JP2006269587A - Pulse width variable laser resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pulse width variable laser resonator the revision of the length of which is achieved without the need for revising the size of the whole resonator, capable of attaining high mechanical stability, and preventing a remarkable change in a laser output and the occurrence of damages to an optical component. <P>SOLUTION: The laser resonator is provided with a pair of roof prisms whose ridgelines are orthogonal to each other, a laser medium located on the optical axis of the laser resonator, a stimulation light source for stimulating the laser medium, and a reflector for confining the stimulated light produced from the stimulation light source. In the resonator, the reflector fixed with the laser medium and the stimulation light source can be moved in parallel in a way of not tilting the end face of the laser medium, so that the number of times of the laser beam passing through the ridgelines of the roof prisms can be varied in response to a required pulse width when the laser beam once circulates the resonator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser resonator of variable pulse width, which is used in, for example, a solid-state laser device for a laser guidance device and employs a roof prism.

A conventional laser resonator includes a pair of reflecting mirrors arranged opposite to each other, a laser medium arranged concentrically between the reflecting mirrors, and an excitation light source for exciting the laser medium. In the laser resonator, in order to change the pulse width, it is necessary to change the input energy of the excitation light source, the resonator length, and the polarizer reflectance. (For example, refer nonpatent literature 1).

Springer series in OPTICAL SCIENCES Vol.1 `` Solid-State Laser Engineering Fifth Revised and Updated Edition '' by Walter Koechner P.219

When the pulse width is changed in the resonator arranged with the two reflecting mirrors as described above, changing the input energy of the excitation light source has a large effect on the laser output. Will drop significantly. In addition, changing the resonator length has an adverse effect such as an increase in the size of the resonator and a decrease in mechanical stability because the interval between the reflecting devices is increased when the resonator length is increased. Also, changing the polarizer reflectivity greatly affects the output energy and the internal energy of the resonator. In some cases, the increase of the internal energy of the resonator damages the optical components constituting the resonator.

  The present invention has been made to solve such a problem, and realizes the change of the resonator length without changing the size of the whole resonator, the high mechanical stability, the remarkable change of the laser output and the resonance. It is an object of the present invention to provide a pulse width variable laser resonator capable of preventing damage to optical components due to an increase in internal energy of the resonator.

A pulse width variable laser resonator according to the present invention has a first roof prism having first and second reflecting surfaces arranged at right angles to each other and third and fourth reflecting surfaces arranged at right angles to each other. A laser resonator including a second roof prism, a laser medium installed on an optical axis of the laser resonator, an excitation light source for exciting the laser medium, and the laser medium and the excitation light source. And a reflector for confining the excitation light generated from the excitation light source, and a translation means for translating the reflector in a direction perpendicular to the optical axis of the laser resonator,
The resonator length of the laser resonator is changed by the parallel moving unit moving the reflector in the direction perpendicular to the optical axis of the laser resonator.

  According to the present invention, the length of the resonator can be changed without changing the size of the entire resonator, and the optical component is small, has high mechanical stability, has a significant change in laser output, and increases the internal energy of the resonator. Thus, it is possible to obtain a laser resonator with a variable pulse width that prevents damage of the laser.

Embodiment 1 FIG.
1 is a configuration diagram showing a pulse width variable laser resonator according to a first embodiment of the present invention. In FIG. 1, a first roof prism 1 and a second roof prism 2 constitute a pair of roof prisms for confining laser light. The ridge line 1a of the first roof prism 1 and the ridge line 2a of the second roof prism 2 are They are orthogonal to each other. Further, as shown in FIG. 2, the first roof prism 1 does not intersect the first ridge line 1a of the first incident surface 1d, and the fifth reflecting surface 1e is installed in the lower half of the roof prism. is doing. The laser medium 3 is excited by an excitation light source 4. The reflector 6 holds the laser medium 3 and the excitation light source 4 and efficiently makes the light from the excitation light source 4 incident on the laser medium 3. The polarizer 7 has a function of an output reflecting mirror. The first roof prism 1, the second roof prism 2, the laser medium 3, the polarizer 7, and the Pockels cell 14 are all concentrically coaxial, and the polarizer 7 is disposed at a Brewster angle with respect to the optical axis. ing. The reflector 6, the polarizer 7, and the Pockels cell 14 are fixed by the ASSY 8 and can be translated by the ASSY translation unit 9.

