Optical Resonator Especially for Stabilizing a Laser Source

The invention relates to an optical resonator especially for stabilizing a laser source useful for homodyne or heterodyne applications. A grating is arranged at an angle relative to the optical axis of the laser source.

Such resonators are known in various versions. For example, German Patent Publication DE-OS 3,144,839 discloses a laser with an unstable optical cavity having an output mirror with an extra-axial or off-axis opening through which a laser beam may be emitted in order to maintain a laser effect in an active medium. The output mirror is shaped and arranged so that it exposes an elliptical cross-section to the impinging laser beam. As is already clear from the drawing of the above publication, the resonator requires a relatively large spacial volume, that is to say, it has a long structural length.

Furthermore, German Patent Publication DE-AS 2,449,123 discloses an output coupling mirror for astable laser resonators with a light-permeable or transparent central region and a highly reflective rim or edge zone. The described output coupling mirror is arranged at an angle in the beam path of the resonator. Even in the arrangement described therein, a relatively large structural size and hence a large space requirement cannot be avoided.

In view of the foregoing it is the aim of the invention to achieve the following objects singly or in combination:

to construct a laser resonator in such a manner that a considerable reduction of the structural length of the laser resonator is achieved;

to reduce the weight and amount of required material in such a laser resonator; and

to achieve an improved adjustability of the laser resonator components, with a decreased adjustment effort.

The above objects have been achieved in a laser resonator for stabilizing laser sources according to the invention, wherein a laser is arranged to emit a beam through a central opening of a grating arranged at an angle relative to the optical axis of the laser. The laser beam is directed through the central opening of the grating and then onto a parabolic mirror from which it is reflected or "folded back" onto the grating. Thus, a folded beam path is formed in a laser resonator so that the structural length of the resonator may be reduced by at least one half. The laser and the grating are connected to an adjustment mechanism which may have a quite simple construction.

In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic side view in partial section through a laser resonator according to the prior art; and

FIG. 2 is a schematic side view in partial section through an embodiment of a laser resonator according to the invention.

As shown in FIG. 1, the typical solid state resonators are constructed so that the light 14a emitted by a laser light source 10 is projected through a lens 15a onto a grating 11 which is arranged at an angle relative to the optical axis 13. The structural size or space required by the resonator is relatively high, as dictated by the necessary developed length of the beam path, including for instance the focal length of the lens 15a.

As shown in FIG. 2, the total structural length or size of the resonator may be reduced according to the invention. Here, a solid state laser 10 is arranged essentially in a central opening 12 of a grating 11, which is arranged at an angle relative to the optical axis 13 of the laser 10. The beam 14 of the laser 10 is directed through the opening 12 onto a parabolic mirror 15 from which it is reflected or "folded back" onto the grating 11. In this manner, it is achieved that the space taken up by the resonator arrangement is reduced by at least half relative to the previously necessary space according to the state of the art.

The present "folded" optical resonator achieves further advantages including a considerably simplified adjusting and directing of the laser 10 relative to the grating 11. The laser 10 is supported in the central opening 12 of the grating 11 by conventional means not shown. An adjustment controller 16, which may be a manual control or an automatic control, operates an adjustment drive 17 which is effective to tilt the grating 11 about one of its spacial axes, or to slide the grating 11 laterally in its plane relative to the laser 10. Once the parabolic mirror and the grating are aligned, the fine tuning is done by x-y-z-control of the laser diode. The tilting of the grating determines the wave length to be emitted by the laser. Laser and grating should not be connected to achieve better adjustability. The adjustment controller 16 is connected at 17 to the grating 11. The controller 16 may also be effective on the laser 10 as shown by the arrow leading from the controller 16 to the laser 10 in FIG. 2. The adjustment and supporting elements 16, 17 may have a relatively simple and compact construction and may operate in several different manners, whereby the elements 16, 17 are merely represented schematically in FIG. 2. Conventional position adjustments are suitable for the present purposes.

Although the invention has been described with reference to specific example embodiments, it will be appreciated, that it is intended to cover all modifications and equivalents within the scope of the appended claims.