CN1332482C - Unstable laser cavity tunned by grating - Google Patents

Abstract

The invention relates to a grating tuning unstable laser resonant cavity, which is suitable for a high-power grating tuning unstable laser resonating cavity, and relates to a laser device. The laser resonant cavity of the present invention is composed of a convex spherical reflector, a concave spherical reflector with a central hole and a grating compound converging optical system behind it, and the convex spherical reflector, a concave spherical reflector with a central hole and a grating compound convergent The optical system has a common optical axis, and the grating normal forms a Littrow angle with the optical axis. The grating is a reflective concave spherical diffraction grating or a reflective plane diffraction grating. The cavity loss of the grating-tuned unstable laser resonator of the present invention is low, and can output high laser energy and laser power, and is suitable for various tunable lasers such as carbon dioxide lasers, carbon monoxide lasers, hydrogen fluoride/deuterium fluoride lasers, etc., in laser chemistry, atmosphere It has broad application prospects in transmission, laser processing, laser radar and other fields.

Description

Grating Tuned Unstable Laser Resonator

technical field

The invention relates to the technical field of lasers, in particular to an unstable laser cavity suitable for high-power grating tuning.

Background technique

High power lasers such as CO ₂ lasers often use unstabilized laser resonators. In some important applications, the wavelength of the laser output needs to be tunable. The existing tunable technology is to replace the concave spherical mirror with a convex lens-reflective plane diffraction grating compound optical system (references: R.Barbini, A.Ghigo, A.Palucci, S.Ribezzo.Line tunable TEA CO ₂ laser using SFUR configuration. Optics Communications, 1988, 68(1): 41-44). This system has the following disadvantages: 1. The resonant cavity using this composite optical system has a relatively large loss. This is because both surfaces of the convex lens need to be coated with an anti-reflection film, and the reflectivity of the grating, that is, the efficiency of the grating, cannot be very high at the current technological level, usually between 90% and 95%. 2. The grating is easily damaged under the direct irradiation of high-power laser. 3. The size of the required grating is very large, it is difficult to manufacture, and the price is relatively high.

Contents of the invention

The object of the present invention is to provide a new grating-tunable unsteady laser resonator suitable for high-power tunable lasers, which uses gratings to form a low-loss resonator to realize high-power tunable laser output.

In order to achieve the above object, the technical solution of the present invention is to provide a grating tuning unstable laser resonator, which is composed of a convex spherical reflector, a concave spherical reflector with a central hole and a grating composite converging optical system behind it. The spherical reflector, the concave spherical reflector with a central hole and the grating compound converging optical system share the same optical axis, and the normal line of the grating forms a Littrow angle with the optical axis.

Said laser resonant cavity, said convex spherical reflector and concave spherical reflector with central hole are metal reflectors, metal reflectors plated with gold or dielectric film, silicon base reflectors plated with gold or plated with dielectric film.

In the laser resonant cavity, the grating composite converging optical system is a reflective concave spherical diffraction grating.

Described laser resonant cavity, its described grating composite converging optical system also includes a converging lens, converging lens is positioned between the concave spherical reflective mirror with central hole and the grating, convex spherical reflective mirror, concave spherical reflective with central hole The mirror, the converging lens and the grating share the same optical axis.

The laser resonant cavity and the grating composite converging optical system further include a concave reflector, the concave surface of the concave reflector is forward, and is located behind the concave spherical reflector with a central hole and the grating. The convex spherical reflector, the concave spherical reflector with a central hole and the concave reflector share an optical axis; the grating is located on the front side of the concave reflector, and its reflective surface corresponds to the concave surface of the concave reflector.

In the laser resonant cavity, the concave reflector is a spherical reflector or an aspheric reflector.

The laser resonator, the composite grating converging optical system, also includes a beam expander, the beam expander is located between the concave spherical reflector with a central hole and the subsequent grating, and the convex spherical reflector, with a center The concave spherical reflector of the hole, the beam expander and the grating have the same optical axis.

Described laser resonant cavity, its described beam expander is made up of diverging lens and converging lens, and converging lens is positioned at the rear of diverging lens, convex spherical reflector, concave spherical reflector with center hole, divergent lens, converging lens and grating A total of one optical axis.

