Quented radiation signal imaging device and method based on cross-polarization modulation

Abstract

The invention relates to a stimulated radiation signal imaging device and method based on cross-polarization modulation. The device is characterized in that a light pulse emitted by an ultra-short pulse laser passes through a first optical polarization regulation and control device to generate two beams of transmission light and reflection light of which the polarization directions are vertical to each other; wherein the transmission light serving as pump light is modulated by the structured light space coding module and then enters the third optical polarization regulation and control device through the second optical polarization regulation and control device, and the reflection light serving as probe light also enters the third optical polarization regulation and control device through the time delay regulation and control module. At the moment, the pump pump light and the probe light are combined and coaxially propagated and irradiated on a sample in the same direction, the sample is irradiated by the two light beams to generate stimulated radiation and emit a transient optical signal, and the optical signal is received by an imaging module after passing through a 4-f optical filtering system and a fourth optical polarization regulation and control 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 technical fields such as optical orthogonal polarization state modulation, optical intensity encoding and spatial filtering, and stimulated emission of biological samples, and particularly relates to a stimulated emission signal imaging device and method based on orthogonal polarization modulation and optical spatial filtering. Background Art

[0002] According to the wave-particle duality of light, light can be regarded as an electromagnetic wave, and light is a transverse wave, whose vibration direction is always perpendicular to the propagation direction. When light propagates, its electric field E and magnetic field H change in the form of waves over time and space. Polarization refers to the directivity of the electric field oscillation direction. Specifically, if the electric field oscillation direction changes randomly over time, the light is randomly polarized; if the electric field oscillation direction is fixed, the light is linearly polarized. Polarized light also has many applications in life, such as 3D glasses based on polarization control, polarization cameras made according to the polarization attributes of the reflected light on the object surface, and polarized light imaging in haze weather.

[0003] Processes such as stimulated emission, stimulated absorption, and spontaneous emission together constitute the microscopic process of the interaction between light and matter. Among them, stimulated emission, as one of the most important principles of laser technology, involves the light emission process caused by energy level transitions inside atoms, and has extensive research and application value in the scientific and engineering fields. At the microscopic level, modeling the stimulated emission process through the internal energy level lifetime of atoms and the dynamics of the radiation process, and revealing the dynamics of the stimulated emission process, through means such as time control and encoded imaging, are the mainstream of current research. Limited by the ratio of the light intensity of the stimulated emission process to the pumping process (10 -4 ~10 -7 ) being too small, how to extract the target signal from a strong light illumination environment is an important task.

[0004] Through literature research and comparison, it is known that for ordinary stimulated emission samples, due to the Stokes effect, there is usually a large difference in wavelength (~20nm) between the radiation light and the absorption light of the sample, and the pump light and the radiation light can be distinguished by an optical filter or other methods. However, due to the relatively close wavelengths of the stimulated absorption light and the radiation light of some samples, it is difficult to effectively block the excitation light through an optical filter. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to effectively extract the target signal by combining optical polarization control with optical spatial filtering, so as to provide a stimulated emission signal imaging device based on orthogonal polarization modulation and its method.

[0006] The technical solution adopted by the present invention is as follows:

[0007] Stimulated emission signal imaging device based on orthogonal polarization modulation, the device comprising: an ultrashort pulse laser, an optical polarization control device, a structured light spatial encoding module, a time delay control module, a 4-f optical filtering system and an imaging module; the optical pulse emitted by the ultrashort pulse laser generates two transmitted lights and reflected lights with mutually perpendicular polarization directions after passing through the first optical polarization control device, wherein the transmitted light is used as pump light, which is first modulated by the structured light spatial encoding module and then incident on the third optical polarization control device through the second optical polarization control device, and the reflected light is used as probe light, which is also incident on the third optical polarization control device after passing through the time delay control module. At this time, the pump light and the probe light are combined and propagate coaxially and in the same direction to irradiate the sample. After the sample is irradiated by these two lights, stimulated emission occurs and a transient optical signal is emitted. The optical signal is received by the imaging module after passing through the 4-f optical filtering system and the fourth optical polarization control device.

[0008] Further, the polarization directions of the second optical polarization control device and the fourth optical polarization control device are perpendicular to each other.

[0009] Further, the optical polarization control device includes one or more of an optical polarizer, an optical polarization beam splitter prism, and a laser Glan-Taylor crystal. The polarization states of the optical pulses modulated by the optical polarization control device include one or more of a linear polarization state, a circular polarization state, and an elliptical polarization state.

[0010] Further, 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 a spatial frequency.

[0011] Further, the spatial light modulator is one or more of a phase modulation type or an amplitude modulation type.

[0012] Further, the time delay control 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.

[0013] Further, the right-angle prism mirror group adopts 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.

[0014] 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.

[0015] Further, the device 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.

