Stimulated radiation signal imaging device and method based on orbital angular momentum modulation

Abstract

The invention relates to a stimulated radiation signal imaging device and method based on orbital angular momentum modulation. The device is characterized in that a light pulse emitted by an ultra-short pulse laser passes through a first light splitting device to generate transmission light and reflected light, and the transmission light as pump pump light is modulated by a structured light space coding module and a first optical orbital angular momentum regulation and control device and then enters a second light splitting device; the reflected light as probe light is modulated by a time delay regulation and control module and a second optical orbital angular momentum regulation and control device and then enters a second light splitting device, the two modulated light beams are combined and coaxially propagated and irradiated on a sample in the same direction, and after the sample is irradiated by the two light beams, stimulated radiation is generated and a transient optical signal is sent out. An optical signal is received by the imaging module after passing through the 4-f optical filtering system and the third optical orbital angular momentum device. According to the invention, stimulated radiation signal light extraction in a strong background illumination environment can be realized.

Description

Technical Field

[0001] The present invention relates to the technical fields of optical orbital angular momentum modulation, optical spatial filtering, stimulated emission of biological samples, etc., and particularly relates to a stimulated emission signal imaging device and method based on orbital angular momentum modulation and optical spatial filtering. Background Art

[0002] Light has wave-particle duality. As an electromagnetic wave, light has parameter attributes such as wavelength (frequency), amplitude, phase, and light polarization. As a fundamental particle, light has parameter attributes such as energy, momentum (linear momentum and spin / orbital angular momentum). Optical orbital angular momentum (Orbital Angular Momentum, abbreviated as OAM), its macroscopic manifestation is the vortex phenomenon of electromagnetic waves, specifically that the beam has a helical phase characteristic in the plane perpendicular to the propagation direction. Microscopically, OAM represents an intrinsic property of photons. Different from optical spin angular momentum (Spin Angular Momentum, abbreviated as SAM), SAM can only take two modes of ±1, while OAM has an infinite number of modes, and the modes are orthogonal to each other, providing natural conditions for the communication and detection of vortex waves.

[0003] Since the frequency, phase, propagation direction, and angular momentum state of the stimulated emission field are exactly the same as those of the external radiation field, how to separate the light of the radiation field from the light emitted by the sample and reconstruct it in chronological order is a very important research method. Summary of the Invention

[0004] Since the wavelengths of the stimulated absorption light and the radiation light of some samples are relatively close, it is difficult to effectively block the excitation light through an optical filter. In view of this, the purpose of the present invention is to effectively extract the target signal by combining optical orbital angular momentum regulation and optical spatial filtering, so as to provide a stimulated emission signal imaging device and method based on orbital angular momentum modulation.

[0005] The technical solution adopted by the present invention is as follows:

[0006] Stimulated emission signal imaging device based on orbital angular momentum modulation, the device comprising: an ultrashort pulse laser, an optical orbital angular momentum modulation device, a structured light spatial encoding module, a time delay modulation module, a 4-f optical filtering system, and an imaging module, wherein the optical orbital angular momentum modulation device is used to modulate the angular momentum mode of the light field; the light pulse emitted by the ultrashort pulse laser generates transmitted light and reflected light after passing through the first beam splitter device, wherein the transmitted light is used as pump light and is incident on the second beam splitter device after being modulated by the structured light spatial encoding module and the first optical orbital angular momentum modulation device, and the reflected light is used as probe light and is also incident on the second beam splitter device after being modulated by the time delay modulation module and the second optical orbital angular momentum modulation device. The two modulated beams are combined and propagate coaxially and in the same direction to irradiate the sample. After the sample is irradiated by these two beams of light, stimulated emission occurs and transient optical signals are emitted. The optical signals are received by the imaging module after passing through the 4-f optical filtering system and the third optical orbital angular momentum device.

[0007] Further, the orbital angular momentum mode modulated by the second optical orbital angular momentum modulation device is different from the orbital angular momentum mode modulated by the first optical orbital angular momentum modulation device, and the orbital angular momentum mode modulated by the third optical orbital angular momentum modulation device is the same as the orbital angular momentum mode modulated by the second optical orbital angular momentum modulation device.

[0008] Further, the optical orbital angular momentum modulation device includes one or more of a vortex wave plate, a spatial light modulator (SLM), and a Dammann grating.

