JPS6248203B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical pulse shaper for obtaining optical pulses of arbitrary shapes, particularly optical pulses used in laser fusion.

The light pulse used in laser fusion is a light pulse that rises in several nanoseconds while its slope (differential coefficient) increases rapidly. However, a high-speed optical pulse with such a shape cannot be obtained from a normal laser oscillator, nor can it be obtained using a conventional low-speed (compared to the desired rise of the optical pulse) modulator. It is necessary to newly shape the optical pulse using an optical pulse shaper.

Conventionally, an optical pulse shaper for laser fusion, which will be explained in detail later with reference to FIG. The method used was to divide the pulses into an appropriate number of pulses, give them different relative delay times, and recombine them.

In this case, since one pulse is extracted from the pulse train, most of the energy obtained from the laser oscillator is wasted, and the energy is not used effectively.

Furthermore, since a large number of mirrors such as semi-transparent mirrors and total reflection mirrors are used, it is extremely difficult to adjust the optical axis, and the system is susceptible to fluctuations in environmental conditions such as temperature and atmospheric pressure, making maintenance difficult in practice.

In addition, the optical pulse shaper in this case can only obtain the same pulse waveform, and is therefore lacking in versatility.

In other conventional optical pulse shapers as well, as will be described in detail later with reference to FIG.
It uses two light pulses. A light pulse of a desired shape was obtained by a pulse cutter from an envelope light pulse (light pulse containing multiple light pulses) obtained by inputting one extracted light pulse into an etalon plate. .

Also in this optical pulse shaper, one optical pulse is extracted from the optical pulse train, so the laser oscillation output energy is not effectively utilized.

The purpose of the present invention is to utilize a plurality of optical pulses of a mode-locked optical pulse train obtained by a laser oscillator, to require only a small number of mirrors (three at the minimum), to facilitate optical axis adjustment, and to reduce maintenance. It is an object of the present invention to provide an optical pulse shaper that is easy to use and can appropriately select a pulse waveform, particularly for use in laser fusion.

According to the present invention, an optical pulse shaper that shapes a mode-locked optical pulse train of equal time intervals into a predetermined envelope optical pulse includes an input semi-transparent mirror, an output semi-transparent mirror, and at least one total reflection mirror. ,
A light pulse circulation route is configured to sequentially guide one optical pulse incident on the input semi-transparent mirror to the output semi-transparent mirror, the total reflection mirror and the input semi-transparent mirror and direct it again to the output semi-transparent mirror. Then, a part of the optical pulse is branched out from the output semi-transparent mirror in the middle of the optical pulse circulation route, and one rotation time of the optical pulse is equal to the period between the mode-locked optical pulses. A ring type optical circuit which is set to a value close to the time interval value and into which the mode-locked optical pulse train is input, and a predetermined one envelope from a plurality of envelope optical pulses emitted from the ring type optical circuit. An optical pulse shaper characterized in that it has an optical pulse extractor for extracting pulses is obtained.

Next, a detailed explanation will be given with reference to the drawings.

FIG. 1 is an example of a conventional pulse shaper. A single optical pulse 2 is extracted from an optical pulse train 1 obtained by a mode-locked laser oscillator using an optical pulse extractor 10. A single optical pulse 2 is divided into an appropriate number of optical pulses (four optical pulses in the case of the figure) by an optical pulse combiner 11, given different relative delay times, and combined as an envelope optical pulse 3. Ru. Regarding the principle of the optical pulse shaper shown in Figure 1,
Applied optics
Optics), Vol. 15, No. 12, pages 3054 to 3061, so the details will be omitted here.

In this optical pulse shaper, one of the optical pulse trains obtained by the mode-locked laser oscillator is
Since only one optical pulse is extracted and used, the other optical pulses in the optical pulse train are discarded and the energy is not used effectively. The pulse synthesizer 11 shown in Fig. 1 is constructed using a total of 8 mirrors, 6 semi-transparent mirrors and 2 reflecting mirrors (the actual one is constructed with 20 or more mirrors). Therefore, it was difficult to adjust the optical axis, and maintenance was difficult because it was susceptible to fluctuations in environmental conditions such as temperature and atmospheric pressure. Furthermore, this optical pulse shaper can only obtain optical pulses of the same shape and lacks versatility.

