A real-time terahertz single-pixel super-resolution imaging system

Abstract

The present invention is applicable to the field of terahertz single-pixel imaging technology and provides a real-time terahertz single-pixel imaging system, comprising: a terahertz source module, a high-speed terahertz spatial light modulator module, a test object module, a terahertz detection module, and a data acquisition and imaging display module; the high-speed terahertz spatial light modulator, when pumped by a continuous visible light source, can achieve excellent modulation effects and a high switching rate, thereby increasing the switching rate of the terahertz mask and facilitating real-time imaging; the use of a continuous terahertz source and a terahertz pyroelectric detector can detect changes in terahertz intensity in real time, thereby achieving real-time imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz single-pixel imaging, and in particular relates to a real-time terahertz single-pixel super-resolution imaging system. Background Art

[0002] The imaging speed of existing terahertz single-pixel imaging systems is primarily limited by two factors. First, it is limited by the scanning speed of the delay line. Previous terahertz single-pixel imaging systems mostly used detection optical paths based on terahertz time-domain spectroscopy systems, which rely on coherent detection via delay lines. A single round-trip scan of the delay line takes more than a second, while a single-pixel image requires hundreds or even thousands of round trips. Second, it is limited by the switching speed of the terahertz spatial light modulator. Previous terahertz spatial light modulators were mostly based on terahertz strong-field time-domain spectroscopy systems, which used high-energy pulsed lasers to change the carrier concentration of semiconductors to create terahertz masks. However, high-energy lasers have a relatively low repetition rate and are relatively expensive.

[0003] Terahertz imaging resolution has always been a core issue in the development of terahertz imaging technology. Most existing single-pixel terahertz imaging technologies focus on far-field imaging. Far-field imaging is limited by the wavelength of terahertz waves, resulting in a theoretical limit of far-field imaging resolution of half the wavelength. However, since terahertz wavelengths range from a few millimeters to hundreds of microns, in practice, terahertz far-field imaging resolution has struggled to break through the millimeter range. Summary of the Invention

[0004] In view of this, the present invention provides an imaging method and an imaging system for real-time terahertz single-pixel super-resolution imaging to solve the problems of limited imaging speed and imaging resolution in the prior art.

[0005] The present invention provides a real-time terahertz single-pixel imaging system, comprising a terahertz source module, a high-speed terahertz spatial light modulator module, a test object module, a terahertz detection module, and a data acquisition and imaging display module.

[0006] Among them, the high-speed terahertz spatial light modulator module includes four sub-modules: a visible light continuous source, a lens group, a digital micro-vibration mirror, and a semiconductor coated with organic materials.

[0007] The positions of the high-speed terahertz spatial light modulator module and the object to be measured module can be interchanged without affecting the execution of this embodiment.

[0008] The terahertz source module radiates terahertz waves. In the high-speed terahertz spatial light modulator module, a continuous visible light source radiates visible light, a lens group expands and collimates the visible light, and a digital micro-mirror encodes the visible light to form an optical mask. Under the irradiation of the optical mask, a semiconductor coated with an organic material produces a terahertz mask. In other words, the organic material-coated semiconductor under the irradiation of the optical mask can be considered a terahertz mask. The terahertz mask encodes the terahertz waves radiated by the terahertz source module.

[0009] The object template is used to place the object to be imaged.

[0010] The terahertz detection module is used to collect terahertz signals and convert them into electrical signals. The data acquisition and imaging display module is used to convert the current signals into digital signals and transmit them to the computer for reconstruction and imaging.

