A pulsed terahertz wave sparse array synthetic aperture imaging device and imaging system

Abstract

The present invention discloses a pulse terahertz wave sparse array synthetic aperture imaging device and imaging system, belonging to the field of terahertz imaging technology. The present invention includes a laser, a first switching switch, a transmitting photoconductive antenna array and a receiving photoconductive antenna array. The laser generates laser pulses, the transmitting photoconductive antenna array receives laser pulses and transmits terahertz pulses; the receiving photoconductive antenna array receives laser pulses and detects terahertz pulses; the transmitting photoconductive antenna array and the receiving photoconductive antenna array are located in the same plane and form a ring structure. The present invention uses ultra-wideband terahertz pulses generated by optical methods as imaging carriers. The frequency range covered by terahertz pulses is much larger than the bandwidth of electronic devices. Ultra-wideband bandwidth is obtained without frequency scanning, solving the problem of insufficient technical means for high-frequency band imaging of terahertz waves, and enabling terahertz imaging technology to be more widely used in fields such as biomedicine and industrial detection.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz imaging, and in particular to a pulsed terahertz wave sparse array synthetic aperture imaging device and an imaging system. Background Art

[0002] Terahertz waves refer to waves with frequencies ranging from 0.1 THz to 10 THz (1 THz=10 12 Hz), which is between infrared and microwaves in the electromagnetic spectrum. Electromagnetic waves in this band have many unique properties: first, water molecules and some biological molecules have characteristic absorption responses in the terahertz frequency band; second, terahertz communication has the characteristics of large bandwidth and low latency; third, terahertz radiation has good penetration ability for a variety of industrial materials; fourth, terahertz radiation photons have low energy and are completely harmless to biological tissues; fifth, terahertz waves can easily penetrate severe weather such as dust, haze, etc. In view of the above characteristics, terahertz technology has unique application value and broad market prospects in many fields such as biomedicine, high-speed communication, industrial detection and public safety. Terahertz imaging technology is an important development direction for the application of terahertz technology and is the basic technology for the application of terahertz technology in various fields.

[0003] In 1995, BB Hu et al. first reported terahertz imaging (BB Hu and MC Nuss, Imaging with THz waves, Opt. Lett., 20, 1716 (1995)). This scheme places the imaged object on a two-dimensional translation stage, then focuses the terahertz wave and irradiates it onto the sample, and detects the terahertz signal that passes through the sample. The terahertz image of the object can be obtained by scanning the sample in two dimensions perpendicular to the propagation direction of the terahertz wave through the translation stage. The metal pins in the integrated circuit and the water distribution in the leaves can be clearly seen from the terahertz image. Due to the characteristics of terahertz imaging itself, other terahertz imaging technologies have also developed rapidly, such as focused scanning imaging, active real aperture imaging, passive real aperture imaging, synthetic aperture imaging and other methods.

[0004] Focus scanning imaging places the sample at the focus of the terahertz wave and performs a two-dimensional scan of the sample perpendicular to the propagation direction of the terahertz wave to obtain a transmission or reflection image of the sample. This imaging method is simple and easy to operate. The image signal-to-noise ratio is high. For layered samples, internal layer information can be obtained by measuring the time delay of the terahertz pulse. However, this method is only applicable to transmission imaging of flat sheet samples and reflection imaging of samples with flat surfaces. It is less applicable to samples with irregular shapes.

[0005] Active real aperture imaging irradiates the sample with terahertz waves, and uses a quasi-optical real aperture imaging system to collect the terahertz waves reflected from the sample surface to form a terahertz reflection distribution intensity image of the sample. Its advantage is that there is an active radiation source and the image signal-to-noise ratio is good. However, the mirror reflection effect on the sample surface causes the image to be uneven, forming bright or dark spots on the image, which affects the image quality.

[0006] Passive real aperture imaging uses a quasi-optical real aperture imaging system to focus the terahertz waves emitted by the sample itself onto the image plane, forming a terahertz radiation distribution intensity image of the sample. The terahertz waves spontaneously emitted by the object have an isotropic property, which is conducive to the detection of the imaging system and forms a uniform terahertz image. However, due to the weak intensity of the spontaneously emitted terahertz waves, they are easily affected by environmental radiation. In addition, high-sensitivity detection devices in the terahertz high-frequency band are not yet mature.

