JP2527299Y2 - Excitation laser device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pumping laser device used for a free electron laser and an electron accelerator.

[0002]

2. Description of the Related Art FIG. 6 shows a conceptual diagram of an RF (high frequency) extraction photocathode. This method is a kind of an electron gun, and irradiates a cathode material 02 with a laser beam hν emitted from a laser 01, and emits photoelectrons e ejected from the cathode material 02 by the irradiation of the laser beam in an RF cavity 03.
It is configured to accelerate by a high frequency signal from the generator 04.

As a conventional excitation laser for exciting the cathode material 02 as described above, a short pulse (mode locked) laser as shown in FIG. 7 is used. This laser is a laser medium (e.g., equivalent to a YAG rod of a YAG laser)
As a Fabry-Perot resonator using the mirror 20, an output mirror (a mirror whose transmittance is set in a range of about 10 to 90% and the other is a reflecting mirror) 08 and a total reflection mirror (a transmittance of 0% and a reflectance of 100)
%) Saturable absorber 1 for generating 09 and short pulses
0, and has a characteristic as shown in FIG. 8 as an output. Although the pulse width depends on the characteristics of the saturable absorber 10 at t2, the pulse pitch t1 is a value proportional to the resonator length (the interval L between the output mirror 08 and the total reflection mirror 09).

[0004]

(Equation 1)

(Where c is the speed of light). Since this type of laser generally includes a saturable absorber or the like in the resonator, L is relatively long, and the pulse pitch t1 is about 10 nsec.

[0006]

[Problems to be Solved by the Invention] In the above conventional method,
Since the laser pulse pitch t1 is too wide at 10 nsec, considering the matching with the RF frequency, 100 MH
Only a z (100 MHz = 1/10 nsec) band RF source can be used, and there is a problem that a long RF cavity is required for electron acceleration.

The present invention has been made in view of the above circumstances, and it is possible to extract a photoelectron of several GHz from a photocathode by reducing the pulse interval output from a laser generator, thereby achieving a compact RF cavity. An object of the present invention is to provide an excitation laser device.

[0008]

The present invention is characterized in that each laser pulse output from a mode-locked laser generator is input to a pulse train generator to generate a pulse train of several GHz. Things. Further, according to the present invention, if necessary, a 1/2 pulse pitch generator is provided on the output side of the pulse train generator, and when the pulse pitch is larger than a predetermined pulse pitch, the pulse pitch is reduced by half to several Gs.
Hz pulse train is obtained.

[0009]

Function: For example, from the mode locked laser generator,
Laser pulses are output at 0 nsec intervals. This laser pulse is input to a pulse train generator and converted into a continuous pulse train of several GHz. When the pitch of the pulse train is larger than a preset value, the pitch is changed to 1/2 by a 1/2 pulse pitch generator. Accordingly, photoelectrons of several GHz are extracted from the photocathode by this pulse train, and the RF cavity can be made compact.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the concept of the excitation laser device of the present invention. The laser generator 05 is the same as the conventional short-pulse (mode-locked) laser shown in FIG. 7, locks the mode of the laser, generates laser pulses at intervals of several tens of nanoseconds, and inputs the laser pulses to the pulse train generator 06. This pulse train generator 06 generates a continuous pulse train from one short pulse,
That is, a pulse train of several GHz is generated within several tens of nanoseconds, which is a short pulse generation interval, and is input to the １ ／ pulse pitch generator 07. This 1/2 pulse pitch generator 07
Is used when the pitch of the continuous pulse train is larger than a preset pulse pitch, that is, when the pitch of the pulse train generated by the pulse train generator 06 is still insufficient. The output is made to the cathode material 02 after being halved.

The pulse train generator 06 is configured as shown in FIG. That is, the pulse train generator 06 reflects the light hν (short pulse) incident from the laser generator 05 on the convex mirror 11, passes through the central hole 12 a of the reflecting mirror 12, further reflects on the reflecting mirror 13, and amplifies the amplifier 14. Incident. The amplifier 14 amplifies the incident light, reflects the light on the reflecting mirrors 15 and 16, and guides the light to the reflecting mirror 12. A part of the light incident on the reflecting mirror 12 is extracted to the outside through the central hole 12a of the reflecting mirror 12, but the other light is reflected by the reflecting mirror 12 and travels to the reflecting mirror 13 again. The light hν incident on the convex mirror 11 from the laser generator 05 in this way is amplified by circulating through the ring resonance optical path of the reflecting mirror 12 → reflecting mirror 13 → amplifier 14 → reflecting mirror 15 → reflecting mirror 16 → reflecting mirror 12. A part of which is a central hole 12 of the reflecting mirror 12.
The operation of being taken out to the outside via a is repeated.
As a result, a pulse train is generated at a pulse pitch proportional to the optical path length as shown in FIG.

