Vortex laser chiral selection system and method based on gain space differential distribution

Abstract

The invention discloses a vortex laser chiral selection system and method based on gain space differential distribution. The system comprises an optical fiber pumping source, a 4f imaging module, a laser input mirror, a differential space distribution gain medium and an output coupler which are connected in sequence. Depending on the characteristics of the gain medium, no extra modulation element needs to be inserted into the resonant cavity, the problems of vortex quality degradation and the like caused by the characteristics of the element are avoided, and high-efficiency single chiral vortex laser output is realized.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic laser technology, and more specifically to a vortex laser chirality selection system and method based on differential gain spatial distribution. Background Art

[0002] Vortex beams, due to their unique light field distribution and orbital angular momentum properties, have shown great potential in the fields of optical tweezers, optical communications, quantum entanglement, material processing, and microscopic imaging. However, the current lack of high-quality stable vortex light sources has greatly limited the scope of application of vortex beams.

[0003] At present, there are two main methods for generating vortex beams: mode conversion through modulation elements and direct generation in the laser resonant cavity. The vortex laser generated directly in the resonant cavity, as the eigenmode of the resonant cavity, not only has ideal quality, but also can achieve the output of high peak power and high-order orbital angular momentum. However, since the cylindrically symmetric vortex optical resonant cavity has no chirality preference, the output laser is a superposition state of positive and negative chirality. This petal-shaped beam destroys the spatial structure and orbital angular momentum characteristics of the laser. Therefore, it is necessary to screen the chirality of the vortex laser. The current vortex laser chirality selection is mainly achieved by introducing asymmetric losses in the cavity. This method not only requires precise angle adjustment, but also affects the symmetry of the resonant cavity, resulting in a reduction in output power and conversion efficiency. Summary of the invention

[0004] In view of this, the present invention provides a vortex laser chirality selection system and method based on differential gain spatial distribution, which are used to achieve high-efficiency single-chirality vortex laser output.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] On one hand, the present invention discloses a vortex laser chirality selection system based on differential gain spatial distribution, comprising: a sequentially connected optical fiber pump source, a 4f imaging module, a laser input mirror, a differential spatially distributed gain medium, and an output coupler.

[0007] Preferably, in a specific embodiment, the optical fiber pump source adopts a multimode optical fiber coupled laser diode pump source.

[0008] Preferably, in the above embodiment, the multimode fiber-coupled laser diode pump source and the 4f imaging module are connected via a fiber flange.

[0009] Preferably, in the vortex laser chirality selection system based on differential gain spatial distribution, the activation ions in the differential spatial distribution gain medium include Nd 3+ , Yb 3+ , Er3+ 、Tm 3+ 、Ho 3+ 、Dy 3+ , Fe 3+ or Cr 3+ Any one of .

[0010] Preferably, in the above-mentioned vortex laser chirality selection system based on differential spatial gain distribution, the differential spatial distribution gain medium has a stimulated emission cross section with spatially non-uniform distribution, and the stimulated emission cross section is expressed as:

[0011]

[0012] Among them, σ XZ (θ) represents the stimulated emission cross section value when the azimuth angle is θ in the XZ plane as the focal plane of the vortex light; σ X Represents the stimulated emission cross section value when the azimuth angle is zero; σ Z Represents the stimulated emission cross section value when the azimuth angle is 90 degrees; σ π / 4 is the stimulated emission cross section when the azimuth angle is 45 degrees.

[0013] Preferably, in an improved embodiment, the above-mentioned vortex laser chirality selection system based on spatially differentiated gain distribution also includes an order measurement device for analyzing the beam quality and orbital angular momentum characteristics of the vortex laser output by the vortex laser chirality selection system.

[0014] Preferably, in the above improved embodiment, the order measurement device includes a power attenuator, a Mach-Zehnder interferometer system and a CCD beam analyzer connected in sequence.

