High-energy Solid-state Lasers Research Articles

Optical properties and concentration optimization of Nd: PbF2 crystal for high-energy pulsed laser

Appropriate saturation flux and long fluorescence lifetime are essential requirements for the gain medium in high-energy solid-state laser systems. A novel laser crystal Nd:PbF2 was grown successfully, and the optical performances were evaluated in detail. A theoretically relatively practical method revealing the relationship between the excited state population and doping concentration was developed to guide the optimization of Nd3+ doping concentration. The optical properties of different doping concentrations of Nd:PbF2 single crystals were studied in detail and compared with our theory to demonstrate the accuracy and feasibility of the proposed method. Furthermore, we found that the optimal doping concentration of Nd3+ in the PbF2 crystal was 1 %, with a fluorescence lifetime of 395.3 μs at ∼ 1.06 μm and a saturation flux of 5.8 J/cm2, which is close to the current one is comparable to phosphate glass widely used in nuclear fusion systems, indicating that the 1 % Nd: PbF2 crystal can be used as an excellent gain medium for high-energy lasers.

Optical and Spectroscopic Properties of Ho:Lu2O3 Transparent Ceramics Elaborated by Spark Plasma Sintering

In this work, transparent ceramics were manufactured from nanopowders synthesized by aqueous coprecipitation followed by Spark Plasma Sintering (SPS) to ensure rapid and full densification. The photoluminescence of Ho:Lu2O3 transparent ceramics was studied in the Visible and IR domains as a function of Ho3+ dopant level from 0.5 at.% to 10 at.%. A cross-relaxation mechanism was identified and favors the 2 μm emission. All of the obtained results indicate that the optical properties are very similar between Lu2−xHoxO3 transparent ceramics and single crystals. Thus, the SPS technique appears to be a very promising method to manufacture such ceramics, which could be used as amplifier media for high-energy solid-state lasers.

Numerical simulation of thermal effects in laser diode end-pumped solid-state lasers utilizing finite element method

Based on the finite element numerical analysis method, the temperature field distribution in the crystal with time is simulated by using the PDE-tool in MATLAB. The critical factors affecting the crystal transient temperature distribution are simulated and analyzed. According to the simulation parameters and results, a simplified method for solving the transient heat conduction equation is proposed. The transient thermal focal length is solved to obtain its distribution expression and an approximate analytical solution. The results provide a theoretical basis for the thermal analysis process of suppressing or utilizing the transient thermal effect in high-energy solid-state lasers.

Research progress of high-frequency and high-energy solid state lasers at 1.6 µm (invited)

Research progress of high-frequency and high-energy solid state lasers at 1.6 µm (invited)

Laser spears for the Russian army

The paper is devoted to the problem of high-energy solid-state laser arms, demonstrating the highest efficiency in the terms of weight and sizing. We can predict a very bright future for such laser systems as a significant means of defeating the enemy. The problem of scalability for such an approach based on fiber laser technology is the key question of our days for many companies of the world. At the same time, it is clear that a tactical LW based on solid-state technology with a weight factor of 5 kg / kW with the total weight of a laser complex significantly less than a ton can be created. But the level of output power around 500 kW is very close to the limit for the fiber technology...

Analysis of the relationship between variations in detuning angle and the harmonic generation efficiency of a KDP crystal

The harmonic generation efficiency of a large aperture KDP (KH2PO4) crystal that is used in the Final Optics Assembly of high-energy solid-state lasers is one of the key points to achieve inertial confinement fusion. The variations in the detuning angle of a KDP crystal are achieved by interferometer and calculation. The harmonic generation efficiency is calculated using variations in the detuning angle. The theoretical prediction model of harmonic generation efficiency based on small-signal approximation theory was built. In the experiment, Crystal off-line Debugging System was used to measure the actual harmonic generation efficiency of a KDP crystal. The predictive harmonic generation efficiency of a KDP crystal and the actual efficiency was compared, which concluded that the theoretical prediction model of harmonic generation efficiency was correct. A simple method to predict the harmonic generation efficiency of a KDP crystal was provided. The method can also be applied to other harmonic generation crystals.

Multiphysics model of liquid-cooled Nd:phosphate split-slabs in large aperture optical amplifiers.

