Heterodyned impulsive stimulated Raman scattering of phonon–polaritons in LiTaO3 and LiNbO3

Crimmins, Timothy F.; Stoyanov, Nikolay S.; Nelson, Keith A.

doi:10.1063/1.1491948

Cited by 69 publications

(51 citation statements)

References 56 publications

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“…For excitation at fluences F < 50 mJ/cm 2 , we observed a reduction in SH intensity to a finite value within approximately 200 fs. As predicted by the model presented above, we observed a rapid exponential recovery and coherent oscillations at 16 THz, which we attribute to a phonon-polariton mode [18,19] associated with the driven Q IR phonon.For fluences above a threshold value of 60 mJ/cm 2 and up to the maximum fluence possible in our setup (95 mJ/cm 2 ), the second harmonic intensity was observed to vanish completely, recover to a finite value, and then vanish again, before relaxing back to the equilibrium state.To derive, whether the ferroelectric polarization was reversed during this dynamics, we measured the time-dependent phase of the SH electric field by interfering it with a reference SH pulse, generated in a non-excited crystal as sketched in Fig. 3(a).…”

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confidence: 54%

Ultrafast Reversal of the Ferroelectric Polarization

et al. 2017

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The ability to manipulate ferroelectrics at ultrafast speeds has long been an elusive target for materials research. Coherently exciting the ferroelectric mode with ultrashort optical pulses holds the promise to switch the ferroelectric polarization on femtosecond timescale, two orders of magnitude faster compared to what is possible today with pulsed electric fields.Here, we report on the demonstration of ultrafast optical reversal of the ferroelectric polarization in LiNbO 3 . Rather than driving the ferroelectric mode directly, we couple to it indirectly by resonant excitation of an auxiliary high-frequency phonon mode with femtosecond mid-infrared pulses. Due to strong anharmonic coupling between these modes, the atoms are directionally displaced along the ferroelectric mode and the polarization is transiently reversed, as revealed by time-resolved, phase-sensitive second-harmonic generation. This reversal can be induced in both directions, a key pre-requisite for practical applications. 2The ferroelectric polarization is typically controlled with static or pulsed electric fields.Switching is in this case an incoherent process, with speed limited to hundreds of picoseconds by the nucleation and growth of oppositely polarized domains [1,2,3]. To overcome these limitations, attempts have been made to drive the ferroelectric mode coherently with light pulses. These strategies, which have been based either on impulsive Raman scattering [4,5,6,7] or direct excitation of the ferroelectric mode [8,9,10] using THz radiation, have not yet been completely successful.Recent theoretical work [11] has analyzed an alternative route to manipulate the ferroelectric polarization on ultrafast timescales. It has been proposed that a coherent displacement of the ferroelectric mode could be achieved indirectly, by exciting a second, anharmonicallycoupled vibrational mode at higher frequency. The underlying mechanism is captured by the following minimal model, which is illustrated in Fig. 1. Consider a double well energy potential along the ferroelectric mode coordinate Q P as shown in Fig. 1Here, ω p is the frequency of the ferroelectric mode for a fixed temperature T below the Curie temperature T C . Take then a second mode Q IR with frequency ω IR , described by the Fig. 1(a), which is anharmonically coupled to the ferroelectric mode with a quadratic-linear dependence of the interaction energy aQ IR 2 Q P . The total lattice potential can then be written asIn equilibrium, Q P takes the value of one of the two minima of the double well potential Fig. 1(b). For finite displacements Q IR , this minimum is first displaced and then destabilized as Q IR exceeds a threshold value (colored lines in Fig. 1(b)).Importantly, the direction of this displacement is always pointed toward the opposite potential well and independent on the sign of Q IR [11].The corresponding dynamics of the two modes for resonant periodic driving of Q IR by a midinfrared light pulse is obtained by solving the equations of motionHere, f t) is the driving pulse ...

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confidence: 54%

Ultrafast Reversal of the Ferroelectric Polarization

et al. 2017

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“…We believe that mapping the dispersion surfaces of 2D phononic crystals should yield even more interesting results. The approach used in this work may be extended beyond phononic crystals: for example, the transient grating technique has been used to measure the dispersion of phonon-polaritons in LiNbO 3 and LiTaO 3 [25]; thus it may prove instrumental for studying the band structure of photonic crystals in the THz range fabricated in these materials [26].…”

Section: Discussionmentioning

confidence: 99%

Mapping the band structure of a surface phononic crystal

Maznev¹,

Wright²,

Matsuda³

2011

New J. Phys.

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Abstract. We map the band structure of surface acoustic modes of a periodic array of copper lines embedded in a SiO 2 film on a silicon substrate by means of the laser-induced transient grating technique. A detailed map of the lowest sheet of the ω(k) surface and partial maps of two higher-order sheets are obtained. We discuss the topology of the ω(k) surface and explain how it arises from the Rayleigh and Sezawa modes of the film/substrate system. In the vicinity of the bandgap formed at the Brillouin zone boundary, the first and second dispersion sheets take the form of a saddle and a bowl, respectively, in agreement with a weak perturbation model. The shape of the third dispersion sheet, however, appears to defy expectations based on the perturbation approach. In particular, it contains minima located off the symmetry directions, which implies the existence of zero group velocity modes with an obliquely directed wavevector.

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“…8 To demonstrate its planar waveguide dispersion properties, we have generated narrowband polaritons through ISRS using crossed beam excitation 9 and monitored their temporal and spatial evolution using polariton imaging. 10 We observe that for large wavevector polaritons, in which the wavelength is still small in comparison to the crystal thickness, confinement effects are negligible and the resulting dispersive properties are the same as in bulk.…”

Section: Ferroelectric Slab Waveguidementioning

confidence: 99%