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GENERATION AND DETECTION OF ULTRASONIC WAVES BEYOND 100 GHz
E. Jacobsen
To cite this version:
E. Jacobsen. GENERATION AND DETECTION OF ULTRASONIC WAVES BEYOND 100 GHz.
Journal de Physique Colloques, 1972, 33 (C6), pp.C6-25-C6-31. �10.1051/jphyscol:1972605�. �jpa-
00215123�
JOURNAL DE PHYSIQUE
Colloque C6, suppliment au no 1 1-1 2, Tome 33, Novembre-Dicembre 1972, page 25
GENERATION AND DETECTION OF ULTRASONIC WAVES BEYOND 100 GHz
E. H. JACOBSEN
Department of Physics and Astronomy, University of Rochester, Rochester, New York, U. S. A.
R6sum6.
- Le phenomene de pido6lectricit6 devrait thkoriquement permettre la production et la detection des ondes sonores dans un domaine de frequences couvrant la totalite du spectre de vibrations d'un solide; soit des frequences atteignant quelque 1013 Hz. Un avantage important de la methode est l'independance pratiquement totale de l'effet piBzoClectrique vis-a-vis des conditions locales de temperature, de pression et des chamsp Blectriques continus.
Un inconvenient apparait dans la detection des ondes elastiques de frequence superieure
A100
GHz ;en effet, le front d'onde doit %re parallkle a la surface piCzo6lectrique ou faire avec celle-ci un angle infkrieur a 1/D environ (1 reprisente la longueur d'onde sonore et D la dimen- sion linkaire de la surface utiliske du transducteur). Cette condition devient de plus en plus difficile a respecter a haute frequence lorsque
1atteint quelque 10 a 100 A, D mesurant habituellement 10-1 cm environ.
M6me si cette condition geomktrique Btait parfaitement remplie, de petits dkfauts de l'khantillon crkraient une distorsion suffisante du front d'onde.
Ces conditions n'empechent pas, cependant, la production, par effet pi6zo6lectrique, d'ondes klastiques de haute frequence.
Diffkrents procedes permettent la detection d'ondes sonores de haute frkquence
:1) utilisation de dktecteurs incoherents (par exemple spins) sensibles a des champs sur des distances de l'ordre de grandeur des dimensions atomiques, ou
2) utilisation de syst6mes de detection macroscopiques (par exernple jonction Josephson) qui bien que de dimensions superieures A celles de l'atome sont beaucoup plus petits que les dimen- sions transversales de l'ichantillon.
Ces mkthodes sont couramment CtudiCes dans notre laboratoire et seront discutkes plus longue- ment.
Abstract. -
The phenomenon of piezoelectricity should permit the generation of sound waves over virtually the entire elastic vibrational spectrum of a solid which covers frequencies up to some 1013 Hz. A great advantage of the piezoelectric method is that its dynamical behavior is almost totally independent of the local environment as regards temperature, pressure, and ambient
D. C . fields.A disadvantage presents itself in the detection of elastic waves above roughly 100
GHzowing to the fact that the wave front must be parallel to the piezoelectric surface to within an angle of approximately (AID), where
Iis the sonic wavelength and D is the cross-sectional dimension of the transducer surface. This condition becomes increasingly difficult to meet at high frequencies where
Imay range from ten to hundreds of Angstroms, and D will be typically about 10-1 cm.
Even if perfect geometric alignment were possible, small imperfections in the sample would distort the wave front to a significant degree. These conditions do not, however, prevent efficient gene- ration of high frequency elastic waves by means of the piezoelectric effect.
Possible ways to detect high frequency sound are to
:1) employ incoherent detectors (e. g.
spins) which respond to fields over atomic dimensions or 2) use macroscopic detection systems (e. g. Josephson junctions) which, though larger than an atom, are much smaller than typical transverse dimensions of the sample. These methods are currently under study in our laboratory and will be discussed at greater length.
