Coherent light coupling device

The present invention relates to a laser apparatus, and more particularly to a technique for increasing the intensity by photocoupling a plurality of laser beams.

In recent years, research and development on creating a fusion reaction by instantaneously heating an ultrahigh-density plasma (plasma of solid or higher density) using high-intensity short-pulse laser light has been actively carried out. It's coming. Conventionally, in order to obtain such a high-intensity laser beam, the laser light emitted from the laser light source is focused by using a lens system or a condenser mirror (see, for example, Patent Document 1).

<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2004-55819</text></patcit>

<p> In the conventional laser device disclosed in Patent Document 1, one laser beam emitted from the laser light source is focused by using a lens system or a condenser mirror, so that the output of the laser light source is increased. There is a problem that the increase in intensity of the laser beam is limited due to the limitation of the laser beam and the light resistance of the lens system and the condensing mirror.</p><p> The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to increase the intensity of a laser beam in a laser apparatus.</p>

<p> The coherent optical coupling device according to the present invention includes a distribution unit that distributes a laser beam output from a laser light source to a plurality of laser beams, an amplification unit that amplifies the plurality of laser beams distributed by the distribution unit, and the above. Based on the observation results of the light intensity distribution in the condensing unit that condenses the plurality of laser beams amplified by the amplification unit and the plurality of laser beams focused by the condensing unit, the condensing unit condenses the light. It is provided with a light intensity distribution control unit that controls the light intensity distribution in a plurality of laser beams to be generated.</p>

<p> According to the present invention, in a coherent optical coupling device, laser light output from a laser light source is distributed to a plurality of laser beams, amplified, and then the plurality of laser beams are focused so as to obtain a desired light intensity distribution. However, it is possible to increase the intensity of the laser beam.</p>

Embodiment 1. The coherent optical coupling device according to the first embodiment of the present invention distributes the laser light output from the laser light source into a plurality of laser beams, amplifies each of them, and then determines the phase difference between the laser beams. By controlling the phase difference so as to reduce the time fluctuation and further controlling the phase difference so as to obtain a desired light intensity distribution and condensing the light, it is possible to increase the intensity of the laser beam. It is a thing.

FIG. 1 is a configuration diagram showing a coherent optical coupling device according to the first embodiment of the present invention. In FIG. 1, 1 is a laser light source, 2 is a distribution unit, 3 is a first phase controller, 4 is an amplification unit, 5 is a first separation unit, 6 is a second phase controller, and 7 is a condensing unit. , 8 is the second separation part, 9 is the phase observation part, and 10 is the light intensity distribution observation part. The first phase controller 3, the first separation unit 5, and the phase observation unit 9 form a phase control unit. The second phase controller 6, the second separation unit 8, and the light intensity distribution observation unit 10 constitute a light intensity distribution control unit. In FIG. 1, a case where the distribution unit 2 distributes to four laser beams is shown as an example, but the number of distributions is not limited to this. The first phase controller 3 and the second phase controller 6 may be installed anywhere as long as they are between the distribution unit 2 and the light collection unit 7 in the drawing.

Next, the operation will be described. In FIG. 1, the pulsed laser beam output from the laser light source 1 is distributed to four laser beams by the distribution unit 2, amplified by the amplification unit 4, and condensed to a predetermined focusing point by the focusing unit 7. Coherent photocoupled. The coherent optical coupling means that a plurality of coherent lights are phase-matched and coupled. Here, since the laser beam is distributed, amplified, and then condensed, the limit of high output of the laser light source 1 and the optics in the optical path such as the lens system of the condensing unit 7 and the condensing mirror. The intensity can be increased according to the number of distributions, exceeding the limit due to the light resistance of the parts. In the first embodiment, since the light intensity is divided into four, it is possible to increase the intensity by about four times in the electric field, that is, about 16 times in the light intensity. Although the case where the laser beam is a pulse is shown, the same effect can be obtained even if the laser beam is a continuous wave.

Next, the operation of phase matching will be described. In the first separation unit 5, a part of each of the four laser beams is separated, and in the phase observation unit 9, the phase difference between the separated laser beams is observed. Then, the first phase controller 3 controls the phase difference between the four laser beams so that the time variation of the observed phase difference is reduced. Since the time variation of the phase difference of each laser beam is always generated due to the mechanical vibration of the optical component in each optical path, the ambient temperature fluctuation, etc., the phase difference control in this case is more than the time variation. You always have to do it fast. However, if the time fluctuation of the phase difference is not a problem due to the mechanical vibration of the optical component or the measures for reducing the ambient temperature fluctuation, the phase control unit may be omitted.