[0009] Further, the structured light spatial encoding module and the first optical orbital angular momentum modulation device share the same device.

[0010] Further, the structured light spatial encoding module includes a spatial light modulator and a mirror, and the spatial light modulator optically encodes the pump light to introduce spatial frequency.

[0011] Further, the time delay modulation module includes a right-angle prism mirror group and a one-dimensional translation stage, and the one-dimensional translation stage is used to adjust the position of the right-angle prism mirror group.

[0012] Further, the right-angle prism mirror group uses four identical isosceles right prisms with inclined surfaces coated with film. Among them, the first and second right prisms are assembled back to back, and the included angle between the coated reflective inclined surfaces is 90°. The right-angle sides of the third and fourth right prisms are arranged in a straight line, and the included angle between the coated inclined surfaces is also 90°. The hypotenuses of the first and third right prisms are parallel, and the hypotenuses of the second and fourth right prisms are also parallel; the third and fourth right prisms are fixed on the one-dimensional translation stage.

[0013] Further, the 4-f optical filtering system includes two lenses and an aperture stop. The aperture stop is vertically placed on the focal plane between the two lenses, and the target optical signal is filtered out by adjusting the center position of the aperture.

[0014] Further, the imaging module includes an imaging sensor and an image processing module. The imaging sensor is used to receive the optical signal, convert it into a digital image, and transmit it to the image processing module for image spectrum analysis and processing.

[0015] The present invention also provides a method for using the above-described stimulated emission signal imaging device based on orbital angular momentum modulation. Specifically, first, the light source emitted by the ultrashort pulse laser generates two beams of light, namely pump pump light and probe probe light, after passing through the beam splitter device. The pump pump light is spatially modulated to load a periodic fringe or speckle pattern, and the pump pump light is modulated by the orbital angular momentum mode, so that the beam carries high-frequency information and orbital angular momentum attributes in space. Then, the light intensity is irradiated on the sample according to the loaded pattern structure in the transmission direction, so that the sample regionally absorbs the pump pump light; the probe probe light does not carry spatial high-frequency information. The optical path difference between the probe probe light and the pump pump light is ensured to be approximately equal through the time delay control module, and then it is modulated by the second optical orbital angular momentum control device to load the orbital angular momentum, and then uniformly irradiated on the sample, so that the sample region that has absorbed the energy of the pump pump light generates stimulated emission transition; then, the probe probe light is filtered out by the 4-f optical filtering system, and the pump pump light is filtered out by the third optical orbital angular momentum control device, so that only the signal light emitted by the sample propagates to the imaging module.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) By using the orbital angular momentum control device, combining the spatial frequency information generated by introducing the spatial light modulator and the 4-f optical filtering system, the present invention can separate the sample signal light from the pump structural pump light and the probe plane probe light in the stimulated emission scenario (filter out the probe probe light through the 4-f system and filter out the pump pump light through the orbital angular momentum control device). Therefore, the target weak light signal can be separated under the background of ultra-high light intensity, and then the stimulated emission signal can be collected by single exposure on the spatial scale.

[0018] (2) By combining the time delay system composed of a right-angle mirror group, the present invention realizes the analysis of the transient optical process on the time scale, and the time accuracy can reach the order of ~10 fs.

[0019] (3) For samples where the wavelengths of stimulated absorption and stimulated emission light are relatively close, the present invention can effectively compensate for the defect that ordinary optical filters cannot fully block pump light, achieving more effective signal extraction. Combining with the ultra-high time resolution of the pump-probe optical path structure, it can be applied to the field of exploring the luminescence mechanism of stimulated emission.

[0020] (4) The weak signal extraction carried out by the device and method of the present invention has almost no requirements for the wavelengths of pump light, probe light, and sample radiation light. Therefore, it is more convenient to collect and analyze data during the luminescence process, which has relatively important research significance for disciplines such as solid state physics and atomic physics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, where:

[0022] Figure 1 is a schematic diagram of the imaging device provided by an embodiment of the present invention.

[0023] Figure 2 is a schematic diagram of the structured light generated by modulating in the pump pump light according to an embodiment of the present invention.

[0024] Figure 3 is a cross-sectional view of the optical field phase after modulating the orbital angular momentum (OAM) state of the optical field according to an embodiment of the present invention.

[0025] Figure 4 is a top view schematic diagram of the assembly of the mirror group and the one-dimensional displacement stage according to an embodiment of the present invention.

