arXiv subjects

Benjamín Alonso

Publications and source records attributed to Benjamín Alonso.

11 recordsLinked to original sources

arXiv2026

Quantification of phase instabilities in amplitude swing for ultrashort pulse train characterization

The temporal dynamics of ultrashort pulses are a fundamental feature in ultrafast optics. These dynamics can often be extracted from a two-dimensional trace consisting of a set of nonlinear spectra, using an iterative algorithm. Typically, the measurement of this trace requires integrating the signal of many pulses, which implies that the trace does not correspond to a single pulse when shot-to-shot variations occur. In this case, the pulse train can be characterized by a base pulse and a metric that quantifies its instabilities. Here, we demonstrate that the amplitude swing technique is highly sensitive to pulse-train instabilities, allowing not only for their detection but, crucially, for their quantification. First, we examine the analytical components of the amplitude swing trace. We then introduce a robust parameter designed to assess the instabilities, evaluating its performance in the presence of noise. Finally, we validate this approach using simulated unstable pulse trains, introducing random spectral phase fluctuations, establishing amplitude swing as a simple yet powerful diagnostic tool for full pulse-train characterization.

physics.optics↗

arXiv2026

Visible optical vortices measured with bulk lateral shearing interferometry

Ultrafast pulse optical vortices are spatiotemporal structures with a diverse range of applications. There are different ways to generate them, often restricted to a wavelength range. Likewise, characterization techniques frequently possess similar limitations. In this work, we first generate ultrashort optical vortices in the near-infrared from Ti:sapphire laser pulses by means of structured waveplates and beam manipulation. Then, we produce the visible vortices through up-conversion using a second-harmonic generation crystal. The resulting beams require spatiotemporal characterization, which is performed by bulk lateral shearing interferometry. The reference pulse is temporally characterized with the amplitude swing technique. In this manner, we present the generation of these pulses in the visible range, which is experimentally validated, and demonstrate that bulk lateral shearing interferometry can be used for pulsed beams across widely different spectral regions with the same setup. This finding is significant for future applications of the technique with various sources.

physics.optics↗

arXiv2025

Measuring ultrafast laser pulses using a single-shot amplitude swing implementation

Single-shot characterization techniques are crucial when dealing with shot-to-shot pulse-shape fluctuations (e.g., unstable laser systems, high-power, or with low repetition rate) since the scanning configurations cannot measure single pulses. The demand for simple setups that can be easily adapted to a wide variety of experimental conditions is continuously rising. In this work, we propose a single-shot implementation of amplitude swing, maintaining the compactness, versatility, and robustness of the scanning versions of this technique. First, we theoretically study the proposed implementation, based on a pair of uniaxial wedges. Then, we present the retrieval ptychographic algorithm. Finally, we experimentally demonstrate the setup by comparing the single-shot and scanning traces and their retrieved pulses. In sum, we provide the ultrafast science community with a simple and versatile setup capable of measuring single laser pulses, which is necessary for characterizing fluctuating pulse trains, meeting the current increasing demand.

physics.optics↗

arXiv2025

Ptychographic retrieval for complete ultrashort pulse amplitude swing reconstruction

Ultrafast experiments require precise temporal characterization of laser pulses, where pulse reconstruction is typically achieved through iterative retrieval algorithms. In this context, the amplitude swing technique has emerged as a robust and versatile tool for measuring scalar and vector pulses, using a compact inline setup. Here, we develop a unified theory of amplitude swing and introduce a ptychographic iterative engine algorithm to retrieve scalar and vector pulses from the different amplitude swing implementations (conventional and generalizing). For scalar pulses, we show the new capability of retrieving both amplitude and phase. The algorithm is validated with simulated and experimental traces of scalar and vector pulses, which are benefited from the new algorithm. In conclusion, a powerful tool for pulse characterization is provided, extending the capabilities of amplitude swing (e.g., to double pulses) and enhancing the ultrafast optics measurement toolkit.

physics.optics↗

arXiv2022

Roadmap on spatiotemporal light fields

Spatiotemporal sculpturing of light pulse with ultimately sophisticated structures represents the holy grail of the human everlasting pursue of ultrafast information transmission and processing as well as ultra-intense energy concentration and extraction. It also holds the key to unlock new extraordinary fundamental physical effects. Traditionally, spatiotemporal light pulses are always treated as spatiotemporally separable wave packet as solution of the Maxwell's equations. In the past decade, however, more generalized forms of spatiotemporally nonseparable solution started to emerge with growing importance for their striking physical effects. This roadmap intends to highlight the recent advances in the creation and control of increasingly complex spatiotemporally sculptured pulses, from spatiotemporally separable to complex nonseparable states, with diverse geometric and topological structures, presenting a bird's eye viewpoint on the zoology of spatiotemporal light fields and the outlook of future trends and open challenges.

physics.optics↗

arXiv2020

Complete spatiotemporal and polarization characterization of ultrafast vector beams

