High-energy short-pulse laser systems demonstrated to date have been limited to low repetition rates due to significant thermal management challenges associated with scaling these systems to high average power, including the need to understand the thermal fracture limits of laser gain media. In this paper, we demonstrate the thermal fracture limits of two high-average-power gain media in a realistic diode-pumped amplifier geometry: a 5 mm thick Nd:APG-1 slab and a 2 mm thick Tm:YLF slab, both cooled by room-temperature helium gas. Finite element analysis revealed maximum tensile stress at fracture of 25 ± 3 MPa for Nd:APG-1 and 30 ± 3 MPa for Tm:YLF. These stress levels correspond to average volumetric heat loads of 13 ± 1 W/cm3 in Nd:APG-1 and 247 ± 12 W/cm3 in Tm:YLF. Additional simulations show geometric scaling: thinner slabs tolerate higher heat loads before fracture, while larger pump spots reach the fracture stress at lower heat loads.

We report on a laser amplifier architecture designed as a modular element for scaling to multi-megajoule laser facilities intended for inertial fusion energy (IFE) power plants. This kilojoule-class module features a stacked mosaic of gain media integrated with a diode delivery system for efficient optical pumping of the mosaic-structured gain medium, enabling high-repetition-rate operation at high wall plug efficiencies, necessary for an IFE driver. Details of a diode delivery system capable of pumping the mosaic architecture are presented. Comprehensive numerical modeling demonstrates that the stacked-mosaic approach reduces transverse gain by five orders of magnitude compared to a conventional full-aperture Yb:YAG based amplifier, substantially suppressing transverse amplified spontaneous emission (TASE) and enabling enhanced longitudinal energy extraction. Detailed analysis of thermal management and wavefront distortion in a 4 × 4 mosaic array indicates that temperature gradients and thermally induced aberrations are effectively controlled using gas cooling and commercially available phase-plate and deformable mirror technologies. We further discuss the applicability of a stacked-mosaic architecture to direct-drive IFE schemes, where broad spectral bandwidth is critical, and its compatibility with frequency conversion modules for up-conversion to blue wavelengths. Finally, an example point design for a 10 kJ, 10 Hz Yb:YAG module operating at 175 K with wall-plug efficiency exceeding 10 % is presented, underscoring the feasibility of this approach for next-generation high-energy lasers for IFE drivers. The results establish the stacked-mosaic amplifier as a scalable, robust platform not only for IFE but also for a broad range of advanced scientific and industrial laser applications.

We characterize a large-aperture gas-cooled Faraday rotator (FR) designed to mitigate stress-induced depolarization in high-energy, high-power laser systems. The rotator, based on ceramic TGG, was tested using a 150 mW probe beam at 1047 nm and a pump beam at 1070 nm. Compensating for the birefringence induced by the surrogate depolarization plate at 3.3 kW of effective pump power, the rotator reduces the spatially in-homogeneous depolarized light containing linear, circular, and elliptical polarization states to nearly linear with approximately 0.8% (or −21 dB) of residual depolarized energy. The FR demonstrated effective depolarization compensation across its 58×58 mm 2 aperture.

We present an innovative design for a two-head, gas-cooled multi-slab high-energy, high-repetition-rate amplifier aimed at mitigating thermally induced depolarization in a wide-bandwidth neodymium-doped glass gain medium.This architecture employs two quartz rotators(QRs) with opposite-handedness, strategically positioned within each multi-slab amplifier head, to enhance depolarization compensation. Theoretical modeling of this amplifier configuration demonstrates a 20× reduction in depolarization losses for a 70 mm beam operating at the central wavelength, compared to conventional approaches that utilize a single QR positioned between the amplifier heads. In addition, for a wide bandwidth source, the integration of QRs with opposite-handedness yields a 9× improvement in depolarization losses at the spectral extremes compared to the use of two QRs exhibiting the same optical handedness in both amplifier heads.