1. Introduction.
-The piezoelectric effect should permit the generation and detection of elastic waves in matter over virtually the entire vibrational spec- trum, i. e., from zero t o about loi3 Hz. An attractive feature of the piezoelectric transducer lies in its insensitivity to temperature, and ambient electric and magnetic fields. Moreover, it can be deposited as a thin film directly on a sample [I], and electrically coupled in a simple manner to the driving and receiv-
ing circuit. Aside from signal loss due t o attenuation, which can be reduced by subjecting the sample t o liquid helium temperatures [2], a major problem arises, however, in detecting sound at high frequencies.
The difficulty centers on the short sonic wave length ; e. g., the wave length will be thousands of Angstroms at 10'' Hz, and hundreds of Angstroms o r less a t 1012 Hz. These numbers refer t o a solid ; in a liquid the wave length will be some five t o ten times less
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972605
C6-26 E. H. JACOBSEN
for the same frequency because of the reduced inter- atomic forces.
For maximum detection sensitivity, the piezo- electric surface should be flat and parallel to the wave front (assuming a plane wave) to within an angle of approximately 1/D, where I is the sound wave length and D the average cross sectional dimen- sion (typically millimeters) of the surface. This condition insures that the entire surface is driven at the same phase so that the piezoelectric polarization field is coupled maximally to the external circuit, e. g., resonant cavity. (Transformation from electric to sonic energy, and vice versa, takes place over a surface depth of one half the sonic wave length [3]).
At the higher frequencies this condition becomes increasingly difficult to meet because imperfections in the medium will scatter the wave and so produce an irregular wave front, and because even small misalignments between the wave front and piezo- electric surface will easily exceed AID. It is to be noted that these geometrical conditions need not be satisfied in the generation of high frequency sound
:complex and misaligned wave fronts will be generated readily by irregular piezoelectric surfaces and will propagate accordingly. Conventional piezoelectric detection of such waves, however, will prove difficult if not impos- sible at high frequencies.
In recent years, spin systems [4] and superconduct- ing tunnel junctions
[5]have been used to detect (and also generate) elastic waves above 100 GHz.
These systems respond to elastic waves over atomic volumes and therefore can detect wave fronts which lack phase coherence over macroscopic dimensions.
Detection sensitivity is further enhanced by operating these systems in conjunction with synchronous amplifiers.
2. Conventional piezoelectric generation and detec- tion of sound up to 100 GHz. - The piezoelectric generation and detection of sound up to perhaps 25 GHz is quite straight forward
:a re-entrant cavity, see figure 1, provides a convenient method of applying a microwave electric field to the surface of a piezo- electric crystal during sound generation. The same
FIG. 1. -Typical re-entrant cavity used in the range of 2 to 25 GHz to match piezoelectric transducer to exciting and
receiving microwave circuits.
cavity also serves to couple the piezoelectric surface polarization, produced by an incident sound wave, to the receiver. For simplicity we assume that the sound field is a pulse which propagates as a plane wave normal to thg crystal surface. (This assumption is usually valid if the cross-sectional dimensions of the sample are much larger than the sonic wave length.) Maximum detection sensitivity will obtain when the sound wave front is parallel to the piezoelectric surface. As departure from parallelism occurs, part of the surface will produce a polarization field of opposite phase so that the average polarization field seen by the cavity is accordingly reduced. As the angle between wave front and surface increases further, the average polarization oscillates through a series of nulls and decreasing maxima. The limits in angle are set, of course, by the sound intensity and receiver sensitivity. Typical pulse, superheterodyne microwave receivers in this frequency range routinely provide sensitivities of some 90 dbm (decibels below milliwatt).
Using such a receiver we have been able to detect a I milliwatt sound pulse in quartz at 24 GHz with a misorientation angle exceeding 100 AID.
At higher frequencies, e. g., beyond 100 GHz, the ratio 1/D becomes smaller and harder to satisfy.
Moreover, anharmonic attenuation becomes more serious
:the attenuation is typically proportional to fT4 at microwave frequencies and low tempera- tures, where f is the frequency and T is the sample temperature [6]. Finally geometrical scattering of the wave by small imperfections will increase and tend to produce a nonplanar front. Consequently the net piezoelectric polarization presented to the microwave cavity for coupling to the receiver is substantially reduced. Nonetheless, it is possible to piezoelectrically generate and detect sound waves in the 100 GHz range by paying careful attention to transducer alignment and receiver design. Such experiments have been carried out at 114 GHz 121, and are described below.
