Ultra-fast imaging device based on vector space coding

Abstract

The invention relates to the technical field of ultrafast imaging, and discloses an ultrafast imaging device based on vector space coding, comprising: an ultrafast pulse laser, a pulse shaper for regulating and controlling a single pulse emitted by the ultrafast pulse laser to obtain a pulse envelope with time corresponding to a spectrum; the reflective dark field microscopic imaging system is arranged behind the pulse shaper, so that the pulse envelope is reflected after illuminating the target object in the first direction, and is emitted out of the reflective dark field microscopic imaging system in the second direction; the vector space coding optical system is arranged in the second direction and comprises a 4F optical system and a multi-layer film phase plate arranged in the 4F optical system, and the multi-layer film phase plate is used for carrying out optical coding on the pulse envelope; and the imaging system is arranged on the output surface of the 4F optical system to obtain a coded vector space image. According to the invention, the multi-layer film phase plate with a sub-wavelength thickness is used, and the vector space characteristics of light with different frequencies are used for coding, so that single-exposure ultrafast imaging is realized.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast imaging technology, and in particular, to an ultrafast imaging device based on vector space encoding. Background Art

[0002] The changes of transient events such as photochemistry, laser-induced plasma, nematocyst discharge dynamics, shock waves, laser-induced fluorescence, laser-induced incandescence, and capturing terahertz beams have reached the atomic time scale (picosecond to femtosecond order of magnitude 10 -12 -10 -15 seconds), which indicates that at least a camera with a frame rate as high as Tfps (10 12 ) is required to clearly observe the instant or process of these events. However, such a high frame rate far exceeds the response speed of traditional CCD or CMOS cameras.

[0003] The existing work has demonstrated various single-shot ultrafast measurement techniques, which are mainly divided into the active frame division form based on pump-probe technology and the passive electronic frame division form represented by Compressed ultrafast photography (CUP). For the CUP technology, it is necessary to use a DMD for encoding, demix through compressed sensing technology, and the camera used for detection requires an expensive streak camera, which increases the complexity and cost of measurement. The methods of realizing multiple detections with a single pump are mainly divided into polarization discretization, spectral dispersion, angle, real-space discretization, and Fourier-space discretization. Real-space discretization is to make a beam of light have a small delay in the path through an echelon, and then split it into several "sub-detection lights" in time and hit different positions on the target surface. This is a limitation for materials with uneven surface roughness and flatness distribution. Fourier-space discretization is to utilize the different positions of the high-frequency information of different structured lights in the vector space, and then extract the ultrafast dynamic image by means of high-pass filtering and translation. Polarization discretization is to make different polarized lights pass through an ultrafast moving object at different times through an encoded microlens array, and then obtain a series of continuous dynamic images. Spectral dispersion pump-probe relies on the mapping relationship between wavelength (light wave frequency) and time (time Fraunhofer mode, the input spectral frequency can be mapped to the output time), and uses a dispersion component to disperse different wavelengths (light wave frequencies) contained in a pulsed light onto the detector to form a time series.

[0004] The pump-probe technology of spectral dispersion has high integration, simple structure, and large tunability. However, due to the diffraction effect of the dispersion element, the imaging quality will decrease and the optical path is relatively long. Summary of the Invention

[0005] The object of the present invention is to provide an ultrafast imaging device based on vector space encoding, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows: According to the specific embodiments of the present invention, the present invention discloses an ultrafast imaging device based on vector space encoding, including: an ultrafast pulsed laser; A pulse shaper that modulates the single pulse emitted by the ultrafast pulsed laser to obtain a pulse envelope corresponding to time and spectrum; A reflection dark-field microscopy imaging system is arranged behind the pulse shaper, so that the pulse envelope is reflected after illuminating the target in the first direction and exits the reflection dark-field microscopy imaging system in the second direction; A vector space encoding optical system is arranged in the second direction, including: a 4F optical system and a multilayer film phase plate arranged in the 4F optical system, and the multilayer film phase plate is used for optically encoding the pulse envelope; An imaging system is arranged on the output surface of the 4F optical system to obtain an encoded vector space image.

[0006] As an optional embodiment, the detection wavelength range of the ultrafast pulsed laser is: 1020 - 1040 nm; The multilayer film phase plate is a multilayer film structure in which tantalum pentoxide optical thin films and silicon dioxide optical thin films are alternately arranged.