FIG. 2 shows another conventional example of an optical pulse shaper.
When a single optical pulse 2 extracted from an optical pulse train 1 obtained by a mode-locked laser oscillator using an optical pulse extractor 10 enters an etalon 12, an optical pulse train 4 having a repetition time determined by the etalon spacing is obtained. . A desired optical pulse is obtained as an envelope optical pulse 5 extracted from the optical pulse train 4 using an optical pulse extractor 13. Regarding this optical pulse shaper, please refer to the publication material UCRL-
51908 1976, Issue 1, 7, detailed explanation is omitted here.

This optical pulse shaper also uses only one optical pulse from the optical pulse train obtained by the mode-locked laser oscillator, and therefore does not utilize energy effectively.

The third embodiment of the optical pulse shaper according to the present invention is
It is shown in Fig. 4. This optical pulse shaper is composed of a ring type optical circuit 31 and an optical pulse extractor 32. The ring-shaped optical circuit 31 includes an input semi-transparent mirror 311, an output semi-transparent mirror 312, and a total reflection mirror 3.
It is formed from three mirrors of 13, and the time for one round of light is t ₀
can be varied by, for example, moving the position of the reflecting mirror 302.

The function of this optical pulse shaper will be explained when an envelope optical pulse 20 such as that obtained from a Q-switch mode-locked laser oscillator is incident. The envelope light pulse 20 consists of component pulses 201, 2 with equal time intervals t ₁
02, 203, 204, 205, 206, 207
have.

First, consider the case where t ₁ > t ₀ and t ₀ is set to a value near t ₁ (Figure 3). First envelope light pulse 2
When the first component pulse 201 of 0 enters the ring-shaped optical circuit 31, a part 211 of the component pulse 201 is outputted through the output semi-transparent mirror 312. On the other hand, a part of the component pulse 201 reflected at 312 is 3
13, 311 and enters the second circuit, but after (t ₁ - _{t 0} ) time from that point, the second component pulse 202 of the envelope optical pulse 20 enters the ring-shaped optical circuit 31. Therefore, after time t ₀ from the first emitted optical pulse 211, the component pulse 20
1 and part of the component pulse 202 are emitted. The spacing between the components of envelope light pulse 212 is _t2 = _t1 - _t0 .

Similarly, the _envelope pulse 213,
214, 215, . , and the time width is (n-1)×(t ₁ −t ₀ ). The light intensity P _Nput of the Nth component pulse of the nth output envelope light pulse is expressed by the following equation.

P _Nput = P _Nio × T _n1 × T _n2 (R _n1 × R _n2 × R _n3 ) ^nN (However, nN) Here, P _Nio is the N of the incident envelope optical pulse 20.
The light intensity of the th component pulse, T _n1 and T _n2 are the transmittances of the semi-transparent mirrors 311 and 312, respectively, R _n1 and R _n2 ,
R _n3 are reflectances of 311, 312, and 313, respectively.

Finally, 211, 212, 213, 214, 2
The optical pulse extractor 32 extracts and outputs a desired envelope pulse 22 from the output envelope optical pulse group 21 consisting of the output envelope optical pulses 15, .

Next, the case where t ₁ <t ₀ and t ₀ is set to a value near t ₁ (FIG. 4) will be explained.

When the first component pulse 201 of the envelope optical pulse 20 first enters the ring-shaped optical circuit 31,
A portion 231 of the component pulse 201 is emitted through the semi-transparent mirror 312 for emission. On the other hand, a part of the component pulse 201 reflected at 312 is reflected at 313 and 311 and enters the second round, but from that point on (t ₀
Since the second component pulse 202 of the envelope light pulse 20 has already entered before the time t ₁ ), the envelope light pulse 232 that is emitted after t ₁ time from the first emitted light pulse 231 is , the order of the incident envelope light pulses 20 is reversed. Do the same below
_Envelope light pulses 233, 234, 235,
... is emitted. These envelope light pulses 231,
The n-th envelope optical pulse of the envelope optical pulse group 23 consisting of 232, 233, 234, 235, ... has n component pulses, and the N-th component pulse is the (n -N+1)
(where Nn), its light intensity P _Nput is P _Nput = P _(o-N+1)io ×T _n1 ×T _n2 × (R _n1 × R _n2 × R _n3 ) ^{( N-1)} . Here, P _(o-N+1)io is the optical intensity of the (n-N+1)th component pulse of the incident envelope optical pulse.

