CN104577680B - Axicon, optical resonator and laser - Google Patents

Abstract

The present invention is suitable for optical technical field, provides a kind of axicon, is coniform crystal axicon, including the conical surface and bottom surface, and the angle theta between the conical surface and bottom surface meets：The light of central shaft transmission of axicon is parallel to after the conical surface is incident to axicon inside, can be totally reflected in bottom surface, and meet：When light is injected and projected through the conical surface, the reflectivity of parallel component is respectively less than or is equal to 0.5%.The optical principle that the present invention is propagated using total reflection principle and light in medium and air, the base angle θ of axicon is defined, incident light is set to be totally reflected in the bottom surface of axicon, reflection loss of the parallel component on the conical surface of axicon is limited within 1% simultaneously, parallel component photon is caused to form radial polarisation laser in intracavitary oscillation amplification.The axicon is simple for structure, can effectively select parallel component photon to form intracavitary oscillation, suitable in the equipment for generating radial polarisation light.

Description

Axicon, optical resonator and laser

Technical field

The invention belongs to optical technical field, more particularly to a kind of axicon, optical resonator and laser.

Background technology

Polarization is one of essential characteristic of light, and common polarised light has linearly polarized light, elliptically polarized light, circularly polarized light and diameterTo polarised light, since radial polarisation light has perfect axial symmetry distribution character so that it with linearly polarized light, circularly polarized light and ellipseCircularly polarized light, which is compared, many dramatically different characteristics.As radial polarisation light have along the symmetrical field distribution of optical axis and inThe beam arrangement of empty circular ring shape；Radial polarisation light can generate the minimum coke for surmounting diffraction limit when high numerical lens focusSpot, smaller than the focal beam spot of linear polarization, circular polarization, elliptical polarization is more, and becomes very in the longitudinal electric field of focus areaBy force；Radial polarisation light only has lateral magnetic field and the electric field along axis longitudinal direction；Radial polarisation just eigenstate of polarization, it is tangentially brilliant in CWhen being propagated in body, crosstalk will not occur.In recent years, these characteristics of radial polarisation light have obtained many applications.Such as guidingAccelerate with capture particle, particle, improve microscopical resolution ratio, Metal Cutting and improve storage density etc., with peopleTo the understanding to deepen continuously of radial polarisation light, it will be applied in more and more fields.

The first beam radial polarisation light was obtained in 1972 by testing by the Y.Mushiake of Japan in the world；Domestic theA branch of radial polarisation it is just glued using four pieces of fan-shaped half slides by the Zhuan Jiejia of Institute of High Energy Physcis, Academia Sinica andAt optical component generate.In the past 10 years, scientific research personnel finds various effective methods to generate radial polarisation light one after another.DiameterIt is divided to two classes, i.e. intracavitary method and chamber external schema conversion method to the production method of polarised light.Radial polarisation light is generated by intra-cavitary methodologyHave：Jianlang Li et al. people generate radial polarisation light in optical fiber laser with dual circular shaft prism；Inon Moshe etc.People selects the pattern of polarization by the way of placing aperture on thermotropic bifocal position in laser cavity；Ram Oron et al.In laser cavity radial polarisation light is generated with discontinuous phase element；A.V.Nesterov et al. is placed in intracavitary has axisRadial polarisation light is generated to polarization selectivity sub-wavelength diffraction.

It is above-mentioned that an intracavitary improvement and design generation radial polarisation just complicated engineering is carried out to existing laser,For engineers and technicians, more feasible method is External reforming using the progress of certain optical device outside laser cavity.I.J.Cooper, S.Quabis et al. are generated using 4 pieces of fan-shaped half wave plate groups at a round optical device approximate radial inclinedShake light；G.Machavariani et al. is then improved using 8 fast half-wave plates, and generation tends to perfect radial polarisation light；C.Steve et al. generates radial polarisation light using the two orthogonal linearly polarized light in beam polarization direction of interferometer coherent superposition；M.Stalder generates radial polarisation light using twisted nematic liquid crystal polarization converter.The method of above-mentioned generation radial polarisation light is stillMore complex, cost is also higher, and the present invention will provide the scheme of another generation radial polarisation light effectively easily implemented.

