Ptychography implemented with coherent high-harmonic (HHG) sources enables high-resolution, high-fidelity imaging of nanostructures and biosystems. However, when driven by mid-infrared lasers to generate light at higher photon energies, HHG inherently produces a broadband quasi-continuum, which is less suited for coherent imaging compared with a single harmonic order. Consequently, experiments typically select a narrow bandwidth of ≈1%, leaving most of the HHG photons unused, increasing exposure times. In this work, we demonstrate broadband ptychography utilizing an extreme UV (EUV) continuum centered at 92 eV, with a bandwidth of up to 7.9 eV (a relative bandwidth of ~9%). By focusing the HHG beam to a sub-micrometer spot size to relax the temporal coherence constraints, and utilizing a multi-wavelength ptychographic reconstruction algorithm, we achieve a spatial resolution of 42 nm, which is near the diffraction limit of ~30 nm for our setup. To the best of our knowledge, this represents the broadest spectral bandwidth successfully employed to date for EUV ptychography, with the potential to increase the usable photon flux by up to an order of magnitude relative to previous approaches. In the future, broadband soft X-ray ptychography can be used to image hydrated samples around the carbon K-edge and magnetic textures at the L-edges of transition metals.

We demonstrate a 2 µ m Ho:YLF laser system comprising a regenerative amplifier and cryogenically cooled booster, driving a broadband 3 µ m OPCPA centered at 3.48 µ m supporting 3-cycle pulses with 120 µ J pulse energy.

High-harmonic upconversion driven by a mid-infrared femtosecond laser can generate coherent soft x-ray beams in a tabletop-scale setup. Here, we report on a compact ytterbium-pumped optical parametric chirped pulse amplifier (OPCPA) laser system seeded by an all-fiber front-end and employing periodically poled lithium niobate (PPLN) nonlinear media operated near the pulse fluence limits of current commercially available PPLN crystals. The OPCPA delivers 3 µm wavelength pulses with 775 µJ energy at 1 kHz repetition rate, with transform-limited 120 fs pulse duration, diffraction-limited beam quality, and ultrahigh 0.33% rms energy stability over >18 h. Using this laser, we generate soft x-ray high harmonics (HHG) in argon gas by focusing into a low-loss, high-pressure gas-filled anti-resonant hollow core fiber (ARHCF), generating coherent light at photon energies up to the argon L-edge (250 eV) and carbon K-edge (284 eV), with high beam quality and ∼1% rms energy stability. This work demonstrates soft x-ray HHG in a high-efficiency guided-wave phase matched geometry, overcoming the high losses inherent to mid-IR propagation in unstructured waveguides, or the short interaction lengths of gas cells or jets. The ARHCF can operate in the long term without damage and with the repetition rate, stability, and robustness required for demanding applications in spectromicroscopy and imaging. Finally, we discuss routes for further optimizing the soft x-ray HHG flux by driving He at higher laser intensities using either the signal (1.5 μm) or idler wavelengths (3 μm).

We report a compact and reliable ultrafast fiber laser system optimized for seeding a high energy, 2 μ m pumped, 3 μ m wavelength optical parametric chirped pulse amplification to drive soft X-ray high harmonics. The system delivers 100 MHz narrowband 2 μ m pulses with >1 nJ energy, synchronized with ultra-broadband optical pulses with a ∼1 μ m FWHM spectrum centered at 3 μ m with 39 pJ pulse energy. The 2 μ m and 3 μ m pulses are derived from a single 1.5 μ m fiber oscillator, fully fiber integrated with free-space downconversion for the 3 μ m. The system operates hands-off with power instabilities <0.2% over extended periods of time.

We report our progress developing a high average power ultrafast OPCPA at 1.5-μm pumped by a multi-channel Yb-fiber laser. The pump laser delivers 200-μJ, 250-fs pulses at 1-MHz repetition rate and parametric amplification was demonstrated.

We report emission cross-section, absorption cross-section and excited-state lifetime measurements of Ho:CaF2 and Ho:YLF(θ) at room and cryogenic temperatures. We also report numerical simulations confirming sub-ps amplification to the 10-mJ, 1-kHz level using these materials.

We report the generation of high harmonics in an anti-resonant hollow-core fiber driven by an ultrastable ~0.3% RMS, kHz laser at 3 µm wavelength. This geometry enables lower-loss guiding of mid-IR lasers.

We report the generation of 250 μJ, near transform-limited 2.4-cycle duration, 3 μm wavelength pulses at 1 kHz repetition rate via nonlinear self-compression in a multi-pass cell.

We present a fiber-based laser delivering synchronized pulses at 2 μm and 3 μm wavelengths to seed an OPCPA system. The simple architecture provides robust, stable mid-IR light for amplification to generate SXR high harmonics.