[0007] As an optional embodiment, the multilayer film phase plate includes: a first high-reflection double distributed Bragg reflector structure and a second high-reflection double distributed Bragg reflector structure symmetrically arranged, and an intermediate layer arranged between the first high-reflection double distributed Bragg reflector structure and the second high-reflection double distributed Bragg reflector structure.

[0008] As an optional embodiment, the first high-reflection double distributed Bragg reflector structure includes: four layers of tantalum pentoxide optical thin film layers and four layers of silicon dioxide optical thin film layers arranged alternately; the tantalum pentoxide optical thin film layer is adjacent to the intermediate layer in the middle.

[0009] As an optional embodiment, the thickness of the tantalum pentoxide optical thin film layer is 136 nm, and the thickness of the silicon dioxide optical thin film layer is 197 nm.

[0010] As an optional embodiment, the intermediate layer is a silicon dioxide layer, and the thickness of the intermediate layer is 249 nm.

[0011] As an optional embodiment, the reflection dark-field microscopy imaging system includes: A semi-transmissive semi-reflective lens is disposed on the outgoing light path of the pulse shaper, reflecting the pulse envelope and transmitting the pulse envelope carrying object information reflected by the object. A first objective lens is disposed on the reflected light path of the semi-transmissive semi-reflective lens, for collecting the pulse envelope carrying object information reflected by the object.

[0012] As an optional implementation manner, the 4F optical system includes: a first objective lens and a second objective lens, and the multilayer film phase plate is disposed between the first objective lens and the second objective lens; the numerical apertures of the first objective lens and the second objective lens are 0.7NA.

[0013] As an optional implementation manner, it further includes: a reconstruction unit, which decodes the encoded vector space image to obtain a reconstructed spectrum.

[0014] As an optional implementation manner, the expression of the process that the reconstruction unit decodes the encoded vector space image to obtain a reconstructed spectrum is: (1); Wherein, is the optical transfer function; is a preset value; are different response wavelengths in the range of 1020nm to 1040nm; is the Gaussian function of the different response wavelengths; i is the number of encoded pixels of the encoded vector space image; is the response current value corresponding to the encoded pixel.

[0015] Compared with the prior art, the above solution of the disclosed embodiment of the present invention has at least the following beneficial effects: By using a multilayer film phase plate with a sub-wavelength thickness, the present invention encodes using the vector space characteristics of light with different frequencies, thereby realizing single-shot ultrafast imaging. The ultrafast imaging device of the present invention shortens the imaging light path, realizes miniaturization, and has a high imaging frame rate of trillions of frames per second (1012fps). Description of the Drawings

[0016] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing embodiments in line with the disclosure of the present invention, and are used together with the specification to explain the principles disclosed by the present invention. Obviously, the accompanying drawings in the following description are only some embodiments of the disclosure of the present invention. For those of ordinary skill in the art, other accompanying drawings can be obtained based on these drawings without creative efforts. In the accompanying drawings: Figure 1 It is a schematic structural diagram of an ultrafast imaging device based on vector space encoding provided by an embodiment of the present invention; Figure 2 It is a schematic structural diagram of a multilayer film phase plate provided by an embodiment of the present invention; Figure 3 It is a transmittance curve graph of light with different wavelengths passing through the multilayer film phase plate provided by an embodiment of the present invention; Figure 4 It is a vector space image of light with different wavelengths encoded provided by an embodiment of the present invention; Figure 5 It is a comparison graph of the actual spectrum and the reconstructed spectrum provided by an embodiment of the present invention.

[0017] Reference numerals: 1 - Multilayer film phase plate, 1.1 - First high - reflection double - distributed Bragg reflector structure, 1.2 - Intermediate interlayer, 1.3 - Second high - reflection double - distributed Bragg reflector structure; 2 - Ultrafast pulse laser, 3 - Pulse shaper, 4 - Detector, 5 - First objective lens, 6 - Second objective lens, 7 - Half - transparent and half - reflecting mirror, 8 - Microscopic objective lens, 9 - Target object, 10 - Imaging lens. Detailed implementation manners

[0018] In order to make the purpose, technical solutions and advantages of the disclosure of the present invention clearer, the following will further describe in detail an ultrafast imaging device based on vector space encoding of the present invention in combination with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the disclosure of the present invention, rather than all embodiments. Based on the embodiments of the disclosure of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the disclosure of the present invention.

[0019] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a", "the" and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Plural" generally includes at least two.

[0020] It should be understood that the term "and / or" used herein is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, the character " / " in this text generally represents an "or" relationship between the associated objects before and after.

