High-power Solid-state Laser Systems Research Articles

Analysis and optimization of repetitive positioning precision for kinematic couplings of opto-mechanical components considering uncertainty

Kinematic coupling, as an efficient form of connection, is frequently employed for the repeated assembly and accurate positioning of replaceable opto-mechanical assemblies within high-power solid-state laser systems. During the kinematic coupling process, uncertainties in the mechanical behavior within the contact region often hinder the attainment of consistent positioning precision, potentially leading to an inability to meet operational requirements. This study aims to enhance the repetitive positioning precision of kinematic couplings. A predictive model for repetitive positioning precision is established, accounting for uncertainties in contact region forces. Based on this model, an optimization design of kinematic couplings is conducted to mitigate these challenges. Initially, accounting for uncertainties in mechanical parameters within the contact region, we formulate a static analysis computational model to elucidate the probabilistic distribution of these parameters. Subsequently, employing Hertz contact theory and Holm-Archard wear theory, we quantify the elastic deformation and equivalent wear for each contact region through the calculation of normal pressures. Building upon this foundation, we establish a predictive model for repetitive positioning precision. Finally, optimization design is carried out on the friction coefficient of contact surfaces and the structural dimensions of positioning elements. The proposed optimization design is validated through experimental verification. The findings demonstrate that optimization of structural dimensions and contact surface friction coefficients resulted in enhanced repetitive positioning precision of 35.9 %, effectively ameliorating the assembly quality. This study contributes a quantifiable analytical approach to the prediction and optimization design of repetitive positioning precision in kinematic couplings.

Femtosecond laser direct writing of Nd:YAG waveguide with Type I modification: Positive refractive index change in track

Abstract Nd:YAG crystal is one of the major gain media used in high-power solid-state laser systems. In this work, the single-line waveguides with Type Ⅰ modification have been fabricated in Nd:YAG crystal by femtosecond laser writing. The waveguides show good guiding properties in both TE and TM polarizations, which is different from the well-developed Type II structures. The high-resolution confocal micro-photoluminescence and micro-Raman spectra images obtained by scanning the cross-section of the track region certify a positive refractive-index change induced in femtosecond laser irradiated region. The fluorescence properties remain 82% in the waveguide region, which shows the potential for active photonic devices.

High-Power Ultrashort Pulse Lasers to Pump Plasma-Based Soft X-Ray Lasers

High-energy ultrashort pulse optical lasers operating at high repetition rate are required to drive intense compact coherent soft X-ray sources, including soft X-ray lasers, for applications in nanoscience and nanotechnology, material studies, and high field science. This paper reviews two types of high-power solid-state laser systems developed at Colorado State University to pump compact, high repetition rate, and plasma-based soft X-ray lasers. One is a flashlamp-pumped, petawatt-class Ti:sapphire chirped-pulse amplification laser that generates 0.85 PW pulses of 30 fs duration at 3.3 Hz repetition rate. Using a fraction of the output energy from this laser, we have demonstrated gain-saturated, compact, repetitive lasers down to 6.85 nm in Ni-like Gd and have observed gain in shorter wavelength transitions, down to 5.85 nm in Ni-like Dy. The second type of pump laser is an all diode-pumped chirped-pulse amplification system based on cryogenically cooled Yb:YAG active mirror amplifiers that produces 1 J pulses of picosecond duration at 500 Hz repetition rate. These compact diode-pumped laser systems have enabled new advances in high-average-power tabletop soft X-ray lasers that include 100 Hz demonstrations at wavelengths ranging from 10.9 to 18.9 nm, as well long duration operation at these high repetition rates for periods up to one hour. These and other recent results that include the operation of an 18.9 nm laser Ni-like Mo laser at 400 Hz repetition rate open a path to compact kilohertz repetition rate soft X-ray lasers.