Invention content

The purpose of the present invention is to provide a kind of axicons simple for structure, easily fabricated, for being produced in laser resonatorRaw radial polarisation light.

The invention is realized in this way a kind of axicon, is coniform crystal axicon, including the conical surface and bottom surface, instituteThe angle theta stated between the conical surface and bottom surface meets：The light for being parallel to the central shaft transmission of the axicon is incident to through the conical surfaceBehind axicon inside, it can be totally reflected in the bottom surface, and meet：When light is injected and projected through the conical surface, put downThe reflectivity of row component is respectively less than or is equal to 0.5%.

Another object of the present invention is to provide a kind of laser resonator, including laser output mirror and the axicon,The laser output mirror is parallel with the bottom surface of the axicon, and the laser output mirror forms Fabry-Perot with the axiconSieve resonant cavity.

Another object of the present invention is to provide a kind of lasers, including above-mentioned laser resonator.

The optical principle that the present invention is propagated using total reflection principle and light in medium and air, to the base angle θ of axiconIt is defined, makes incident light that total reflection occur on the bottom surface of axicon and generate transmission loss in bottom surface to avoid parallel component,When simultaneously by making conical surface incidence and outgoing of the light by axicon to the restriction at base angle, the reflection loss of parallel component existsWithin 0.5%, and then incident light is made often to pass through an axicon, the loss of parallel component is far smaller than the loss of vertical component,And it is not more than 1%, cause parallel component photon to form radial polarisation laser in intracavitary oscillation amplification.The axicon is simple for structure, justIt is at low cost in design and manufacture, parallel component photon can be effectively selected to form intracavitary oscillation, be suitble to this field engineering technology peopleMember implements, suitable in the equipment for generating radial polarisation light.

Description of the drawings

Fig. 1 is the structural schematic diagram of axicon provided in an embodiment of the present invention；

Fig. 2 is light incidence Nd provided in an embodiment of the present invention：The index path of YAG dielectric surfaces；

Fig. 3 is propagation path schematic diagram of the light provided in an embodiment of the present invention inside and outside axicon；

Fig. 4 is that the relationship of the incidence angle and the incidence angle of incident bottom surface of light incidence axicon provided in an embodiment of the present invention is bentLine；

Fig. 5 is light provided in an embodiment of the present invention from the anti-of parallel component when axicon first conical surface incidence and vertical componentPenetrate the relation curve of rate and base angle θ；

Fig. 6 is light provided in an embodiment of the present invention from the saturating of parallel component when axicon first conical surface incidence and vertical componentPenetrate the relation curve of rate and base angle θ；

Fig. 7 is the anti-of parallel component and vertical component when light provided in an embodiment of the present invention is projected from second conical surface of axiconPenetrate the relation curve of rate and base angle θ；

Fig. 8 is the saturating of parallel component and vertical component when light provided in an embodiment of the present invention is projected from second conical surface of axiconPenetrate the relation curve of rate and base angle θ；

Fig. 9 is the structural schematic diagram of laser resonator provided in an embodiment of the present invention（One）；

Figure 10 is the structural schematic diagram of laser resonator provided in an embodiment of the present invention（Two）.

Specific implementation mode

In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to the accompanying drawings and embodiments, rightThe present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, andIt is not used in the restriction present invention.

The specific implementation of the present invention is described in detail below in conjunction with specific embodiment：

Fig. 1 shows the structural schematic diagram of axicon provided in an embodiment of the present invention, and Fig. 2 shows light incidence Nd：YAG is situated betweenThe index path on matter surface, Fig. 3 show that propagation path schematic diagram of the light inside and outside axicon illustrates only for convenience of descriptionPart related to the present embodiment.

