CN102064458B - Hollow round table resonant cavity gas laser - Google Patents

Abstract

The invention discloses a hollow circular truncated cone resonant cavity gas laser, belongs to the field of optics and optical engineering, and constructs and provides a gas laser for generating laser beams with special spatial distribution shapes. The light beam output by the laser evolves from a hollow light beam into a solid light beam and then evolves into a hollow light beam along with the increase of the transmission distance. The invention adopts the annular partial reflection output mirror, the waist spot position of the light beam is positioned outside the cavity, the power density which needs to be born by the output mirror is effectively reduced, the selection of the material of the output mirror is easy to realize even under the condition of high power, and the sample position is far enough away from the output mirror and can effectively utilize the maximum power density distribution position of the light beam. Because the invention realizes beam combination outside the cavity directly through the laser, high-power output is easy to realize. The invention can realize medium and small power laser and high power laser. The laser beam realized by the invention can be used for biomedicine, scientific research, special treatment of materials and the like.

Description

Hollow circular frustum resonator gas laser

Technical field The present invention relates to the field of optics and optical engineering, mainly a method and device for obtaining a gas laser with a special shape of a laser beam by a hollow circular frustum resonator.

Background Art The spatial shape of a laser beam is usually divided into a solid beam and a hollow beam. They play an important role in their respective fields of application. Realization of hollow beams can be obtained by transforming solid beams. The gas laser beam has good quality and stable directionality. Patent ZL2007100483280 constructs and provides a gas laser that can directly generate a hollow laser beam. The invention is simple and feasible. However, the waist spot of the output beam of the inventive laser is just at the position of the output mirror. In order to obtain a high-power laser, the selection of the material of the output mirror and the cooling treatment must be considered. And because the waist spot of the laser output beam is located at the position of the output mirror, where the power density distribution is the largest, in the process of use, because the sample must be placed at a certain distance from the output mirror to ensure that the output mirror will not be polluted by sputtering, so The place where the laser output power density distribution is maximum cannot be effectively utilized. The third is that the output beam of the laser needs to be focused to obtain hollow laser beams of various sizes including extremely small sizes.

SUMMARY OF THE INVENTION The present invention is aimed at the more universal method and device invented by the patent ZL2007100483280. The purpose is to construct and provide a gas laser that generates a laser beam with a special spatial shape. The beam output by the laser increases from The hollow beam evolves into a solid beam, and then evolves into a hollow beam. By properly setting the resonant cavity, the output beams of the two lasers can also realize the laser area of hollow drum shape. The invention not only inherits the advantages of ZL2007100483280 to directly generate hollow beams and gas laser beams with good quality and stable direction, but also overcomes the disadvantage that its output beams diverge from the position of the output mirror. Because the present invention adopts a rotationally symmetrical ring to partially reflect the output mirror, and the waist spot of the light beam is located outside the cavity, it effectively reduces the power density that the output mirror needs to withstand, and even in the case of high power, it is easy to select the material of the output mirror Realized, and the minimum beam radius position of the output beam is far enough away from the output mirror, so that the experimental sample can effectively use the maximum power density distribution position of the beam without splashing the output mirror. Since the invention realizes summing directly outside the cavity through the laser, it is easy to realize high power output. The invention can realize small and medium power lasers and high power lasers, and the laser beams realized by the invention can be used in biomedicine, scientific research, and special treatment of materials.

