JPH11261176A - Free-electron laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillator supporting structure of a free-electron laser, that is capable of minimizing a relative positional shift of oscillator mirror to stabilize laser output, readily adjusting the relative positions between an oscillator and an amplifying medium, and omitting alignment after a shift. SOLUTION: A mirror supporter is provided with a low-expansion member 9 stretched along the length of an oscillator, including a pair of oscillator mirrors 1 and 1', which fare opposite each other so as to sandwich an inserting light source 5. The oscillator mirrors 1 and 1' are fixed respectively on both ends of the low-expansion member 9. The low-expansion member 9 is fixed such that the central part can be adjusted to the inserting light source 5, which is fixed between the oscillator mirrors. Furthermore, the ends of the low- expansion member 9 are preferably supported by oscillator mirror pedestals 4 and 4' via supporting structures 10 and 10' which can expand and contract, and via shifting structures 14 and 14' which pull out the mirror supporter at an axial position of the oscillator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a free electron laser oscillator, and more particularly, to a support structure for a resonator mirror.

[0002]

2. Description of the Related Art In a free electron laser device, an insertion light source such as an undulator is inserted in an electron beam orbit.
A pair of resonator mirrors are provided with the insertion light source interposed therebetween. While the light pulse generated by the electron beam bunch meandering in the insertion light source reciprocates many times between the resonator mirrors,
Interacting with the newly supplied electron beam bunch amplifies the light intensity and causes laser oscillation.

[0003] Bending electromagnets are provided on both sides of the insertion power supply in order to guide the electron beam to an insertion power supply installed between the resonator mirrors to make the trajectory of light coincide with the trajectory of the electron beam.
Furthermore, in order to oscillate the free electron laser, it is necessary to adjust the electron beam bunches passing through the insertion power supply to overlap with the light pulses that linearly reciprocate between the resonator mirrors to cause an interaction. Must.

As described above, in order to obtain a free electron laser, there are severe restrictions not only on the installation accuracy of the resonator mirror, but also on the correlation between the light pulse and the electron beam bunch passing through the insertion light source. For this reason, extremely high precision is required for the arrangement of devices in the portion of the free electron laser oscillator.

FIG. 5 is an elevational view showing an arrangement example of a resonator portion of a conventional free electron laser device, and FIG. 6 is a plan view thereof. In a conventional free electron laser device, as shown in FIG. 5, a pair of resonator mirrors constituting a resonator and a vacuum chamber for storing the mirrors are mounted on respective pedestals mounted on the floor on which the laser device is installed. Mounted on and fixed.

An insertion light source such as a wiggler or an undulator (hereinafter referred to as an undulator) is provided between the pair of resonator mirrors, and an electron beam bunch supplied from a linac or a storage ring is deflected by a deflection magnet. And emits light in a meandering manner through an undulator. The light pulse generated by the passage of the electron beam bunch through the undulator is adjusted so that it just meets the electron beam bunch supplied to the undulator during a large number of round trips between the resonator mirrors. Amplifying the light intensity with repeated interaction leads to laser oscillation.

[0007] In the conventional free electron laser device, as shown in the figure, a pair of resonator mirrors are supported by independent mounts. For this reason, if the state of the floor surface on which the laser device is installed or the state of the resonator fixed base changes due to changes in the environment, it appears as a distance deviation between the resonator mirrors.
Even a very small deviation causes a large deviation of the optical pulse during a large number of round trips between the mirrors, so that there is a deviation in timing from the electron beam bunch and no interaction occurs, and stable operation cannot be performed. In particular, the effects of thermal expansion and contraction caused by the temperature change of the materials constituting these components cannot be ignored.

In addition, the influence of thermal expansion and the like affects not only the distance between the resonator mirrors but also the mutual positional relationship between the undulator and the resonator, which hinders the interaction between the light pulse and the electron beam bunch. In a normal laser device, the accuracy of the distance between the cavity mirrors is required, but the accuracy of the relative position between the cavity mirror and the laser medium is not so required. Therefore, extremely strict relative position accuracy is required as described above.

Further, in the conventional laser device, once the resonator mirror is installed, the position of the resonator mirror cannot be moved in advance beyond the movable range in the resonator mirror chamber. Note that when the resonator mirror is moved, it is necessary to re-align the resonator mirror even when trying to translate the resonator mirror. Furthermore, in the conventional laser device, once the resonator is removed,
When re-attaching, the mounting work and the position adjusting work were not easy.

[0010]

Accordingly, an object of the present invention is to provide a support structure for a free electron laser resonator capable of minimizing the relative position change of the resonator mirror in order to stabilize the laser output. Another object of the present invention is to provide a resonator support structure that can easily adjust the relative position between the resonator and the amplifying medium and can omit the alignment after the movement. Yet another object is to provide a resonator support structure that allows easy attachment and detachment of a resonator portion from a laser device.

