The Role of Epsilon Near Zero and Hot Electrons in Enhanced Dynamic THz Emission from Nonlinear Metasurfaces

Minerbi, Eviatar; Sideris, Symeon; Khurgin, Jacob B.; Ellenbogen, Tal

doi:10.1021/acs.nanolett.2c01400

Cited by 19 publications

(28 citation statements)

References 34 publications

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“…( 9) is obtained self-consistently from the electron distribution via the e − e, e − ph and e − imp scattering rates (see [12]). This is in contrast with the phenomenological methods addressing the permittivity damping term in previous studies [3,5,10,11,30]. Below, we show that this self-consistent form successfully explains the experimental data [4,9,14] without introducing phenomenological adjustments.…”

Section: B Self-consistent Field Calculations and Model For A Time-de...mentioning

confidence: 58%

“…where τ e−e is the e − e relaxation time. In many previous studies [4,5,10,11,49], τ e−e was estimated using the Gurzhi formula [50][51][52],…”

Section: Conclusion/discussionmentioning

confidence: 99%

“…For LEDD materials with a non-parabolic conduction band such as ITO, the Gurzhi formula (B5) suggests that τ −1 e−e exhibits a super-quadratic growth with T e (since the plasma frequency Eq. ( 10) decreases with T e [3,5,10,11,30]). In contrast, in the ANTHEM, we calculate the e − e relaxation time from the functional derivative of the e−e collision term.…”

Section: Conclusion/discussionmentioning

confidence: 99%

“…If the damping term η is approximated to be energy-independent, then, Eq. ( 9) reproduces the Drude formula for the relative permittivity with an electron-distribution-dependent plasma frequency [3,5,10,11,30] [31], namely,…”

Section: B Self-consistent Field Calculations and Model For A Time-de...mentioning

confidence: 96%

“…More recent models employed a Relaxation Time Approximation (RTA)-based extended Two Temperature Model (eTTM) [4,5,10,11]. However, in the latter, some of the eTTM parameters were computed from equations derived for parabolic bands, the importance of momentum conservation to the e−ph interactions was not yet known [12], the e−e interaction were accounted for in a simplistic manner [13], it was not shown how the phonon temperature dynamics affects the ITO permittivity, and the analysis of the nonlinear response was specific for the experimental configuration.…”

Section: Introductionmentioning

confidence: 99%

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An electronic-based model of the optical nonlinearity of low-density Drude materials

Un¹,

Sarkar²,

Sivan³

2022

Preprint

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Low electron density Drude (LEDD) materials such as indium tin oxide (ITO) are receiving considerable attention because of their combination of CMOS compatibility, unique epsilon-near-zero (ENZ) behavior, and giant ultrafast nonlinear thermo-optic response. However, the understanding of the electronic and optical response of LEDD materials is so far based on simplistic extensions of known models of noble metals, frequently without the inclusion of the interplay among the lower electron density, relatively high Debye energy, and the non-parabolic band structure. To bridge this knowledge gap, this work provides a complete understanding of the nonlinear electronic-thermaloptical response of LEDD materials. In particular, we rely on state-of-the-art electron dynamics modeling, as well as the newly derived time-dependent permittivity model for LEDD materials under optical pumping within the adiabatic approximation. We find that unlike noble metals, the electron temperatures can reach the Fermi temperature, in which case the effective chemical potential dramatically decreases and even becomes negative, thus, transiently converting the Drude metal into a semiconductor. We further show that the nonlinear optical response of LEDD materials originating from the changes to the real part of the permittivity is because of changes to population. This resolves the argument about the rise time of the permittivity and shows that it is instantaneous. In this vein, we show that referring to the LEDD permittivity as having a "saturable" nonlinearity is unsuitable since its permittivity dynamics does not originate from population inversion. Finally, we analyze the probe pulse dynamics and unlike previous work, we obtain a quantitative agreement with the results of recent experiments.

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Section: B Self-consistent Field Calculations and Model For A Time-de...mentioning

confidence: 58%

“…where τ e−e is the e − e relaxation time. In many previous studies [4,5,10,11,49], τ e−e was estimated using the Gurzhi formula [50][51][52],…”

Section: Conclusion/discussionmentioning

confidence: 99%

Section: Conclusion/discussionmentioning

confidence: 99%

Section: B Self-consistent Field Calculations and Model For A Time-de...mentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

An electronic-based model of the optical nonlinearity of low-density Drude materials

Un¹,

Sarkar²,

Sivan³

2022

Preprint

View full text Add to dashboard Cite

show abstract

Nonlinear Terahertz Generation: Chiral and Achiral Meta‐Atom Coupling

Wang

Zhang

et al. 2023

Adv Funct Materials

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Generation and manipulation of terahertz (THz) waves are of vital importance for advancing THz technology. Nonlinear metasurfaces allow effective integration of both processes into a single compact device. However, such existing THz devices commonly rely on utilizing a single meta‐atom, which has fixed THz generation properties and thus limits the range of achievable functionalities. Here, it is demonstrate how coupling between different meta‐atoms within the unit‐cell can be used as a degree of freedom for controlling nonlinear THz generation, where achiral coupling provides full control over the amplitude of the generated THz field, while chiral coupling makes the THz generation sensitive to the handedness of the pump polarization. In particular, chiral coupling allows the realization of multiplexed pump‐handedness‐selective nonlinear metasurfaces, which is illustrated experimentally by selectively generating THz beams with different orbital angular momentum with a single nonlinear metasurface. This approach provides opportunities for developing various integrated nonlinear THz devices.

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Excitation of Epsilon‐Near‐Zero Mode in Optical Fiber

Yang

Minn

Anopchenko

et al. 2023

Laser & Photonics Reviews

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Experimental excitation of a highly confined epsilon‐near‐zero (ENZ) mode in a side‐polished optical fiber coated with a deep subwavelength thick layer of aluminum‐doped zinc oxide (AZO) is reported. The uniform AZO layer on the fiber is fabricated by atomic layer deposition technique and optimized to exhibit close‐to‐zero permittivity at the near‐infrared wavelength. Highly polarization‐ and wavelength‐dependent transmission with strong resonance strength up to 25 dB is observed in a 30‐nm ENZ‐coated fiber that is 17 mm long. Different from the excitation of the ENZ mode in a planar conducting oxide thin film, the hybrid ENZ mode can be excited via direct phase matching between the fundamental mode of the fiber and the ENZ mode supported by the AZO thin film. The hybrid ENZ mode in the fiber exhibits a relatively long propagation/light–matter interaction length which is a few orders of magnitude longer than those on the planar ENZ substrates. It is further shown that the hybrid resonance in the ENZ fiber can be actively tuned through the refractive index of surrounding medium and the large ENZ's nonlinearity. These ENZ‐optical fibers serve as emerging in‐fiber optical devices, such as advanced in‐fiber ultrafast optical switches/modulators, mode‐locked fiber lasers, and in‐fiber optical gas/biomolecule sensors.

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The Role of Epsilon Near Zero and Hot Electrons in Enhanced Dynamic THz Emission from Nonlinear Metasurfaces

Cited by 19 publications

References 34 publications

An electronic-based model of the optical nonlinearity of low-density Drude materials

An electronic-based model of the optical nonlinearity of low-density Drude materials

Nonlinear Terahertz Generation: Chiral and Achiral Meta‐Atom Coupling

Excitation of Epsilon‐Near‐Zero Mode in Optical Fiber

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