The purpose of the present invention is achieved by the following measures: the device of the hollow circular platform gas laser is divided into helium-neon laser or carbon dioxide laser according to the laser working substance, adopts the radio frequency discharge mode that is easy to realize glow discharge in the special-shaped discharge area, and the laser is characterized in that The resonant cavity is a hollow frustum-shaped resonant cavity. The bottom of the resonant cavity is a rotationally symmetrical concave circular full-reflection mirror, and the top is a rotationally symmetrical convex circular partial reflection output mirror. The frustum interlayer is the laser medium area. The concave mirror surface and the convex mirror surface are rotationally symmetrical about the central axis of the frustum-shaped medium area. The transmission light clusters in the longitudinal section of the resonator along the central symmetric axis of the laser medium area form a concave-convex stable cavity, which is called hollow. The sub-cavity of the frustum-shaped resonant cavity, the cavity axis of the sub-cavity intersects the central symmetry axis of the laser medium area, and the position of the waist spot of the output beam of the sub-cavity can be set at the distance between the output mirror and the symmetry axis of the sub-cavity and the laser medium area. The points of intersection of the central symmetry axes may also be coincident with or outside of the intersection points. Therefore, the laser provided by this construction method has the advantage that the volume of the gain region and the output power are much larger (order of magnitude increase) compared with the general gas laser with the same discharge region length. Since the waist spot of the output beam is located outside the output mirror, in the same In the case of output power, the output mirror of the present invention needs to bear much less power per unit area than the output mirror of the patent ZL2007100483280 (order of magnitude reduction), and because the waist spot of the output beam is located outside the output mirror, it is beneficial for the sample to effectively use the beam to the maximum The power density distribution position is more practical than the patent ZL2007100483280 (the waist spot of the output beam is located on the output mirror). Therefore, a laser device with a smaller volume and higher output can be made. Moreover, the position of the waist spot of the sub-cavity can be set reasonably according to the needs, so that the spatial distribution of the beam can evolve from a hollow beam to a solid beam and then to a hollow beam. The low-power output beam of the present invention can be used in laser biomedical research (realizing optical wrench, optical tweezers, optical acupuncture, etc.), microelectronics, and laser teaching experiments. High-power helium-neon lasers can be used in photodynamic medical treatment. High-power carbon dioxide lasers can be used for special processing of materials.

For helium-neon lasers, the discharge tube is made of glass or quartz tube. Carbon dioxide laser, the laser wavelength ranges from 9.2 to 10.8 microns, the discharge tube is made of glass or quartz tube or other insulating materials, and the large carbon dioxide laser adopts radio frequency discharge excitation method or pre-ionization excitation method, the working mode is continuous, and the work is driven by a fan Gas and water cooling heat dissipation method, when the radio frequency power supply is modulated to perform pulse discharge, the working mode is pulse.

BRIEF DESCRIPTION OF THE DRAWINGS Figures 1, 2, and 3 are perspective views of the structure of the hollow frustum-shaped gas laser device, a cross-sectional view of the device, and a schematic diagram of the cavity mirror in the vertical section of the hollow frustum-shaped laser along the axis.

In the accompanying drawings 1-3, 1 is a rotationally symmetrical concave annular total reflection mirror, 2 is an inner electrode, 3 is a hollow frustum-shaped discharge tube, 4 is an outer electrode, 5 is a water cooling jacket, and 6 is a rotationally symmetrical convex ring Part of the mirror, 7 is the fan, 8 is the radio frequency power supply and matching network, 9 is the gas storage tube, 1 is a concave mirror that is rotationally symmetrical relative to 10, and the curvature centers of the upper and lower parts of the mirror are located at O ₁₁ and O respectively in the section. ₁₂ , the radius of curvature is r ₁ , 6 is a convex mirror that is rotationally symmetrical with respect to the axis 10, the centers of curvature of the upper and lower parts of the mirror in the section are located at O ₂₁ and O ₂₂ respectively, the radius of curvature is r ₂ , l is mirror 1 And the distance between the mirror 6, that is, the length of the discharge tube. When being used for the helium-neon laser, in accompanying drawing 1-2, 5 and 7 are unnecessary, so when being used for this laser, 5 and 7 are cancelled. Among Fig. 2, 10 is the axis of symmetry of the truncated conical gas laser medium area, which is consistent with 10 in Fig. 3, and 11 is the intersection line of the central conical surface of the truncated conical gas medium area and the longitudinal section, and is also the axis of the light cluster in the longitudinal section And the sub-cavity axis of the resonant cavity in this section area, the waist spot positions of the output beams of the upper and lower sub-cavities are located at O ₀₁ and O ₀₂ respectively, and the intersection point of the axis 10 and the axis 11 is O. O ₀₁ and O ₀₂ can be designed to be located between the mirror 6 and the intersection point O, or both can coincide with the point O. θ is the apex angle of the central conical surface, a is the radial width of the gas medium zone, and l is the length of the medium zone. When the discharge tube 3 is pumped into a high vacuum, it is filled with a gaseous laser medium, and the medium is excited by the radio frequency discharge of the electrodes 2 and 4, and the stimulated radiation induced by spontaneous emission transmitted along the axis 11 of any cross-section shown in Figure 2 is received Amplified, and repeatedly reflected by mirrors 1 and 6 in this section and oscillation is established, the output is given by the transmission of mirror 6, when the gas medium needs to be cooled, it is performed by 5 and 7, when the gas medium does not need to be cooled, then 5 and 7 are not established, and now the connecting pipes of 5 and 7 and the discharge tube 3 are blocked by vacuum sealing, and the gas storage tube 9 can make the laser have more working substances and prolong the service life.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

