Abstract Dynamical control of the nonlinear optical properties of solids – with light itself – will be essential for future ultrafast photonic technologies. Previously, methods to modulate nonlinear processes including second-harmonic generation (SHG) have relied primarily on non-resonant light-matter interaction or photo-generation of hot electrons in nanoscale materials. However, these approaches are typically constrained by limited interaction lengths and the initial frequency conversion is relatively weak under equilibrium conditions. Here, a ~ 30% modulation of efficient phase-matched SHG in bulk beta-barium borate (β-BaB2O4) is achieved through transient lattice deformation by intense terahertz (THz) pulses that are tuned to resonance with an infrared-active phonon mode. The effect originates from modification of the index of refraction ellipsoid and the corresponding nonlinear phase-matching conditions, rather than from direct modulation of the nonlinear susceptibility through THz-mediated $${\chi }^{(3)}$$ χ ( 3 ) processes. This mechanism, of resonant selective lattice excitation, points toward novel THz-control schemes to tune the nonlinear optical response in materials.

The spectral coherence properties of supercontinuum generation in polarization-maintaining all-normal dispersion fibers are investigated. Stochastic phase noise induced by energy fluctuations, along with spectrally resolved intensity-to-phase transfer coefficients, is quantitatively analyzed, confirming the high coherence of the generated supercontinuum. Our results show that the nonlinear process is fundamentally deterministic with ultra-low spectral phase noise yet exhibits significant intensity-to-phase coupling.

Infrared heterodyne interferometry offers a scalable alternative to direct interferometry for long-baseline telescope arrays. However, at near-infrared wavelengths, its sensitivity is limited by the electronic detection bandwidth and shot noise from the optical reference. Parallel detection via spectral multiplexing has long been identified as a potential means to increase the signal-to-noise ratio of heterodyne interferometers. We propose a new heterodyne detection architecture based on highly dispersed broadband pulses from a mode-locked laser, fast photoreceivers, and numerical correlation. This enables straightforward spectral multiplexing with commercial components to increase the SNR, while extending instantaneous wavelength coverage to simultaneous J- and H-band operation. The scheme also supports high-resolution spectroscopic imaging (R ≃ 10^3-10^4). We derive the SNR of a two-arm heterodyne interferometer based on balanced photodetection and apply the model to the proposed scheme, using measurements from a single-spectral-channel, all-fiber interferometer operating at 1.56 micrometer over an 8 nanometer bandwidth. We experimentally demonstrate an SNR exceeding 2 for a spectral flux density of 188 pW/nm, with an integration time of 0.4 ms. Scaling the integration time and number of spectral channels suggests that fringe visibility of the brightest H-band stars could be achieved with 1 m^2 telescopes within the typical atmospheric coherence time. These results represent a significant step toward broadband, scalable heterodyne interferometers, demonstrating the potential of ultrafast laser and telecommunications technologies for astronomical interferometry in the J+H bands. By combining broadband spectral multiplexing with numerical correlation, the architecture also opens a route to direct spectro-imaging without an additional spectrometer.

We introduce and characterize a fast (50 kHz), long range (50 ps) and random-access optical delay line based on an acousto-optic deflector inserted in the Fourier plane of a zero-dispersion line. The advantages of this agile delay line are demonstrated in the context of impulsive stimulated Raman imaging in the low-frequency range (<200 cm-1). Besides fast imaging with a spectral resolution of 1.5 cm-1, we show that random-access delay may be exploited to selectively image molecular species at high speed.

Supercontinumm generation (SCG) in nonlinear media is a highly efficient method to extend the spectrum of femtosecond pulses and a crucial part of carrier-envelope phase stabilized systems, both for seed generation and f-to-2f interferometers. All-normal dispersion (ANDi) optical fibers have recently gained significant attention for SCG due to their ability to produce highly coherent spectra with low noise [1]. In previous a work, we introduced a modified Bellini-Hänsch interferometer to characterize the intrapulse coherence of a SCG in bulk materials [2]–[4]. Building on these studies, this work focuses on the experimental quantification of the spectral intrapulse coherence of SCG generated in a commercial ANDi polarization-maintaining (PM) fiber (NKT Photonics).