Axicon provided in an embodiment of the present invention is used to carry out incident light the selection of parallel component, and then is formed radial inclinedShake light, which is coniform crystal axicon, which can be laser gain crystal, can also be that non-gain is brilliantBody, including the conical surface and bottom surface are defined the base angle of the axicon according to the material of axicon, can be to the parallel of incident lightComponent is selected to form radial polarisation light, a kind of concrete implementation mode presented below：With reference to figure 1, the axicon 1 is by yttriumAluminium garnet（YAG）Crystal or neodymium-doped yttrium-aluminum garnet（Nd：YAG）Crystal pro cessing forms, and the shape of axicon 1 is isoceles triangleShape rotated a circle as axis using its central axes to be formed it is coniform comprising bottom surface 11 and the conical surface 12.With further reference to Fig. 2, S in figure⁽ⁱ⁾For incident light, S^(r)For reflected light, S^(t)Material for transmitted light, axicon 1 is YAG or Nd：YAG, YAG and Nd：The folding of YAGThe rate of penetrating is sufficiently close to, and based on 1.82, the light obtained according to Fei Nier formula enters YAG or Nd from air：YAG media are rolled overThe formula of transmissivity and reflectivity when penetrating and reflecting is as follows：

R_∥+T_∥=1 （3）

R_⊥+T_⊥=1 （4）

Wherein, T_∥For the transmissivity of parallel component, T_⊥For the transmissivity of vertical component, R_∥For the reflectivity of parallel component,R_⊥For the reflectivity of vertical component, θ_iFor the incidence angle on light incidence axicon surface, θ_tEnter the refraction of axicon for anaclasisAngle.

With continued reference to FIG. 3, the figure illustrates the propagation path of light by taking 1 one longitudinal section of axicon as an example.For convenience of description,The top half of the conical surface 12 in Fig. 3 is known as first conical surface 121, lower half portion is known as second conical surface 122, axicon base angleFor θ, the angle of " base angle " between bottom surface 11 and the conical surface 12, that is, from the vertex O of axicon 1 draw perpendicular to the conical surface 12With the angle between the straight line L and bottom surface 11 of 11 intersection of bottom surface.The light of flat output mirror reflection is parallel to the angles θ in axicon 1First reflection and refraction, refraction angle θ occur on first conical surface 121 for first conical surface 121 of axis incidence axicon 1₁,The light of axicon is refracted into θ₂Through bottom surface 11 second secondary reflection and refraction, refraction angle θ occur for incident bottom surface 11₃, refractionThe light for going out axicon 1 is lost, and third secondary reflection and refraction, folding occur at second conical surface 122 for the light reflected by bottom surface 11Firing angle is θ.Light passes through an axicon 1, it may occur that triple reflection and refraction.It is flat due to include in the refracted light of bottom surface 11Row component, which is more than, is even far longer than vertical component, therefore in order to reduce loss of the parallel component at bottom surface 11, the present embodimentIt using total reflection principle, is defined by the base angle θ to axicon 1, is allowed to meet the condition of total reflection.When light is penetrated by mediumWhen to air, meet optics formula：n_Air×sinθ′=n_Nd：YAG× sin θ ' ', wherein θ ' is light by medium directive airRefraction angle, θ ' ' are that the incidence angle on light incident medium surface is totally reflected when θ '=90 °, n_Air=1, n_Nd：YAG=1.82,Therefore θ ' '=33.3293 °, the critical angle θ of total reflection_c=θ′′=33.3293°.The base angle θ of the axicon 1 of the present embodiment is underFormula is stated to be calculated：

sinθ=1.82sinθ₁（5）

θ=θ₁+θ₂（6）

θ₂=θ′′=33.3293° （7）

Thus it obtains：θ=62.496 ° can be sent out when light axicon incident with 62.496 °≤θ≤90 ° of incidence angle in bottom surfaceRaw total reflection, avoids parallel component transmission loss.According to above-mentioned formula, figure 4 also shows the incidence angle θ of incident axicon with enterPenetrate the incidence angle θ of bottom surface 11₂Relational graph.Because light is parallel to the incidence of axicon central axes, in turn, the bottom of axicon 1Angle is equal with incidence angle θ, and base angle θ meets 62.496 °≤θ≤90 °.

