Photo of the Week

December 13, 2005

    

Federico Canè, an MIT graduate student who has worked on the Walsworth Group Dual Noble Gas Maser experiment (Related details here) for the last five years celebrated his successful PhD thesis defense last week. It was another milestone for the group as well, and the second successful PhD student from MIT to graduate from the group this year, after Ruopeng Wang in February. Federico is shown at left above presenting his work during the defense presentation at MIT early in the day. Later in the day, he celebrated appropriately with champagne and chocolate cake with most of the group back in the CFA office area. Beers followed the next night, but we didn't take the camera along for that one! Federico still has a number of thesis corrections to take care of, before taking a well-earned vacation in Italy for the holidays. Congratulations Federico! 
 

December 5, 2005

    

The 4.7 T superconducting NMR magnet and associated spectrometer and micro-imaging unit has been operating in the Walsworth Group laboratory at the Center for Astrophysics for 18 months now. The system has the capability of a wide range of experiments, including a continuation of our prior porous-media flow studies, or condensed matter experiments focusing on heterogenous condensed systems such as mirco-emulsions or solutions whose polarization has been enhanced artificially using para-hydrogen induced polarization techniques. Currently, the system is being used by new graduate student Ryan McGorty for studies of gas exchange rates in gas-fluidized particle beds. At left above, Ryan is show in charge of the helium fill of the NMR magnet, a vital operation performed every 5 weeks. Liquid helium is pumped into the magnet in order to keep the magnet field-generating coil in the superconducting state, and hence generating the high magnetic field without power input. At right is a close-up photograph of the fluidized bed aparatus incorporating RF coil, which is filled with alumina particles, and then placed into the NMR magnet. Spin-polarized 129Xe gas flows in from below, fluidizes the particles, and the gas dynamics is probed by NMR techniques. Related details here
 

November 21, 2005

    

The second generation, human-research very-low-field MRI system is nearing completion in the Walsworth Group laboratory at the Center for Astrophysics. The magnet and associated hardware has been under construction for 18 months now, and we recently acquired the first two-dimensional images from the system. The very-low-field MR system operates with an applied magnetic field ~ 2-3 orders of magnitude below that of hospital MRI systems and our own superconducting MR microimaging system, however the open-access design of the magnet will allow imaging of the lungs of human subjects in a variety of orientations and postures. Design and construction of different RF coils for human chest imaging is now under way. Rigid forms large enough to accomodate the human chest can be prohibitively expensive, so as an interim measure we purchased a 20" diameter cardboard sonotube, designed for forming concrete columns. The tube is shown at left above, on Matt Rosen's car, arriving at the CFA - where it will be chopped into 2-3' lengths to provide forms for ~ 5 RF coils of different designs - and all for less than $100! Meanwhile, Leo continues to shim the magnet field for optimal homogeneity - reflected in a single-shot signal from a 100 cm3 water sample (right) that exhibits T2* > 100 ms and a spectral SNR of > 1000 at a field strength of ~ 65 Gauss (276 kHz).  
 

November 1, 2005

    

The second generation, human-research very-low-field MRI system is nearing completion in the Walsworth Group laboratory at the Center for Astrophysics. The magnet and associated hardware has been under construction for 18 months now, and in the past week, grad student Leo Tsai acquired the first two-dimensional images from the system. The open-access magnet is shown at left above, while a photograph and 1H MR image of a glass pitcher filled with water are at the right. The very-low-field MR system operates with an applied magnetic field ~ 2-3 orders of magnitude below that of hospital MRI systems and our own superconducting MR microimaging system. At such low field strengths, the very small spin polarization achieved at thermal equilibrium in the applied field implies that 1H MR images should be difficult to acquire due to sensitivity limitations. The environmental noise attenuation specifically designed and implemented for this system allows images like that above to be acquired in ~ 10 minutes. The open-access magnet will be used for imaging the lungs of human subjects in a variety of orientations and postures, as the magnet design allows for two-dimensional rotation of subjects between the magnet coils. 
 

October 18, 2005

    

Mason Klein is shown using the Walsworth Group's high-vacuum cell-filling station, preparing a new cell for use in rubidium-based stored light measurements. At left, he is heating the rubidium metal with a heat gun, in order to melt and "chase" the rubidium metal into the optical cell. At right, the rubidium and optical cells are shown in close up on the cell-filling station manifold. Related details here
 

August 29, 2005

    

The Walsworth group's Dual Noble Gas Maser system has been undergoing a major overhaul and reconstruction to permit a new series of precision frequency measurements. In addition to an overhaul of the hardware, including a new dual-bulb glass cell hot-air oven, we have also added a new generation laser to the system. The Toptica laser, shown at left, produces a narrower laser line at the desired wavelenth of 795 nm for Rubidium absorption, which can lead to far higher polarization levels for the 129Xe and 3He atoms in the glass bulbs, and so increases the sensitivty of frequency measurements performed. At right, the entire re-assembled system is shown. Related details here
 