In the second separation unit 8, a part of the four laser beams focused on a predetermined focusing point by the focusing unit 7 is separated while being focused, and in the light intensity distribution observation unit 10, the light intensity distribution observation unit 10 separates the laser beams. A part of the light intensity distribution of each laser beam separated and focused on the conjugate point of the predetermined focusing point is observed. Then, the second phase controller 6 controls the light intensity distribution by controlling the phase difference between the four laser beams so that the observed light intensity distribution becomes a desired light intensity distribution. Since the time variation of the phase difference between the laser beams is reduced by the first phase controller 3, the phase difference control in this case may normally be performed as necessary at the time of initial setting or the like. This reduces the static phase difference remaining between each distributed and amplified laser beam and corrects the deformation of the light intensity distribution due to this phase difference, for example, peak intensity at a single peak. It can be focused as a high-intensity laser beam with a desired light intensity distribution such as high.

In addition, the desired light intensity distribution is used by using both the static phase difference observation result remaining between each laser beam by the phase observation unit 9 and the light intensity distribution observation result by the light intensity distribution observation unit 10. The phase difference between the four laser beams may be controlled by using the second phase controller 6 so as to obtain the above. This makes it possible to improve the convergence of the phase difference control and improve the accuracy of the phase difference control.

Next, the operation in each part will be described. The laser light source 1 is, for example, a solid-state laser or an optical fiber laser to which neodymium ions are added, and the laser wavelength is about 1 μm. Similarly, the amplification unit 4 is a solid-state laser amplifier or an optical fiber laser amplifier to which neodymium ions are added, and the amplification wavelength is about 1 μm. Needless to say, the types of lasers and amplifiers and the operating wavelengths are not limited to the above.

In the distribution unit 2, the first separation unit 5, and the second separation unit 8, a partially reflective optical mirror installed at an angle of 45 degrees in the optical path separates the reflected light and the transmitted light into different optical paths. ..

In the condensing unit 7, each laser beam is condensed to a predetermined condensing point by a condensing optical system arranged in the optical path. The condensing optical system is configured by using, for example, a lens or a mirror. Further, the number of lenses and mirrors may be one for each beam or one for all beams.

In the first phase controller 3 and the second phase controller 6, the phase difference controller moves the distance between the optical mirrors installed in parallel in the optical path by an actuator to move the optical path length of the laser beam passing through. Phase difference control is performed by changing. As the actuator, for example, a piezo actuator is used. Alternatively, an electro-optical crystal may be placed in the optical path, and the refractive index may be changed by a voltage applied to the crystal to change the optical path length of the passing laser beam to control the phase difference.

In the phase observation unit 9, the phase difference sensor that detects the phase difference between the four laser beams uses one of the four laser beams as a reference, and the reference beam laser and the other three laser beams, respectively. Phase difference is detected from the difference in interference light intensity. The phase difference sensor includes an optical system for interfering the reference beam laser with the other three laser beams, and an optical sensor for detecting the interference light intensity, for example, a silicon optical sensor.

In addition to the laser light source 1, a reference laser light source that outputs a reference laser beam is additionally configured, and in the phase observation unit 9, the distribution unit 2 distributes the laser beam from the laser light source 1 into four parts. With the reference laser beam as a reference, the phase difference may be detected from the interference light intensity difference between each reference beam and each laser beam from the laser light source 1. If the reference laser beam is a continuous wave instead of a pulse, it is not necessary to consider the adjustment of the pulse position with the laser beam from the laser light source 1, and the detection is easy.