Foregoing provide the optional ranges for meeting the base angle θ that light is totally reflected in axicon 1, this is to realize parallel pointMeasure one of the condition of selection.In addition, light occurs to reflect and reflect in first conical surface 121 and second conical surface 122, vertical component andThe loss of parallel component is included in the reflection loss of first conical surface 121 and second conical surface 122.For being configured to cause parallel pointThe optical resonator for measuring photon oscillation, to select the photon of parallel component in intracavitary, it is necessary to make the photon numbers of vertical componentLoss rate be much larger than parallel component photon numbers loss rate, for plane mirror and flat output mirror composition methodFabry-Perot-type optical resonator, according to the use experience of theory of laser and industrial lasers resonant cavity, laser cavity internal reflectorReflectivity is necessary >=and 99%.The axicon 1 of the present embodiment acts as the effect of speculum in optical resonance intracavitary, i.e. axicon 1 is right>=99% is wanted in the reflectivity of the photon of parallel component, can be all-trans in the bottom surface of axicon 1 11 in the photon of parallel componentUnder the premise of penetrating, loss occurs mainly on the conical surface of axicon, the damage of the photon of parallel component on the conical surface of axiconConsume necessary≤1%, i.e. total reflectivity≤1% of the parallel component at first conical surface 121 and second conical surface 122.Further, light byIn the central axes incidence axicon 1 of axicon 1 reflection and refraction of light occur at first conical surface 121 for air parallel, due to axisThe axially symmetric structure of cone 1, light can be parallel to incident direction injection at second conical surface 122.Light is 1 from air incidence to axiconIt is incident on air, incidence angle and refraction angle reciprocity from axicon 1 with light, it is anti-at first conical surface 121 and second conical surface 122It penetrates rate and equally defers to formula（1）、（2）, according to above-mentioned formula（1）、（2）, the reflectivity of parallel component is in light parallel incident firstThe conical surface 121 and light are lost identical from being identical when the second 122 parallel injection of the conical surface.So parallel component is in the first coneThe reflectivity of face 121 and second conical surface 122 is ≤0.5%.

Further, light can be calculated in first conical surface 121, second conical surface in conjunction with the optics formula in the present embodiment122 reflectivity, the transmissivity of bottom surface 11, incident bottom surface 11 incidence angle θ₂, cirtical angle of total reflection θ_cAnd axicon base angle θRelationship, table 1 show above-mentioned calculating data, wherein Fig. 5,6,7,8 also respectively illustrate first conical surface of axicon and second conical surfaceThe relationship for locating parallel component and the reflectivity and transmissivity and base angle θ of vertical component, referring to following table：

By upper table as it can be seen that when base angle θ≤65.61 ° of axicon, parallel component is damaged in the reflection of first conical surface 121Consumption≤0.5%, in conjunction with the condition of above-mentioned total reflection：62.496 °≤θ≤90 °, show that the base angle θ of the axicon meets：62.496°≤ θ≤65.61 °, there are 2 ' tolerances, i.e. 62.496 ° of ± 2 '≤θ≤65.61 ° ± 2 ' with lower limiting value for the upper limit value of the range.Its maximum magnitude be 62.496 ° -2 '≤θ≤65.61 °+2 ', minimum zone be 62.496 °+2 '≤θ≤65.61 ° -2 ', preferablyRanging from 62.496 °≤θ≤65.61 °.

After the base angle θ of axicon 1 is carried out above-mentioned restriction, according to table 1 as it can be seen that when base angle θ=62.496 °, vertical componentReflectivity R_①⊥=0.3022, the reflectivity R of parallel component_①∥=3.6*10^-4, the proportion of goods damageds of vertical component and parallel component itThan being 839, when base angle θ=65.61 °, the reflectivity R of vertical component_①⊥=0.3419, the reflectivity R of parallel component_①∥=5*10^-3, the ratio between proportion of goods damageds are 68, and therefore, the loss of vertical component easily selects parallel component much larger than the loss of parallel componentPhoton simultaneously causes photon to vibrate in resonant cavity, and then generates radial polarisation laser.

