Mid-infrared real-time imaging system

Abstract

The application provides a kind of middle infrared real-time imaging system, including visible-near infrared light source, frequency doubler, first light splitting component, middle infrared illumination light generating component, first optical delay line, vortex beam generator, first light parametric amplifier, first imaging component, second imaging component and CCD camera.The first light parametric amplifier uses strong femtosecond vortex pulse laser as pump light, and converts middle infrared signal light of middle infrared wave band carrying object information into visible light for detection and recording with high gain.The strong femtosecond vortex pulse laser as pump light provides high optical gain and large spatial frequency bandwidth in imaging, the high gain provides conditions for realizing extremely high sensitivity of photon order, and the large spatial frequency bandwidth ensures micron-level spatial resolution.In addition, vortex pump light realizes vortex phase contrast imaging, further improving image contrast.

Description

Technical Field

[0001] This invention relates to the fields of mid-infrared light source generation technology, nonlinear optical frequency conversion technology, and optical imaging technology. Its core is to provide a mid-infrared real-time imaging system with high sensitivity, high spatial resolution, and high contrast. Background Technology

[0002] Mid-infrared imaging has attracted widespread attention in many fields, such as biomedical imaging and diagnosis, and materials property analysis, due to its unique spectral characteristics. However, constrained by the lagging development of mid-infrared materials, the performance of mid-infrared components and detectors is far inferior to that of related devices in the visible-near-infrared band, which leads to significant challenges in their application across various fields. For example, compared with the visible-near-infrared band, mid-infrared optical components typically have greater absorption, narrower bandwidth, and greater aberrations, while mid-infrared detectors have higher readout noise, lower spatial resolution, lower quantum efficiency, and slower response speed.

[0003] In recent years, the performance of mid-infrared imaging, including spatial resolution, signal-to-noise ratio, and image contrast, has been significantly improved. Photoacoustic or photothermal principles have overcome the diffraction limit, raising spatial resolution to the sub-micron level while maintaining good image contrast. However, these methods cannot achieve real-time imaging and are difficult to implement in low-illumination or high-sensitivity conditions.

[0004] Although other methods based on two-photon absorption or nonlinear frequency conversion can also acquire mid-infrared images with photon number resolution by converting mid-infrared information into the visible / near-infrared region, their spatial resolution can only reach the order of 10 micrometers or even 100 micrometers.

[0005] Therefore, it is evident that there is currently no mid-infrared real-time imaging system in the world that simultaneously possesses high sensitivity, high spatial resolution, and high contrast. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to balance the high sensitivity, high spatial resolution, and high contrast of a mid-infrared real-time imaging system.

[0007] To address the aforementioned technical problems, this invention provides a mid-infrared real-time imaging system, comprising:

[0008] Visible-near-infrared light source, used to provide fundamental frequency light in the visible-near-infrared band;

[0009] A frequency multiplier is used to multiply a portion of the fundamental frequency light in the visible-near-infrared band to obtain frequency-doubled light;

[0010] The first beam splitting component is used to split the frequency-doubled light and the remaining un-frequency-doubled fundamental light.

[0011] A mid-infrared illumination light generating component is used to convert the remaining unmultiplied fundamental frequency light separated by the first beam splitting component into mid-infrared illumination light, which is used to illuminate a target object to obtain mid-infrared signal light carrying information about the target object.

[0012] The first optical delay line is used to adjust the optical delay of the frequency-doubled light split by the first beam splitter.

[0013] A vortex beam generator is used to generate femtosecond vortex pulses based on frequency-doubled light with adjusted optical delay, wherein the femtosecond vortex pulses are time-synchronized with the mid-infrared signal light.

[0014] The first imaging component is used to microscopically magnify the mid-infrared signal carrying the target object information;

[0015] The second imaging component is used to image the magnified mid-infrared signal light.

[0016] The first optical parametric amplifier is placed on the Fourier spectrum plane of the second imaging component and uses the femtosecond vortex pulse as pump light to convert the microscopically magnified mid-infrared signal light into visible idler light, so that the second imaging component can image the mid-infrared signal light in the form of visible idler light.

[0017] A CCD camera is used to detect and record the image formed by the second imaging component.

