DE4311305C2 - Laser with an unstable resonator for ring-shaped active media - Google Patents

Description

The invention relates to lasers with an unstable resonator according to the preamble of claim 1, the annular Use media effectively, regardless of whether it is are solid, liquid or gaseous media.

Conventional laser systems make use of zylindri reinforcing media with spherically curved Resonator end mirrors, their apex and curvature center points lie on an axis through Folds the arrangement of the active medium is adjusted.  

In addition to cylindrical excited media, ring are also formally excited reinforcing media used, their Geometry also by folding, partly with spherical curved folding mirror is used.

Such resonators designed according to DE 35 15 679 C1 can be both stable and unstable. In addition to cylindrical media, certain La systems the use of media with an annular Cross-section advantageous in terms of compactness and price be (e.g. gas laser with coaxial electrode arrangement, with coaxial Nd-YAG lasers and liquid (dye) lasers axial pump light source).

To use ring-shaped reinforcing media different resonators used.

When using stable resonators according to L.W. Casperson, M.S. Shekhani "Mode properties of annular gain lasers" Appl. Optics, vol. 14, no. 11, 1975 becomes a resonator with a toroidal mirror in which the "curvature center "of the mirror surface outside the symmetry axis lies on a circle, and a plan Auskop pel mirror described.

The laser beam is decoupled over the entire circumference pelt and therefore has an outer diameter that the Radius of the outer boundary of the reinforcing medium corresponds.

The authors point out that a summary the laser beam leads to improved mode control, without, however, proposing a specific embodiment.  

With the laser described in DE 35 15 679 C1, the one Beam of light - multiple using two spherical mirrors folds through a coaxial gas discharge, this is ver strengthening medium used only incompletely.

Furthermore, is for further use of laser media with an annular cross-section thanks to stable reso nators have been proposed to end mirrors of the reso nators as a ring mirror with a toroidal surface to train.

The center of curvature circles of the torus mirrors are like this chosen that the cylindrical defined thereby "Optical axis" placed in the amplifying medium is that the losses are minimized and the exploitation of the Medium is optimized.

The radiation inside the Reso nators by one or more Axicon mirrors on one partially transmitting decoupling mirror with adapted Curvature summarized.

US 4,050,036 describes unstable resonators for active ones Media presented with an annular cross section, at which the radiation inside the resonator through Axicon to the axis of rotation of the excitation system or to Axis of rotation of the convex end mirror summarized becomes.

The decoupling is done by transmitting Window with end mirror or through scra perspective.  

In P.B. Mumola, H.J. Robertson, G.N. Steinberg, I.L. Kreuzer, A.W. Mc Cullough "Unstable resonators for annular gain volume lasers "Appl. Optics, vol. 17, no. 6, 1978 and R.A. Chodzko, S.B. Mason, E.F. Cross "Annu lar converging wave cavity "Appl. Optics, vol. 15, no. 9, 1976 continue to describe unstable resonators ben who use annular media.

This is the "converging wave unstable (CWUR) resonator "and on the other hand the" half-symmetric unstable resonator with internal axicon (HSURIA) ".

With the CWUR, the radius of the outcoupled beam lies in the order of magnitude of the outer radius of the reinforcing Medium.

The HSURIA uses an Axicon mirror, which consists of two there are conical mirror surfaces, for summary of the laser beam.

Both CWUR and HSURIA are unstable resonators, because of high losses only for high gain Media are suitable. These resonators have one high adjustment sensitivity. The expansion of the optical axis to a circular cylinder and the high one Fresnel numbers in the azimuthal direction lead to occurrence of modes with high azimuthal mode order.

In addition, DE 41 23 024 A1 and DE-GM 90 03 331 Resonators known in which an unstable Reso nator using a non-rotationally symmetrical torus mirror ("Spiral mirror") is realized.

The beam path within the resonator  by shaping the mirror in the circumferential direction directs. The coupling takes place via a hole on End of the "Wendel". The mirrors necessary for this are because of the complex manufacturing process essential more expensive than rotationally symmetrical mirrors.