[0011] The present invention also provides another implementation of a real-time terahertz single-pixel imaging system, comprising: a visible light continuous source, a lens assembly, an aperture, a digital micro-vibration mirror, a reflector assembly, and a semiconductor coated with an organic material; the terahertz continuous source, a first terahertz lens, a second terahertz lens, a terahertz pyroelectric detector, a current amplifier, a data acquisition card, and a computer. The first terahertz lens is used to collimate the terahertz waves emitted by the terahertz continuous source; the visible light continuous source radiates visible light, the lens assembly expands and collimates the visible light, the aperture adjusts the size of the visible light, the digital micro-vibration mirror encodes the visible light to form an optical mask, and the reflector assembly adjusts the radiation direction of the optical mask, so that the optical mask radiates onto the organic material surface of the semiconductor coated with the organic material. The optical mask generated by the digital micro-vibration mirror excites photogenerated carriers within the semiconductor coated with the organic material, thereby forming a terahertz mask. This system includes, but is not limited to, near-field imaging. In the DUT module, the DUT (e.g., a metal cross) is fabricated on the other side of a semiconductor coated with an organic material through thermal evaporation and photolithography. The terahertz waves radiated by the terahertz source module interact with the organic-coated semiconductor, the terahertz mask, and the DUT. A second terahertz lens focuses the terahertz waves transmitted through the organic-coated semiconductor onto a terahertz pyroelectric detector. The terahertz pyroelectric detector absorbs the terahertz waves and generates a current signal, which is amplified by a current amplifier. A data acquisition card collects the current signal amplified by the current amplifier and converts it into a digital signal. A computer then collects the digital signal and reconstructs the image.

[0012] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0013] The present invention has a simple structure and low cost. The terahertz continuous source has the advantages of high integration, small size, simple operation, and relatively low cost. The high-speed terahertz spatial light modulator, when pumped by a visible light continuous source, can achieve excellent modulation effects and high switching rates, thereby increasing the switching rate of the terahertz mask and facilitating real-time imaging. The use of a terahertz continuous source and a pyroelectric detector can detect changes in terahertz intensity in real time, thereby achieving real-time imaging. The present invention is compatible with both near-field and far-field imaging. In near-field imaging, super-resolution imaging can be achieved, with the imaging resolution being much smaller than the wavelength of the terahertz wave.

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 This is a schematic diagram of the structure of a real-time terahertz single-pixel imaging system provided by the first embodiment of the present invention;

[0016] Figure 2 This is a system device diagram of a real-time terahertz single-pixel imaging system provided by the second embodiment of the present invention;

[0017] Figure 3 1 is a diagram showing the modulation effect and switching speed of a high-speed terahertz spatial light modulator in an embodiment of the present invention;

[0018] Figure 4 is a schematic diagram of the results of real-time imaging according to an embodiment of the present invention;

[0019] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0020] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0021] like Figure 1As shown, a real-time terahertz single-pixel imaging system provided in this embodiment includes: a terahertz source module, a high-speed terahertz spatial light modulator module, a test object module, a terahertz detection module, and a data acquisition and imaging display module.

[0022] Among them, the high-speed terahertz spatial light modulator module includes four sub-modules: a visible light continuous source, a lens group, a digital micro-vibration mirror, and a semiconductor coated with organic materials.

[0023] The positions of the high-speed terahertz spatial light modulator module and the object to be measured module can be interchanged without affecting the execution of this embodiment.

[0024] The terahertz source module is used to radiate terahertz waves; in the high-speed terahertz spatial light modulator module, the visible light continuous

[0025] The source radiates visible light, which is then expanded and collimated by a lens assembly. A digital micro-mirror encodes the visible light to form an optical mask. A semiconductor coated with an organic material, when exposed to the optical mask, produces a terahertz mask. This means the organic material-coated semiconductor exposed to the optical mask can be considered a terahertz mask. The terahertz mask encodes the terahertz waves emitted by the terahertz source module.

[0026] In this embodiment, the organic material includes but is not limited to poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylene vinylene] (abbreviated as Mehppv); the organic material is spin-coated on the surface of the semiconductor using a coating machine, the semiconductor includes but is not limited to high-resistance silicon, and the thickness of the organic material is submicron level (e.g., 200 nm). After spin coating, the semiconductor coated with the organic material is placed on a heating plate for heating, so that the organic material is solidified on the surface of the semiconductor.

[0027] The object template is used to place the object to be imaged.

[0028] The terahertz detection module is used to collect terahertz signals and convert them into current signals. The data acquisition and imaging display module is used to convert the current signals into digital signals and transmit them to the computer for reconstruction and imaging.