Repetition-rate upscaling of intense, femtosecond-duration pulses in the short-wave infrared is necessary to further develop and apply tabletop, ultrafast soft-X-ray sources. Here, we present a 20 fs-pulse-duration, 2.1 µm-central-wavelength, optical parametric chirped-pulse amplification laser, which outputs 52 W of amplified signal power at a repetition rate of 52.6 kHz. Despite the potential for deleterious thermal processes, the laser output exhibits excellent spatial and temporal profiles in a 45 W beam at a soft-X-ray-generation target after ∼5 m of propagation. In argon gas, this enables high-harmonic generation up to ∼190 eV photon energies, demonstrating the system’s potential for ultrashort soft-X-ray-pulse production.

We investigate the resistance to the laser flux of a complex multilayer structure containing liquid crystal, focusing on the behavior of a spatial light modulator operating in the femtosecond regime. Our findings show that exceptionally high third-harmonic generation at the interfaces between the liquid crystal layer and its substrates, driven by the discontinuity in third-order nonlinear susceptibility, is the primary cause of laser damage. A quantitative study of the chromatic laser-induced damage threshold (LIDT) of a thermo-optically addressed spatial light modulator (TOA-SLM) is then presented. Since the device operates over an ultrabroadband spectrum, the study focuses on the behavior in the ultrashort pulse regime. The chromatic analysis offers a detailed map of the device's operational limits in ultrafast optics. With a maximum LIDT value of 500 GW/cm2, the modulator is an excellent candidate for integration into ultrafast optical systems. Additionally, the study examines the laser-induced functional threshold (LIFT), showing that the device remains fully operational nearly up to its damage threshold.

We study the coherence properties of continuum generation in YAG crystals seeded by 180 fs pulses at 1035 nm when the driving beam exhibits small fluctuations of the spatial phase. The relative stability of the continuum spectral phase is first assessed as a function of the driver wavefront aberrations. Furthermore, we evidence and quantify a coupling mechanism between these fluctuations and the spectral phase of the continuum. The coupling coefficients increase with the spectral broadening and are also unexpectedly large (up to tens of rad/rad at similar or equal to 750 nm). Experimental evidence supports that longitudinal shifts of the position of the filament within the crystal are responsible for such strong effects.

The vibrational motion of a molecule is intrinsically linked to its structure and composition, which provides a way to identify it. Raman spectroscopy, utilizing the inelastic scattering of light, investigates these molecular vibrations. While Raman shifts exceeding 200 cm(-1) primarily capture intramolecular vibrations, lower Raman shifts ( < 200 cm(-1)) provide insights into the collective motion of molecules, thereby revealing valuable structural information. Although frequency domain imaging effectively addresses higher Raman shifts, a time domain approach proves more practical for lower Raman shifts. Impulsive Stimulated Raman Scattering (ISRS) is a time domain technique that employs a pump pulse to instantaneously excite a molecule, activating all modes within its bandwidth and inducing a transient refractive index modulation. This modulation can be probed by a second pulse, enabling analysis of spatial profile, spectrum, and polarization changes. In this study, we elucidate the implementation of transient vibrational refractive index detection for the acquisition of ultrafast hyperspectral images, including the integration of a random access delay line into the existing setup that enables scanning windows of up to 50 picoseconds at random time delays.

Nobel laureate Charles Hard Townes is well known for his work in quantum electronics, which led to the invention of the maser and lasers. He was also a notable figure in astrophysics and astronomy, particularly recognized as the architect of the first high-resolution optical stellar interferometer.

Ultrashort time-domain spectroscopy and field-resolved spectroscopy of molecular fingerprints are gold standards for detecting samples' constituents and internal dynamics. However, they are hindered by the Nyquist criterion, leading to prolonged data acquisition, processing times, and sizable data volumes. In this work, we present the first experimental demonstration of compressed sensing on field-resolved molecular fingerprinting by employing random scanning. Our measurements enable pinpointing the primary absorption peaks of atmospheric water vapor in response to terahertz light transients while sampling beyond the Nyquist limit. By drastically undersampling the electric field of the molecular response at a Nyquist frequency of 0.8 THz, we could successfully identify water absorption peaks up to 2.5 THz with a mean squared error of 12 * 10^-4. To our knowledge, this is the first experimental demonstration of time-domain compressed sensing, paving the path towards real-time field-resolved fingerprinting and acceleration of advanced spectroscopic techniques.

