Influence of self-focusing of ultrashort laser pulses on optical third-harmonic generation at interfaces

Barbano, E. C.; Zílio, Sérgio Carlos; Misoguti, Lino

doi:10.1364/ol.38.005165

Cited by 7 publications

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“…In the process of moving the excitation focal point from air into the glass slide, a strong TH signal was observed when the focal point is at the air/glass interface. This agrees with the previously reported strong THG at the interface between different materials [22,23]. No TH was measurable in the bulk of the glass due to the limitation of the coherence length with respect to the Gouy phase shift [24].…”

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confidence: 93%

“…Therefore, when the focus is moved away from the surface of the glass slide, the magnitude of this longitudinal component gradually diminishes, and is eventually suppressed completely when the focal point is deep inside the glass slide. It should be pointed out that no noticeable bulk SHG was observed inside the bulk glass in previous THG experiments in which glass slides were also excited by focused excitation fields [22,23]. This was due to the relatively small numerical aperture of the focusing objective lens used in those experiments, which resulted in a greatly reduced field gradient at the focal region, and thus much lower SHG efficiency inside the bulk [21].…”

mentioning

confidence: 84%

“…Both SHG in the two-beam scheme [8] and third-harmonic generation (THG) under focused field excitation [22] from BK7 glass have been previously studied, SHG based on a focused excitation field inside the bulk of a glass slide has not been reported. We first used a borosilicate glass cover slide as the sample, and the excitation beam was focused inside the bulk of the glass slide.…”

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Direct observation of bulk second-harmonic generation inside a glass slide with tightly focused optical fields

et al. 2016

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Bulk second-harmonic generation (SHG) inside glass slides is directly detected unambiguously without interference from surface contributions. This is enabled by tightly focused and highly localized ultrashort laser pulses. The theoretical calculations based on vector diffraction theory and the phenomenological model of SHG inside centrosymmetric materials agree well with the measured far-field SHG radiation patterns for different polarization states of the fundamental beam. The results indicate that the observed bulk SHG is predominantly related to the bulk parameter δ and originates from the three-dimensional field gradient in the focal region. DOI: 10.1103/PhysRevB.93.161109 Under the electric dipole approximation of light-matter interaction, second-harmonic generation (SHG) is usually considered forbidden in bulk centrosymmetric materials. Dipolar SHG is allowed through a surface contribution arising at the interface between centrosymmetric materials where centrosymmetry is broken [1,2]. However, when higher-order multipole interactions [3,4], such as magnetic-dipole and electric-quadrupole interactions, are taken into account, SHG can occur even inside bulk centrosymmetric materials, which was observed in several experiments [5][6][7][8]. When SHG is used as a surface or interface probe, it is essential to separate bulk contributions from the measured SH signal and verify that such multipolar contributions are actually negligible [9]. In addition, as suggested recently, strong multipole interactions may bypass the noncentrosymmetry requirement and promote applications of new nonlinear materials [10,11]. Therefore, a thorough understanding of the physical mechanisms behind bulk SHG from bulk centrosymmetric materials is fundamental for many practical applications utilizing SHG [12].Various attempts have been made to characterize surface and bulk contributions to SHG [7,8,13,14]. For example, the SHG based on two noncollinear fundamental beams [7,8] has been widely used to study surface and bulk contributions in a quantitative way. However, up to now, the separation of surface and bulk contributions is still known to be a fundamental difficulty in the field of SHG from centrosymmetric materials. Since two-beam overlap in a spatial region is usually several millimeters long [8], the excitation field is not highly localized. Furthermore, as the SH signal is often too weak to detect when the interaction volume is deep inside the bulk material, the excitation region is often chosen to be near the surface in order to maximize signal intensity [15]. Thus the surface dipolar response cannot be completely avoided, which often perturbs the bulk response. This contributes to the wide variation of results reported in the literature. So far, the mechanism of bulk SHG inside centrosymmetric materials still remains unclear.Bulk SHG has been previously observed in centrosymmetric gaseous materials [16,17] with focused laser pulses, where * Corresponding author: rhui@ku.edu SHG was attributed to the ponderomotive force cau...

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Direct observation of bulk second-harmonic generation inside a glass slide with tightly focused optical fields

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“…Source: BARBANO; ZILIO; MISOGUTI. 26 In Fig. 4.4 we present the normalized TH peaks generated at the entrance and exit interfaces.…”

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confidence: 99%

“…49 Third-Harmonic Generation at Optical Glasses Interfaces † Main results already published in Optics Letters. 26 …”

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Third-harmonic generation at interfaces with femtosecond pulses: self-focusing contribution and nonlinear microscopy

Barbano¹

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Nonlinear ellipse rotation measurements in optical thick samples

et al. 2015

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Influence of self-focusing of ultrashort laser pulses on optical third-harmonic generation at interfaces

Abstract: We report on the third-harmonic generation of femtosecond laser pulses at interfaces. We measured slabs of different types of optical glasses and demonstrated that the asymmetric intensity profile observed for a tightly focused beam can be explained by self-focusing effects.

Cited by 7 publications

References 16 publications

Direct observation of bulk second-harmonic generation inside a glass slide with tightly focused optical fields

Direct observation of bulk second-harmonic generation inside a glass slide with tightly focused optical fields

Third-harmonic generation at interfaces with femtosecond pulses: self-focusing contribution and nonlinear microscopy

Nonlinear ellipse rotation measurements in optical thick samples

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