Periodic femtosecond filamentation in birefringent media

Abstract

phenomenon of multiple refocusing [5]. Up to three peaks of on-axis luminescence intensity were observed when the authors of [6] focused a femtosecond laser pulse into an isotropic fused silica sample with a high-NA objective. Multiple irregular refocusing of tightly focused femtosecond laser pulse, with the distance between the refocusing maxima varying from 20 to 40 μm, was observed inside fused silica in [7]. The phenomenon was associated with the focal spot extension along the propagation axis due to the spherical aberration, induced by the air-sample interface. It was shown in [8] that filaments generated by pulsed Bessel beams form discrete equidistant damage spots in borosilicate glass. These discrete damage traces are attributed to the beating between the Bessel beam and the axial radiation. Regular focusing-refocusing events of similar nature were observed in [9] in barium fluoride crystal in the filaments, excited by axicon-formed femtosecond Bessel pulses.Several papers examined femtosecond filamentation in solid birefringent media, which are of great interest as structural materials for femtosecond lasers (see, e.g., [10][11][12][13][14][15]). A simplified case of the filament excitation only by ordinary or extraordinary ray was addressed in most of these studies.In this paper, we report on the observation of longitudinally periodic filamentation of femtosecond laser radiation in positive (n o < n e ; crystalline quartz) and negative (n o > n e ; sapphire) birefringent crystalline media in loose focusing conditions (NA = 0.02). We focus on little studied and unattainable in isotropic material peculiarities of the filamentation process, which are caused by spatial and temporal overlap of ordinary (o) and extraordinary (e) pulses inside the crystal. It is in this case the specificity of femtosecond filamentation in birefringent medium is shown in full. AbstractWe report on the experimental observation of periodic modulation of the axial luminescence intensity along the femtosecond filament track in sapphire and crystal quartz. The physical reason for the modulation is a cyclic transformation of the polarization state of the light pulse traveling in birefringent medium, caused by the phase raid between the ordinary and extraordinary rays, and different cross sections of multiphoton absorption for linear and circular polarizations.

Regular ‘breathing’ of a near-single-cycle light bullet in mid-IR filament

“…The periodic structures in Mid-IR filament observed in isotropic LiF have a quite another origin than those reported beforehand under an investigation of filamentation in different media. The observed behavior is opposite to a periodic filamentation of laser femtosecond pulses observed in recent experiments with birefringent crystals, which is caused by the periodic change in the polarization of the pulse travelling in birefringent medium in combination with the cross-sectional difference in multiphoton absorption for the linear and circular polarizations [22]. A period of a single filament structure in these experiments increased with the excitation pulse wavelength increasing in contrast to our measurements with isotropic crystal LiF.…”

“White Supercontinuum” and “Conical Emission” of Femtosecond Filaments in Birefringent Media

“…1. The same cycle repeats with a period of 101 m in sapphire and 90 m in quartz: as soon as the phase incursion between the ordinary and extraordinary rays becomes equal to 2 , where is an integer number [11]. Therefore, in what follows, we will discuss only the circular input polarization.…”

“…Similar researches can provide information about such slightly studied phenomena that accompany the filamentation as, e.g., the CE generation. A periodic filamentation phenomenon, which was experimentally observed in sapphire and crystalline quartz [11], became another new effect revealed in the recent years. The physical origin of the observed periodicity consists in the cyclic transformation of the polarization state of a light pulse at its propagation in a birefringent medium owing to the incursion of the phase difference between the ordinary and extraordinary rays.…”

Ultrashort Light Pulses in Transparent Solids: Propagation Peculiarities and Practical Applications

“…The temporal width of the autocorrelation function of compressed pulses, = 90 fs, is obtained, which corresponds to the 63-fs duration of the pulse at FWHM. It was shown that the physical cause for the temporal compression is the power dependence of the selffocusing distance, which is described by a Marburger formula [7]. Thus, the laser pulse compressed two and a half times was obtained.…”

“…Earlier, we recorded several spectacular phenomena accompanying the formation of fs filaments in transparent Kerr media such as the temporal self-compression of a fs pulse in filaments [3], phase-dependent repulsive and attractive interactions of two intersecting fs filaments [4][5][6], longitudinal periodicity, which appears in the luminescence of an axial plasma column of filaments in anisotropic crystal media [7].…”