At frequencies beyond about 25 GHz the re-entrant cavity becomes impractical as a means of coupling the external microwave circuit to a piezoelectric crystal because the cavity dimensions and Q become very small [7]. A way around this limitation is to replace the re-entrant cavity by an enclosed cylindrical or rectangular cavity operating in a higher-order mode.
Such an arrangement is shown in figure 2. If the quartz crystal is made to fill the cavity such that the x-axis of the crystal coincides with the long dimension, a corrugated wave front will be generated at each end as indicated. The corrugation results from the fact that the phase of the electric driving field Ex oscillates with distance along the transverse direction of the cavity. The resulting sound wave is mainly compressional but contains a small shear component.
Such a wave will propagate in fact over several
centimeters before the phase of the shear wave
changes enough, relative to that of the compressional
GENERATION AND DETECTION OF I JLTRASONIC WAVES BEYOND 100 GHz 05-27
wave, to alter significantly the shape of the wave front [S]. It is likely, however, that other sources of wave front distortion, e. g., misalignment and scat- tering, are much more effective in diminishing the average surface polarization available to the cavity for
((reading out
))the signal. A rectangular TM3,4,8 cavity filled with quartz and bathed in liquid helium will have dimensions of 0.328 x 0.425 x 0.85 cm3, a Q - 1000 (assuming the use of copper), and be resonant at 114 GHz [2].
W a v e g u i d e Q u a r t z
\
a v i t y x - a x i s
/ S o u n d W a v e
,\
fronts
FIG. 2. - Cylindrical high mode cavity for use above 25 GHz.
A receiver sensitivity exceeding 100 dbm will be required for detection at these frequencies unless microwave driving powers of at least a hundred milliwatts are available. We found it expeditious to operate a superheterodyne receiver of standard design as a phase sensitive detector so as to achieve the required sensitivity. A block diagram of such a scheme appears in figure 3. The basic operation entails comparing the average of a series of receiver output pulses containing signal plus noise with the average of an equal number of receiver pulses containing noise only. (Prior to taking the noise only samples, the phonon generator klystron is quiescent.).
'2 = f l / "
P u l s e closed closed
11111 Ulli -
I I
FIG. 3. - Superheterodyne receiver operated as a synchronous detector to achieve higher rensitivity at ultramicrowave fre- quencies. For any given series of echoes the synchronous ampli- fier compares the output of the I. F. amplifier containing the
noise-plus-signal with the output containing noise only.
The pulses are selected and averaged by a delayable gate and box car integrator, the output of which is fed to a synchronous amplifier, and hence to a recorder.
In this way the effective receiver band pass is greatly reduced and the noise averaged out. The delay of the pulse sampling gate is slowly and continuously increased so that the output of synchronous amplifier gradually sweeps through the various phonon echo pulses.
This procedure will yield
areceiver sensitivity of about 100 dbm, and will permit detecting phonon echoes generated by a microwave drive power of some tens of milliwatts. Non-piezoelectric samples can be studied in the same system by evaporating a piezoelectric film on one surface [I]. Since geometric alignment is critical at these frequencies, it will often prove rewarding to test the propagation of phonon signals in the sample first at 10 GHz. The samples which yield the best signals at 10 GHz usually also yield the best signals at 100 GHz.
It is clear that successful experiments in elastic wave propagation in the 100 GHz range depend on the combination of sample perfection, attenuation, available microwave source power, and receiver sensitivity. Of these items, increases in microwave source power and detection sensitivity appear to be the only practical route for improved research at 100 GHz frequencies and beyond by means of the piezoelectric effect. At this writing carcinotrons are available which produce a watt of power between 100 and 300 GHz. At 900 GHz, the HCN laser can produce about the same power. At frequencies above 100 GHz the attenuation of electromagnetic waves in metal wave guides increases rapidly so that dielectric guides, mirrors, or hybrid systems will be required for energy transmission to (and possibly from) the sample. For the same reason it will be necessary to replace the enclosed resonant cavity by structures such as the Fabry-Perot and zone plate systems shown in figures 4 and 5. While it seems
Sample C a v i t y
FIG. 4. - Fabry-Perot cavity for coupling to piezoelectric transducer above 200 GHz.
likely that more powerful high frequency microwave sources will be developed, a more immediate prospect of improvement appears to lie in the direction of greater detection sensitivity.
