Description
Tabletop high-harmonic generation (HHG) sources can provide coherent, ultrashort extreme-ultraviolet (EUV) pulses with direct relevance to nonlinear spectroscopy, attosecond science, and element-specific studies of condensed matter [1–3]. We present ongoing developments at the University of Porto towards an integrated platform for waveform-controlled high-harmonic generation and EUV nonlinear spectroscopy.
Our HHG beamline is being developed to generate EUV radiation in gas targets in the 45–72 eV photon-energy range, with linear or circular polarization and the possibility of applying a magnetic field at the sample. The source will be characterized under different generation conditions, including gas-target parameters, driving-pulse duration, and polarization. While the current source is based on multicycle driving pulses, the platform is being extended towards few-cycle and single-cycle, carrier-envelope-phase (CEP)-stabilized pulses, which have already been achieved in our lab [4], targeting the generation of isolated attosecond EUV pulses. In parallel, high-harmonic generation in solid targets will be investigated as a complementary route towards compact and robust EUV sources.
The generated EUV light will be used for ultrafast spectroscopies, in particular transient absorption spectroscopy (TAS) and EUV magnetic circular dichroism (MCD), with optical and THz excitation. A key component of the laboratory is a time-resolved magneto-optical pump-probe setup based on a Ti:sapphire amplifier and a state-of-the-art hollow-core-fiber/chirped-mirror compressor [4], delivering sub-5-fs CEP-stabilized pulses at the sample plane, characterized using the d-scan technique [5,6]. These few-cycle, CEP-stable pulses enable electric-field-sensitive excitation schemes and magneto-optical probing. In addition, broadband single-cycle THz pulses generated by two-color air-plasma filamentation, with polarization control currently being implemented, will be integrated for THz-pump/EUV-probe studies of ultrafast magnetic dynamics and strongly correlated materials.
References
[1] J. Li et al., Nat. Commun. 11, 2748 (2020).
[2] M. Chergui et al., Nat. Rev. Phys. 5, 578–596 (2023).
[3] J. Lloyd-Hughes et al., J. Phys.: Condens. Matter 33, 353001 (2021)
[4] F. Silva et al., Opt. Express 22, 10181-10191 (2014)
[5] M. Miranda et al., Opt. Express 20, 18732-18743 (2012)
[6] M. Miranda et al., Opt. Lett. 44, 191-194 (2019)