Now, the optical path length between the reflecting mirror 13 and the reflecting mirror 15 is L1, and the optical path length between the reflecting mirror 15 and the reflecting mirror 16 is L1.
2. If the pulse pitch is t3, t3 = 2 (L1 + L2) / c (c is the speed of light).

[0013] Since the circulating light beam has a gentle spread angle, it eventually becomes larger than the mirror outer diameter and the loss increases. On the other hand, since there is amplification by the amplifier 14, the loss (including the loss due to the light passing through the hole of the reflecting mirror 12) and the gain are balanced. (In FIG. 2, the broken line indicating the light flux indicates the first optical path, and the solid line indicates the stationary optical path.

FIG. 3 shows an output example of the pulse train generator 06. In FIG.

[0015]

(Equation 2)

Is considered to be a general value of the shorter one, so that the pulse pitch t3 is

[0017]

(Equation 3)

## EQU1 ## This corresponds to 1.5 GHz.

Here, if the pulse pitch of the continuous pulse train generated by the pulse train generator 06 is larger than a preset pulse pitch, the 1/2 pulse pitch generator 0
7 is used. This 1/2 pulse pitch generator 07
As shown in FIG. 4, the incident laser light is split by a beam splitter 19, and
And the other light, which is refracted by 90 °, is condensed by the concave mirror 17 and irradiated on the cathode material 02.

At this time, the optical path length between the beam split 19 and the cathode material 02 is LL1, and the beam split 19 is
Assuming that the optical path length between the concave mirror 17 and the concave mirror 17 is LL2, the optical path length between the concave mirror 17 and the cathode material 02 is LL3, and the pitch of the pulse output from the 1/2 pulse pitch generator 07 is t4. t4 is Becomes Now, assuming that the optical path difference between “LL2 + LL3” and “LL1” is, for example, “LL2 + LL3−LL1 = 100 mm”, the pulse pitch t4 becomes

[0021]

(Equation 4)

## EQU1 ##

As described above, the interval between the laser pulses can be narrowed, so that several GH
The z photoelectrons are extracted. As a result, a pump laser device having a compact RF cavity can be realized.

[0024]

As described above in detail, according to the present invention, since each laser pulse from the laser generator is converted into a pulse train of several GHz by the pulse train generator, the photoelectron extraction from the photocathode is performed by several GHz. It can be.
When the pulse train generated by the pulse train generator is larger than a preset pulse pitch, the pulse pitch is reduced to に よ り by the パ ル ス pulse train generator. The RF cavity can be made compact by setting the photoelectron extraction from the photocathode to several GHz.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an excitation laser device according to the present invention.

FIG. 2 is a configuration diagram of a pulse train generator in the embodiment.

FIG. 3 is a characteristic diagram of the pulse train generator shown in FIG.

FIG. 4 is a configuration diagram of a 1/2 pulse pitch generator in FIG. 1;

FIG. 5 is a characteristic diagram of the パ ル ス pulse pitch generator shown in FIG. 4;

FIG. 6 is a conceptual diagram of an RF extraction photocathode.

FIG. 7 is a configuration diagram of a conventional mode-locked laser.

8 is a characteristic diagram of the mode-locked laser shown in FIG.

[Explanation of symbols]

01 laser, 02 cathode material, 03 RF cavity, 04 RF generator, 05 laser generator, 06 pulse train generator, 07 1/2 pulse pitch generator, 11
... Convex mirror, 12 ... Reflector, 13 ... Reflector, 14 ... Amplifier, 15 ... Reflector, 16 ... Reflector, 17 ... Concave mirror, 18
... Lens, 19 ... Beam split.

Claims (2)

(57) [Scope of request for utility model registration] 1. An excitation laser comprising: a mode-locked laser generator; and a pulse train generator for generating a pulse train of several GHz for each laser pulse output from the laser generator. apparatus. 2. A mode-locked laser generator, a pulse train generator for generating a continuous pulse train for each laser pulse output from the laser generator, and a pitch of a pulse train output from the pulse train generator 1/2
And a 1/2 pulse pitch generator.