Fundamentally, detection of sound can proceed
by incoherent or coherent processes. Quantum detec-
tion by means of paramagnetic ions in crystals [4],
E. H. JACOBSEN
Zone Plate
J Sample /
/ Piezoelectric Surface
FIG. 5,
-
Zone plate as a means of coupling to piezoelectric transducer above several hundred GHz.and Cooper pairs in superconductors
[S]are examples of the former. In this process only the intensity and not the phase of the wave is detected, the obvious advantage being that detection is unaffected by wave shape and sample geometry. Piezoelectric detection, by contrast, is a coherent process
;the phase is preserved and the instantaneous amplitude is amplified at the signal frequency. So long as wave shape and sample geometry are not limiting factors, coherent detection offers the advantage of relatively high gain through the property of the superheterodyne principle wherein the intensity at the difference frequency (I. F.) is proportional to the square root of the product of signal and local oscillator intensities.
In the light of these remarks it is of interest to consider methods for improving both coherent and incoherent detection of sound at ultra-microwave frequencies and beyond. We propose in the following paragraphs some possible schemes for doing so.
3. New methods of detecting sound above 100 GHz.
-
3.1 JOSEPHSON
JUNCTION PIEZOELECTRICALLY COU- PLED TOSOUND. - A novel method of phonon detection arises in the use of a weak-link superconduct- ing Josephson junction. This device is highly sensitive to oscillating electric and magnetic fields [9], and may be deposited on a piezoelectric surface in micro- geometry. Such an arrangement is expected to couple to the local piezoelectric polarization field on the scale of the junction dimensions, which means that the sound wave need be phase coherent over a much smaller spacial extent.
The coupling of a Josephson junction to an oscil- lating field produces a series of steps in the d. c.
current-voltage characteristic of the junction. If only one frequency is present, each step occurs at a voltage corresponding to a multiple of the excitation frequency, according to the relation V
=nhf/2 e.
V is the d. c. voltage applied to the junction, n is an integer, h is Planck's constant, f is the excitation frequency, and e is the electron charge. If two fre- quencies are present, the steps in the I-V curve occur at voltages corresponding to sum and difference frequencies, and multiples and combinations thereof.
Two weak-link geometries suitable for coupling to the piezoelectric polarization field and outlined in figures 6 and 7. Figure 6 shows a point-contact junction afixed to the end of a sample. The junction comprises a sputtered film and point of niobium, separated by a thin (1 000 A) piezoelectric layer of cadmium sulfide. The point is pressed through the piezoelectric layer by means of a differential spring drive mechanism so as to establish a weak link.
Coupling to the local polarization field occurs over a small volume surrounding the point. The piezoelec- tric properties of the thin transducer determine whether transverse or longitudinal waves will be coupled to the junction. In the arrangement outlined here both a longitudinal and transverse wave can produce a parallel field which will couple to the junction.
FIG. 6.
-
Niobium point contact Josephson junction excited by polarization field in thin piezoelectric film of cadmium sulfide.This geometry is sensitive to vibration and ambient fields.
x - a x i s
Junction m
Wave
-Normal w Q u a r t z
FIG. 7.
-
Constricted film bridge Josephson junction excited by transverse piezoelectric fieid produced by sound wave pro- pagating along film normal. This geometry is relatively insen-sitive to ambient fields and is immune to vibration.
Unfortunately the scheme in figure 6 is rather sensitive to mechanical vibration and external a. c.
