We report on a diode-pumped passively Q-switched Tm:YLF laser emitting at 2.3 µm. To promote emission at this wavelength, a cascade laser scheme is implemented, combining the consecutive 3H4 → 3H5 and 3F4 → 3H6 transitions in the Tm3+-doped material. In this configuration, laser operation at 1.9 µm is deliberately isolated from the Cr:ZnSe saturable absorber avoiding undesired saturation of the absorber. The 1.9-µm laser then runs alone in continuous-wave (cw) regime and the 2.3 µm laser in passively Q-switched regime. The Q-switch laser dynamics reveal intrinsic instabilities, which are further analyzed using Poincaré maps to uncover the underlying structures of an atypical Q-switched behavior. A detailed study demonstrates that these instabilities originate from the slightly multimode nature of the beam. Therefore, a stabilization process is settled by spatial filtering of the laser mode to reach a stable regime. In this stable regime, we obtain 1.5 µs pulses with an energy of 4 µJ with a repetition rate up to 5 kHz. Finally, the dynamics correlation between the two lasers of the cascade is also studied.

We report on a narrow linewidth nanosecond pulse optical parametric amplifier (OPA) seeded by a tunable continuous wave (CW) laser diode emitting around 1647 nm with a high spectral contrast. The system is pumped by a 1030 nm fiber laser delivering an average power of 10 W, pulses with a duration of 10 ns at a repetition rate of 100 kHz. A maximum signal conversion efficiency of 21% is achieved, corresponding to 2.16 W of average power and 20 µJ pulse energy with a beam quality factor of M 2 < 1.25. Optical spectrum analysis shows a spectral purity > 99.97%, and optical heterodyne measurements demonstrate near Fourier transform-limited operation with a spectral linewidth < 110 MHz for 10 ns pulses. Methane absorption spectroscopy is demonstrated using a gas cell, confirming the narrow linewidth and spectral stability of the source. These results highlight the potential of CW-seeded OPAs as laser sources for gas-sensing LIDAR systems.

We experimentally demonstrate efficient generation of tunable UV pulses at 100 kHz via resonant dispersive wave emission in an argon-filled hollow capillary. We measure a few µJ UV pulse energies both in linear and circular polarization. The dispersive wave emission is driven by 1030 nm 28 fs pulses generated by a ytterbium laser temporally compressed in a single-stage multipass cell. The UV source has a short-term (over a 1 s time scale) relative intensity noise of 0.58%. Coupled with the high repetition rate and the versatile polarization state, this makes it a relevant source for statistically demanding spectroscopy.

We experimentally study energy scaling properties of gas-filled multipass cell-based nonlinear compression setups by employing increasing azimuthal orders of Laguerre-Gauss LG0ℓ modes. First, we analyze the mode conversion from a Gaussian beam to LG0ℓ modes using spiral phase plates and spatial low-pass filtering. Then, these beams are sent to a first gas-filled multi-pass cell (MPC) to verify the energy scaling and spatial properties at the output. In a second experiment that allows more nonlinearity, we compare pulse compression conducted with either a Gaussian or an LG03 beam in terms of energy scaling, output temporal, spatial, spatio-spectral, and spectrally-resolved topological charge properties. The use of this structured beam allows for an increase in the input energy from 50 μJ up to 150 μJ with a final pulse duration of 60 fs, while the other parameters are essentially kept equal.

This work deals with a 343 nm UV laser based on the frequency tripling of a 1030 nm hybrid fiber/bulk MOPA amplifier. The seed laser source is designed to suit the molecular wind lidar application: 25 ns pulses at 40 kHz repetition rate, spectrally shaped as a frequency-comb matched to the two-waves interferometer used as lidar receiver. The signal is amplified in single-mode and LMA fibers up to a peak power of 15 kW limited by stimulated Brillouin scattering. Then, the signal is amplified in an Yb:YAG free-space amplifier to reach 36 kW peak power. Afterward, the fundamental frequency comb is converted in the UV by frequency tripling using LBO crystals with a conversion efficiency of 26%, resulting in an average power of 9.2 W (230 µJ per pulse at a repetition frequency of 40 kHz). The effect of the nonlinear conversion on the comb and its compatibility with the lidar receiver is studied.

