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SECOND HARMONIC GENERATION IN METAMATERIALS. Kasumova Rena J. Baku State University, Physics Department 2012. CONTENTS The theme of my speech is SHG in metamaterials. There will be considered the following issues. CONSTRUCTIONs of Metamaterial.
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SECOND HARMONIC GENERATION IN METAMATERIALS Kasumova Rena J. Baku State University, Physics Department 2012
CONTENTSThe theme of my speech is SHG in metamaterials. There will be considered the following issues CONSTRUCTIONs of Metamaterial Well-known optical conseptions in metamaterials Experimental confirmation of possibility of creatiNGmetamaterialS Phase effects AT Shg in a metamaterial CurrentState of THE Problem and prospects of development
Forty five years ago prof. of MPhTI V.G.Veselago put forward first the hypothesis on possibility of existence of materials with the negative refractive index. In them the • light waves should move in direction against ray spreading andamazingly behave. As to • lenses from these materials, they must possess the unique properties and record characteristics. In like materials • the laws and notions of linear and nonlinear optics on rays behavior in a medium get broken. However, refraction index of the substances known to that time was positive. For several years of intense searches Veselago had found no material with appropriate electromagnetic properties and his idea was well forgotten. They recollected it only in the beginning of the XXI c.! Only due to the recent achievements in the field of material study, namely technology and preparation of materials, Veselago’s idea has been revived. In 1997 the scientists from the Centre of Technology of Materials af. Marconi in England havedeveloped metamaterials which consist of macroscopic elements and disperse electromagnetic waves not in a way, any known substances do. • In perspective, the investigations on elaborations of metamaterials refractingvisible light are being carried out. The practical interest to metamaterials is connected by broad applications which may be realized with their development. List two of them : • creationof invisible objects and • optical lenses with improved resolving ability. • Veselago V.G., Usp. Fiz. Nauk, 1967, v.92, p.517
Constructions of Metamaterial The scientific groups have used the different constructions of periodical structures, for instance:
k1 kx kx S b 2) Refraction law , a k2
Experimental confirmationof possibility of creating metamaterialS The first experimental confirmation of possibility to create material with negative refractive index was received in 2000 in California University in San Diego (UCSD) for microwave diapason. Now, we’ll speak on experimental receiving metamaterials. The existence of media possessing the negative refraction in optical (more precisely, in IR) diapason was experimentally demonstrated. The materials with the negative refraction existing at present have high losses, however, recently there have been achieved an essential improvement of quality of these materials. Just this gives hope of receiving the transparent materials with negative refraction in future calls forth an expediency of carrying out the researches of their optical nonlinear properties. As elementary tiny bricks of metamaterial are to be much less than wavelength the researchers wave working with radiation of centimetre diapason and used the elements of size in some millimetre.(Similarly quantum electronics where at first was realized quantum generator - maser, and then was developed the laser) .
On this picture experimentally realized superlens is depicted. Superlens suggested by the authors presents a plate of silver Ag, separated from depicted object (small nanowires from chromium Cr) by layer of polymethyemetacrylate (PMMA) of thickness equal to plate thickness (~40nm). Over silver plate is covered by the layer of photoresist (PR), in which depiction is registered. Silver plate functions as material strengthening damping modes of high spatial harmonics on the account of resonance excitement of surface plasmons. In spite of modesty of the given value, note, that it is nevertheless, more than length of damping which for the dimension of details in 60nm, made up 11nm. Resolution of depiction in 60nm at wavelength of UV radiation of 365nm has been achieved. Superlens, flatparalllel plate Ag of thickness in 40nm, creates depiction of nanowires of chromium (diameter 60nm) in a layer of photoresist (PR). Fang N., Lee H., Sun C, Zhang X, 2005, Science, v.308, p.534
Phase Effects at Second-harmonic generation in a metamaterial
This effect can be explained by the fact that the metamaterial plays the role of a mirror reflecting the SH wave at the input to the metamaterial, i.e. the maximum efficiency of frequency conversion takes place at the input (not output) of the metamaterial.
Taking into account the reverse reaction of the SH wave on the phase of the fundamental-radiation leads to qualitatively new effects (not present in the CFA). Tagiev Z.H., Kasumova R.J., Gadjieva L.S. J. Rus. Las. Research. 2011, v. 32, 152. • First, the location of minima of the SH intensity depends on the pump intensity. • Second, with increase in the FW intensity the zeroes of the curves are shifted to the direction of greater values of mismatch, and the width of the curve for increases. This effect allows to use efficiently the materials with critical synchronism. • Third, with increase in the intensity of the FW, the central maximum of the curves decreases, but that of the lateral maxima increases.
From obtained expression (18) follows that in the metamaterial the phase velocity of the excitation wave and the refractive index of the medium depend on the pump intensity, i.e., the self-action effectof the light wave is observed.
In conclusion we’ll offer the table reflecting a modern state of the researches on metamaterials in the following scientific groups. As is seen, owing to the achievements in elaboration of metamaterials we have managed to come close to the visible diapason. So, Parduaye’s group has received a metamaterial which worked on a wavelength of 710 nanometers. CurrentState of affairs
Development stages Thus metallic nanowires are ideal source, as wavelength in excitement may reach 1-2nanometres. The research of such nanowirespresent the first perspective direction of studies in metamaterials. At present there are being elaborated three perspective directions. • Optical properties of metal are well depicted by the model of free electrons. Assume that light acts on a metal, i.e. variable electric field with frequency influences of a medium. That is, we sent electron in one side, but it moves to the opposite one. You might draw attention to that in optics metamaterials become more simple, if in VHF there are some spirals, then in optics there are fishnet or two little sticks. It is connected with that in optics we have negative response free of charge, as a property of metal. We have only to receive the negative magnetic response from our metals. Both in metals and optics the electric current is directed against the field. Metall in optics is all the same as inductance, but if to consider metallic particle, it behaves itself as inductance, the surrounding does as a capacity, and all this together makes up LC-a chain, and resonance in it –plasmonic resonance on metal. A wave will run along it. The length at wave running by chain is in no way connected with that of what length is linht, it is determined by geometry of a wire itself.