[0007] Synthetic aperture imaging irradiates the sample with terahertz waves, receives the terahertz waves scattered by the sample, and reconstructs the terahertz image of the sample using the synthetic aperture imaging algorithm. There is an active radiation source, and the image signal-to-noise ratio is good. A larger aperture can be synthesized, and the image resolution is high. It can solve the shortcomings of active real aperture imaging to a certain extent. However, the system is highly complex and is limited by the current level of terahertz transceiver links, so it is still difficult to apply it in the terahertz high frequency band. Summary of the invention

[0008] 1. Technical problem to be solved by the invention

[0009] In order to solve the image quality deterioration caused by the mirror reflection effect of active real aperture terahertz imaging, and the difficulty that passive real aperture terahertz imaging and synthetic aperture terahertz imaging cannot be applied in the high frequency band of terahertz waves due to the limited development level of terahertz devices, the present invention proposes a pulse terahertz wave sparse array synthetic aperture imaging device and imaging system. The present invention uses optical methods to generate and detect terahertz pulses, solves the problem of insufficient imaging technology means in the high frequency band of terahertz waves, and enables terahertz imaging technology to be more widely used in the fields of biomedicine and industrial detection.

[0010] 2. Technical solution

[0011] In order to achieve the above object, the technical solution provided by the present invention is:

[0012] The invention discloses a pulse terahertz wave sparse array synthetic aperture imaging device, comprising a laser, a first switching switch, a plurality of transmitting photoconductive antenna arrays and a plurality of receiving photoconductive antenna arrays, wherein the laser generates laser pulses, the transmitting photoconductive antenna array receives the laser pulses and transmits terahertz pulses via the first switching switch; the receiving photoconductive antenna array receives the laser pulses and detects terahertz pulses via a second beam splitter; the transmitting photoconductive antenna array and the receiving photoconductive antenna array are located in the same plane, and the transmitting photoconductive antenna array and the receiving photoconductive antenna array are cross-arranged to form a ring structure.

[0013] As a further improvement of the present invention, the laser pulses generated by the laser are respectively emitted into the transmitting photoconductive antenna array and the receiving photoconductive antenna array through the first beam splitter.

[0014] As a further improvement of the present invention, the laser pulses generated by the laser are split by the first beam splitter, then emitted into the first switching switch through the variable optical delay line, and then respectively emitted into each transmitting photoconductive antenna array; all transmitting photoconductive antenna arrays work in time-sharing manner.

[0015] As a further improvement of the present invention, the laser pulse generated by the laser is split by the first beam splitter, split again by the second beam splitter, and respectively emitted into each receiving photoconductive antenna array; all the receiving photoconductive antenna arrays work simultaneously.

[0016] As a further improvement of the present invention, the transmitting photoconductive antenna array includes a second switching switch, a transmitting optical fiber, a transmitting lens and a transmitting antenna electrode array, and the second switching switch, the transmitting optical fiber, the transmitting lens and the transmitting antenna electrode array are connected together in sequence.

[0017] As a further improvement of the present invention, the transmitting antenna electrode array includes a transmitting antenna substrate, a transmitting electrode and a bias device, the transmitting electrode is arranged on the transmitting antenna substrate, the transmitting electrode is divided into two parts, a transmitting antenna electrode gap is arranged between the two parts of the transmitting electrodes, and the bias device is electrically connected to the transmitting electrode; the electrodes of each array unit are interconnected and use a bias voltage provided by the same bias device.

[0018] As a further improvement of the present invention, the receiving photoconductive antenna array includes a third beam splitter, a receiving optical fiber, a receiving lens and a receiving antenna electrode array, and the third beam splitter, the receiving optical fiber, the receiving lens and the receiving antenna electrode array are connected in sequence.

[0019] As a further improvement of the present invention, the receiving antenna electrode array includes a receiving antenna substrate, a receiving electrode and a current collector, the receiving electrode is arranged on the receiving antenna substrate, the receiving electrode is divided into two parts, a receiving antenna electrode gap is arranged between the two parts of the receiving electrodes, and the current collector is electrically connected to the receiving electrode; the electrodes of each array unit are independent of each other, and each outputs current to the current collector separately.

