Verification of the physical mechanism of THz generation by dual-color ultrashort laser pulses

Li, Min; Li, Wenxue; Shi, Yi; Lu, Peifen; Pan, Haifeng; Zeng, Heping

doi:10.1063/1.4759268

Cited by 49 publications

(29 citation statements)

References 11 publications

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“…With a π/2 relative phase, the pump field exhibits a temporal asymmetry around the electric field maxima and the current density J (t) develops a low-frequency component due to the stepwise increase of the electron density. This component is then the major THz source [35]. Following the local current theory [23], ionization happens near the relative extrema of E(t) at the instants t 1 , t 2 , t 3 , .…”

Section: Increase In the Pump Wavelengthmentioning

confidence: 97%

Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength

Nguyen¹,

Martínez²,

Dechard³

et al. 2017

Opt. Express

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We theoretically and numerically study the influence of both instantaneous and Raman-delayed Kerr nonlinearities as well as a long-wavelength pump in the terahertz (THz) emissions produced by two-color femtosecond filaments in air. Although the Raman-delayed nonlinearity induced by air molecules weakens THz generation, four-wave mixing is found to impact the THz spectra accumulated upon propagation via self-, cross-phase modulations and self-steepening. Besides, using the local current theory, we show that the scaling of laser-to-THz conversion efficiency with the fundamental laser wavelength strongly depends on the relative phase between the two colors, the pulse duration and shape, rendering a universal scaling law impossible. Scaling laws in powers of the pump wavelength may only provide a rough estimate of the increase in the THz yield. We confront these results with comprehensive numerical simulations of strongly focused pulses and of filaments propagating over meter-range distances.

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Section: Increase In the Pump Wavelengthmentioning

confidence: 97%

Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength

Nguyen¹,

Martínez²,

Dechard³

et al. 2017

Opt. Express

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“…As a first example, figure 3(a) shows the efficiency factor g THz plotting separately the integrals ofR andÎ for a classical two-color pulse with f = 0 1 . We retrieve the best SH phase angle f p = 2 2 for THz production by photocurrents [30], which induces a substantial increase inN e L at FH frequency, hence inR. Indeed, if we apply the approximation that ionization occurs at the maxima of E L 2 and neglect the envelope effects, Another example illustrates in figure 3(b) the spectrum of the electron density computed on the first harmonics of a sawtooth wave shape, known to supply the highest THz yields to date at fixed ionization level [29].…”

Section: An 'Optical' Criterion To Evaluate the Laser-to-thz Conversimentioning

confidence: 99%

THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

et al. 2018

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We numerically study the influence of chirping and delaying several ionizing two-color light pulses in order to engineer terahertz (THz) wave generation in air. By means of comprehensive 3D simulations, it is shown that two chirped pulses can increase the THz yield when they are separated by a suitable time delay for the same laser energy in focused propagation geometry. To interpret these results, the local current theory is revisited and we propose an easy, accessible all-optical criterion that predicts the laser-to-THz conversion efficiencies given any input laser spectrum. In the filamentation regime, numerical simulations display evidence that a chirped pulse is able to produce more THz radiation due to propagation effects, which maintain the two colors of the laser field more efficiently coupled over long distances. A large delay between two pulses promotes multi-peaked THz spectra as well as conversion efficiencies above 10 −4 .

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“…However, measurement of Δϕ at the generation point is a very difficult task. In [23], the authors have claimed that Δϕ at the generation point was successfully obtained and concluded that the photocurrent model is the dominant process for the THz generation through two-color filamentation. However, π∕2 phase shift at SHG [24] and Gouy phase shift are not taken into account at the phase determination.…”

mentioning

confidence: 99%

Controlling the carrier-envelope phase of single-cycle mid-infrared pulses with two-color filamentation

et al. 2015

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Carrier-envelope phase (CEP) of single-cycle pulses generated through two-color filamentation has been investigated. We have observed a particular behavior of the phase: the phase of high-frequency components of the generated pulses changes continuously and linearly with the relative phase between the two-color input pulses, whereas the phase of the low-frequency components takes only two discrete values. The transition of the phase behavior has been clearly observed by using frequency-resolved optical gating capable of CEP determination. We have found out that such a phase behavior is a unique feature of single-cycle pulses generated with a passive CEP stabilization scheme.

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Verification of the physical mechanism of THz generation by dual-color ultrashort laser pulses

Cited by 49 publications

References 11 publications

Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength

Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength

THz field engineering in two-color femtosecond filaments using chirped and delayed laser pulses

Controlling the carrier-envelope phase of single-cycle mid-infrared pulses with two-color filamentation

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