[0018] Compared with existing technologies, this invention utilizes a mid-infrared illumination light generation component that converts a visible-near-infrared light source into a mid-infrared band to provide mid-infrared illumination light. A first optical parametric amplifier employs a powerful femtosecond vortex pulse laser as pump light, converting the mid-infrared signal light carrying object information into visible light with high gain for detection and recording. The powerful femtosecond vortex pulse laser provides high optical gain and a large spatial frequency bandwidth in imaging. The high gain means the mid-infrared signal light can be very weak, enabling extremely high sensitivity at the photon level without damaging the object. The large spatial frequency bandwidth ensures micrometer-level spatial resolution. Furthermore, the vortex pump light achieves vortex phase-contrast imaging, enhancing object edges and further improving image contrast. Therefore, this invention achieves real-time mid-infrared imaging with extremely high sensitivity, high spatial resolution, and high contrast simultaneously. Attached Figure Description

[0019] Figure 1 This is an optical structure diagram of the mid-infrared real-time imaging system provided in the first embodiment of the present invention;

[0020] Figure 2This is an optical structure diagram of the mid-infrared real-time imaging system provided in the second embodiment of the present invention;

[0021] Figure 3 This is an optical structure diagram of the mid-infrared illumination light generating component in the first and second embodiments of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Reference Figure 1 The mid-infrared real-time imaging system provided in the first embodiment of the present invention includes a visible-near-infrared light source 11, a frequency multiplier 12, a first beam splitter 13, a mid-infrared illumination light generating component 14, a first imaging component 15, a first optical delay line 16, a vortex beam generator 17, a first optical parametric amplifier (OPA) 18, a second imaging component 19, and a CCD camera 10.

[0024] In addition, reflectors M can be placed between the aforementioned components as needed to change the direction of beam propagation. This allows for a more compact and smaller imaging system, facilitating the design of desired shapes. For example, Figure 1 A reflector M is placed between the first beam splitter 13 and the mid-infrared illumination light generating component 14, between the mid-infrared illumination light generating component 14 and the target object, between the first beam splitter 13 and the first optical delay line 16, and between the first optical delay line 16 and the vortex beam generator 17. The position and number of reflectors M can be flexibly set according to actual needs.

[0025] Among them, the visible-near-infrared light source 11 is used to provide fundamental frequency light in the visible-near-infrared band. The fundamental frequency light is linearly polarized light. As one embodiment, a Ti:sapphire femtosecond laser can be selected.

[0026] Frequency multiplier 12 is used to multiply a portion of the fundamental frequency light in the visible-near infrared band 11 to obtain frequency-doubled light. Specifically, frequency multiplier 12 can be a β-BBO (barium metaborate) crystal in type-I phase-matched mode.

[0027] The first beam splitting component 13 is used to split the frequency-doubled light and the remaining un-frequency-doubled fundamental light. Specifically, a dichroic mirror can be used, which has the function of splitting two different frequencies of light.

[0028] The mid-infrared illumination light generating component 14 is used to convert the remaining undivided fundamental frequency light separated by the first beam splitter 13 into mid-infrared illumination light. This illumination light is used to illuminate a target object to obtain mid-infrared signal light carrying information about the target object. As an embodiment, this mid-infrared illumination light generating component 14 can be specifically implemented using an optical parametric amplifier.

[0029] The first imaging component 15 is used to magnify the mid-infrared signal carrying the target object information using light microscopy.

[0030] The first optical delay line 16 is used to adjust the optical delay of the frequency-doubled light split by the first beam splitter 13.

[0031] The vortex beam generator 17 is used to generate femtosecond vortex pulses based on the frequency-doubled light after adjusting the optical delay. The femtosecond vortex pulses can be used as pump light. Since the pulse time is short, it is easy to be out of sync with the mid-infrared signal light. After the optical delay of the first optical delay line 16, the femtosecond vortex pulses and the mid-infrared signal light can be synchronized in time.

[0032] The second imaging component 19 is used to image the magnified mid-infrared signal light into the CCD camera 10.

[0033] The first optical parametric amplifier 18 is placed on the Fourier spectral plane of the second imaging component 19, and uses the femtosecond vortex pulse as pump light to convert the microscopically magnified mid-infrared signal light into visible idler light, so that the second imaging component 19 can image the mid-infrared signal light in the form of visible idler light, which is convenient for the detection and recording of the CCD camera 10. Specifically, the first optical parametric amplifier 18 can be implemented using a β-BBO crystal in type-I phase-matched mode.