fields. An alternative arrangement which is much
less sensitive to external influences is outlined in
figure 7. Here the junction comprises a thin film in
the shape of an
((H
))with the central region function-
ing as the weak-link. The assembly is deposited directly
GENERATION AND DETECTION OF ULTRASONIC WAVES BEYOND 100 GHz C6-29
on a piezoelectric surface, so that the lateral polari-
zation field between the legs of the
((H
))excite the junction and produce steps in the I-V curve as in figure 6 . The central (weak-link) region of the junction must be small, typically 0.5 micron long by 0.25 micron wide. An ingenious method of producing such micro- geometry has been reported [lo]. Electron beam lithography [ l l ] appears especially attractive as a means of fabrication, since all dimensions of the junction can then be made small, e. g., a cross-sec- tional width of order ten microns. The orientation of the junction relative to the piezoelectric substrate will determine the polarization of the sound wave to be detected. Figure 7 shows a junction oriented on quartz in such a way that a transverse wave pola- rized along the c-axis and propagating along the x-axis will generate a polarization field along the c-axis and thereby excite the junction. A different choice of orientation, crystal, and piezoelectric tensor would permit detection of a longitudinal wave by means of the same configuration. An alter- native procedure would be to misorient the plane of the junction by a small angle relative to the wave front so that the two halves of the junction would be driven out of phase. The angle would be of order AID, where D is the cross sectional dimension of the junction. Our experience with waves at 10 GHz indicates that it is possible to create controlled small angle misorientations by applying a small force at right angles to the sample. Hence, it may be possible to mechanically
((tune
))such a system so as to achieve maximum phase difference between the two halves of the junction.
In addition to detecting high frequency elastic waves by means of a Josephson junction, it appears possible in principle to generate them according to the relation f
=2 eV/h. This relation states that an a. c. voltage at frequency f will appear across the junction when the applied d. c. voltage is V. The a. c. voltages and resulting fields will be small under typical conditions. However, it may be possible to develop a resonant geometry which will substantially increase the effective a. c. field. Generation of sound by such a device is attractive in that the frequency can be continuously tuned over a vast range. Further efforts in this direction may prove rewarding.
As noted earlier, superheterodyne detection is attractive because of the possibility of power gain and the convenience of processing the signal at the difference frequency. It is well known that the Joseph- son junction is a non-linear device which permits the mixing of two microwave signals [9]. This feature offers the possibility of operating the junction confi- gurations of Figures 6 and 7 in the superheterodyne mode, instead of searching for steps in the I-V curve, as a means of detecting the presence of high frequency phonons. While this method appears interesting, there exists an alternative method of perhaps greater potential by which to employ the superheterodyne
principle with its consequent enhancement of detection sensitivity. This method, non-piezoelectric in nature, utilizes the relatively strong coupling between Cooper pairs and phonons with energies which exceed the gap energy of a superconductor. Hence the system functions as a square law detector in the same way as a photoelectric cell exposed to light. These ideas are described further below.
3.2 SUPERHETERODYNE
DETECTOR (FOR[hw > E
GAP).
- When a superconductor-insulator-super- conductor sandwich is biased as in figure 8, very little quasiparticle tunneling current will flow from side [2] to [I] since there are relatively few particles above the gap at low temperatures. If, however,
FIG. 8. - Density of states and gap for two identical super- conductors biased across an insulating barrier. For excitations exceeding the gap energy, quasiparticles are lifted above the gap
resulting in net current flow from film (2) to film (1).
phonons with hw > E gap are incident on the sandwich the tunnel current from [2] to [I] will increase as a result of breaking Cooper pairs and sending quasi- particles above the gap [5], [Ill. The same process should also occur for incident photons provided that hw > E gap [12]. Moreover, the increase in tunnel current will be proportional to the number of phonons or photons present, i. e., proportional to the intensity of the incident sound or light wave. This situation raises the possibility of detecting phonons in a super- conducting sandwich by means of the superhete- rodyne principle (i. e., by using the superconductor as a square law detector). In this arrangement the sandwich would be simultaneously excited by phonons (signal at o,) and photons at a slightly different frequency from a klystron (local oscillator at o,) through a suitable wave guide assembly. Assuming the sandwich to be excited coherently by the two waves, the tunnel current will be of the form I
=I [ ~ A sin o, t
CbE sin (o, t + q)I2
where A and E are, respectively, the amplitudes of
the sound and electromagnetic waves, and a and b
are the corresponding coupling constants between
wave and Cooper pairs. The current will contain
frequency components at 2 w,, 2 o,, o, + o, and
w,
-o,. We are interested in the latter which repre-
sents the cross
e m sin the above expression. Since
C6-30 E. H. JACOBSEN
the current component which vaires at (o,
-0.1,) is proportional to the product (AE)', power gain is possible by making the local oscillator amplitude E large. (Should the cross mixing of phonon and photon amplitudes appear questionable, it should be recalled that the sound wave is really an oscillating electric field on the local scale.) The difference frequency (a, - o,) could easily be adjusted to fall between 1 and 100 MHz, and it should be quite practical to extract currents at these low frequencies from the junction and amplify them with conventional I. F.
amplifiers. Figure 9 outlines such an arrangement.
