CN1630148A - Annular laser beam generator having orbital angular momentum - Google Patents

Abstract

A circular laser beam generator having orbital angular momentum consists of semiconductor laser, coupling lens, laser crystal, output coupling lens, mode matching lens and three torsional cylindrical mirrors. Said invention adopts semiconductor laser pump solid laser to general Hermite-Gauss light beam, then making the Hermite-Gauss light beam pass through optical system composed of three torsional cylindrical mirrors C1, C2, and C3 wherein the C1 and C3 have equal focus and mutual parallel symmetric axle, the C2 focus is twice of that of C1 and C3, C2symmetric axle is vertical to that of C1, when C1 symmetric axle is in 90 degree with the symmetric axle of Hermite-Gauss light beam, the circular laser beam having orbital angular momentum is generated. Said invention can generate circular light beam by normal optical component.

Description

Loop laser beam generator with orbital angular momentum

Technical field

The invention belongs to laser technology field.

Background technology

The angular momentum of light beam has two kinds: because the angular momentum that the angular momentum that the polarization characteristic of light beam produces and spirality phase structure (torsiversion mutually) owing to light beam produce.Be familiar with by people already by the beam angle momentum that the polarization characteristic of light beam causes, for example make circularly polarized light pass through a half-wave band plate that hangs with silica fiber, can be observed because the angular momentum that the circular polarization characteristic of light beam causes, and can measure the angular momentum that causes by polarization by the moment of torsion of accurate measuring optical fiber.And the orbital angular momentum of light beam just just is familiar with by people in recent years, studies show that when light beam contains the relevant position of angle and distributes mutually (also claim torsiversion mutually or spiral position phase), this type of light beam have and the angle position relevant angular momentum (being called as orbital angular momentum) that distributes mutually.If contain the light field function of the light beam of torsiversion phase be

U (r, φ)=f (r) exp[ig (φ)] (1) then the orbital angular momentum of this light beam be

$J=-\frac{2}{\mathrm{\ω}}P\frac{\∂g\left(\mathrm{\φ}\right)}{\∂\mathrm{\φ}}---\left(2\right)$

Wherein r is a position vector, the torsiversion phase of g (φ) expression light beam, and ω is the angular frequency of light field, P is the gross energy of light beam.

Annular laser beams with orbital angular momentum has application prospect at aspects such as laser biology, genetic engineering and material science.For example, the laser beam and the light tweezer that will have orbital angular momentum combine, can realize to particulate contactless catch, translation and rotation, in the operating process of pair cell, avoid the damage of pair cell surface and inner organelle, therefore in artificial insemination and transgenic experiments process, can shorten required time, improve cell survival rate.

Summary of the invention

The object of the present invention is to provide a kind of method and apparatus that can produce annular laser beams, for applications such as biotechnology, material science provide a kind of new experimental technique and means with orbital angular momentum.

Generation provided by the invention has the method for the annular laser beams of orbital angular momentum, is divided into two steps:

(1) produces Ermy-Gaussian beam with the zlasing mode generator;

(2) utilization is reversed the cylindrical mirror optical system and Ermy-Gaussian beam is transformed to the annular laser beams with orbital angular momentum.

Realize that device of the present invention is made up of semiconductor laser, coupled lens, laser crystal, output coupling mirror, pattern matching lens, three cylindrical mirrors that reverse etc.

The generation of Ermy-Gaussian beam

In apparatus of the present invention, at first need produce the adjustable Ermy-Gaussian beam of order, it is realized by the solid state laser of semiconductor laser pumping.Specifically comprise: semiconductor laser pumping source, coupling optical system, laser crystal, optical resonator etc.The technical characterictic of each part is as follows: (1) laser pumping source adopts single tube semiconductor laser or semiconductor laser array, by coupling optical system pump light is focused on laser crystal.When laser crystal was the Nd:YAG crystal, pumping source was chosen the semiconductor laser that wavelength is 808nm; Also can adopt the semiconductor laser of optical fiber output to do pumping source.Two suitable optical medium films of end face plating of laser crystal.When the laser crystal that uses is Nd:YAG, the anti-reflection film of crystal front end face plating 808nm and the film that is all-trans of 1064nm, the anti-reflection film of crystal rear end face plating 1064nm.

(2) optical resonator is made up of total reflective mirror that directly is plated in the laser crystal front end face and output coupling mirror.Choosing of the radius of curvature of output coupling mirror should make laser works in the stable region.When outgoing mirror is a radius of curvature when being the concavees lens of 100mm, resonant cavity chamber length should be less than the radius of curvature of concavees lens.The deielectric-coating that the concavees lens plating has certain transmitance to oscillating laser, the size of its transmitance is by the pumping level decision of laser, and for example for the Nd:YAG laser of watt level semiconductor laser pumping, outgoing mirror generally gets 3% to the transmitance of 1064nm.

