Terahertz response of acoustically driven optical phonons

Poolman, Rhys Huw; Muljarov, Egor A.; Ivanov, A. L.

doi:10.1103/physrevb.81.245208

Cited by 10 publications

(12 citation statements)

References 27 publications

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“…is proportional to the AW amplitude (I ac is the acoustic intensity) and to the Fourier transform of the third-order derivative of the interatomic potential Φ (3) . A careful investigation 8 shows that, to good approximation, any dependence on phonon wave vectors in Φ (3) can be safely neglected. The operating acoustic frequencies are all limited to the linear regime of the acoustic phonon dispersion given by…”

Section: Formalismmentioning

confidence: 99%

“…However, as shown in Appendix A, this leads to linearly dependent combinations of plane waves, so that the double Fourier transform of E and P is effectively reduced to the form of Eqs. (7) and (8). We substitute them into Eqs.…”

Section: Formalismmentioning

confidence: 99%

“…Then, using the fact that D = ε b E + 4πP, where E is the electric field and ε b is the background dielectric constant, the TO-phonon polariton in the field of a coherent pump AW is described by a system of coupled Maxwell's and material equations. 5,8 In what follows, we concentrate on collinear propagation of the acoustic and light waves, normal to the semiconductor surface. In case of a semiconductor occupying half space z > 0, the system can be effectively reduced to a one-dimensional geometry and is described by the following differential equations ( = 1 is used for simplicity of notations)…”

Section: Formalismmentioning

confidence: 99%

“…This picture is typical for conventional, nonresonant acousto-optics. 4 In contrast, resonant acoustooptics, which has been introduced very recently, [5][6][7][8] deals with acoustically induced spectral changes which are comparable to the background signal. This is achieved by a resonant coupling of the incoming light to such fundamental excitations in the solid state as excitons or transverse optical (TO) phonons leading to the formation of polaritons.…”

Section: Introductionmentioning

confidence: 99%

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Resonant acousto-optics in the terahertz range: TO-phonon polaritons driven by an ultrasonic wave

Muljarov¹,

Poolman²,

Ivanov³

2011

Phys. Rev. B

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The resonant acousto-optic effect is studied both analytically and numerically in the terahertz range where the transverse-optical (TO) phonons play the role of a mediator which strongly couples the ultrasound and light fields. A propagating acoustic wave interacts with the TO phonons via anharmonic channels and opens band gaps in the TO-phonon polariton energy dispersion that results in pronounced Bragg scattering and reflection of the incoming light. The separation in frequency of different Bragg replicas, which is at the heart of acousto-optics, allows us to study the resonant acousto-optic effect in the most simple and efficient geometry of collinear propagation of electromagnetic and ultrasonic waves. The acoustically induced energy gaps, Bragg reflection spectra, and the spatial distribution of the electric field and polarization are calculated for CuCl parameters, in a wide range of frequencies and intensities of the pumping acoustic wave. Our results show drastic changes in terahertz spectra of semiconductor crystals that open the way for efficient and accessible manipulation of their infrared properties by tuning the parameters of the acoustic wave.

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Section: Formalismmentioning

confidence: 99%

Section: Formalismmentioning

confidence: 99%

Section: Formalismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Resonant acousto-optics in the terahertz range: TO-phonon polaritons driven by an ultrasonic wave

Muljarov¹,

Poolman²,

Ivanov³

2011

Phys. Rev. B

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“…The coupling constants are derived from the potential of the anharmonic components added to the Hopfield Hamiltonian. 17,[20][21][22] In this paper, the coupling to a plane bulk acoustic wave with a moderate intensity I ac (r, t) = I ac = 25kW/cm 2 is considered. The values of the phase shift φ = φ 3 − φ 4 between the complex anharmonic coupling parameters in Eq.…”

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confidence: 99%

Ultrasonic control of terahertz radiation via lattice anharmonicity in LiNbO3

Poolman

Muljarov

Ivanov

2011

Applied Physics Letters

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We propose a novel tunable terahertz (THz) filter using the resonant acousto-optic (RAO) effect. We present a design based on a transverse optical (TO) phonon mediated interaction between a coherent acoustic wave and the THz field in LiNbO 3 . We predict a continuously tunable range of the filter up to 4 THz via the variation of the acoustic frequency between 0.1 and 1 GHz. The RAO effect in this case is due to cubic and quartic anharmonicities between TO phonons and the acoustic field. The effect of the interference between the anharmonicities is also discussed.In recent years terahertz (THz) radiation has become a tool to study a wide variety of phenomena, necessitating the development of experimental techniques to access this spectral band. 1 Radiation in the THz range has been used to study picosecond phonon dynamics, polariton propagation, optical properties of various materials, and has been used for imaging purposes. [2][3][4][5] There are also several commercial applications that cover a variety of fields, including sub-mm wave astronomy, chemical recognition and biomedical imaging for disease diagnostics, THz imaging and sensing for security applications. [6][7][8] As a result, spectrally resolved control of THz radiation has become an important research topic. One implementation uses optical control of carrier densities in type-I/type-II GaAs/AlAs multiple quantum wells at cryogenic temperatures. 9 Other implementations include magnetically tuned liquid crystals in metallic hole arrays and Lyot and Sloc filters, which were shown to be tunable over various ranges between 0.1 and 0.8 THz. 10-12 A relative lateral translation of two metallic photonic crystals has also resulted in a THz filter (tunable between 0.365 and 0.385 THz). 13 In this Letter we show that the concept of the resonant acousto-optic (RAO) effect could be used to produce a tunable THz filter. We present a design and model numerically a LiNbO 3 -based filter which is tunable in a wide range of up to 4 THz. The RAO effect which we use is in general a mediation of the interaction between an acoustic wave and a light field by a solid state excitations, when the light field and the excitation are in resonance. [14][15][16][17][18] In ionic crystals with soft TO-phonon modes, the interaction between a coherent acoustic wave and the THz field is mediated by a TO phonon. 17,18 The TO phonon is coupled to the acoustic wave via the anharmonicity present in the interatomic potential of the crystal lattice. This makes LiNbO 3 an excellent candidate for the filter, as it is both ionic and very strongly anharmonic. In fact, the strength of the anharmonicity in LiNbO 3 is such that both the cubic and quartic terms of the Taylor expansion of the interatomic potential have to be considered.The design of the LiNbO 3 -based tunable filter is shown schematically in Fig. 1. A thin slab of LiNbO 3 (1 mm thick or less) is placed between doped semiconductor contacts producing a resonator for ultrasound waves but at the same time transparent for THz light. Owing...

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