Here, the resonator length R, the speed of light c ₀ , the resonator internal loss L, the resonator circulation time is t _R = 2R / c ₀ , the small signal gain of the laser medium 3 is g ₀ l, and the variable Z = 2g ₀ l / L, a = when (Z-1) / (zln (Z)), the Q-SW laser when the output bond content optimal conditions, the pulse width _{t p is, t p = t R / L} [ln (Z) / {Z (1-a (1-ln (a)))}]. Pulse width t _p and the resonator length R is in proportional relation, if the cavity length is increased to n times the pulse width also increases to n times. Thus, by varying the resonator length R, it is possible to adjust the pulse width t _p.

Next, the operation will be described. FIG. 3 is an explanatory diagram showing the operation of the pulse width variable laser resonator when the resonator length is R. FIG. The light in the same direction as the optical path 5a of the light generated from the laser medium 3 excited by the excitation light source 4 proceeds to the roof prism 2 and is reflected by the third reflection surface 2b and the fourth reflection surface 2c, and is opposite to the incident light. The light travels in the direction along the optical path 5a, passes through the laser medium 3, is amplified, passes through the Pockels cell 14, the polarizer 7, travels to the first roof prism 1, and the first and second reflecting surfaces 1b, 1c. After being reflected, the light passes through the polarizer 7 and the Pockels cell 14 sequentially along the optical path 5a in the direction opposite to the incident light, and then passes through the laser medium 3 again. This operation is repeated, and when the energy accumulated in the laser medium 3 becomes larger than the loss inside the resonator, laser light is output from the polarizer 7. At this time, the resonator length is R [mm], and the pulse width is t _p [ns].

Next, a method for extending the resonator length from R to 2R will be described. 4A and 4B are cross-sectional views with respect to the yz plane including the first optical path 5a of FIG. 1, in which FIG. 4A is a diagram before the ASSY 8 is translated, and FIG. 4B is a diagram after the ASSY 8 is translated. When extending the resonator length from R to 2R, the ASSY 8 is translated in the y-axis direction by the ASSY parallel moving means 9 in FIG. The light does not enter the second ridge line 2a of the second roof prism 2, and all the light is reflected on the third reflection surface 2b and the fourth reflection surface 2c.

FIG. 5 is an explanatory diagram showing the operation when the resonator length is 2R. The light in the same direction as the optical path 5a of the light excited by the excitation light source 4 and generated from the laser medium 3 proceeds to the roof prism 2, reflects the third reflecting surface 2b, travels along the second optical path 5b, 4 is reflected on the reflecting surface 2c, travels along the third optical path 5c, enters the first roof prism 1, reflects on the first and second reflecting surfaces 1b, 1c, and in a direction opposite to the incident light. Proceed along the optical path 5c, enter the second roof prism 2, reflect the fourth reflecting surface 2c, proceed along the second optical path 5b, reflect the third reflecting surface 2b, and enter the optical path 5a. And then enters the laser medium 3, is amplified, passes through the Pockels cell 14 and the polarizer 7, proceeds to the first roof prism 1, and is incident on the first and second reflecting surfaces 1 b and 1 c after being reflected. The light passes through the polarizer 7 and the Pockels cell 14 sequentially along the optical path 5a in the opposite direction to the light, It passes through the laser medium 3. This operation is repeated, and when the energy accumulated in the laser medium 3 becomes larger than the loss inside the resonator, laser light is output from the polarizer 7. At this time, the resonator length is 2R [mm], and the pulse width is 2 t _p [ns]. Note that the distance between the third reflecting surface 2b and the fourth reflecting surface 2c is much smaller than the distance R between the first roof prism 1 and the second roof prism 2, and is ignored. Yes.

Next, a method for extending the resonator length from 2R to 4R will be described. 6A and 6B are cross-sectional views with respect to the xz plane including the first optical path 5a of FIG. 1, in which FIG. 6A is a diagram before ASSY is translated, and FIG. 6B is a diagram after ASSY translation. When extending the resonator length from 2R to 4R, the ASSY 8 is translated in the x-axis direction by the ASSY parallel moving means 9 in FIG. The incident light does not enter the first ridge line 1a of the first roof prism 1, and all the light is reflected on the first reflecting surface 1b or the second reflecting surface 1c.

