CN117096716A

CN117096716A - Phase-programmable laser

Info

Publication number: CN117096716A
Application number: CN202311151488.3A
Authority: CN
Inventors: 汪喜林; 任志成; 王慧田
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2023-09-07
Filing date: 2023-09-07
Publication date: 2023-11-21

Abstract

The invention discloses a laser with randomly programmable phase, wherein pump light in the laser is transmitted into a laser gain crystal through a focusing objective lens and an input concave mirror to excite the laser gain crystal to generate laser; when the laser is transmitted in the anticlockwise direction, the laser is emitted from the laser gain crystal, reflected by the reflecting concave mirror, irradiated onto the first spatial light modulator for spatial phase modulation, and then passes through the first lens and the second lens to the second spatial light modulator; loading a phase conjugate to the first spatial light modulator onto the second spatial light modulator; after the laser is restored by the second spatial light modulator, the laser is restored into a Gaussian beam of a fundamental mode, the Gaussian beam is transmitted to an input concave mirror, and the Gaussian beam is reflected and reaches the laser gain crystal again for re-amplification. The clockwise laser is transmitted and amplified in the cavity, and the two lasers travel along a common route, and only the surrounding directions are opposite. The invention can realize highly coherent, phase-programmable and arbitrarily controllable space phase laser output.

Description

Phase-programmable laser

Technical Field

The invention relates to the field of optical field regulation and control and the field of laser, in particular to a laser with randomly programmable phase.

Background

The laser has good coherence: from the relatively stable phase of the laser, phase modulation has great value for the application of the laser. Since the laser has extremely unique excellent properties such as high brightness, high collimation, high coherence and the like, the laser has rapid development and extremely wide application since the first ruby laser in the 60 th century, and has wide application and irreplaceable functions in the fields such as scientific research, medical treatment, industry, military and the like.

However, currently existing lasers often output only a limited number of cavity eigenmodes, such as a fundamental mode gaussian beam, or a lagrangian gaussian mode, which are eigenmodes of the laser cavity and are therefore limited by the laser cavity structure, the spatial output modes of the laser are often not tunable and are extremely limited in number. The adjustment of the light field phase is often realized by adopting a mode of subsequent processing outside a laser cavity.

Therefore, a technology is needed to realize highly coherent, phase-programmable and arbitrarily controllable spatial phase laser output, fill the blank in the field, and further break through the limitation that a laser can only output laser with a specific spatial mode.

Disclosure of Invention

The invention aims to provide a laser with a randomly programmable phase, which can realize highly coherent, programmable phase and randomly controllable space phase laser output.

In order to achieve the above object, the present invention provides the following solutions:

a phase arbitrarily programmable laser, comprising: the system comprises a pumping source, a focusing objective lens, an input concave mirror, a laser gain crystal, a reflecting concave mirror, a first spatial light modulator, a first lens, a second lens and a second spatial light modulator;

after the pump light emitted by the pump source is focused and reduced by the focusing objective lens, the pump light is transmitted into the laser gain crystal by the input concave mirror, the particle number in the laser gain crystal is inverted and laser is generated, and the laser is in a Gaussian fundamental mode and is transmitted in clockwise and anticlockwise directions respectively; when the laser is transmitted in the anticlockwise direction, the laser is reflected by the reflecting concave mirror after exiting from the laser gain crystal, irradiates the first spatial light modulator, is subjected to spatial phase modulation by the first spatial light modulator, and is imaged on the second spatial light modulator through a 4-f system consisting of a first lens and a second lens; loading a phase conjugate to the first spatial light modulator onto the second spatial light modulator; after the laser is restored by the second spatial light modulator, the laser is restored into a basic mode Gaussian beam, and is transmitted to the input concave mirror, and the basic mode Gaussian beam is reflected by the input concave mirror and reaches the laser gain crystal again for re-amplification; simultaneously, clockwise laser transmits and amplifies in the laser cavity; the laser routes in the clockwise direction and the laser routes in the anticlockwise direction are the same, and the surrounding directions are opposite.

Optionally, the pump source is a semiconductor laser.

Optionally, the wavelength of the pump source is 879nm.