[0034] CCD camera 10 is used to detect and record the aforementioned visible idler light.

[0035] As a specific implementation method, such as Figure 2 As shown, the first beam-splitting component 13 is a first dichroic mirror, used to reflect the frequency-doubled light and transmit the remaining undoubled fundamental frequency light. The first imaging component 15 may further include a microscope objective 151 and a first lens 152 arranged sequentially along the optical path, with the image plane of the first imaging component 15 located at one focal length of the first lens 152. The first optical retardation line 16 may be a mirror with two orthogonal reflecting surfaces. The second imaging component 19 includes a second lens 191 and a third lens 192 arranged sequentially along the optical path, with the first optical parametric amplifier 18 placed between the second lens 191 and the third lens 192, specifically at one focal length of the second lens 191, which serves as the Fourier spectral plane of the second imaging component 19.

[0036] In addition, a first variable attenuator (VOA) can be set between the mid-infrared illumination light generating component 14 and the target object to attenuate the illumination light generated by the mid-infrared illumination light generating component by a preset amplitude.

[0037] The mid-infrared real-time imaging system may further include a second dichroic mirror 110, which is placed between the second lens and the first optical parametric amplifier 18 to allow the mid-infrared signal light to pass through to the first optical parametric amplifier 18 and reflect the femtosecond vortex pulse to the first optical parametric amplifier 18.

[0038] The first optical parametric amplifier 18 can convert mid-infrared signal light carrying object information into visible light that is easy to detect and record through infrared optical parametric imaging with high gain. This conversion process can be described by the nonlinear optical three-wave coupling equation as follows:

[0039]

[0040] In the formula, the subscripts M, P, and V represent the mid-infrared illumination light, pump light, and wavelength-converted visible light, respectively; E represents the complex amplitude of the light field; E' represents the complex amplitude of the conjugate light field; and ρ and Let ω represent the radius and azimuth angle in the Fourier spectral plane polar coordinates, respectively; let i represent the imaginary unit; let n and c represent the refractive index and the speed of light in vacuum, respectively; and let d represent the light frequency. eff is the effective nonlinear coefficient, z is the transmission distance, and β and Δk are the non-collinearity angle and phase mismatch, respectively. Considering the use of Fourier spectral plane optical parametric magnification imaging and the addition of vortex pumping, the wavelength-converted visible light output can be obtained as follows:

[0041]

[0042] E above M0 It is the initial mid-infrared illumination field of the optical parametric amplification, E Pn This is the normalized pump light intensity, where r and φ represent the radius and azimuth angle in polar coordinates of the object plane, respectively. These are the convolution and Fourier transform operators, respectively, and G is the optical gain. This shows that the imaging system will output a high-gain visible light signal.

[0043] Combination Figure 1 , Figure 2To illustrate the working principle of a mid-infrared real-time imaging system, let's take a Ti:sapphire femtosecond laser generating a linearly polarized femtosecond pulse laser with a center wavelength of 800nm, a pulse width of 35fs, and an energy of 3.5mJ as an example: First, the laser passes through an optical frequency doubler 12. This frequency doubler 12 uses a type-I phase-matched β-BBO crystal with a cutting angle of 29.2° and a thickness of 0.2mm. After frequency doubling, a 400nm frequency-doubled femtosecond laser of approximately 1mJ is obtained. This frequency-doubled femtosecond laser and the remaining approximately 2.5mJ of unfrequency-doubled 800nm ​​fundamental frequency light are spatially separated by a first dichroic mirror 13. The laser then passes through a first optical delay line 16 and a vortex phase plate 17 to generate vortex pulses, and then passes through a second dichroic mirror 110 and is incident on a first optical parametric amplifier 18 as pump light. The signal light of the first optical parametric amplifier 18 is a 2-3 μm mid-infrared illumination light generated from the fundamental frequency light remaining after the frequency multiplier 12. This mid-infrared illumination light is irradiated onto the target object placed on the object plane after passing through the first optical attenuator VOA to carry the object information. Then, it is magnified by a microscope objective 151 and a first lens 152, and projected into the first optical parametric amplifier 18 placed on the Fourier spectrum plane through a second lens 191. The first optical parametric amplifier 18 uses a β-BBO crystal with a type-I phase-matched mode and a cut angle of 23.8°. By adjusting the angle between the mid-infrared signal light and the femtosecond vortex pump light, the time delay, and the matching angle of the crystal, optical parametric amplification is achieved. The visible idler light of approximately 460-500 nm can then be output through the third lens 192, and the target object information can be acquired by a high-performance visible light band CCD camera 10.