Described laser resonant cavity, its described beam expander is made up of convex reflector and concave reflector, the convex and concave surfaces of two mirrors are opposite, the convex surface of convex reflector is forward, the concave surface of concave reflector is backward, and the concave reflector The mirror is located at the front side of the convex reflector; the convex spherical reflector, the concave spherical reflector with a central hole and the convex reflector share an optical axis.

In the laser resonant cavity, the convex reflector and the concave reflector are spherical reflectors or aspheric reflectors.

In the laser resonant cavity, the grating is a reflective plane diffraction grating or a reflective concave spherical diffraction grating.

In the laser resonant cavity, the laser beam is directly coupled out from the edge of the convex spherical mirror.

The laser resonator adopts the side annular laser output mode, and a plane output coupling reflector with a central hole is set between the convex spherical reflector and the concave spherical reflector with a central hole, and the convex spherical reflector and the concave spherical reflector with a central hole The planar outcoupling mirror with a hole, the concave spherical mirror with a central hole and the grating composite converging optical system share an optical axis, and there is an inclination angle between the normal of the planar outcoupling mirror with a central hole and the optical axis, and the inclination range is 20° to 70°.

The cavity loss of the grating-tuned unstable laser resonator of the present invention is low, and can output high laser energy and laser power, and is suitable for various tunable lasers such as carbon dioxide lasers, carbon monoxide lasers, hydrogen fluoride/deuterium fluoride lasers, etc., in laser chemistry, atmosphere It has broad application prospects in transmission, laser processing, laser radar and other fields.

Description of drawings

Fig. 1 is a schematic diagram of a common untuned unstable laser resonator;

2 is a schematic diagram of an existing grating-tuned unstable laser resonator;

Fig. 3 is a schematic diagram of a grating-tuned non-stable laser resonator of the present invention;

Fig. 4 is the first embodiment of the present invention;

Fig. 5 is the second embodiment of the present invention;

Fig. 6 is the third embodiment of the present invention;

Fig. 7 is the fourth embodiment of the present invention;

Fig. 8 is the fifth embodiment of the present invention;

Fig. 9 is a sixth embodiment of the present invention.

Detailed ways:

In order to further illustrate the features and structures of the present invention, the present invention will be described in detail below in conjunction with the accompanying drawings.

Refer to Figure 1 for a schematic diagram of a confocal positive branch unstable cavity usually without tuning. The resonant cavity consists of a convex spherical reflector 1, a 45° planar out-coupling reflector 2 with a central hole and a concave spherical reflector 3. The radius of curvature of the convex spherical reflector 3 is R ₁ , which is a divergent reflector with a focal length of f ₁ = R ₁ /2; the radius of curvature of the concave spherical reflector 3 is R ₂ , which is a converging reflector with a focal length of f ₂ = R ₂ /2. The distance between the convex spherical reflector 1 and the concave spherical reflector 3 is L. The 45° planar out-coupling mirror 2 with a central hole is located near the convex spherical mirror 1, and the central part has a hole with a diameter a, and the axis of the hole is also at 45° to the plane mirror, as shown in the figure, in fact this is An elliptical hole with a major-to-short axis ratio of .

According to the usual unstable cavity theory (for example, reference: A.E.Siegman. "Lasers", Mill Valley, California: University Science Books.1986) has the following relationship:

L=f ₂ -f ₁

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="f"\; filenames="C20041008118500091.png,C20041008118500111.png"\; state="\{\{state\}\}">f</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula, M is the amplification factor of the unstable cavity, and L is the cavity length of the resonant cavity. The actual illumination diameter on the convex spherical reflector 1 is a ₁ , where a ₁ =a. The actual illumination diameter on the planar outcoupling mirror 2 is a ₂ , where a ₂ =Ma. According to the unstable cavity theory, for a spherical mirror resonator, the power loss of one round trip in the cavity is , as output coupling. The corresponding gain feedback is

The difference between the existing grating tuning non-stable laser resonator shown in Fig. 2 and the usual non-tuning non-stable laser resonator shown in Fig. 1 is that the optical system composed of converging lens 4 and reflective plane diffraction grating replaces Concave spherical mirror 3. The equivalent focal length of this composite optical system is the same as the focal length _f2 of the concave spherical reflector 3, so the resonant cavity in Fig. 2 is similar to the unstable cavity in Fig. 1 for the wavelength meeting the grating self-collimation condition, only It is the effective reflectivity of this composite optical system that is lower than that of a standard total reflection mirror.

