolant temperature.

Enhancing TEM00-Mode Solar Laser With Beam Merging and Ring-Array Concentrator

Abstract It is reported here a large improvement in numerically calculated TEM00-mode side-pumped solar laser efficiency, and brightness figure-of-merit by pumping two thin Nd:YAG laser rods simultaneously with a ring-array solar energy primary concentrator. Two side-pumping configurations were investigated. A single-rod configuration was used to pump a typical single thick laser rod with the full collection area of the ring-array concentrator, and a dual-rod to pump two thin laser rods simultaneously. A three-folding-mirror laser beam merging technique was used, enabling the emission of only one laser beam from the two rods. For the dual-rod single laser beam configuration, 27.50 W continuous-wave TEM00-mode solar laser output power was numerically achieved, corresponding to 16.10 W/m2 TEM00-mode solar laser collection efficiency, 1.70% solar-to-laser power conversion efficiency, 25.00 W brightness figure-of-merit, and 1.54% brightness conversion efficiency, being 1.46, 1.30, 1.75, and 1.40 times, respectively, higher than the previous numerical records, and also 2.04, 1.60, 3.87, and 2.03 times, respectively, more than the previous state-of-the-art experimental records.

40 W Continuous Wave Ce:Nd:YAG Solar Laser through a Fused Silica Light Guide

The solar laser power scaling potential of a side-pumped Ce:Nd:YAG solar laser through a rectangular fused silica light guide was investigated by using a 2 m diameter parabolic concentrator. The laser head was formed by the light guide and a V-shaped pump cavity to efficiently couple and redistribute the concentrated solar radiation from the parabolic mirror to a 4 mm diameter, 35 mm length Ce(0.1 at.%):Nd(1.1 at.%):YAG laser rod. The rectangular light guide ensured a homogeneous distribution of the solar radiation along the laser rod, allowing it to withstand highly concentrated solar energy. With the full collection area of the parabolic mirror, the maximum continuous wave (cw) solar laser power of 40 W was measured. This, to the best of our knowledge, corresponds to the highest cw laser power obtained from a Ce:Nd:YAG medium pumped by solar radiation, representing an enhancement of two times over that of the previous side-pumped Ce:Nd:YAG solar laser and 1.19 times over the highest Cr:Nd:YAG solar laser power with a rectangular light-guide. This research proved that, with an appropriate pumping configuration, the Ce:Nd:YAG medium is very promising for scaling solar laser output power to a higher level.

First Demonstration of a Led-Side-Pumped Acousto-Optic Q-Switched Nd:Yag Rod Laser With High Repetition Rate And Beam Quality Operation

First Demonstration of a Led-Side-Pumped Acousto-Optic Q-Switched Nd:Yag Rod Laser With High Repetition Rate And Beam Quality Operation

Nd:YAG laser rod manufactured by femtosecond laser-induced chemical etching

We present a cylindrical rod of single-crystal Nd:YAG fabricated from a bulk crystal using femtosecond laser-induced preferential etching. The rod is pumped at 808 nm, and the laser characteristics at 1064 nm emission and the thermal stability are investigated. The slope efficiency was determined with a maximum optical-to-optical efficiency of 7.9%±0.29% and a FWHM linewidth of 299 ± 63 pm. The etched rod shows parameters consistent with existing Nd:YAG gain crystals. This fabrication technology will find use in composite micro-optical devices where microfluidics, active and passive optics, and structures can be etched out of many different materials and combined into a single device.