[0020] As a further improvement of the present invention, two of the transmitting photoconductive antenna array and two of the receiving photoconductive antenna array are provided, the transmitting photoconductive antenna array and the receiving photoconductive antenna array form a square structure, the two transmitting photoconductive antenna arrays are provided in parallel, and the two receiving photoconductive antenna arrays are provided in parallel.

[0021] The present invention also provides a pulse terahertz wave sparse array synthetic aperture imaging system, comprising a plurality of the above-mentioned imaging devices, wherein the transmitting photoconductive antenna arrays and the receiving photoconductive antenna arrays in the plurality of imaging devices are located in the same plane.

[0022] 3. Beneficial effects

[0023] Compared with the existing known technologies, the technical solution provided by the present invention has the following significant effects:

[0024] (1) The present invention provides a sparse array synthetic aperture imaging device and imaging system for pulsed terahertz waves. Ultra-wideband terahertz pulses generated by optical methods are used as imaging carriers. The frequency range covered by terahertz pulses is much larger than the bandwidth of electronic devices, and ultra-wideband bandwidth is obtained without frequency sweeping. Moreover, the terahertz pulses generated by the method continuously cover the spectrum range of the entire system bandwidth in terms of frequency. The spectrum components can be increased by simply increasing the relative time delay between the detection laser pulse and the measured terahertz pulse, so that more frequency information can be used when reconstructing the terahertz image.

[0025] (2) At present, imaging based on terahertz time-domain spectroscopy mainly includes transmission scanning imaging, reflection scanning imaging and time-of-flight three-dimensional imaging, etc. These imaging methods all require focusing of terahertz waves. Due to the limitations of available lens materials in the terahertz band, the quality of terahertz quasi-optical devices is far behind that of the visible light band. However, the terahertz wave sparse array synthetic aperture imaging device and imaging system of the present invention, in which the terahertz wave is divergently irradiated to the imaged target, avoids the image deterioration problem caused by the real aperture focusing problem of the lens in the prior art.

[0026] (3) It avoids the following problems existing in existing imaging methods in the terahertz high frequency band: 1) The synthetic aperture imaging method based on electronics is limited to the device level and cannot be applied to the high frequency band of terahertz waves; 2) Active real aperture imaging has the problem of mirror reflection of the imaging target in the terahertz band, causing the echo to deviate from the receiving range, resulting in a decrease in imaging quality; 3) There is a lack of high-performance low-noise amplifiers and high-sensitivity passive terahertz detectors working in the high frequency band, and passive real aperture imaging cannot be achieved in the terahertz high frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the overall structure of the imaging device of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the terahertz emission photoconductive antenna array in the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of the terahertz emission photoconductive antenna electrode array in the present invention;

[0030] Figure 4 This is a schematic diagram of the structure of the terahertz receiving photoconductive antenna array in the present invention;

[0031] Figure 5 This is a schematic diagram of the structure of the terahertz receiving photoconductive antenna electrode array in the present invention;

[0032] Figure 6 It is a schematic structural diagram of a single imaging device of the present invention;

[0033] Figure 7 The figure is a schematic diagram of the structure of an imaging system composed of multiple imaging devices of the present invention.

[0034] Description of the numbers in the schematic diagram:

[0035] 1. Laser; 2. First beam splitter; 3. Variable optical delay line; 4. First switching switch; 5. Second beam splitter; 6. Transmitting photoconductive antenna array; 61. Second switching switch; 62. Transmitting optical fiber; 63. Transmitting lens; 64. Transmitting antenna electrode array; 641. Transmitting antenna substrate; 642. Transmitting electrode; 643. Transmitting antenna electrode gap; 644. Bias device; 7. Object to be measured; 8. Receiving photoconductive antenna array; 81. Third beam splitter; 82. Receiving optical fiber; 83. Receiving lens; 84. Receiving antenna electrode array; 841. Receiving antenna substrate; 842. Receiving electrode; 843. Receiving antenna electrode gap; 844. Current collector. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the invention more obvious and understandable, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0041] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0042] Example 1

