Spontaneous Raman Scattering by Polaritons. I. General Theory

Physica Status Solidi (b)

et al. 1974

First experimental observation of inverse Raman scattering (IRS) from polaritons are reported. The I R S frequency shifts measured in LiIO, crystals using different scattering geometries are discussed and compared with SRS experiments. Using extraordinary continua and ordinary laser fields, the polaritons associated with the 769 cm-l El-phonon shift to 595 cm-l. I n addition in this scattering geometry an absorption at 860 cm-I was detected, due to a polariton in the upper dispersion branch. It is shown that the polariton absorption frequencies in I R S can be determined as in SRS from "undamped" quasimomentum conservation laws. The IRS absorption coefficient for polaritons has a Lorentzian form. I n some scattering geometries in anisotropic crystals, I R S and SRS can result in different polariton frequencies for the same fixed laser polarization; especially large polariton shifts in SRS are accompanied by small shifts in I R S and vice versa.Erstmalig wurde das inverse Ramanstreuspektrum (IRS) an Polaritonen experimentell registriert, und zwar am hexagonalen LiJO,-Einkristall. Fur verschiedene Streugeometrien und Polarisationsvarianten von Laser und Antistokeskontinuum wurden die Frequenzverschiebungen in I R S gemessen und theoretisch gedeutet. Bei auBerordentlich polarisiertem Kontinuum und ordentlichem Laserfeld verschob sich die zur &(El) = 769 cm-lSchwingung zugehorige Polaritonenfrequenz bis zu 595 cm-1; ebenso gelang der Nachweis der Polaritonen am oberen Ast der Dispersionskurve bei 860 cm-l im IRS-Absorptionsspektrum. Es wird gezeigt, daB die Polaritonenfrequenzen sich in analoger Weise wie bei der SRS aus dem ,,dampfungsfreien" Quasiimpulserhaltungssatz bestimmen und der IRS-Absorptionskoeffizient im Polaritonenfalle Lorentzform besitzt. Die Untersuchung und Klassifikation der verschiedenen moglichen IRS-Streuvarianten fur anisotrope Kristalle ergab, da13 bei fester Laserpolarisation in I R S und SRS grundsatzlich verschiedene E'requenzverschiebungen existieren konnen und insbesondere groBe Verschiebungen in I R S auftreten konnen, wenn in SRS nur geringe Verschiebungen existieren, und umgekehrt.

Section: Theoretical Considerations About Irs By Polaritonsmentioning

confidence: 99%

Inverse Raman Effect by Polaritons in LiIO₃ Single Crystals

Kneipp

Werncke²,

Physica Status Solidi (b)

et al. 1974

“…Id. The solid curve corresponds to formula (2), and the dashed line is the result of the above-mentioned precise calculations5) (compare also with [Z]). The factor a,,(8) has no singularity a t 8 = 8,.…”

mentioning

confidence: 97%

The influence of polariton motion on the polariton Raman scattering spectra

Strizhevskiǐ¹,

Yashkir²,

Physica Status Solidi (b)

1975

Self Cite

The influence of the relative group velocity finiteness of the scattering polariton on the polariton Raman scattering (RS) intensities is discussed. It is proved that this effect is not very essential only in the region of polariton frequencies wp near the frequency wf of the corresponding polar mechanical phonon because here the relative group velocity tP of the polariton is small. But the influence of the group velocity tp finiteness appears t o be essential in the case of sufficiently distant frequencies wP from of. This influence results not only in essential quantitative changes but also in qualitative changes, in particular, of the angular dependence of the polariton RS intensity. It is manifested particularily in the vicinity of the "critical" scattering angles where the neglection of this effect distorts absolutely the character of the above-mentioned dependence. The Ep-finiteness influence is illustrated by numerical calculations for a number of real crystals (ZnO, ZnSe, Gap, CdS, LiIO,). Experimental investigations are made of the RS-intensity angular dependence in the region of the upper polariton branch in LiIO, crystals in the vicinity of the critical scattering angle. The results confirm the conclusion of the theory about the essential influence of the effect mentioned above on the polariton R S intensity.

“…Rci eincm einfachen Rcsponseverhalten der Materie (2a) fdlt die )tlKI1:-Signaliritensitat aucli bei belicbigen Koirclstionseigciischafteii der Anregungafelder A L , A S ) exponentiell init dcr Vcrziigcningszeit t, und einer Zeitkonstanteri (2Re u,)-l ah (24), ( 2 5 ) , (29 geniigt niit (A 2) wicder der GI. (7). Zur Aufstellung der verkiirzten Gleichung mu13 G(o, k ) nach (0u p , kw und dt:nI'L,I, J:,,analog zii (S), (8a, b) entwickelt werden.…”

Section: Yehliibhemcrkiingeriunclassified

Nichtstationärer ramaninduzierter Kerreffekt in Flüssigkeiten und einachsigen Piezokristallen

Kneipp

1978

Annalen der Physik

Sonstationary ltaman-Induced Herr Effect in Liquids and Uniaxial PiezocrystalvS b s t r a c t . A nonstationary probe-beam method using Baman-induced Kerr effect (RIKE) for ineasuring the (transversal) relaxation constant 1'( = TT') of piezo crystals and Raman active liquids is disc~~ssed. T n isotropic media, in every scattering geometry phase matching is realised automatically for all frequencies and therefore, in contrast to coherent act.ive Raman spectroscopy (CARS), the complete Raman spectrum is generated simultaneously and also its time behavionr can be studied. (In anisotropic crystals the appearing of RIKE will bc drastically reduced.)For arbitrary corrclation bchaviour of the pump fields the nonstationary signal intensity vanishes exponentially with the effective vibration damping constant and with the delay-time of the testpulse. The dependence of the signal on the characteristic interaction length betwcen the pulses (L,s), on the phase modulation times T , , , ,~, and on the probe length L arc studied. The malogies between the methods of active Itaman spcctroscopy (AHS), RIKIS, and induced two-plioton-emission-cxperiments will be illustrated. EinleitungRei der gleichzcitigen Ucstrahlung cines ra.manaktiven Medium niit einer zirlrular polarisierten I'umplaserwelle (Frequenz oL) und eineni linear polarisierteri St.okes ( w ,~) -(oder auch Antistokes-)Kontinuum verursacht die nichtlineare Wechsclwirkung der Felder irii Mediuiii die Entstehung einer neuen Stokes-~eldkomponente, die senlrrecht zur urspriinglichen Stolreswelle polarisiert, ist irnd Hesonanzohnraktcr bcsitzt, wenn