[0026] Figure 5 is the 4-f optical filtering system provided by an embodiment of the present invention.

[0027] Figure 6 is a flowchart of the imaging method provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] Refer to the attached Figure 1Describe the stimulated emission signal imaging device and method based on orbital angular momentum modulation and optical spatial filtering according to the embodiments of the present invention. Among them, introducing optical intensity spatial encoding into the process of weak signal extraction can solve the problem that it is difficult to effectively filter out because the wavelengths of the external probe light and the light emitted by the sample are the same. Introducing the optical orbital angular momentum dimension into the optical pumping process can effectively filter out the external pumping light, so as to only retain the radiation light of the sample. The present invention realizes the acquisition and imaging of weak signal light in a strong background light environment by regulating and separating the pumping light, probe light and radiation light.

[0030]

Optical Orbital Angular Momentum Regulation Module

[0031] Among them, the orbital angular momentum regulation device includes one or more of a vortex wave plate, a spatial light modulator SLM, and a Dammann grating. In this embodiment, the spatial light modulator SLM is multiplexed, and the above scheme can also be implemented by using three orbital angular momentum modulation devices. After the light pulse passes through the orbital angular momentum regulation device, effects such as absorption, reflection, interference, or diffraction can be generated to realize the modulation of the angular momentum state of the light field.

[0032]

Structured Light Spatial Encoding Module

[0033]

Pump Light and Probe Light Time Delay Regulation Module

[0034] Fix the ③ and ④ right-angled prism mirror group on the one-dimensional translation stage (as shown in Figure 4 ), by moving the displacement stage (the displacement stage moves back and forth along the right-angled side of the ③ right-angled prism), the optical path between the right-angled prism mirror groups changes accordingly. The one-dimensional translation stage can achieve an accuracy of displacement resolution of 1 μm. Therefore, by changing the optical path difference through displacement, the minimum adjustable optical pulse time interval can be 6.66 fs (the calculation method is: Δt = Δx / c0 = 2×1×10 -6 m / 3.0×10 8 m / s = 6.66 fs). Considering the influence of device errors, the fine-tuning time accuracy of this system is about ~10 fs.

[0035] The present invention controls a right-angle mirror group to control the relative time delay between the pump light and the probe light, thereby achieving time-resolution scanning imaging at the femtosecond level.

[0036]

Controlling the 4-f system to gate the target weak signal and block the background noise

[0037] The original unmodulated stimulated emission signal is denoted as I x , at this time, since the optical signal is uniformly irradiated, the energy of the frequency spectrum of this signal is concentrated at the fundamental frequency position; after passing through the SLM spatial light modulator, the fringe I s (such as a sine fringe) is loaded. At this time, the process of the pump light interacting with the fringe signal is equivalent to the process of point multiplication at the corresponding positions, that is, I x · I s . At this time, after the modulation signal passes through the equivalent Fourier transform of the lens L1, we get:

[0038]

[0039] Among them, FT() represents taking the Fourier transform of the variable inside the parentheses, "·" represents the dot multiplication operation, and "*" represents the convolution process. This process is equivalent to introducing high-frequency components into the spatial light field through the SLM. It can be obtained from the frequency spectrum diagram that the frequency term of the target signal is shifted to the high-frequency position.

[0040] At this time, a band-pass filter I mask is introduced at the position of the rear focal plane of the lens L1 (which is also the front focal plane of the lens L2), so that only the frequency term after the convolution of the signal and the fringe can pass through, blocking other signals (including the pump light, probe light, and ambient light that are not absorbed by the sample, etc.); after the band-pass filtered signal passes through the equivalent inverse Fourier transform of the lens L2, it is converted into a spatial domain light intensity signal, that is:

[0041] FT -1 {[FT(I x · I s )] · I mask}

[0042] Among them, FT -1() represents the inverse Fourier transform operation. Finally, the signal is received by the detection device. Since only the high-frequency part of the optical signal is retained in the collected image at this time, post-processing and other methods are needed to optimize the image.

[0043] Figure 5 This is a structural detail diagram of the 4-f optical filtering system provided by the embodiment of the present invention. It includes two lenses and an aperture stop, and the aperture stop is placed on the focal plane in the middle of the two lenses. The 4-f system is controlled to block the low-frequency information of the stimulated emission signal generated in the biological tissue sample and select the high-frequency optical information with a certain spatial frequency.