[0043] Combination Figure 1 In this embodiment, a pulsed terahertz wave sparse array synthetic aperture imaging device includes a laser 1. In this embodiment, the laser 1 is a femtosecond laser for generating femtosecond laser pulses. The femtosecond laser pulse generated by the laser 1 is injected into the first beam splitter 2 for splitting, and is respectively injected into the transmitting photoconductive antenna array 6 and the receiving photoconductive antenna array 8. The first beam splitter 2 in this embodiment is a one-to-two optical beam splitter, which divides the femtosecond laser pulse generated by the laser 1 into two beams, one of which is used to generate terahertz pulses, called pump light; and the other is used to detect terahertz pulses, called detection light. In this embodiment, one of the two femtosecond laser pulses is injected into the first switching switch 4 through the variable optical delay line 3, and then injected into multiple transmitting photoconductive antenna arrays 6 by the first switching switch 4. Among them, the variable optical delay line 3 is used to change the optical path of the pump light, thereby changing the optical path difference between the pump light and the detection light, so as to measure the time domain waveform of the entire terahertz pulse. In this embodiment, the terahertz time-domain pulse waveform is transformed into the frequency domain through fast Fourier transformation, and a longer time-domain waveform can be obtained by increasing the time delay of the variable optical delay line 3 to obtain a higher spectral resolution, thereby obtaining a larger maximum unambiguous distance.

[0044] The first switch 4 is a single-pole double-throw optical switch, which is used to switch the pump light, and transmit the pump light to different transmitting photoconductive antenna arrays 6 at different time periods, so that each transmitting photoconductive antenna array 6 generates a terahertz pulse. Another femtosecond laser pulse is split again by the second beam splitter 5 and is respectively emitted into each receiving photoconductive antenna array 8.

[0045] In this embodiment, multiple transmitting photoconductive antenna arrays 6 and receiving photoconductive antenna arrays 8 are provided, and the multiple transmitting photoconductive antenna arrays 6 and receiving photoconductive antenna arrays 8 are located in the same plane, and the transmitting photoconductive antenna arrays 6 and receiving photoconductive antenna arrays 8 are cross-arranged to form a ring structure. The transmitting photoconductive antenna array 6 receives laser pulses and emits terahertz pulses through the first switching switch 4; the receiving photoconductive antenna array 8 receives laser pulses and detects terahertz pulses through the second beam splitter 5. Specifically in this embodiment, two transmitting photoconductive antenna arrays 6 and two receiving photoconductive antenna arrays 8 are provided, and the transmitting photoconductive antenna arrays 6 and the receiving photoconductive antenna arrays 8 are connected to form a square "mouth" shaped structure, wherein the two transmitting photoconductive antenna arrays 6 are arranged oppositely and in parallel, and the two receiving photoconductive antenna arrays 8 are also arranged oppositely and in parallel. This embodiment constitutes a terahertz sparse array transceiver array.

[0046] Since two receiving photoconductive antenna arrays 8 are provided, the second beam splitter 5 is a one-to-two beam splitter. If more receiving photoconductive antenna arrays 8 are provided, the second beam splitter 5 is a one-to-many beam splitter. The second beam splitter 5 divides the detection light into several beams with equal power, and transmits the detection light to multiple receiving photoconductive antenna arrays 8, and detects the terahertz pulse at the same time. In this embodiment, each part is connected by an optical fiber, and the optical fiber is used for the laser pulse generated by the laser 1 to propagate between the components.

[0047] Combination Figure 2 and Figure 3In this embodiment, the transmitting photoconductive antenna array 6 includes a second switching switch 61, a transmitting optical fiber 62, a transmitting lens 63 and a transmitting antenna electrode array 64, and the second switching switch 61, the transmitting optical fiber 62, the transmitting lens 63 and the transmitting antenna electrode array 64 are connected together in sequence. Among them, the second switching switch 61 is a single-pole multi-throw optical switch, which is used to switch the pump light, and transmit the pump light to different transmitting antenna electrode arrays 64 at different time periods to generate terahertz pulses respectively. The transmitting optical fiber 62 transmits the laser pulse output by the second switching switch 61 to the transmitting antenna electrode array 64. The transmitting lens 63 is a self-focusing lens that focuses the laser pulse and irradiates it into the gap between the electrodes on the transmitting antenna electrode array 64. The transmitting antenna electrode array 64 also includes a transmitting antenna substrate 641, a transmitting electrode 642 and a bias device 644. The transmitting electrode 642 is arranged on the transmitting antenna substrate 641, and the transmitting electrode 642 is arranged in two parts. The transmitting antenna electrode gap 643 is arranged between the two parts of the transmitting electrode 642, and the bias device 644 is electrically connected to the transmitting electrode 642. The transmitting antenna substrate 641 is a semiconductor substrate, which generates photogenerated carriers in cooperation with laser pulses, and generally uses low-temperature grown gallium arsenide (GaAs) as the semiconductor substrate material. The transmitting electrode 642 introduces the voltage generated by the bias device 644 into the transmitting antenna electrode gap 643, and the transmitting antenna electrode gap 643 forms a local electric field to provide power for the movement of photogenerated carriers; the bias device 644 provides an external voltage to the transmitting electrode 642.

