Quartz Optical Activity And Polarization Interference Spectrum Test

Quartz crystal is an important kind of optical material. Optical activity is one of its important properties. Devices made with optical activity of quartz crystal have important applications in the field of dispersion filtering, optical communication, depolarization and so on.. Referring to related literatures, study of quartz crystal is mainly concerned with birefringence of the material and the application of its optical activity, while work on the nature of optical activity has little been done.In the paper, the following knowledge is systematically studied. It includes category of quartz crystal system, specific rotation of quartz crystal, relevant knowledge of rotatory dispersion, magneto-optical rotation, Fresnel assumption etc.Reference to spiral model of organic liquid theory, the internal relation between the optical activity of quartz crystal and micro-spiral structure is analyzed. With pitch changing, directivity and thermal effect of specific rotation of quartz as well as its difference from specific rotation of the organic liquid are explained. Helical length l is definite at a certain temperature and the largest pitch goes along the optical axis, which is independent on spiral structure characteristic of quartz crystal. This just reflects the characteristics that optical rotation is the most obvious and specific rotation is the largest. As propagation direction deviates from the optical axis, projection of pitch along the light propagation direction and specific rotation get smaller, till optical rotation of vertical optical axis decreases to zero. When the temperature increases, thermal expansion arises and internal atomic distance increase. As a result, the pitch s gets larger and specific rotation increases relevantly. This interpretation is well consistent with test results about specific rotation. An explanation about the cause of optical activity has been given with micro-electromagnetic theory. The cause of optical activity of quartz crystal is further verified. It is supposed that antisymmetry rotation tensor (?) is the basic reason for optical rotation of the material and when all elements of matrix (?) or the corresponding rotation vector gαβare not zero, the material performs optical activity. Quartz crystal belongs to hexagonal crystal system, whose gαβhas three independent elements. Symmetry of crystal can make independent elements of gαβdecrease.On the basis of theoretical analysis of transmittance of quartz crystal, polarization interference spectrum range from 300nm to 1500nm is measured with double beam path measuring method. Experimental results show that the peak transmission ratio is low due to obvious absorption of quartz in the ultraviolet region. This is different from theoretical results to some extent. And period of spectral line is small because specific rotation of quartz crystal changes greatly with wavelength in this region, while period of spectral line is large in infrared light district because the change rate of specific rotation with wavelength is almost zero. In visible region, the peak transmission ratio is 60% or so. Because of specific rotation changing little with wavelength, thickness of crystal has a apparently impact on period of spectral line. A test is done at different temperature within 300-1500nm. According to the analysis of spectral line, as the temperature increases, there is a shift of the spectral line towards long wave. Further analysis shows that the main cause is that specific rotation of quartz crystal gets large with temperature increasing. The increase of specific rotation may be explained by spiral theory here, i.e. it is because thermal expansion results in pitch increasing in microstructure.The third chapter and the fourth chapter are main part of the paper, and they are also main innovation points:1. Characteristics of quartz crystal optical activity is explained by means of spiral theory. Pitch change in micro-spiral structure better interpret directivity and thermal effect of specific rotation of quartz as well as its difference from specific rotation of the organic liquid.2. Polarization interference spectrum of quartz crystal in visible region is measured with double beam path measuring method and analysis of the experimental spectral line is presented. According to the results, thickness of crystal has a significantly impact on period of spectral line in visible region at room temperature because specific rotation changes little with wavelength. While there is a shift of the spectral line towards long wave as the temperature increases. Further analysis shows that the main cause is that specific rotation of quartz crystal gets large with temperature increasing. And thermal expansion results in pitch increasing in microstructure. The spiral theory is verified.Study of both theoretical analysis and experimental tests is made in the paper. It provide a reference to studying the nature of the optical activity of quartz crystal and relevant applications.