[0044] The stimulated emission optical signal carries spatial frequency information, and its energy is concentrated at high frequencies; the background light does not carry high-frequency information, so its energy is concentrated at the central low frequencies; at this time, in this Fourier plane ( Figure 4 at the Aperture position), an aperture stop is placed, with the center of the aperture of the stop in the high-frequency energy region, and the size of the aperture of the stop should block the central low-frequency region. The position of the hole and the light that can pass through are as described in the aperture stop Aperture in Figure 4 In the vertical position, the distance from the center of the aperture to the optical axis can be calculated according to the formula Δ = λ·f·u0, where λ is the wavelength of the incident light, f is the focal length of the convex lens, and u0 is the spatial frequency of the loaded sine stripe.

[0045] Figure 1 Other optical elements and mechanical parts in : The front and rear aperture stops (Aperture) are respectively used for circular modulation of the output light and optical filtering in the 4-f system; the reflector (Reflector) is used to change the propagation direction of the light beam, and it is one or more of a silver-plated reflector, a gold-plated reflector, or a dielectric film reflector, which has a high reflectivity for the used light band.

[0046]

Separation of orbital angular momentum states of the optical field by the orbital angular momentum modulation device

[0047]

Image processing of light field information

[0048] The above overall process can be summarized as Figure 6 described below. First, the optical pulse generated by the ultra-short pulse laser is split by the beam splitter device according to the light intensity ratio of 5:5, generating two beams of light, namely pump pump light and probe probe light, and the optical orbital angular momentum states of the two beams of light are different. The pump pump light is spatially modulated to load a periodic fringe or speckle pattern and becomes a structured pump light carrying high-frequency information in space, and is incident into the subsequent optical orbital angular momentum beam splitter device along the light propagation direction; the probe probe light does not carry spatial high-frequency information. Through the optical time delay control module, an additional optical path is added to ensure that the optical path difference between the pump optical path and the probe optical path is approximately equal. Then, it is modulated by the optical orbital angular momentum control device to load the orbital angular momentum, and finally the probe light propagates to the optical orbital angular momentum beam splitter device. After being combined by the beam splitter device, the pump structured pump light and the probe plane probe light propagate coaxially and in the same direction. The two beams of light are coincident in space and time, but the difference between the two beams of light is that their orbital angular momentum states are different and they have different spatial frequency spectra. After the two beams of light reach the sample, the structured pump light is stimulated and absorbed by the sample. Since the light intensity of the pump light presents a structured distribution in space, there are also differences in the stimulated absorption in the structure of the sample in space; at the same time, the probe probe light uniformly irradiates the sample. Therefore, obvious stimulated radiation phenomena will occur in the places where the stimulated absorption of the sample is relatively strong, emitting stronger radiation light, and less or no stimulated radiation phenomena will occur in the places where the stimulated absorption is relatively weak. Therefore, the signal light radiated by the sample has the same spatial structure characteristics as the pump light, and at the same time has the same wavelength and orbital angular momentum characteristics as the probe light (known from the stimulated radiation principle). After passing through the sample, the light field has three sources, namely the pump structured pump light, the probe probe plane light, and the signal light emitted by the stimulated radiation sample. The purpose of the method of the present invention is to separate the signal light emitted by the sample, and the light intensity of the signal light is extremely weak compared with the former two, at 10 -4 -10 -7The order of magnitude is such that it can be called a weak signal. The signal light is submerged in extremely strong background light, and the optical sensor cannot distinguish the signal light. The specific method for separating the signal light is as follows: First, the probe light is filtered out through an optical 4f filtering system, and then the pump light is filtered out through an optical orbital angular momentum device. At this time, only the desired signal light continues to propagate and is finally received by a two-dimensional imaging sensor.

[0049] Through the processing of the 4-f optical filtering and orbital angular momentum modulation device of the present invention, the background light and part of the signal light can be physically blocked. At this time, all the signals collected by the optical sensor are signal lights, realizing the measurement of weak light signals. By introducing optical orbital angular momentum and structured light spatial filtering, on the one hand, the stimulated emission signal light can be extracted under strong background light illumination conditions, and on the other hand, the problem that it is difficult to separate the excitation light and the radiation light of the stimulated emission sample due to their similar wavelengths can be effectively solved. Therefore, the signal-to-noise ratio of weak signal acquisition can be greatly improved.