[0048] In this embodiment, the process of generating terahertz pulses is as follows: the femtosecond laser pulse generated by the laser 1 passes through the first beam splitter 2, the variable optical delay line 3, and the first switching switch 4 in sequence to reach the transmitting photoconductive antenna array 6. After passing through the second switching switch 61, the transmitting optical fiber 62 and the transmitting lens 63 in sequence, it is irradiated onto the transmitting antenna substrate 641 between the transmitting antenna electrode gaps 643, and localized photogenerated carriers are generated at the transmitting antenna electrode gaps 643 of the transmitting antenna substrate 641. The external voltage provided by the bias device 644 forms a local electric field at the transmitting antenna electrode gaps 643. The photogenerated carriers are accelerated under the action of the electric field to form terahertz pulses for external radiation. By switching the first switching switch 4 and the second switching switch 61, all antenna units in the multiple transmitting photoconductive antenna arrays 6 can be operated in time-sharing manner.

[0049] Combination Figure 4 and Figure 5In this embodiment, the receiving photoconductive antenna array 8 includes a third beam splitter 81, a receiving optical fiber 82, a receiving lens 83 and a receiving antenna electrode array 84, and the third beam splitter 81, the receiving optical fiber 82, the receiving lens 83 and the receiving antenna electrode array 84 are connected in sequence. Among them, the third beam splitter 81 is a one-to-many optical beam splitter, which divides the detection light into multiple beams with equal power, and transmits the detection light to all the receiving antenna electrode arrays 84 at the same time, and detects the terahertz pulse at the same time. The receiving optical fiber 82 transmits the laser pulse output by the third beam splitter 81 to the receiving antenna electrode array 84. The receiving lens 83 is a self-focusing lens, which focuses the laser pulse and irradiates it onto the receiving antenna electrode gap 843 between the receiving electrodes 842 on the receiving antenna electrode array 84.

[0050] In this embodiment, the receiving antenna electrode array 84 includes a receiving antenna substrate 841, a receiving electrode 842 and a current collector 844. The receiving electrode 842 is arranged on the receiving antenna substrate 841. The receiving electrode 842 is divided into two parts. A receiving antenna electrode gap 843 is arranged between the two parts of the receiving electrode 842. The current collector 844 is electrically connected to the receiving electrode 842. Among them, the receiving antenna substrate 841 is a semiconductor substrate, which generates photogenerated carriers in conjunction with laser pulses. Generally, low-temperature grown gallium arsenide (GaAs) is used as the semiconductor substrate material. The receiving electrode 842 introduces the current generated by the receiving antenna electrode gap 843 into the current collector 844. The receiving antenna electrode gap 843 is used to form a current for the movement of photogenerated carriers. The current collector 844 collects the current generated between the receiving antenna electrode gaps 843.

[0051] In this embodiment, the process of detecting terahertz pulses is as follows: the femtosecond laser pulse generated by the laser 1 passes through the first beam splitter 2 and the second beam splitter 5 in sequence to reach the receiving photoconductive antenna array 8. After passing through the third beam splitter 81, the receiving optical fiber 82, and the receiving lens 83 in sequence, it is irradiated onto the receiving antenna substrate 841 between the receiving antenna electrode gaps 843, and localized photogenerated carriers are generated at the receiving antenna electrode gaps 843 on the receiving antenna substrate 841. When there is an external terahertz wave electric field to be detected, the photogenerated carriers move under the action of the terahertz wave electric field to form a current, which is collected by the current collector 844. The magnitude of the current is proportional to the magnitude of the detected terahertz wave electric field. In this embodiment, through the beam splitting of the second beam splitter 5 and the third beam splitter 81, all antenna units in the multiple receiving photoconductive antenna arrays 8 can be operated simultaneously.

