Research on isolated attosecond pulses (IAPs) based on high-order harmonic generation changed substantially around 2010. Before then, the Ti:sapphire laser was the de facto standard as the driving ...light source, so the cutoff energy was limited to ~100 eV. After 2010, the mid-infrared optical parametric amplifier became the mainstream driving source. The shortest pulse width of an IAP has reached ~50 as, an intensity over a gigawatt has been achieved, and the photon energy has been extended to 500 eV. However, owing to the low flux of IAPs, the use of IAPs is still limited in terms of applications. Here we focus on the vigorous efforts in the past decade to extend the performance of IAPs.Recent progress of table-top isolated attosecond light sources is reviewed with a focus on the related technologies for high-average-flux and high-peak-intensity attosecond bursts of light. An outlook on its applications is also provided.
Abstract
Few–cycle short–wave infrared (SWIR) pulses are useful tools for research on strong–field physics and nonlinear optics. Here we demonstrate the amplification of sub–cycle pulses in the SWIR ...region by using a cascaded BBO–based optical parametric amplifier (OPA) chain. By virtue of the tailored wavelength of the pump pulse of 708 nm, we successfully obtained a gain bandwidth of more than one octave for a BBO crystal. The division and synthesis of the spectral components of the pulse in a Mach–Zehnder–type interferometer set in front of the final amplifier enabled us to control the dispersion of each spectral component using an acousto–optic programmable dispersive filter inserted in each arm of the interferometer. As a result, we successfully generated 0.73–optical–cycle pulses at 1.8
μ
m with a pulse energy of 32
μ
J.
Since the first observation of high-order harmonics about two decades ago, research on high-order harmonic generation (HHG) has progressed while changing its focus. In its infancy, a major concern of ...research was to understand the underlying physics of HHG, then interest shifted to the development of a coherent source in the soft X-ray region. Research is now focused on attosecond science. Because HHG is based on tunneling ionization followed by radiative recombination during a single optical cycle of the fundamental excitation pulse, it can manifest itself as a variety of interesting phenomena caused by the interaction of light waves with electrons on the attosecond time scale. Therefore, HHG is a unique phenomenon that provides us with a method of observing attosecond quantum dynamics in atoms and molecules as well as with a unique coherent source covering a spectrum spanning several tens of octaves from ultraviolet to the soft X-ray region. In this report, I review the recent progress in attosecond pulse generation by HHG and its application to observing attosecond dynamics in atoms and molecules while focusing on our recent works.
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.
Femtosecond lasers have unique characteristics of ultrashort pulse width and extremely high peak intensity; however, one of the most important features of femtosecond laser processing is that strong ...absorption can be induced only at the focus position inside transparent materials due to nonlinear multiphoton absorption. This exclusive feature makes it possible to directly fabricate three-dimensional (3D) microfluidic devices in glass microchips by two methods: 3D internal modification using direct femtosecond laser writing followed by chemical wet etching (femtosecond laser-assisted etching, FLAE) and direct ablation of glass in water (water-assisted femtosecond laser drilling, WAFLD). Direct femtosecond laser writing also enables the integration of micromechanical, microelectronic, and microoptical components into the 3D microfluidic devices without stacking or bonding substrates. This paper gives a comprehensive review on the state-of-the-art femtosecond laser 3D micromachining for the fabrication of microfluidic, optofluidic, and electrofluidic devices. A new strategy (hybrid femtosecond laser processing) is also presented, in which FLAE is combined with femtosecond laser two-photon polymerization to realize a new type of biochip termed the ship-in-a-bottle biochip.
Femtosecond laser micromachining can directly fabricate three-dimensional (3D) microfluidic devices integrated with functional microcomponents in glass microchips.
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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