[0011]

In order to solve the above-mentioned problems, a free electron laser oscillator according to the present invention, which oscillates a free electron laser by a resonator including a pair of resonator mirrors facing each other with an insertion light source interposed therebetween, has a resonance. A low-expansion material extending in the longitudinal direction of the vessel, the resonator mirrors being fixed to both ends thereof, and a substantially central portion being fixed to the insertion light source structure fixed between the mirrors. A mirror support that can be fixed so that the position can be adjusted is provided.

Further, the end of the low expansion coefficient material can be supported by the gantry via an extendable support structure.
Further, it is preferable to provide a moving structure for pulling the mirror support out of the axial position of the resonator so that the resonator mirror can be retracted or replaced as a unit. Note that a cooling pipe may be added to the low expansion coefficient material so that the temperature can be controlled by the refrigerant.

According to the present invention, since the pair of resonator mirrors are both fixed to an integral low expansion coefficient material, even if there is a change in environmental temperature or a temperature change due to heat generated during operation, the resonator mirror is not affected. The distance between the mirrors hardly changes. Since the resonance condition of the free electron laser is maintained in this way, stable laser oscillation for a long time can be realized. As the low expansion coefficient material, an invar alloy, in particular, an extremely low expansion coefficient material called super invar can be used. Granite can also be used.

Further, since the position relative to the insertion light source is adjusted and then fixed to the insertion light source at the center of the low expansion coefficient material, the phase matching between the electron beam bunch and the light pulse is once performed through strict adjustment. After it is obtained, the matching is less likely to be lost due to an environmental change, and stable operation is possible. Position adjustment between the resonator mirrors can be performed by adjusting the installation position on the low expansion coefficient material. Furthermore, in order to adjust the position of the resonator mirror with respect to an insertion light source such as an undulator, for example, a long slot is provided in the direction of the resonator axis on the floor of a base on which the insertion light source is mounted, and a low expansion coefficient It is only necessary to fit a bolt set up at the center of the material, adjust the axial position of the resonator, and then fix it.

In the free electron laser oscillator according to the present invention, the amount of change in the position of the floor or the gantry caused by a temperature change due to the difference in the coefficient of thermal expansion between the support of the resonator mirror and the floor or the gantry and low expansion. Since the change in the length of the index material is different, the mirror support is subjected to a tensile stress by the gantry, thereby hindering the stability of the distance between the resonator mirrors or having a structural weakness. However, if it is a free electron laser oscillator having a support structure in which the end of the low expansion coefficient material can expand and contract,
Because the base and the mirror support slide freely, no extra stress is applied to the low expansion coefficient material, and the distance between the resonator mirrors varies extremely only depending on the temperature characteristics of the low expansion coefficient material. Only occurs. By providing a combination of rails and wheels or a linear guide between the mirror support and the gantry, it is possible to provide a support device that allows the low expansion coefficient material to expand and contract freely.

Further, by providing a moving structure for pulling out the mirror support from the axial position of the resonator so that the resonator mirror can be retracted or replaced as a unit, the mirror can be removed from the free electron laser device and stored as it is. You can make adjustments and return to the original location again when needed. Moving the mirror support does not affect the relative position of the pair of resonator mirrors, so there is no need to precisely adjust the distance between the two resonator mirrors when returning to the original position.

In the case where the temperature control by the refrigerant can be performed by adding a cooling pipe to the low expansion coefficient material, even if a low expansion coefficient material having a relatively high expansion coefficient is used, the temperature change itself is suppressed. As a result, required dimensional stability can be ensured, and the manufacturing cost of the device can be reduced.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings. FIG. 1 is an elevation view showing an embodiment of a free electron laser oscillator according to the present invention, and FIG. 2 is a plan view thereof. 3 and 4 are conceptual diagrams illustrating the interaction between the electron beam bunch and the light pulse.

In the free electron laser oscillator of this embodiment, a pair of resonator mirrors 1 and 1 'forming a resonator and vacuum chambers 2 and 2' for storing mirrors are provided on a floor 3 on which a laser device is installed. It is mounted and fixed on each of the mounted resonator mirror mounts 4, 4 '. An insertion light source 5 such as an undulator is provided between the two resonator mirrors 1 and 1 ′, and deflection magnets 6 and 6 ′ are interposed before and after the insertion light source 5. The insertion light source 5 and the deflection magnets 6 and 6 ′ are connected to an insertion light source base 4 ″ fixed to the floor 3.
It is disposed on the upper platen and is fixed so that its positional relationship with respect to the electron beam supply source does not change.

The electron beam bunch 7 supplied from a linac (not shown) or the like and deflected by the deflection magnet 6
Light pulses 8 are emitted while meandering while passing through the undulator 5. The resonator mirrors 1, 1 'reflect the emitted light pulse 8 and reciprocate the resonator many times. As shown in FIG. 3, the light pulse 8 in the resonator
Is adjusted with the timing of the electron beam bunches 7 supplied thereto, and during the reciprocation between the resonator mirrors, the light pulse 8 and the electron beam bunches 7 just meet and interact with each other to amplify the light intensity and cause laser oscillation. Up to

If the distance between the resonator mirrors 1 and 1 'is not appropriate, the position of the light pulse 8 is shifted while the light is reciprocating between the two, and the light energy cannot be accumulated. The stability of the resonator length is also important.
When an electron beam of ps enters the resonator, if the light reciprocates 200 times in the resonator before oscillation, it is necessary to suppress the change in the resonator length to within 400 nm. The electron beam bunch after passing through the undulator 5 is deflected by a deflecting magnet 6 ′ downstream of the undulator 5 and extracted from the trajectory of the light pulse.

