An ultrafast imaging device based on vector space encoding

Abstract

The present invention relates to the field of ultrafast imaging technology, and discloses an ultrafast imaging device based on vector space encoding, comprising: an ultrafast pulse laser, a pulse shaper, which regulates a single pulse emitted by the ultrafast pulse laser to obtain a pulse envelope corresponding in time and spectrum; a reflective dark field microscopy imaging system, disposed after the pulse shaper, causing the pulse envelope to illuminate a target in a first direction and then reflect, emitting the reflective dark field microscopy imaging system in a second direction; 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 used to optically encode the pulse envelope; and an imaging system, disposed at the output surface of the 4F optical system, which obtains an encoded vector space image. The present invention achieves single-exposure ultrafast imaging by using a sub-wavelength multilayer film phase plate and utilizing the vector space characteristics of light of different frequencies for encoding.

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 coding. Background Art

[0002] The changes of transient events such as photochemistry, laser-induced plasma, nematode cyst discharge dynamics, bombardment waves, laser-induced fluorescence, laser-induced incandescence, and captured terahertz beams have reached the atomic time scale (picosecond to femtosecond level 10 -12 -10 -15 seconds), which means that at least Tfps (10 12 ) frame rate can clearly observe the moment or process of these events, but such a high frame rate far exceeds the response speed of traditional CCD or CMOS cameras.

[0003] Existing work has demonstrated various single-shot ultrafast measurement techniques, primarily categorized as active framing based on pump-probe technology and passive electronic framing, exemplified by Compressed Ultrafast Photography (CUP). CUP requires encoding using a DMD and demixing using compressed sensing. Furthermore, the detection camera requires an expensive streak camera, which increases measurement complexity and cost. Methods for achieving multiple detections with a single pump shot are primarily categorized into polarization discretization, spectral dispersion, angle, real-space discretization, and Fourier-space discretization. Real-space discretization uses an echelon array to introduce a small delay into a beam of light, thereby temporally splitting it into several "sub-probe beams" that strike different locations on the target surface. This poses limitations for materials with uneven surface roughness and flatness. Fourier-space discretization exploits the different positions of high-frequency information from different structured light in vector space, enabling the extraction of ultrafast dynamic images through high-pass filtering and subsequent shifting. Polarization discretization uses a coded microlens array to allow light of different polarizations to pass through an ultrafast moving object at different times, thereby producing a series of continuous dynamic images. Spectrally dispersive pump detection relies on the mapping relationship between wavelength (light wave frequency) and time (the temporal Fraunhofer mode, where the input spectral frequency can be mapped to the output time). It uses dispersive components to disperse the different wavelengths (light wave frequencies) contained in a pulse of light onto the detector to form a time sequence.

[0004] Spectral dispersion pump-probe technology has high integration, simple structure, and great tunability. However, due to the diffraction effect of the dispersion element, it will lead to reduced imaging quality and a longer optical path. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultrafast imaging device based on vector space coding, which can solve at least one of the above-mentioned technical problems. The specific solution is as follows:

[0006] According to a specific embodiment disclosed in the present invention, the present invention discloses an ultrafast imaging device based on vector space coding, comprising: an ultrafast pulse laser;

[0007] a pulse shaper for regulating the single pulse emitted by the ultrafast pulse laser to obtain a pulse envelope corresponding to time and spectrum;

[0008] a reflective dark field microscopy system, disposed after the pulse shaper, causing the pulse envelope to reflect after illuminating the target in a first direction and exit the reflective dark field microscopy system in a second direction;

[0009] A vector space encoding optical system is arranged in the second direction, comprising: a 4F optical system and a multilayer film phase plate arranged in the 4F optical system, wherein the multilayer film phase plate is used to optically encode the pulse envelope;

[0010] The imaging system is arranged on the output surface of the 4F optical system to obtain the encoded vector space image.

[0011] As an optional implementation, the detection band range of the ultrafast pulse laser is: 1020-1040nm;

[0012] The multilayer film phase plate is a multilayer film structure in which tantalum pentoxide optical films and silicon dioxide optical films are overlapped and arranged.