[0021] It should be understood that although terms such as first, second, and third may be used to describe in the embodiments of the present application, these should not be limited to these terms. These terms are only used to make distinctions. For example, without departing from the scope of the embodiments of the present application, the first can also be referred to as the second, and similarly, the second can also be referred to as the first.

[0022] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a commodity or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent to such commodity or device. Without further limitation, an element defined by the statement "comprising one" does not exclude the existence of additional identical elements in the commodity or device comprising the said element.

[0023] The following will Figures 1-5 detail the optional embodiments of the present invention in conjunction with the appended

[0024] Embodiment 1 As Figure 1 shown, according to the specific implementation manner of the present invention, the present invention provides an ultrafast imaging device based on vector space encoding, comprising: An ultrafast pulsed laser 2.

[0025] A pulse shaper 3 that regulates the single pulse emitted by the ultrafast pulsed laser 2 to obtain a pulse envelope corresponding to time and spectrum.

[0026] A reflection dark-field microscopy imaging system, arranged behind the pulse shaper 3, such that the pulse envelope is reflected after illuminating the target 9 in the first direction and exits the reflection dark-field microscopy imaging system in the second direction.

[0027] A vector space encoding optical system, arranged in the second direction, comprising: a 4F optical system and a multilayer film phase plate 1 arranged in the 4F optical system, where the multilayer film phase plate 1 is used to optically encode the pulse envelope.

[0028] An imaging system, arranged at the output surface of the 4F optical system, to obtain an encoded vector space image.

[0029] The present invention realizes single - exposure ultrafast imaging by using the vector space characteristics of light with different frequencies through a multilayer film phase plate with a sub - wavelength thickness, without relying on a streak camera or a DMD micromirror array for encoding, reducing the measurement complexity and system cost. It not only shortens the imaging optical path but also enables the imaging device to have a high imaging frame rate of trillions of frames per second (10^12 fps).

[0030] As an alternative embodiment, the ultrafast pulse laser 2 is a femtosecond mode - locked pulse laser, and its detection wavelength range is: 1020 - 1040 nm. When light with different wavelengths having ultrashort pulses passes through the pulse shaper 3, it will propagate at different speeds, causing the pulse to gradually broaden to the picosecond level.

[0031] That is, when the total group - velocity dispersion D is much larger than the square of the pulse duration the mapping relationship between the time t and the frequency ω of the light source is t = Dω. It belongs to the time - Fourier (Fraunhofer) region, where the input spectrum (frequency) can be mapped to the output time.

[0032] Therefore, the pulse shaper 3 can realize the regulation of a single pulse emitted by the ultrafast pulse laser 2 to obtain a pulse envelope corresponding to time and spectrum.

[0033] Furthermore, the pulse envelope enters the reflection dark - field microscopy imaging system to illuminate the target 9, thereby obtaining the pulse envelope carrying the target information.

[0034] Specifically, the reflection dark - field microscopy imaging system includes: a beam splitter 7 and a microscope objective 8. The microscope objective 8 illuminates the target 9 from behind and collects the pulse envelope carrying the target information reflected by the target 9.

[0035] As an alternative embodiment, the reflection dark - field microscopy imaging system is coaxially arranged with the vector - space - encoding optical system. After the pulse envelope carrying the target information passes through the beam splitter 7, it enters the vector - space - encoding optical system.

[0036] In other embodiments, after the pulse envelope carrying the target information passes through the beam splitter 7, the pulse envelope carrying the target information is reflected into the vector - space - encoding optical system.

[0037] The vector - space - encoding optical system includes: a 4F optical system and a multilayer film phase plate 1 disposed in the 4F optical system. The multilayer film phase plate 1 is used to optically encode the pulse envelope.

[0038] Specifically, the 4F optical system includes a first objective lens 5 and a second objective lens 6 for realizing the conversion between the time domain and the frequency domain. A multilayer film phase plate 1 is arranged between the first objective lens 5 and the second objective lens 6 to optically encode the pulse envelope. The encoded pulse envelope is converted into parallel light in the time domain through the first objective lens 5.

[0039] Furthermore, the working wavelength band of the multilayer film phase plate 1 is consistent with the detection wavelength band range of the ultrafast pulse laser, which is 1020 - 1040 nm in this embodiment.

