A continued study of optical sound generation and amplification

Abstract : This report discusses research on two projects (1 ) the optoacoustic generation in fluids and (2) the propagation sound through gases with a nonequilibrium distribution of vibrational energy states. The experimental method for the optoacoustic experiment involves observing the pressure pulse created when an 800 ps pulse of UV (337 nm) from an N2 laser is absorbed in a liquid. The pressure pulse created by the absorption of the UV is observed by the deflection produced in a second parallel laser beam transversing the liquid. Measurements are concerned with non linear dependence of the deflection of the detecting beam upon energy deposited in the liquid. The results indicate a change of state in the very small irradiated volume. With the propagation of sound through excited gases, an effort has been made to observe SACER in CO. Difficulty has been encountered in heating the vibrational mode in this gas with an electrical discharge. However, CO has been added to N2 in small amounts to act as a indicator of the vibrational temperature in N2. Due to a relatively fast v-v transfer the vibrational modes of the two gases stay in equilibrium. The I.R. radiation coming from the I.R. active CO is then an indicator of the vibrational temperature of the mixture. The decay of the vibrational temperature previously only inferred from the rise and fall of the translational temperature has been measured directly. This gives confidence to conduction and relaxation times previously deduced from the translational-temperature vs time curves. An effort will now be made to measure vibrational relaxation times in H2 and H2 mixtures.