Slab Amplifier Research Articles

Innozag amplifier: optimizing the Innoslab platform to improve beam quality and gain

This study presents an innovative zigzag-type Innoslab amplifier platform, termed ‘Innozag,’ that merges the essential attributes of both Innoslab and zigzag slab amplifiers. A thorough theoretical and experimental examination has been performed to analyze and compare the gain and amplified beam wavefront distortion of the Innoslab and Innozag amplifiers. Our investigation includes detailed optical path difference computation coupled with examination of the far-field amplified beam profile. The results confirm that the Innozag amplifier reduces the thermally induced wave distortion by up to 40%. Geometric features, particularly the overlapping zones in the zigzag path, increase the gain of the Innozag amplifier. The Innozag design achieves an amplification factor 1.4 times greater than that of the Innoslab amplifier in a five-pass structure.

4.4 kW Nd:YAG slab amplifier with a high repetition frequency and high beam quality

Using the self-developed fused indium wetting technology and planar waveguide, the uniform heat dissipation of the slab crystal and uniform pumping of the pump light were achieved, respectively. Based on the master oscillator power amplification (MOPA) scheme, the power was then amplified when the seed light source passed through the Nd:YAG slab crystal three times. Additionally, the image transfer system that we added to the amplified optical path achieved high beam quality. Finally, we obtained a rectangular pulsed laser with an output average power of 4461 W, a repetition frequency of 20 kHz, a pulse width of 62 ns, an optical-to-optical conversion efficiency of 26.8%, and a beam quality of β x =7.0 and β y =7.7.

Foucault knife-edge test for the characterization of mid-spatial frequencies to optimize liquid-cooled Nd:Phosphate split-slab amplifiers

The Foucaut knife-edge test has been used as a simple and effective metrology process to characterize the transmitted wavefront of optical systems for more than a century. We apply this method to estimate the optical quality of the transmitted wavefront in the mid-spatial frequencies domain. We compare the results obtained by this approach and interferometry to estimate RMS on three calibrated reference phase plates and evidence a difference smaller than 9%. The Foucaut knife-edge method is applied to a liquid cooled Nd:phopshate split slab amplifier. This method is shown to be particularly suitable to optimize liquid cooled slab amplifiers down to the sub-nanometer RMS quality values that are generally required in high-power laser systems.

1.36 J nanosecond laser at 1 kHz repetition based on a slab amplifier chain.

A high beam quality diode-pumped Nd:YAG master oscillator power-amplifier (MOPA) laser with three end-pumped slab amplifiers is developed. The Q-swtiched side-pumped rod oscillator presented a pulse energy 3.1mJ with beam quality factors of M x2=1.17 and M y2=1.15 at a repetition of 1kHz. The MOPA system delivered a pulse energy of 1.36J with a pulse width of 48.2ns and an extraction efficiency of 44.8%. The beam quality factors of M x2=1.72 and M y2=3.85 are measured without any phase-conjugators or adaptive optics.

FLASH free electron laser pump-probe laser concept based on spectral broadening of high-power ytterbium picosecond systems in multi-pass cells.

Within the FLASH2020+ upgrade, the pump-probe laser capabilities of the extreme ultraviolet and soft x-ray free-electron laser (XFEL) FLASH in Hamburg will be extended. In particular, providing wavelength tunability, shorter pulse durations, and reduced arrival time jitter will increase the scientific opportunities and the time resolution for the XFEL-optical laser pump-probe experiments. We present here a novel concept for the pump-probe laser at FLASH that is based on the post-compression of picosecond pulses emitted from high-power Ytterbium:YAG slab amplifiers. Flexible reduction of the pulse duration is facilitated by spectral broadening in pressure-tunable multi-pass cells. As an application, we show the pumping of a commercial optical parametric amplifier with 150fs post-compressed pulses. By means of an additional difference frequency generation stage, tunable spectral coverage from 1.3 to 16μm is reached with multi-μJ, sub-150fs pulses. Finally, a modular reconfiguration approach to the optical setups close to the free-electron laser instruments is implemented. This enables fast installation of the nonlinear frequency converters at the end stations for user operation and flexibility between different instruments in the two experimental halls.