[0050] In this specification, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0051] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A stimulated radiation signal imaging device based on orbital angular momentum modulation, characterized in that The device includes: an ultra-short pulse laser, an optical orbital angular momentum modulation device, a structured light spatial encoding module, a time delay modulation module, a 4-f optical filtering system, and an imaging module. The optical orbital angular momentum modulation device is used to modulate the angular momentum mode of the light field. The light pulse emitted by the ultra-short pulse laser generates transmitted light and reflected light after passing through the first beam splitter device. The transmitted light is used as pump light and is incident on the second beam splitter device after being modulated by the structured light spatial encoding module and the first optical orbital angular momentum modulation device. The reflected light is used as probe light and is also incident on the second beam splitter device after being modulated by the time delay modulation module and the second optical orbital angular momentum modulation device. The two modulated beams are combined and propagate coaxially and in the same direction to irradiate the sample. After being irradiated by these two beams, the sample generates stimulated radiation and emits transient optical signals. The optical signals are received by the imaging module after passing through the 4-f optical filtering system and the third optical orbital angular momentum device.

2. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, characterized in that, The orbital angular momentum mode modulated by the second optical orbital angular momentum modulation device is different from the orbital angular momentum mode modulated by the first optical orbital angular momentum modulation device, and the orbital angular momentum mode modulated by the third optical orbital angular momentum modulation device is the same as the orbital angular momentum mode modulated by the second optical orbital angular momentum modulation device.

3. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, wherein The optical orbital angular momentum modulation device includes one or more of a vortex wave plate, a spatial light modulator (SLM), and a Dammann grating.

4. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, characterized in that The structured light spatial encoding module and the first optical orbital angular momentum modulation device share the same device.

5. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, wherein The structured light spatial encoding module includes a spatial light modulator and a mirror. The spatial light modulator optically encodes the pump light and introduces spatial frequency.

6. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, wherein The time delay modulation module includes a right-angle prism mirror group and a one-dimensional translation stage. The one-dimensional translation stage is used to adjust the position of the right-angle prism mirror group.

7. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 6, wherein The right-angle prism mirror group consists of four identical isosceles right prisms with coated inclined surfaces. Among them, the first and second right prisms are assembled back to back, and the included angle between the coated reflective inclined surfaces is 90°. The right-angle sides of the third and fourth right prisms are arranged in a straight line, and the included angle between the coated inclined surfaces is also 90°. The hypotenuses of the first and third right prisms are parallel, and the hypotenuses of the second and fourth right prisms are also parallel. The third and fourth right prisms are fixed on the one-dimensional translation stage.

8. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, characterized in that, The 4-f optical filtering system includes two lenses and an aperture stop. The aperture stop is vertically placed on the focal plane between the two lenses, and the target optical signal is filtered out by adjusting the center position of the aperture.

9. The stimulated emission signal imaging device based on orbital angular momentum modulation according to claim 1, wherein The imaging module includes an imaging sensor and an image processing module. The imaging sensor is used to receive the optical signal and convert it into a digital image, and then transmit it to the image processing module for image spectrum analysis and processing.

10. A method of using the stimulated radiation signal imaging device based on orbital angular momentum modulation as described in claim 1, characterized in that The method is specifically as follows: First, the light source emitted by the ultra-short pulse laser generates two beams of light, namely pump light and probe light, after passing through the beam splitter device. The pump pump light is spatially modulated to load a periodic fringe or speckle pattern, and the pump pump light is modulated by an orbital angular momentum mode, so that the beam carries high-frequency information and orbital angular momentum attributes spatially. Then, the light intensity is irradiated onto the sample according to the loaded pattern structure in the transmission direction, so that the sample absorbs the pump pump light regionally; The probe probe light does not carry spatial high-frequency information. The time delay control module is used to ensure that the optical path difference between the probe probe light and the pump pump light is approximately equal. Then, it is modulated by the second optical orbital angular momentum control device to load the orbital angular momentum, and then uniformly irradiates the sample, so that the sample region that has absorbed the energy of the pump pump light undergoes a stimulated emission transition; Then, the probe probe light is filtered by a 4-f optical filtering system, and the pump pump light is filtered by the third optical orbital angular momentum control device, so that only the signal light emitted by the sample propagates to the imaging module.

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