We demonstrate the first LED-pumped Nd:glass regenerative amplifier. It delivers 2 ns pulses at 1053 nm with an energy of 3.8 mJ at a repetition rate of 2 Hz. This performance is achieved using a Ce:LuAG luminescent concentrator producing 3.4 kW of optical peak power in the yellow spectral range and pumped by 3200 blue LEDs. This indirect LED pumped technology demonstrates high power-scaling capabilities and shows great potential for high energy Nd:glass laser chains.

Increasing the repetition of kilojoule-class laser chains has recently strongly gained in interest, especially in the context of inertial confinement fusion (ICF). A promising approach is the coherent beam combination (CBC) of smaller-scaled laser sources of higher repetition rate, to overcome the critical cooling problems of single very large aperture amplifiers. This method has already proved its worth in low-energy systems and especially with very higher repetition rates [1] and has been widely applied in industrial settings using fiber systems [2]. However, since high-energy laser chains have diameters of several tens of centimeters, new challenges appear. First, the spatial issues must be taken into account, as phase correction limited to piston adjustment is insufficient. Second, due to the low repetition rate a feedback loop relying solely on laser shots is inadequate because it lacks information on phase variations occurring between shots. Many large laser facilities thus see coherent beam combining as an up-and-coming technique, but paradoxically, the literature lacks data on the wavefront evolution during the flash duration [3]. We therefore propose a study to characterize these phenomena aiming to conclude on the key issues and any potential no-go for combining coherently kilojoule-class lasers.

Flashlamp Nd:glass is used in many high-energy laser facilities as power amplifiers for nanosecond and CPA-based sub-picosecond pulses [1]. Despite all the problems associated with flashlamps (high voltage handling, high thermal effects, short lifetime), this pumping architecture is still in use in today's facilities and is still considered for the next generation. LED pumping could be an interesting alternative, since the lighting market offers a mass production of LEDs at a cost per watt much lower than laser diodes. Direct LED pumping of Nd:glass has been recently demonstrated [2] but with a limited small signal gain (typically 1.05) and with pump power scaling limited by the LED density and by the surface of the Nd:glass rod. In this paper, we propose an alternative approach to indirectly pumping Nd:glass using LEDs via a luminescent concentrator. In fact, this architecture has already proven its efficiency for low gain transition metal lasers [3]. It consists of a Ce-doped luminescent concentrator pumped by blue LEDs. At the output of the concentrator, the pump power density can reach 10 kW/cm2, matching the power density typically achievable with laser diodes. The emission spectrum is in the yellow-orange range and it can be used to pump Nd-doped materials [4].

Broadband incoherent laser pulses have recently gained significant interest, particularly in the context of inertial confinement fusion (ICF). Since the 2022 demonstration of fusion by the National Ignition Facility (NIF) [1], numerous academic laboratories and startups have been rapidly growing with the shared goal of achieving decarbonized electricity production. The scientific corpus of plasma physics suggests that broadband incoherent laser sources could play a pivotal role by improving the deposition of laser energy onto targets while mitigating deleterious effects that reduce the coupling efficiency of the laser to the target. Such effects include cross-beam energy transfer (CBET), as well as Brillouin and Raman scattering. To the best of our knowledge, no laser source currently available on the market meets all the parameters required for traditional high-intensity laser facilities, particularly in terms of the temporal shaping of large-bandwidth pulses. Nowadays, temporal pulse shaping in intense laser facilities is typically achieved using classical electro-optic modulators (EOMs) coupled with arbitrary waveform generators (AWGs). However, due to the Mach-Zehnder structure of EOMs, they are inherently limited in terms of contrast versus bandwidth.

Spatial coherent beam combining (CBC) strategies are particularly promising for lasers dedicated to nuclear fusion applications for the purpose of developing high-energy and high-repetition-rate lasers. Let us examine their potential application to high-energy, large-size beams with repetition rates that preclude phase correlation between subsequent pulses. Both passive and active CBC approaches are investigated in this study to identify the most appropriate and effective strategy for large-aperture, high-energy laser amplifiers. Specific experiments have been conducted to validate promising architectures for lasers dedicated to inertial confinement fusion (ICF) applications. Based on these experimental results, examples of suitable and well-adapted setups are proposed.

Flashlamp-pumped Nd:glass is used as a power amplifier in many high energy laser facilities. Despite the problems of this old technology, flashlamps are still being considered for the next generation of lasers as diode laser pumping is far from being ready. This work presents an alternative for pumping high energy lasers: LEDs combined with luminescence concentrators. Using a pump head consisting of a green-yellow Ce:LuAG luminescent concentrator pumped by 2240 LEDs, we demonstrate a Nd:glass laser oscillator producing 25 mJ at 1053 nm for an absorbed pump energy of 138 mJ. The small signal gain reaches 1.25 in a single pass despite the short length of the Nd:glass rod (20 mm). These results reveal the potential of indirect LED pumping for Nd:glass amplifiers in high energy lasers. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Broadband incoherent laser pulses have recently gained significant interest, particularly in the context of inertial confinement fusion (ICF). Since the 2022 demonstration of fusion by the National Ignition Facility (NIF) [1], numerous academic laboratories and startups have been rapidly growing with the shared goal of achieving decarbonized electricity production. The scientific corpus of plasma physics suggests that broadband incoherent laser sources could play a pivotal role by improving the deposition of laser energy onto targets while mitigating deleterious effects that reduce the coupling efficiency of the laser to the target. Such effects include cross-beam energy transfer (CBET), as well as Brillouin and Raman scattering. To the best of our knowledge, no laser source currently available on the market meets all the parameters required for traditional high-intensity laser facilities, particularly in terms of the temporal shaping of large-bandwidth pulses. Nowadays, temporal pulse shaping in intense laser facilities is typically achieved using classical electro-optic modulators (EOMs) coupled with arbitrary waveform generators (AWGs). However, due to the Mach-Zehnder structure of EOMs, they are inherently limited in terms of contrast versus bandwidth.

