Browsing by Author "Alles, H."
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- Cooled video camera for optical investigations below 1 mK
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1994) Alles, H.; Ruutu, J. P.; Babkin, A. V.; Hakonen, Pertti J.; Manninen, A. J.; Pekola, Jukka P.An optical imaging system for milliKelvin temperatures has been developed based on a regular B/W surveillance camera (25 frames/s), with its CCD sensor inside the 4‐K vacuum can of our nuclear demagnetization cryostat. The heat leak to the nuclear stage, caused by the operation of the video camera, was reduced below 1 nW by careful rf shielding. The construction of the system and its limits of operation are discussed. - First optical observations of superfluid 3He
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1992-10-19) Manninen, A. J.; Pekola, J. P.; Kira, G. M.; Ruutu, J. P.; Babkin, A. V.; Alles, H.; Lounasmaa, O. V.The shape of the free surface of rotating superfluid B3 has been investigated optically. The drastic change in viscosity at the superfluid transition was seen directly. Focusing of light reflected from the liquid surface and expansion of the light beam when it travels through the He3 sample show that the meniscus of the rotating superfluid has the same parabolic shape as that of the normal liquid, which implies an equilibrium density of vortices. The fountain effect in B3 could be seen directly as well: Liquid accumulates into the illuminated region. - First optical observations of superfluid He 3
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1992) Manninen, A. J.; Pekola, Jukka P.; Kira, G. M.; Ruutu, J. P.; Babkin, A. V.; Alles, H.; Lounasmaa, O. V.The shape of the free surface of rotating superfluid B3 has been investigated optically. The drastic change in viscosity at the superfluid transition was seen directly. Focusing of light reflected from the liquid surface and expansion of the light beam when it travels through the He3 sample show that the meniscus of the rotating superfluid has the same parabolic shape as that of the normal liquid, which implies an equilibrium density of vortices. The fountain effect in B3 could be seen directly as well: Liquid accumulates into the illuminated region. - Observation of a New Surface State on 4He Crystal Interfaces
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1995) Babkin, A. V.; Alles, H.; Hakonen, Pertti J.; Parshin, A. Ya.; Ruutu, J. P.; Saramäki, J. P.The equilibrium shape of hcp 4He crystals has been studied at temperatures 0.05≤T≤0.7 K by means of a high-precision optical interferometer. We find that the profile of the interfacial boundary, close to an almost horizontal c-facet, has a well-defined slope discontinuity separating two angular regions with different behavior of the surface stiffness α̃. For surfaces tilted by an angle φ≲100 μrad with respect to the c-facet, we obtain α̃=κ/φ, contrary to the linear angular dependence predicted by current theories. Our results on four large crystals yield κ=(11±3)×10 exp −4T erg/ cm exp 2 K. - Observation of dispersion in the J=2+ collective modes of 3B by nonlinear acoustic spectroscopy
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1992-06-22) Manninen, A. J.; Alles, H.; Babkin, A. V.; Pekola, J. P.; McKenzie, R. H.Parametric excitation yields new results, which cannot be obtained by conventional linear spectroscopy, on the collective modes in superfluid B3. In our ultrasonic experiments, performed in a chamber with four quartz crystals, we have excited the real squashing (J=2+) modes by two simultaneous sound waves which are mutually either parallel, orthogonal, or antiparallel. Qualitatively these results are in agreement with the theoretical dispersion relation of the J=2+ modes, and quantitatively we have been able to extract the collective-mode velocities from the line splittings in zero magnetic field. - Observation of dispersion in the J=2+ collective modes of B3 by nonlinear acoustic spectroscopy
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1992) Manninen, A. J.; Alles, H.; Babkin, A. V.; Pekola, Jukka P.; McKenzie, R. H.Parametric excitation yields new results, which cannot be obtained by conventional linear spectroscopy, on the collective modes in superfluid B3. In our ultrasonic experiments, performed in a chamber with four quartz crystals, we have excited the real squashing (J=2+) modes by two simultaneous sound waves which are mutually either parallel, orthogonal, or antiparallel. Qualitatively these results are in agreement with the theoretical dispersion relation of the J=2+ modes, and quantitatively we have been able to extract the collective-mode velocities from the line splittings in zero magnetic field. - Observations on Superfluid Meniscus in Rotating 3He-B
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1995) Alles, H.; Ruutu, J. P.; Babkin, A. V.; Hakonen, Pertti J.; Lounasmaa, O. V.; Sonin, E. B.The parabolic superfluid meniscus has been seen for states in which only (1) the normal or (2) the superfluid component of 3He-B rotates. A reduced, temperature-dependent meniscus (1) was formed at small speeds Ω≲0.21 rad /s. A deeper-than-expected meniscus (2) was observed after a rapid halt of the cryostat, when the normal fluid stops during a short relaxation time, followed by slow decay of the superfluid circulation. The depth of the meniscus (2) was explained by a reactive radial force between the rotating superfluid and the stationary normal liquid. - Wetting of Superfluid 4He by Liquid 3He
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(1994) Alles, H.; Ruutu, J. P.; Babkin, A. V.; Hakonen, Pertti J.We have investigated optically the spreading of He3 on top of the He4-rich solution in phase-separated helium-mixture films, 20-50 μm thick. In equilibrium, the He3 layer wets the He4-rich phase completely, but nearly circular or stripelike pools of He3-rich phase are stabilized instead when He4 atoms are condensed to the liquid sample at the rate 10 exp 15-5 × 10 exp 15 atoms/cm2s. For the contact angle we obtain about 10 mrad, which suggests a fractional change of the He3 surface tension by a factor of 10 exp −5 from the equilibrium value.