[0013] As an optional embodiment, the multilayer film phase plate includes: a symmetrically arranged first high-reflection double distributed Bragg reflector structure, a second high-reflection double distributed Bragg reflector structure, 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.

[0014] 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 layers are adjacent to the middle interlayer.

[0015] As an optional implementation, 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.

[0016] As an optional implementation manner, the intermediate interlayer is a silicon dioxide layer, and the thickness of the intermediate interlayer is 249 nm.

[0017] As an optional embodiment, the reflective dark-field microscopy system includes:

[0018] a half-reflecting half-mirror, arranged on the outgoing light path of the pulse shaper, reflecting the pulse envelope and transmitting the pulse envelope carrying target information reflected by the target;

[0019] The first objective lens is arranged on the reflection light path of the half-reflecting half-mirror lens, and is used to collect the pulse envelope carrying the target information reflected by the target.

[0020] As an optional embodiment, the 4F optical system includes: a first objective lens and a second objective lens, the multilayer phase plate is arranged between the first objective lens and the second objective lens; the numerical aperture of the first objective lens and the second objective lens is 0.7NA.

[0021] As an optional implementation manner, the method further includes: a reconstruction unit, which decodes the encoded vector space image to obtain a reconstructed spectrum.

[0022] As an optional implementation manner, the reconstruction unit decodes the encoded vector space image to obtain a reconstructed spectrum. The expression is:

[0023] (1);

[0024] in, is the optical transfer function; is the default value;

[0025] Different response wavelengths within the range of 1020nm to 1040nm;

[0026] is the Gaussian function of the different response wavelengths;

[0027] i is the number of coded pixels of the coded vector space image;

[0028] is the response current value corresponding to the coding pixel.

[0029] Compared with the prior art, the above solution of the embodiment disclosed in the present invention has at least the following beneficial effects:

[0030] This invention uses a subwavelength multilayer phase plate to encode the vectorial spatial properties of light of different frequencies, thereby achieving single-exposure ultrafast imaging. The ultrafast imaging device shortens the imaging optical path, enabling miniaturization and a high imaging frame rate of 1012 fps. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are incorporated into and constitute a part of the specification, illustrating embodiments consistent with the present disclosure and, together with the specification, explaining the principles of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort. In the drawings:

[0032] Figure 1 A schematic structural diagram of an ultrafast imaging device based on vector space coding provided by an embodiment of the present invention;

[0033] Figure 2 A schematic structural diagram of a multilayer film phase plate provided by an embodiment of the present invention;

[0034] Figure 3 A transmittance curve diagram of light of different wavelengths after passing through a multilayer film phase plate provided by an embodiment of the present invention;

[0035] Figure 4 Vector space images of light of different wavelengths encoded according to an embodiment of the present invention;

[0036] Figure 5 A comparison diagram of the actual spectrum and the reconstructed spectrum provided by an embodiment of the present invention.

[0037] Reference numerals:

[0038] 1-multilayer film phase plate, 1.1-first high-reflection double distributed Bragg reflector structure, 1.2-intermediate layer, 1.3-second high-reflection double distributed Bragg reflector structure;

[0039] 2-ultrafast pulse laser, 3-pulse shaper, 4-detector, 5-first objective lens, 6-second objective lens, 7-semi-transparent and semi-reflective mirror, 8-microscope objective lens, 9-target, 10-imaging lens. DETAILED DESCRIPTION

[0040] To further clarify the objectives, technical solutions, and advantages of the present invention, the following describes in further detail an ultrafast imaging device based on vector space coding, with reference to the accompanying drawings. It should be understood that the embodiments described herein represent only a portion of the present invention, and not all of its embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments disclosed herein without inventive effort are intended to fall within the scope of protection of the present invention.

[0041] The terms used in the examples of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The singular forms "a," "the," and "the" used in the examples of this application and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0042] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0043] It should be understood that although the terms first, second, third, etc. 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 distinguish. For example, without departing from the scope of the embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.

