Saturation of the All-Optical Kerr Effect

Brée, Carsten; Demircan, Ayhan; Steinmeyer, Günter

doi:10.1103/physrevlett.106.183902

Cited by 111 publications

(73 citation statements)

References 31 publications

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“…Specifically, lowest-order cascading comes from a phase-mismatched third-harmonic generation (THG) process, which we show generates an n 4 term that is negative and of significant strength. Similarly, cascading of HOKE terms gives contributions to subsequent orders of nonlinearity (n 6 ; n 8 ; …) with values comparable with recent experimental [1,2] and theoretical HOKE coefficients [15]. This implies that in the strong cascading limit, defined later, cascading may contribute significantly to the nonlinear dynamics.…”

supporting

confidence: 80%

Higher-order Kerr effect and harmonic cascading in gases

2012

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The higher-order Kerr effect (HOKE) has been recently advocated to explain measurements of the saturation of the nonlinear refractive index in gases. Here we show that cascaded third-harmonic generation results in an effective fifth order nonlinearity that is negative and significant. Higher-order harmonic cascading will also occur from the HOKE, and the cascading contributions may significantly modify the observed nonlinear index change. At lower wavelengths cascading increases the HOKE saturation intensity, while for longer wavelengths cascading will decrease the HOKE saturation intensity.Comment: Optics Letters, in pres

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supporting

confidence: 80%

Higher-order Kerr effect and harmonic cascading in gases

2012

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“…A higherorder Kerr effect would add terms of the form n 2m I m (t), where m > 1 [4]. No negative instantaneous phase is observed at any intensity in Ar or N 2 , nor do we see evidence of saturation [18], in disagreement with the results of Loriot et al [4]. A simulation of the phase shift expected using the coefficients reported in [4] is shown as a dashed line in Fig.…”

contrasting

confidence: 73%

“…One measurement [13] found that the electron density was two orders of magnitude higher than predicted by a calculation including higher-order nonlinearities, but agreed with a simulation based on plasma defocusing alone [5]. A physical mechanism for the saturation and negative response was proposed based on the nonlinear response near the threshold of ionization [17,18]. What is missing from this debate is a direct measurement of the nonlinearity that corroborates or refutes the intensity dependence observed by Loriot et al Here, we describe such a measurement in Ar and N 2 using spectral interferometry.…”

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confidence: 76%

Optical Nonlinearity in Ar andN2near the Ionization Threshold

et al. 2011

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We directly measure the nonlinear optical response in argon and nitrogen in a thin gas target to laser intensities near the ionization threshold. No instantaneous negative nonlinear refractive index is observed, nor is saturation, in contrast with a previous measurement [Loriot et al., Opt. Express 17, 13429 (2009)] and calculations [Brée et al., Phys. Rev. Lett. 106, 183902 (2011)]. In addition, we are able to cleanly separate the instantaneous and rotational components of the nonlinear response in nitrogen. In both Ar and N2, the peak instantaneous index response scales linearly with the laser intensity until the point of ionization, whereupon the response turns abruptly negative and ∼constant, consistent with plasma generation.The optical Kerr effect, the intensity-dependent refractive index experienced by an optical pulse in a transparent medium, plays an important role in phenomena from nonlinear propagation in optical fibers [1] to modelocking in pulsed lasers [2] to filamentary propagation in condensed media and the atmosphere [3]. A recent transient birefringence measurement in the components of air reported by Loriot et al. [4] purported to show that the optical Kerr effect saturates and then becomes negative for intensities greater than 26 TW/cm 2 . A strong higher-order Kerr effect, with a crossover from positive to negative nonlinear index at intensities well below the ionization threshold, would have a huge impact on the nonlinear optics of transparent media, and has inspired theoretical works predicting plasma-free light filamentation [5] and exotic new effects in light propagation [6]. It would overturn the picture most have of the mechanism behind long-range filamentary propagation of intense ultrashort pulses -as arising from an interplay between self-focusing due to the positive optical nonlinearity from bound electrons and defocusing due to the plasma generated by ionization. The existence of a higher-order Kerr effect would also have implications for the general nonlinear susceptibility in transparent media [7,8], including harmonic generation [9][10][11].Subsequent experimental studies of light filaments [12][13][14][15] have not supported the higher-order Kerr model, with one exception [16]. One measurement [13] found that the electron density was two orders of magnitude higher than predicted by a calculation including higher-order nonlinearities, but agreed with a simulation based on plasma defocusing alone [5]. A physical mechanism for the saturation and negative response was proposed based on the nonlinear response near the threshold of ionization [17,18]. What is missing from this debate is a direct measurement of the nonlinearity that corroborates or refutes the intensity dependence observed by Loriot et al. Here, we describe such a measurement in Ar and N 2 using spectral interferometry. We find no saturation and no negative instantaneous nonlinear phase, in contrast to the original experiment [4].The technique we use, single-shot supercontinuum spectral interferometry [19], provides...

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“…As a consequence, the HOKE can ensure self-defocusing in filaments and balance Kerr self-focusing [10], in place of the plasma, especially for short pulses [9]. This result raised an active controversy [11][12][13][14][15][16] in the lack of direct experimental confirmation.…”

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confidence: 99%

Transition from Plasma-Driven to Kerr-Driven Laser Filamentation

et al. 2011

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While filaments are generally interpreted as a dynamic balance between Kerr focusing and plasma defocusing, the role of the higher-order Kerr effect (HOKE) is actively debated as a potentially dominant defocusing contribution to filament stabilization. In a pump-probe experiment supported by numerical simulations, we demonstrate the transition between two distinct filamentation regimes at 800 nm. For long pulses (1.2 ps), the plasma substantially contributes to filamentation, while this contribution vanishes for short pulses (70 fs). These results confirm the occurrence, in adequate conditions, of filamentation driven by the HOKE rather than by plasma. *

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Saturation of the All-Optical Kerr Effect

Cited by 111 publications

References 31 publications

Higher-order Kerr effect and harmonic cascading in gases

Higher-order Kerr effect and harmonic cascading in gases

Optical Nonlinearity in Ar andN2near the Ionization Threshold

Transition from Plasma-Driven to Kerr-Driven Laser Filamentation

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