Superconducting quantum interference apparatus and method for high resolution imaging of samples
A method and apparatus performs high resolution imaging. The disclosed apparatus includes a low temperature SQUID sensor mounted in close proximity to a dewar thin window. A radiation shield has an extension surrounding the detection coil.
1. An apparatus for high resolution imaging of a sample, comprising:
a SQUID evacuated dewar;
a SQUID sensor cooperating with the dewar to sense magnetic flux from the sample being imaged, the sensor having a detection coil;
a cold finger;
the dewar having a thin window;
means for mounting the sensor remotely from the coil;
the detection coil being electrically connected to the SQUID sensor;
a mechanism for mounting the detection coil at the distal end of the cold finger in close proximity to the thin window, the mechanism including a bobbin having a tip;
a material disposed on the bobbin tip for cooling the detection coil below the transition temperature
a radiation shield mounted within the dewar and having an extension surrounding the detection coil to help maintain its cold temperature; and
wherein the extension prevents or reduces circular currents in the plane of the detection coil.
2. An apparatus according to claim 1 , further including a thick backing window overlying the thin window on the vacuum side thereof.
3. An apparatus according to claim 2 , wherein said thick backing window includes a hole therein for receiving the detection coil and the distal end of the shield extension.
4. An apparatus according to claim 3 , wherein the shield extension is conical and the window hole is tapered.
5. An apparatus according to claim 2 , wherein the thick backing window is composed of sapphire material.
6. An apparatus according to claim 1 , wherein the thin window is composed of sapphire material.
7. An apparatus according to claim 1 , further including a positioning mechanism for moving the detection coil adjustably toward and away from the thin window along a substantially straight path of travel.
8. An apparatus according to claim 7 , wherein the positioning mechanism includes a lever.
9. An apparatus according to claim 8 , wherein said positioning mechanism includes a flexure bearing.
10. An apparatus according to claim 1 , wherein said detection coil is a bare SQUID magnetometer.
11. An apparatus according to claim 10 , wherein said detection coil is an all-thin film SQUID magnetometer.
12. An apparatus according to claim 1 , wherein said detection coil is a magnetometer coil connected to a SQUID sensor.
13. An apparatus according to claim 1 , wherein said detection coil is a first derivative gradiometer.
14. An apparatus according to claim 1 , wherein said detection coil is an asymmetric gradiometer.
15. An apparatus according to claim 1 , wherein said detection coil is an apodized magnetometer coilgradiometer.
16. An apparatus according to claim 1 , wherein said detection coil is a vector magnetometer.
17. An apparatus according to claim 1 , wherein said detection coil is a gradiometer.
18. An apparatus according to claim 1 , wherein said detection coil is a fractional turn SQUID magnetometer.
19. An apparatus according to claim 1 , wherein the extension includes at least one longitudinally extending slot.
20. An apparatus according to claim 19 , wherein
the extension being generally conical in shape; and
the upper portion of the extension being larger than the lower portion of the extension.
21. An apparatus according to claim 1 , wherein the extension is composed of aluminum.
22. An apparatus according to claim 1 , wherein the extension is composed of coil foil.
23. An apparatus according to claim 1 , wherein the extension is composed of G-10 fiber composite for reducing circular currents in the plane of the detection coil.
24. An apparatus according to claim 1 , further including a cold finger reservoir and a radiation shield reservoir.
25. An apparatus according to claim 24 , wherein the cold finger reservoir contains liquid helium.
26. An apparatus according to claim 24 , wherein the radiation shield reservoir contains liquid nitrogen.
27. An apparatus according to claim 24 , wherein the radiation shield surrounds the cold finger reservoir and the radiation shield reservoir.
28. An apparatus according to claim 24 , wherein the radiation shield reservoir is disposed above the cold finger reservoir.
29. An apparatus according to claim 1 , wherein the material is aluminum Mylar.
30. A method of high resolution imaging of a sample, comprising:
sensing magnetic flux from the sample using a SQUID evacuated dewar and a SQUID sensor having a detection coil;
mounting the SQUID sensor within the dewar remotely of the detection coil;
mounting the detection coil on a bobbin having a tip at the distal end of a cold finger in close proximity to a thin window forming a part of the dewar;
placing a material on the bobbin tip for cooling the detection coil below the transition temperature;
mounting a radiation shield having an extension within the dewar and surrounding the detection coil; and
using the extension to prevent or reduce circular currents in the plane of the detection coil via the extension.
31. A method according to claim 30 , wherein the material is aluminum Mylar.
32. A method according to claim 30 , further including replacing the detection coil with another detection coil.
33. A method according to claim 30 , further including applying a magnetic field to the sample being imaged prior to or during said sensing.