[0044] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprising a" does not exclude the presence of other identical elements in the product or device comprising the element.

[0045] The following is combined with Figure 1-5 Alternative embodiments of the present invention are described in detail.

[0046] Example 1

[0047] like Figure 1 As shown, according to a specific embodiment of the present invention, the present invention provides an ultrafast imaging device based on vector space coding, comprising:

[0048] Ultrafast pulsed laser2.

[0049] The pulse shaper 3 regulates the single pulse emitted by the ultrafast pulse laser 2 to obtain a pulse envelope corresponding to time and spectrum.

[0050] The reflective dark field microscopy system is arranged after the pulse shaper 3, so that the pulse envelope is reflected after illuminating the target object 9 in the first direction and then emitted from the reflective dark field microscopy system in the second direction.

[0051] The vector space encoding optical system is arranged in the second direction, and includes: a 4F optical system and a multilayer film phase plate 1 arranged in the 4F optical system, and the multilayer film phase plate 1 is used to optically encode the pulse envelope.

[0052] The imaging system is arranged on the output surface of the 4F optical system to obtain the encoded vector space image.

[0053] The present invention achieves single-exposure ultrafast imaging by encoding the vector space characteristics of light of different frequencies through a multi-layer film phase plate with sub-wavelength thickness. It does not need to rely on a streak camera or 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 one trillion frame rate (1012fps).

[0054] As an optional embodiment, the ultrafast pulse laser 2 is a femtosecond mode-locked pulse laser with a detection wavelength range of 1020-1040 nm. When ultrashort pulses of light of different wavelengths pass through the pulse shaper 3, they propagate at different speeds, causing the pulses to gradually broaden to the picosecond level.

[0055] That is, when the total group delay dispersion D is much larger than the square of the pulse duration The time of the light source t The mapping relationship between and frequency ω is: t = Dω. Belongs to the temporal Fourier (Fraunhofer) region, where the input spectrum (frequency) can be mapped to the output time.

[0056] Therefore, the pulse shaper 3 can realize the control of the single pulse emitted by the ultrafast pulse laser 2 and obtain a pulse envelope corresponding to the time and spectrum.

[0057] Furthermore, the pulse envelope enters a reflective dark-field microscopy system to illuminate the target object 9, thereby obtaining the pulse envelope carrying target object information.

[0058] Specifically, the reflective dark field microscopy system includes a semi-transparent and semi-reflective mirror 7 and a microscope objective lens 8. The microscope objective lens 8 illuminates the target object 9 and collects the pulse envelope reflected by the target object 9 and carrying the target object information.

[0059] As an optional embodiment, the reflective dark field microscopy system is coaxially arranged with the vector space coding optical system, so that the pulse envelope carrying the target object information passes through the half-reflective half-mirror 7 and enters the vector space coding optical system.

[0060] In other embodiments, the pulse envelope carrying the target object information is transmitted through the half-reflective half-mirror 7, and then the pulse envelope carrying the target object information is reflected into the vector space coding optical system.

[0061] The vector space encoding optical system comprises: a 4F optical system and a multilayer film phase plate 1 arranged in the 4F optical system, wherein the multilayer film phase plate 1 is used for optically encoding the pulse envelope.

[0062] Specifically, the 4F optical system includes a first objective lens 5 and a second objective lens 6 for converting between the time domain and the frequency domain. A multilayer film phase plate 1 is positioned 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 by the first objective lens 5.

[0063] Furthermore, the operating wavelength range of the multilayer film phase plate 1 is consistent with the detection wavelength range of the ultrafast pulse laser, and in this embodiment, both are 1020-1040 nm.

