CN111399309A - A method for controlling the focus position of a chirped Airy vortex beam - Google Patents

Abstract

The invention discloses a method for controlling the focusing position of a chirped Airy vortex beam. On the modulator, the Airy vortex beam is generated through the lens; the chirp generator is used to modulate the Airy vortex beam, that is, in the intensity modulator, the beam is intensity-modulated and driven by a radio frequency signal, and the radio frequency is loaded. The intensity pulse signal of information; the beam is transmitted into the quadratic refractive index medium, and the phase adjustment is performed by adjusting the position of the DC bias working point in the intensity modulator to control the loaded chirp and change the chirped Airy vortex. The focal position of the vortex beam propagating in the quadratic refractive index medium is used in the fields of optical micro-manipulation and medical treatment, which can improve the accuracy and stability of the vortex beam to capture the particles, effectively avoid obstacles and push the particles along the second Secondary curve trajectory motion.

Description

A method for controlling the focus position of a chirped Airy vortex beam

technical field

The invention relates to the technical field of optics, in particular to a method for controlling the focus position of a chirped Airy vortex beam.

Background technique

Airy beams have non-diffraction, self-healing properties and their unique self-acceleration properties, which have aroused the enthusiasm of many scientists in recent years. The non-diffractive characteristic means that the beam does not diffract within a certain propagation distance. Self-healing means that even if the light beam encounters a block during propagation, which blocks part of the light intensity, it can return to the original light field distribution shape after propagating for a certain distance. The self-acceleration characteristic refers to the lateral offset acceleration of the main lobe of the beam in the propagation section. Due to the unique properties of Airy beam, it has been used in many fields such as nonlinear photobombs, micro-nano processing, medical treatment and so on.

Vortex beams have a special helical wavefront structure and carry a certain orbital angular momentum, which can effectively capture particles and rotate the captured particles. It has very important applications in optical micro-manipulation, quantum communication, biomedicine and other fields. value.

In 2009, scientists successfully obtained the Airy vortex beam by introducing the helical phase on the basis of the cubic phase of the Airy beam, and studied its characteristics. Since then, many scholars have been attracted to continue to conduct in-depth research on Airy vortex beams, and many achievements have been achieved. Optical vortex does not affect the propagation trajectory of Airy beam, the propagation properties of Airy vortex beams with different topological charges, and the propagation properties of Airy vortex beams in uniaxial crystals.

SUMMARY OF THE INVENTION

In view of this, in order to facilitate the application and development of vortex beams in the field of optical micromanipulation, the present invention proposes a method for controlling the focus position of chirped Airy vortex beams.

The technical scheme adopted by the present invention to solve its technical problems is:

The present invention provides a method for controlling the focus position of a chirped Airy vortex beam, comprising the following steps:

emit a beam with a laser;

The cubic phase of the Airy beam and the helical phase of the vortex beam are superimposed to obtain a modulation phase, which is loaded on the spatial light modulator, and then generates the Airy vortex beam through the lens;

A chirp generator is used to modulate the Airy vortex beam, that is, in the intensity modulator, the beam is intensity-modulated and driven by a radio frequency signal, and an intensity pulse signal loaded with radio frequency information is obtained;

The beam is transmitted into a quadratic refractive index medium, and the phase is adjusted by adjusting the position of the DC bias working point in the intensity modulator to control the loaded chirp, and control the chirped Airy vortex beam in the quadratic. The focal position of the propagation in the square refractive index medium can improve the accuracy and stability of the vortex beam to capture particles when applied to particle manipulation. At the same time, due to the self-healing and self-acceleration characteristics of the Airy beam, it can effectively avoid obstacles and push the particles to move along the quadratic trajectory.

Further, the new modulation phase obtained by the superposition of the cubic phase and the helical phase is specifically:

其中f₁和f₂分别是立方相位和螺旋相位，k_x和k_y分别是x和y方向的波矢，i是虚数单位，arg(·)为复数的辐角，m为拓扑荷数，k_x1和k_y1表示立方相位中心与螺旋相位中心间的位错。

where f ₁ and f ₂ are the cubic phase and the helical phase, respectively, k _x and _ky are the wave vectors in the x and y directions, respectively, i is the imaginary unit, arg( ) is the complex argument, m is the topological charge number, k _x1 and k _y1 represent the dislocations between the cubic phase center and the helical phase center.

Further, changing the dislocation between the cubic phase and the helical phase controls the loading of the optical vortex at different positions of the Airy beam.

Further, the beam propagates periodically in a quadratic refractive index medium, and the focus position of the beam is controlled by changing the chirp.

Compared with the prior art, the beneficial effects of the present invention at least include:

The invention adopts the spatial light modulator method to generate the Airy vortex beam, changes the dislocation between the cubic phase and the helical phase, obtains different modulation phases, and can obtain the Airy vortex beam with different initial fields. At the same time, a new type of chirp generator is adopted, which saves cost, improves efficiency, and can well control beam focusing control, which is of great significance for the application and development of particle capture, particle cleaning and other fields.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

Fig. 1 is the flow chart of the method for controlling the chirped Airy vortex beam focus position of the present invention;

Fig. 2 is the cubic spiral phase diagram of the present invention, the topological charge number m=1, k _x1 = _ky1 =0;

Fig. 3 is a graph of the first-order chirped Airy vortex beam of the present invention when the topological charge number m=1, k _x1 = _ky1 =0, attenuation factor a=b=0.1, chirp factor β=0.1, which is related to the refractive index The intensity distribution and phase distribution of propagating in the quadratic refractive index medium when the parameter α=0.2m and the propagation period L=2πα; (b) is the propagation evolution diagram of the light beam in the medium; (a1)-(a6) and ( c1)-(c6) are the lateral phase distribution and intensity distribution of the beam at the position of the corresponding dotted line;

Fig. 4 is the first-order chirped Airy vortex beam of the present invention when the topological charge number m=1, k _x1 = _ky1 =0, the attenuation factor a=b=0.1, the parameter α=0.2m related to the refractive index, the propagation Intensity distribution and intensity evolution propagating in quadratic refractive index medium with period L=2πα; (a1), (b1) correspond to chirp factor β=-2; (a2), (b2) correspond to chirp factor β=0.1; (a3), (b3) correspond to the chirp factor β=2.