We show via numerical simulations that the regime of enhanced frequency chirp can be achieved in gas-filled multipass cells. Our results demonstrate that there exists a region of pulse and cell parameters for which a broad and flat spectrum with a smooth parabolic-like phase can be generated. This spectrum is compatible with clean ultrashort pulses, whose secondary structures are always below the 0.5% of its peak intensity such that the energy ratio (the energy contained within the main peak of the pulse) is above 98%. This regime makes multipass cell post-compression one of the most versatile schemes to sculpt a clean intense ultrashort optical pulse.

We report the generation of soft X-ray radiation up to the carbon K-edge (284 eV) in nitrogen gas driven by a millijoule-class 3 µm OPCPA featuring 135 fs pulses at 1 kHz repetition rate.

We report a robust long-term stable >19mJ energy, 1kHz repetition rate cryogenic Yb:YAG regenerative amplifier and its application in pumping a mJ-class, 3µm wavelength OPCPA. We highlight the benefits of cryo-Yb:YAG over alternative systems.

We numerically investigate the regime of nonlinear pulse compression at mid-IR wavelengths in a multi-pass cell (MPC) containing a dielectric plate. This post-compression setup allows for ionization-free spectral broadening and self-compression while mitigating self-focusing effects. We find that self-compression occurs for a wide range of MPC and pulse parameters and derive scaling rules that enable its optimization. We also reveal the solitonic dynamics of the pulse propagation in the MPC and its limitations and show that spatiotemporal/spectral couplings can be mitigated for appropriately chosen parameters. In addition, we reveal the formation of spectral features akin to quasi-phase matched degenerate four-wave mixing. Finally, we present two case studies of self-compression at 3-μm and 6-μm wavelengths using pulse parameters compatible with driving high-field physics experiments. The simulations presented in this paper set a framework for future experimental work using few-cycle pulses at mid-IR wavelengths.

We demonstrate record efficiencies of nonlinear optical-to-terahertz conversion near 1% for narrowband terahertz generation. This is achieved by strongly-cascaded difference frequency generation in periodically-poled LiNbO3 crystals using a novel multi-mJ laser source with two narrow spectral lines of tunable separation and pulse duration.

We report a robust, 3µm wavelength OPCPA system with sub-mJ pulse energies at 1kHz repetition rate. The use of high-pressure hollow-core waveguides, both regular and anti-resonant, provide a pathway for phase-matched soft X-ray generation.

Despite the popularity and ubiquity of the tilted-pulse-front technique for single-cycle terahertz (THz) pulse generation, there is a deficit of experimental studies comprehensively mapping out the dependence of the performance on key setup parameters. The most critical parameters include the pulse-front tilt, the effective length of the pump pulse propagation within the crystal as well as effective length over which the THz beam interacts with the pump before it spatially walks off. Therefore, we investigate the impact of these parameters on the conversion efficiency and the shape of the THz beam via systematically scanning the 5D parameter space spanned by pump fluence, pulse-front-tilt, crystal-position (2D), and the pump size experimentally. We verify predictions so far only made by theory regarding the optimum interaction lengths and map out the impact of cascading on the THz radiation generation process. Furthermore, distortions imposed on the spatial THz beam profile for larger than optimum interaction lengths are observed. Finally, we identify the most sensitive parameters and, based on our findings, propose a robust optimization strategy for tilted-pulse-front THz setups. These findings are relevant for all THz strong-field applications in high demand of robust high-energy table-top single-cycle THz sources such as THz plasmonics, high-harmonic generation in solids as well as novel particle accelerators and beam manipulators.

We identify, via numerical simulations, the regime of enhanced frequency chirp during nonlinear propagation in multipass cell. This regime - used before the dawn of chirped pulse amplification to generate ultrashort pulses - paves the way for the generation of temporally clean few-cycle pulses. Here, we demonstrate numerically that the spectra of pulses from an Yb-based laser system can be broadened into a flat supercontinuum with a smooth spectral phase compatible with a clean few-cycle pulse with temporal secondary structures with peak intensity below 0.5% that of the main peak.

We map out the impact of the interaction lengths on the efficiency and terahertz spatial profile in tilted-pulse-front setups via systematically scanning the 5D-parameter space spanned by fluence, pulse-front tilt, crystal-position, and beam size.

We report a compact, cryogenic Yb:YAG regenerative amplifier that delivers >19-mJ energy pulses at 1-kHz with near-TEM00 spatial profile. The excellent power and pointing stabilities are ideal for OPCPA pumping over weeks-long continuous operation.

We report on phase and intensity pulse shaping of the 1.5-μm signal beam of a 3-μm wavelength OPCPA system. This shaper and associated algorithms enable in-situ optimization of nonlinear processes driven at mid-IR wavelengths.