JP2003023194A - Solid-state laser amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid-state laser amplifier utilizing a laser crystal in which amplification is repeated a large number of times using a single amplifier by spatially turning back a laser light emitted from the laser crystal using a laser crystal having opposite ends cut at Brewster's angle or an angle close to that and directing the laser light again toward the laser crystal while varying the incident angle. SOLUTION: Using a single laser crystal having opposite ends cut at Brewster's angle or an angle close to that, an incident light is directed toward that crystal and the outgoing laser light from the crystal is directed again toward the crystal a plurality of times while varying the incident angle spatially. Since the laser light advances each time through the crystal while reflecting in zigzag a plurality of times, the laser crystal is thoroughly utilized for irradiation resulting in a solid state laser amplifier having an enhanced optical energy takeout efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light amplifier using a laser crystal. In particular,
The present invention uses a laser crystal whose both ends are cut at Brewster's angle or at an angle close to it, spatially folds the laser light emitted from the laser crystal, changes the incident angle, and re-enters the laser crystal to produce one laser light. It is a solid-state laser amplifier characterized by being amplified many times by the amplifier of.

[0002]

2. Description of the Related Art Conventionally, in order to amplify the output of laser light generated by a solid-state laser oscillator, the laser light from the oscillator is made incident on a plurality of amplifiers or is folded back and forth through the amplifiers to increase the output. Is used.

In the method using a plurality of amplifiers, laser light is gradually amplified by each amplifier in order to enhance the output. For this reason, there is a problem that a considerable part of the energy accumulated in each amplifier is not extracted as light and remains in the amplifier, resulting in low laser oscillation efficiency.

In the folding amplification method, a method of changing the incident angle to the laser crystal in order to make the laser beam reciprocate, or utilizing one of the crystals as a reflecting surface is used. In the conventional methods, it is very difficult to adjust the optical path and correct the thermal lens effect because the angle of the laser beam that emerges also changes when the angle of incidence on the laser crystal changes.

[0005]

The folding amplifier described above has the following problems, and it is necessary to solve them. First of all, when the laser output becomes high,
The laser crystal is distorted by heat, and as a result, the crystal acts like a lens (thermal lens effect) and, in the worst case, focuses inside the crystal and destroys it.

Secondly, although energy is stored in the laser crystal, it cannot be efficiently extracted with one turn.

[0007]

The present invention is intended to solve the above problems. First, in order to solve the first problem, the present invention uses an amplified incident laser beam spatially. Re-enters the laser crystal at different angles. Therefore, at this time, the thermal lens effect is suppressed by performing image transfer so that the lens effect does not occur.

Further, in order to solve the second problem, in the present invention, the energy extraction efficiency can be improved by returning the laser light a plurality of times under the conditions described below.

That is, the present invention uses one laser crystal whose both ends are cut at a Brewster's angle or an angle close thereto, and after the incident light is incident on the crystal, a plurality of laser lights emitted from the crystal are spatially separated. Improves the extraction efficiency of light energy by turning back and re-incident on the crystal by changing the incident angle, and by making total reflection of the laser light in zigzag multiple times in the crystal to make progress and irradiating the laser crystal evenly. This is a solid-state laser amplifier.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The above Brewster angle is such that when monochromatic linearly polarized light such as laser light is incident on a crystal or the like, the reflection coefficient of light whose polarization direction is perpendicular to the incident surface is zero (loss is Incident angle. As shown in FIG. 3, this angle (θ) changes depending on the refractive index (n) of the medium into which light is incident, and is represented by θ = tan ⁻¹ n. For example, since the Nd: YAG crystal has a refractive index of 1.818, its Brewster angle is about 61.19 degrees.

In order to perform the above-mentioned multiple reflection of the laser light, for example, the crystal cutting angle is about 28.8 degrees and the crystal length is 81 mm. The conditions are selected so that the total number of times of total reflection within the laser crystal is an integer. For example, if the incident angle is 6
It is 15 times at 1.5 degrees, 17 times at 51.8 degrees, 19 times at 44.1 degrees, 21 times at 37.8 degrees, and so on. By using this condition, for example, the incident angle to the crystal is changed at the above-mentioned angle, and the laser light incident at the last 37.8 degrees is folded back by using the mirror, thereby making it possible to carry out folding amplification eight times in total. Become. The critical angle of YAG crystal is 3
Since it is 3.3 degrees, if the reflection angle of the laser light in the crystal is more than this, the incident light will be totally reflected in the crystal and come out, so that it can be folded eight times or more. .

