We have measured the thermal diffusivity Dth and the nonradiative relaxation rates Γ for the double transitions Q1(0) + S2(0) and Q2(0) + S1(0) in solid parahydrogen in the temperature range from 5.2 K to 12.2 K by the technique of transient thermal lensing spectroscopy (TTLS). We have derived a formula which reproduces the temporal evolution of the TTLS signal. In this formula, we have defined a characteristic wave-vector magnitude, with which we can examine the achievement of local thermal equilibrium in the system. The characteristic wave-vector magnitude also enables quantitative comparisons between the TTLS and the transient thermal grating spectroscopy, which is a similar technique to the TTLS. We have obtained the temperature dependences of Dth and Γ by least-squares fit of the derived function to the observed signals without employing any other temperature-dependent parameters. At relatively low temperatures, the temperature dependence of Dth has been found to be in good agreement with that in the previous measurements, while at relatively high temperatures the values of Dth are slightly smaller than those in the previous measurements. We have found that Γ is almost temperature independent in the investigated temperature range as has been theoretically predicted. The value of Γ obtained is 4.3 × 104 s−1, which is substantially slower than the value 3.0 × 105 s−1 reported by Kuo et al. [Phys. Rev. Lett. 53, 2575 (1984)].
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2003 Dec 31|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics