A second harmonic rotation angle adjustable system based on vector structured light field generation

Abstract

The present invention discloses a second harmonic rotation angle adjustable system based on vector structured light field generation, comprising a laser, a beam expansion and collimation component, a 4f system component, a second harmonic crystal component, a dichroic mirror, and a CCD camera. After the collimated light beam passes through the 4f system, a first light field is obtained. After passing through the second harmonic crystal component and the dichroic mirror, a second harmonic with a wavelength halved and a frequency doubled is obtained, namely the second light field. The angle of the second harmonic light field can be arbitrarily controlled by regulating the rotation angle of the dichroic mirror along the xy plane. These results provide a new platform for more flexible use of structured light fields to perform vector manipulation of nonlinear light-matter interactions. The system has potential application prospects in corresponding fields such as ultraviolet micromachining, optical manipulation, and quantum optics. The device has the characteristics of flexible control, easy installation, low price, and a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the field of optical light field control and nonlinear optical technology, and in particular to a second harmonic rotation angle adjustable system based on vector structure light field generation. Background Art

[0002] Laser development is gaining increasing attention. In recent years, vector light fields with spatially inhomogeneous polarization states have been extensively studied due to their unique spatial polarization distribution. Manipulating their vectors inevitably yields numerous novel physical phenomena. The interaction of light and matter with spatially varying structured beams has sparked heated discussions in the field of nonlinear optics, opening up new applications. Due to their customizable spatial distribution of polarization state, phase, and amplitude, structured light fields have revealed novel features and applications in the emerging fields of particle micromanipulation, free-space polarization conversion, biomedicine, super-resolution imaging, optical information transmission, second (or higher) harmonic generation, and nonlinear frequency conversion. Therefore, structured light fields involving light-matter interactions can provide additional degrees of freedom to manipulate nonlinear optical processes. Furthermore, nonlinear optical processes enable multidimensional and flexible manipulation of structured light fields in both the spatial and frequency domains.

[0003] In the field of second-order nonlinear optical effects, researchers focus on studying the novel physical phenomena of sum frequency, difference frequency, and frequency doubling brought about by various light fields. In recent years, the second harmonic effect of light fields has been widely favored by scientific researchers. However, to date, the complete vectorial experimental characterization of second harmonics, especially the simultaneous operation of radial and azimuthal mode transitions and spatially varying polarization state structures, remains a fundamental challenge. However, the use of radially and azimuthal variable polarization states to simultaneously achieve radial and azimuthal mode transitions of second harmonics and simultaneously control the rotation angle of the second harmonics plays a crucial role in the full-field selection rules of specific nonlinear processes and quantum information processing. Summary of the Invention

[0004] In order to overcome the above-mentioned defects in the prior art, the present invention provides a second harmonic rotation angle adjustable system based on vector structured light field generation, which utilizes a polarization structured light field with variable radial and azimuth polarization to flexibly control the rotation angle of the second harmonic on the basis of achieving radial and azimuth mode transitions.

[0005] Technical Solution

[0006] A second harmonic rotation angle adjustable system based on vector structured light field generation includes a laser, a beam expansion and collimation component, a 4f system component, a second harmonic crystal component, a dichroic mirror and a CCD camera.

[0007] Furthermore, the first light field generated by the combination of the laser, the beam expansion and collimation component, and the 4f system component is expressed as:

[0008]

[0009] in m,n are the azimuthal and radial polarization topological charges, φ is the azimuth angle, φ0 represents the additional phase, r a is the waist radius, e x and e y are the unit vectors in the x and y directions respectively, and Δθ represents e x and e y The phase difference Δθ between the two components 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 localized linear polarization 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 must all satisfy the phase matching with the crystal in the second harmonic crystal assembly.

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

[0012] Furthermore, the BBO crystal is mounted on an angle adjustment bracket, and the angle of the BBO crystal can be flexibly adjusted.

[0013] Furthermore, if the BBO crystal is rotated by an angle of φ in the xy plane, the nonlinear expression of the polarization intensity of the second light field after the first light field passes through the second harmonic crystal assembly can be described as

[0014]

[0015] Wherein Δθ=0 indicates the use of a quarter wave plate, and Δθ=π / 2 indicates the use of a half wave plate.

[0016] Furthermore, the radial and helical modulation components of the first light field decrease with increasing rotation angle φ in the interval [kπ / 4, (k+1)π / 4], where k is an integer. Specifically, when the rotation angle φ = kπ / 4, the first light field degenerates into a uniform plane wave.

[0017] The formula is as follows

[0018] Where, They represent the unit basis vectors of right-handed circular polarization and left-handed circular polarization respectively; They represent the unit basis vectors in the π / 4 and -π / 4 directions respectively.

[0019] Furthermore, the first light field with a wavelength of 800 nm can be filtered out by the dichroic mirror, and only the second light field is obtained.

[0020] Furthermore, compared with the first light field, the wavelength of the light beam of the second light field is halved, and the corresponding light frequency is doubled.

[0021] Furthermore, it is relatively easy to obtain a light field in an invisible band, and a structured light field in a non-additive band with a specific light field distribution can be obtained through an easily adjustable visible light field.

[0022] Furthermore, by regulating the first light field, the radial and angular modes in the second harmonic light field can be converted simultaneously.

[0023] Furthermore, by regulating the rotation angle of the dichroic mirror in the xy plane, not only the angle of the first light field can be regulated, but more importantly, the angle of the second harmonic light field can be arbitrarily regulated.

[0024] Beneficial effects

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] It can realize the second harmonic of the vector light field with hybrid polarization distribution, adjust its topological charge in the azimuthal and radial directions, and regulate its polarization state while realizing the regulation of its angular rotation. It provides a new platform for the vector manipulation of the interaction between nonlinear light matter and structured light field, and has potential application prospects in related fields such as ultraviolet microprocessing, optical manipulation and quantum optics. It provides a simple, flexible and convenient tool for further research on the second harmonic application of vector light field. This device has high flexibility and is suitable for applications with personalized requirements for polarization state in the second harmonic. It can easily, simply and quickly obtain the target light field, and is easy to install and inexpensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of a system for adjusting the second harmonic rotation angle based on vector structured light field generation according to the present invention;

[0028] Figure 2 When m=1, n=1 and the BBO crystal is rotated at different angles, the corresponding intensity distribution of the first light field (Figure a) and the second light field (Figure b) of the local linear deflection;

[0029] Figure 3 When m=2, n=0, and the BBO crystal is rotated at different angles, the corresponding light intensity distribution of the first light field (Figure a) and the second light field (Figure b) of the hybrid vector.

[0030] Reference numerals

[0031] Laser A, beam expansion and collimation assembly B, 4f system assembly C, second harmonic crystal assembly D, dichroic mirror E, and CCD camera F. DETAILED DESCRIPTION

[0032] To better illustrate the present invention, the following is a detailed description with reference to the accompanying drawings and implementation examples:

[0033] like Figure 1-3 As shown, a second harmonic rotation angle adjustable system based on vector structured light field generation includes a laser A, a beam expansion and collimation component B, a 4f system component C, a second harmonic crystal component D, a dichroic mirror E and a CCD camera F.

[0034] Furthermore, the first light field generated by the combination of the laser A, the beam expansion and collimation component B, and the 4f system component C is expressed as:

[0035]

[0036] in m,n are the azimuthal and radial polarization topological charges, φ is the azimuth angle, φ0 represents the additional phase, r a is the waist radius, e x and e y are the unit vectors in the x and y directions respectively, and Δθ represents e x and e y The phase difference Δθ between the two components is determined by the wave plate in the 4f system component C. When the wave plate is a quarter wave plate, a first light field with a localized linear polarization 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.

[0037] Furthermore, different components of the first light field must all satisfy the phase matching with the crystal in the second harmonic crystal assembly D.

[0038] Furthermore, the crystal in the second harmonic crystal assembly 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 signal light and idle light are two types of linearly polarized light (extraordinary light and ordinary light), and the generated second harmonic is a linearly polarized light in one state (extraordinary light).

[0039] Furthermore, the BBO crystal is mounted on an angle adjustment bracket, and the angle of the BBO crystal can be flexibly adjusted.

[0040] Furthermore, if the BBO crystal is rotated by an angle of φ in the xy plane, the nonlinear expression of the polarization intensity of the second light field after the first light field passes through the second harmonic crystal component D can be described as

[0041]

[0042] Wherein Δθ=0 indicates the use of a quarter wave plate, and Δθ=π / 2 indicates the use of a half wave plate.

[0043] Furthermore, the radial and helical modulation components of the first light field decrease with increasing rotation angle φ in the interval [kπ / 4, (k+1)π / 4], where k is an integer. Specifically, when the rotation angle φ = kπ / 4, the first light field degenerates into a uniform plane wave.

[0044] The formula is as follows

[0045] Where, They represent the unit basis vectors of right-handed circular polarization and left-handed circular polarization respectively; They represent the unit basis vectors in the π / 4 and -π / 4 directions respectively.

[0046] Furthermore, the first light field with a wavelength of 800 nm can be filtered out by the dichroic mirror E, and only the second light field is obtained.

[0047] Furthermore, compared with the first light field, the wavelength of the light beam of the second light field is halved, and the corresponding light frequency is doubled.

[0048] Furthermore, it is relatively easy to obtain a light field in an invisible band, and a structured light field in a non-additive band with a specific light field distribution can be obtained through an easily adjustable visible light field.

[0049] Furthermore, by regulating the first light field, the radial and angular modes in the second light field, which is the second harmonic, can be converted simultaneously.

[0050] Furthermore, by adjusting the rotation angle of the dichroic mirror E in the xy plane, the angle of the second harmonic light field can be arbitrarily adjusted.

[0051] Specifically, the light source is an 800nm nonlinear laser source. A second harmonic rotation angle-adjustable system based on vector structured light field generation can simultaneously control the radial and chiral topological charge parameters to obtain the corresponding second harmonic, a second light field, thereby obtaining a frequency-doubled light field with half the wavelength and doubled frequency.

[0052] Figure 2When the radial and localized line-biased vector light field is simultaneously controlled by the angular topological charge, the BBO crystal rotates at different angles, which corresponds to the influence of the fundamental frequency and the doubled frequency light field. x Represents the polarization component in the horizontal direction of the first light field, I y Represents the polarization component of the first light field in the vertical direction, I P represents the (second harmonic) light intensity distribution of the corresponding second light field;

[0053] Figure 3 When the radial and hybrid vector light fields are simultaneously controlled by the angular topological charge, the BBO crystal rotates at different angles, corresponding to the influence of the first and second light fields, where I x Represents the polarization component of the first light field in the horizontal direction, I y Represents the polarization component of the first light field in the vertical direction, I P represents the (second harmonic) light intensity distribution of the corresponding second light field.

[0054] 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 it. Although the technical solutions of the present invention have been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A second harmonic rotation angle adjustable system based on vector structured light field generation, characterized by: Includes laser (A), beam expansion and collimation assembly (B), 4f system assembly (C), second harmonic crystal assembly (D), dichroic mirror (E) and (CCD) camera (F); The first light field generated by the combination of the laser (A), the beam expansion and collimation component (B), and the 4f system component (C) is expressed as: in m,n are the angular and radial polarization topological charges, respectively. is the azimuth, represents the additional phase, r a is the waist radius, e x and e y are the unit vectors in the x and y directions respectively, and Δθ represents e x and e y The phase difference Δθ between the two components is determined by the wave plate in the 4f system component (C). When the wave plate is a quarter wave plate, a first light field with a localized linear polarization 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. The crystal in the second harmonic crystal assembly (D) is a type II BBO crystal, and the polarization property is that e light + o light generates e light; The BBO crystal is mounted on an angle adjustment bracket, which can flexibly adjust the angle of the BBO crystal; If the BBO crystal is rotated by an angle of φ in the xy plane, the nonlinear expression of the polarization intensity of the second light field after the first light field passes through the second harmonic crystal component (D) can be described as: Where Δθ = 0 means using a quarter wave plate, and Δθ = π / 2 means using a half wave plate; The radial and chiral modulation components of the first light field decrease with increasing rotation angle φ in the interval [kπ / 4, (k+1)π / 4], where k is an integer. Specifically, when the rotation angle φ=kπ / 4, the first light field degenerates into a uniform plane wave. The formula is as follows: Where, They represent the unit basis vectors of right-handed circular polarization and left-handed circular polarization respectively; They represent the unit basis vectors in the directions of π / 4 and -π / 4 respectively; The first light field with a wavelength of 800 nm can be filtered out by the dichroic mirror (E), and only the second light field can be obtained; Compared with the first light field, the wavelength of the light beam of the second light field is halved, and the corresponding light frequency is doubled; It is relatively easy to obtain the light field in the invisible band, and the structured light field in the non-additive band with a specific light field distribution can be obtained through the easily adjustable visible light field.

2. The second harmonic rotation angle adjustable system based on vector structured light field generation according to claim 1, characterized in that: Different components of the first light field must all satisfy the phase matching with the crystal in the second harmonic crystal assembly (D).

3. The second harmonic rotation angle adjustable system based on vector structured light field generation according to claim 2, characterized in that: By controlling the first light field, the radial and angular modes in the second harmonic light field can be converted simultaneously.

4. The second harmonic rotation angle adjustable system based on vector structured light field generation according to claim 3, characterized in that: By regulating the rotation angle of the dichroic mirror (E) in the xy plane, it is possible not only to regulate the angle of the first light field but also, more importantly, to arbitrarily regulate the angle of the second light field, the second harmonic.

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