(a) The unmodulated pump beam represented as a train of delta functions with an angular frequency of . (b) The pump beam after passing through an EOM. (c) Modulation due only the fundamental harmonic component of the EOM.
(a) The pump beam input to the sample modulated by the fundamental component of the EOM. (b) The surface temperature of the sample in response to the pump input. (c) The probe pulses arrive at the sample delayed by a time, , and are reflected back to a detector with an intensity proportional to the surface temperature. (d) The fundamental harmonic components of the reference wave and measured probe wave. The amplitude and phase difference between these two waves is recorded by the lock-in amplifier at every delay time.
(a) The amplitude signal returned by the lock-in for a sample with an exponential response for three different pulse periods: , , and . Results are plotted as a function of time . (b) The pulse period is fixed and the exponential decay time, , is varied from to . Amplitudes are normalized to the amplitude of the steady periodic response, .
The one-dimensional single-pulse solutions for a 100 nm layer of Al on two substrates, Si and , over 12.5 ns, the time between pulses from the Ti:sapphire oscillator.
(a) Sensitivity of the signal to the pump spot radius at three frequencies for a sample of coated with 100 nm of Al, plotted as a function of the pump spot radius. (b) Sensitivity of the signal to the cross-plane thermal conductivity of the under the same conditions.
(a) Sensitivity of the signal to the pump spot radius at three frequencies for a sample coated with 100 nm of Al, now plotted as a function of the sample thermal conductivity. The pump radius is fixed at and the probe radius is . Sensitivity to radial transport increases with decreasing substrate thermal conductivity due to stronger accumulation effects. (b) Sensitivity of the signal to the cross-plane thermal conductivity of the substrate under the same conditions.
An image of our HOPG sample coated with 72 nm of Al. Large grains are clearly visible. The pump and probe spots are focused within the white circle in the image.
Sensitivity of the signal from HOPG to in-plane thermal conductivity. The delay time is fixed at and the probe radius is fixed at , while the pump radius is varied.
Phase and amplitude data for HOPG, along with best-fit curves for cross-plane thermal conductivity, at a modulation frequency of 11.6 MHz, a probe radius of , and a pump radius of . In this regime, in-plane transport is not a factor.
HOPG phase data and best-fit curves for in-plane thermal conductivity, , at 3.6 MHz (a) and 1 MHz (b). Solutions obtained by varying by are also shown.
Results for HOPG at 300 K.
Article metrics loading...
Full text loading...