The Advanced Research Project Agency-Energy (ARPA-E) has the mission to advance high-impact technologies that have the potential to transform the energy industry. Fusion energy sits in the highest risk part of the ARPA-E portfolio. Accelerating the development of enabling technologies for Inertial fusion energy (IFE) is a key focus of ARPA-E. ARPA-E intends to surgically target technologies, which will significantly reduce the time to market and engineering risk of any first of a kind commercial fusion power plant. I will provide a summary of existing ARPA-E IFE related programs and the vision for future programs.

In this paper, we demonstrate a single-pass Cr²⁺:ZnSe amplifier system with nearly 20 dB of net gain and 38 dB of on-off gain at 2304 nm under single-mode QCW pumping condition. In the experiment, the achromatic focusing technique and increased pump power allow for a gain enhancement over what we were able to obtain using an aspheric lens. Moreover, we will present the simulation results of this system.

We report 3.8-5.0 μm tunable three-stage double-pass Fe:ZnSe solid-state MOPA with approximately 30-fold overall amplification coefficient operating at RT and pumped by EO Q-switched Cr:Er:YSGG laser system radiation. EO Q-switched Cr:Er:YSGG MOPA with the Q-switch based on a La3Ga5SiO14 crystal providing 90 ns pulses with energy up to 350 mJ at a 3 Hz repetition rate was used as a pump source. The maximum output energies of Fe:ZnSe system in 90 ns pulses exceeded 55 mJ at 4.4 μm under 220 mJ of pumping. The pulse jitter was measured to be ⪅8 ns and was limited by the Er:Cr:YSGG laser jitter.

The achievement of coherent beam combination is of paramount importance in the advancement of high-power laser systems across various fields, such as defense and communication. In this context, we present a novel filled-aperture coherent beam combiner that integrates essential components including polarization-maintaining fiber elements, Electro-Optic Modulators (EOMs), Erbium-Doped Fiber Amplifiers (EDFA), a Multi-Plane Light Converter, and a feedback loop employing the Stochastic Parallel Gradient Descent (SPGD) algorithm. By leveraging the SPGD algorithm, we attain precise control over the EOMs, enabling stable optical output power. Our experimental results demonstrate the effectiveness of this approach, as it achieves coherent combination of up to six input channels with high efficiency. Additionally, we observe negligible power loss throughout the duration of the process, while maintaining precise control over thermal and mechanical perturbations. One advantage of this MPLC technology is its direct scalability across different wavelengths. This feature enhances its applicability in a wide range of laser systems.

Diamond Raman lasers (DRLs) are novel high power, narrow linewidth sources with output wavelengths challenging to generate by other means, such as the 589 nm guide star line. While DRLs have been demonstrated to operate single-frequency at high powers for short durations, locking to a frequency reference has not yet been achieved. Here, we report an intracavity frequency doubled, 589 nm DRL stabilised to a wavemeter. Frequency fluctuations of +/- 75 MHz of the frequency setpoint were obtain over a 15 minute period. The effective and intrinsic linewidths were also measured, yielding 8 MHz and <900 Hz (resolution limited) respectively.

We develop the concept of degenerate distributed feedback (DDFB) laser operating close to Exceptional Points of Degeneracy (EPDs) of fourth-order, known as a Degenerate Band Edge (DBE), where four different Bloch eigenmodes coalesce. A waveguide operating near a DBE displays a large group delay that leads to a strong light-matter interaction enhancement upon the inclusion of a gain medium. This enhancement results in an ultralow lasing threshold that scales anomalously with cavity length. The resulting DDFB laser is expected to enforce mode selectivity and a coherent single-frequency operation that is resistant to small perturbations, load variations and distributed losses.

A thin-disk multipass amplifier in an industrial package provides pulse energy and power scaling up to an average power in the kW regime with 10 mJ compressed pulses or 40 mJ CPA free pulses. The flexibility of the slab (TRUMPF TruMicro 6000 based) seed laser, such as choice of repetition rate, pulse duration, bursts or pulse on demand is maintained. Due to its mechanical and thermal stability, different applications like surface structuring or generation of EUV or X-ray radiation can be addressed.

Ytterbium (Yb)-based femtosecond lasers have gained significant attention in recent years due to their unique combination of high average power, high pulse energy, and pulse control capabilities for both industrial and scientific applications. In this talk we will review the most recent advancements in obtaining high power infrared (IR) and ultraviolet (UV), while maintaining the stability, as well repetition rate options and wavelength extensions.

We investigated in-band pumping of Tm,Ho,Lu:CaGdAlO4 (CALGO) using a Raman shifted Er-fiber laser (1678 nm) in the continuous-wave (CW) and mode-locked (ML) regimes. The 6-mm long, antireflection-coated, a-cut CALGO was doped with 4.48at.% Tm (sensitizer), 0.54at.% Ho (emission) and 5.51at.% Lu (compositional disorder). For mode-locking we employed a GaSb SESAM and chirped mirrors (round-trip group-delay dispersion: -1250 fs2). Pumping with 5.5 W (unpolarized), the average output power (0.2% output coupler) was 148 mW at ⁓96 MHz. The spectrum was centered at 2071.5 nm with a FWHM of 21.5 nm (sigma-polarization) and the pulse duration was 218 fs (time-bandwidth product: 0.327).

We present a chirped pulse amplification (CPA) Yb:YAG laser based on Innoslab amplifier and post pulse-compression technique to achieve an average power of 83 W at a repetition rate of 175 kH with pulse width of 38 fs. The diode laser pumped Innoslab amplifier with a plane-convex hybrid cavity efficiently suppressed the self-lasing to reach high power amplification, while achieve a nearly diffraction-limited beam quality. After the grating compressor, two stages of post-compression were used for shorter pulse width. The final compressed beam quality was characterized as M2=1.2, with a measured long time power stability of 0.28%.