FIG. 9. - Biased, tunnel junction (two superconductors sepa- rated by an insulating layer) deposited on sample and used as square law detector. Output is taken at the difference frequency
between phonon signal at f~ and local oscillator at f2.
The advantages of the above detection scheme are
:(i) Very high frequency phonons should be detectable with good sensitivity because of the rela- tively strong coupling between Cooper pairs and phonons for h o > E gap, and because of the super- heterodyne principle. (ii) Accurate determination of the signal phonon frequency spectrum is possible provided a stable, monochromatic local oscillator is available. (iii) The method is well suited to both pulsed and steady state phonon signals. (iv) The system is relatively simple, compact, and flexible over a vast frequency range. For example, no magnetic fields are needed to tune spin levels to a high fre- quency. More-over, as an aside, it should be possible to explore in detail the frequency spectrum of phonons generated by reconstituting Cooper pairs in a super- conductor, which reflects the shape of the density of states at the gap edges.
Maximum sensitivity requires that the detector be driven coherently by the sound wave which implies that the wave front be parallel to the plane of the sandwich to within (ideally) an angle 6 - AID, where A
is the sonic wavelength and D is the average lateral dimension of the sandwich. Clearly, this condition will be increasingly difficult to meet as the frequency is raised. However, the situation is not as severe as it may seem. As noted earlier the detection sensitivity oscillates through a series of diminishing maxima as
8exceeds AID so that significant detection is still possible for 6 - 10 AID. Also, the effective lateral dimension of the sandwich can be made very small if necessary, although doing so will reduce the maximum amplitude of tunnel current. Further encouragement as to the feasibility of achieving phase coherence over the detector area comes from recent experiments on phonon interference in liquid helium I1 films via tunnel junctions at 100-150 GHz [12]. Hence it appears that sufficient leeway exists for achieving superior detection sensitivity up to several hundred GHz, and possibly into the 10'' Hz region, a range offering considerable exploratory interest.
4. Piezoelectric generation of sound above 100 GHz.
-
Whereas the piezoelectric detection of high fre- quency sound presents difficulties because of the short wave length, the generation of sound does not. Generation merely requires an electromagnetic source of sufficient intensity and a means of coupling to the piezoelectric transducer. With present techno- logy two approaches to this problem suggest them- selves as likely candidates for development in the near future.
One approach is to drive the piezoelectric transducer at the frequency of the source by a coupling scheme similar to that of figures 4 and 5. At the present time molecular lasers produce powers of about a watt at discrete frequencies near 900 GHz. The upper frequency limit of electron tube devices is about 300 GHz so that a gap exists between 300 and 900 GHz for which no monochromatic source exists presently.
It seems likely, however, that this part of the spectrum will be filled in due course by some form of laser oscillator. Above 900 GHz molecular gas lasers furnishing milliwatts at discrete frequencies are becoming practical 1131. Future laser development will undoubtedly provide more powerful monochro- matic sources in the range between 10'' and 1013 Hz.
A second approach to sound generation by piezo- electric conversion of electromagnetic energy is to mix two laser beams in a non-linear device and drive the transducer at the difference frequency.
Recent experiments in mixing the outputs of two
CO, lasers (f - 3 x 1013 HZ) in a thin slab of GaAs
yielded microwatts of power at a difference frequency
of some 900 Hz [14]. The lasers were pulsed and
yielded a peak output power of about 2 kW. Calcu-
lations indicate that such a system could generate
output at a difference frequency over the range of
300 GHz to about 6 000 GHz. The low conversion
efficiency resulted from the lack of phase matching
of the primary waves in the crystal with the result
that generation occurred over a coherence length
of 0.7 mm. I1 the conversion efficiency could be
improved to the level of yielding watts of power
at the difference frequency, very useful sources for
generating monochromatic sound at thermal fre-
quencies would become available.