An intelligent computation system for precise assembly of large laser optics

PurposeIt is a huge technical and engineering challenge to realize the precise assembly of thousands of large optics in high power solid-state laser system. Using the 400-mm aperture-sized transport mirror as a case, this paper aims to present an intelligent numerical computation methodology for mounting performance analysis and modeling of large optics in a high-power laser system for inertial confinement fusion (ICF).Design/methodology/approachFundamental principles of modeling and analysis of the transport mirror surface distortion are proposed, and a genetic algorithm-based computation framework is proposed to evaluate and optimize the assembly and mounting performance of large laser optics.FindingsThe stringent specifications of large ICF optics place very tight constraints upon the transport mirror’s assembly and mounts. The operational requirements on surface distortion [peak-to-valley and root mean square (RMS)] can be met as it is appropriately assembled by the close loop of assembly-inspection-optimization-fastening. In the end, the experimental study validates the reliability and effectiveness of the transport mirror mounting method.Originality/valueIn the assembly design and mounting performance evaluation of large laser optics, the whole study has the advantages of accurate evaluation and intelligent optimization on nano-level optical surface distortion, which provides a fundamental methodology for precise assembly and mounting of large ICF optics.

Active frequency matching in stimulated Brillouin amplification for production of a 2.4 J, 200 ps laser pulse.

A frequency matching Brillouin amplification in high-power solid-state laser systems is proposed. The energy extraction efficiency could be maintained at a high level in a non-collinear Brillouin amplification structure using an exact Stokes frequency shift. Laser pulses having a width of 200 ps and energy of 2.4 J were produced. This method can be used to transfer energy from a long pulse to a short pulse through a high-power solid-state laser system.

Wavefront Shaping by a Small-Aperture Deformable Mirror in the Front Stage for High-Power Laser Systems

We demonstrate a method for wavefront distribution compensation with a low-cost small-aperture deformable mirror in the front stage of a complex high-power solid-state laser system. Meanwhile, an iterative algorithm for improving wavefront quality is indicated. Using this method, the wavefront compensation was studied in our single-shot high-power laser system that operated with and without the main amplifiers, respectively. The wavefront was compensated effectively, showing the near-flopped-shape output with the peak-to-valley value of 0.29 λ and root meam square (RMS) of 0.06 λ at 1053 nm.

Robust modeling and performance analysis of high-power diode side-pumped solid-state laser systems.

In this paper, we present an enhanced high-power extrinsic diode side-pumped solid-state laser (DPSSL) model to accurately predict the dynamic operations and pump distribution under different practical conditions. We introduce a new implementation technique for the proposed model that provides a compelling incentive for the performance assessment and enhancement of high-power diode side-pumped Nd:YAG lasers using cooperative agents and by relying on the MATLAB, GLAD, and Zemax ray tracing software packages. A large-signal laser model that includes thermal effects and a modified laser gain formulation and incorporates the geometrical pump distribution for three radially arranged arrays of laser diodes is presented. The design of a customized prototype diode side-pumped high-power laser head fabricated for the purpose of testing is discussed. A detailed comparative experimental and simulation study of the dynamic operation and the beam characteristics that are used to verify the accuracy of the proposed model for analyzing the performance of high-power DPSSLs under different conditions are discussed. The simulated and measured results of power, pump distribution, beam shape, and slope efficiency are shown under different conditions and for a specific case, where the targeted output power is 140W, while the input pumping power is 400W. The 95% output coupler reflectivity showed good agreement with the slope efficiency, which is approximately 35%; this assures the robustness of the proposed model to accurately predict the design parameters of practical, high-power DPSSLs.

Optimizing average power in low quantum defect lasers.

Waste heat generation is a generic problem in high-power solid-state laser systems. One way to reduce heat loading while improving efficiency is to reduce the laser's quantum defect. This paper presents a simple analysis of low quantum defect laser materials. In these laser materials, the effects of fluorescent cooling and weak loss processes should not be ignored. Simple expressions are developed for efficiency and heating in a steady-state purely radiative material. These expressions are then extended to include weak losses and fluorescence reabsorption. Evaluation of these relations using ytterbium-doped YAG is used to illustrate several optimization schemes and the impact of realistic losses.

高功率固体激光器的大口径反射镜装配误差分析

高功率固体激光器的大口径反射镜装配误差分析

Propagation characteristics of small-bandwidth pulsed beams with smoothing by spectral dispersion in high power laser system

In this paper, we numerically study the propagation characteristics through spatial filter and free space of small-bandwidth pulsed beams with smoothing by spectral dispersion (SSD) in high power solid-state laser system. The numerical simulation with time-, space-and spectrum-resolution is achieved by using laser propagation and amplification software developed by Research Center of the Laser Fusion. The graphs of corresponding time-, space-and spectrum-distribution are presented, and the propagation characteristics between the SSD and non-SSD beam are compared. Besides, the effects of some SSD parameters on the diffraction propagation are further discussed. The results can help to choose the proper beam divergence of SSD which matches with the size of the spatial filter hole, to design the appropriate modulation frequency and the color circle number and so on. Moreover, it could guide the design of the light path, especially the design of free space propagation of small-diameter laser.

