The microwave dielectric constant and conductivity of MEM(TCNQ)₂ were studied in the neighbourhood of the monomer to dimer transition at 61°C using cavity-perturbation techniques at 9 GHz. The conductivity was found to be in general agreement with four-probe d.c. results. Thus, doubts about the reliability of the d.c. measurements above the destructive transition have been removed. The complex dielectric constant of TTF-TCNQ at liquid helium temperatures was studied using dielectric resonance techniques. Some anomalies regarding the interpretation of the dielectric resonance mode plots were resolved. Values for Є’ of (3.0±0.4)X10³ and for Є’of greater than 9 were implied by the results. Finally, preliminary results and proposed directions for a bolometric absorption measurement in TTF-TCNQ in the microwave bands are presented. This technique may prove useful for the direct observation of the pinned charge density wave in TTF-TCNQ. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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A variation of the excite-and-probe technique is used to measure the picosecond evolution of laser-induced transient gratings that are produced in germanium by the direct absorption of 40 psec optical pulses at 1.06-μm. Grating lifetimes are determined for free carrier densities between 10¹⁸ cm⁻³ and 10²¹ cm⁻³ . For carrier densities less than 10¹⁹ cm⁻³ , a linear diffusion-recombination model for the grating provides a good fit to the experimental data and allows the extraction of the diffusion coefficient and an estimation of the linear recombination lifetime. Above carrier densities of approximately 10²⁰ cm⁻³ , the density dependence of the diffusion coefficient and nonlinear recombination processes must be considered. Numerical solutions to the resulting nonlinear partial differential equation are obtained that allow extraction of information concerning the high density diffusion coefficient and the nonlinear recombination rates.