THz pulse measurement with an optical streak camera
First Claim
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1. A system for measuring a terahertz frequency pulse propagating in a free-space optical path, the system comprising:
- an optical streak camera; and
an electro-optical modulator positioned before the optical streak camera in the free-space optical path, wherein the streak camera measures an optical intensity as a function of time, and wherein the terahertz frequency pulse comprises subpicosecond free-space electromagnetic radiation with a bandwidth in a range from 10 gigahertz to 40 terahertz, and the terahertz frequency pulse modulates a probe pulse.
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Abstract
A method and apparatus for measuring electromagnetic pulses as a function of time. Radiation measurement, including measurement of single-shot, free-space terahertz femtosecond pulses, is realized using an electro-optical modulator in combination with an optical streak camera. This method and apparatus allow measurement of electromagnetic pulses previously unmeasurable due to the time resolution restrictions dictated by the time-frequency correlation.
15 Citations
35 Claims
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1. A system for measuring a terahertz frequency pulse propagating in a free-space optical path, the system comprising:
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an optical streak camera; and
an electro-optical modulator positioned before the optical streak camera in the free-space optical path, wherein the streak camera measures an optical intensity as a function of time, and wherein the terahertz frequency pulse comprises subpicosecond free-space electromagnetic radiation with a bandwidth in a range from 10 gigahertz to 40 terahertz, and the terahertz frequency pulse modulates a probe pulse. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
an electro-optical crystal; and
a polarization analyzer.
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8. The system of claim 7, wherein the electro-optical crystal comprises one of a ZnTe crystal, a GaAs crystal, a CdTe crystal, a CdZnTe crystal, and an organic DAST crystal.
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9. The system of claim 7 wherein the polarization analyzer converts a polarization modulation into an intensity modulation.
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10. The system of claim 7 wherein the polarization analyzer is in a crossed-polarizer geometry.
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11. The system of claim 1 wherein the streak camera comprises an electron tube comprising a photo cathode, an accelerating mesh, at least two electrodes, a multi-channel plate, and a phosphor screen.
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12. The system of claim 11 wherein the streak camera further comprises a data processing device to process data from the phosphor screen.
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13. The system of claim 12 wherein the data processing device is a CMOS.
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14. The system of claim 12 wherein the data processing device is a charge coupled device camera.
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15. The system of claim 1 further comprising an optical source, for providing the probe pulse and a pump pulse, and an emitter wherein the pump pulse excites the emitter to emit the terahertz frequency pulse.
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16. The system of claim 15 wherein the optical source is a laser.
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17. The system of claim 16 wherein the laser is a Ti:
- sapphire laser.
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18. The system of claim 1 further comprising a probe pulse polarizer positioned before the electro-optical modulator in a probe pulse optical path.
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19. The system of claim 1 further comprising a trigger to synchronize the streak camera and the probe pulse.
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20. The system of claim 19 wherein the trigger is a PIN diode.
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21. The system of claim 15 further comprising one or more lenses between the emitter and the electro-optical modulator.
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22. A system for measuring a free-space terahertz frequency pulse emitted from an emitter and propagating in an optical path, the system comprising:
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an optical streak camera;
an optical source and related optics for providing a pump pulse to excite the emitter to emit the terahertz frequency pulse and a probe pulse to probe the terahertz frequency pulse;
a probe pulse stretcher that produces a stretched probe pulse;
a probe pulse polarizer that produces a polarized stretched probe pulse from the stretched probe pulse;
a trigger that synchronizes the streak camera and the probe pulse; and
an electro-optical modulator positioned before the optical streak camera in the optical path, the electro-optical modulator comprising an electro-optical crystal and a polarization analyzer;
wherein an electric field is generated by the terahertz frequency pulse when the terahertz frequency pulse propagates through the electro-optical crystal, the electric field modulates the polarization of the polarized stretched probe pulse in the electro-optical modulator, generating a polarization modulation, wherein the polarization modulation is converted to an intensity modulation by the polarization analyzer, and the intensity modulation is measured by the streak camera. - View Dependent Claims (23, 24, 25, 26, 27)
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28. A method for measuring terahertz frequency electromagnetic pulses as a function of time, the method comprising the steps of:
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(a) providing an optical pump pulse and an optical probe pulse;
(b) exciting a terahertz frequency emitter with the optical pump pulse to generate an emitted pulse from the terahertz frequency emitter;
(c) stretching the optical probe pulse relative to the optical pump pulse;
(d) polarizing the optical probe pulse;
(e) modulating the probe pulse with a local electromagnetic field generated by the emitted pulse in an electro-optical modulator, the modulating resulting in a probe pulse polarization modulation;
(f) converting the polarization modulation into an intensity modulation; and
(g) measuring the intensity modulation as a function of time with a streak camera. - View Dependent Claims (29, 30)
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31. An apparatus for measuring a free-space terahertz frequency pulse in a time-dependent manner, said apparatus comprising:
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an electro-optical crystal positioned so that the free-space terahertz frequency pulse passes therethrough, thereby changing an index of refraction of the electro-optical crystal;
means for generating an optical probe signal to impinge the electro-optical crystal simultaneously with the free-space terahertz frequency pulse passing therethrough, the optical probe signal having a polarization modulation after impinging upon the electro-optical crystal;
means for determining the polarization modulation of the optical probe signal after impinging upon the electro-optical crystal;
means for characterizing the free-space terahertz frequency pulse by evaluating the polarization modulation of the optical probe signal; and
a streak camera. - View Dependent Claims (32, 33, 34, 35)
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Specification