[0029] The proposed solution involves spin-coating a layer of organic material onto the semiconductor surface to passivate the semiconductor surface. The non-equilibrium carriers generated by optical pumping are transported to the organic-semiconductor interface due to diffusion. Because the state density of organic materials is much higher than that of semiconductors, the non-equilibrium carriers accumulate at the organic-semiconductor interface. Therefore, under the same optical pumping power, the organic-semiconductor structure has a higher carrier density than the pure semiconductor structure, resulting in excellent modulation effects under visible light continuous source pumping. However, the passivation of the semiconductor surface by the organic material has a side effect: the recombination rate of surface carriers is significantly slowed, the effective carrier lifetime of the organic-semiconductor structure is prolonged, and the switching rate of the terahertz spatial light modulator is slowed. To address this issue, the present invention reduces the thickness of the semiconductor to change the carrier density within the semiconductor, thereby increasing the recombination rate within the semiconductor. This helps shorten the effective carrier lifetime of the organic-semiconductor structure and increase the switching rate of the terahertz spatial light modulator. Therefore, by combining the two improvements of spin-coating an organic material on a semiconductor surface and reducing semiconductor thickness, a high-speed terahertz spatial light modulator achieves both excellent modulation performance and high switching speeds. The organic material used in this invention is poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (Mehppv for short); the semiconductor is high-resistance silicon with a thickness of 260 μm. The organic material and semiconductor options include, but are not limited to, combinations of the above.

[0030] Figure 2 The system device diagram is another embodiment of the present invention. Figure 2 The embodiment provides a diagram of a real-time terahertz single-pixel imaging system. Figure 2 In the figure, the terahertz single-pixel imaging system includes: a visible light continuous source 1, a lens group 2, an aperture 3, a digital micro-vibration mirror 4, a reflector group 5, 6, 7, a semiconductor coated with an organic material 8; a terahertz continuous source 9, a first terahertz lens 10, a second terahertz lens 11, a terahertz pyroelectric detector 12, a current amplifier 13, a data acquisition card 14 and a computer 15.

[0031] The first terahertz lens 10 is used to collimate the terahertz waves emitted by the terahertz continuous wave source 9. The visible light continuous wave source 1 emits visible light, which is then expanded and collimated by the lens assembly 2. The aperture 3 adjusts the visible light intensity. The digital micro-mirror 4 encodes the visible light to form an optical mask. The reflectors 5, 6, and 7 adjust the radiation direction of the optical mask, which is then irradiated onto the organic material surface of the organic material-coated semiconductor 8. The optical mask generated by the digital micro-mirror 4 excites photogenerated carriers within the organic material-coated semiconductor 8, thereby forming a terahertz mask. In other words, the organic material-coated semiconductor under the irradiation of the optical mask can be considered a terahertz mask. After the terahertz waves emitted by the terahertz source module 9 interact with the organic material-coated semiconductor 8, the terahertz mask, and the object to be measured, the second terahertz lens 11 focuses the terahertz waves transmitted through the organic material-coated semiconductor 8 onto the terahertz pyroelectric detector 12. After absorbing the terahertz wave, the terahertz pyroelectric detector 12 generates a current signal, which is amplified by the current amplifier 13. The data acquisition card 14 collects the current signal amplified by the current amplifier 13 and converts it into a digital signal. The computer 15 collects the digital signal and reconstructs the image.

[0032] In this embodiment, near-field imaging can be used, but is not limited to, in the DUT module. The DUT (e.g., a metal cross) is fabricated on the other side of the organic-coated semiconductor 8 through thermal evaporation and photolithography. When far-field imaging is used, the DUT can be separated from the organic-coated semiconductor 8 and placed anywhere between the organic-coated semiconductor 8 and the terahertz pyroelectric detector 12, or between the first terahertz lens 10 and the organic-coated semiconductor 8.

[0033] The present invention utilizes a terahertz continuous source 9 and a terahertz pyroelectric detector 12 as a terahertz source and a terahertz detector. This incoherent detection method gets rid of the dependence on the delay line, improves the imaging speed, and is the prerequisite for terahertz real-time imaging. The terahertz continuous source 9 can radiate continuous terahertz waves, and the continuous terahertz waves are continuous on the time scale. Terahertz continuous sources include but are not limited to: electron sources based on avalanche diodes, terahertz quantum cascade lasers, and terahertz continuous radiation sources using optically pumped gases. The response time of the terahertz pyroelectric detector is on the order of picoseconds. Based on the characteristics of the terahertz continuous source 9 and the terahertz pyroelectric detector 12, real-time detection of terahertz waves is achieved, which greatly improves the imaging speed of the terahertz single-pixel imaging system.