The rotationally symmetrical concave annular total reflection mirror 1 of the present invention adopts a circular optical glass or a quartz block as a base, is suitable for He-Ne lasers and _CO2 lasers, and adopts a round copper block with good compactness and high hardness as a base , which is suitable for very high-output CO ₂ lasers, use a hole cutting device to cut the middle part according to the size of the inner edge of the ring mirror, but the middle part should be glued together with the ring block to facilitate grinding. The abrasive tool for grinding the mirror surface is made of low-carbon steel material and processed by CNC machine tools according to the design. Since the mirror surface does not have a single center of curvature, the abrasive tool does not have a single center of curvature. Therefore, it is more difficult to design and process, but its curved surface has strict Due to the symmetric nature of the rotation axis, there is no major difficulty in the processing of abrasive tools. After the abrasive tool is processed, the mirror grinding process should still maintain strict rotational axis symmetry requirements. After the mirror surface is ground and polished, remove the glued piece in the center to obtain a rotationally symmetrical curved surface mirror. After strict cleaning and full plating The back of the anti-film can be used on the device of the present invention. Convex ring partial reflection mirror 6 of the present invention, grinding process is consistent with the grinding process of mirror 1, and difference is that mirror 6 is a convex surface as a partial reflection mirror reflective surface coating partial reflection film, and the other side opposite to the convex surface faces the center from Viewed from the direction of the axis of symmetry, it is conical, and the generatrix of the conical shape is perpendicular to the cavity axis of the concavo-convex cavity in the section. The material of the base of the mirror 6 can be selected from glass for the helium-neon laser, and can be selected from germanium or zinc selenide according to the power requirement for the carbon dioxide laser.

The hollow frustum-shaped discharge tube 3 of the present invention is made by injecting glass or quartz molten liquid into a graphite mold at a certain temperature for a He-Ne laser and then gradually cooling it. The hollow frustum-shaped discharge tube is composed of two layers of frustum-shaped glass or quartz tubes inside and outside, so there should be two sets of graphite molds. Graphite has good strength, so it can be machined on the lathe more accurately according to the design, and the accuracy can reach 0.1 mm. When the mold is longer, several pieces of graphite material can be processed in sections and then assembled, and certain auxiliary fixtures can be used for the inner and outer layers of the mold. If the precision of the mold is not enough after use, it should be repaired or replaced with a new mold. The hollow truncated circular discharge tube of the present invention is made of aluminum, copper or thin stainless steel for the _CO2 laser, and the inner and outer hollow truncated circular metal tubes are directly used as two discharge electrodes.

