We report on a new experimental technique aimed to investigate femtosecond filamentation process in transparent condensed dielectrics. The proposed method is based on a highly resolved shadow photography and wideband (about 100MHz) photoacoustic imaging. We demonstrate, that combination of these techniques allows conducting comprehensive filament investigation by retrieving the value of the energy deposition into a medium, plasma electron density and the size of the filament formation region. Moreover, applying these techniques we studied the dependence of filament properties on a filamentation regime.
This article addresses theoretical and numerical investigation of image formation in photoacoustic (PA) imaging with complex-shaped concave sensor arrays. The spatial resolution and the size of sensitivity region of PA and laser ultrasonic (LU) imaging systems are assessed using sensitivity maps and spatial resolution maps in the image plane. This paper also discusses the relationship between the size of high-sensitivity regions and the spatial resolution of real-time imaging systems utilizing toroidal arrays. It is shown that the use of arrays with toroidal geometry significantly improves the diagnostic capabilities of PA and LU imaging to investigate biological objects, rocks, and composite materials.
Spatio-spectral distribution of THz radiation generated by two-color femtosecond laser breakdown in air is investigated theoretically. The theoretical model is based on the fast oscillating light field propagation and self-consistent free electron generation process. We find that the THz emission spectrum has both the low-frequency component related to the transient photocurrent with the maximum spectral intensity at ~1 THz, and the high-frequency component at ~10 THz related to the nonlinear response of bound electrons.
We investigate the features of femtosecond laser pulses interaction with pure and dye-doped nematic liquid crystals. For femtosecond laser pulses interacting with dye-doped nematic liquid crystal we found the distinction between the efficiency of liquid crystal director reorientation in comparison to the continuous wave irradiation. The mechanisms responsible for such distinction associated with changes of intermolecular forces under two-photon
absorption and light induced changes of anchoring conditions are discussed.
We report here on experiments with surface plasmon excitation and propagation along corrugated and smooth aluminum surface in the terahertz frequency range. Plasmon excitation by a picosecond terahertz pulse is shown to be a transient process and plasmon propagation sufficiently changes its measured time profile. Plasmon duration and life-time were defined and plasmon propagation lengths on smooth and corrugated surface were measured. Plasmon propagation length on flat surface turned out to be much smaller than the Drude model predicts.
We present educational programs on nonlinear optics and laser physics in the ILC MSU. These programs are aimed on both full-t ime students of physics faculty and students of retraining courses. As a part of life-l ong learning we offer different types of programs ranging from short courses to one-y ear long retraining programs. These programs include lecture courses, practical work in the training laboratories, and graduate research work in the scientific labs under a supervision of an expert. Special attention will be paid to new tendencies in the educational activities at the ILC MSU: developing and using multimedia courses, short-range practical courses in adjacent fields, constantly developing university teaching laboratory on laser physics and optics.
International laser Center of Moscow State University offers teaching setups for undergraduate students and students of retraining courses who apply photonics, lasers, and optical communication methods in different fields. Each teaching task is targeted to make a student carry out a real experiment. Most of laboratory works are intended both for phenomena demonstration and for in-depth study of physical mechanisms. The developers of the laboratory works tried to link them to the concepts from other physics courses: quantum mechanics, electricity and magnetism, solid-state physics. Laboratory experience with lasers and photonics reinforces ideas learned in these courses.
The self-focusing of elliptically polarized gaussian beam in isotropic gyrotropic medium with spatial dispersion of nonlinearity has been investigated numerically. Along with the effects predictable by traditional self-focusing theories the new peculiarities of the self-focusing have been found which cannot be described in principle by the aberrationless approximation theory. The dynamics of the light beam cross-section polarization state distribution changes in a process of the beam propagation have been investigated.
We theoretically investigate in the aberrationless approximation the self-action of the elliptically polarized Gaussian pulse during its propagation in a thin dish with a nematic liquid crystal in the isotropic phase. Quadrature formulas are obtained to describe the time history of the intensity, the elliptisity degree and the rotation angle of the polarization ellipse of the output radiation at the different points of the beam cross-section. They are expressed in terms of the parameters describing two, essential near the temperature of the isotropic-nematic phase transition, mechanisms of the spatial nonlocality of the nonlinear medium optical response, and in terms of the other parameters, which describe the nematic liquid crystal and the elliptically polarized incident pulse. The former mechanism is specified by the medium heating due to light absorption; the latter is determined by the fluctuations of the nematic liquid crystal order parameter tensor near the temperature of the isotropic-nematic phase transition.