The self-collimation condition of the grating is the Littrow condition: 2dSinα=λ. Where d is the grating constant, α is the angle between the grating normal and the optical axis of the resonator, and λ is the laser wavelength.

因此该等效光学系统的损耗很小，效率很高。此外在光栅复合会聚光学系统20中采用了扩束器7，光栅5上的激光强度也将大大下降，从而防止了光栅5受强激光作用而破坏。为了使激光器能够在高功率下运转，光栅5和反射镜6可采用高热导率基底材料制造并且用冷却液冷却。Fig. 3 is a schematic diagram of the grating-tuned unstable laser resonator of the present invention. The laser resonator of the present invention is composed of a convex spherical reflector 1, a 45° planar output coupling reflector 2 with a hole in the center, a concave spherical reflector 6 with a center hole, and a grating composite converging optical system 20, wherein the grating composite converging optical system 20 Composed of a beam expander 7 and a reflective diffraction grating 5, a convex spherical reflector 1, a concave spherical reflector 6 with a central hole, the beam expander 7 and the reflective diffraction grating 5 share an optical axis. The focal length of the concave spherical reflector 6 with a central hole is the same as that of the concave spherical reflector 3 in FIG. 1 , both being f ₂ . The diameter of the central hole on the concave spherical reflector 6 with a central hole is the same as the diameter of the hole on the 45° planar output coupling reflector 2, which is a. The equivalent focal length of the grating composite optical system 20 composed of the beam expander 7 and the grating 5 is also f ₂ . According to the design of the present invention, the equivalent converging focal length composed of the concave spherical reflector 6 and the grating composite converging optical system 20 is f ₂ , which is the same as the concave spherical reflector 3 in FIG. 1 . The concave spherical reflector 6 is an optical element with high reflectivity. For example, for CO2 laser, a gold-plated copper reflector is used, and its reflectivity can reach more than 99%. Because the percentage of the occupied area of the concave spherical reflector 6 in the entire equivalent optical system composed of the concave spherical reflector 6 and the grating compound converging optical system 20 is very large, as

Therefore, the loss of this equivalent optical system is very small and the efficiency is very high. In addition, the beam expander 7 is used in the grating composite converging optical system 20, and the laser intensity on the grating 5 will also be greatly reduced, thereby preventing the grating 5 from being damaged by the strong laser. In order to enable the operation of the laser at high power, the grating 5 and the mirror 6 can be made of a substrate material with high thermal conductivity and cooled with a coolant.

FIG. 4 is the first embodiment of the present invention, wherein a beam expander 7 is composed of a concave lens 8 and a convex lens 9 .

Fig. 5 is the second embodiment of the present invention, wherein is formed beam expander 7 by convex reflector 10 and concave reflector 11, and the convex of two mirrors, concave are opposite, and the convex surface of convex reflector 10 is forward, and the convex surface of concave reflector 11 The concave surface is backward, and the concave reflector 11 is located at the front side of the convex reflector 10; the convex spherical reflector 1, the concave spherical reflector 6 with a central hole and the convex reflector 10 share an optical axis. The convex mirror 10 and the concave mirror 11 are spherical mirrors. In order to reduce the optical aberration and improve the optical quality of the laser beam, the two mirrors can also be aspheric mirrors.

FIG. 6 shows the third embodiment of the present invention, which is a simplified situation. The beam expander 7 is not used in the grating compound converging optical system 20 , but is replaced by a converging lens 12 . The converging lens 12 is located between the concave spherical mirror 6 with a central hole and the subsequent reflective diffraction grating 5 , and the concave spherical reflector 6 with a central hole, the converging lens 12 and the reflective diffraction grating 5 share an optical axis.

Fig. 7 is the fourth embodiment of the present invention, is another kind of simplified situation, does not adopt the beam expander 7 in the grating composite converging optical system 20, is replaced by a concave reflector 13, the concave surface of the concave reflector 13 is forward, is located at Behind the concave spherical reflector 6 with the center hole and the reflective diffraction grating 5 rear, the concave spherical reflector 6 with the center hole and the concave reflector 13 share an optical axis; the reflective diffraction grating 5 is located at the front side of the concave reflector 13 , its reflective surface is backward, corresponding to the concave surface of the concave reflector 13. The concave mirror 13 is a spherical mirror. In order to reduce optical aberrations and improve the optical quality of the laser beam, the reflector 13 can also be an aspheric reflector.