[0034] The imaging resolution of terahertz single-pixel near-field imaging is not limited by the wavelength of the terahertz wave, but is limited by the size of each pixel of the terahertz mask. The optical mask generated by the digital micro-vibration mirror 4 is converted into a terahertz mask inside the semiconductor 8 coated with an organic material. When the thickness of the semiconductor 8 coated with an organic material is much smaller than the wavelength of the terahertz wave, the size and distribution of the pixels of the terahertz wave mask can be considered equivalent to the optical mask. The size and distribution of the pixels of the optical mask are determined by the coding unit of the digital micro-vibration mirror 4. Therefore, when the coding unit of the digital micro-vibration mirror 4 is much smaller than the wavelength of the terahertz wave, super-resolution imaging can be achieved, that is, the imaging resolution breaks through the Fresnel diffraction limit. The digital micro-vibration mirror 4 is often used to encode visible light, and the size of each coding unit (such as: less than 20um) is much smaller than the wavelength of the terahertz wave.

[0035] The terahertz single-pixel imaging system proposed in the present invention is compatible with near-field imaging and far-field imaging. In near-field imaging, the imaging resolution of terahertz single-pixel imaging depends on the height of the object to be measured from the terahertz spatial light modulator and the size of each pixel of the terahertz spatial light modulator, rather than being limited by the wavelength of the terahertz wave. Since the pixel size of the terahertz spatial light modulator depends on the unit size of the digital micro-vibration mirror, and each unit of the digital micro-vibration mirror is on the order of microns, the resolution of terahertz single-pixel near-field imaging can easily break through to hundreds of microns, or even within the range of hundreds of microns, which is much smaller than the wavelength of the terahertz source. Therefore, in near-field imaging, the terahertz single-pixel imaging system proposed in the present invention is easier to achieve super-resolution imaging. In far-field imaging, the object to be measured can exist independently from the semiconductor coated with organic material, and can be placed at any position between the semiconductor coated with organic material and the terahertz pyroelectric detector, or the terahertz lens and the semiconductor coated with organic material.

[0036] Figure 3 The figure shows the modulation effect and switching rate of high-speed terahertz spatial light modulation. Figure 3 As shown in (a), under the same visible light continuous source pump intensity, the modulation effect of the semiconductor (Mehppv-Si260) spin-coated with organic material (Mehppv) is better than that of 500um thick high-resistance silicon (Si500). Figure 3As shown in (b), when switching from a pumped to an unpumped state, the normalized transmittance slope of the semiconductor (Mehppv-Si260) coated with an organic material (Mehppv) is steeper than that of 500µm thick high-resistance silicon (Si500). This indicates that the non-equilibrium carrier recombination rate in the semiconductor (Mehppv-Si260) coated with an organic material (Mehppv) is faster than that in 500µm thick high-resistance silicon (Si500). The carrier recombination time for the semiconductor (Mehppv-Si260) spin-coated with MEHPPV is 38µs, while that for 500µm thick high-resistance silicon (Si500) is 56µs. Therefore, the semiconductor (Mehppv-Si260) spin-coated with an organic material can support a switching rate of 27kHz, which is faster than the switching rate of commercial digital micro-mirrors (25kHz). Therefore, the modulation effect of the high-speed terahertz spatial light modulator of the present invention is limited by the pump light intensity of the visible light continuous source, and the switching rate is limited by the switching rate of the digital micro-vibration mirror, rather than the recombination rate of the non-equilibrium carriers in the semiconductor.

[0037] Figure 4 This is a schematic diagram of the real-time imaging results of an embodiment of the present invention. As the switching rate of the digital micro-mirror increases, the reconstructed image loses structural similarity compared to the original image, but the cross structure and its surrounding circular border are still clearly resolved. Currently, without using compressed sensing algorithms, real-time terahertz single-pixel imaging with a resolution of less than one-third the wavelength of the terahertz wave can be achieved at a frame rate of 25 frames per second (16 x 16 pixels). When the imaging pixel size is 32 x 32 pixels, the imaging resolution is less than one-sixth the wavelength of the terahertz wave, and the imaging speed is 10 frames per second.

