Paul A. Warkentin

Static magnetization of superfluid 3He

New measurements of the static magnetization of 3He-B in contact with a variety of wall configurations are presented and compared with previous measurements in both A and B phases. At high pressure the data tend toward agreement with resonant-magnetism experiments, while near the polycritical point a large discrepancy between the results of the two methods remains.

Time-dependent thermal convection in dilute solutions of 3He in superfluid 4He

Time-dependent thermal convection can occur in a unity-aspect-ratio Rayleigh-Beńard convection cell containing a dilute solution of 3He in superfluid 4He when the fluid is heated from above. Results are presented primarily for a 0.24 mole % He solution at 0.925 K. Means is provided for introducing heat at the top and separately for a central plug and an outer ring such that both are at a constant temperature gDT above the bottom. A critical temperature difference δTcfor convection can be defined above which both steady and time-dependent convection occur. The time-dependent effects include a region of δT. near δTcand characterized only by excessive noise, a region of somewhat higher δT where there are intermittent major changes in the plug heating rate with a time distribution like that for random events, and a region at still higher δT where periodic but nonsinusoidal variation of the heat flow is observed. When a long enough time, several months, has elapsed after cooling down the apparatus, time-dependent states no longer occur, and the heat flow above δTcis limited to steady convection. Briefly raising the temperature of the apparatus to 77 K is sufficient to restore the possibility of time-dependent states.

Longitudinal magnetic relaxation in superfluid 3He

Longitudinal magnetic relaxation in both 3He-A and 3He-B is studied in a variety of magnetic fields and three different geometries. Relaxation as described by Leggett and Takagi is observed for particular geometries in both 3He-A and 3He-B within a very limited range of magnetic field and temperature near Tc. Under certain other conditions the longitudinal magnetization in 3He-A does not relax monotonically in time. Relaxation in 3He-B very near the critical temperature is shown to be remarkably different following nominal 90‡ and 180‡ pulses. Other observations using RF pulses with a time-dependent frequency provide evidence for a negative frequency shift in 3He-B at large tipping angles in certain geometries.

A Comparison of Optical Gaussian Beam Lithography with Conventional E-beam and Optical Lithography

The photolithographic properties of scanned laser imaging systems are discussed in comparison with conventional optical projection printers and e-beam imaging systems. Because a scanned laser system can effectively stitch together a large number of small fields, the customary trade-off between resolution and field size does not have to be made, and higher NA lenses can be used. Residual system astigmatism can be corrected by adjustments to the input illumination of the lens. The imaging properties of a Gaussian beam system are fundamentally incoherent and are a strong function of the input beam truncation. Contrast curves are developed for different amounts of truncation and compared with the theoretical and experimental contrast of projection printers. Although e-beam systems can resolve smaller features than optical systems, the effective image contrast of features substantially larger than their minimum spot sizes is reduced by electron back-scattering. E-beam contrast curves are compared with those of modern optical lithography tools. Finally, the resolution limit for laser scanned lithography is explored based on available deep UV CW laser light sources and high NA lens technology: it is estimated to be below 0.2 μm.