Trace Gas Remote Sensing by Lasers

AbstractActive remote sensing represents a promising technology to accurately measure the atmospheric concentration of the climate‐relevant trace gases carbon dioxide and methane. For this application, frequency stabilized laser sources with high pulse energy emitting at specific absorption lines around 1.6 μm wavelength are required. While Raman frequency conversion of high power solid‐state laser systems provides sources suitable for CO2 detection, compact resonantly pumped Er:YAG lasers are demonstrated to be feasible for CH4 absorption measurements.

Quantitative relation between "defects" distribution on optics and near-field quality in high power solid-state laser system

Based on beam propagation theory, the quantitative relation between PSD (power spectral density) of "defects" distribution on optics and that of near field intensity was studied. Its validity was discussed on linear medium, nonlinear medium and spatial filter. The results show that PSD of "defects" distribution on optics and PSD of near field intensity are connected by a system propagation factor when the modulation is weak, which is determined by system architecture and operation state. These results provide a theoretical basis for specifications of "defects" distribution on optics, and also a guidance to enhancing the power of high power solid-state laser system.

Diffractive Optical Elements for Laser Materials Processing

Recent developments of high-power and high-quality solid-state laser systems, in particular diode-pumped Nd: YAG lasers and fiber lasers, allow the development of various kinds of laser materials processing applicationsin production industries. Diffractive optical elements are employed as a key technology to achieve such applications. In this paper, the author describes the practical examples of a diffractive beam splitter, a diffractive beam homogenizer, a hybrid lens, and a long-focal-depth diffractive lens for a femtosecond laser.

Pulsed solid-state laser system with fiber phase conjugation and 315 W average output power

Solid-state laser sources with high average output power and high beam quality are required for numerous applications in industry and science. To improve the beam quality, stimulated Brillouin scattering (SBS) mirrors based on optical phase conjugation are used to compensate for phase distortions in master oscillator power amplifier (MOPA) systems. SBS phase conjugation in commercially available silica optical fibers facilitates the construction of high-power solid-state laser systems with high beam quality. Here we present a flash lamp-pumped, passively Q-switched Nd:YAP system which delivers an average output power of 315 W with M2=2.6 at a wavelength of 1.08 μm.

Progress in the YAG Crystal Growth Techniqe for Solid State Lasers.

Nd: YAG is the most popular crystal for solid-state lasers because it has some good properties. Recent high power solid-state laser systems demand high quality and large scale YAG crystals. A new style automatic diameter control system is effective in crystal growth technique to produce YAG laser device for high power systems. YAG crystals that have some doping elements are applicable to measurement instruments, optical communication and the others. We are making efforts to improve the crystal growth technique for new applications.

Future development of high-power solid-state laser systems

The future trends in the development and design of high-power pulsed solid-state laser systems are considered in relation to the laser fusion problem. Attention is concentrated on neodymium-doped glass lasers, but the possibility of using other media, particularly ion-doped crystals, is also discussed. New methods for pumping such systems (both existing and future) are reviewed. Ways and means of tuning the emission wavelengths, methods for increasing the average power, and characteristic features of the design of systems as a whole are also discussed.

Use of circularly polarized optical beams to suppress self-focusing instability in a nonlinear cubic medium with repeaters

A theoretical and experimental investigation is made of the suppression of small-scale self-focusing in high-power solid-state laser systems with repeaters by using circular polarization. The improvement in the output focused energy obtained experimentally for circular polarization as compared to that for linear polarization (~ 1.5 times higher) shows good agreement with the calculated value.

Ultrashort pulse generation in lasers with active mode locking (review)

A review is given of the recent progress in the application of active mode-locking techniques in transient highpower pulsed solid-state laser systems. A theoretical description of the mode-locking method is presented and a comparison is made of active and active-passive mode locking. The experimental performance of these systems is described with special regard to the reliability, pulse duration, and synchronization with external events.