[0015] Preferably, in the above embodiment, the Mach-Zehnder interferometer system is an improved Mach-Zehnder interferometer system, including two non-polarizing beam splitters, two total reflection mirrors and a tight focusing lens, wherein the first non-polarizing beam splitter splits the vortex laser input through the power attenuator into two beams; one of the vortex laser beams is reflected by the first total reflection mirror and then input into the second non-polarizing beam splitter, and the other vortex laser beam is reflected by the second total reflection mirror and then passed through the tight focusing lens and then input into the second non-polarizing beam splitter.

[0016] On the other hand, the present invention discloses a vortex laser chirality selection method based on differential distribution of gain space, which uses the vortex laser chirality selection system based on differential distribution of gain space described in any one of the first aspects to perform vortex laser chirality selection and output a vortex laser of a single chirality.

[0017] Furthermore, the above method also includes: analyzing the output single-chirality vortex laser to obtain the beam quality and orbital angular momentum characteristics of the vortex laser.

[0018] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a vortex laser chirality selection system and method based on differential gain spatial distribution, which has the following beneficial effects:

[0019] The present invention relies on the characteristics of the gain medium itself and does not require the insertion of additional modulation elements in the resonant cavity, thus avoiding problems such as vortex quality degradation caused by the characteristics of the elements themselves, and reducing the complexity of the optical path and the difficulty of adjustment; on the other hand, the present invention will not destroy the symmetry of the resonant cavity and can maintain high-efficiency laser operation and high-power laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0021] Figure 1 Schematic diagram of the structure of the chiral selection device based on gain differentiated spatial distribution provided by the present invention.

[0022] Figure 2 A schematic diagram of vortex light propagating along the Y-axis provided in an embodiment of the present invention.

[0023] Figure 3 A schematic diagram of the lateral components of two chiralities in the XZ plane provided by an embodiment of the present invention.

[0024] Figure 4 A schematic cross-sectional diagram of stimulated emission from a Nd:LYSO laser crystal provided in an embodiment of the present invention.

[0025] Figure 5 A schematic structural diagram of a chiral selection device including an order measurement device provided in an embodiment of the present invention.

[0026] Figure 6 A schematic structural diagram of an improved Mach-Zehnder interferometer provided in an embodiment of the present invention.

[0027] Figure 7 A schematic diagram of a power curve of a chiral selection device for generating 1078nm single chiral vortex light provided in an embodiment of the present invention.

[0028] Figure 8 Schematic diagram of the laser spot and interference pattern output by the chiral selection device for generating 1078nm single chiral vortex light provided for the implementation of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1 As shown, the chiral selection device based on differential spatial distribution of gain disclosed in an embodiment of the present invention comprises: a fiber pump source 1, a 4f imaging module 3, a laser input mirror 4, a differential spatial distribution gain medium 5, and an output coupler 6 connected in sequence.

[0032] Preferably, the optical fiber pump source 1 adopts a multi-mode optical fiber coupled laser diode pump source, and the multi-mode optical fiber coupled laser diode pump source is connected to the 4F imaging system through an SMA905 optical fiber flange 2.

[0033] In the multimode fiber coupled laser diode pump source system, the wavelength depends on the absorption characteristics of the gain medium, and the power depends on the actual demand; the output wavelength of the chiral selection device based on the gain differential spatial distribution depends on the activation ions in the gain medium. The activation ions in the spatially differentially distributed gain medium used in the present invention can be Nd 3+ , Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ 、Dy 3+ , Fe 3+ Cr 3+ Any one of them, the matrix material can also be flexibly selected to achieve the desired single chiral vortex laser output of any band; different resonant cavity types can be selected according to actual needs. In the implementation mode of the present invention, the laser operates in a continuous working state, and the cavity type used is mainly a Fabry-Perot resonant cavity. In other implementation modes, other cavity types such as V-cavity, Z-cavity or X-cavity can also be used.

[0034] In the chiral selection device based on gain differential spatial distribution of the present invention, the 4f imaging module 3 is composed of two convex lenses, which are used to image the fiber-coupled pump light again, thereby increasing the power density and reducing the laser threshold.

