Below is a sampler of my previous research work <\/p>\n\n\n\n
\nFor about a decade, the nonlinear optics community has been investigating the phenomenon\nof ultrashort pulses which can propagate in nonlinear media for distances that are\nmuch longer than expected based on their beam diameters.\nIn Phys. Rev. Lett. 92 (2004) 253901, we identified a general mechanism responsible\nfor the long-distance propagation in optical filaments in condensed media. This is based on\nthe notion of dynamic X-waves, which constitute a class of wavepackets that are localized\nand are resistant to dispersion spreading and diffraction.\n<\/p>\n\n\n\n
\nThe self-focusing instability in high-power, wide-beam pulses leads to the formation\nof multiple high-intensity spots, or filaments in the transverse cross-section of the beam.\nDepending on conditions, filamentation can persist for hundreds of meters. The mechanism\nthat keeps the beam from falling appart is based on continuous energy exchange\nbetween the individual filaments and a low-intensity background that plays the role of an\nenergy reservoir.\nThis scenario was for the first time described in our work in Phys. Rev. Lett. 83 (1999)\n2938, and it was the simulation that made this result possible. This often cited work \nwas a crucial contribution to the current understanding of high-power optical filamentation \n(also called light-string formation) in gases.\n<\/p>\n\n\n\n
\nSupercontinuum generation is a fascinating nonlinear phenomenon in which the spectrum\nof a light pulse explosively broadens to span the whole visible spectrum. Because of\nits many applications, it has been studied for several decades. Yet, new insights continue\nto appear in the literature. In a series of theoretic and simulation works [e.g. Appl. Phys.\nB 85 (2006) 531, Phys. Rev. Lett. 91 (2003) 043905, Appl. Phys. B 77 (2003) 185 ],\nwe studied supercontinuum generation in bulk media. In a simulated experiment we demonstrated\nthat “the old explanation” cannot be correct, and have shown that the shape and extent of the \nsupercontinuum spectrum, as well as its dependence on the material band-gap, are all tightly \nrelated to the linear chromatic dispersion of the medium.\n<\/p>\n\n\n\n
\nThird harmonic generation by intense light pulses in gases has been creating a lot of\ninterest, both for its applications and the underlying physics. We have published a work\n[ Appl. Phys. B 85 (2006) 531. ] that for the first time revealed the common principles\nthat govern the production of both the supercontinuum and of the third-harmonic radiation.\n<\/p>\n\n\n\n
\nFor remote sensing applications, it is desirable to be able to deliver high-intensity light\nto the target over long distance. Optical filamentation in high-power pulses has already\nbeen proven to be a feasible approach. However, since the filamentation is driven by several\nnonlinear effects, the accurate control remains a problem. Recently, several avenues\nhas been studied for efficient control of filamentation in high-power optical pulses. However,\ntruly long-distance control is so far possible only with very high-power pulses. I have\nproposed a new approach [ Opt. Lett. 32 (2007) 2753] that allows to control the filamentation,\nplasma formation, and supercontinuum generation at a precisely chosen distance\nwhile using low-energy pulses. This method should open new possibilities in remote sensing\napplications.\n<\/p>\n\n\n\n
\nA great deal of the work mentioned above was enabled by our\nUnidirectional Pulse Propagation Equation (UPPE) solver [ Phys. Rev. Lett. 89\n(2002) 283902, Phys. Rev. E 70 (2004) 036604 ]. This equation bridges, in a transparent\nand consistent manner, the gap between the Maxwell`s equations on one hand and various\nenvelope equations widely used in nonlinear pulse simulations on the other. UPPE\nmakes it possible to perform calculations that are not feasible on the Maxwell solver level\n(due to resolution, memory, and time constraints), and at the same time it consistently\nsolves the problem of corrections to the nonlinear Schroedinger equations. In fact, every\npulse propagation equation found in the nonlinear optics literature can be obtained as an\napproximation from the UPPE. We used the UPPE solver to predict universal\nstructures in the angularly resolved supercontinuum spectra [Phys. Rev. Lett. 92 (2004)\n253901 ] before they were observed experimentally, and to improve our understanding\nof femtosecond pulse filamentation in general.\n<\/p>\n\n\n\n