[0064] In optical thin film design, to ensure that phase plates exhibit dispersive properties in wave vector space (Fourier space), thereby achieving the purpose of light splitting (separating light of different frequencies (wavelengths)), phase plates are typically designed as multilayer thin film structures. The high-refractive-index tantalum pentoxide (Ta2O5) and the low-refractive-index silicon dioxide (SiO2) work well together, and the desired phase difference can be achieved by precisely controlling the film thickness. Therefore, the multilayer film phase plate in this embodiment comprises an overlapping arrangement of tantalum pentoxide and silicon dioxide optical thin films.

[0065] Specifically, such as Figure 2 As 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 interlayer 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.

[0066] As an optional embodiment, the first high-reflection double distributed Bragg reflector structure 1.1 includes: taking one side of the intermediate interlayer 1.2 as the starting layer, alternately stacking a first tantalum pentoxide optical film layer, a first silicon dioxide optical film layer, a second tantalum pentoxide optical film layer, a second silicon dioxide optical film layer... and so on, a total of eight layers.

[0067] Similarly, the second high-reflection double distributed Bragg reflector structure 1.3 includes: starting from the other side of the intermediate interlayer 1.2, away from the first high-reflection double distributed Bragg reflector structure 1.1, tantalum pentoxide optical film layers and silicon dioxide optical film layers are alternately stacked in sequence, totaling eight layers.

[0068] Furthermore, the middle interlayer is a silicon dioxide layer, which is equivalent to a Fabry-Perot cavity. By adjusting its thickness, the transmission spectrum characteristics of the multilayer film phase plate can be precisely controlled.

[0069] As an optional 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.

[0070] Figure 3 The multilayer film phase plate of this embodiment is shown in FIG. )Down s Polarization direction and p Polarization direction and The transmittance curve is shown in Figure 2. The horizontal axis represents the wave vector, and the vertical axis represents the response range of the multilayer film phase plate. In this embodiment, the numerical aperture of the first objective lens and the second objective lens is 0.7NA, so the horizontal axis ranges from 0 to 0.7.

[0071] Since the pulse envelope has different and , so and This can be solved using the TMM (transfer matrix method), so that light of different wavelengths has different electric field amplitudes after passing through the multilayer film phase plate 1, thereby achieving optical encoding.

[0072] Furthermore, according to the known and The optical transfer function used to decode the encoded vector space image can be obtained .

[0073] Specifically, when a beam of light passes through the multilayer film phase plate 1, the amplitude of the outgoing light in the polar coordinate system is , which can be expressed as:

[0074]

[0075] in, is the radial wave vector, A is the amplitude;

[0076] and ( and They are s Polarization and p The polarization wave vector) is mainly related to the angle of incidence It can be expressed as: ; is the wave vector constant, yes r Radial and y The angle between the axes is in real space.

[0077] Therefore, the transfer function The expression is:

[0078] (2)

[0079] in, In Fourier space and Angle.

[0080] Continue to see Figure 1 The pulse envelope encoded by the multilayer phase plate 1 is output as an encoded vector space image through the imaging system.

[0081] As an optional embodiment, the imaging system includes an imaging lens 10 for focusing and a detector 4. The detector can be obtained as follows Figure 4 Vector space images of the different bands shown.

[0082] Further, yes Figure 4 The spectrum can be reconstructed by decoding the vector space image in the image, thereby achieving an imaging speed of trillion frames per second.

[0083] As an optional implementation, the ultrafast imaging device based on vector space coding further includes: a reconstruction unit, configured to decode the encoded vector space image to obtain a reconstructed spectrum.

[0084] Specifically, the process of decoding the encoded vector space image is as follows.

[0085] Assume that the incident unknown spectrum is , the decoding process can be expressed as:

[0086]

[0087] in, 1020 nm to 1040 nm Different response wavelengths within the range;

[0088] iis the number of coded pixels of the coded vector space image;

[0089] is the response current value corresponding to the coding pixel, that is, Figure 4 The response current corresponding to each pixel in the vector space image at each wavelength;

[0090] is the optical transfer function.

[0091] Furthermore, the formula (3) can be expanded into the form of a trial solution:

[0092] in, is a Gaussian function of the different response wavelengths, with a bandwidth of 0.5 nm; is the default value.