[0044] Figure 3 The structure of the mid-infrared illumination light generating assembly 14 is shown, including an optical wedge 141, a fourth lens 142, a Kerr medium 143, a collimating lens 144, a second optical delay line 145, a third dichroic mirror 146, and a second optical parametric amplifier 147.

[0045] Among them, the optical wedge 141 is used to further divide the remaining undoped fundamental frequency light into reflected light and transmitted light.

[0046] The fourth lens 142 is used to focus the reflected light onto the Kerr medium 143 to excite the Kerr medium 143. The Kerr medium 143 is placed at the focusing position of the fourth lens 143 and is used to excite a near-infrared supercontinuum by the reflected light. The collimating lens 144 is used to collimate the excited near-infrared supercontinuum.

[0047] In the optical path of the transmitted light, the second optical delay line 145 is used to optically delay the transmitted light split off by the optical wedge 141. The second optical delay line 145 can also be a mirror with two orthogonal reflecting surfaces.

[0048] The third dichroic mirror 146 is used to allow the collimated near-infrared supercontinuum to pass through to the second optical parametric amplifier 147, and to reflect the optically delayed transmitted light back to the second optical parametric amplifier 147.

[0049] The second optical parametric amplifier 147 is used to convert the near-infrared supercontinuum spectrum transmitted through the third dichroic mirror 146 as signal light and the optically delayed transmitted light reflected by the third dichroic mirror 146 as pump light into mid-infrared idler light for use as the illumination light.

[0050] In addition, a second variable attenuator 148 can be set in the optical path of the reflected light to attenuate the power of the reflected light split off by the optical wedge 141 by a preset amplitude.

[0051] Similarly, some reflectors M can be placed between the above-mentioned devices as needed to change the propagation direction of the light beam, for example, Figure 3 A reflector M is set between the second variable attenuator 148 and the fourth lens 142, and multiple reflectors M are set between the second optical delay line 145 and the third dichroic mirror 146, which can be flexibly set according to actual needs.

[0052] Taking the generation of a linearly polarized femtosecond pulse laser with a center wavelength of 800 nm, a pulse width of 35 fs, and an energy of 3.5 mJ by a Ti:sapphire femtosecond laser as an example, the unfrequency-doubled 800 nm femtosecond pulse laser split from the first beam splitter 13 first passes through the optical wedge 141, where 1% of its energy is reflected, and the remainder is transmitted. This reflected light passes through the second variable attenuator 148 and is then focused onto the Kerr medium 143 by the fourth lens 142, exciting a near-infrared supercontinuum with a wavelength of approximately 1 μm to 1.5 μm. Then, after passing through the collimating lens 144 and the third dichroic mirror 146, it is incident as signal light along with the pump light onto the second optical parametric amplifier 147. The pump light is the transmitted light after passing through the optical wedge 141. This transmitted beam is reflected by the third dichroic mirror 146 through the second optical delay line 145 to the second optical parametric amplifier 147. The second optical delay line 145 is used to adjust the time synchronization between the signal light and the pump light. The second optical parametric amplifier 147 uses a β-BBO crystal with a type-I phase-matched mode and a cut angle of 21.5°. After optical parametric amplification, it can output mid-infrared idler light of 2μm to 3μm for the mid-infrared illumination light required by the system.