A cylindrical symmetrical unstable resonator with Coupling on the optical axis using toric optics in the resonator is described in US 3,873,942 described.

Likewise, an article by E.F. Yelden et al., "Multichannel laser resonator - an experimental study", Optical and Quantum Electronics, 24, 1992, pp. 889-902 3 on page 892 shows a cross-sectional representation of a resonator, the mirror with toric ge has shaped mirror surfaces.

So far, the referenced statements (with the exception the resonators described in DE 35 15 679 C1 at klei services) no distribution and no commercial goal le usage found because the unstable used Resonators rely on high-gain media goods and tend to high instabilities in operation.

Is derived from the prior art shown it is the object of the invention to be complete and therefore effective use of the active medium by the ensure instable resonator used and reduce the number of components to be adjusted.

An inventive solution to this problem is in Claim 1 specified. Further training of the Erfin are marked in the subclaims.  

According to the invention, a laser with an unstable resonator, which has an active medium with an annular cross section between two ring mirrors, the mirror surfaces of which correspond to the surface of a section of a torus, is designed in such a way that the beam is coupled out along an uninterrupted annular gap which is between a cylindrical boundary wall for the active medium and the inside or outside edge of one of the two ring mirrors ( 1 , 2 ) is made. The annular gap is in particular not interrupted by structural fastening measures. Furthermore, according to the invention, it is a mirror arrangement for bringing the annular exit beam directly passing through the gap into a laser beam with a reduced beam cross section outside the resonator and, together with the annular mirror forming the gap, forms part or all of a unit.

Based on the annular structure of the fiction, ge moderate resonator is not a singular optical axis available.

Due to the large ratio of circumference to gap the resonator can be quasi one-dimensional to get nabbed.

The connection of the centers of curvature of the two toroidal ring mirror with a fixed azimuth kei represents a local optical axis Rotational symmetry creates a conical surface more optically Axes through the center lines of curvature of the two  toroidal shaped annular mirror surfaces is determined.

The unstable resonator can be arranged so that the conical surface of the optical axes either on the Inside or outside of the unstable resonator lies. The decoupling gap is located accordingly on the side opposite the optical axes the ring mirror, because in unstable resonators Radiation migrates away from the optical axis.

After decoupling from the annular gap, together measurement of the radiation towards the axis of rotation z. B. by means of an axicon or Re known per se flaxicons.

When uncoupled on the inside of the ring mirror can ring mirror and axicon in one part with three Mirror surfaces are made.

Provided that the merged beam not possible along the symmetry axis of the system Lich, can be on the outside of the coupling Ring mirror at least the mirror surface of the ring spike gel, as well as the critical inner cone of a re flaxicons can be executed in one component.

Due to the location of the axicon or reflaxicon outside of the resonator are negative influences of the beam form due to manufacturing-related defects in the conical surfaces, Positioning errors of the conical surfaces to each other, as well due to the singularity of the axicon image in the area the inner cone tip for internal losses in the resonator and beam guidance excluded.  

Significant advantages of the invention are in the large-scale excitation of the active medium and in the associated full utilization of the share medium due to the unstable resonator.

Due to the constructive structure of the invention Resonators becomes the number of functions to be adjusted elements reduced; the disadvantageous arrangement of the Axicons within the unstable resonator are ver avoided.

Furthermore, they can be rotationally symmetrical and therefore inexpensive mirrors used and depending on each specific constructive structure several adjustment-sensitive mirrors in one component to get nabbed.

The invention is based on execution examples with reference to the drawing exempla risch described on the rest of the Revelation of all not explained in the text explicitly referenced details becomes. Show it:

Fig. 1-sectional view of an unstable resonator with an external optical axis,

Fig. 2 analog sectional view with an internal optical axis,

Fig. 3 sectional view of an unstable laser resonator with devices for combining the laser radiation.

Fig. 1 shows an unstable resonator for ring-shaped active media in section. The laser resonator has two ring mirrors with a toroidal section surface 1 , 2 and is enclosed by the walls of the ring gap to excite the medium or the cylindrical inner and outer boundary 3 , 4 of the excited medium.