[0093] The solution process becomes a minimization problem:

[0094]

[0095] Use Tikhonov regularization to find the minimum L2 norm, and then use Generalized Cross Validation (GCV) to automate the regularization coefficient. The reconstructed spectrum can be obtained. .

[0096] Figure 5 The spectral comparison diagram of the reconstructed spectrum of a known target object obtained by the ultrafast imaging device based on vector space encoding of the present invention shows that in the detection band of 1020nm-1040nm, the spectrum obtained using the multi-layer phase plate of the present invention is close to the real spectrum, achieving an imaging speed of trillion frame rate.

[0097] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. References to the common and similar parts between the various embodiments will be sufficient. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, their descriptions are relatively simple; for relevant details, refer to the descriptions of the methods.

[0098] The above embodiments are only used to illustrate the technical solutions disclosed in 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. However, 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 disclosed in the present invention.

Claims

1. An ultrafast imaging device based on vector space coding, characterized in that: include: Ultrafast pulsed lasers; a pulse shaper for regulating the single pulse emitted by the ultrafast pulse laser to obtain a pulse envelope corresponding to time and spectrum; a reflective dark field microscopy system, disposed after the pulse shaper, causing the pulse envelope to reflect after illuminating the target in a first direction and exit the reflective dark field microscopy system in a second direction; A vector space encoding optical system is arranged in the second direction, comprising: a 4F optical system and a multilayer film phase plate arranged in the 4F optical system, wherein the multilayer film phase plate is used to optically encode the pulse envelope; The multilayer film phase plate comprises: a symmetrically arranged first high-reflection double distributed Bragg reflector structure, a second high-reflection double distributed Bragg reflector structure, and an interlayer arranged between the first high-reflection double distributed Bragg reflector structure and the second high-reflection double distributed Bragg reflector structure; The imaging system is arranged on the output surface of the 4F optical system to obtain the encoded vector space image.

2. The ultrafast imaging device based on vector space coding according to claim 1, characterized in that: The detection band range of the ultrafast pulse laser is: 1020-1040nm; The multilayer film phase plate is a multilayer film structure in which tantalum pentoxide optical films and silicon dioxide optical films are overlapped and arranged.

3. The ultrafast imaging device based on vector space coding according to claim 2, characterized in that: 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 layers are adjacent to the middle interlayer.

4. The ultrafast imaging device based on vector space coding according to claim 2 or 3, 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.

5. The ultrafast imaging device based on vector space coding according to claim 4, characterized in that: The intermediate interlayer is a silicon dioxide layer, and the thickness of the intermediate interlayer is 249 nm.

6. The ultrafast imaging device based on vector space coding according to claim 1, characterized in that: The reflective dark field microscopy system comprises: a half-reflecting half-mirror, arranged on the outgoing optical path of the pulse shaper, reflecting the pulse envelope and transmitting the pulse envelope carrying target information reflected by the target; The first objective lens is arranged on the reflection light path of the half-reflecting half-mirror lens, and is used to collect the pulse envelope carrying the target information reflected by the target.

7. The ultrafast imaging device based on vector space coding according to claim 1, characterized in that: The 4F optical system includes: a first objective lens and a second objective lens, and the multilayer film phase plate is arranged between the first objective lens and the second objective lens; the numerical aperture of the first objective lens and the second objective lens is 0.7NA.

8. The ultrafast imaging device based on vector space coding according to claim 1, characterized in that: Also includes: A reconstruction unit is configured to decode the encoded vector space image to obtain a reconstructed spectrum.

9. The ultrafast imaging device based on vector space coding according to claim 8, characterized in that: The reconstruction unit decodes the encoded vector space image to obtain the reconstructed spectrum. The expression is: （1）； Among them, R i is the optical transfer function; ψ j is the default value; λ is the different response wavelengths ranging from 1020nm to 1040nm; β j (λ) is the Gaussian function of the different response wavelengths; i is the number of coded pixels in the coded vector space image; I i is the response current value corresponding to the coding pixel.

Images