During the assembly process of the laser of the present invention, the support and fixation of the inner and outer circular table surfaces of the hollow truncated circular discharge tube 3 of the present invention are realized by using special brackets. When it is a helium-neon laser, the bottom and top of the two glass or quartz circular table tops are all ground, the longitudinal section of the bottom ring mirror 1 is a concave surface, the diameter of the midpoint passing through the concave surface is parallel to the generatrix of the circular table, and the top ring mirror The reflective surface of the longitudinal section of 6 is a convex surface, and the diameter passing through the midpoint of the convex surface is parallel to the generatrix of the circular frustum. The back surface of the mirror 1 is ground into a plane. When the mirror 1 and the hollow frustum discharge tube are glued together, the back plane of the mirror 1 is perpendicular to the symmetry axis 10 of the hollow frustum discharge tube. The back surface of the mirror 6 is ground into a conical surface. The longitudinal section of the tapered surface is a straight line perpendicular to the generatrix of the hollow circular frustum discharge tube. Choose a glass or quartz ring with two sides parallel to each other and high flatness, the inner radius of the ring is slightly smaller than the inner radius of the bottom of the inner table, and the outer radius is slightly larger than the outer radius of the outer bottom of the outer table. Place this ring on the flat top of a metal bracket that is not too high, then place the slightly loose mirror 1 whose inner and outer edges match the size of the bottom of the truncated tube on the ring, and place the lighter electrode on the ring. The inside of the inner frustum-shaped glass or quartz tube, and then place the bottom of the inner frustum-shaped tube on the ring and within the inner edge of the axisymmetric curved mirror, then place the bottom of the outer circular table on the ring and Set on the outer edge of the mirror 1, because the processing of the components ensures the accuracy, so the requirements can be met after proper monitoring of the optical calibration instrument and proper adjustment of each component through auxiliary means, and then use vacuum sealant to seal the mirror 1, inside and outside The circular platform tube and the ring are glued together, and the mirror 6 on the top is installed and glued under the monitoring of the calibrated light beam that has been aligned with the axis in advance. Then install the outer electrodes. The laser can work vertically on the bracket and output from the top, which has the advantages of easy assembly and little stress on the optical components. It can also be placed horizontally or upside down after assembly, but the support should be treated before it is placed horizontally or upside down, so that it has a certain strength of auxiliary support for the inner and outer layer of the frustum-shaped tube, so that the inner and outer layers can be placed horizontally or upside down. The gravity of the circular platform tube and the electrode is almost all supported by the bracket, and the laser output mirror outputs from the side or from below. When it is a carbon dioxide laser, since the inner and outer frustum-shaped tubes are metal tubes and serve as electrodes at the same time, the strength of the tube is very high, and its support problem is easy to solve. The preparation and assembly process before assembly are basically the same as those of the helium-neon laser. It is worth noting The problem lies in the insulation between the two electrodes. When using a glass or quartz substrate axisymmetric curved mirror, there is no problem if it is coated with a dielectric film. If it is coated with a metal film, it should be between the bottom of the two cones and the connection of the total reflection mirror. There is an insulating layer, but the voltage of the RF power supply is relatively low.

After the laser is assembled, the discharge tube and connecting parts are pumped into a high vacuum. For helium-neon lasers, when the vacuum degree reaches 10 ^-6 × 133.3Pa, according to the ratio of Ne: He = 1: 8, the pressure of the mixed gas is 0.8 × 133.3Pa, and the reflectivity of the half mirror to the light wave with a wavelength of 0.6328 microns is 98%, the reflectivity of the total reflection mirror is above 99.8%, and the output can be obtained by applying radio frequency discharge to it. For carbon dioxide lasers, when the vacuum degree reaches 10 ^-3 × 133.3Pa, according to CO ₂ : N ₂ : He = 1: 1.5: 7.5, the total pressure is 10 × 133.3Pa, and the reflectivity of the half-reflector to 10.6 micron wavelength light wave is 80%, the reflectivity of the total reflection mirror is over 99%, and the output can be obtained by applying radio frequency discharge to it.