The use of structured ultrashort pulses with coupled spatiotemporal properties is emerging as a key tool for ultrafast manipulation. Ultrafast vector beams are opening exciting opportunities in different fields such as microscopy, time-resolved imaging, nonlinear optics, particle acceleration or attosecond science. Here, we implement a technique for the full characterization of structured time-dependent polarization light waveforms with spatiotemporal resolution, using a compact twofold spectral interferometer, based on in-line bulk interferometry and fibre-optic coupler assisted interferometry. We measure structured infrared femtosecond vector beams, including radially polarized beams and complex-shaped beams exhibiting both temporal and spatial evolving polarization. Our measurements confirm that light waveforms with polarization evolving at the micrometer and femtosecond scales can be achieved through the use of structured waveplates and polarization gates. This new scale of measurement achieved will open the way to predict, check and optimize applications of structured vector beams at the femtosecond and micrometer scales.

physics.optics↗

arXiv2020

Characterizing ultrashort laser pulses with second harmonic dispersion scans

The dispersion scan (d-scan) technique has emerged as a simple-to-implement characterization method for ultrashort laser pulses. D-scan traces are intuitive to interpret and retrieval algorithms that are both fast and robust have been developed to obtain the spectral phase and the temporal pulse profile. Here, we give a review of the d-scan technique based on second harmonic generation. We describe and compare recent implementations for the characterization of few- and multi-cycle pulses as well as two different approaches for recording d-scan traces in single-shot, thus showing the versatility of the technique.

physics.optics↗

arXiv2020

Single-shot d-scan technique for ultrashort laser pulse characterization using transverse second-harmonic generation in random nonlinear crystals

We demonstrate a novel dispersion-scan (d-scan) scheme for single-shot temporal characterization of ultrashort laser pulses. The novelty of this method relies on the use of a highly dispersive crystal featuring antiparallel nonlinear domains with a random distribution and size. This crystal, capable of generating a transverse second-harmonic signal, acts simultaneously as the dispersive element and the nonlinear medium of the d-scan device. The resulting in-line architecture makes the technique very simple and robust, allowing the acquisition of single-shot d-scan traces in real time. In addition, the technique can be further simplified by avoiding the need of dispersion pre-compensation. The retrieved pulses are in very good agreement with independent FROG measurements. We also apply the new single-shot d-scan to a TW-class laser equipped with a programmable pulse shaper, obtaining an excellent agreement between the applied and the d-scan retrieved dispersions.

physics.optics↗

arXiv2019

Tailoring the spatio-temporal distribution of diffractive focused ultrashort pulses through pulse shaping

Focusing control of ultrashort pulsed beams is an important research topic, due to its impact to subsequent interaction with matter. In this work, we study the propagation near the focus of ultrashort laser pulses of ~25 fs duration under diffractive focusing. We perform the spatio-spectral and spatio-temporal measurements of their amplitude and phase, complemented by the corresponding simulations. With them, we demonstrate that pulse shaping allows modifying in a controlled way not only the spatio-temporal distribution of the light irradiance in the focal region, but also the way it propagates as well as the frequency distribution within the pulse (temporal chirp). To gain a further intuitive insight, the role of diverse added spectral phase components is analyzed, showing the symmetries that arise for each case. In particular, we compare the effects, similarities and differences of the second and third order dispersion cases.

physics.optics↗

arXiv2019

Measurement of ultrashort vector pulses from polarization gates by in-line, single-channel spectral interferometry

The growing use of ultrashort laser pulses exhibiting time-varying polarization (vector pulses) demands simple and robust characterization techniques capable to perform measurements in a broad range of experimental and environmental conditions. Here we present in-line, single-channel setup based on spectral interferometry to characterize ultrashort vector pulses. The use of a bulk interferometer based on birefringence is key for the stability and sensitivity of the technique, thus being simple and highly robust. The technique is used to measure vector pulses corresponding to polarization gates, which are used in many applications. Those results are validated by simulations. The technique here presented has a number of potential applications in nonlinear effects (e.g. transient birefringence and nonlinear phenomena with vector pulses).

physics.optics↗

arXiv2017

Tunable high-harmonic generation by chromatic focusing of few-cycle laser pulses

In this work we study the impact of chromatic focusing of few-cycle laser pulses on high-order harmonic generation (HHG) through analysis of the emitted extreme ultraviolet (XUV) radiation. Chromatic focusing is usually avoided in the few-cycle regime, as the pulse spatio-temporal structure may be highly distorted by the spatiotemporal aberrations. Here, however, we demonstrate it as an additional control parameter to modify the generated XUV radiation. We present experiments where few-cycle pulses are focused by a singlet lens in a Kr gas jet. The chromatic distribution of focal lengths allows us to tune HHG spectra by changing the relative singlet-target distance. Interestingly, we also show that the degree of chromatic aberration needed to this control does not degrade substantially the harmonic conversion efficiency, still allowing for the generation of supercontinua with the chirped-pulse scheme, demonstrated previously for achromatic focussing. We back up our experiments with theoretical simulations reproducing the experimental HHG results depending on diverse parameters (input pulse spectral phase, pulse duration, focus position) and proving that, under the considered parameters, the attosecond pulse train remains very similar to the achromatic case, even showing cases of isolated attosecond pulse generation for near single-cycle driving pulses.

physics.optics↗