We propose a new spatial light modulator (SLM) concept, relying on a local thermal modification of a thick liquid crystal layer, that is optically-induced through the absorption of a control beam. This innovative thermo-optically addressed SLM, coined TOA-SLM, has shown dynamic phase control capabilities over multi-octave light spectrum, as a promising candidate for spatial or temporal manipulation of ultrafast pulses. In addition to being ultra-broadband and programmable, such a device is low-cost, large-aperture and un-segmented with a high number of control points. The construction and training of a neural network-based statistical model provides configurable design of a prototype TOA-SLM. This step, together with the ultra-broadband acceptance of the device and its ability to introduce continuous and deep phase modulation over a large aperture, opens the way for ultrafast laser aberration compensation using this new technology.

We present a comprehensive strategy and its practical implementation using the commercial ScanImage software platform to perform hyperspectral point scanning microscopy when a fast time-dependent signal varies at each pixel level. In the proposed acquisition scheme, the scan along the X-axis is slowed down while the data acquisition is maintained at a high pace to enable the rapid acquisition of the time-dependent signal at each pixel level. The ScanImage generated raw 2D images have a very asymmetric aspect ratio between X and Y, the X axis encoding both for space and time acquisition. The results are X-axis macro-pixel where the associated time-dependent signal is sampled to provide hyperspectral information. We exemplified the proposed hyperspectral scheme in the context of time-domain coherent Raman imaging, where a pump pulse impulsively excites molecular vibrations that are subsequently probed by a time-delayed probe pulse. In this case, the time-dependent signal is a fast acousto-optics delay line that can scan a delay of 4.5ps in 25μs at each pixel level. With this acquisition scheme, we demonstrate ultra-fast hyperspectral vibrational imaging in the low frequency range [10cm-1, 150 cm-1] over a 500 μm field of view (64 x 64 pixels) in 130ms (∼ 7.5 frames/s). The proposed acquisition scheme can be readily extended to other applications requiring the acquisition of a fast-evolving signal at each pixel level.

We present a high-average power OPCPA system that produces CEP-stable, few-cycle pulses centered at 2.1 μm. The system was built at the Helmholtz-Zentrum Berlin and serves as a driver for a table-top, coherent, ultrashort-pulse soft X-ray source.

White light generation (WLG) in bulk media is an efficient way to extend the spectrum of optical femtosecond pulses and is currently a common block of so-called third generation femtosecond systems. In this paper, we address the case of WLG seeded with Yb-based laser systems.

Abstract We report on an ultrafast infrared optical parametric chirped-pulse amplifier (OPCPA), pumped by a 200-W thin-disk Yb-based regenerative amplifier at a repetition rate of 100 kHz. The OPCPA is tunable in the spectral range 1.4–3.9 $$\upmu $$ μ m, generating up to 23 W of < 100-fs signal and 13 W of < 200-fs idler pulses for infrared spectroscopy, with additional spectral filtering capabilities for Raman spectroscopy. The OPCPA can also yield 19 W of 49-fs 1.75- $$\upmu $$ μ m signal or 5 W of 62-fs 2.8- $$\upmu $$ μ m idler pulses with active carrier-to-envelope-phase (CEP) stabilisation for high-harmonic generation (HHG). We illustrate the versatility of the laser design, catering to various experimental requirements for probing ultrafast science.

Time domain spectroscopy, in particular, field-resolved spectroscopy has been a crucial tool for characterizing the transient electric field for decades [1]. Here, upon light-matter interaction, a detailed description of the constituent and internal dynamics of the matter is encoded on the electric field of light. When short laser pulses are used, the response of the medium is temporally separated from the main excitation pulses. This response which is enriched with the entire spectroscopic information of the sample lasts from hundreds of femtoseconds to tens of nanoseconds and is analytically shown to be sparse in the frequency domain [2]. To resolve the electric field and temporal decay of the transmitted or reflected transient, a short laser pulse probes the response at various temporal delays. By subsequent Fourier transformation, the full spectroscopic information is acquired. However, the measurement's speed is limited by i) the required number of sample points dictated by Nyquist-Shannon criteria, and ii) the speed of the delay line. In this work, we overcome these limitations and demonstrate field-resolved spectroscopy of vapor water molecules by Compressed Sensing. To the best of our knowledge, this is the first report on the reconstruction of absorption frequencies in the time domain beyond the Nyquist-Shannon limit. Our approach is enabled by developing a randomly sampling, rapidly scanned delay line, which speeds up the measurement time by three orders of magnitude allowing for sensitive, real-time sample analysis.