Abstract
The investigation of fundamental mechanisms taking place on a femtosecond time scale is enabled by ultrafast pulsed laser sources. Here, the control of pulse duration, center wavelength, and especially the carrier-envelope phase has been shown to be of essential importance for coherent control of high harmonic generation and attosecond physics and, more recently, also for electron photoemission from metallic nanostructures. In this paper we demonstrate the realization of a source of 2-cycle laser pulses tunable between 1.2 and 2.1 μm, and with intrinsic CEP stability. The latter is guaranteed by difference frequency generation between the output pulse trains of two noncollinear optical parametric amplifier stages that share the same CEP variations. The CEP stability is better than 50 mrad over 20 minutes, when averaging over 100 pulses. We demonstrate the good CEP stability by measuring kinetic energy spectra of photoemitted electrons from a single metal nanostructure and by observing a clear variation of the electron yield with the CEP.
Highlights
Ultrafast pulsed laser sources are an important tool to directly observe fundamental processes taking place on a femtosecond time scale, such as for example the motion of electron wave packets during electronic excitation of atoms or molecules [1] or during chemical processes [2]
The approach is based on difference frequency generation (DFG) between the output of two Noncollinear optical parametric amplifiers (NOPAs), which are seeded by the same WL and share the same carrier-envelope phase (CEP)
By means of a reflective neutral density filter used as a 50:50 beam splitter (BS), the WL is split into two replicas, which serve as the seed light sources for the two NOPA stages
Summary
Ultrafast pulsed laser sources are an important tool to directly observe fundamental processes taking place on a femtosecond time scale, such as for example the motion of electron wave packets during electronic excitation of atoms or molecules [1] or during chemical processes [2]. Similar effects have been demonstrated for photoemission from metallic nanostructures: In the case of multiphoton ionization, CEP effects are ascribed to changing interferences of electron wave packets, which are emitted in subsequent cycles of the driving laser field [12], while in the case of strong-field electron emission the changing maximum field strength directly influences the electron motion [13]. The latter indicates control of electron motion via the laser field and may become an enabling step towards the generation and application of attosecond electron pulses.
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