One low expansion coefficient material 9 is passed between the resonator mirror mounts 4 and 4 ′, and the resonator mirrors 1 and 1 ′ and the vacuum chambers 2 and 2 ′ are formed of the low expansion coefficient material 9. Each is fixed at a position near the ends on both sides. A linear guide or a low-friction support member 10, 10 'is interposed between the low expansion coefficient material 9 and the resonator mirror bases 4, 4'. Does not affect the low-expansion material 9 even if the distance changes. Therefore, the distance between the resonator mirrors 1 and 1 'does not change.

The linear expansion coefficient of the Invar alloy is 10 ^-7 (K ^-1 )
Therefore, if a resonator having a length of 3 m is supported, a change in the resonator length of about 300 nm can be suppressed for a temperature change of 1K. Therefore, the low expansion coefficient material 9
A cooling pipe is added to the cooling medium, and temperature-controlled cooling water is circulated to suppress the temperature change of the low expansion coefficient material 9. The action can be ensured. By using a material having a smaller linear expansion coefficient, such as Super Invar or granite, a resonator support mechanism can be constructed at lower cost.

A bolt hole is provided at a substantially central position of the low expansion coefficient material 9, and a bolt hole 13 is also provided at a position corresponding to the surface of the base of the insertion light source base 4 ". The bolt hole 13 provided in the cavity is a long hole elongated in the axial direction of the resonator.
After the position is adjusted, the bolts 12 can be passed through these bolt holes and fixed. The number of fixing points is not limited to one at the center, and a plurality of fixing points may be provided. When such a mechanism is used, the relative position with respect to the insertion light source 5 is easily adjusted while maintaining the relative positional relationship between the resonator mirrors 1 and 1 'by loosening the bolts, and the optimum alignment of the resonator is facilitated. Can be done.

Further, the supporting members 10 and 1 of the low expansion coefficient material 9
Linear guides 14 and 14 'are laid in the direction perpendicular to the resonator axis between 0' and the respective resonator mirror mounts 4 and 4 ', and the entire resonator can be slid in the horizontal direction and removed as it is. I can do it. Rails and wheels may be used instead of the linear guide. Also when changing the oscillation condition, it is possible to replace the resonator that has been adjusted in advance according to the new oscillation condition by using this laterally movable guide, and to omit the fine adjustment.

[0026]

As described above, the free electron laser resonator according to the present invention can stabilize the laser output by minimizing the relative position change of the resonator mirror and stabilize the laser output. The relative position can be easily adjusted, and the alignment can be performed extremely easily even after the movement. Further, it is easy to attach and detach the resonator portion from the laser device, and it is possible to easily cope with a change in laser specifications.

[Brief description of the drawings]

FIG. 1 is an elevational view showing one embodiment of a free electron laser oscillator of the present invention.

FIG. 2 is a plan view of the present embodiment.

FIG. 3 is a conceptual diagram illustrating an interaction between an electron beam bunch and a light pulse in the present embodiment.

FIG. 4 is a conceptual diagram showing a state where no interaction between an electron beam bunch and a light pulse is performed.

FIG. 5 is an elevation view illustrating an example of a conventional free electron laser oscillator.

FIG. 6 is a plan view illustrating the free electron laser oscillator of FIG.

[Explanation of symbols]

 1, 1 'resonator mirror 2, 2' vacuum chamber for mirror 3 installation floor 4, 4 'resonator mirror base 4 "insertion light source base 5 insertion light source 6, 6' deflection magnet 7 electron beam bunch 7 8 light pulse 9 Low expansion coefficient material 10 Low friction support material 12 Bolt 13 Bolt hole 14, 14 'Linear guide

Claims (4)

[Claims] 1. A low-expansion coefficient of a mirror support in a resonator of a free electron laser constituted by a pair of mirrors facing each other across an insertion light source and extending in the longitudinal direction of the resonator. The mirror is fixed to both ends of the low-expansion material, and the center of the low-expansion material is fixed at a position sandwiched between the mirrors. A free electron laser oscillator comprising a mirror support that can be fixed so that its position can be adjusted. 2. The free electron laser oscillator according to claim 1, wherein an end portion of said low expansion coefficient material is supported on a gantry using a supportable structure. 3. A structure in which both ends of the mirror support are provided with a moving structure for pulling the mirror support out of the axial position of the resonator so that the resonator mirror can be integrally retracted or replaced. The free electron laser oscillator according to claim 1 or 2, wherein 4. The free electron laser oscillator according to claim 1, wherein a cooling pipe is added to said low expansion coefficient material so that temperature control by a refrigerant is possible.