Within the frame work of Pekar's model for a spatially dispersive, bounded medium, optical spectra of thin crystals, reported by us recently, are analyzed, showing a structure due to the interference of additional waves and the Pabry-Perot structure deviating markedly from the one expected in the classical case in the neighbourhood of exciton resonances.A comparison of the experimental reflectivity with that obtained numerically provides values for all physical parameters defining dispersion and damping of the photoexcitons. Some additional experimental results for excitons in thin crystals are reported: evidence for the induced surface wave, an effect of the forbidden exciton, etc. HaK HaMM J7Xe COO6waJlOCb, I3 MHTep@epeHUMOHHbIX CIIeHTpaX TOHKMX KPII-CTaJIJIOB B OKpeCTHOCTH 3KCHTOHHbIX pe30HaHCOB IIpORBJKRIOTCfi ABa TMIIa OCO-6eHHOCTefi: CTpYKTYpa, BO3HHKaH)II~aR 113-38 MHTCpl$epeHqMII n06aBOxIHbIX BOJlH II CTpyIcTypa CDaBpn-nepo, 3HacWITeJlLH0 OTXM~aIOwaXCH OT TOB, I-iOTOpaH OifcE1.1-PYIOTCH B paMKaX MOaeJIII neKapa OrpaHH4eHKKOt CpenbK C IIpOCTpaHCTBCHHOfi naeTcx B KnaccmYecKoM cnyqae. €3 Hamoxwet3 pa6oTe ~T M cnei-FTpbI a~an113k1nncnepcneii. Cpameme s~c n e p r n~e~~a n~,~o r o EI pacqwawioro cnempa n03BOJ-ReT HafiTm ~H~Y~H M R

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Recently, there has been considerable interest to study changes in the refractive index of highly excited direct-gap semiconductors below the band edge. Interference spectroscopy on thin crystal platelets represents an appropriate method for corresponding experimental investigations. First experiments of this kind were reported by Miiller et al. /1/ for CdS. But the purpose of these measurements was mainly a correct determination of the optical gain.Detailed investigations on the refractive index of highly excited CdS were carried out by Klingshirn and co-workers /2/. The thickness of the crystal platelets used was, however, of the order of some microns. From this two difficulties arose:

The results of theoretical and experimental investigations of novel magneto-optical effects connected with the magneto-spatial dispersion of the principal dielectric axes are presented. For this purpose the low-temperature transmission spectra of thin CdSe crystals are measured near the A (n=1) exciton resonance in the Voigt configuration k 1 H(O), H(O) 11 C,, H(O) being the external magnetic field and k being the light wave vector. It is observed that for the polarizer position P C, or P 1 C, the transmitted light is polarized elliptically and the major axis of the polarization ellipse is rotated with respect to the incident light polarization plane. The derived theory of resonant magneto-spatial dispersion of the axes is in agreement with experimental data. The constant of th-k-linear term of the exciton energy spectrum is determined from the comparison of theory and experiment. pEi30BaH II rJIaBHafI O C b 3JIJIHIICa IIOJIapI43aqHH IIOBepHyTa OTHOCElTeJIbHO IIJIOCKOCTII n o n a p~i 3 a q~~l nanamqero caeTa. P a a s~l~a a B p a 6 o~e Teopm p e 3 o~a~c~o t MarHmoEiHHYJJHPOBaHHO6i IIpOCTpaHCTBeHHO~ nIICIIepCHEl OCeg HaXOnHTCR B COrJIaCIIII C BKCIIepHMeHTaJIbHbIMH AaHHbIMII. kl3 CpaBHeHHII TeOpIlII C BKCIIepElMeHTOM OnpeneJIeHa KOHCTaHTa np&i nmetHbIx no k qneHax B 3~e p r e~n q e c~o~ cnewpe BICCHTOHOB.

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A study of additional waves in the exciton region of CdS crystals is reported. Transmittivity and reflectivity of thin crystals is measured showing a structure due to the Fabry‐Perot interference and the interference of additional waves. This structure is a direct reflection of the polariton dispersion law. Using the formulas for a spatially dispersive platelet and Pekar's additional boundary conditions the theoretical reflectivity curves are obtained numerically reproducing the essential experimental results. Values for all physical parameters defining dispersion and damping of the polaritons are found. Some evident deviations between the experimental curves and the present computer results for the reflectivity are pointed in connection with a discussion of the role of the surface exciton potential.