HAL Id: jpa-00215078
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Submitted on 1 Jan 1972
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GENERAL INTRODUCTORY
SESSIONTECHNIQUES AND RESULTS OF HEAT PULSE EXPERIMENTS
R. von Gutfeld
To cite this version:
R. von Gutfeld. GENERAL INTRODUCTORY SESSIONTECHNIQUES AND RESULTS OF HEAT PULSE EXPERIMENTS. Journal de Physique Colloques, 1972, 33 (C4), pp.C4-1-C4-1.
�10.1051/jphyscol:1972401�. �jpa-00215078�
GENERAL INTRODUCTORY SESSION
TECHNIQUES AND RESULTS OF MEAT PULSE EXPERIMENTS
R. J. VON GUTFELD
IBM Thomas J. Watson Research Center Yorktown Heights, New York 10598
Abstract. - A general review of experimental heat pulse techniques with interpretations of some typical data is given. Several heat pulse generators are described including thin films utilizing pulsed currents, tunnel junctions and superconducting films in which the down-conversion of high frequency phonons occurs. The black body radiation model will be reviewed and related to the temperature of the pulsed current generator and the resulting phonon propagation. A brief review of heat pulse detectors will be given in order to characterize their properties as a function of tempe- rature and magnetic field. Results of heat pulse experiments will be presented by interpreting several portions of some detected heat pulse signals including [I] the ballistic region and the relation between the energy and phase velocities [2], the second sound regime (if any) and its rela- tion to normal and umklapp scattering rates [3], the scattered or diffusive portions and their relation to crystal defects and phonon polarization. Of the specific examples of scattering to be discussed, emphasis will be on phonon scattering in Ge due to donor impurities.
DISCUSSION H. F. BUDD. - Could you say something about
how you measure the response times of the heater ? Do you observe any power dependence of the relaxation times ?
R. J. VON GUTFELD.
-
The relaxation times were measured by shining laser light on a bolometer and observing its thermal decay with time. At low tempe- ratures the light source was a GaAs laser. At higher temperatures a pulsed ruby laser exciting a dye laserpropagation time. This time is difficult to predict or control and may account in large part for the fact that observed pulses have a different shape than the generated pulses. This is, of course, in addition to the effects of phonon scattering in the propagation medium.
C. J. ADKINS.
-
Where do flux lines come in if there is no magnetic field ? If the bias current is small enough, the magnetic field it generates will be smaller thanH,,
"A so flux-line nucleation is not involved.(CAP) was used.
R. J. VON GUTFELD. -There may be some flux
J.
K. WIGMORE--
Even with the use a fast lines from the bias current though we have never thin film bolometer, on a Pure substrate, the detected attempted to take any account of this. Typical bias heat pulses are not usually square. Do you have any currents are only-
10-3-10-2 amps.feelings on the reasons for this ?
S. J. ROGERS. - The preferential scattering of the R' J' 'ON GuTELD' This may be due to effects transverse mode by Sb impurities in Ge is quite similar caused by scattering from the wall or defects within
in its to Rayleigh scatte~ng which is propor- the More may be tional to the fourth power of the wave vector (not w4).
caused by poor contact of the films to the surfaces
Since in thermal equilibrium the transverse phonons which would tend to increase the relaxation times.
have larger wave vectors than the longitudinal phonons, A. ZYLBER~ZTEJN.
-
What is the influence of being they are preferentially scattered in a point scatteringi( partially superconducting >> for the thermal relaxa- process.
tion time of films ?
R. J. VON GUTFELD. - We have assumed no effect.
Thus, only heating or thermalization of the normal electrons or the electron just below the gap is assumed to increase the electrical resistance of the bolometer.
C. ELBAUM. - Thin films used for bolometers behave as type I1 superconductors, therefore their response time depends on flux line nucleation and
R. J. VON GUTFELD. - This is true for point defect scattering. However, in the Keyes and Griffin and Carruthers mechanisms, the anisotropy factor is such that only the transverse mode is scattered along the 100 direction. Thus, Sb should only cause trans- verse mode to scatter, leaving the longitudinal mode unaffected. This is in agreement with our experimental results.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972401