GENERATION AND DETECTION OF ULTRASONIC WAVES BEYOND 100 GHz C6-3 1
References
[I] DEKLERK John, in
Physical Acoustics,vol. IV, Part A,
edited by W. P. Mason (Academic Press, New York, 1966), 195.
[2] ILUKOR John and JACOBSEN E. H., in Physical Acous- tics, vol.
V,edited by
W.P. Mason (Academic Press, New York, 1968), 221.
[3] JACOBSEN E. H., in Phonons and Phonon Interac- tions, edited by Thor A. Bak (W.
A.Benjamin, Inc., New York, 1964) 51 1-522.
[4] ANDERSON
C.H. and SABISKY E. S., in Physical Acoustics, vol. VIII, edited by W. P. Mason and, R.
N.Thurston (Academic Press, New York, 1971), 1
;SHIREN
N.S.,
Phys. Rev. Lett., 6(1961), 168.
[5] EISENMENGER
W.and DAYEM A.-H.,
Phys. Rev.Lett. 18
(1967) 125
;BLACKFORD B. L.,
ibid.28
(1972) 414
;KINDLER H.,
ibid. 28(1972) 1564.
[6] HUMPHREY MARIS J., in Physical Acoustics, vol. VIII, 280.
[7] TANNENWALD P. E. and THAXTER J. B.,
Appl. Phys.Lett. 5
(1964) 67.
[8] Mechanical Waveguides by Martin R. Redwood (Pergamon Press Ltd., London, 1960).
[9] GRIMES C.
C.and SHAPIRO S.,
Phys. Rev. 169(1968) 397
;HAMILTON C. A. and SHAPIRO
S., Phys.Lett. 32A
(1970) 223.
[lo] GREGERS-HANSEN P. E. and LEVINSEN M. T.,
Phys.Rev. Lett. 27
(1971) 847.
[ll] HATZAKIS M. and BROERS
A.N., in Rec. 10th Symp.
Electron, Ion and Laser Beam Technology.
(San Francisco Press, 1969), 107
;HERZOG R.
F.et al., IEEE Trans. Electron Devices ED 19
(1972) 635.
[I21 BLACKFORD B. L.,
Phys. Rev. Lett. 28(1972) 414.
[13] PATEL C. K.
N. et al., Appl. Phys. Lett. 4(1964) 18
;GEBBIE H. A.
et al., Nature 203(1964) 285
; ibid. 211(1966) 62.
[14] BRIDGES T. J. and STRNAD
A. R., Appl. Phys. Lett.20
(1972) 382.
DISCUSSION
B. R. TITTMANN.
-1) In what materials do you J. LEWINER. - Could
YOUsay a few words on conduct your experiments
?2) What is the phonon loss at 100 GHz
?E. H. JACOBSEN.
-1) Primarily natural quartz.
2) Approx. 0.2 db/cm at 4 OK. It would be nice to conduct studies in other materials such as ZnO but this for the future.
C. ELBAUM.
-YOU propose that the use of tunnel junction detectors would permit detection of waves with frequencies up to, or even in excess of
1012CIS. Would the detection process not be limited, essentially to the superconducting gap frequencies (because of the falling efficiency in breaking Cooper pairs as the frequency increases above o -
Alh) ?E. H. JACOBSEN.
-It's a question of how fast the electron phonon interaction decreases as we go up to frequency beyond 1012 c/s. It seem to recall that the interaction is still sufficiently strong at these frequencies, but should check this again.
M. PAPOULAR.
-Could you give a typical figure for the sensitivity of the Josephson jonction device
?E. H. JACOBSEN. - We expect to be able to detect sound power levels of lo-'' W/cm2 using the weak link Josephson jonction.
the technique you use to get a Josephson jonction thiner than a micron
?E. H. JACOBSEN.
- Method# 1
:Use a diamond to scratch piezoelectric surface, then evaporate thin (1 000 A) superconducting film, then make light cut in direction at right angles. (See ref. to Gregor- Hansen of Lenenson in my paper for details.)
Method