High resolution spectral characterization of a nanosecond PPKTP BWOPO is carried out by optical heterodyne measurement. Unexpected spectra with side-lobe structures are observed and attributed to spatial inhomogeneity of the quasi-phase matching condition.

Scaling the efficiency of optical parametric amplifiers (OPAs) without degrading spatio-temporal pulse quality is fundamentally limited by spatio-temporal walk-off, intensity dependent gain, and back-conversion. Here, we numerically and experimentally demonstrate an OPA architecture based on a free-propagating quasi-periodic geometry that overcomes these bottlenecks. Operating within a single nonlinear crystal, the system utilizes pass-by-pass dichroic idler rejection to suppress back-conversion, a birefringent crystal for temporal resynchronization, and free-space diffraction to improve the spatial overlap along propagation. Starting from 1.9 μJ 330 fs pulses at 515 nm and a continuous-wave seed at 783 nm, the generation of 0.8 μJ 160 fs signal pulses at the same wave-length is obtained at a repetition rate of 500 kHz. This simple architecture achieves a 64

Over the last few years, temporal compression in nonlinear multipass cells (MPCs) has been proven to be a very promising method for future ultrafast laser sources. Although the majority of the work has been done with Gaussian beams, a few studies have touched upon using structured beams in such subsystems. Here, based on coupled-mode theory and numerical simulations, we focus on the behavior of MPCs upon excitation with either a single higher-order spatial mode or a combination of such modes. This includes their nonlinear properties, linear spatial dynamics upon propagation, and selection rules for efficient nonlinear energy transfer between modes. In particular, we show that the use of high-angular-order Laguerre-Gauss modes should prove efficient to scale the pulse energy inside MPCs.

Lidar instruments sensitivity strongly rely on laser performances. For atmospheric applications, the emitter specifications depend on the targeted observation. Wind lidars require high energy, with a linewidth compatible with wind speed assessment by heterodyne detection. Trace gas detection by the differential absorption method (DIAL) moreover relies on the emission of very specific wavelength in the near/mid-IR, in line with the absorption lines of the targeted species, which can be obtained by 1 μm lasers followed by frequency conversion stages in optical parametric oscillators and amplifiers [1]. In such a context, developing new narrow-linewidth, mJ level 1 μm lasers remains a topic of high interest for atmospheric lidars. In a previous work [2], we thus proposed a tunable Yb3+ hybrid fiber/solid-state amplifier architecture, to benefit from both the robustness of fiber systems and wavelength agility, and the high output energy achievable using solid-state free space amplifiers. Here we present our latest results, which allowed us to demonstrate a 12 ns FT-limited, 4 mJ, 20 kHz, hybrid fiber/bulk laser at 1030 nm, corresponding to an improvement by a factor of 4.5 of the average power from our previous work. Such a laser can be a pump of choice for OPO/OPAs, which could also benefit from its rapid tunability over 10 GHz, leading to an easy gas line probing by the DIAL technique when combined with Backward OPO [3].

We report on a diode pumped, Q-switched, Tm:YLF laser emitting at 2.3 µm. Pulse train instabilities analysis shows that dynamics of the different transversal modes is different and stability can be achieved by spatial selection.

Self-phase modulation (SPM) of gaussian-like pulses induces spectral broadening. This nonlinear effect enables the implementation of post-compression techniques, using a multipass cell (MPC) [1] for instance. Coupled to temporally shaped input pulse, SPM can lead to other applications such as spectral tunability as shown for low energy pulses in [2]. Here, we report a deterministic spectral phase-only pulse-shaping technique that is a generalized version of the method presented in [3]. It introduces a nonlinear chirp to generate arbitray shapes in the time domain. We illustrate the technique with the spectral tunability application for high energy pulses.