Further, the time width of the n-th envelope optical pulse is (n-1)(t ₀ -t ₁ ).

In this case as well, the output envelope optical pulse group 23 is finally
From there, a desired envelope light pulse 22 is extracted and emitted by the light pulse extractor 32.

By the way, as mentioned above, since the one-round time t ₀ of the ring-shaped optical circuit 31 in the example of FIGS. 3 and 4 is variable, the gain can be obtained by setting t ₀ to another value around t ₁ . The time width (n-1) |t ₀ -t ₁ | of the envelope light pulse 22 or 24 is variable.

Therefore, by using the optical pulse shaper shown in Figures 3 and 4, the shape of the incident envelope optical pulse can be reversed or the time width can be varied, allowing for a wider range of uses than conventional ones. can.

Further, the ring type optical circuit 31 includes a semi-transparent mirror 311,
Since only three mirrors, 312 and 313, are used, optical axis adjustment is easy and maintenance is easy.

FIG. 5 shows an optical pulse shaper which is an embodiment of the present invention, in which a light intensity modulator 30 is added to the optical pulse shaper shown in FIG.

In this case, an appropriately shaped envelope optical pulse 25 is obtained from the optical pulse train 1 obtained by the mode-locked laser oscillator using the optical intensity modulator 30.
Note that the optical intensity modulator 30 that obtains the envelope optical pulse 25 from the optical pulse train 1 can be operated at a relatively low speed.
It can be easily obtained by conventional techniques.

When the envelope light pulse 25 enters the ring-shaped optical circuit 31, an envelope light pulse group 26 is emitted, from which a desired envelope light pulse 27 is extracted and emitted by using the light pulse extractor 32. .

Since this optical pulse shaper uses the optical intensity modulator 30, the shape of the optical envelope optical pulse 27 obtained can be arbitrary, making it more versatile.

The optical pulse shapers shown in Figures 3, 4, and 5 use multiple optical pulses for shaping, so they are better than the conventional optical pulse shapers shown in Figures 1 and 2. , the energy use efficiency is high.

As detailed above, according to the present invention, a ring type optical circuit is used to utilize a plurality of optical pulses.
An optical pulse shaper with variable time width and shape reversibility is obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional optical pulse shaper using a large number of mirrors, Fig. 2 is a block diagram of a conventional optical pulse shaper using an etalon plate and a pulse cutter, Figs. 4 and 5 are block diagrams of optical pulse shapers according to embodiments of the present invention, respectively. In the figure, 31 is a ring-type optical circuit that obtains a group of output envelope light pulses having a shape different from that of the input envelope pulse, and 32 is a pulse extractor that obtains a desired single envelope light pulse from the group of output envelope light pulses. , 30 is a light intensity modulator.

Claims (1)

[Claims] 1. An optical pulse shaper that shapes a mode-locked optical pulse train of equal time intervals into a predetermined envelope optical pulse, which has an input semi-transparent mirror, an output semi-transparent mirror, and at least one total reflection mirror, and A light pulse circulation route is configured in which one optical pulse incident on the transmissive mirror is sequentially guided to the emitting semi-transparent mirror, the total reflecting mirror, and the incident semi-transparent mirror and directed back to the emitting semi-transparent mirror, and the light pulse is A part of the optical pulse is branched out from the output semi-transparent mirror in the middle of the pulse circulation route, and one round trip time of the optical pulse is in the vicinity of the time interval value between the mode-locked optical pulses. a ring-shaped optical circuit into which the mode-locked optical pulse train is input, and an optical pulse for extracting a predetermined one envelope pulse from a plurality of envelope optical pulses emitted from the ring-shaped optical circuit; An optical pulse shaper characterized by having an extractor.