[0040] In the design of optical thin films, in order to endow the phase plate with dispersion properties in the wave vector space (Fourier space) so as to achieve the purpose of beam splitting (light with different frequencies (wavelengths) is separated), the phase plate usually needs to be designed as a multilayer thin film structure. Tantalum pentoxide Ta2O5 with a high refractive index and silicon dioxide SiO2 with a low refractive index can cooperate well, and the required phase difference can be achieved by precisely controlling the film layer thickness. Therefore, the multilayer film phase plate in this embodiment is a multilayer film structure in which tantalum pentoxide optical thin films and silicon dioxide optical thin films are arranged alternately.

[0041] Specifically, as Figure 2 shown, the multilayer film phase plate includes a symmetrically arranged first high - reflection double - distributed Bragg reflector structure 1.1, a second high - reflection double - distributed Bragg reflector structure 1.3, and an intermediate layer 1.2 arranged between the first high - reflection double - distributed Bragg reflector structure 1.1 and the second high - reflection double - distributed Bragg reflector structure 1.3.

[0042] As an alternative embodiment, the first high - reflection double - distributed Bragg reflector structure 1.1 includes, starting from one side of the intermediate layer 1.2, alternately stacking a first tantalum pentoxide optical thin film layer, a first silicon dioxide optical thin film layer, a second tantalum pentoxide optical thin film layer, a second silicon dioxide optical thin film layer... in sequence, with a total of eight layers.

[0043] Similarly, the second high - reflection double - distributed Bragg reflector structure 1.3 includes, starting from the other side of the intermediate layer 1.2 and in the direction away from the first high - reflection double - distributed Bragg reflector structure 1.1, alternately stacking tantalum pentoxide optical thin film layers and silicon dioxide optical thin film layers, with a total of eight layers.

[0044] Furthermore, the intermediate layer is a silicon dioxide layer, which is equivalent to a Fabry - Perot cavity, and the transmission spectrum characteristics of the multilayer film phase plate can be precisely controlled by adjusting its thickness.

[0045] As an alternative embodiment, the thickness of the tantalum pentoxide optical thin film layer is 136 nm, the thickness of the silicon dioxide optical thin film layer is 197 nm, and the thickness of the intermediate layer is 249 nm.

[0046] Figure 3 shows the transmittance curves of the multi-layer film phase plate of this embodiment in different wave vectors (angle of incidence ). s polarization directions and p in the polarization direction and . The abscissa is the wave vector, and the ordinate is the response range of the multi-layer film phase plate. In this embodiment, based on the numerical apertures of the first objective lens and the second objective lens being 0.7NA, the value range of the abscissa is 0 - 0.7.

[0047] Since the pulse envelope has different and at different frequencies (wavelengths), so and can be obtained by solving with the TMM (transfer matrix method). Thus, the electric field amplitudes of lights with different wavelengths are different after passing through the multi-layer film phase plate 1, thereby realizing optical encoding.

[0048] Furthermore, according to the known and , the optical transfer function for decoding the encoded vector space image can be obtained .

[0049] Specifically, when a beam of light passes through the multi-layer film phase plate 1, the amplitude of the outgoing light in the polar coordinate system can be expressed as:

[0050] wherein, is the radial wave vector, A is the amplitude; and ( and are the wave vectors of s polarization and p polarization respectively) are mainly related to the angle of incidence and can be expressed as: ; is the wave vector constant, is r the angle between the radial direction and y axis in the real space.

[0051] Therefore, the expression of the transfer function is: (2) wherein, is in the Fourier space The included angle with .

[0052] Continuing to refer to Figure 1 , the pulse envelope encoded by the multi-layer film phase plate 1 passes through the imaging system and outputs the encoded vector space image.

[0053] As an alternative embodiment, the imaging system includes an imaging lens 10 for focusing and a detector 4. Vector space images of different bands as shown in Figure 4 can be obtained on the detector.

[0054] Furthermore, decoding the vector space image in Figure 4 can reconstruct the spectrum, thereby achieving an imaging speed of trillions of frames per second.

[0055] As an alternative embodiment, the ultrafast imaging device based on vector space encoding further includes: a reconstruction unit for decoding the encoded vector space image to obtain a reconstructed spectrum.

[0056] Specifically, the process of decoding the encoded vector space image is as follows.

[0057] Assume that the incident unknown spectrum is , then the decoding process can be expressed as:[[]]END]]

[0058] where is the different response wavelengths in the range of 1020 nm to 1040 nm ; i is the number of encoded pixels of the encoded vector space image; is the response current value corresponding to the encoded pixel, that is, the response current corresponding to each pixel in the vector space image at each wavelength in Figure 4 ; is the optical transfer function.