[0016] The present invention also provides a method for using the above-mentioned stimulated emission signal imaging device based on orthogonal polarization modulation, specifically as follows: First, after the light source emitted by the ultrashort pulse laser is split by the first optical polarization control device, two beams of light, namely pump pump light and probe probe light, are generated; the pump pump light is spatially modulated to load a periodic fringe or speckle pattern, so that the beam carries high-frequency information in space. According to the transmission direction, the light intensity passes through the second optical polarization control device and the third optical polarization control device and then irradiates the sample, so that the sample regionally absorbs the pump pump light; the probe probe light does not carry spatial high-frequency information. The time delay control module ensures that the optical path difference between the probe probe light and the pump pump light is approximately equal, and then the probe probe light uniformly irradiates the sample through the third optical polarization control device, so that the sample region that has absorbed the pump pump light energy generates a stimulated emission signal; then, the probe probe light is filtered out by the 4-f optical filtering system, and the structured light of the pump pump is filtered out by the fourth optical polarization control device, so that only the signal light emitted by the sample propagates to the imaging module.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) By using the polarization 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 realize the separation of the sample signal light, the pump structured pump light, and the probe plane probe light in the stimulated emission scenario (filtering out the probe probe light through the 4-f system and filtering out the pump pump light through the polarization 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.

[0019] (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.

[0020] (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, and achieve 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.

[0021] (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

[0022] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0023] Figure 1 is a schematic diagram of the imaging device provided by an embodiment of the present invention.

[0024] Figure 2 is a schematic diagram of the structured light generated by modulating in the pump light of an embodiment of the present invention.

[0025] Figure 3 is a top view schematic diagram of the assembly of the mirror group and the one-dimensional displacement stage in an embodiment of the present invention.

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

[0027] Figure 5 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 drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0029] Refer to the attached Figure 1 Describe the stimulated emission signal imaging device and method based on orthogonal polarization modulation and optical spatial filtering according to an embodiment of the present invention. By modulating and separating pump light, probe light, and radiation light, the collection and imaging of weak signal light in a strong background light environment are realized.

[0030]

Optical Polarization Modulation Device

[0031]

Structured Light Spatial Encoding Module

[0032]

Pump Light and Probe Light Time Delay Regulation Module

[0033] Fix the ③④ right-angled prism mirror group on a one-dimensional translation stage (as Figure 3 shown). 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. This one-dimensional translation stage can achieve a displacement accuracy of 1 μm resolution. Therefore, by changing the optical path difference through displacement, the minimum adjustable optical pulse time interval can be achieved as 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.

[0034] The present invention realizes the time resolution scanning imaging in the femtosecond level by controlling the right-angled mirror group to control the relative time delay between the pump pump light and the probe probe light.

[0035]

Controlling the 4-f optical filtering system to block the probe probe light

[0036] 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 spectral diagram of this signal is concentrated at the fundamental frequency position; after being loaded with the stripe I s (such as a sine stripe) by the SLM spatial light modulator, the process of the pump light interacting with the stripe signal is equivalent to the process of dot 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:

[0037]

[0038] Among them, FT() represents performing a Fourier transform on the variable inside the parentheses, "·" represents a dot product operation, and "*" represents a 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 spectrogram that the frequency term of the target signal is shifted to the high-frequency position.

[0039] At this time, a band-pass filter I is introduced at the position of the rear focal plane of lens L1 (which is also the front focal plane of lens L2) mask , so that the frequency term after the signal is convolved with the fringe can pass through, blocking other signals (including the pump pump light, probe probe light, and ambient light that are not absorbed by the sample); after the band-pass filtered signal undergoes the equivalent inverse Fourier transform of lens L2, it is converted into a spatial domain light intensity signal, that is:

[0040] FT -1 {[FT(I x ·I s )]·I mask}

[0041] Among them, FT -1 () represents the inverse Fourier transform operation. Finally, this signal is received by the detection device. Since only the high-frequency part of the optical signal is retained in the image collected at this time, post-processing and other methods are needed to optimize the image.

[0042] Figure 4 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 light information with a certain spatial frequency.

[0043] The stimulated emission optical signal carries spatial frequency information, and the energy is concentrated at the high-frequency position; the background light does not carry high-frequency information, so the energy is concentrated at the central low-frequency position; at this time, an aperture stop is placed on this Fourier plane ( Figure 4 at the Aperture position in it), so that the center of the aperture of the stop is 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 between the center of the aperture and 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 fringe.

[0044] Figure 1Other optical components and mechanical components: The front and rear aperture diaphragms are respectively used for circular modulation of the output light and optical filtering in the 4-f system; the polarizer is used for modulation of the linear polarization state and has multiple functions of polarization and depolarization. In the example, the higher the extinction ratio of the polarizer (generally, the extinction ratio is 10,000:1), the better the polarization control effect that can be achieved by this solution, and the better the extraction effect of weak signals; the reflector is used to change the propagation direction of the light beam and 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 optical band.

