Note that essential in orders

Note that essential (in 1–2 orders of magnitude) aberration reduction was a result of small complication of the () function. For > 0 is less than that for = 0, and as result, SCR 7 dispersion is decreased. For large angles when the dispersion becomes larger, the parameter ≠ 0 in () does not give any gain in aberration spot size. Thus, the method of two-dimensional potential building up for providing ideal focusing in a plane was studied. It was proposed a new kind of regularizing function (). In particular case, it reduces the system to well-known trans-axial one. It was investigated the field continuation to three-dimensional space by means of series (). The field calculated was applied to make correct trajectory analysis of the system. Dispersive properties of the field were studied. In some examples it was found that the system has transversal focusing for a set of start angles dependent on a form of () function.
Introduction The materials laser processing technologies based on the laser ablation are widely used in high-tech industry operations such as microprocessing and modification of parts and their surfaces, thin-film coatings [1,2]. As it was noted by the authors [1,2], an important aspect of the problems associated with laser ablation is the probabilistic nature of destruction processes. There are several reasons for this: random spatial distribution of absorbing defects, different characteristics of these defects leading to different threshold laser breakdown values, probabilistic nature of the birth of seed electrons which initiate the development of plasma avalanche ionization, and the close relationship between the breakdown threshold and laser interaction area size (size effect). Earlier works [3–6] were performed to study polymeric materials laser ablation under the action of high-energy pulsed laser radiation and to develop probabilistic methods for predicting the optical strength of such samples. This required a detailed study of the dynamics and mechanism of plasma generation during polymer laser ablative destruction in the range of laser pulse energy density up to 100 J/cm2. The aim of the present work is to study experimentally laser ablation threshold characteristics of some glass nanocomposites of different compositions, made by sol–gel technology [7], under the action of YAG–Nd laser pulsed radiation, and to study the dependence of these characteristics on the optical and physical properties of nanocomposites.
Experimental All the measurements were carried out on nanocomposite samples which were rectangular plates sized from 4 to 7 cm and produced of clear float glass coated with different oxides: a single layer of SiO2 or TiO2, two or three layers of SiO2, a double layer of SiO2 + TiO2. X-ray microphotographs of the first two and the last samples are shown in Fig. 1 as an example. For the experimental investigation of nanocomposite laser ablation, measuring the laser radiation threshold energy density was performed at which the breakdown of the sample surface started. Laboratory laser ablation apparatus was assembled on the basis of [3,5,6] experimental set-up and its structural scheme is shown in Fig. 2. The radiation source was a laser (1). YAG–Nd laser generated pulses with the wavelength of 1064 nm of two types:
Generation was produced in two modes of Q-switching and with different passive valves. The laser radiation was focused onto the nanocomposite surface by a special lens (4). The change in the laser pulse energy density in the range from 0.1 to 100 J/cm2 was achieved by selecting the focal length of the lens (4) and by weakening the radiation by calibrated neutral filters (2). The presence of the breakdown was recorded via the appearance the laser plasma glow which was recorded by the microspectrometer (7) (type FSD-8, production of GPI RAS) with the fiber input (6). To control the laser pulse energy and to sync all the laboratory set-up, the photodiode (10) with the optical filter (9) (type IRF-1) were used. The delay line (8) controlled by the computer was required to start the work of the spectrometer (7) relative to the laser pulse leading edge. The spectrometer (7) operation modes and the measurement results processing were also carried out by the computer.