The embodiment of the present invention is by by YAG or Nd：The base angle θ of YAG axicons 1 be limited to 62.496 ° of ± 2 '≤θ≤65.61 ° ± 2 ', makes incident light that total reflection occur on bottom surface 11 and generate transmission loss in bottom surface 11 to avoid parallel component, togetherWhen limit reflection loss of the parallel component on the conical surface 12 of axicon 1, make incident light often pass through an axicon 1, put downLoss≤1% of row component, to cause parallel component photon to form radial polarisation laser in intracavitary oscillation amplification.1 knot of axiconStructure is succinct, at low cost convenient for manufacturing and designing, and can effectively select parallel component photon to form intracavitary oscillation, be very suitable for thisDomain engineering technical staff implements, suitable in the equipment for generating radial polarisation light.

It is appreciated that the axicon can also use the crystal of other materials, the YAG crystal of Yb is such as mixed, is set according to above-mentionedMeter principle calculates the intracavitary oscillation that parallel component can be realized in its base angle range, and specific calculating process the present embodiment is no longer superfluousIt states.

The present invention further provides a kind of laser resonators comprising laser output mirror 2 and above-mentioned axicon 1, laserOutgoing mirror 2 is parallel with the bottom surface of axicon 1, which constitutes Fabry-Perot cavity with laser output mirror 2.Laser is defeatedAppearance 2 can be plane mirror.Such as Fig. 9, when the material of axicon 1 is non-gain crystal（Such as YAG crystal）When, in axicon 1 and swashGain media 3 is additionally provided between light output mirror 2（Such as Nd：YAG gain medias）, and in the profile pump of gain media 3.

Such as Figure 10, when the material of axicon 1 is gain crystal（Such as Nd：YAG crystal）When, axicon 1 and laser output mirror 2Between can not set gain media 3, axicon 1 itself is used as speculum and gain media, is pumped at this time in the end of axicon 1.It is of course also possible to gain media 3 be arranged between axicon 1 and laser output mirror 2, at this time simultaneously in the side of gain media 3And the end pumping of axicon 1.

Above-mentioned laser resonator carries out the selection of parallel component by axicon and is amplified to export diameter by vibrating back and forthTo polarization laser, novelty simple for structure, at low cost, exploitativeness is good.It is appreciated that including the laser of the laser resonatorWithin the scope of the present invention.

The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present inventionAll any modification, equivalent and improvement etc., should all be included in the protection scope of the present invention made by within refreshing and principle.

Claims (5)

1. a kind of axicon, which is characterized in that for coniform crystal axicon, including the conical surface and bottom surface, the conical surface and bottomAngle theta between face meets：The light for being parallel to the central shaft transmission of the axicon is incident to through the conical surface inside axiconAfterwards, it can be totally reflected, and meet in the bottom surface：When light is injected and is projected through the conical surface, parallel component it is anti-It penetrates rate and is respectively less than or is equal to 0.5%；The crystal axicon is YAG or Nd：YAG axicons, between the conical surface and bottom surfaceAngle theta is：62.496°≤θ≤65.61°.

2. a kind of laser resonator, which is characterized in that described to swash including laser output mirror and axicon described in claim 1Light output mirror is parallel with the bottom surface of the axicon, and the laser output mirror forms Fabry-Perot resonance with the axiconChamber.

3. laser resonator as claimed in claim 2, which is characterized in that described to swash when the axicon is YAG axiconsOptical cavity further includes the gain media being set between the axicon and the laser output mirror.

4. a kind of laser, which is characterized in that including the laser resonator described in claim 3.

5. laser as claimed in claim 4, which is characterized in that when the axicon in the laser resonator is YAG axial conesWhen body, pumping source is equipped in the side of the gain media；When the axicon in the laser resonator is Nd：YAG axiconsWhen, pumping source is equipped at the bottom center of the axicon.