Department of Laser and Light Engineering

This paper describes a prototype of the authors own design used to measure the relative inclinations of engineering objects and inanimate nature phenomena. A set of measurements can be used to determine ground surface deformation caused by mining activities or due to influences of hydro-geological, geotechnical or construction. The instrument was built with elements of the optoelectronic technique. Fiber optic, CCD camera and semiconductor laser are the basic building blocks of the device. The elaborated device runs on a Central Registration and Data Processing (CRPD) System. The deflection of freely suspended fiber are recorded by a CCD camera and next are transmitted to an external recorder (eg. notebook). Natural light or laser light was introduced into the fiber. The length of the fiber and the optical construction affects the measuring range of the device. The accuracy of instruments depends on: method of fiber suspension, method of fiber attenuation fluctuations, resolution CCD camera and identification method of the image laser spot recorded. Experiments have shown that the built prototype device is able to obtain a submillimetre accuracy.

Volume chirped Bragg gratings (volume CBG) recording optical scheme is implemented and calculated. Chirped gratings are recorded in photo-thermo-refractive (PTR) glass and can be used in near-infrared (near-IR) spectral range. The set of elements of optical scheme is optimized in order to realize recording of chirped Bragg gratings with various characteristics using limited set of elements. 1. Introduction Currently, holographic optical elements (HOE) play an increasing role in a various fields of science and technology connected with managing and/or conversion of optical radiation. In the first place it is due to progress in creation and development of holographic media. Thus, volume holographic media are of great demand for production of spectral and spatial selectors, combiners/decombiners of optical beams, narrow-band optical filters, Bragg mirrors for increasing of spectral radiance and thermal stabilization of emission wavelength of semiconductor lasers [1, 2]. Physical properties of bulk crystalline and glass holographic materials enable recording of chirped Bragg grating (CBG) within them. Chirped grating is a volume 3-D hologram with its period variation along the direction of the beam propagation (along the grating vector). In this grating Bragg condition for different wavelengths of incident radiation is occurred at appropriate depth inside the grating. The main functions of chirped grating are stretching of ultra-short laser pulse in time to amplify it (spectral chirp acquisition) and subsequent pulse compression to duration close to initial one. Stretched pulses have lower power density and can be amplified without damage of elements of amplifying system. This technique called chirped pulse amplification (CPA) was proposed in [3]. Initially, pulse stretching and compression in CPA systems were carried out almost exclusively by pairs of surface diffraction gratings [4, 5]. But such stretchers and compressors are bulky, difficult to align, and sensitive to vibrations. An important advancement in the development of CPA systems was made by the use of fiber-chirped Bragg gratings [6, 7]. Their use enabled creation of much more simple and flexible schemes. But limited aperture of chirped fiber Bragg gratings lead to limitations on the peak power achievable with fiber-based pulse compressors. To increase the peak power of stretched/compressed laser pulses the use of volume chirped Bragg gratings (volume CBG) was proposed [8]. The sufficient progress in formation and implementation of volume CBGs is strongly connected with the development of a new bulk holographic material-photo-thermo-refractive (PTR) glass, which enables recording of high-efficient volume holograms [9

Analytical consideration of the problem of optimization of laser radiation focusing systems in order to obtain maximum power density has been carried out. Explicit expressions are obtained for the optimal focal length of systems in the presence of spherical aberration and for permissible values of astigmatism and coma. The effect of laser beam characteristics and lens parameters on the maximum power density achievable in focusing is discussed in the example of a thin lenses. The results of analytical evaluations were compared with the results of direct numerical calculations.

Analytical consideration of the problem of aberrations of spherical mirrors and thin lenses was carried out for the case of their conversion of laser beams of ring cross-section. Explicit expressions for the Strel number of the converted beam are obtained in the presence of spherical aberration, astigmatism and coma. The results of analytical evaluations were compared with the results of direct numerical calculations. The range of applicability of the obtained formulas is defined. The relationship between the Strel number and angular divergence of radiation in the presence of said aberrations was analyzed.

This paper analyzes the features of the limitation of light beams in telescope systems in which the distortions of the primary mirror are compensated by holographic methods. Explicit expressions are obtained for the maximum possible field of view of such systems and for the maximum possible range of compensatable distortions. The optimum parameters of the telescope from the viewpoint of vignetting are determined.