Amplification of high repetition-rate, picosecond laser pulses using a zig-zag slab configuration

Laser sources which generate high peak-pulse energy, picosecond pulse duration outputs at high repetition rates are of particular interest for applications including laser ignition and space fragment detection. In this work, we demonstrate the design and operation of a zig-zag slab, solid-state master oscillator power amplifier (MOPA) which yields high energy amplification. The system uses a weakly-doped Nd:YAG slab as the amplifier medium, to amplify laser pulses from a passively Q-switched microchip seed laser. The seed laser beam undergoes four passes of the slab amplifier resulting in an amplified output pulse with hundreds of picoseconds pulse duration. We investigate the relationship between the angle of incidence of the seed laser beam into the amplifier slab and its effect on the slab fill-factor and overall laser field amplification. We also investigate the impact that the temperature of the laser diode array (LDA) which is used to pump the slab amplifier, has on the amplification efficiency of the MOPA. Experimentally, we demonstrate an amplification factor of ∼90 times from the optimized slab amplifier, and a resultant output laser field with a pulse energy of 99.58 mJ, a pulse duration of 491 ps, and a repetition rate of 200 Hz. We believe that this work will pave the way towards the development of novel all-solid-state amplifier designs for the generation of high-energy, high repetition frequency, sub-nanosecond laser outputs.

Nd:YAG end-pumped zigzag multi-pass slab amplifier optimization: numerical and experimental study regarding the saturation effects.

A numerical modeling of Nd:YAG end-pumped zigzag multi-pass slab amplifier is developed. Spatial dependent rate equations have been solved taking into consideration the pump and laser beam saturation effects with regard to overlap correction of the signal path through gain medium. Based on our results, efficient amplifier structure with optimized output power could be designed with respect to the change in the number of signal beam-pass, doping concentration and slab length. In order to verify our modeling an experimental setup is designed.

Characterization of surface defects using a phase retrieval technique in a high-power laser system.

In the framework of high-power lasers, surface defects on optics can generate strong light intensification and induce damage sites on downstream optics. To evaluate this intensification during high-energy laser shots, a three-step method is proposed. First, a dedicated measurement bench is designed to measure the intensification induced by defects on a wide variety of optics, including amplifier slabs, KDP crystals, mirrors, gratings, and vacuum windows, for propagation distances up to 2000 mm. A multi-resolution single-beam multiple-intensity reconstruction phase retrieval algorithm is then used to reconstruct a model of the defect, in both amplitude and phase, from a set of intensification measurements. Finally, the impact of the modeled defect on downstream optics is evaluated with a simulation of the high-power laser system. This method is experimentally validated through a case study of damage identified on one of the Laser Mégajoule (LMJ) beams, characterized with the method presented in this paper. The long-distance impact on the LMJ beam is estimated by simulation and compared to a direct near-field measurement.

Dynamic Drift of Laser in 4×2 Assembled Slab Amplifier with 400 mm Aperture

Dynamic Drift of Laser in 4×2 Assembled Slab Amplifier with 400 mm Aperture

Generation of one-dimensional high-order Hermite-Gaussian laser beams with large mode volume

Hermite-Gaussian (HG) beams have many important applications in the optical frontier, and the limited output power of the high-purity HG beams is partly due to the small gain volume of the mode. The commonly used off-axis end-pumped scheme offers a narrow gain volume whose diameter is about a hundred microns. In this work, a new method of generating the HG beams based on a slab resonator that has a large mode volume is proposed and experimentally demonstrated. According to the optical resonator theory, the intra-cavity modes in thickness and width direction of the slab resonator are restricted by inserting two size-adjustable apertures, respectively. The one-dimensional HG beam generation is mainly guaranteed by the size of the aperture along the thickness direction of the slab, which matches the diameter of the fundamental mode. The different order one-dimensional HG beams are obtained by refined intra-cavity mode modulation. Since the higher-order modes are less sensitive to the misalignment of the cavity mirror than the lower-order modes, and the manipulation of the modes-loss at different orders is achieved by combining the tilt control of the coupled output mirror and the size control of intra-cavity apertures. By adjusting the optical gain and loss in the resonant cavity, the single mode wins the competition of laser modes. Therefore, high-purity one-dimensional HG beams with 0 to 9 orders (HG<sub>00</sub> to HG<sub>09</sub>) are generated. The pump module is comprised of a two-dimensional laser diode array which offers face-pumping to the large surface of the slab, therefore the width of the mode volume is extended to several millimeters. By further incorporating the 100mm-level long slab, the total gain volume is much larger than the counterpart in the off-axis pumping scheme. In this work, the output power of the highest order HG<sub>09</sub> mode increases up to 244 mW. Owing to the large gain volume and uniform gain distribution caused by the face-pumped slab, the purity of high order HG modes is quite good. The correlation coefficient <inline-formula><tex-math id="M3">\begin{document}$ \rho $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M3.png"/></alternatives></inline-formula> between the measured intensity distribution and the theoretical value is larger than 0.95. The beam quality factor <inline-formula><tex-math id="M4">\begin{document}$ {M}^{2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20221422_M4.png"/></alternatives></inline-formula> is also in good agreement with the theoretical one. Finally, a conversion from Hermite-Gaussian beams to the donut-shaped Laguerre-Gaussian beams is realized by using an astigmatic mode converter. Hopefully, power scaling of the HG beam output is also expected by employing cascaded slab amplifiers, and the approach in this paper provides a novel solution for generation of high power HG beams.