The Apollon laser facility reached recently the 3.7 PW operational level. In this presentation we discuss the main development works of the 10 PW beamline such as the compressor qualification and the last stage amplifier.

We present, for the first time, coherent beam combination of 10 Joules nanosecond pulses in a Sagnac-interferometer configuration including large-diameter Nd:glass amplifiers. Efficiency over 90 % is demonstrated while maintaining good stability between shots.

The Apollon laser facility has recently increased its peak power capacity to the 3.7 PW level. In this presentation we discuss the commissioning of the laser system and provide feedback from the first experimental campaigns.

We present, coherent combining of two 10-Joules nanosecond pulses in a Sagnac-interferometer configuration including large-diameter Nd:glass flash-pumped amplifiers. A good stability between the shots and an average efficiency of 92 % is demonstrated.

We demonstrate a passive and automatic correction of high-energy laser wavefront using stimulated Brillouin scattering (SBS) based phase conjugating mirror (PCM) establishing a new record in terms of input energy level of 122 J together with an extremely high reflectivity, leading to efficiencies of 99 % with both high temporal fidelity and good spatial profile conservation. For this achievement, we developed an innovative design of high-energy SBS-PCM based on high numerical aperture focusing and on the temporal shaping of the input pulse, guaranteeing good SBS initiation before the arrival of the main part of the pulse. An original approach was introduced compared to previous works where the temporal fidelity was a limitation for energy scale-up. This approach allows, for the first time in an SBS cell, perfect conservation of the input pulse temporal profile, demonstrated for several temporal pulse shapes of interest. Pulsed laser sources with nanosecond duration and energy levels above the kilojoule represent a crucial tool for a wide range of plasma and shock physics experiments. This work will unlock a crucial bottleneck by addressing the correction of the wavefront distortions due to the accumulating thermal load in these lasers and opens the way to higher repetition rate kilojoule systems.

We report the successful operation of a phase conjugate mirror operating at unprecedented energy level of 122 J. The component was able for the first time to reflect arbitrary temporal profiles with good fidelity

We demonstrate a laser source generating mJ-level temporally-flat-top pulses of arbitrary duration between 1 ns and 100 ns simultaneously at 1064 nm and 532 nm operating at 10 Hz with 0.3 % RMS energy stability.

A simple and straightforward technique is presented as a novel temporally controllable front-end for nanosecond very-high energy laser systems. It is based on an original utilization of a semiconductor optical amplifier (SOA) used as an intensity modulator. The essential characteristics of the component are analyzed in order to evaluate potential limitations. Various parameters of interest for standard operation are displayed, demonstrating its usability and its effectiveness. We demonstrate arbitrary and controllable pulse temporal profiles with duration ranging from 1 nanosecond to 100 nanoseconds and a temporal precision of 1.1 ns. A high extinction ratio is also achieved ensuring a modulation contrast up to 53 dB. The SOA is then integrated into an existing operating system in an ultra-compact, reliable all-fibered system. It is used to seed a 2*200 J laser system, exhibiting excellent performance, and validating its usability under operation conditions without any detrimental effects.

The post-compression technique based on self-phase modulation of high-energy pulses leads to an increase in achievable peak power and intensity. Typically, the pulses considered in experiments have been less than 100 fs in duration. Here, the method is applied to the ELFIE laser system at the LULI facility, for a pulse of 7 J energy and an initial measured duration of 350 fs. A 5-mm-thick fused silica window and a 2 mm cyclic-olefin polymer were used as optical nonlinear materials. The 9 cm diameter beam was spectrally broadened to a bandwidth corresponding to 124 fs Fourier-limited pulse duration, and then it was partly post-compressed to 200 fs. After measuring the spatial spectra of the beam fluence, a uniform gain factor of 4 increase in the fluctuations over the studied range of frequencies is observed, due to small-scale self-focusing.

Spectral-broadening of the APOLLON PW-class laser pulses using a thin-film compression technique within the longfocal-area interaction chamber of the APOLLON laser facility is reported, demonstrating the delivery of the full energy pulse to the target interaction area. The laser pulse at 7 J passing through large aperture, thin glass wafers is spectrally broadened to a bandwidth that is compatible with a 15-fs pulse, indicating also the possibility to achieve sub-10-fs pulses using 14 J. Placing the post-compressor near the interaction makes for an economical method to produce the shortest pulses by limiting the need for high damage, broadband optics close to the final target rather than throughout the entire laser transport system.

We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility (located in Saclay, France), which was performed with the first available laser beam (F2), scaled to a nominal power of 1 PW. Under the conditions that were tested, this beam delivered on-target pulses of 10 J average energy and 24 fs duration. Several diagnostics were fielded to assess the performance of the facility. The on-target focal spot and its spatial stability, the temporal intensity profile prior to the main pulse, and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized, with the goal of helping users design future experiments. Emissions of energetic electrons, ions, and electromagnetic radiation were recorded, showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities. This will be followed in 2022 by a further commissioning stage at the multi-petawatt level.