We present an intra-cavity upconversion pumping scheme for Thulium lasers operating on the 3 H 4 → 3 H 5 transition. It is based on detuning the pump wavelength from the resonance of excited-state absorption, 3 F 4 → 3 F 2,3 , around 1 µm. This scheme is validated using a Tm:LiYF 4 -based laser. The pump source consists of a diode-pumped Nd:YVO 4 laser emitting at 1.064 µm. This architecture permits for power scaling of 2.3-µm Tm-lasers. An output power of 2.7 W is generated in the continuous-wave regime for 62.3 W of intracavity pump power at 1.064 µm corresponding to 21 W of primary laser-diode power, making this kind of pumping competitive in terms of power, laser gain and efficiency with direct diode pumping at 0.78 µm. We also describe the heat management in this double-cavity laser benefiting from the intra-cavity pumping architecture allowing to share the thermal load between two gain crystals. The low absorption caused by the non-resonant 3 F 4 → 3 F 2,3 Tm 3+ transition allows the Nd pump laser to reach higher intracavity power compensating for the low pump absorption efficiency in the Tm-crystal. The proposed off-resonance pumping scheme opens a new paradigm that holds great promise for high-power, high-gain 2.3 µm solid-state lasers based on thulium ions.

In this paper we present an alexandrite (Cr3+:BeAl2O4) multipass amplifier pumped by blue LEDs via a luminescent concentrator (LC). This emerging pump technology provides up to 2.6 kW optical pump power during 400 µs at 10 Hz in the 530-630 nm range for low cost, simple and robust implementation. We achieve a single-pass gain of 1.38, the highest ever reported in alexandrite for a semiconductor-based pump source, and a total gain of 34 after 16 passes. The amplifier is injected by a single-frequency laser operating in a quasi-continuous wave at 761 nm. It delivers µs pulses with a peak power of 14 W. This power could significantly improve penetration depth for in vivo acousto-optic imaging.

Q-switched Tm lasers operating at 2.3 μm are of great interest in view of their potential applications [1], [2]. However, these lasers seem to exhibit systematic instabilities and chaotic behaviors [3]. Despite extensive research, the mechanisms driving these instabilities remain not analyzed. This study tends to investigate the chaotic dynamics in a Tm:YLF laser operating at 2.3 μm, highlighting an atypical type-I intermittency route to chaos. This chaotic behavior with intermittency appears inherently linked to the cascade transitions within the laser [4]. Using a Cr:ZnSe saturable absorber, the laser transitions from stable to chaotic regimes changing the pump power. Analytical methods, including Poincaré maps, phase space reconstruction and entropy calculations, reveal laminar phases and cubic behaviors consistent with type-I intermittency scenario (Fig. 1.c). Moreover, entropy rises from 0 (stable) to 1.55 (chaotic) versus pump power, giving a quantitative criterion to discriminate the different laser behavior. Moreover, phase-space reconstructions (Fig. 1.d) confirm the chaotic nature of the system giving an embedding dimension of 10 (Fig. 1.e).

Acousto-optic imaging (AOI) aims at producing in-depth images in highly scattering biological tissues, by tagging scattered photons with ultrasound (US) waves as they propagate through the sample. By selectively detecting photons traversing the insonified region, AOI generates images of the local optical absorption [1]. To approach video-rate imaging of in-vivo samples, a single-shot acquisition protocol is necessary. This requires laser sources in the 650 nm ≤ $\lambda$ ≤ 900 nm spectral range (corresponding to low absorption of haemoglobin and water) with both a high peak power and a narrow spectral linewidth (<20 MHz). The penetration depth is currently limited by the optical power available from single-frequency diode laser devices. Coherent beam combination ─ based on the constructive interference of multiple coherent laser beams ─ offers a promising solution as it enhances optical power while preserving beam quality and spectral purity.

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.

We report an experimental demonstration of soliton self-frequency shift in a nitrogen-filled multipass cell. The use of a molecular gas combined with the flexible geometry of the multipass platform enables efficient wavelength conversion from 1030 nm to 1110 nm. By employing 24-fs input pulses with energies up to 150 µJ, we generate soliton pulses with energies up to 55 µJ and durations below 50 fs, corresponding to peak powers as high as 0.5 GW. Experimental results are supported by numerical simulations, which emphasize how a suitable combination of dispersion, input pulse energy and duration, and gas pressure enables a wavelength-tunable, high-power, and high-energy source. This approach offers enhanced scalability in terms of average power and pulse energy compared to previously studied systems based on waveguides.

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].

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