The development of high pulse energy and high repetition rate lasers based on Yb:YAG ceramics is expected to achieve high average power in areas not previously achieved by high energy diode pumped solid state lasers (DPSSL). Such lasers are of interest for advanced materials processing, surface treatments such as laser peening, and pumping ultra-intense lasers for compact radiation and particle sources. The choices of gain media, amplifier geometry, thermal management, and extraction architecture are important aspects for development of a scalable high repetition rate and high energy laser system. We are aiming to develop a pulse energy of 100 J, repetition rate of 100 Hz using conductive-cooled Yb:YAG active-mirror amplifier with a liquid-nitrogen cooling. We report on the status of the development our laser.

A 100 J DiPOLE amplifier with the capability to have arbitrary pulse shaping has been successful installed at XFEL Hamburg for High Energy Density Physics. We have demonstrated 70 J at 1 Hz and has been delivered to the target chamber for experiment using frequency doubled energy at 60% efficiency. During the experimental period the system was run for 24 hours over a period of seven days.

EPAC is a world-class research facility currently under development at the STFC Rutherford Appleton Laboratory in the United Kingdom. It will house a titanium-doped sapphire (Ti:Sa) amplifier, which will be capable of delivering PW-level pulses at an unprecedented repetition rate of 10 Hz. Such combination of high peak power and repetition rate will be achieved by pumping the Ti:Sa amplifier with a Diode-Pumped Solid State Laser (DPSSL) based on the Central Laser Facility’s DiPOLE technology.

We report on the successful commissioning of DiPOLE-100Hz, a DPSSL amplifying nanosecond pulses to 10 J energy at 100 Hz repetition rate. As part of initial commissioning experiments, the system was configured to amplify 15 ns pulses at 100 Hz pulse rate to an energy of 7 J. The system was operated at this level for four hours (corresponding to 1.44·10⁶ shots) with an energy stability of 1% rms. Subsequently, the laser demonstrated amplification of 15 ns pulses to the full specification of 10 J, 100 Hz, corresponding to 1 kW average power, with an optical-to-optical efficiency of 25.4% and long-term energy stability of less than 1% rms measured over one hour. To the best of our knowledge, this is the first time long-term, reliable operation of a kW-class high energy nanosecond pulsed DPSSL at 100 Hz has been demonstrated.

This talk highlights advances in the growth of new single crystal fiber materials with potential laser applications. Of particular interest are lutetia based single crystal fibers and Yb doped analogs. The Yb:Lu2O3 materials are attractive because the high thermal conductivity of Lu2O3 single crystals is not significantly reduced by doping with Yb in any concentration. The growth of faceted, single crystal 5-10% Yb:Lu2O3 fibers by LHPG is discussed. Also included are early attempts in hydrothermal single crystal cladding of undoped Lu2O3 onto the faceted core.

We report Q-switched operation in a dual-cavity Nd:YAG laser using an acousto-optic modulator. A dual-cavity laser configuration allows selection of the TEM00 mode, LG01 mode, or multimode as a laser output simply by adjusting an aperture size in each cavity. Employing the acousto-optic modulator, the Nd:YAG laser produced Q-switched pulses of a 146 μJ pulse energy in the TEM00 mode, 140 μJ in the LG01 mode, and 160 μJ in the multimode.

Free-running single-cavity dual-comb lasers offer cost-effective, high-performance solutions to dual-comb LiDAR. Precision requires ultra-low timing jitter whereas high sampling-speeds require ⪆1-GHz oscillators which often exhibit increased jitter. We address this challenge by exploring Yb:CaF2-based solid-state lasers optimized for ultra-low high-frequency noise. Such oscillators already demonstrated ultra-low noise but scaling to 1 GHz repetition rates faced challenges because of low gain crystal nonlinearities and Q-switching-induced damage of the SESAM susceptibility to Q-switching damage. Overcoming this, our in-house produced SESAM and optimized laser design enabled self-starting and, robust soliton modelocking at 1 GHz, with excellent performance, and timing-jitter power spectral density reaching 7e-5 fs2/Hz offset frequency of 10 kHz. Our platform shows promise for high-precision phase-sensitive dual-comb applications.

We present a record brightness of 0.3 PW/(sr∙cm²) using a passively cooled Nd:YAG/Cr4+:YAG microchip laser at 10 Hz. It delivers a peak power of 26.4 MW, an energy of 10.5 mJ, a pulse duration of 398 ps, and a M2 value of 2.7. The achieved brightness, utilizing an unstable resonator and a Gaussian mirror with a maximal reflection of 60%, exceeds that of a conventional flat-flat resonator by over 20 times at the same peak power. This increase enables a 150 mm long-focusing air-breakdown and a 7-point air-breakdown, suitable for multi-point ignition and multi-point Laser Induced Breakdown Spectroscopy (LIBS).

We report on a Kerr-lens mode-locked Yb:CALGO (Yb:CaGdAlO4) oscillator providing 50 fs pulses at 59.4 MHz repetition with an output power of 8.6 W that is pumped by a diode laser coupled to a multimode fiber. The mode-locking was initiated near the cavity stability edge of the CW mode, where the Kerr lensing at the gain crystal in the pulse mode reduces the cavity loss of the spatial mode and suppresses the CW mode build-up. The obtained pulse energy of 0.15 μJ and peak power of 2.5 MW from a simple laser cavity without saturable absorber, pumped by a conventional diode laser, are competitive in comparison to other Yb-doped bulk oscillators. An overview of previously demonstrated mode-locked oscillators reveals that the Yb:CALGO oscillator employing Kerr-lens mode-locking is a promising candidate to achieve ultrashort high-power pulses near 1040 nm.