[0052] Combination Figure 6 The specific imaging process of this embodiment is as follows: the object to be measured 7 is placed in front of the terahertz sparse array transceiver array.

[0053] Step 1, switching the first switch 4 and the second switch 61 to control the pump light to reach the first transmitting unit of the first transmitting photoconductive antenna array 6, generating a terahertz pulse to irradiate the object to be measured 7;

[0054] Step 2: All detection units of all receiving photoconductive antenna arrays 8 simultaneously detect the terahertz pulse scattered by the object to be measured 7;

[0055] Step 3: changing the time delay of the variable optical delay line 3, the current collector 844 simultaneously collects the time domain waveform of the terahertz wave detected by all detection units of all receiving photoconductive antenna arrays 8;

[0056] Step 4, the first switching switch 4 and the second switching switch 61 control the pump light to reach the next transmitting unit of the transmitting photoconductive antenna array 6 to generate a terahertz pulse to irradiate the object to be measured 7;

[0057] Step 5: All detection units of all receiving photoconductive antenna arrays 8 simultaneously detect the terahertz pulse scattered by the object to be measured 7;

[0058] Step 6: The time delay of the variable optical delay line 3 is changed, and the current collector 844 simultaneously collects the time domain waveform of the terahertz wave detected by all the detection units of the receiving photoconductive antenna array 8;

[0059] Step 7, repeat steps 4-6 until all transmitting units of all transmitting photoconductive antenna arrays 6 are traversed, and a total of m×n terahertz scattering time domain pulse data are obtained, where m is the number of transmitting units of all transmitting photoconductive antenna arrays 6, and n is the number of receiving units of all receiving photoconductive antenna arrays 8.

[0060] Step 8: Perform fast Fourier transform of the m×n terahertz scattering time-domain pulse data into the frequency domain to obtain scattering data for each frequency point.

[0061] Step 9: Generate a three-dimensional terahertz image of the imaged object 7 using a synthetic aperture imaging image reconstruction algorithm.

[0062] Example 2

[0063] Combination Figure 7 This embodiment provides a pulse terahertz wave sparse array synthetic aperture imaging system, including multiple imaging devices of embodiment 1, wherein the transmitting photoconductive antenna array 6 and the receiving photoconductive antenna array 8 in the multiple imaging devices are located in the same plane. The imaging system of this embodiment generally adopts M rows and N columns to place imaging devices to form an M×N rectangular array. The specific working process is as follows:

[0064] Step S1, switching the first switch 4 and the second switch 61 to control the pump light to reach the first transmitting unit of the first transmitting photoconductive antenna array 6, generating a terahertz pulse to irradiate the object to be measured 7;

[0065] Step S2, all detection units of all receiving photoconductive antenna arrays 8 simultaneously detect the terahertz pulse scattered by the object to be measured 7;

[0066] Step S3, changing the time delay of the variable optical delay line 3, and the current collector 844 simultaneously collects the time domain waveform of the terahertz wave detected by all detection units of all receiving photoconductive antenna arrays 8;

[0067] Step S4, the first switch 4 and the second switch 61 control the pump light to reach the next transmitting unit of the next transmitting photoconductive antenna array 6 to generate a terahertz pulse to irradiate the object to be measured 7;

[0068] Step S5, all detection units of all receiving photoconductive antenna arrays 8 simultaneously detect the terahertz pulse scattered by the object to be measured 7;

[0069] Step S6, changing the time delay of the variable optical delay line 3, and the current collector 844 simultaneously collects the time domain waveform of the terahertz wave detected by all detection units of all receiving photoconductive antenna arrays 8;

[0070] Step S7, repeat steps S4-S6 until all transmitting units of all transmitting photoconductive antenna arrays 6 are traversed, and a total of i×j terahertz scattering time-domain pulse data are obtained, where i is the number of transmitting units of all transmitting photoconductive antenna arrays 6, and j is the number of receiving units of all receiving photoconductive antenna arrays 8.

[0071] Step S8, performing fast Fourier transform on the i×j terahertz scattered time-domain pulse data to the frequency domain to obtain scattering data at each frequency point.

[0072] Step S9: Generate a three-dimensional terahertz image of the imaged object 7 using a synthetic aperture imaging image reconstruction algorithm.

