In situ characterization of few-cycle laser pulses in transient absorption spectroscopy

Abstract

Fig. 1. Dipole control model. (a)Perturbations to the field-free evolution of the dipole response (dashed blue) are treated as instantaneous modifications of the amplitude and phase expressed by the complex factor A. The perturbed decay (dark purple, light purple) is shown for two time-delays ( 1 , 2 ) leading to very different spectral line shapes (inset). (b) Treatment of a ponderomotive shift in the dipole control model. Instead of a continuously modified dipole phase ( ) , the effect of the dressing field is approximated by a single phase step at time , the peak of the intense laser pulse envelope. Since the temporal profile of the dressing laser pulse intensity is mapped onto ( ) via Eq. (4), it is possible to determine both the pulse duration and intensity.In situ characterization of few-cycle laser pulses in transient absorption spectroscopy Attosecond transient absorption spectroscopy has thus far been lacking the capability to simultaneously characterize the intense laser pulses at work within a time-resolved quantum-dynamics experiment. However, precise knowledge of these pulses is key to extracting quantitative information in strong-field highly nonlinear light-matter interactions. Here, we introduce and experimentally demonstrate an ultrafast metrology tool based on the time-delay-dependent phase shift imprinted on a strong-field driven resonance. Since we analyze the signature of the laser pulse interacting with the absorbing spectroscopy target, the laser pulse duration and intensity are determined in situ. As we also show, this approach allows for the quantification of time-dependent bound-state dynamics in one and the same experiment. In the future, such experimental data will facilitate more precise tests of strong-field dynamics theories.In the transformative field of ultrafast light-matter interaction, characterization of strong-field laser pulses is crucial in order to draw quantitative conclusions from measurement results. Based on the detection of photoelectrons, the attosecond streaking technique provides insight into the system's underlying quantum dynamics on the natural electronic time scale, combined with a powerful characterization of the used strong-field laser pulses [1][2][3]. Being capable of resolving bound-state quantum dynamics, the all-optical method of attosecond transient absorption spectroscopy (ATAS) [4][5][6][7][8][9][10][11][12] is an important complement to photoelectron-based methods. In addition to being sensitive to bound-bound transitions, ATAS allows targets to be studied all the way from a natural -weak-field -environment up to the strong-field regime. Using attosecond pulsed extreme-ultraviolet (XUV) light together with (typically) femtosecond nearinfrared (NIR) pulses in a pump-probe scheme, dynamical processes leave their fingerprints in the spectrum of the transmitted XUV light. Yet unlike streaking, up to now ATAS lacks the possibility for in-situ characterization of the femtosecond NIR laser pulse, which drives and controls the underlying electron dynamics. ...

Universal route to optimal few- to single-cycle pulse generation in hollow-core fiber compressors

“…Furthermore, their long-term stability can be greatly improved by using, e.g., piezo-driven mirror mounts to ensure stable and constant spatial coupling of the input laser pulses into the HCF via a simple feedback loop. Hollow-core fiber post-compressed pulses have shown a great potential in a wide range of applications, such as pump-probe experiments in conjunction with attosecond pulses [29], ultrafast measurement of electrical and optical properties of solids [30,31], time-resolved studies of Coulomb explosion dynamics [32], ultrafast spectroscopy techniques [33][34][35][36][37][38][39], and very recently a new generation of compact kHz laser-plasma accelerators based on single-cycle pulses [40].To access the Fourier Limit of a pulse after a nonlinear propagation process one has to deal with the complex phase that the pulse acquires due to the interplay of different linear and nonlinear effects. In general, researchers optimize their HCF compressors by empirically adjusting several key parameters, such as gas type and pressure, input pulse characteristics and coupling conditions, with the final result usually involving a delicate compromise between output efficiency, amount of spectral broadening and achievable degree of compression (pulse duration and quality) for their particular system and chirped mirror set.…”

“…Furthermore, their long-term stability can be greatly improved by using, e.g., piezo-driven mirror mounts to ensure stable and constant spatial coupling of the input laser pulses into the HCF via a simple feedback loop. Hollow-core fiber post-compressed pulses have shown a great potential in a wide range of applications, such as pump-probe experiments in conjunction with attosecond pulses [29], ultrafast measurement of electrical and optical properties of solids [30,31], time-resolved studies of Coulomb explosion dynamics [32], ultrafast spectroscopy techniques [33][34][35][36][37][38][39], and very recently a new generation of compact kHz laser-plasma accelerators based on single-cycle pulses [40].…”

Attosecond transient absorption instrumentation for thin film materials: Phase transitions, heat dissipation, signal stabilization, timing correction, and rapid sample rotation

“…Using the gas cell, a transient absorption measurement can be performed in neon gas at a backing pressure of 100 Torr. The neon response allows an in situ determination of both time-zero and the instrument response function, 28 which is then used to retroactively correct time-delay drifts and synchronize scans in the data analysis. 29 A representative time-delay drift trace is shown in Fig.…”

Analyte-induced spectral filtering in femtosecond transient absorption spectroscopy

“…Since the introduction of commercial femtosecond lasers, transient absorption (TA) spectroscopy has become an established technique that is used by thousands of scientists in almost all fields of natural sciences [1][2][3][4][5][6][7]. In recent years commercial TA instruments have made this technique available to researchers with a wide variety of backgrounds other than non-linear optics.…”