Further, the phase states include a phase difference (positional deviation of the equiphase plane), an inclination of the equiphase plane, and a shape of the equiphase plane (distortion from the plane). In the first embodiment, a phase difference sensor is configured as the phase observation unit 9 to detect the phase difference, and a phase difference controller is configured as the first phase controller 3 to control the phase difference. However, if necessary, a tilt sensor for the equiphase plane and a tilt controller for the equiphase plane may be added to detect and control the tilt of the equiphase plane. Since the distortion of the shape of the equiphase plane is mainly caused by the distortion of the lens and the mirror, the time fluctuation is usually not a problem and is not as good as the first phase controller 3. The equiphase plane tilt sensor is, for example, a Shackhardman sensor that divides a laser beam by a microlens array and focuses it, and detects the tilt of the equiphase plane from the focused position, or a four-quadrant silicon optical sensor. .. The equiphase plane tilt controller controls the tilt of the equiphase plane by moving the tilt of the optical mirror installed in the optical path with an actuator.

The light intensity distribution observation unit 10 detects the light intensity distribution of the focused laser beam using, for example, a two-dimensional silicon optical sensor.

As described above, in the coherent optical coupling device according to the first embodiment of the present invention, the laser light output from the laser light source is distributed to a plurality of laser beams, amplified, and then the phase difference between the laser beams. It is possible to increase the intensity of the laser beam by controlling the phase difference so as to reduce the time fluctuation of the laser beam and controlling the phase difference so as to obtain the desired light intensity distribution. it can.

Embodiment 2. In Embodiment 1, the light intensity distribution is observed by the light intensity distribution observation unit 10, and the position between the four laser beams is obtained by the second phase controller 6 so that the desired light intensity distribution can be obtained. Although the phase difference is controlled, in the second embodiment, instead of the second phase controller 6, a phase difference controller, an equiphase plane tilt controller, an equiphase plane shape controller, and a focusing position are used. At least one of the controller and the polarization rotation controller is arranged, and the phase difference of the four laser beams, the inclination of the equiphase plane, the shape of the equiphase plane, the focusing position, and the polarization are arranged so that the desired light intensity distribution can be obtained. It controls at least one of the states.

The configuration of the second embodiment is the same as that of the first embodiment shown in FIG. However, for example, when an equiphase plane tilt controller is arranged in the second phase controller 6, the equiphase plane tilt control is performed by moving the tilt of the optical mirror installed in the optical path with an actuator. Do. In the equiphase plane shape controller, a plurality of actuators are installed on the back surface of the optical mirror, and the shape of the equiphase plane is controlled by an active support mechanism that deforms the shape of the mirror by pushing the mirror with the actuators. The condensing position controller controls the condensing position by changing the distance between the condensing unit 7 and the predetermined condensing point. The polarization rotation controller controls the polarization state so that the polarization planes of the four laser beams are aligned by the polarization rotator arranged in the optical path. The polarized rotator is configured by using, for example, an optical mirror or the like.

In addition to the light intensity distribution observation unit 10, at least one of a phase difference sensor, an equiphase plane inclination and equiphase plane shape sensor, and a polarization measurement sensor is configured, and a controller corresponding to these observation results is used. It may be controlled. Here, the equiphase plane inclination and equiphase surface shape sensor is a Shackhardman sensor that divides a laser beam by a microlens array and condenses it, and detects the equiphase surface inclination from the condensing position.

As described above, in the coherent optical coupling device according to the second embodiment of the present invention, the laser light output from the laser light source is distributed to a plurality of laser beams, amplified, and then the phase difference between the laser beams. The phase difference is controlled so that the time variation of the laser is reduced, and at least the phase difference, the inclination of the equiphase plane, the shape of the equiphase plane, the focusing position, and the polarization state are obtained so that the desired light intensity distribution can be obtained. By controlling one and condensing it, it is possible to increase the intensity of the laser beam.

In the first and second embodiments of the present invention, the frequency of the pulsed laser beam output from the laser light source 1 is chirped, and a pulse compressor arranged between the amplification unit 4 and the condensing unit 7 is used. A pulsed laser beam whose frequency is chirped and amplified may be pulse-compressed. This makes it possible to obtain a pulsed laser beam with high peak intensity. The frequency chirp and pulse compression can be performed by using, for example, a grating. Further, the arrival time of each of the four pulses may be measured by the pulse delay measurement sensor arranged at the position of the light intensity distribution observation unit 10 to confirm the pulse position.

<figref num="1">Configuration diagram showing the coherent optical coupling device according to the first embodiment of the present invention.</figref>

Code description

1 Laser light source 2 Distributor 3 Distributor 3 First phase controller 4 Amplifier 5 First separation 6 Second phase controller 7 Condensing 8 Second separation 9 Phase observation 10 Light intensity distribution observation