Depolarization from thermal stress remains a major limitation in high-average-power laser amplifiers, often addressed by complex, costly active methods or by using magneto-optical effects to restore the polarization. We demonstrate a novel, passive polarization self-compensation technique using a quartz rotator in a relay-imaged, multi-pass amplifier geometry. A detailed theoretical framework is presented and validated experimentally, showing a 40× reduction in depolarized light in a relay-imaged 4-pass cavity. This approach employs a high-damage-threshold, reciprocal material and avoids the use of polarizers or active controls, thereby simplifying system design and reducing costs. Scalability is discussed for realistic inertial fusion energy driver designs, including effectiveness for broadband lasers and thick gain media.

We present experimental results that showhow diode-pumped Tm:YLF can be used to develop the next generation of laserswith high peak andhigh average power. Wedemonstrate the production of broad bandwidth, lambda approximate to 1.9 mu mwavelength, high energy pulses with up to 1.6 J output energy and subsequent compression to sub-300 fs duration. This was achieved using a single 8-pass amplifier to boost stretched similar to 50 mu J pulses to the Joule-level. Furthermore, we show the average power capability of this material in a heliumgas-cooled amplifier head, achieving a heat removal rate almost 10 times higher than the state-of-the-art, surpassing 20 W/cm(2). These demonstrations illustrate the capabilities of directly diode-pumped Tm:YLF to support TW to PW-class lasers at kW average power.

We report on the demonstration of a diode-pumped, Tm:YLF-based, chirped pulse amplification laser system operating at λ ≈ 1.9 µm that produces amplified pulse energies exceeding 1.5 J using a single 8-pass power amplifier. The amplified pulses are subsequently compressed to sub-300 fs durations by a diffraction grating pair, producing record >1 TW peak power pulses. To the best of our knowledge, this is the highest peak power demonstrated for any solid-state, near-2 µm laser architecture and illustrates the potential of Tm:YLF for the next generation of high-power, diode-pumped ultrashort lasers.

We report high energy pulses from compact, diode-pumped Tm:YLF amplifiers. We demonstrated pulse energies of 21.7J for 20ns pulses and 108J for long pulses. CPA produced broadband 1.6J pulses that were subsequently compressed to 270fs.

We present Tm:YLF laser technology development including joule-level short pulse amplification and gas-cooling at high heat loads in two separate experiments, which shows the potential suitability of Tm:YLF based lasers for drivers of emerging applications.

Thermal management of the laser gain medium poses a challenge for the next generation of high-average power, petawatt laser systems. Current systems employ gas-cooled multi-slab amplifiers to achieve necessary heat extraction for operation at high repetition rates. The purpose of this work is to examine the flow within a representative gas-cooled laser amplifier, and to identify key areas where the amplifier design may be improved so that optimal cooling of the gain medium may be achieved. Flow solutions are obtained numerically from unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations with conjugate heat transfer. A fully turbulent URANS simulation is used as a reference for a URANS simulation with the gamma-Re-theta transition model enabled for transition prediction. The transition model predicts laminar flow beyond typical transition Reynolds numbers in the vicinity of the gain medium. The conjugate heat transfer results further show that the presence of relaminarization leads to increased slab temperatures and irregular optical path length distributions. Careful consideration must be taken of the entrance and vane geometries in future amplifier designs so that separation and relaminarization are minimized.

We report the demonstration of a diode-pumped, chirped pulse amplification Tm:YLF laser that produces broadband pulses up to 1.3 J pulse energy. Amplified pulses at the 100 mJ-level were compressed using gratings to sub-400 fs duration.

We demonstrate a large-aperture gas-cooled Faraday rotator designed to mitigate stress-induced depolarization in high-energy, high-power laser systems. Compensating for a surrogate depolarization plate at 3.3 kW, the rotator reduces the relative depolarized energy from 36% to 1%.