Optionally, the method further comprises: a half wave plate and a polarization beam splitter prism;

the half wave plate and the polarization splitting prism are arranged on a light path between the second lens and the second spatial light modulator;

the laser transmitted from the second lens rotates in the polarization direction through the half-wave plate, and is split by the polarization splitting prism to be respectively output as a laser and transmitted to the second spatial light modulator; the polarization beam splitter prism divides the laser modulated by the first spatial light modulator into two beams, one beam is output outside the cavity, and the other beam is transmitted to the second spatial light modulator and is restored into a Gaussian light field similar to the fundamental mode.

Optionally, the method further comprises: splitting a flat piece;

the light splitting flat sheet is arranged on a light path between the first spatial light modulator and the second spatial light modulator;

and the front and back sides of the beam splitting flat sheet can reflect laser to output two paths of laser in opposite directions.

Optionally, the two paths of laser output by the beam splitting flat sheet respectively carry phases loaded on the first spatial light modulator and the second spatial light modulator.

Optionally, the laser with the arbitrarily programmable phase outputs laser with an arbitrary phase structure, and after loading the arbitrary phase on the first spatial light modulator and the second spatial light modulator, the laser with the arbitrarily programmable phase structure is generated.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

the laser with the phase capable of being programmed randomly provided by the invention realizes the digital laser with programmable control by using the first spatial light modulator and the second spatial light modulator, so that output laser is not limited by the intrinsic mode of the laser resonant cavity any more, laser with any spatial phase structure can be flexibly output according to requirements, adjustment is very simple and quick, different phase diagrams can be flexibly changed by switching different phase diagrams on the spatial light modulator through computer control, and the spatial light modulator has refresh frequency of about 100Hz, so that the digital laser with the phase capable of being programmed randomly can be realized by switching and outputting laser with 100 different bit spatial structures every second.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a laser with a randomly programmable phase according to embodiment 1 of the present invention;

FIG. 2 is a graph showing the measurement results of vortex laser carrying a single topology charge vortex phase;

FIG. 3 is a schematic diagram of a laser with a plurality of orbital angular momentums (vortex components) that are relatively flat;

FIG. 4 is a schematic diagram of measurement results of an orbital angular momentum comb laser carrying multiple topological charge vortices simultaneously;

fig. 5 is a schematic diagram of a phase-programmable laser according to embodiment 2 of the present invention.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.

The invention provides a laser with randomly programmable phase, comprising: a pump source 101, a focusing objective 102, an input concave mirror 103, a laser gain crystal 104, a reflecting concave mirror 105, a first spatial light modulator 106, a first lens 107, a second lens 108, and a second spatial light modulator 111;

after the pump light emitted by the pump source 101 is focused and reduced by the focusing objective lens 102, the pump light is transmitted into the laser gain crystal 104 by the input concave mirror 103, the particle number in the laser gain crystal 104 is inverted and laser with the wavelength of 1064nm is generated, and the laser is in a Gaussian fundamental mode and is transmitted along the clockwise direction and the anticlockwise direction respectively; when transmitting in the anticlockwise direction, the laser is emitted from the laser gain crystal 104, reflected by the reflecting concave mirror 105, irradiated onto the first spatial light modulator 106, spatially phase modulated by the first spatial light modulator 106, and imaged onto the second spatial light modulator 111 by a 4-f system consisting of the first lens 107 and the second lens 108; the second spatial light modulator 111 is loaded with a phase conjugate to the first spatial light modulator 106; after being restored by the second spatial light modulator 111, the laser light is restored to a fundamental mode gaussian beam, and is transmitted to the input concave mirror 103, reflected by the input concave mirror 103, and reaches the laser gain crystal 104 again for re-amplification.

The laser beam in a partial region of the cavity has an arbitrarily controllable spatial phase distribution, which is phase modulated by a spatial light modulator, while the remainder (especially at the laser crystal) is a fundamental mode gaussian beam or other type of cavity eigenmode laser.

