  Specific heat and linear thermal expansivity are fundamental thermal dynamics
and have been proven as interesting relaxing quantities to investigate in glass
transition and glassy state. However, their possibility has much less been
exploited compared to mechanical and dielectric susceptibilities due to the
limited spectroscopy bandwidth. This work reports on simultaneous spectroscopy
of the two by making use of ultrafast time-resolved thermal lens (TL)
spectroscopy. Detailed modeling of the thermoelastic transients of a relaxing
system subjected to ultrashort laser heating is presented to describe the TL
response. The model has been applied to analyze a set of experimentally
recorded TL waveforms, allowing the determination of relaxation strength and
relaxation frequency from sub-kilohertz to sub-100 MHz and in a wide
temperature range from 200-280 K.