[0038] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A real-time terahertz single-pixel imaging system, characterized in that: The terahertz single-pixel imaging system includes: a terahertz source module, a high-speed terahertz spatial light modulator module, a test object module, a terahertz detection module, and a data acquisition and imaging display module; The high-speed terahertz spatial light modulator module includes four submodules: a visible light continuous source, a lens group, a digital micro-vibration mirror, and a semiconductor coated with an organic material; The terahertz source module is used to radiate terahertz waves; in the high-speed terahertz spatial light modulator module, the visible light continuous source radiates visible light, the lens group is used to expand and collimate the visible light, and the digital micro-vibration mirror encodes the visible light to form an optical mask, which is radiated onto the organic material surface of the semiconductor coated with the organic material; The semiconductor coated with the organic material generates a terahertz mask under the radiation of the optical mask, that is, the semiconductor coated with the organic material under the radiation of the optical mask serves as a terahertz mask, and the terahertz mask encodes the terahertz wave radiated by the terahertz source module; The object to be tested module is manufactured on the other side of the semiconductor coated with organic material through thermal evaporation and photolithography processes; The terahertz detection module is used to collect terahertz signals and convert them into electrical signals; the data acquisition and imaging display module is used to convert current signals into digital signals and transmit them to a computer for reconstruction and imaging; The semiconductor material is high-resistance silicon with a thickness of 260um.

2. The real-time terahertz single-pixel imaging system according to claim 1, wherein: The organic material includes poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene].

3. The real-time terahertz single-pixel imaging system according to claim 1, wherein the thickness of the organic material is submicron level.

4. A real-time terahertz single-pixel imaging system, characterized in that: The terahertz single-pixel imaging system comprises: a visible light continuous source (1), a lens group (2), an aperture (3), a digital micro-vibration mirror (4), a reflector group (5, 6, 7), a semiconductor coated with an organic material (8); a terahertz continuous source (9), a first terahertz lens (10), a second terahertz lens (11), a terahertz pyroelectric detector (12), a current amplifier (13), a data acquisition card (14) and a computer (15); The first terahertz lens (10) is used to collimate the terahertz wave radiated by the terahertz continuous source (9); The visible light continuous source (1) is used to radiate visible light; The lens group (2) is used to expand and collimate visible light; The aperture (3) is used to adjust the size of visible light; The digital micro-vibration mirror (4) is used to encode visible light to form an optical mask; The reflector group (5, 6, 7) is used to adjust the radiation direction of the optical mask, and the optical mask radiates on the organic material surface of the semiconductor (8) coated with the organic material; the object to be tested is made on the other side of the semiconductor (8) coated with the organic material; the optical mask generated by the digital micro-vibration mirror (4) excites photogenerated carriers inside the semiconductor (8) coated with the organic material, thereby forming a terahertz mask; After the terahertz wave radiated by the first terahertz lens (10) interacts with the semiconductor (8) coated with an organic material, the terahertz mask, and the object to be measured, the second terahertz lens (11) is used to focus the terahertz wave that has passed through the semiconductor (8) coated with an organic material, and focuses it on the terahertz pyroelectric detector (12); the terahertz pyroelectric detector (12) is used to generate a current signal after absorbing the terahertz wave, and the current amplifier (13) is used to amplify the current signal; the data acquisition card (14) is used to collect the current signal amplified by the current amplifier (13) and convert it into a digital signal, and the computer (15) is used to collect the digital signal and reconstruct an image; The semiconductor material is high-resistance silicon with a thickness of 260um; The response time of the terahertz pyroelectric detector (12) is on the order of picoseconds.

5. The real-time terahertz single-pixel imaging system according to claim 4, characterized in that: The organic material includes poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]. 6 . The real-time terahertz single-pixel imaging system according to claim 4 , wherein the thickness of the organic material is on the submicron level.

7. The real-time terahertz single-pixel imaging system according to claim 4, wherein the terahertz continuous source comprises: Electron sources based on avalanche diodes, terahertz quantum cascade lasers, and terahertz continuous radiation sources using optically pumped gases.

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