Abstract
High-repetition rate attosecond pulse sources are indispensable tools for time-resolved studies of electron dynamics, such as coincidence spectroscopy and experiments with high demands on statistics or signal-to-noise ratio, especially in the case of solid and big molecule samples in chemistry and biology. Although with the high-repetition rate lasers, such attosecond pulses in a pump-probe configuration are possible to achieve, until now, only a few such light sources have been demonstrated. Here, by shaping the driving laser to an annular beam, a 100 kHz attosecond pulse train (APT) is reported with the highest energy so far (51 pJ/shot) on target (269 pJ at generation) among the high-repetition rate systems (>10 kHz) in which the attosecond pulses were temporally characterized. The on-target pulse energy is maximized by reducing the losses from the reflections and filtering of the high harmonics, and an unprecedented 19% transmission rate from the generation point to the target position is achieved. At the same time, the probe beam is also annular and low loss of this beam is reached by using another holey mirror to combine with the APT. The advantages of using an annular beam to generate attosecond pulses with a high-average power laser are demonstrated experimentally and theoretically. The effect of nonlinear propagation in the generation medium on the annular-beam generation concept is also analyzed in detail.
Highlights
Since the first experimental realizations of an attosecond pulse train (APT) [1] and an isolated attosecond pulse (IAP) [2] at 1 kHz in 2001, attosecond pulses have been widely used to investigate electron dynamics in gases [3], liquids [4], and solids [5]
The reflected annular beam is used for attosecond pulse generation, while the transmitted central part serves as the probe beam for experiments and temporal characterization
As predicted by wave optics, if a holey mirror is placed at a proper position, the residual annular IR beam can be almost fully reflected and the harmonics can be transmitted through the central hole
Summary
Since the first experimental realizations of an attosecond pulse train (APT) [1] and an isolated attosecond pulse (IAP) [2] at 1 kHz in 2001, attosecond pulses have been widely used to investigate electron dynamics in gases [3], liquids [4], and solids [5]. One route is multipass high-harmonic generation (HHG) in a laser cavity or a resonant enhancement cavity [6]; in which cases, the lasers with a low pulse energy (nJ~μJ) and a very high repetition rate (>MHz) are used. Because the time necessary for data collection can be shortened, high repetition rate is beneficial in a wide range of experiments such as coherent diffraction imaging [11], transient absorption [12], and attosecond pump-probe spectroscopy [13]. It will enhance the scope of single-particle structural dynamics studies [14] and allows to investigate the newly emerged Schrödinger cat states using strong laser fields [15, 16]. Thanks to the continuous development of laser technology, high-repetition rate and high-average power lasers have become available, and Ultrafast Science
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