FIG. 8 is a fifth embodiment of the present invention, which is a further simplification of the present invention. The grating composite converging optical system 20 is a reflective concave spherical diffraction grating 14 .

FIG. 9 is the sixth embodiment of the present invention, in which no 45° planar outcoupling reflector with a central hole is provided, and the laser beam is directly outcoupled from the edge of the convex spherical reflector 1 .

Claims (14)

1. unstable laser cavity tunned by grating, by the concave spherical mirror of protruding spherical reflector, band centre bore and the compound convergence optical system of grating after being positioned at the concave spherical mirror of band centre bore forms, it is characterized in that: the compound convergence optical system of grating after this unstable laser resonant cavity comprises the concave spherical mirror of a band centre bore and is positioned at the concave spherical mirror of being with centre bore; The concave spherical mirror of protruding spherical reflector, band centre bore and the compound convergence optics of grating be an optical axis altogether, and the grating normal becomes the Littrow angle with optical axis.

2. laserresonator as claimed in claim 1 is characterized in that: the concave spherical mirror of described protruding spherical reflector and band centre bore is metallic mirror or silicon base speculum gold-plated or the plating deielectric-coating.

3. laserresonator as claimed in claim 1 is characterized in that: the concave spherical mirror of described protruding spherical reflector and band centre bore is metallic mirror gold-plated or the plating deielectric-coating.

4. laserresonator as claimed in claim 1 is characterized in that: the compound convergence optical system of described grating is a reflective concave spherical surface diffraction grating.

5. laserresonator as claimed in claim 1, it is characterized in that: the compound convergence optical system of described grating, comprise that one assembles lens, convergent lens is between the concave spherical mirror and grating of band centre bore, and concave spherical mirror, convergent lens and the grating of protruding spherical reflector, band centre bore be totally one optical axis.

6. laserresonator as claimed in claim 1 is characterized in that: the compound convergence optical system of described grating, comprise a concave mirror, and the concave surface of concave mirror is positioned at the concave spherical mirror and the grating rear of band centre bore forward; The concave spherical mirror of protruding spherical reflector, band centre bore and concave mirror be totally one optical axis; Grating is positioned at the front side of concave mirror, and its reflecting surface backward, and is corresponding with the concave surface of concave mirror.

7. laserresonator as claimed in claim 6 is characterized in that: described concave mirror is spherical reflector or non-spherical reflector.

8. laserresonator as claimed in claim 1, it is characterized in that: the compound convergence optical system of described grating, comprise a beam expander, this beam expander is between the concave spherical mirror and grating thereafter of band centre bore, and concave spherical mirror, beam expander and the grating of protruding spherical reflector, band centre bore be totally one optical axis.

9. laserresonator as claimed in claim 8, it is characterized in that: described beam expander, be made up of divergent lens and convergent lens, convergent lens is positioned at the divergent lens rear, and concave spherical mirror, divergent lens, convergent lens and the grating of protruding spherical reflector, band centre bore be totally one optical axis.

10. laserresonator as claimed in claim 8 is characterized in that: described beam expander, form by convex reflecting mirror and concave mirror, two mirrors protruding, concave surface is relative, the convex surface of convex reflecting mirror forward, the concave surface of concave mirror backward, concave mirror is positioned at the front side of convex reflecting mirror; The concave spherical mirror of protruding spherical reflector, band centre bore and convex reflecting mirror be totally one optical axis.

11. laserresonator as claimed in claim 10 is characterized in that: described convex reflecting mirror and concave mirror are spherical reflector or non-spherical reflector.

12. as claim 5,6,8,9 and 10 each described laserresonator wherein, it is characterized in that: described grating is reflective plane diffraction grating or reflective concave spherical surface diffraction grating.

13. laserresonator as claimed in claim 1 is characterized in that: the laser beam output that directly outside the edge of protruding spherical reflector, is coupled.

14. laserresonator as claimed in claim 1, it is characterized in that: adopt the side annular laser way of output, the plane output coupled mirrors of band centre bore is set between the concave spherical mirror of protruding spherical reflector and band centre bore, the plane output coupled mirrors of protruding spherical reflector, band centre bore, the concave spherical mirror of band centre bore and the compound convergence optics of grating be an optical axis altogether, and the inclination angle is 20 ° to 70 ° between the normal of the plane output coupled mirrors of band centre bore and the optical axis.

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