Zigzag Multirod Laser Beam Merging Approach for Brighter TEM00-Mode Solar Laser Emission from a Megawatt Solar Furnace

An alternative multirod solar laser end-side-pumping concept, based on the megawatt solar furnace in France, is proposed to significantly improve the TEM00-mode solar laser output power level and its beam brightness through a novel zigzag beam merging technique. A solar flux homogenizer was used to deliver nearly the same pump power to multiple core-doped Nd:YAG laser rods within a water-cooled pump cavity through a fused silica window. Compared to the previous multibeam solar laser station concepts for the same solar furnace, the present approach can allow the production of high-power TEM00-mode solar laser beams with high beam brightness. An average of 1.06 W TEM00-mode laser power was numerically extracted from each of 1657 rods, resulting in a total of 1.8 kW. More importantly, by mounting 399 rods at a 30° angle of inclination and employing the beam merging technique, a maximum of 5.2 kW total TEM00-mode laser power was numerically extracted from 37 laser beams, averaging 141 W from each merged beam. The highest solar laser beam brightness figure of merit achieved was 148 W, corresponding to an improvement of 23 times in relation to the previous experimental record.

Experimental investigation of thermal lens effect in a flashlamp pumped CTH:YAG laser rod

In this article, the thermal lens effect in a CTH:YAG laser crystal was studied experimentally using the probe beam technique. The thermally induced changes of the refractive index were made using flashlamp pumping in the CTH:YAG laser rod along with the transmission of a low power probe beam (532nm) through the crystal. The time-resolved dynamics of the lens-like behavior of the rod were inspected within a range of pumping energies, several repetition rates, and cooling temperatures. For 1ms pumping pulse length, it can be concluded from the results that in the early stage of the pumping pulse (500−600µs after the initiation of the pump pulse), the rod focal length is negative. It takes around 1 s for the rod to return to its equilibrium after the lamp was turned on which is around half of the thermal time constant for a 6 mm CTH:YAG rod. It has been shown that the dioptric power of the three mode lenses increases when pumping energy increases. The effect of increasing the flashlamp repetition rate (1, 5, and 10Hz) as well as the coolant temperature (8−20°C) for constant lamp energy and constant pulse length is also discussed.

Luminescence sensitization properties of Ce: Nd: YAG materials for solar pumped lasers

The study of the process of energy transfer in an active medium with a sensitizer based on Ce: Nd: YAG material under pumping by LED at a wavelength of 454 nm and by solar radiation is carried out. Based on the results of experimental studies of the energy transfer process with blue LED excitation, it was determined that the overall efficiency of energy transfer from Ce ions to active Nd ions in a Ce: Nd: YAG laser rod is ∼76%. The conducted comparative studies of Nd: YAG and Ce: Nd: YAG luminescence with the excitation by solar radiation has shown 1.5 fold increase of Nd luminescence in Ce:Nd:YAG which means that the threshold power of Ce:Nd:YAG solar lasers can be reduced by 1.5 times. At the same time, the pumping efficiency is increased by the same factor compared to Nd:YAG solar laser. Thus, under the same pumping conditions, the output power of Ce:Nd:YAG solar laser can reach two fold increase compared to Nd:YAG solar laser. Our study confirms that Ce: Nd: YAG is one of the best alternatives to Nd: YAG in solar pumped lasers.

Ce:Nd:YAG side-pumped solar laser

A significant advancement in the Ce:Nd:YAG solar laser performance using a side-pumping configuration is reported. A solar laser head was composed of a double-stage semispherical lens and a trapezoidal-shaped pumping cavity, which coupled and redistributed the concentrated solar radiation from the focal zone of a parabolic mirror into a laser rod. The laser output performance of a 4.0-mm diameter, 35-mm length Ce:Nd:YAG laser rod was tested and compared with that from a Nd:YAG rod with the same dimensions. At an incoming solar power of 600 W, the Ce:Nd:YAG solar laser achieved 23.6-W / m2 collection efficiency, 4.4% slope efficiency, and 2.8% solar-to-laser power conversion efficiency, which are 1.57, 1.47, and 1.56 times, respectively, higher than the ones obtained with the Nd:YAG rod. The Ce:Nd:YAG side-pumped solar laser has also 1.39 and 1.15 times more collection efficiency and solar-to-laser power conversion efficiency, respectively, than the previous record by Nd:YAG side-pumped solar laser. We demonstrate the great potential of the Ce:Nd:YAG ceramic rod as a gain medium for side-pumped solar lasers.