As shown in fig. 1 and 5, the laser cavity is of an "8" shaped laser cavity structure. The laser cavity structure utilizes a spatial light modulator. That is, two spatial light modulators (a first spatial light modulator 106 and a second spatial light modulator 111) are used in the laser resonator, and the spatial light modulators can flexibly load various phase diagrams, so that the laser light irradiated to the surface thereof is spatially modulated, and the laser light reflected/transmitted from the spatial light modulator (depending on whether the reflective spatial light modulator or the transmissive spatial light modulator is used) will carry the loaded phase. After imaging by a 4-f imaging system composed of two lenses (a first lens 107 and a second lens 108), the two spatial light modulators are made to be image plane positions, and phases which are conjugate and complementary to the first spatial light modulator 106 are loaded on the surface of the second spatial light modulator 111, the centers of the two spatial light modulators are aligned by adjustment, the spatial phase carried by the intracavity oscillation laser after passing through the first spatial light modulator is offset and restored to a fundamental mode gaussian beam after passing through the second spatial light modulator, and transmission is continued until being amplified again by the laser gain crystal 104. In the middle of two spatial light modulators, namely in the intracavity circuit of which the spatial structure phase is not restored, a half wave plate 109 and a polarization beam splitter prism 110 are arranged, so that the output rate of the laser can be adjusted, and the output laser carries the spatial phase loaded by the spatial light modulator at the moment. In addition, since the laser cavity structure of the present invention ensures that the laser can oscillate in both clockwise and counterclockwise directions, if the polarization splitting prism 110 and the half-wave plate 109 are replaced with the splitting plate 112, both clockwise and counterclockwise laser beams can be output, and the two laser beams are coherent with each other.

The pump source 101 is a semiconductor laser around a wavelength of 879nm.

The wavelength of the pump source 101 is 879nm, and the pump source is well matched with the resonance pump absorption peak 879nm of the laser crystal Nd: YVO4, so that the absorption rate of pump light can be improved. The laser gain crystal 104 used was a YVO4/Nd: YVO4/YVO4 double-end-bonded crystal, the crystal length was 10mm, and the crystal end face was coated with an antireflection film in the vicinity of a 1064nm wavelength, and the input concave mirror 103 was made to have a high transmittance in the vicinity of a 879nm wavelength and a high reflectance in the vicinity of a 1064nm wavelength by coating. The reflective concave mirror 105, the first spatial light modulator 106, and the second spatial light modulator 111 are coated with a high reflectivity for 1064nm wavelength.

As shown in fig. 1, in embodiment 1, a phase-programmable laser according to the present invention further includes: a half wave plate 109 and a polarization splitting prism 110.

The half-wave plate 109 and the polarization splitting prism 110 are disposed on the optical path between the second lens 108 and the second spatial light modulator 111.

When the laser beam with horizontal polarization is transmitted from the second lens 108, it is rotated in the polarization direction through the half-wave plate 109, and is split by the polarization splitting prism 110, and is output as a laser and transmitted to the second spatial light modulator 111, respectively.

After the polarization direction rotation is performed by the half-wave plate 109, the laser is still linearly polarized, the polarization direction is no longer horizontal, after the polarization direction is split by the polarization splitting prism 110110, the vertical polarization component of the laser radiation is reflected by the light splitting surface of the polarization splitting prism 110 by 45 degrees and then output, and is used as a laser output port, and the rest of the horizontal polarization components are transmitted through the polarization splitting prism 110 and then are continuously transmitted to the second spatial light modulator 111, so as to cancel the phase loaded by the first spatial light modulator 106 carried by the optical field.

The structure of embodiment 1 can output laser light of an arbitrary phase, and the digital laser can output laser light of an arbitrary phase by changing the phase pattern loaded by the spatial light modulators 106 and 111. As an example, two broad classes of very characteristic lasers were output: a. vortex laser carrying a single topology charge vortex phase (fig. 2); b. an orbital angular momentum comb laser (fig. 4) carrying multiple topologically charged vortices simultaneously.

As shown in fig. 2, by switching the topology charges of the vortex phase loaded on the spatial light modulator, the output vortex beam topology charges of the laser are changed, so that flexible control output of vortex lasers with different topology charges is realized, and the vortex lasers with the topology charges m=8, 16, 32, 48, 64 and 128 are respectively switched. And the spot at the image plane position (first line of fig. 2) and at the focus plane position (second line of fig. 2) was recorded using the CCD. In addition, the topology load of the output vortex laser is measured by adopting a method of carrying out phase reduction outside the laser cavity by a third spatial light modulator, the vortex spectrum is measured by coupling the vortex laser into a single mode fiber after reduction, the light spots after the phase reduction by the third spatial light modulator are shown in the third row of the figure 2, and the result of the vortex spectrum measurement is shown in the bottom four rows of the figure 2. Experimental results show that the arbitrary phase digital laser can flexibly output vortex lasers with different topological charges, and the topological charge spectrum (namely the orbital angular momentum spectrum) of the vortex is very pure.

