High-energy isolated attosecond pulses required for the most intriguing nonlinear attosecond experiments as well as for attosecond-pump/attosecond-probe spectroscopy are still lacking at present. ...Here we propose and demonstrate a robust generation method of intense isolated attosecond pulses, which enable us to perform a nonlinear attosecond optics experiment. By combining a two-colour field synthesis and an energy-scaling method of high-order harmonic generation, the maximum pulse energy of the isolated attosecond pulse reaches as high as 1.3 μJ. The generated pulse with a duration of 500 as, as characterized by a nonlinear autocorrelation measurement, is the shortest and highest-energy pulse ever with the ability to induce nonlinear phenomena. The peak power of our tabletop light source reaches 2.6 GW, which even surpasses that of an extreme-ultraviolet free-electron laser.
We demonstrate high-energy infrared femtosecond pulse generation by a dual-chirped optical parametric amplification (DC-OPA) scheme Opt. Express19, 7190 (2011). By employing a 100 mJ pump laser, a ...signal pulse energy exceeding 20 mJ at a wavelength of 1.4 μm was achieved before dispersion compensation. A total output energy of 33 mJ was recorded. Under a further energy scaling condition, the signal pulse was compressed to an almost transform-limited duration of 27 fs using a fused silica prism compressor. Since the DC-OPA scheme is efficient and energy scalable, design parameters for obtaining 100 mJ level infrared pulses are presented, which are suitable as driver lasers for the energy scaling of high-order harmonic generation with sub-keV photon energy.
Expansion of the wavelength range for an ultrafast laser is an important ingredient for extending its range of applications. Conventionally, optical parametric amplification (OPA) has been employed ...to expand the laser wavelength to the infrared (IR) region. However, the achievable pulse energy and peak power have been limited to the mJ and the GW level, respectively. A major difficulty in the further energy scaling of OPA results from a lack of suitable large nonlinear crystals. Here, we circumvent this difficulty by employing a dual-chirped optical parametric amplification (DC-OPA) scheme. We successfully generate a multi-TW IR femtosecond laser pulse with an energy of 100 mJ order, which is higher than that reported in previous works. We also obtain excellent energy scaling ability, ultrashort pulses, flexiable wavelength tunability, and high-energy stability, which prove that DC-OPA is a superior method for the energy scaling of IR pulses to the 10 J/PW level.
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We demonstrate the generation of a coherent water window x ray by extending the plateau region of high-order harmonics under a neutral-medium condition. The maximum harmonic photon energies attained ...are 300 and 450 eV in Ne and He, respectively. Our proposed generation scheme, combining a 1.6 microm laser driver and a neutral Ne gas medium, is efficient and scalable in output yields of the water window x ray. Thus, the precept of the design parameter for a single-shot live-cell imaging by contact microscopy is presented.
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We propose and demonstrate the generation of a continuum high-order harmonic spectrum by mixing multicycle two-color (TC) laser fields with the aim of obtaining an intense isolated attosecond pulse. ...By optimizing the wavelength of a supplementary infrared pulse in a TC field, a continuum harmonic spectrum was created around the cutoff region without carrier-envelope phase stabilization. The obtained harmonic spectra clearly show the possibility of generating isolated attosecond pulses from a multicycle TC laser field, which is generated by an 800 nm, 30 fs pulse mixed with a 1300 nm, 40 fs pulse. Our proposed method enables us not only to relax the requirements for the pump pulse duration but also to reduce ionization of the harmonic medium. This concept opens the door to create an intense isolated attosecond pulse using a conventional femtosecond laser system.
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The control of the electronic states of a hydrogen molecular ion by photoexcitation is considerably difficult because it requires multiple sub-10 fs light pulses in the extreme ultraviolet (XUV) ...wavelength region with a sufficiently high intensity. Here, we demonstrate the control of the dissociation pathway originating from the 2pσu electronic state against that originating from the 2pπu electronic state in a hydrogen molecular ion by using a pair of attosecond pulse trains in the XUV wavelength region with a train-envelope duration of ∼4 fs. The switching time from the peak to the valley in the oscillation caused by the vibrational wavepacket motion in the 1sσg ground electronic state is only 8 fs. This result can be classified as the fastest control, to the best of our knowledge, of a molecular reaction in the simplest molecule on the basis of the XUV-pump and XUV-probe scheme.
High-energy infrared (IR) femtosecond laser sources are important for applications in ultrafast and strong-field laser science; thus, considerable effort has recently been made to develop such laser ...systems. In this paper, we review our recent work on developing TW-class mid-infrared (MIR) femtosecond laser pulses in the 1-4 <inline-formula><tex-math notation="LaTeX">\mu</tex-math></inline-formula>m region using a dual-chirped optical parametric amplification (DC-OPA) method. By employing a Ti:sapphire laser with sub-joule energy to pump the DC-OPA system, MIR femtosecond pulses with 100-mJ-class energy are demonstrated. Efficient energy scalability and flexible wavelength tunability in DC-OPA are confirmed experimentally. Different features of DC-OPA from those of conventional OPA and narrow-band pumped optical parametric chirped pulse amplification (OPCPA) are observed. By precisely optimizing the chirps of the seed and pump pulses in the DC-OPA system, bandwidth narrowing of amplified pulses can be minimized in an energy-scaling strategy. Moreover, DC-OPA can be universally employed for the energy scaling of near-IR, MIR, and far-IR pulses, regardless of the type of nonlinear crystal, and is helpful for efficiently generating few-cycle carrier-envelope phase stable IR pulses with TW-class peak power.
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