[0059] Furthermore, using the form of a trial solution, equation (3) can be expanded as:[[]]END]]

[0060] where is the Gaussian function of the different response wavelengths, with a bandwidth of 0.5 nm; is a preset value.

[0061] Then the solution process becomes a minimization problem:[[]]END]]

[0062] The minimum value of the L2 norm is obtained by using Tikhonov regularization, and then the regularization coefficient is automated by using Generalized Cross Validation (GCV). The reconstructed spectrum can be obtained. .

[0063] Figure 5 It is a comparison graph of the spectra of a known target object and the reconstructed spectrum obtained by using the ultrafast imaging device based on vector space encoding of the present invention. It can be seen that in the detection band of 1020 nm - 1040 nm, the spectrum obtained by using the multi-layer phase plate of the present invention is close to the real spectrum, and the imaging speed of trillion frames per second is achieved.

[0064] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and the relevant parts can be referred to the descriptions in the method section.

[0065] The above embodiments are only used to illustrate the technical solutions disclosed by the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An ultrafast imaging device based on vector space encoding, characterized in that, Comprising: An ultrafast pulsed laser; A pulse shaper for regulating a single pulse emitted by the ultrafast pulsed laser to obtain a pulse envelope corresponding to time and spectrum; A reflective dark-field microscopy imaging system disposed behind the pulse shaper, configured to reflect the pulse envelope after illuminating an object in a first direction and emit the pulse envelope in a second direction out of the reflective dark-field microscopy imaging system; A vector space encoding optical system disposed in the second direction, comprising: a 4F optical system and a multilayer film phase plate disposed in the 4F optical system, the multilayer film phase plate being configured to optically encode the pulse envelope; An imaging system disposed on an output surface of the 4F optical system to obtain an encoded vector space image.

2. The ultrafast imaging device based on vector space encoding according to claim 1, wherein: The detection wavelength range of the ultrafast pulsed laser is: 1020 - 1040 nm; The multilayer film phase plate is a multilayer film structure formed by overlapping tantalum pentoxide optical thin films and silicon dioxide optical thin films.

3. The ultrafast imaging device based on vector space encoding according to claim 2, wherein: The multilayer film phase plate comprises: a first high-reflection double distributed Bragg reflector structure and a second high-reflection double distributed Bragg reflector structure symmetrically disposed, and an intermediate layer disposed between the first high-reflection double distributed Bragg reflector structure and the second high-reflection double distributed Bragg reflector structure.

4. The ultrafast imaging device based on vector space encoding according to claim 3, wherein The first high-reflection double distributed Bragg reflector structure comprises: four layers of tantalum pentoxide optical thin film layers and four layers of silicon dioxide optical thin film layers alternately arranged; the tantalum pentoxide optical thin film layer is adjacent to the intermediate layer in the middle.

5. The ultrafast imaging device based on vector space encoding according to claim 3 or 4, characterized in that, The thickness of the tantalum pentoxide optical thin film layer is 136 nm, and the thickness of the silicon dioxide optical thin film layer is 197 nm.

6. The ultrafast imaging device based on vector space encoding according to claim 5, wherein The intermediate layer is a silicon dioxide layer, and the thickness of the intermediate layer is 249 nm.

7. The ultrafast imaging device based on vector space encoding according to claim 1, characterized in that The reflective dark-field microscopy imaging system comprises: A semi-reflective semi-transmissive lens disposed on an outgoing light path of the pulse shaper, configured to reflect the pulse envelope and transmit the pulse envelope carrying object information reflected by the object; A first objective lens disposed on a reflected light path of the semi-reflective semi-transmissive lens, configured to collect the pulse envelope carrying object information reflected by the object.

8. The ultrafast imaging device based on vector space encoding according to claim 1, wherein: The 4F optical system comprises: a first objective lens and a second objective lens, the multilayer film phase plate is disposed between the first objective lens and the second objective lens; the numerical aperture of the first objective lens and the second objective lens is 0.7 NA.

9. The ultrafast imaging device based on vector space encoding according to claim 1, characterized in that, Further comprising: A reconstruction unit for decoding the encoded vector space image to obtain a reconstructed spectrum.

10. The ultrafast imaging device based on vector space encoding according to claim 9, characterized in that, The expression of the process of the reconstruction unit decoding the encoded vector space image to obtain a reconstructed spectrum is: （1）； Among them, is the optical transfer function; is a preset value; are different response wavelengths in the range of 1020 nm to 1040 nm; is the Gaussian function for the different response wavelengths; i is the number of encoded pixels of the encoded vector space image; is the response current value corresponding to the encoded pixel.

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