[0073] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A pulsed terahertz wave sparse array synthetic aperture imaging device, characterized in that: The invention comprises a laser (1), a first switch (4), a plurality of transmitting photoconductive antenna arrays (6) and a plurality of receiving photoconductive antenna arrays (8), wherein the laser (1) generates laser pulses, the transmitting photoconductive antenna array (6) receives the laser pulses via the first switch (4) and transmits terahertz pulses; the receiving photoconductive antenna array (8) receives the laser pulses via a second beam splitter (5) and detects terahertz pulses; the transmitting photoconductive antenna array (6) and the receiving photoconductive antenna array (8) are located in the same plane, and the transmitting photoconductive antenna array (6) and the receiving photoconductive antenna array (8) are arranged crosswise to form a ring structure; The laser pulse generated by the laser (1) is split by the first beam splitter (2), then injected into the first switch (4) via the variable optical delay line (3), and then injected into each transmitting photoconductive antenna array (6) respectively; all the transmitting photoconductive antenna arrays (6) work in time-sharing manner; The transmitting photoconductive antenna array (6) comprises a second switching switch (61), a transmitting optical fiber (62), a transmitting lens (63) and a transmitting antenna electrode array (64), wherein the second switching switch (61), the transmitting optical fiber (62), the transmitting lens (63) and the transmitting antenna electrode array (64) are connected together in sequence; The transmitting antenna electrode array (64) comprises a transmitting antenna substrate (641), a transmitting electrode (642) and a bias device (644); the transmitting electrode (642) is arranged on the transmitting antenna substrate (641); the transmitting electrode (642) is divided into two parts; a transmitting antenna electrode gap (643) is arranged between the two parts of the transmitting electrodes (642); the bias device (644) is electrically connected to the transmitting electrode (642); the electrodes of each array unit are interconnected and share a bias voltage provided by the same bias device (644).

2. The pulsed terahertz wave sparse array synthetic aperture imaging device according to claim 1, characterized in that: The laser pulses generated by the laser (1) are respectively emitted into the transmitting photoconductive antenna array (6) and the receiving photoconductive antenna array (8) via the first beam splitter (2).

3. The pulsed terahertz wave sparse array synthetic aperture imaging device according to claim 2, characterized in that: The laser pulse generated by the laser (1) is split by the first beam splitter (2), split again by the second beam splitter (5), and respectively emitted into each receiving photoconductive antenna array (8); all receiving photoconductive antenna arrays (8) work simultaneously.

4. The pulsed terahertz wave sparse array synthetic aperture imaging device according to claim 1, characterized in that: The receiving photoconductive antenna array (8) comprises a third beam splitter (81), a receiving optical fiber (82), a receiving lens (83) and a receiving antenna electrode array (84); the third beam splitter (81), the receiving optical fiber (82), the receiving lens (83) and the receiving antenna electrode array (84) are connected in sequence.

5. The pulsed terahertz wave sparse array synthetic aperture imaging device according to claim 4, characterized in that: The receiving antenna electrode array (84) comprises a receiving antenna substrate (841), a receiving electrode (842) and a current collector (844); the receiving electrode (842) is arranged on the receiving antenna substrate (841); the receiving electrode (842) is divided into two parts; a receiving antenna electrode gap (843) is arranged between the two parts of the receiving electrodes (842); the current collector (844) is electrically connected to the receiving electrode (842); the electrodes of each array unit are independent of each other and each outputs a current to the current collector (844).

6. A pulsed terahertz wave sparse array synthetic aperture imaging device according to any one of claims 1 to 5, characterized in that: Two of the transmitting photoconductive antenna arrays (6) and two of the receiving photoconductive antenna arrays (8) are provided, the transmitting photoconductive antenna arrays (6) and the receiving photoconductive antenna arrays (8) form a square structure, the two transmitting photoconductive antenna arrays (6) are provided in parallel, and the two receiving photoconductive antenna arrays (8) are provided in parallel.

7. A pulsed terahertz wave sparse array synthetic aperture imaging system, characterized in that: It comprises a plurality of imaging devices according to any one of claims 1 to 6, wherein the transmitting photoconductive antenna array (6) and the receiving photoconductive antenna array (8) in the plurality of imaging devices are located in the same plane.

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