Transmission mode terahertz computed tomography
AssigneeRensselaer Polytechnic Institute
InventorsBradley Stuart Ferguson, Shaohong Wang, Xi-Cheng Zhang
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Abstract
A method of obtaining a series of images of a three-dimensional object by transmitting pulsed terahertz (THz) radiation through the entire object from a plurality of angles, optically detecting changes in the transmitted THz radiation using pulsed laser radiation, and constructing a plurality of imaged slices of the three-dimensional object using the detected changes in the transmitted THz radiation. The THz radiation is transmitted through the object as a scanning spot. The object is placed within the Rayleigh range of the focused THz beam and a focusing system is used to transfer the imaging plane from adjacent the object to a desired distance away from the object. A related system is also disclosed.
Claims25
An apparatus for performing coherent terahertz (THz) wave computed tomography, the apparatus comprising:
- i. a sensor for modulating an amplitude of incident optical radiation as a result of illuminating the sensor with THz-frequency electromagnetic radiation;
- ii. means for generating a probe beam, said probe beam including pulsed optical radiation directed onto the sensor along a first path and exiting the sensor along a second path and;
- iii. means for generating a pulsed THz radiation beam directed onto the sensor through a third path wherein said third path includes:
- a. a sample area,
- b. a THz radiation beam focusing system having at least one focusing element with a diameter,
- c. a support for holding a sample in the sample area at a first orientation relative to a propagation direction of the pulsed THz radiation beam, and
- d. means for altering the first orientation;
- and
- iv. a detector in the second path for detecting the amplitude of the pulsed optical radiation beam;
- wherein:
- a. the sample area is smaller than the Rayleigh range of the THz beam;
- and
- b. the focusing system is designed to focus an imaging plane adjacent the sample area onto the sensor.
A method for performing computed tomography using THz-frequency radiation, the method comprising:
- I. obtaining a reference signal by:
- i. transmitting pulsed THz radiation through a path that includes a sample holding area and a focusing system and impinging the pulsed THz radiation onto a sensor, wherein the sample holding area is smaller than a Rayleigh range of a focused THz beam and the focusing system is designed to focus a plane adjacent the sample holding area onto the sensor;
- ii. transmitting a pulsed optical radiation probe beam having a first amplitude through the sensor when the sensor is illuminated with THz-frequency electromagnetic radiation, and
- iii. detecting a second amplitude of the optical pulse following passage through the sensor;
- II. placing a sample in the sample holding area;
- III. transmitting a pulsed THz radiation beam through a pixel area of the sample;
- IV. impinging the pulsed THz radiation beam following transmission through the sample onto the sensor while transmitting the optical probe beam through the sensor;
- V. detecting an amplitude of the probe beam emerging from the sensor;
- VI. repeating steps III–V a plurality of times to obtain a temporal profile of the THz pulse and calculate a frequency domain THz amplitude and frequency;
- VII. repeating steps III–VI a plurality of times for a plurality of sample pixel areas and for a plurality of sample orientations relative to the THz beam to obtain the composite frequency domain for a plurality of pixels from a plurality of angles;
- and
- VIII. reconstructing an image of the sample from the composite frequency domain.
A method for performing computed tomography using THz-frequency radiation, the method comprising:
- I. obtaining a reference signal by:
- A. transmitting pulsed THz radiation through a path that includes a sample holding area and a focusing system and impinging the pulsed THz radiation onto a sensor, wherein the sample holding area is smaller than a Rayleigh range of a focused THz beam and the focusing system is designed to focus a plane adjacent the sample holding area onto the sensor,
- B. transmitting a chirped pulsed optical radiation probe beam having a first amplitude profile through the sensor when the sensor is illuminated with THz-frequency electromagnetic radiation, and
- C. detecting a second amplitude profile of the chirped optical pulse following passage through the sensor;
- II. placing a sample in the sample holding area;
- III. transmitting a pulsed THz radiation beam through a pixel area of the sample;
- IV. impinging the pulsed THz radiation beam following transmission through the sample onto the sensor while transmitting the optical probe beam through the sensor;
- V. detecting an amplitude as a function of frequency of the chirped probe beam emerging from the sensor and converting the amplitude as a function of frequency to an amplitude as a function of delay time thereby to obtain a temporal profile of the THz pulse;
- VI. calculating a frequency domain THz amplitude and frequency;
- VII. repeating steps III–VI a plurality of times for a plurality of sample pixel areas and for a plurality of sample orientations relative to the THz beam to obtain the composite frequency domain for a plurality of pixels from a plurality of angles;
- and
- VIII. reconstructing an image of the sample from the composite frequency domain.
Dependencies are inferred from the claim text.