Embodiment The discharge tube 3 adopts a 300 mm long hollow truncated glass tube, the distance between the inner and outer layers of the truncated truncated tube is a=4 mm, the apex angle of the truncated circular truncated tube is 2.29 degrees (0.04 radians), and the total reflection mirror 1 is a rotationally symmetrical concave circular ring mirror, the inner and outer rim radii are respectively: 16 millimeters and 20 millimeters, and the radius of curvature of the concave surface of the section is 1100 millimeters; The radius of curvature of the convex surface is 900 mm, and the concave-convex cavity of the cross-section constitutes a stable cavity. The beam wavelength output by mirror 6 is 632.8 nanometers, the annular beam ring width is 0.66 mm, the dark center radius of the annular beam is 11.67 mm, and the outer ring radius of the annular beam is 12.33 mm. The ring width of the ring beam at a distance of 600 mm is 0.53 mm, the dark center radius of the ring beam is 1.73 mm, and the outer ring radius of the ring beam is 2.26 mm.

Hollow frustum-shaped resonator gas laser, including rotationally symmetrical concave annular total reflection mirror, hollow frustum-shaped discharge tube, rotationally symmetrical convex circular partial reflector, inner electrode, outer electrode, gas storage tube, fan, RF power supply and matching network , water cooling jacket, referring to Fig. 1 to Fig. 2, the rotationally symmetrical concave annular total reflection mirror 1 is connected with the bottom of the hollow frustum-shaped discharge tube 3, the convex circular ring partial reflector 6 is connected with the top of the discharge tube 3, and the inner electrode 2 Close to the inside of the discharge tube 3 or the inner electrode directly from the inner wall (when it is a metal material), the outer electrode 4 is close to the outside of the discharge tube or directly from the outer wall to the outer electrode (when it is a metal material), the storage The gas tube 9 is connected to and surrounds the discharge tube, the water cooling jacket 5 surrounds the discharge tube, the fan 7 is connected to the discharge tube through the gas storage tube, and the radio frequency power supply and matching network 8 are connected to the inner electrode 2 and the outer electrode 4 . It is characterized in that the discharge tube 3 is a hollow frustum-shaped discharge tube, the inner and outer walls of which are frustum-shaped tubes, and the discharge area is formed by the frustum-shaped interlayer space between the two frustum-shaped tubes, and its bottom and top are respectively composed of total reflection mirror 1 and Part of the reflector 6 is vacuum sealed, so that the hollow frustum-shaped interlayer space can be evacuated to a high vacuum, and the helium-neon mixed gas or the carbon dioxide, nitrogen, helium mixed gas is filled into the discharge tube 3 under high vacuum conditions, and the characteristic is that the resonant cavity It is a hollow frustum-shaped resonant cavity, which is composed of a rotationally symmetrical concave annular total reflection mirror 1 installed at the bottom of the hollow frustum-shaped discharge tube and a rotationally symmetrical convex annular partial reflector 6 installed at the top of the discharge tube. The total reflection The axis of symmetry of the mirror 1 and the axis of symmetry of the partial reflection mirror 6 coincide with the axis of the discharge tube 3. In any section of the laser along the axis of the discharge tube, the total reflection mirror 1 and the partial reflection mirror 6 have two symmetrical centers of curvature respectively. Distributed on both sides of the discharge tube axis, the resonant cavity forms two concave-convex cavity sub-cavities for the light clusters in the section, designed as a stable cavity, and the waist spot of the output beam of the sub-cavity is located outside the cavity.

Compared with the existing hollow laser beam generation technology, the present invention has the following characteristics:

1. The beam generated by the present invention evolves into a solid beam and then evolves into a hollow beam as the transmission distance increases.

2. The present invention uses a gas laser with good beam quality and stable directionality.

3. The present invention proposes a hollow truncated circular resonator to directly generate a hollow laser beam, and the acquisition of the hollow laser beam has good repeatability.

