No abstract

No abstract

We report the first positive experimental observation of the optical activity effect on normal reflection. The experiment was performed along the optic axis in a gyrotropic semiconductor crystal of a-HgS, cinnabar, in a spectral region of strong absorption. Reflected light polarization azimuth rotation resulting from the reflection is of the order of 10 ~4 rad and has pronounced dependence on hco -E g .

No abstract

The preceding Comment by L. C. Lew Yan Voon et al. does not provide any grounds to doubt the results and interpretations developed in the commented paper.The paper' commented on by Lew Yan Voon, Fainstein, Etchegoin, Santos, and Cardona reports the experimental results on the observation of time-nonreversible polarization-sensitive interaction of light with zincblende crystals, namely, GaAs and InSb. It is mainly devoted to observation of the change of the natural timenonreversible effect resulting from stimulation of the crystal with intense optical excitation. Also, a microscopic picture of time-nonreversible light-matter interaction is discussed.The comment does not dispute the interpretation of the high-excitation experiments.However, it criticizes the attribution of the observed low intensity dichroism to symmetric terms linear in the light wave vector. If this comment were based on correct arguments, it could be a valuable contribution to the problem of reversality of light-matter interaction. However, we found that all the arguments produced in the comment are either mistaken or based on misunderstanding of paper 1.Specific points are made as follows. (i) The comment claims that Fig. 5(b) of Ref. 1 is incorrect. However, the corresponding part of the cornment clearly indicates that the commentators have not understood this figure and the explanations given in the figure caption and the text (p. 11512, lines 17 -33, first column). Of course ". .. helicity is defined with respect to the propagation direction" and therefore does not change in the time-reversed scenario. This is indeed a very well known fact. We relied on this fact in our interpretation and it is clearly stated in the text as follows: ". .. time reversal does not affect the handedness of light polarization. " However (according to the selection rules), the time-reversed scenario presented on the left side of Fig. 5(b) requires light of opposite polarization (right instead of left) to promote the corresponding time-reversed transition. Thus, diagram 5(b) indicates a clash with the assumption of time reversality. This is depicted as a cross (sign of forbiddance) on the arrow connecting left and right sides of the diagram. Consequently, we believe that Fig. 5 is correct and the commentators have not spotted any mistake in the figure.(ii) The comment states that the time-reversal operator commutes with the Hamiltonian inclusive of the spinorbit interaction and on this basis claims that gyrotropic linear dichroism could not be caused by the spin-orbit interaction. In response to this comment, we need to declare very clearly that there is an essential physical difference between the question of reversality of the crysta/ Hamiltonian itself and reversality of the Hamiltonian of the whole system, which includes the crystal and the light interacting with it. We, of course, do not doubt reversality of the crystal Hamiltonian, i.e. , its commutivity with the time-reversal operator. This is in fact clearly stated in the text of the paper as follows: ". .....