A scheme for constructing a search optical-electronic system designed to detect and determine the movement parameters of low-luminous moving objects on a stationary background is proposed. The main properties of the system are considered. The results of calculating the main parameters of the system located on the Earth's surface for the case of searching for "space debris"are presented.

The possibility of compensating for small-scale wave-front distortions using a spatial light modulator which is optically controlled by the output beam of a Zernicke interferometer was studied theoretically. The optimal parameters of the system, requirements of its elements, the range of the compensated distortions, and the compensation quality are determined for the case of compensation for sinusoidal distortions. It is shown that this technique allows for the compensation of small-scale sinusoidal phase distortions with a depth of up to 3λ and a 20-fold gain in the Strehl number can be achieved.

The possibility of phasing a large number of subapertures with a spatial light modulator optically addressed by the output beam of a Zernike interferometer is investigated theoretically. The optimum parameters of the system, the requirements for its elements, the range of compensated distortions upon phasing, and the phasing quality are determined. It is demonstrated that the proposed technique allows one to compensate effectively for the wavefront distortions of the piston difference, the tilt, and the curvature type with a total depth of the phase relief up to 8λ. In this case, it is possible to obtain a beam with a Strehl ratio larger than 0.8.

The possibility of compensating small-scale wavefront distortions in an optical feedback scheme by using a spatial light modulator optically addressed by the output beam of a Zernike cell is theoretically considered. The optimal parameters of the system for compensating sinusoidal distortions and distortions characteristic of phasing of subapertures, the requirements for the elements of the system, the range of compensated distortions, and the quality of compensation are determined. It is shown that the use of this method makes it possible to compensate small-scale phase distortions with a peak-to-peak amplitude of up to 3λ; in this case, the gain in the Strehl number can be as high as 80.

Shear interferometric and shadow methods can be applied for the small-scale gas flows structure study, including turbulence characteristics. Shear interference and shadow patternsare often used to visualize the gas flow at small shear values and withmaximum possible fringe width. Neverthelessmentioned patterns intensity spatial modulationcontains various information especially about the flow statistical characteristics. This paper analyzeddifferences between the information contained in shear interferograms and shadow patterns. Mentioned difference is illustrated by modeling experimental data

For a projection objective of a lithographic setup designed for the wavelength range λ = 13 nm, optical distortions of its mirror components should not exceed a value of about 1 nm. The fabrication of mirrors of such an optical quality is very expensive. We have studied the possibility of using the thermal deformation of an optical element to improve the quality of its surface shape. It is shown, in particular, that, with this method, quasistatic large-scale (no smaller than 20% of the element diameter) optical distortions with an amplitude of about 15 nm can be compensated with an error up to 0.5 nm, that is, λ/20–λ/30.

For a projection objective of a lithographic setup designed for the wavelength range λ = 13 nm, optical distortions of its mirror components should not exceed a value of about 1 nm. The fabrication of mirrors of such an optical quality is very expensive. We have studied the possibility of using the thermal deformation of an optical element to improve the quality of its surface shape. It is shown, in particular, that, with this method, quasistatic large-scale (no smaller than 20% of the element diameter) optical distortions with an amplitude of about 15 nm can be compensated with an error up to 0.5 nm, that is, λ /20-λ /30 .

The possibility of compensating for small-scale wave-front distortions using a spatial light modulator which is optically controlled by the output beam of a Zernicke interferometer was studied theoretically. The optimal parameters of the system, requirements of its elements, the range of the compensated distortions, and the compensation quality are determined for the case of compensation for sinusoidal distortions. It is shown that this technique allows for the compensation of small-scale sinusoidal phase distortions with a depth of up to 3λ and a 20-fold gain in the Strehl number can be achieved.

Analytical consideration of the problem of optimization of laser radiation focusing systems in order to obtain maximum power density has been carried out. Explicit expressions are obtained for the optimal focal length of systems in the presence of spherical aberration and for permissible values of astigmatism and coma. The effect of laser beam characteristics and lens parameters on the maximum power density achievable in focusing is discussed in the example of a thin lenses. The results of analytical evaluations were compared with the results of direct numerical calculations.

This paper analyzes the features of the limitation of light beams in telescope systems in which the distortions of the primary mirror are compensated by holographic methods. Explicit expressions are obtained for the maximum possible field of view of such systems and for the maximum possible range of compensatable distortions. The optimum parameters of the telescope from the viewpoint of vignetting are determined.

