A second harmonic system device based on the generation of a vector structured light field

Abstract

The present invention discloses a second harmonic system device based on the generation of a vectorial structured light field, which includes a laser, a beam expanding and collimating component, a 4f system component, a second harmonic crystal component, a dichroic mirror, and a CCD camera. After the collimated beam passes through the 4f system, a first light field can be obtained. After passing through the second harmonic crystal component and the dichroic mirror, a second light field (second harmonic) with a halved wavelength and doubled frequency of the light field can be obtained. Moreover, the second light field can simultaneously convert the radial and angular modes in the second light field by regulating the first light field. These results provide a new platform for more flexible utilization of structured light fields to perform vector manipulation on the interaction between non-linear light and matter, and have potential application prospects in corresponding fields such as ultraviolet microfabrication, optical manipulation, and quantum optics. This device has the characteristics of flexible regulation, convenient installation, low price, and wide application range.

Description

Technical Field

[0001] The present invention relates to the technical fields of optical light field regulation and nonlinear optics, and particularly relates to a second harmonic system device based on the generation of a vector structured light field. Background Art

[0002] The development of lasers has received increasing attention nowadays. In recent years, vector light fields with spatially inhomogeneous polarization states have been widely studied due to their unique spatial polarization distributions, and many novel physical phenomena are bound to occur during their vector regulation. The interaction between light with spatially varying structured beams and matter has sparked intense discussions in the field of nonlinear optics, opening up new applications. Due to their customizable spatial distributions of polarization states, phases, and amplitudes, they simultaneously reveal some novel features and applications of structured light fields in emerging fields such as particle micro-manipulation, free-space polarization conversion, biomedicine, super-resolution imaging, optical information transmission, second (or higher-order) harmonic generation, and nonlinear frequency conversion. Therefore, structured light fields involving the interaction between light and matter can provide additional degrees of freedom to manipulate nonlinear optical processes. On the other hand, nonlinear optical processes can perform multi-dimensional and flexible manipulation of structured light fields in both space and frequency domains.

[0003] In second-order nonlinear optical effects, researchers focus on studying novel physical phenomena brought about by various light fields, such as sum-frequency generation, difference-frequency generation, and second-harmonic generation. In recent years, the second-harmonic effect of light fields has received extensive favor from scientific researchers. However, so far, the complete vector experimental characterization of second harmonics, especially the simultaneous operation of radial and azimuthal mode conversions and spatially varying polarization state structures, remains a fundamental challenge. Summary of the Invention

[0004] To overcome the defects in the above-mentioned prior art, the present invention provides a second harmonic system device based on the generation of a vector structured light field, which simultaneously realizes the radial and azimuthal mode transitions of second harmonics by using a structured light field with radially and azimuthally variable polarization states.

[0005] Technical Solution

[0006] A second harmonic system device based on the generation of a vector structured light field includes a laser, and a beam expanding and collimating component, a 4f system component, a second harmonic crystal component, a dichroic mirror, and a CCD camera are sequentially arranged on the right side of the laser.

[0007] Further, the first light field generated by combining the laser, the beam expanding and collimating component, and the 4f system component is expressed as:

[0008]

[0009] Where m and n are the azimuthal and radial polarization topological charges respectively, φ is the azimuthal angle, φ 0 represents the additional phase, r a is the beam waist radius, e x and e y are the unit vectors in the x and y directions respectively, Δθ represents the phase difference between the e x and e y two components. Δθ is determined by the wave plate in the 4f system component. When the wave plate is a quarter-wave plate, a first light field with a local linearly polarized distribution can be obtained; when the wave plate is a half-wave plate, a first light field with a hybrid polarization distribution can be obtained.

[0010] Furthermore, different components of the first light field need to satisfy phase matching with the crystal in the second harmonic crystal component.

[0011] Furthermore, the crystal in the second harmonic crystal component is a type-II BBO crystal, and its polarization property is that e light + o light generates e light.

[0012] Furthermore, the non-linear expression of the polarization intensity of the second light field generated after the first light field passes through the second harmonic crystal component can be described as where d 22 is the non-linear coefficient in the second term of the non-linear polarization intensity.

[0013] Furthermore, after passing through the dichroic mirror, the first light field with a wavelength of 800 nm can be filtered out, and only the second light field can be obtained.

[0014] Furthermore, compared with the first light field, the wavelength of the beam of the second light field becomes half, and the corresponding optical frequency doubles.

[0015] Furthermore, it is relatively easy to obtain a light field in the invisible band, and a structured light field in the non-additive light band with a specific light field distribution can be obtained through an easily adjustable visible light field.

[0016] Furthermore, by controlling the first light field, simultaneous conversion of the radial and azimuthal modes in the second light field can be achieved.

[0017] Advantageous Effects

[0018] Compared with the prior art, the present invention has the following advantageous effects:

[0019] The second harmonic of the vector optical field that can achieve a hybrid polarization distribution can simultaneously adjust its topological charges in the azimuthal and radial directions and control its polarization state, providing a new platform for the vector manipulation of the interaction between non-linear light matter and structured optical fields. It has potential application prospects in related fields such as ultraviolet microprocessing, optical manipulation, and quantum optics, providing a simple, flexible, and convenient tool for further application research on the second harmonic of vector optical fields in the future. This device has high flexibility and is suitable for applications with personalized requirements for polarization states in second harmonics. It can easily, simply, and quickly obtain the target optical field, and is easy to install and inexpensive. Brief Description of the Drawings

[0020] Figure 1 FIG. is a schematic structural diagram of a second harmonic system device based on a vector structured optical field according to the present invention;

[0021] Figure 2 FIG. is the light intensity distribution of the first optical field (FIG. a) and the second optical field (FIG. b) corresponding to separately regulating a topological charge parameter n;

[0022] Figure 3 FIG. is the light intensity distribution of the first optical field (FIG. a) and the second optical field (FIG. b) corresponding to simultaneously regulating two topological charge parameters m and n.