[0053] In summary, the mid-infrared illumination light generating component 14 converts the visible-near-infrared light source into the mid-infrared band, providing a mid-infrared illumination source. The first optical parametric amplifier 18 uses a strong femtosecond vortex pulse laser as the pump light, converting the mid-infrared signal light carrying object information into visible light with high gain for detection and recording. Therefore, a high-performance visible light CCD camera can be used as the detector, effectively avoiding the limitations caused by low quantum efficiency, high noise, and large pixel size of mid-infrared detectors. Simultaneously, the strong femtosecond vortex pulse laser as the pump light provides high optical gain and a large spatial frequency bandwidth in imaging. The high gain provides the conditions for achieving extremely high sensitivity at the photon level, and the large spatial frequency bandwidth ensures micrometer-level spatial resolution. Furthermore, the vortex pump light enables vortex phase-contrast imaging, further improving image contrast. Therefore, this invention achieves real-time mid-infrared imaging with extremely high sensitivity, high spatial resolution, and high contrast simultaneously.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A mid-infrared real-time imaging system, characterized in that, include: Visible-near-infrared light source, used to provide fundamental frequency light in the visible-near-infrared band; A frequency multiplier is used to multiply a portion of the fundamental frequency light in the visible-near-infrared band to obtain frequency-doubled light; The first beam splitting component is used to split the frequency-doubled light and the remaining un-frequency-doubled fundamental light. A mid-infrared illumination light generating component is used to convert the remaining unmultiplied fundamental frequency light separated by the first beam splitting component into mid-infrared illumination light, which is used to illuminate a target object to obtain mid-infrared signal light carrying information about the target object. The first optical delay line is used to adjust the optical delay of the frequency-doubled light split by the first beam splitter. A vortex beam generator is used to generate femtosecond vortex pulses based on frequency-doubled light with adjusted optical delay, wherein the femtosecond vortex pulses are time-synchronized with the mid-infrared signal light. The first imaging component is used to microscopically magnify the mid-infrared signal carrying the target object information; The second imaging component is used to image the magnified mid-infrared signal light. The first optical parametric amplifier is placed on the Fourier spectrum plane of the second imaging component and uses the femtosecond vortex pulse as pump light to convert the microscopically magnified mid-infrared signal light into visible idler light, so that the second imaging component can image the mid-infrared signal light in the form of visible idler light. A CCD camera is used to detect and record the image formed by the second imaging component.

2. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The fundamental frequency light is linearly polarized light.

3. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The first beam splitter is a first dichroic mirror, used to reflect the frequency-doubled light and transmit the remaining undoubled fundamental frequency light.

4. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The first imaging component includes a microscope objective and a first lens arranged sequentially along the optical path.

5. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The second imaging component includes a second lens and a third lens arranged sequentially along the optical path direction; The first optical parametric amplifier is placed between the second lens and the third lens.

6. The mid-infrared real-time imaging system as described in claim 5, characterized in that, The mid-infrared real-time imaging system also includes: A second dichroic mirror is placed between the second lens and the first optical parametric amplifier to allow the mid-infrared signal light to pass through to the first optical parametric amplifier and to reflect the femtosecond vortex pulse to the first optical parametric amplifier.

7. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The mid-infrared real-time imaging system also includes: A first variable attenuator is placed between the mid-infrared illumination light generating component and the target object to attenuate the illumination light generated by the mid-infrared illumination light generating component by a preset amplitude.

8. The mid-infrared real-time imaging system as described in claim 1, characterized in that, The mid-infrared illumination light generating component includes: An optical wedge is used to further divide the remaining undoped fundamental frequency light into reflected light and transmitted light; The fourth lens is used to focus the reflected light; A Kerr medium, placed at the focusing position of the fourth lens, is used to excite a near-infrared supercontinuum by reflected light; Collimating lenses are used to collimate the excited near-infrared supercontinuum. The second optical delay line is used to optically delay the transmitted light split from the optical wedge, so as to adjust the time synchronization between the transmitted light and the reflected light split from the optical wedge. The third dichroic mirror is used to allow the collimated near-infrared supercontinuum to pass through and to reflect optically delayed transmitted light. The second optical parametric amplifier is used to convert the near-infrared supercontinuum spectrum transmitted through the third dichroic mirror into mid-infrared idler light, using the signal light as the signal light and the transmitted light reflected by the third dichroic mirror as the pump light, so as to use it as the illumination light.

9. The mid-infrared real-time imaging system as described in claim 8, characterized in that, The mid-infrared illumination light generating component further includes: The second variable attenuator is placed in the optical path of the reflected light and is used to attenuate the power of the reflected light split from the optical wedge by a preset amplitude.

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