T h e G o n f a l o n I would like to start by saying that author of this writing this article is not one of those Leonardo fans who are looking for traces of his work everywhere. Indeed, my interest in Leonardo so far has mostly been limited to the demythologization of his reputation as a genius. One day I gave a lesson on the art of the young Perugino and I was explaining how an anonymous gonfalon found in a Franciscan convent in Farneto (fig. 1), near Perugia, which had previously been attributed to the Umbrian painter Fiorenzo di Lorenzo, had been then, after a more careful analysis, attributed to Perugino. This was also because little attention had been paid to the youthful phase of this important painter. The painting had also been neglected because it was not an oil painting, but a gonfalon, that is, a banner to be used in processions or other religious ceremonies. The canvas represented a typical subject of Umbrian art of that period, a Pietà. This theme was made famous by Michelangelo, but it has an origin that has little to do with the Florentine tradition. Pietà is a Nordic theme, used in particular in Germany, where wooden statues with sorrowful Virgin mourning the dead Christ were called Vesperbild (literally, "evening images"). In Perugia there are other samples of this subject, for example, we find two in which the theme of pietà turns into a sort of triptych, as two saints are added to the sides. In one case we find St. Jerome and St. Leonardo, and in the other instead, we find St. John and Magdalene. This combination of saints is significant because in the banner we find Leonardo and the Gonfalon of Piety: A Contribution to the Attribution Theory 110 St. Jerome and the Magdalene, placed in the same positions, that is, he on the left and she on the right of Christ. It, therefore, seems that the banner can be placed in this series, probably between the first and the second. All this suggests an all-Umbrian work rooted in the Umbrian cultural context of that period. The first attribution to Fiorenzo di Lorenzo, established at the end of the nineteenth century ＊ 1 , was mainly based on the comparison with another series of anonymous paintings, which deals with the Stories of St. Bernardino. This series shows undeniable influences from Urbino, highlighted by the predominance of architecture and the rigidity of the drapery. However, another circumstance must also be taken into account. In that period after the many studies on Tuscan and Venetian art, the discourse on Renaissance art recently rediscovered (the very concept of Renaissance is a few years earlier and is still confused in Italy with that of Risorgimento), we went expanding on hitherto neglected realities such as the so-called "Umbrian school". In other words, the Umbrian school was a new classifying container that needed to be filled, going beyond Piero della Francesca and Perugino. So, although only 3 certain works remain of Fiorenzo, it was assumed that he was the author of the Stories of St. Bernardino. Then, given that the Gonfalon had evident similarities in the drapery with the Stories, it was consequently thought that it was the work of Fiorenzo. If, however, the draperies of the Gonfalon show similarities with those of the Stories, they do not show significant ones with the certain works of Fiorenzo. In the end, the scholars came to the conclusion that not even the Stories were the work of Fiorenzo, or not only of Fiorenzo but of a group of Umbrian artists, among whom there must also have been Perugino. The only assonances between Gonfalon and Fiorenzo's works are found in the way of performing the hands and in the way in which the face of the Virgin is treated. This may suggest two things: that Fiorenzo intervened in the Gonfalon or that Perugino, even though he was a pupil of Bonfigli, had also worked with Fiorenzo since in a small city like Perugia (then of about 20,000 inhabitants) there wasn't a real division of workshops and the painters of different workshops all formed a large family. So the reasoning of the previous historians stopped at comparisons in the local area, which find partial confirmation in the drapery and then in the hands and face of the Madonna. However, all the other elements remain to be explained.

Analytical consideration of the problem of aberrations of spherical mirrors and thin lenses was carried out for the case of their conversion of laser beams of ring cross-section. Explicit expressions for the Strel number of the converted beam are obtained in the presence of spherical aberration, astigmatism and coma. The results of analytical evaluations were compared with the results of direct numerical calculations. The range of applicability of the obtained formulas is defined. The relationship between the Strel number and angular divergence of radiation in the presence of said aberrations was analyzed.

Shear interferometric and shadow methods can be app lied for the small-scale gas flows structure study, including turbulence characteristics. Shear interfe r nce and shadow patternsare often used to visualiz e the gas flow at small shear values and withmaximum possible fringe width. Neverthelessmentioned patterns inten si y spatial modulationcontains various information espe cially about the flow statistical characteristics. This paper analyzeddifferences between the information contain ed i shear interferograms and shadow patterns. Men tioned difference is illustrated by modeling experimental d ta