High repetition rates in high energy solid-state laser systems can yield to a rise of temperature in amplifiers despite the use of cooling systems. This effect can significantly impact the performance of amplifiers by inducing thermal stress, birefringence or thermal lensing. Here, we develop a multiphysics model to support the design, optimization and commissioning of a liquid-cooled large aperture split-slab laser glass amplifier. This multiphysics model includes optical pumping in the amplifying medium, heat loading, hydraulic effects induced by the liquid coolant, mechanical deformation and their potential coupled effects on the optical wavefront. The accuracy of each model is assessed by carrying out specific experimental measurements and characterizations. We show that this set of models allows the prediction of performance of a liquid-cooled amplifier from the flash-lamp emission to the amplified wavefront at a repetition rate of one shot per minute.

Enhancing Depth of Penetration in PLD-Based Photoacoustic Imaging: Preliminary Results.

In most cases, high energy solid state lasers such as Nd:YAG are used as source of illumination for Photoacoustic Tomography (PAT). However the bulkiness, high cost and low pulse repetition frequency (PRF) poses a challenge in translating this technology to an affordable clinical imaging option at bed-side. Pulsed Laser Diodes (PLD) on the other hand is portable, inexpensive and offers high PRF. However, the achievable depth of penetration using PLD is much lower than the solid state lasers. In this work, we demonstrate the feasibility of using sub-pitch translation approach on the receive-side ultrasound transducer to increase the depth sensitivity in PAT imaging system while using PLD as a source of illumination. The preliminary results obtained from experiments suggest that the higher density data obtained by augmenting raw RF lines from λ/2 positions of a linear array transducer provides better signal strength from deeper located targets and thereby increasing the depth of penetration by about 15% that reaches up to a depth of 14.3 mm.

A “Star Wars” sequel? The allure of directed energy for space weapons

ABSTRACTThe high-energy lasers of the 1980s were unwieldy assemblages of tanks, tubes, and plumbing that produced light by burning flowing gases, and the space shuttle was not ready for “space trucking.” In the decades since then, though, laser technology has come a long way, and the giggle factor of these technologies – dubbed “Star Wars” weapons by their detractors – is gone. High-energy solid-state lasers, not available in the Reagan era, are now being tested to shoot down rockets, mortars, and drones at hundreds of meters or more on the battlefield. Their success so far has led the Pentagon to reconsider high-energy lasers and other directed energy weapons for missile defense and perhaps other military applications on the fringes of space and in orbit. But are new actors merely making the same mistakes again, in an updated setting?

Development status of high power fiber lasers and their coherent beam combination

High-power fiber laser has been emerged great potential in a wide range of applications and becomes a robust candidate for high energy solid state laser system. To further increase the output brightness of single-channel fiber laser, high-brightness pump sources and high-power-handling passive components should be fabricated and utilized in the fiber laser systems, in addition to the advanced techniques for multiple nonlinear effects managements. The state-of-the-art high power fiber lasers are reviewed, in terms of narrow-linewidth fiber lasers, broadband fiber lasers and fiber lasers at 2 $\mu$m. Coherent beam combining is a promising technique to obtain higher output power while maintaining excellent beam quality simultaneously, which breaks through the bottlenecks of single-channel fiber laser. Based on a series of key techniques for coherent beam combining, high-power coherent beam combining of fiber lasers could be enabled with high combining efficiency. In this paper, we review the progress of high-power fiber lasers and their coherent beam combining in the recent decade, particularly the relevant work in our group. The future prospects of fiber lasers and coherent beam combining technique are also discussed.

In situ 3-D temperature mapping of high average power cryogenic laser amplifiers.

Heat generation is a key obstacle to scaling high energy solid-state lasers to the multi-kilowatt average powers required for several key applications. We demonstrate an accurate, in situ, noninvasive optical technique to that makes three-dimensional (3-D) temperature maps within cryogenic amplifiers operating at high average power. The temperature is determined by analyzing the fluorescence spectra with a neural network function. The accuracy of the technique relies on a calibration that does not depend on simulations. Results are presented for a cryogenic Yb:YAG active mirror laser amplifier operating at different pump conditions. The technique is applicable to other solid-state lasers materials.

Overview of ytterbium based transparent ceramics for diode pumped high energy solid-state lasers

Development of high energy laser sources with nanosecond pulses at several hertz values for repetition rate has been very attractive in recent years due to their great potential for practical applications. With the recent advancement in fabricating large size laser quality transparent ceramics, diode pumped solid-state laser generating pulse energy of 100 J at 10 Hz has been recently realized at HiLASE center using Yb:YAG ceramic with Cr:YAG cladding. This review discusses Yb based high energy lasers, specific laser geometries for efficient thermal management and the role of transparent ceramics in such diode pumped high-energy-class solid-state lasers around the world.