[0023] Reference Signs

[0024] Laser A, beam expander and collimator assembly B, 4f system assembly C, second harmonic crystal assembly D, dichroic mirror E, and CCD camera F. Detailed Description of the Invention

[0025] To better illustrate and explain the content of the present invention, the following is described in conjunction with the drawings and implementation examples:

[0026] As Figures 1 - 3 shown, the present invention discloses a second harmonic system device based on a vector structured optical field, including a laser A, and a beam expander and collimator assembly B, a 4f system assembly C, a second harmonic crystal assembly D, a dichroic mirror E, and a CCD camera F are sequentially arranged on the right side of the laser A.

[0027] Furthermore, the first optical field generated by combining the laser A, the beam expander and collimator assembly B, and the 4f system assembly C is expressed as:

[0028]

[0029] where m and n are the angular and radial polarization topological charges respectively, φ is the azimuth angle, φ 0 represents the additional phase, r a is the beam waist radius, e x and ey are unit vectors in the x - direction and y - direction respectively, and Δθ represents the x phase difference between the two components of e y and e

[0030] Furthermore, different components of the first optical field need to satisfy phase matching with the crystal in the second - harmonic crystal component D.

[0031] Furthermore, the crystal in the second - harmonic crystal component D is a type - II BBO crystal, and its polarization property is that e - light + o - light generates e - light. For example, the incident fundamental - wave signal light and idler light are two linearly polarized lights (extraordinary light and ordinary light), and the generated second - harmonic is a linearly polarized light in one state (extraordinary light).

[0032] Furthermore, the non - linear expression of the polarization intensity of the second optical field generated after the first optical field passes through the second - harmonic crystal component D can be described as where d 22 is the non - linear coefficient in the second term of the non - linear polarization intensity.

[0033] Furthermore, after passing through the dichroic mirror E, the first optical field with a wavelength of 800 nm can be filtered out, and only the second optical field is obtained.

[0034] Furthermore, compared with the first optical field, the wavelength of the beam of the second optical field becomes half, and the corresponding optical frequency doubles.

[0035] Furthermore, it is relatively easy to obtain an optical field in the invisible band, and a structured optical field in the non - additive optical band with a specific optical field distribution is obtained through an easily adjustable visible - light optical field.

[0036] Furthermore, by controlling the first optical field, simultaneous conversion of the radial and angular modes in the second optical field can be achieved.

[0037] Specifically, the light source is a non - linear laser source with a wavelength of 800 nm. After passing through a second - harmonic system device based on the generation of a vectorial structured optical field, the radial and helical topological charge parameters can be simultaneously controlled to obtain the corresponding second - harmonic second optical field, thereby obtaining a frequency - doubled optical field with a wavelength halved and a frequency doubled;

[0038] Figure 2 The light - intensity distribution of the first optical field after passing through different polarizers and the distribution of the second optical field (second - harmonic) are given, and it is explained that by separately controlling the radial topological charge number n in the first optical field, the corresponding second - harmonic second optical field can be easily obtained;

[0039] Figure 3 The light intensity distribution of the first optical field after passing through different polarizers and the distribution of the second optical field (second harmonic) are given, and it is expounded that the radial topological charge number n and the helical topological charge number m in the first optical field can be simultaneously regulated to obtain the second optical field (second harmonic) with a corresponding polarization state distribution of mixed polarization.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the technical solutions of the present invention have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A second harmonic generation system device based on the generation of a vector structured light field, characterized in that: it includes a laser (A), and a beam expanding and collimating component (B), a 4f system component (C), a second harmonic crystal component (D), a dichroic mirror (E) and a CCD camera (F) are sequentially arranged on the right side of the laser (A); the first light field generated by combining the laser (A), the beam expanding and collimating component (B) and the 4f system component (C) is expressed as: Among them m and n are the azimuthal and radial polarization topological charges respectively is the azimuth angle represents the additional phase, r a is the beam waist radius and are the unit vectors in the x - direction and y - direction respectively, Δθ represents and the phase difference between the two components. Δθ is determined by the wave plate in the 4f system component (C). When the wave plate is a quarter - wave plate, the first light field with a local linear polarization distribution can be obtained; when the wave plate is a half - wave plate, the first light field with a hybrid polarization distribution can be obtained different components of the first light field need to satisfy phase matching with the crystal in the second harmonic crystal component (D); the crystal in the second harmonic crystal component (D) is a type-II BBO crystal, and its polarization property is that e-light + o-light generate e-light; The non - linear expression of the polarization intensity of the second optical field (second - harmonic wave) generated after the first optical field passes through the second - harmonic crystal assembly (D) can be described as where d 22 is the non - linear coefficient in the second term of the non - linear polarization intensity; after passing through the dichroic mirror (E), the first light field with a wavelength of 800 nm can be filtered out, and only the second light field can be obtained.

2. The second harmonic generation system device based on the generation of a vector structured light field according to claim 1, characterized in that: compared with the first light field, the wavelength of the light beam of the second light field becomes half, and the corresponding optical frequency doubles.

3. The second harmonic generation system device based on the generation of a vector structured light field according to claim 2, characterized in that: it is relatively easy to obtain a light field in the invisible band, and a structured light field in the invisible light band with a specific light field distribution is obtained through an easily adjustable visible light field.

4. The second harmonic generation system device based on the generation of a vector structured light field according to claim 3, characterized in that: by regulating the first light field, simultaneous conversion of the radial and angular modes in the second light field can be achieved.

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