Generation of One-dimensional High-order Hermite-Gaussian Laser Beams with Large Mode Volume

Hermite-Gaussian (HG) beams have many important applications in the optical frontier,and the limited output power of the high-purity HG beams is partly due to the small gain volume of the mode.The commonly used off-axis end-pumped scheme offers a narrow gain volume whose diameter is about a hundred microns.In this paper,a new method for generation of HG beams based on a slab resonator that has a large mode volume is proposed and experimentally demonstrated.According to the optical resonator theory,the intra-cavity modes in thickness and width direction of the slab resonator are restricted by inserting two size-adjustable apertures,respectively.The one-dimensional HG beam generation is mainly guaranteed by the size of the aperture along the thickness direction of the slab,which matches the diameter of the fundamental mode.The different order one-dimensional HG beams are obtained by refined intra-cavity mode modulation.Since the higher-order modes are less sensitive to the misalignment of the cavity mirror than the lower-order modes,the manipulation of the modes-loss at different orders is achieved by combining the tilt control of the coupled output mirror and the size control of intra-cavity apertures.Through the adjustment of the optical gain and loss in the resonator,the single mode wins out in the laser modes competition.Consequently,high-purity one-dimensional HG beams with orders 0 to 9(HG<sub>00</sub> to HG<sub>09</sub>) are generated.The pump module is comprised of a two-dimensional laser diode array which offers face-pumping to the large surface of the slab,therefore the width of the mode volume is extended to several millimeters.By further incorporating the 100mm-level length slab,the total gain volume is much larger than the off-axis pumping scheme.In this paper,the output power of the highest order HG<sub>09</sub> mode is up to 244 mW.Due to the large gain volume and uniform gain distribution brought by the face-pumped slab,the purity of high order HG modes is quite good.The correlation coefficient ρ between the measured intensity distribution and the theoretical value is larger than 0.95.The beam quality factor ρ is also in good agreement with the theory.Finally,a conversion from Hermite-Gaussian beams to the donut-shaped Laguerre-Gaussian beams is realized by using an astigmatic mode converter.Hopefully,power scaling of the HG beam output is also expected by employing cascaded slab amplifiers,and the approach in this paper provides a novel solution for generation of high power HG beams.

High efficiency, 41.6 W, 10 kHz picosecond output based on a Nd:YAG double-pass multi-folded Innoslab amplifier

We designed a novel structure of double-pass multi-folded partially-end-pumped slab (Innoslab) amplifier, which could effectively improve the extraction efficiency. High efficiency and high power picosecond (ps) radiation was obtained by the Nd:YAG Innoslab amplifier. A 4.5 W seed at a repetition rate of 10 kHz was amplified to 41.6 W under an absorbed pump power of 124.7 W, corresponding to extraction efficiency of 29.8%. The pulse duration was approximately 86.5 ps, and the corresponding peak power was up to 48.1 MW. The beam quality factor M2 at the maximum output power was measured to be 2.28 and 1.52 in the horizontal and vertical directions, respectively. To the best of our knowledge, this study was the first to report high efficiency double-pass multi-folded Innoslab amplifier.

Ti:Sa Crystals in Ultra-High Peak and Average Power Laser Systems

In this paper, Ti:Sa amplifiers with crystals of the different geometries are discussed. Benefits of using this active medium for a thin disk (TD) and slab amplifiers are evaluated numerically and tested experimentally. Thermal management for amplifiers with multi-kW average power and multi-J pulse energy has been demonstrated. The presented numerical simulations revealed the existing limitations for heat extraction in TD geometry in the sub-joule energy regime for higher repetition rate operation. Geometry conversion from TD to thin-slab (TS) and cross-thin-slab (XTS) configurations significantly increases the cooling efficiency with an acceptable crystal temperature for pump average power values up to few kW with room temperature cooling, and up to tens of kW with cryogenic cooling. The abilities to attain 0.3 J output energy and a greater than 50% extraction efficiency were demonstrated with a repetition rate exceeding 10 kHz with room temperature cooling and one order more of a repetition rate with cryogenic conditions with pulsed pumping. Direct diode pumping simulated for CW regimes demonstrated 1.4 kW output power with 34% extraction efficiency using room temperature cooling and more than 10 kW and ~40% efficiency with cryogenic cooling.