The generation of annular beam

Produce the employed cylindrical mirror of annular beam system by three cylindrical mirror C1, C2, C3 forms, and as shown in Figure 2, wherein the focal length of C1 and C3 equates, and symmetry axis is parallel to each other, and the focal length of C2 is C1, the twice of the focal length of C3, the C2 symmetry axis is vertical with C1.When the symmetry axis of the symmetry axis of C1 and Hermite-Gauss beam is π/4, can produce annular laser beams with orbital angular momentum.The size of f is mated with the Rayleigh length of the Ermy-Gaussian beam of outgoing after the spherical lens conversion.After the incident Ermy-Gaussian beam is by the cylindrical mirror optical transform system that satisfies above-mentioned relation, be transformed to have an orbital angular momentum reverse the symmetrical ring shaped light beam.

Main feature of the present invention is:

(1) diameter of the annular beam that produces and the variable size of orbital angular momentum;

(2) employed optical component is conventional optical element, behind the anti-reflection film of lens surface plating to incident light, and the energy conversion efficiency height;

(3) device is reliable and stable, and debugging is simple, and integrated easily, cost is lower.

Description of drawings

Fig. 1 is a systematic schematic diagram of the present invention.

Fig. 2 is the cylindrical mirror beam shaping system schematic diagram among the present invention.

Ermy-Gaussian beam (the TEM that Fig. 3 is in apparatus of the present invention to be produced _6,0) the hot spot pattern.

Fig. 4 is the hot spot pattern with the annular laser beams with orbital angular momentum that is produced among the present invention.

Fig. 5 is the overall structure schematic diagram with loop laser beam generator of orbital angular momentum.As shown in Figure 5, apparatus of the present invention are made up of two parts, comprise ld pumping solid state laser that produces Ermy-Gaussian beam and the beam shaping system of being made up of cylindrical mirror.Each component names is as follows: 1 temperature control system; 2 semiconductor laser pumping sources; 3 optical fiber (or coupled lens); 4 laser crystals; 5 deielectric-coating; 6 travel mechanisms; 7 output coupling mirrors; 8 spherical lenses; 9 cylindrical mirror C1,10 cylindrical mirror C2,11 cylindrical mirror C3,12 power source of semiconductor laser.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described further.

As shown in Figure 5, apparatus of the present invention are made up of zlasing mode generator and cylindrical mirror beam shaping system two large divisions.The effect of zlasing mode generator is to produce Ermy-Gaussian beam, and its pumping source is a semiconductor laser 2, and power source of semiconductor laser is 12, and the wavelength of semiconductor laser is by temperature control system 1 control.Semiconductor laser is coupled into optical fiber 3 and is used for the pumped solid laser crystal 4.In order to obtain Ermy-Gaussian beam, optical fiber 3 needs to be moved along horizontal direction in the plane perpendicular to optical axis by a travel mechanism 6.Laser crystal 4 and output coupling mirror 7 constitutes the optical resonator of solid state lasers, and wherein the plating of the front end face of laser crystal is high saturating and to the high anti-deielectric-coating 5 of oscillating laser to pump light.When the pump power of semiconductor laser was higher than the threshold pump power of solid state laser, the laser starting oscillation was also exported laser.The light beam of output is introduced into the beam shaping system that is made of cylindrical mirror 9, cylindrical mirror 10 and cylindrical mirror 11 through behind the spherical lens 8.Cylindrical mirror 9 is identical with the focal length of cylindrical mirror 11, and the focal length of cylindrical mirror 10 is twices of the focal length of cylindrical mirror 9, and the spacing of cylindrical mirror 9 and cylindrical mirror 10, cylindrical mirror 10 and cylindrical mirror 11 equals the focal length of cylindrical mirror 9.

The exportable annular laser beams with orbital angular momentum of the present invention, spot pattern when changing pump light focus on position on the crystal in perpendicular to the plane of optical axis, can change the diameter of annular beam and the size of orbital angular momentum as shown in Figure 4.

Claims (2)

1, a kind of generation has the generator that reverses the symmetrical ring shaped light beam of orbital angular momentum, this generator is by 2 semiconductor lasers, 3 coupled lens, 4 laser crystals, 7 output coupling mirrors, 8 pattern matching lens, three cylindrical mirrors that reverse (9, composition such as 10 and 11), it is characterized by: at first adopt ld pumping solid state laser to produce Ermy-Gaussian beam, the Hermite-Gauss beam that makes generation then is by three cylindrical mirror C1 that reverse, C2, the optical system that C3 forms, wherein the focal length of C1 and C3 equates, symmetry axis is parallel to each other, the focal length of C2 is C1, the twice of the focal length of C3, the C2 symmetry axis is vertical with C1; When the symmetry axis of the symmetry axis of C1 and Hermite-Gauss beam is π/4, can produce annular laser beams with orbital angular momentum; The diameter of the position change annular beam by regulating diode-end-pumped light and the size of orbital angular momentum.

2, a kind of experimental provision that is used to produce Ermy-Gaussian beam, it is characterized by: the pump beam scioptics coupled system of semiconductor laser output or optical fiber coupling, focus on the solid state laser, when in the plane vertical, changing the pumping position of Nd of semiconductor laser with the solid state laser optical axis, can obtain Ermy-Gaussian beam, the mode step of Hermite-Gauss beam is inferior to the pump light determining positions.

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