4. The wavelength range of the present invention is wide, which is suitable for various needs.

Compared with the existing patent ZL2007100483280, the present invention has the following characteristics:

1. The section of the resonance cavity adopted in the present invention along the axis of symmetry is a concave-convex stable cavity (sub-cavity), and the waist spot of the output beam of the sub-cavity is located outside the cavity. For the same high power situation, the power density distribution that the output mirror needs to bear is greatly reduced (order of magnitude lower).

2. The position of the minimum beam radius of the output beam of the present invention is far enough from the position of the output mirror, so that the experimental sample can effectively use the position of the maximum power density distribution of the beam without splashing the output mirror.

3. In the present invention, the laser beam is directly realized outside the cavity, and high power output can be easily realized.

Claims (2)

1. A hollow circular frustum resonator gas laser device is characterized in that the resonant cavity is a hollow circular frustum shape, and the gain medium is a hollow circular frustum shape, and the light beam output by this hollow circular frustum resonator gas laser device increases from the hollow light beam with the increase of the transmission distance Evolving into a solid beam, and then evolving into a hollow beam, the hollow frustum resonator gas laser device is attached to the bottom of the hollow frustum-shaped discharge tube with a rotationally symmetrical concave circular ring-shaped total reflection mirror (1), and on the top of the hollow frustum-shaped discharge tube Attach a rotationally symmetrical convex annular partial reflector (6), the rotationally symmetrical convex annular partial reflective mirror (6) is used as an output mirror, and the hollow circular platform resonant cavity is resonant in any longitudinal section along the central symmetry axis (10). For the light clusters, two concave-convex cavities that are independent of each other and axisymmetric to the central symmetry axis (10) of the hollow frustum resonator are formed. The cavity axis (11) of the cavity itself intersects the central symmetry axis of the hollow circular frustum resonator at point O, and the waist spot positions of the output beams of the two concave-convex cavities coincide with the intersection point O, or do not coincide with the intersection point O. At this time, the rotationally symmetrical concave ring The longitudinal section of the shaped total reflection mirror (1) is a concave total reflection mirror, the longitudinal section of the rotationally symmetrical convex ring partial reflection mirror (6) is a convex surface partial reflection mirror, and the output surface end is a straight line. 2. A hollow circular table resonator gas laser device, comprising glass or quartz discharge tube (3), a rotationally symmetrical concave annular total reflection mirror (1), a rotationally symmetrical convex annular partial reflector (6), an inner electrode ( 2), external electrode (4), gas storage tube (9), fan (7), water cooling jacket (5), radio frequency power supply and matching network (8), rotationally symmetrical concave annular total reflection mirror (1) and discharge tube (3) Bottom connection, rotationally symmetric convex ring partial reflection mirror (6) is connected to the top of the discharge tube (3), the inner electrode (2) is close to the inner wall of the discharge tube (3), and the outer electrode (4) is connected to the discharge tube (3) The outer wall of the tube (3) is closely attached, the radio frequency power supply and matching network (8) are connected with the inner electrode (2) and the outer electrode (4), and the gas storage tube (9) is connected with the discharge tube (3) and surrounds the discharge tube (3) , the water-cooling jacket (5) is connected to the outer wall of the discharge tube (3), and the fan (7) is connected to the discharge tube (3). A frustum-shaped tube, the discharge area is formed by a hollow frustum-shaped interlayer space between two frustum-shaped tubes. The bottom and top of the hollow frustum-shaped discharge tube are respectively composed of a rotationally symmetrical concave annular total reflection mirror (1) and a rotationally symmetrical convex circular mirror (1). The ring partial reflection mirror (6) is vacuum sealed, so that the hollow frustum-shaped interlayer space can be evacuated to a high vacuum, and the helium-neon mixed gas or the carbon dioxide, nitrogen, helium mixed gas is charged into the discharge tube under high vacuum conditions.

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