The delay between plasma initiation and femtosecond pulse propagation was established in the range of few tens of nanoseconds. Figure 2Experimental setup for harmonic generation in plasma plumes. FP: femtosecond selleckchem Enzastaurin probe pulse, HP: picosecond heating pulse, A: aperture, HHGC: high-order harmonic generation chamber, FM: focusing mirror, L: focusing lens, T: target, P: plasma, XUVS: extreme …The femtosecond pulses propagating in a direction orthogonal to that of the heating pulse were focused into the laser plasma using the reflective mirrors. The position of the focus with respect to the plasma area was chosen to maximize the harmonic signal, and the intensity of femtosecond pulses at the plasma area at these conditions was estimated to be in the range of 1014�C1015Wcm?2.

The harmonics were analyzed using the XUV spectrometers. The details of these setups and registration systems are presented in [6, 7] and will also be presented in this review. Now, once we briefly discussed the basics of harmonics generation in isotropic media and described the experimental schemes, let us consider some results of the HHG in various plasmas produced by laser ablation. Whilst the first stage of these successful studies was entirely focused on the improvements of harmonic yield from plasma, at the current stage of knowledge of the high-order nonlinear optical processes in ablation plume one can consider this method as a new tool for material science. Thus the search of the dual role of plasma HHG as a method for efficient coherent XUV light generation and of materials probing is a milestone of further developments in this field.

Below, we show new trends emerged during recent years, which demonstrate the attractiveness of this method. In this review, we discuss the realization of new ideas, which allowed further improvement of the HHG efficiency through harmonic generation in specially prepared plasmas and allowed the spectral and structural studies of matter through the plasma harmonic spectroscopy. We also present the current status of laser ablation induced high-order harmonic generation spectroscopy (LAIHOHGS) and show the perspectives in the developments of this filed. 2. New Trends in Plasma HHGPlasma HHG has become considerably mature during the last few years and continues to attract the growing attention of various laboratories worldwide.

Currently, the experimental studies of plasma HHG are carried out in Japan, Canada, India, Uzbekistan, USA, Ireland, Germany, Korea, France, Spain, and the United Kingdom. Below, the most recent developments and some fresh approaches, experimental schemes, and ideas are described, which could considerably push this field toward the dramatic Entinostat improvement of the output characteristics of harmonics and better understanding of the matter properties through the LAIHOHGS.