Hyper‐Raman Scattering by Phonons and Mixed Polaritons in a Calcite Crystal

Abstract

The polarized hyper-Raman spectra of a calcite crystal in different scattering geometries are obtained. Two silent A1u-vibrntions a t 227 and 1085 cm-l as well as infrared active vibrations are found. The upper branch of mixed A2,-poIaritons and their resonance with E,-vibrations is investigated. The calculation of mixed polariton dispersion curves is presented.IIonywm,r nonRpmooairnbre cnewrpbr r~n e p~~o w B~i~a~~~o~r s o r o paccemms K~M C T~J I J I~ 1 i ; l J l L L~I I T~~ npa paamiwmx reo3teTpmx p a c c e m m . Iipoixe nr~rr~rir xmtonmbrx ~o n e 6 arrrrii o6rrapyirccrm nnc JIMAEIH ,,wmhIx" &,-I;one6amii 227 rI 1085 em-'. HccneAosaiia ncpsrrris UCTBL cmmarnmx A g u -n~n~p~~~~~~~ II peaona~rc ~T E I X ~O~R~~T O E I O R c E,-Rone-lI1>HBCJClI ~laCrlC?T AI4CnepCr/IOIIHI~IX KpIiBLIX CRICUlaHIIbIX IIOJfHpEITOHOB. In trodnctionItecently the hyper-ltaman scattering in some crystals mas studied [l to 51. The interest in the hyper-ltainan scattering as an independent spectroscopic method has grown over the last few years becaiisc of the ability to allow the observation of silent modes which is inaccessible by other methods. Silent vibrations forbidden in the Itainan scattering and Ilt-absorption may be active in hyper-Raman spectra due to selection riilcs [GI. For example, two silent vibrations of B1,-sysmmetry at 113 and 406 cn1-I were observed in a rutile hyper-Itaman spectrum 143. Dipole vibrations arc always active in the hyper-Raman scattering. Therefore, the study of polaritons in both noncentrosymmetric and centrosymmetric crystals is possibleThe calcite vibration spectrum was carefully studied by different methods: 11%-absorption and reflection [8], Raman scattering [9], hyper-Raman scattering [3, 101 inelastic neutron scattering [11], theoretical calculations El1 to 131. A small part of the calcite hyper-Kaman spectrum in the frequency region below 300 cm-' was studied and only some IR-active modes were found [3, 101.In the present paper we study the hyper-Raman scattering by phonons and polaritons in a CaCO, centrosymmetric crystal. Some polarized spectra in the frequency region of fundamental calcite vibrations (0 to 1600 cm-l) were obtained and two silent modes were observed, Besides, the polariton hyper-Raman spectra associated with Kaman inactive mixed A*,-vibrations were studied.[5, 71. ExperimentalHyper-Raman spectra were excited by the polarized light of a YAG laser (mi = = 9396 cm-l) and were detected by a niultichannel photoelectric instrument described previously [14]. The power density of the exciting light did not exceed lo8 W/crna inside the crystal. I n the 90" and 180" hyper-Raman scattering geometries t,he laser 142092 Troitsk, Moscow Region, USSR.

High-temperature relaxor ferroelectric behavior in Pr-dopedSrTiO3

“…Their occurrence is made possible by relaxation of these rules by unintentional and intentional structural defects. By comparison with previously published Raman and infrared scattering results on bulk STO [16][17][18][19][20][21] and on thin STO films 22 we identified the four Raman modes near 175, 475, 540, and 795 cm −1 as TO 2 , LO 3 , TO 4 , and LO 4 , modes, respectively. The appearance of TO 2 and TO 4 modes, has been considered as evidence of polar nanoregions ͑PNRs͒ which characterize a relaxor ferroelectric system.…”

Hyper-Raman scattering enhanced by anisotropic dimer plasmons on artificial nanostructures

“…14 Hyper-Raman scattering ͑HRS͒, which is inelastic scattering in the second-order nonlinear optical process, is expected to be a useful spectroscopic technique for completing vibrational information; the selection rule of HRS is rather similar to that of infrared ͑IR͒ absorption. [15][16][17] However, HRS has extremely weak effect with scattering cross sections on the order of 10 −65 cm 4 s, 14 and hence, enhancement of HRS signals is indispensable. In a similar manner of SERS, surface-enhanced hyper-Raman scattering ͑SEHRS͒ has been reported in metal colloid or roughed electrode sytems.…”

Identification of longitudinal optical modes by hyper-Raman scattering in noncentrosymmetric ceramics

“…4,5 Hyper-Raman is a nonlinear scattering process that involves two incoming photons with frequency L and wave vector k L , and one phonon with frequency q and wave vector q. The scattered light contains a signal with frequency s and wave vector k s , which is shifted by the phonon mode frequency relative to the second harmonic 2k L of the incoming fundamental light: 2 L ± q = s and 2k L ± q = k s .…”