As shown in fig. 3, by designing a special phase structure, the laser can be realized to have a relatively flat structure and contain a plurality of orbital angular momentum (vortex component), and as the intensity of each orbital angular momentum component is the same, the comb is called as an orbital angular momentum comb like a comb. Wherein, as shown in part D of FIG. 3, if N topology charges are to be generated, in turnOrbital angular momentum comb (where n=1, 2, … N), then the phase will be as shown in part a of fig. 3The figure is uniformly divided into 2N sectors, and the phase structures of every two opposite sectors are identical, namely N pairs of sectors are all arranged, and the phase distribution of each sector is as follows: />Wherein->For the initial phase of each sector, the initial phase of each sector is calculated by numerical value, so that the initial phase solution of a relatively flat spectrum can be obtained, and then the phase is loaded, and the laser of a relatively flat orbital angular momentum spectrum can be obtained.

As shown in fig. 4, a relatively flat orbital angular momentum comb laser having a plurality of orbital angular momentums (eddy components) is output. By changing the phase loaded by the spatial light modulator, the output of the orbital angular momentum spectrums of 8-dimension, 16-dimension, 32-dimension, 48-dimension and 64-dimension is realized respectively. The first column of fig. 4 is a phase diagram loaded by the spatial light modulator, the second column of fig. 4 is a spot diagram of output laser recorded at the image plane position of the spatial light modulator, the third column and the fourth column of fig. 4 are focal spot diagrams after focusing corresponding laser calculated by experiments and theory respectively, the fifth column of fig. 4 is a laser diagram after conjugate phase reduction, and the sixth column is an orbital angular momentum spectrum of the output laser obtained after orbital angular momentum projection measurement by using the extra-cavity spatial light modulator and a single-mode fiber, and experimental results show that the digital laser can flexibly output orbital angular momentum comb laser with different dimensions according to requirements. The orbital angular momentum comb laser has potential applications in high-dimensional communications and encoding.

As shown in fig. 5, in embodiment 2, a phase-programmable laser according to the present invention further includes: and a beam splitting plate 112.

The beam splitting plate 112 is disposed on the optical path between the second lens 108 and the second spatial light modulator 111.

Both the front and back surfaces of the beam-splitting flat sheet 112 reflect the laser to output two paths of laser beams with opposite directions.

In the above-described embodiment 2, the half-wave plate 109 and the polarization splitting prism 110 in embodiment 1 are replaced with a splitting plate 112 having a fixed transmittance and reflectance ratio.

The two paths of laser beams output by the beam splitting flat plate 112 respectively carry the phases loaded on the first spatial light modulator 106 and the second spatial light modulator 111.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.

The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.

Claims

1. A phase arbitrarily programmable laser, comprising: the system comprises a pumping source, a focusing objective lens, an input concave mirror, a laser gain crystal, a reflecting concave mirror, a first spatial light modulator, a first lens, a second lens and a second spatial light modulator;

2. A phase-arbitrarily programmable laser as claimed in claim 1, wherein the pump source is a semiconductor laser.

3. A phase-arbitrarily programmable laser as claimed in claim 1 wherein the wavelength of the pump source is 879nm.

4. A phase arbitrarily programmable laser as claimed in claim 1, further comprising: a half wave plate and a polarization beam splitter prism;

5. A phase arbitrarily programmable laser as claimed in claim 1, further comprising: splitting a flat piece;

6. The laser of claim 5, wherein the two paths of laser light output by the beam splitting plate carry phases loaded on the first spatial light modulator and the second spatial light modulator, respectively.

7. The phase-arbitrarily programmable laser of claim 1, wherein the phase-arbitrarily programmable laser outputs laser light of an arbitrary phase structure, and the arbitrary phase-arbitrarily programmable laser light of the phase structure is generated after loading the arbitrary phase on the first spatial light modulator and the second spatial light modulator.