## 4 Applications
### Attosecond Pulse Generation
In these experiments, a parallel and a perpendicular polarization configuration was explored for the two colors. In both cases, an XUV supercontinuum spectrum, extending above 100 eV, was measured. The lack of harmonics features in the HHG spectrum can be unequivocally attributed to a single burst of XUV emission with a potential attosecond duration. A similar approach, based on the superposition of two few-cycle CEP-stable mid-IR laser pulses with different wavelengths (1.35 \(\upmu\)m, 1.75 \(\upmu\)m), was successfully implemented [87; 88]. In 2012, a new scheme for IAPs generation was proposed, named attosecond lighthouse [89]. Experimental demonstrations were soon after performed [90; 91] by using 800-nm laser pulses. The attosecond lighthouse method is based on the selection of an IAP within the train of XUV bursts by imprinting each of them with a different propagation direction. This can be obtained by acting on the space-time properties of the driving pulse, specifically by rotating the wavefront. As a result, a different front angle can be associated with each half-cycle of the pulse. Attosecond bursts are thus emitted at different angles, and by spatially selecting a well-defined direction of propagation, IAPs can be obtained. Experimental evidence of IR-driven IAPs' generation were reported in 2015 by [PERSON] et al. [92] and [PERSON] et al. [93]. In both cases, 13-fs pulses at \(\sim\)1.8 \(\upmu\)m with an energy on the hundreds-\(\upmu\)J level were uses. The availability of a kHz repetition rate parametric system allowed [PERSON] and coworkers to detect an extremely broad XUV emission, up to the carbon K-edge (284 eV), potentially supporting 30-as pulse duration. As already said, a remarkable progress in isolated attosecond pulse generation in the long wavelength regime is provided by the work in [84]. Here, a complete temporal characterization of IAPs generated by means of few-cycle CEP-stable parametric pulses in the near-IR was reported for the first time. A 1-kHz OPCPA system delivering a 12.7-fs pulse at 1.7 \(\upmu\)m with an energy of 1.5 mJ was used. A fraction of the pulse energy, 570 \(\upmu\)m, was focused into a gas cell filled with Ar, and XUV emission was detected up to 100 eV. The high-energy part of the spectrum was selected ( 90 eV) by means of a Mo/Si mirror. Spectral selection led to the isolation of a single burst of XUV radiation. The attosecond streaking technique was then used for retrieving the amplitude and the phase of the IAP. For this characterization, the XUV pulse in combination with the co-propagating 1.7-\(\upmu\)m fundamental pulse is sent into a neon gas jet. The XUV pulse ionizes the target gas, generating a photoelectron wave packet, which is a replica of the XUV pulse. The photoelectron energy is modulated by the interaction with the IR streaking pulse. The photoelectron energy distribution is acquired by means of a time-of-flight spectrometer as a function of the delay between the two pulses. In such a away, a streaking map is obtained (Figure 11a) encoding information on the attosecond pulse temporal profile, as shown in Figure 11b. This experiment provided the first demonstration of photoelectron streaking measurement in the near-IR domain, opening the way towards ultrafast soft X-ray photoelectron spectroscopy.