Thermal scattering of light in diamond

Abstract

Recent determinations by Bhagavantam and Bhimasenachar of the velocity of sound in diamond show it to be large, about 18,000 metres per sec. for longitudinal waves and about 9,600 metres per sec. for transverse waves along the (111) direction. A simple calculation using these values and the known refractive index of diamond (μ = 2.61) shows that the resulting Doppler displacements in the frequency of monochromatic light scattered transversely in diamond should be large enough to be recorded directly without interferometric aid using a quartz spectrograph of moderate power ; the separation of the two components shifted in opposite directions would be 16 cm^-1 for longitudinal waves and 8 cm^-1 for transverse waves. These values refer to the case in which the λ2536.5 radiation of the mercury arc in quartz is the incident radiation. A special advantage in using this radiation is that parasitic illumination of unaltered wave-length can be quenched by the use of a mercury vapour filter placed in front of the slit of the spectrograph, thereby enabling the Doppler-shifted components in the scattered light from within the crystal to be recorded without any intervening line of unaltered wave-length.