A Simple and “Green” Technique to Synthesize Metal Nanocolloids by Ultrashort Light Pulses

In this chapter Ag, Ni and Fe nanocolloids synthesized by “green” ultrashort pulse laser ablation of solid metal targets using different pulse energies and liquid media are characterized by different techniques. Optical extinction spectroscopy (OES), micro-Raman spectroscopy (MRS), transmission electron microscopy (TEM) and electron diffraction (ED) were independently used to analyze optical, morphological and compositional properties of the generated nanocolloids. In a deeper way, the stability characteristics of Ag nanocolloids in aqueous solutions with different stabilizers were studied owing to their potential use in biocompatible compounds. Besides, due to their interesting applications, few atoms Ag nanoclusters (NCs) were synthesized using the same ablation technique, analyzing their fluorescent and photocatalytic properties. On the other hand, to expand the characterization of the nanocolloids, their magnetic behavior was inspected for the Ni and Fe by vibrating sample magnetometry (VSM).

Coherent modulation of the electron temperature and electron–phonon couplings in a 2D material

Ultrashort light pulses can selectively excite charges, spins, and phonons in materials, providing a powerful approach for manipulating their properties. Here we use femtosecond laser pulses to coherently manipulate the electron and phonon distributions, and their couplings, in the charge-density wave (CDW) material 1T-TaSe2. After exciting the material with a femtosecond pulse, fast spatial smearing of the laser-excited electrons launches a coherent lattice breathing mode, which in turn modulates the electron temperature. This finding is in contrast to all previous observations in multiple materials to date, where the electron temperature decreases monotonically via electron–phonon scattering. By tuning the laser fluence, the magnitude of the electron temperature modulation changes from ∼200 K in the case of weak excitation, to ∼1,000 K for strong laser excitation. We also observe a phase change of π in the electron temperature modulation at a critical fluence of 0.7 mJ/cm2, which suggests a switching of the dominant coupling mechanism between the coherent phonon and electrons. Our approach opens up routes for coherently manipulating the interactions and properties of two-dimensional and other quantum materials using light.

Ultrafast acoustics for modulating matter / Bayer M.

Illumination of matter by intense ultrashort light pulses can lead to launching of coherent phonon pulses through the ultrafast thermal expansion. The duration of these pulses may be as short as a ps and their amplitude may reach one thousandth of a crystal lattice constant. This dynamic change of the lattice can vary the band gap of a semiconductor on corresponding time scales, which can be exploited to modulate light emitters on sub-THz frequencies. Further, in magnetic materials the acoustic pulses can be used to vary the magnetic anisotropy, by which a precession of the magnetization can be triggered. In suitably tailored structures, this precessing magnetization can serve as ultacompact source of microwave radiation with frequencies up to 100 GHz and more, by which high resolution magnetic resonance spectroscopy may be achieved. In this contribution we will discuss the basic principles of ultrafast acoustics of matter and gives examples of applications. The author acknowledges, among others, the long-lasting collaboration with Andrey Akimov (Nottingham), Alexey Scherbakov (St. Petersburg & Dortmund), and Dmitri Yakovlev (Dortmund & St. Pertersburg), without which the work would not have been possible

Ultrashort Light Pulses in Transparent Solids: Propagation Peculiarities and Practical Applications

The peculiarities of the femtosecond filamentation in Kerr media has been studied using a set of time-resoling experimental techniques. These include the temporal self-compression of a laser pulse in the filamentation mode, repulsive and attractive interactions of filaments, and influence of the birefringence on the filamentation. The propagation of femtosecond laser pulses at the 1550-nm wavelength in c-Si is studied for the first time using methods of time-resolved transmission microscopy. The nonlinear widening of the pulse spectrum due to the Kerr- and plasma-caused self-phase modulation is recorded.