[0035] In a specific embodiment, the differentiated spatially distributed gain medium 5 adopts Nd:LYSO laser crystal; the multimode fiber-coupled laser diode 1 has a central wavelength of 808nm and a maximum power of 20W; the laser input mirror 4 is a dielectric film plane mirror, which has high transmittance in the 700nm-90nm band and high reflection in the 1000nm-1100nm band; the output coupler 5 has a transmittance of 10% in the 1000nm-1100nm band. Through the above implementation scheme, the chirality selection device based on gain differentiated spatial distribution can generate 1078nm single chiral vortex light.

[0036] The following is a brief introduction to the chiral selection method and results in the case:

[0037] Stimulated emission is an important step in generating lasers. The stimulated emission cross section is a physical quantity that describes the stimulated emission ability of the gain medium. Its expression is:

[0038]

[0039] Among them, σ XZ (θ) represents the stimulated emission cross section value when the azimuth angle is θ in the XZ plane as the focal plane of the vortex light; σ X Represents the stimulated emission cross section value when the azimuth angle is zero; σ Z Represents the stimulated emission cross section value when the azimuth angle is 90 degrees; σ π / 4 is the stimulated emission cross section when the azimuth angle is 45 degrees.

[0040] In the present invention, the differentiated spatially distributed gain medium has a stimulated emission cross section with a spatially non-uniform distribution, that is, in the stimulated emission cross section, the values ​​of the stimulated emission cross section at different azimuth angles are different.

[0041] The principle of the invention is further explained below. For a vortex beam, since the vortex beam propagates in a spiral shape, it is a vortex light beam that propagates along the Y axis on a macroscopic level. On a microscopic level, there is also a transverse component in its propagation path, that is, the component in the XZ plane. The direction of this transverse component is constantly changing during the propagation process. Generally, only the direction of the XZ plane (i.e., the focal plane) where the pump beam focus is located is considered. Figure 2 As shown: The purple and orange lines represent the microscopic propagation paths of the two chiral vortex lights. The XZ plane at Y = 0 is the focal plane. Figure 3 It can be seen that at the focal plane, the two arrowed line segments represent the transverse components of the two chiralities in the XZ plane, and their directions are different. Assume that the angles between these two line segments and the X-axis are a and b respectively. Figure 4The stimulated emission cross section of the Nd:LYSO crystal XZ plane, where the 0-degree line is the X-axis, the 90-degree line is the Z-axis, and the ring represents the intensity. As shown in the figure, for the vortex light whose transverse component is at an angle of 30 degrees with the X-axis, the stimulated emission cross section is about 9, the angle of 60 degrees is 8.4, and the angle of 90 degrees is 5.4. Figure 4 It can be seen that the stimulated emission cross section of the Nd:LYSO crystal selected in this embodiment is an 8-shaped emission cross section, which means that the value of the stimulated emission cross section is different at different azimuth angles. Therefore, the crystal has an uneven gain spatial distribution phenomenon, resulting in two chiral vortex lasers obtaining different gains in the laser crystal, thereby realizing the chiral selection function.

[0042] Example 2

[0043] like Figure 5 , Figure 6 As shown, based on the specific implementation method disclosed in Example 1, Example 2 adds an order measurement device for detecting and analyzing the output single chiral vortex light. The order measurement device is composed of a power attenuator 7, a Mach-Zehnder interferometer system 8 and a CCD beam analyzer 9, which are used to analyze the beam quality and OAM characteristics of the output vortex laser.

[0044] In this embodiment, the Mach-Zehnder interferometer system 8 is an improved Mach-Zehnder interferometer composed of two non-polarizing beam splitters, two total reflection mirrors and a tight focusing lens. Interference is generated by beam splitting and beam recombining. The interference pattern can show the beam quality and OAM characteristics of the laser. Figure 6 As shown, in the improved Mach-Zehnder interferometer, the first non-polarizing beam splitter 801 splits the vortex laser input through the power attenuator 7 into two beams; one of the vortex laser beams is reflected by the first total reflection mirror 811 and then input into the second non-polarizing beam splitter 802, and the other vortex laser beam is reflected by the second total reflection mirror 812 and then passed through the tight focusing lens 820 and then input into the second non-polarizing beam splitter 802.