[0045]

Polarization control device blocks the pump light

[0046]

Image processing of the light field information

[0047] The above overall process can be summarized as Figure 5Description. First, the optical pulse generated by the ultra-short pulse laser is split by the optical polarization device according to the orthogonal polarization states to generate two beams of light, namely the pump light and the probe light. The optical polarization states of the two beams of light are perpendicular to each other. The 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 polarization beam splitter device along the light propagation direction; the probe light does not carry spatial high-frequency information and passes through the optical time delay control module to increase the additional optical path, aiming to ensure that the optical path difference between the pump optical path and the probe optical path is approximately equal, and finally the probe light propagates to the polarization beam splitter device. After being combined by the polarization beam splitter device, the structured pump light and the planar probe light are coaxial and propagate in the same direction. The two beams of light overlap in space and time, but the difference between the two beams of light is that their polarization states are perpendicular to each other 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 shows a structured distribution in space, there are also structural stimulated absorption differences in the sample in space; at the same time, the probe light uniformly irradiates the sample. Therefore, obvious stimulated emission 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 emission 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 the same wavelength and polarization characteristics as the probe light (known according to the principle of stimulated emission). After passing through the sample, the light field has three sources, namely the structured pump light, the planar probe light, and the signal light emitted by the stimulated emission 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, on the order of 10 -4 -10 -7 orders of magnitude, so it can be called a weak signal. The signal light is submerged in the extremely strong background light, and the optical sensor cannot distinguish the signal light. The specific method for separating the signal light is: first, filter out the probe light through the optical 4f filtering system, and then filter out the pump light through the optical polarization device. At this time, only the desired signal light continues to propagate, and finally the signal light is received by the two-dimensional imaging sensor.

[0048] Through the polarization control device and 4-f optical filtering process 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 orthogonal polarization modulation and spatial filtering, on the one hand, the present invention can extract the stimulated emission signal light in a strong background light illumination environment, and on the other hand, it can effectively solve 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, so it can greatly improve the signal-to-noise ratio of weak signal acquisition.

[0049] In this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0050] 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 emission signal imaging device based on orthogonal polarization modulation, characterized in that The device includes: an ultrashort pulse laser, an optical polarization 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 pulse emitted by the ultrashort pulse laser generates two transmitted lights and reflected lights with mutually perpendicular polarization directions after passing through the first optical polarization modulation device, where the transmitted light is used as the pump light, which is first modulated by the structured light spatial encoding module and then incident on the third optical polarization modulation device through the second optical polarization modulation device, and the reflected light is used as the probe light, which is also incident on the third optical polarization modulation device after passing through the time delay modulation module. At this time, the pump light and the probe light are combined and propagate coaxially and in the same direction to irradiate the sample. After the sample is irradiated by these two lights, stimulated emission occurs, and a transient optical signal is emitted. The optical signal is received by the imaging module after passing through the 4-f optical filtering system and the fourth optical polarization modulation device.

2. The stimulated emission signal imaging device based on orthogonal polarization modulation according to claim 1, characterized in that, The polarization directions of the second optical polarization modulation device and the fourth optical polarization modulation device are perpendicular to each other.

3. The stimulated emission signal imaging device based on orthogonal polarization modulation according to claim 1, wherein The optical polarization modulation device includes one or more of an optical polarizing plate, an optical polarization beam splitter prism, and a laser Glan-Taylor crystal. The polarization states of the optical pulses modulated by the optical polarization modulation device include one or more of a linear polarization state, a circular polarization state, and an elliptical polarization state.

4. The stimulated emission signal imaging device based on orthogonal polarization modulation according to claim 1, characterized in that, 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 a spatial frequency.

5. The stimulated emission signal imaging device based on orthogonal polarization modulation according to claim 4, characterized in that, The spatial light modulator is one or more of a phase modulation type or an amplitude modulation type.

6. The stimulated emission signal imaging device based on orthogonal polarization 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 orthogonal polarization modulation according to claim 6, wherein The right-angle prism mirror group uses 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 reflecting 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 orthogonal polarization 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 orthogonal polarization modulation according to claim 1, wherein The imaging module of the device 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 transmit it to the image processing module for image spectrum analysis and processing.

10. A method of using the stimulated emission signal imaging device based on orthogonal polarization modulation as described in claim 1, characterized in that, The method is specifically as follows: First, the light source emitted by the ultrashort pulse laser is split by the first optical polarization modulation device to generate two lights, namely the pump light and the probe light; The pump pump light is spatially modulated to load a periodic fringe or speckle pattern, enabling the beam to carry high-frequency information spatially. According to the propagation direction, the light intensity is irradiated onto the sample after passing through the second optical polarization control device and the third optical polarization control device according to the loaded pattern structure, causing the sample to absorb the pump pump light regionally; The probe probe light does not carry spatial high-frequency information. The time delay control module ensures that the optical path difference between the probe probe light and the pump pump light is approximately equal, and then it is uniformly irradiated onto the sample through the third optical polarization control device, causing the sample region that has absorbed the pump pump light energy to generate a stimulated emission signal; Then, the probe probe light is filtered out by the 4-f optical filtering system, and the structured light of the pump pump is filtered out by the fourth optical polarization control device, so that only the signal light emitted by the sample propagates to the imaging module.

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