It is shown that for some values of temperature and of the nematic liquid crystal parameters the elliptical polarization of the incident pulse, which is constant at the entry of the thin dish, transforms into the linear or another different elliptical one at the exit and keeps this new state up to the pulse tail. The dependence of the ellipticity degree on time becomes significantly nonmonotonic and changes its sign in some cases. The nonlocality of the nonlinear medium optical response weakens these transformations.
Theoretical and experimental investigations of point spread function of focused 32 elements array transducer for laser optoacoustic (OA) tomography have been carried out. The elements were imposed in the radial plane of a cylindrical surface. Specially developed software was used for numerical modeling the problem of OA tomography.
Diode-pumped Q-switched Nd:YAG laser was employed for thermo-optical excitation of probe acoustic transients. The correspondence between numerically calculated and measured temporal profiles of acoustic transients detected by a single transducer over wide area around it focal zone was demonstrated. The maps of spatial sensitivity for transducers with aperture angles 30° and 60° were determined experimentally and theoretically. The possibility of localization of
the array sensitivity area at the beam waist in the plane perpendicular to the imaging plane has been shown. Back projection algorithm was employed for image reconstruction based on experimentally obtained OA transients from point sources located at different distances from the array. The size of the images allowed to determine transverse and longitudinal resolutions in the imaging plane.
The concept of teaching in optics and methodical problems of mathematical student's education are discussed. The fundamental knowledge on modern mathematics and of computer- based methods of investigations acquired by students at the first years allows our professors to represent the different branches of optics and photonics at the high scientific level. The methods of teaching have resulted from the more than thirty year's experience of work of the Chair of General Physics and Wave Processes staff of M. V. Lomonosov Moscow State University on training the mathematical students.
Development of laser physics has resulted in the fact that the limits of this field have fallen far beyond the scope of conventional physical optics and quantum radiophysics. At present laser physics has virtually transformed into 'optical physics' -- the field of fundamental and applied physics, which employs specific laser and -- more widely -- optical approaches in experimental and theoretical investigations. In the present report we outline the concept of teaching in optical physics and discuss methodical problems of education of students at the Department of General Physics and Wave Processes of the Physics Faculty and International Laser Center of the M. V. Lomonosov Moscow State University. The method of teaching in optical physics have resulted from the more than thirty years' experience of work of the Department staff on the training of contemporary highly skilled specialists.
The sum frequency generation from the surface of an isotropic gyrotropic medium is investigated in the reflection geometry for the plane elliptically polarized incident waves. Modified boundary conditions for the electro-magnetic field are employed, which are still correct if the spatial dispersion of the optical response of the medium is taken into account.
The concept of optical education of students in the Departments of Mathematics and Mechanics and in the Department of Computer Science and Cybernetics of Moscow State University is discussed. Methods of teaching of different aspects of optics in these departments are largely determined by a high mathematical training of students.
Based on studies of polarization-state-dependent self-action of a laser pulse in a nonlinear optically active liquid, a method is proposed for determining the possible difference of the orientational relaxation times of the intensity-dependent parts of the refractive indices for different circularly polarized waves.
The interest in nonlinear liqht reflection phenomena is caused by the fact
that they can give a unique information about crystals' surface properties In
this work we have used the boundary conditions on the surface of nonlinear media
with space dispersion (SD) obtained in. We have considered phenomenologically
polarization effects due to interaction of the two arbitrarily polarized waves
durinq both propagation and reflection from crystals of cubic, hexagonal and
tetraqonal crystal systems (the incident angles of light are supposed equal to
zero, and the crystal optical axis to be perpendicular to the boundary). 10 both
cases for media with weak gyrotropy four mechanisms of nonlinear optical rotation
(NLOR) and deformation (NLOD) of polarization ellipses have been determined. It has
been made )fl a first approximation with respect to the parameter of SD Jd/.
(here ci is a characteristic length of spatial non-locality ot response, ?*, is a
wavelength). The influence of linear qyrotrop>' and dissipation on the interaction
ha also been investigated. A nonlinear polarization spectroscopy scheme has been
suggested. This scheme allows one to distinqush between contributions of different
NLtJR and ILOD rnechansms irrespective of the crystal symmetry. The study of NLOR
and NLOD effects during the interaction of two elliptically poirized waves with
the medium is shown to give three or four as much spectroscopy information on the
cubic nonlinearity and )ts SD as in the case of application of a plane polarized
wave. Moreover the joint study of liqht polarization interaction during both
reflection and propagation of waves through the crystal is most effective. This is
connected with the fact that spectroscopy information received in experiments 'on
reflection' and 'on propagation' is complementary to a great degree
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