[0045] The laser operates in a continuous state. Figure 7 and Figure 8 The power curve of the chiral selective device based on the gain differential spatial distribution, the output laser spot and the interference pattern are given respectively. Figure 7 It can be seen that the laser threshold is about 1.2W, the maximum power exceeds 5W, and the slope efficiency reaches 41%, which is much higher than the single chiral vortex laser based on loss modulation; Figure 8 As can be seen from the figure, the chiral selection device based on the differential spatial distribution of gain can generate LG 0,0 LG 0,-1 LG 0,-2The three laser modes (from left to right) are 0-order, -1-order, and -2-order vortex lasers. From the light spots and interference patterns, it can be seen that the output vortex lasers are of single chirality and have good beam quality, which proves that the scheme of the present invention is feasible.

[0046] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0047] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A vortex laser chirality selection system based on gain spatial differential distribution, characterized in that: include: The fiber pump source, 4f imaging module, laser input mirror, differentiated spatially distributed gain medium, and output coupler are connected in sequence.

2. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 1, characterized in that: The optical fiber pump source comprises a multi-mode optical fiber coupled laser diode pump source.

3. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 2, characterized in that: The multimode fiber-coupled laser diode pump source and the 4f imaging module are connected via an optical fiber flange.

4. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 1, characterized in that: The active ions in the differential spatial distribution gain medium include Nd 3+ , Yb 3+ , Er 3+ 、Tm 3+ 、Ho 3+ 、Dy 3+ , Fe 3+ or Cr 3+ Any one of .

5. The vortex laser chirality selection system based on gain spatial differential distribution according to claim 1, characterized in that: The differentiated spatially distributed gain medium has a spatially non-uniformly distributed stimulated emission cross section, which is expressed as: Among them, σ XZ (θ) represents the stimulated emission cross section value when the azimuth angle is θ in the XZ plane as the focal plane of the vortex light; σ X Represents the stimulated emission cross section value when the azimuth angle is zero; σ Z Represents the stimulated emission cross section value when the azimuth angle is 90 degrees; σ π / 4 is the stimulated emission cross section when the azimuth angle is 45 degrees.

6. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 1, characterized in that: The invention also comprises an order measurement device for analyzing the beam quality and orbital angular momentum characteristics of the vortex laser output by the vortex laser chirality selection system.

7. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 6, characterized in that: The order measurement device comprises a power attenuator, a Mach-Zehnder interferometer system and a CCD beam analyzer connected in sequence.

8. A vortex laser chirality selection system based on gain spatial differential distribution according to claim 7, characterized in that: The Mach-Zehnder interferometer system is an improved Mach-Zehnder interferometer system. The invention comprises two non-polarizing beam splitters, two total reflection mirrors and a tight focusing lens, wherein the first non-polarizing beam splitter splits the vortex laser inputted through the power attenuator into two beams; one of the vortex laser beams is reflected by the first total reflection mirror and then inputted into the second non-polarizing beam splitter, and the other vortex laser beam is reflected by the second total reflection mirror and then passed through the tight focusing lens and then inputted into the second non-polarizing beam splitter.

9. A vortex laser chirality selection method based on gain spatial differential distribution, characterized in that: The vortex laser chirality selection system based on gain spatial differential distribution according to any one of claims 1 to 5 is used to perform vortex laser chirality selection to output a vortex laser of a single chirality.

10. The method for selecting chirality of vortex laser based on differential gain spatial distribution according to claim 9, characterized in that: Also includes: The output single-chirality vortex laser is analyzed to obtain the beam quality and orbital angular momentum characteristics of the vortex laser.

Images