August 2, 2005

    

Hydrogen masers have been built in our Hydrogen Maser Lab lab since the 1960's. Providing fractional frequency stability, Δf/f below 10-15 for periods of hours to days, our masers have found a wide variety of applications in precise time keeping and basic atomic physics. Recently, maser P-24 was overhauled and upgraded with the aim of increasing sensitivity by ~ 10 - 100 to aid our next series of experiments testing Lorentz invariance. These precise measurements involve searching for an orientation or velocity dependence of the maser frequency as that maser moves with respect to the fixed stars due to the rotation of the earth or its revolution about the sun. At right above, Smithsonian technician John Test is working on repairs to maser cavity before preparing it, with the help of Suzanne Rousseau, for insertion back into the magnetic shielding. 
 

July 20, 2005

Hydrogen masers have been built in our Hydrogen Maser Lab lab since the 1960's. Providing fractional frequency stability, Δf/f below 10-15 for periods of hours to days, our masers have found a wide variety of applications in precise time keeping and basic atomic physics. These have included spacecraft trackingradio astronomy, atomic physics studies and they have also flown in space for precise tests of general relativity. We are presently performing tests of Lorentz invariance with our hydrogen masers by searching for an orientation or velocity dependence of the maser frequency as that maser moves with respect to the fixed stars due to the rotation of the earth or its revolution about the sun. These precise measurements require external field stabilization. Above, the photo shows the maser surrounded by an enormous pair of Helmholtz coils which provide the required stable magnetic field.  
 

July 11, 2005

Hydrogen masers have been built in our Hydrogen Maser Lab lab since the 1960's. Providing fractional frequency stability, Δf/f below 10-15 for periods of hours to days, hydrogen masers have many uses in time keeping and basic physics. Our H Masers have been used throughout the world for spacecraft trackingradio astronomy, atomic physics and many other applications. They have also flown in space for precise tests of general relativity. We are presently performing tests of Lorentz invariance with our hydrogen masers by searching for an orientation or velocity dependence of a maser frequency as thet maser moves with respect to the fixed stars due to the rotation of the earth or its revolution about the sun.  
 

June 27, 2005

The Walsworth Group's "new" optics lab at the Center for Astrophysics has been in full operation for about 12 months now. A number of atomic clock, stored light, and related quantum optics experiments are in full flight in this new facility. The main photo gives an overview of the main optics table in this lab, with the experiments in progress. At right is a close up of an example glass cell containing rubidium from the Stored Light experiment. Related details here.
 

June 9, 2005

Yanhong Xiao, our newest post-doctoral researcher, took time out from her quantum optics work this week to celebrate her PhD graduation at Harvard University. Here, she is with Federico Cane and David Phillips in the group office area, while still wearing her commencement robes. Related details here.
 

May 10, 2005

Leo Tsai is monitoring the laser-polarized 3He gas polarization level using a dedicated, homebuilt polarimetery system, or very simplified, kHz-frequency NMR spectrometer, running on a Macintosh computer under Labview software. The 3He polarizer, behind Leo, has recently been upgraded with new polarization cells to provide more reliable and stronger 3He MRI signals for human very-low-field MRI experiments here at the Center for Astrophysics 
 

April 15, 2005

The Walsworth Group sent three group members - Ross, Tina and Leo - to the 46th Experimental NMR Conference in Providence, RI, during the week of April 10. Two posters were presented. Here, Tina is seen explaining her poster presentation to Dr. Martin Hurlimann, of Schlumberger Doll Research. The poster describes the measurement of gas interphase exchange in gas-fluidized granular columns, using laser-polarized xenon NMR. Related details here.
 

March 22, 2005

          

The Dual Noble Gas Maser has been undergoing a major overhaul and reconstruction prior to a new series of precision frequency measurements. Above, the major components of the Maser can be seen in various stages of assembly. At left, the new dual-bulb glass cell has been prepared, before being integrated with components of the hot-air oven (center and right) prior to re-assembly.Related details here.
 

February 14, 2005

John Test, a Smithsonian engineer and occaisional collaborator, in the process of re-assemblying our room-temperature Hydrogen Maser, no. P-24. He is being aided by our undergraduate research assistant, Jeff Surette. The Hydrogen Masers built at the SAO remain one of the most precise atomic clocks available today. Related details here.
 

February 6, 2005

Members of the Walsworth group and Misha Lukin group (Harvard University) attending the recent Open House on Atomic, Molecular and Optical Physics at the University of Connecticut, jointly hosted by University of Connecticut and the CFA's ownInstitute for Theoretical Atomic and Molecular Physics Related details here.