Detailed ways

In order to make the above objects, features and advantages of the present invention more clearly understood, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be pointed out that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work The embodiments all belong to the protection scope of the present invention.

Example 1

As shown in Figure 1, the present invention provides a method for controlling the focus position of a chirped Airy vortex beam, comprising:

First, a laser is used to emit a beam, and the cubic phase of the Airy beam and the helical phase of the vortex beam are superimposed to obtain a modulated phase, which is loaded on the spatial light modulator, and then generates an Airy vortex beam through a lens. Then, the Airy vortex beam is modulated by a new type of chirp generator, that is, in the intensity modulator, the beam is intensity-modulated and driven by a radio frequency signal, and an intensity pulse signal loaded with radio frequency information is obtained. The beam is driven into the quadratic refractive index medium, and the phase adjustment is performed by adjusting the position of the DC bias working point in the intensity modulator to control the loaded chirp and change the chirped Airy vortex beam in the quadratic When the focal position propagating in the refractive index medium is applied to particle manipulation, it can improve the accuracy and stability of particles captured by the vortex beam, and at the same time, due to the self-healing and self-acceleration characteristics of the Airy beam, it can effectively avoid obstacles and push The particles move along quadratic trajectories.

Example 2

In this embodiment, on the basis of Embodiment 1, the new modulation phase obtained by the superposition of the cubic phase and the helical phase is specifically:

其中f₁和f₂分别是立方相位和螺旋相位，k_x和k_y分别是x和y方向的波矢，i是虚数单位，arg(·)为复数的辐角，m为拓扑荷数，k_x1和k_y1表示立方相位中心与螺旋相位中心间的位错。

where f ₁ and f ₂ are the cubic phase and the helical phase, respectively, k _x and _ky are the wave vectors in the x and y directions, respectively, i is the imaginary unit, arg( ) is the complex argument, m is the topological charge number, k _x1 and k _y1 represent the dislocations between the cubic phase center and the helical phase center.

Specifically, the spatial light modulator method is used to generate Airy vortex beams, and the dislocation between the cubic phase and the helical phase is changed to obtain different modulation phases, and Airy vortex beams with different initial fields can be obtained.

Specifically, the beam propagates periodically in a quadratic refractive index medium, and the focusing position of the beam can be controlled by changing the chirp.

The invention combines the chirped, vortex and Airy beams to obtain the chirped Airy vortex beam, and the intensity distribution and phase distribution of the beam propagating in the quadratic refractive index medium are in-depth in the invention. The analysis of , Figure 2 is the cubic helical phase diagram used to generate the Airy vortex beam, Figure 3 shows the light intensity distribution and phase distribution of the beam in the propagation period, it can be seen that the beam is focused four times in one period, the beam The contour changes periodically. From Figure 4, it can be seen that under the influence of different chirp factors, the focus position of the beam is different, which also indicates that the focus position of the beam when propagating along the z-axis can be modulated by controlling the loaded chirp factor.

The invention adopts the spatial light modulator method to generate the Airy vortex beam, changes the dislocation between the cubic phase and the helical phase, obtains different modulation phases, and can obtain the Airy vortex beam with different initial fields. At the same time, a new type of chirp generator is adopted, which saves cost, improves efficiency, and can well control beam focusing control.

The above-mentioned embodiment only represents an embodiment of the present invention, and its description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (4)

1. a method for controlling chirped Airy vortex beam focus position, is characterized in that, comprises the steps: emit a beam with a laser; The cubic phase of the Airy beam and the helical phase of the vortex beam are superimposed to obtain a modulation phase, which is loaded on the spatial light modulator, and then generates the Airy vortex beam through the lens; A chirp generator is used to modulate the Airy vortex beam, that is, in the intensity modulator, the beam is intensity-modulated and driven by a radio frequency signal, and an intensity pulse signal loaded with radio frequency information is obtained; The beam is transmitted into a quadratic refractive index medium, and the phase adjustment is performed by adjusting the position of the DC bias working point in the intensity modulator to control the loaded chirp, changing the chirped Airy vortex beam in the quadratic The focal position of the propagation in the square refractive index medium can improve the accuracy and stability of the vortex beam to capture particles when applied to particle manipulation. At the same time, due to the self-healing and self-acceleration characteristics of the Airy beam, it can effectively avoid obstacles and push the particles to move along the quadratic trajectory. 2. the method for controlling the focus position of the chirped Airy vortex beam according to claim 1, is characterized in that, the new modulation phase obtained by the superposition of the cubic phase and the helical phase is specifically:

where f ₁ and f ₂ are the cubic phase and the helical phase, respectively, k _x and _ky are the wave vectors in the x and y directions, respectively, i is the imaginary unit, arg( ) is the complex argument, m is the topological charge number, k _x1 and k _y1 represent the dislocations between the cubic phase center and the helical phase center. 3. The method for controlling the focusing position of a chirped Airy vortex beam according to claim 1, wherein the dislocation between the cubic phase and the helical phase is changed, and the optical vortex is controlled to be loaded at different positions of the Airy beam. . 4. The method for controlling the focus position of a chirped Airy vortex beam according to claim 1, wherein the beam propagates periodically in a quadratic refractive index medium, and the focus position of the beam is controlled by changing the chirp.

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