The entire structure of the resonator is symmetrical about the axis of symmetry 6 .

A laser beam 5.1 is decoupled through an annular gap between the inner boundary 4 of the excitation volume and the inner edge of the annular mirror on the coupling side with a toroidal section surface 2 .

In this embodiment, the optical axis 8 lies outside the unstable resonator.

In Fig. 2, the analog embodiment of a laser sonator with coupling of the laser beam 5.1 between the outer boundary 3 of the active medium and the outer edge of the ring lying on the coupling-out side mirror with a toroidal surface 2 is shown. The optical axis 8 is here within the resonator which is stable.

Fig. 3 illustrates the laser resonator according to the invention with devices for combining the laser radiation 5.1 into a beam 5.2 . It is an essential feature of the invention that these devices are arranged outside of the unstable resonator.

In both embodiment variants according to FIGS. 3.1 and 3.2, the optical elements for shaping the coupled radiation 5.1 are designed such that they are completely or partially confi gured in an optical component together with one of the resonator mirrors 1 , 2 .

In the embodiment according to FIG. 3.1, the coupling takes place on the inside of the ring mirror 2 with the consequence that the ring mirror 2 and the axicon are formed in a single component with three mirror surfaces 7.1 , 7.2 .

When using a 180 ° W axicon 7 , a beam path results from the radiation 5.1 incident on the outer, conical mirror surface 7.1 parallel to the axis of symmetry 6 , reflected in the direction of the axis of symmetry 6 on an inner conical mirror surface 7.2 and reflected from here parallel to Axis of symmetry in the opposite direction to the combined radiation 5.2 .

An embodiment for coupling out the laser beam 5.1 on the outside of the ring mirror 2 is shown in FIG. 3.2.

Here, the mirror surface of the ring mirror 2 and the inner cone of the reflaxicon 9, which is critical with respect to adjustment, are embodied in an optical component.

In this configuration of the device for summarizing the laser radiation, the combined laser beam 5.2 is guided away from the laser resonator in the axial direction.

Claims (6)

1. Laser with an unstable resonator, which has an active medium with an annular cross section between two ring mirrors, the mirror surfaces of which correspond to the surface of a section of a torus, characterized by the combination of the following features:

• - The beam is coupled out along an uninterrupted annular gap, which exists between a cylindrical boundary wall for the active medium and the inside or outside edge of one of the two ring mirrors ( 1 , 2 )
• - A mirror arrangement for beam merging of the directly passing the gap, from the exit beam to a reduced beam cross-section laser beam is provided outside the resonator and forms, together with the, the gap forming ring mirror, all or part of a unit.

2. Laser according to claim 1, characterized in that the mirror arrangement is a 180 ° -W- Axicon ( 7 ), consisting of an outer, conical mirror surface ( 7.1 ) for reflection of radiation ( 5.1 ) incident parallel to the axis of symmetry ( 6 ) in Direction of the axis of symmetry, as well as an inner, conical mirror surface ( 7.2 ) for reflection of the radiation reflected from the outer cone surface parallel to the axis of symmetry with the opposite direction ( 5.2 ) to the radiation ( 5.1 ) incident in the axicon ( 7 ). 3. Laser according to claim 2, characterized in that the 180 ° -W-Axicon ( 7 ) is part of an annular mirror and is adjustment-free with this related party. 4. Laser according to one of claims 1 to 3, characterized in that the coupling of the radiation ( 5.1 ) between the inner boundary wall of the active medium and the inner edge of the ring mirror ( 2 ). 5. Laser according to claim 1, characterized in that the mirror arrangement is a Re flaxicon ( 9 ), the inner cone of which is made as an optical component with the ring mirror ( 2 ) and is freely connected to the latter. 6. Laser according to claim 5, characterized in that the coupling of the radiation ( 5.1 ) between the outer boundary wall of the active medium and the outer edge of the ring mirror ( 2 ).