In an effort to improve thermal management of the gain medium in high-average power, high-intensity lasers, this study focuses on simulating the gas flow through multiple narrow channels. Actively cooling lasers of this class involves flowing helium gas through an array of closely-spaced vanes, where each vane contains a thin slab of gain medium. Since the role of turbulence is crucial to both the thermal management of the gain material and to the optical quality of the laser, it is imperative that the state of the flow within these channels and over the gain medium is properly understood. In the absence of experimental data, the current work utilizes RANS turbulence models and the Langtry-Menter transition prediction model to obtain flow solutions within a representative helium gas-cooled laser amplifier design. The RANS results reveal three flow features within the amplifier head: separation at the inlet diffuser, potential relaminarization within the channels, and a separation region downstream due to the diverging sections of the channels. While computationally inexpensive and suited for exploring optimal aerodynamic design configurations of the amplifier head, the RANS solutions only provide averaged flow quantities. Since the fluctuating density field is necessary for future aero-optical analyses of the laser propagating through the gas flow, a preliminary LES is also introduced. In addition to aero-optics, it is expected the LES will shed light into the inherent unsteadiness of the aforementioned separation regions, which in turn may highlight any links to structural vibrations of the vanes themselves. A comparison of the mean flows of the RANS and LES solutions indicates good agreement within the channels and near the gain medium, and shows that the LES and RANS capture similar separation and recirculation features.

The Matter in Extreme Conditions Upgrade (MEC-U) project will combine a hard x-ray free electron laser with high-power optical lasers to produce and understand matter found in extreme environments. We are developing a 10 Hz, 150 J, 150 fs, 1PW laser system to be installed in this upgraded facility.

We present experimental demonstrations of the energy density storage and extraction capabilities of Tm:YLF using a table-top diode-pumped system. Here, a Tm:YLF-based oscillator, producing mJ-class pulse energies within both short (nanosecond) and long (millisecond) duration pulses, seeds a single far-field multiplexed power amplifier. The amplifier produced pulse energies up to 21.7 J in 20 ns (>1 GW peak power) using a 4-pass configuration, and 108.3 J in a long duration pulse using a 6-pass configuration. Additionally, the system was reconfigured and operated in a burst mode, amplifying a 6.8 kHz few-ms duration burst of 36 pulses up to 3.6 kW average power. An optical-to-optical efficiency of 19% was achieved during the quasi-steady-state amplification, with an individual pulse fluence over an order of magnitude lower than the saturation fluence.

Laser glass fracture and cooling scalability in high average power gas-cooled laser amplifiers were studied by in-situ optical probing of laser glass during actual fracture events under realistic thermal load conditions.

We report on 100J-level pulsed energy extraction from a diode-pumped Tm:YLF system. The table-top laser comprises a Tm:YLF-based oscillator that seeds a single amplifier to produce >21J in 20ns and 108J in long-pulse operation.

The design and status of the diode-pumped 10 Hz, 150 J, 150 fs, 1 PW laser system under development for the Matter in Extreme Conditions Upgrade (MEC-U) project will be presented.

Next-generation, high-peak-power, ultrashort-pulse lasers have the potential to efficiently deliver the high-average-power outputs required by many emerging technologies and areas of research. The combination of large size and low-repetition rates of previous-generation lasers make their effective and widespread usage impractical. The critical step in an effort to increase the repetition rate is a proper management of the waste heat generated in the laser gain medium. The current paper presents a computational approach with which to improve upon current gas-cooled amplifier designs; the ultimate goal being to optimize the head geometry for efficient cooling while maintaining minimal aero-optical distortion. This approach consists of several components, the focus of which are low-fidelity RANS simulations, and high-fidelity LES and aero-optical simulations. Preliminary results indicate that these components interface properly in handling the prescribed base case, and lay the groundwork for continued progress towards simulating, modeling, and optimizing the amplifier head for efficient cooling.