\nPower scaling in semiconductor lasers by designing the active structure area larger and\nlarger is hampered by the inherent tendency of such lasers to filamentation and temporal\ninstability. Lot of effort goes into understanding the dynamics of semiconductor lasers.\nFrom a simulation point of view, this is a class of lasers extremely difficult to model in\na realistic way. The origin of this problem is the strong frequency and carrier-density\ndependence of the real and imaginary parts of the semiconductor gain. I have developed\na method capable of truly realistic simulation of broad-area semiconductor lasers\n[IEEE J. Quantum Electronics, 37 (2001) 936]. The approach, based on the use of multiple\ndigital filters, is highly unconventional from the point of view of numerical solution of\npartial differential equations. It is fair to say that at present it is the only method available\nthat can both perform simulations over long times and correctly capture the extremely wide\nbandwidth and the fast dynamics in these lasers.\n<\/p>\n\n\n\n
\nVertical external cavity semiconductor lasers (VECSEL) are a relatively new member\nof the semiconductor laser family. Of special interest is the high-power, high repetition\nrate, ultrashort pulse generation in VECSELs. It has been investigated intensively both\nexperimentally and theoretically. However, the current models can not be trusted completely\nbecause they fail to capture accurately the frequency dependent response of the\nactive structure. I have proposed a new model [ IEEE J. Quantum Electron. 43 (2007)\n588. ] for VECSELs that allows to build a simulator for a given active structure design,\nand captures its properties accurately over wide ranges of wavelength, temperature and\ncarrier density.\n<\/p>\n\n\n\n
\nOptical damage and degradation in semiconductor lasers is a difficult obstacle for\nbuilding affordable high-power light sources. This difficulty is related to the filamentation\ninstability in high-power lasers. Using methods developed a few years earlier [IEEE J.\nQuantum Electronics, 37 (2001) 936], we have characterized the intensity fluctuations in\nthe broad-area semiconductor lasers. It turns out that the semiconductor laser\nintensity must be viewed as a stochastic quantity since it displays a very broad probability\ndistribution. Quite surprisingly, the fluctuation statistics turns out to be universal, independent\nof the details of the active laser structure. This has consequences for estimating\nthe threshold for the catastrophic optical damage in high-power semiconductor lasers:\nNamely, it turns out that a naive estimate would be an order of magnitude too optimistic!\n<\/p>\n\n\n\n
\nBecause moving interfaces are ubiquitous in nature, their\ndetailed understanding is important for several sciences. In a series of works \nwith Per Rikvold [e.g. PRB 76 (2007) 045422, PRB 73 (2006) 045437, PRE 67 (2003) 066113, \nJ. Phys. A, 35 (2002) L117, PRE 66 (2002) 066116, J. Stat. Phys. 100 (2000), 377 ], \nwe studied a class of moving boundaries subject to microscopic local dynamics of various types. \nContrary to the common belief that any local microscopic dynamics satisfying detailed balance ensures\nnot only proper equilibrium but also the correct evolution, we have demonstrated that the\ninterface dynamics is in general not universal with respect to the details of the underlying\nlocal dynamics. This result means that a whole class of dynamic Monte Carlo simulations\nmight not give realistic results unless it uses correct, first-principles-derived microscopic\ndynamics.\n<\/p>\n\n\n\n
\nIn collaboration with Mark Novotny and Per Rikvold, we investigated different regimes\nof magnetization switching in nanoparticles, the role of disorder, boundaries and growth\nmorphology [e.g. Phys. Rev. B 56 (1997) 11791, Phys. Rev. B 55 (1997) 11521 ].\nExtremely long-lived states in these systems motivated our introduction of a new dynamic\nMonte-Carlo based method [Phys. Rev. Lett. 80 (1998) 3384] capable of simulating\nmetastable systems with exceedingly slow decay.\n<\/p>\n","protected":false},"excerpt":{"rendered":"
Below is a sampler of my previous research work Nonlinear optics of ultrashort pulses Dynamic X-waves in femtosecond pulses: For about a decade, the nonlinear optics community has been investigating the phenomenon of ultrashort pulses which can propagate in nonlinear media for distances that are much longer than expected based on their beam diameters. In Phys. Rev. Lett. 92 (2004)<\/p>\n","protected":false},"author":99,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-9","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/pages\/9","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/users\/99"}],"replies":[{"embeddable":true,"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/comments?post=9"}],"version-history":[{"count":6,"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/pages\/9\/revisions"}],"predecessor-version":[{"id":63,"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/pages\/9\/revisions\/63"}],"wp:attachment":[{"href":"https:\/\/wp.optics.arizona.edu\/kolesik\/wp-json\/wp\/v2\/media?parent=9"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}