Latest News We have a YouTube Channel. Go there...       Dr. Taborek      Publications      Students      Postdocs      Alumni      Current Research      Contact Us      Handbook      UCI      Physical Sciences      Physics Dept.   How were the helium pinch-off pictures taken? A Kodak DCS315 Professional digital still camera was attached to a long range microscope outside the cryostat and focused on the pinch-off location. From the camera mount, a 630nm laser beam is redirected out of the microscope aperture, where it passes under the pinch-off location, and enters a photodetector on the opposite side of the cryostat. A blue glass notch filter is used to attenuate the partial transmission of red laser light into the camera. The image of the drop is allowed to pass through this attenuating filter. 630nm red light is removed, giving the image a blue tint. The disruption of the laser beam by the falling drop triggers the xenon flashlamp. By installing a delayed pulse generator between the photodiode and the flashlamp, several photographs of the drop in various stages of pinch-off can be easily obtained, allowing the frames to be pieced together into a video clip. How do QCMs (Quartz Crystal Microbalances) work? Quartz is a material that exhibits piezoelectric behavior; that is, an applied voltage to the crystal causes a physical distortion of the material. Likewise, a physical distortion of the crystal produces a voltage. When an AC voltage is applied to a QCM such that its frequency matches the resonant frequency of the crystal, a standing wave is established in the crystal. When a mass is applied to the crystal, as would occur in film deposition, or allowing droplets of liquids to exist on its surface, the resonant frequency of the crystal drops. The drop in frequency is linearly proportional to the mass coupled to the crystal's oscillation. The employment of some clever mathematics will convert this drop in frequency into a known mass. Why not put the camera inside the cryostat? Outwardly, it seems like a good idea. Why fuss with all the expense of mounting windows and just put the electronics inside the cryostat itself? The reason we can't do this is because at the temperatures our experiments take place, which is about -456º F, all electronics that involve semiconductors, such as CCD cameras, turn into electric insulators, rendering them useless. Liquid helium boils at 4.2K. How do you achieve temperatures lower than this? Helium-4 evaporative cooling: - Liquid helium can be cooled from its boiling point by pumping on the bath of liquid helium. Using this method alone, temperatures as low as 1K can be achieved. For anything less, other methods must be employed. Helium-3 evaporative cooling- 3He is expensive (about $200 per STP liter of gas), and efforts to recycle the evaporated gas must be employed. Temperatures as low as about 400mK can be obtained with this method. He3-He4 dilution refrigeration- about 100mK Adiabatic spin demagnetization: paramagnetic salt- <10mK Adiabatic nuclear demagnetization- <1µK How did you tilt the cryostat in those sliding droplets videos? We held the dewar aloft with a chain hoist while ratcheting a rope tied to the base of the cryostat and proceeded to hold our breath! All material on this site is the intellectual property of the Taborek/Rutledge research group.