High duty cycle, highly efficient fiber coupled 940-nm pump module for high-energy solid-state lasers

Tailored diode laser single emitters with long (6 mm) resonators and wide (1.2 mm) emission apertures that operate with 940 nm emission wavelength were assembled in novel edge-cooled vertically stacked arrays, and used to construct a compact and highly efficient fiber coupled pump source for Yb:YAG pulsed high-energy class solid-state lasers. The novel configuration is shown to allow repetition rates of 200 Hz at 1 ms pulse duration, at an output power of 130 W per single emitter. The emission of two stacked arrays was then optically combined to realize pump modules that deliver 6 kW peak power (pulse energy 6 J) from a 1.9 mm core diameter fiber, with wall plug efficiency of 50%. This represents a significant improvement in terms of duty cycle and electro-optical efficiency over conventional sources. The pump module has been successfully tested at the Max Born Institute, Berlin during trials for pumping of disk lasers.

Large-energy, narrow-bandwidth laser pulse at 1645 nm in a diode-pumped Er:YAG solid-state laser passively Q-switched by a monolayer graphene saturable absorber

Nonlinear transmission parameters of monolayer graphene at 1645 nm were obtained. Based on the monolayer graphene saturable absorber, a 1532 nm LD pumped 1645 nm passively Q-switched Er:YAG laser was demonstrated. Under the pump power of 20.8 W, a 1645 nm Q-switched pulse with FWHM of 0.13 nm (without the use of etalon) and energy of 13.5 μJ per pulse can be obtained. To the best of our knowledge, this is the highest pulse energy for graphene-based passively Q-switched Er:YAG laseroperating at 1645 nm, suggesting the potentials of graphene materials for high-energy solid-state laser applications.

高能固态激光器技术路线分析

高能固态激光器技术路线分析

高功率固体激光器锥形空间滤波孔应用

高功率固体激光器锥形空间滤波孔应用

高功率固体激光系统空间滤波小孔尺寸设计

高功率固体激光系统空间滤波小孔尺寸设计

Laser system generating 250-mJ bunches of 5-GHz repetition rate, 12-ps pulses

We report on a high-energy solid-state laser based on a master-oscillator power-amplifier system seeded by a 5-GHz repetition-rate mode-locked oscillator, aimed at the excitation of the dynamic Casimir effect by optically modulating a microwave resonator. Solid-state amplifiers provide up to 250 mJ at 1064 nm in a 500-ns (macro-)pulse envelope containing 12-ps (micro-)pulses, with a macro/micropulse format and energy resembling that of near-infrared free-electron lasers. Efficient second-harmonic conversion allowed synchronous pumping of an optical parametric oscillator, obtaining up to 40 mJ in the range 750-850 nm.

Free-electron lasers as pumps for high-energy solid-state lasers

High average-power free-electron lasers may be useful for pumping high peak-power solid-state laser-amplifiers. At very high peak-powers, the pump source for solid-state lasers is non-trivial: flash lamps produce thermal problems and are unsuitable for materials with short florescence-times, while diodes can be expensive and are only available at select wavelengths. FELs can provide pulse trains of light tuned to a laser material's absorption peak, and florescence lifetime. An FEL pump can thus minimize thermal effects and potentially allow for new laser materials to be used. This paper examines the design of a high average-power, efficient high-gain FEL for use as pump source. Specifically, the cases of a 100 J class pump, and a 100 TW-class laser at a planned fourth-generation light-source are considered.

Free-electron lasers as pumps for high-energy solid-state lasers

High average-power free-electron lasers may be useful for pumping high peak-power solid-state laser-amplifiers. At very high peak-powers, the pump source for solid-state lasers is non-trivial: flash lamps produce thermal problems and are unsuitable for materials with short florescence-times, while diodes can be expensive and are only available at select wavelengths. FELs can provide pulse trains of light tuned to a laser material's absorption peak, and florescence lifetime. An FEL pump can thus minimize thermal effects and potentially allow for new laser materials to be used. This paper examines the design of a high average-power, efficient high-gain FEL for use as pump source. Specifically, the cases of a 100 J class pump, and a 100 TW-class laser at a planned fourth-generation light-source are considered.