Furthermore, when the incident angle of the laser beam on the crystal is changed, the number of total reflections in the crystal is changed and the optical path is also changed. As a result, the laser crystal is evenly irradiated.
Therefore, the energy extraction efficiency is further improved. Hereinafter, the present invention will be described based on examples.

[0013]

[Example] (Example 1) In FIG.
It shows the case of going back and forth (passing 8 times). 1 is an incident laser beam, 2 is a polarization element for extracting amplified light, and 3 is a polarization rotation 1
/ 2 wavelength plate, 4 Faraday rotator, 5 laser crystal, 6 image transfer lens, 7 dielectric breakdown preventing vacuum cell, 8 folding mirror, and 9 amplified and extracted laser light.

The incident laser light 1 passes through a polarized element 2 for extracting amplified light, a 1/2 wavelength plate 3 for polarization rotation, and a Faraday rotator 4, and is incident on a laser crystal 5. The laser light emitted from the crystal is transferred into the laser crystal by the two image transfer lenses 6. The incident angle of the laser light at this time is set to the angle described above. That is, the incident angle was set to about 59.1 degrees, which is the Brewster angle or an angle close thereto. This was determined in consideration of the influence of heat at the crystal edge.

The incident laser light is totally reflected inside the crystal, and the amplified laser light emerges from the crystal at the same angle as the incident angle. At this time, similarly to the first time, the image in the crystal is transferred into the crystal again by using the two lenses 6. The angle of incidence of the laser light on the crystal is set to the angle described above, and the same operation is performed twice more. At the end, a mirror 8 is folded at the exit of the crystal.
Is set, the amplified laser beam 9 returns to the same optical path and is extracted outside the optical path by the amplified light extraction polarization element 2. That is, in FIG. 2, the laser light is 4 in total.
It shows the case of reciprocating (passing 8 times) in the recrystallized crystal.

(Embodiment 2) FIG. 2 shows an experimental result when a laser beam is passed through a crystal four times. As the incident light passes through the laser crystal once, 24% of the energy stored in the crystal is extracted as light. This laser light is turned back inside the crystal four times, and 62% of the stored energy is extracted as light.

[0017]

INDUSTRIAL APPLICABILITY In the present invention, one laser crystal whose both ends are cut at Brewster's angle or an angle close to it is used, and after incident light is incident on the crystal, the laser light emitted from the crystal is spatially separated. It is possible to improve the extraction efficiency of light energy by making multiple reflections and re-incidents, and by totally reflecting the laser light in the crystal multiple times in a zigzag manner and by irradiating and utilizing the laser crystal evenly. The remarkable effect peculiar to this invention is produced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a spatial amplification method of the present invention.

FIG. 2 is a diagram showing energy extraction efficiency when laser light is returned four times in a crystal.

FIG. 3 is a diagram showing Brewster angles.

[Explanation of symbols]

1: Incident laser light 2: Polarizing element for extracting amplified light 3: 1/2 wavelength plate for polarization rotation 4: Faraday rotator 5: Laser crystal 6: Lens for image transfer 7: Vacuum cell for insulation breakdown prevention 8: Folding mirror 9: Laser light amplified and taken out

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Kato             4 of 2 Shirane, Shikata, Tokai-mura, Naka-gun, Ibaraki Prefecture               Japan Atomic Energy Research Institute Tokai Research Center F term (reference) 5F072 AB01 AK03 AK09 JJ01 JJ02                       JJ06 KK05 KK15 KK18 KK30                       MM00

Claims (5)

[Claims] 1. A solid-state laser amplifier using a laser crystal whose both ends are cut at a Brewster's angle or an angle close thereto. 2. A solid-state laser amplifier characterized in that laser light is totally reflected in a zigzag manner a plurality of times in a laser crystal. 3. A solid-state laser amplifier characterized in that the incident angle of laser light incident on a laser crystal is variable. 4. A solid-state laser amplifier characterized in that a laser beam emitted from a laser crystal is spatially folded back and is incident on the laser crystal again at a different incident angle so that the laser light is amplified many times by one amplifier. 5. A solid-state laser amplifier characterized by being able to correct the thermal lens effect in a spatial amplification method.