Charge management of electrically isolated objects via modulated photoelectric charge transfer

• US 20080043397A1
• Filed: 06/01/2007
• Published: 02/21/2008
• Est. Priority Date: 06/02/2006
• Status: Active Grant

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Allard, Brett, Sun, Ke-Xun, Buchman, Saps, Byer, Robert
• Granted Patent: US 7,751,170 B2
• Time in Patent Office: Days
• US Class Current: 361/212
• CPC Class Codes: G01V 7/04 Electric, photoelectric, or magnetic indicating or recording means

Abstract

Charge transfer is provided to or from an electrically isolated test body by AC modulation of the photoelectric effect. More specifically, a reference body is disposed near the test body without physical contact between the reference and test bodies. Facing surfaces of the reference and test bodies are illuminated by optical radiation having a sufficiently short wavelength that charged particles are emitted from the reference and test bodies. An electrical bias is established between the reference body and the test body. Both the optical radiation and the electrical bias are modulated at the same frequency. A magnitude and direction of a charge transfer rate between the reference and test bodies is set by selecting a phase relation between the optical radiation and the electrical bias.

Claims

1. A method for transferring charge to or from an electrically isolated test body, the method comprising:

disposing a reference body in proximity to said test body;

applying a modulated electrical bias between said test body and said reference body;

illuminating said reference body and said test body with modulated optical radiation;

wherein said modulation of said electrical bias and said modulation of said optical radiation are phase coherent;

wherein a wavelength of said optical radiation is sufficiently short that charged particles are emitted from surfaces of said test and reference bodies illuminated by said optical radiation;

wherein said emitted charged particles move between said reference body and said test body in response to said electrical bias;

wherein one or more parameters of said modulated electrical bias and of said modulated optical radiation are selected to set a magnitude and direction of a charge transfer rate between said test body and said reference body;

wherein said parameters include a phase relation between said electrical bias and said optical radiation.

2. The method of claim 1, wherein a ratio of a maximum charge transfer rate magnitude to a minimum non-zero charge transfer rate magnitude is greater than about 10,000.

3. The method of claim 1, wherein said parameters further include one or more parameters selected from the group consisting of:

optical radiation duty cycle, electrical bias duty cycle, optical radiation modulation amplitude, electrical bias modulation amplitude, optical radiation amplitude, electrical bias amplitude, optical radiation pulse width, electrical bias pulse width, optical radiation modulation waveform, and electrical bias modulation waveform.

4. The method of claim 1, wherein said phase relation is adjusted during operation to alter said charge transfer rate.

5. The method of claim 4, further comprising controlling said phase relation with a control loop in order to hold a control variable to a predetermined range during operation.

6. The method of claim 5, wherein said control variable is an electrical potential difference between said test body and said reference body, and wherein said predetermined range includes zero.

7. The method of claim 1, wherein said electrical bias and said optical radiation are modulated at substantially the same modulation frequency

8. The method of claim 1, wherein said charged particles comprise electrons, and wherein emission of said electrons from said illuminated surfaces of said reference body and said test body is via the photoelectric effect.

9. A system for transferring charge to or from an electrically isolated test body, the system comprising:

a reference body disposed in proximity to said test body;

bias circuitry for applying a modulated electrical bias between said test body and said reference body;

an optical source for illuminating said reference body and said test body with modulated optical radiation;

wherein said modulation of said electrical bias and said modulation of said optical radiation are phase coherent;

wherein a wavelength of said optical radiation is sufficiently short that charged particles are emitted from surfaces of said test and reference bodies illuminated by said optical radiation;

wherein said emitted charged particles move between said reference body and said test body in response to said electrical bias;

wherein one or more parameters of said modulated electrical bias and of said modulated optical radiation are selected to set a magnitude and direction of a charge transfer rate between said test body and said reference body;

wherein said parameters include a phase relation between said electrical bias and said optical radiation.

10. The system of claim 9, wherein a ratio of a maximum charge transfer rate magnitude to a minimum non-zero charge transfer rate magnitude is greater than about 10,000.

11. The system of claim 9, wherein said modulation parameters further include one or more parameters selected from the group consisting of:

optical radiation duty cycle, electrical bias duty cycle, optical radiation modulation amplitude, electrical bias modulation amplitude, optical radiation amplitude, electrical bias amplitude, optical radiation pulse width, electrical bias pulse width, optical radiation modulation waveform, and electrical bias modulation waveform.

12. The system of claim 9, wherein said optical source comprises a substantially continuous-wave source in combination with a modulator.

13. The system of claim 9, wherein said optical source is directly modulated.

14. The system of claim 9, wherein said optical source comprises a source of ultraviolet radiation selected from the group consisting of:

gas discharge lamps, light emitting diodes, laser diodes, lasers, super-fluorescent sources, and sources including a nonlinear frequency conversion material.

15. The system of claim 9, wherein said test body comprises a proof mass for a space based gravitational wave sensor.

16. The system of claim 15, wherein said modulation frequency is not within an instrumentation bandwidth of said gravitational wave sensor.

17. The system of claim 9, wherein said electrical bias and said optical radiation are modulated at substantially the same modulation frequency.

18. The system of claim 9, wherein said charged particles comprise electrons, and wherein emission of said electrons from said illuminated surfaces of said reference body and said test body is via the photoelectric effect.