Study on the 400 mm 4 × 2 combined slab amplifier system

This paper provides the experiment results of a 400 mm 4 × 2 combined slab amplifier system for high-power laser devices based on a new pumping configuration, which involves 37 nm-diameter pulse xenon lamps, a multilamp arrangement, an operating voltage of 31 kV and a uniform pumping arrangement comprising 12 and 14 xenon lamps in the middle and side flashlamp cassettes, respectively. The experimental results show that the small signal gain coefficient was 5.60% cm−1. The pump-induced wavefront distortion accumulated by six slabs of Nd:glasses is 1.37λ peak-valley (PV) and the pointing offset value of pump beam is about 0.32 μrad/slab/pass. After discharging, the system was purged with clean gas at 0.4 m s−1. The cleanliness in the cavity returned to level 100 within 20 s, and the heat recovery time of the system was about 2 h.

148-W single-frequency Nd:YAG Innoslab μs-amplifier at 1064 nm with high efficiency.

In this paper, a single-frequency quasi-continuous-wave partially pumped slab (Innoslab) amplifier at 1064 nm is reported. The 4.4-W single-frequency seed laser was amplified to 148.1 W with optical-optical efficiency of 30.4%. The output pulse duration was 141.4 μs at the repetition of 500 Hz. The beam quality factors of M2 were 1.41 and 1.37 in the horizontal and vertical direction respectively. The experimental results match well with the numerical simulation. To the best of our knowledge, this is the first report on single-frequency Nd:YAG Innoslab amplifier with such a high output power and efficiency.

7 kHz sub-nanosecond microchip laser amplified by a grazing incidence double pass slab amplifier

To obtain short pulse width and high peak power laser, a 7 kHz sub-nanosecond microchip laser amplified by a grazing incidence double pass slab amplifier is experimentally demonstrated in this Letter. We use a compact side-pumped Nd:YVO4 bounce amplifier with grazing incidence beam for achieving high gains and power extraction. Laser output power of 7.37 W at 7 kHz, 1.2 MW pulse peak power with 877 ps duration and 1.05 mJ energy, 25 pm spectral width, and near diffraction limited mode beam quality are achieved, and the optical-to-optical efficiency is 18%. The laser is packaged in a volume of 356 mm × 226 mm × 84 mm and may be used for applications such as laser altimeters and ladar systems.

Gain and laser output performance of JG2 Nd: glass in 400 mm aperture slab amplifier

Gain and laser output performance of JG2 Nd: glass in 400 mm aperture slab amplifier

High-energy diode-pumped alexandrite amplifier development with applications in satellite-based lidar

Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped master oscillator power amplifier (MOPA) system design. A novel multipass “diamond” slab amplifier geometry is introduced alongside the experimental results of the world’s first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumped Q -switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimization of a two-stage amplifier design is studied numerically and maximized with temperature, wavelength, and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimized alexandrite MOPA design capable of high pulse energy, showing the future potential of diode-pumped alexandrite for satellite-based atmospheric lidar.

Study of long-pulse quasicontinuous wave INNOSLAB amplifier at 1319 nm

We report on a long-pulse, quasicontinuous wave partially end-pumped slab (INNOSLAB) amplifier at 1319 nm. The low-pulse-energy seed laser was amplified to 8.24 mJ at repetition of 500 Hz by five-pass amplification. The beam quality factors are 1.70 and 1.28 in the horizontal and vertical directions, respectively. The optical–optical efficiency was 1.16% under the pump power of 187.5 W. The experimental results match well with the numerical simulation. The optical–optical efficiency can be improved to about 10% with higher absorption efficiency of the pump source and higher overlapping efficiency between the pump light and 1319-nm seed laser. And further improvements can be realized by optimizing the input pulse energy density and the pass of amplification.

An especial configuration for an Nd:YAG end-pumped zigzag slab gain module based on crystalline polytetrafluoroethylene and a specific optical system for pump-beam delivery.

This work experimentally introduces a new single-crystal Nd:YAG end-pumped zigzag slab (EPZS) gain module based on a thin polytetrafluoroethylene (PTFE) sheet as a total internal reflection (TIR) protection layer. In this gain module, a specific optical pump-beam delivery (OPBD) system is used to improve the output beam quality (BQ) of the slab amplifier from 9.4 in a typical OPBD system to 4.7 with the total pump power of 2400 W. The average logarithmic small-signal gain (g0l) in the 0.06% Nd:YAG EPZS gain module at the laser beam incident angle of 7.1° was obtained around 0.64 for the two OPBD systems mentioned above.