FIG. 7 is an explanatory diagram showing the operation when the resonator length is 4R. The light in the same direction as the optical path 5a of the light generated by the pumping light source 4 and generated from the laser medium 3 travels to the second roof prism 2, reflects the third reflecting surface 2b, and follows the second optical path 5b. And then reflected on the fourth reflecting surface 2c, proceeded along the third optical path 5c, reflected on the fifth reflecting surface 1e of the first roof prism 1, and the third optical path in the direction opposite to the incident light. 5c, enters the second roof prism 2, reflects the fourth reflective surface 2c, travels along the second optical path 5b, reflects the third reflective surface 2b, and travels along the optical path 5a. , Enters the laser medium 3, is amplified, passes through the Pockels cell 14 and the polarizer 7, travels to the first roof prism 1, reflects the second reflecting surface 1 c, and travels along the eighth optical path 5 h. And then reflected on the first reflecting surface 1b, proceeded along the seventh optical path 5g, , The third reflecting surface 2b is reflected, the light travels along the sixth optical path 5f, the fourth reflective surface 2c is reflected, the fifth travels along the optical path 5e, and the first roof prism. The first reflection surface 1b is reflected, the light travels along the fourth optical path 5d, the second reflection surface 2c reflects, the third light path 5c travels, and the fifth reflection surface 1e. , And travels along the third optical path 5c in the opposite direction to the incident light, reflects the second reflective surface 1c, travels along the fourth optical path 5d, reflects the first reflective surface 1b, Proceed along the fifth reflective surface 5e, proceed to the second roof prism 2, reflect the fourth reflective surface 2c, proceed along the sixth optical path 5f, reflect the third reflective surface 2b, Proceeds along the seventh reflecting surface 5g, enters the first roof prism 1, reflects the first reflecting surface 1b, and proceeds along the eighth optical path 5h. Reflects the second reflecting surface 1c, proceeds along a first optical path 5a, the polarizer 7, and sequentially passes through the Pockels cell 14, it passes through the laser medium 3 again. This operation is repeated, and when the energy accumulated in the laser medium 3 becomes larger than the loss inside the resonator, laser light is output from the polarizer 7. At this time, the resonator length is 4R [mm], and the pulse width is 4 t _p [ns]. In addition, the distance between the 1st reflective surface 1b and the 2nd reflective surface 1c and the distance between the 3rd reflective surface 2b and the 4th reflective surface 2c are the 1st roof prism 1 and the 2nd roof prism 2. The distance R between them is very small and ignored.

In this way, by moving the ASSY 8, the pulse width can be made variable stepwise, and by increasing the number of turns between the first roof prism 1 and the second roof prism 2, the resonator length is extended. Because of the configuration, it is easy to design a small size of the entire resonator. In addition, loss due to diffraction due to the ridgeline of the roof prism occurs and the use efficiency of the laser light is reduced, but it is not necessary to set the excitation energy near the threshold value and to significantly reduce the laser output. Further, since there is no need to change the amount of output coupling, it is possible to prevent damage to optical components due to an increase in resonator internal energy.
Further, as shown in FIG. 8A, the roof prism 12 has the ridge line 12a sandwiched, the reflecting surfaces 12b and 12c are installed at a right angle, and when the optical axis is incident perpendicular to the incident surface, The angle formed by the axis and the reflecting surfaces 12b and 12c is 45 °. Incident light traveling along an incident optical path 13a parallel to the optical axis 12 travels to the roof prism 12, reflects the reflecting surface 12b at a right angle, travels along the optical path 13c, reflects the reflecting surface 12c at a right angle, and reflects the reflected light path. Proceed along 13b. As shown in FIG. 8B, when the roof prism 12 has an inclination angle θ, the angle formed by the optical axis and the reflecting surfaces 12b and 12c is 45 + θ °, and along the incident optical path 13a parallel to the optical axis 12. The traveling incident light travels to the roof prism 12, reflects off the reflection surface 12b at a reflection angle of 90 + 2θ °, travels along the optical path 13c, reflects off the reflection surface 12c at a reflection angle of 90-2θ °, and travels along the reflection light path 13b. It will go on. As described above, the angle change between the incident light path 13a and the reflected light path 13b is 180 °, so that even if an inclination with the ridge line 12a as the central axis occurs, the light is reflected in parallel and in the opposite direction. For this reason, this resonator is composed of a pair of roof prisms whose ridge lines are orthogonal to each other, so that the inclination of the incident light to the roof prism caused by the inclination of the roof prism and the inclination and deviation of each optical component, deviation, The effect of being strong against vibration is obtained.

Embodiment 2. FIG.
FIG. 9 is a block diagram showing Embodiment 2 of the present invention. In the figure, the first roof prism 1 and the second roof prism 2 constitute a pair of roof prisms that confine the laser beam, and the ridge line 1a of the first roof prism 1 and the ridge line 2a of the second roof prism 2 are Orthogonal. Further, as shown in FIG. 2, the first roof prism 1 does not intersect the first ridge line of the first incident surface 1d, and the fifth reflecting surface 1e is installed in the lower half of the roof prism. ing. 3 is a laser medium, and the laser medium 3 is excited by an excitation light source 4. The reflector 6 holds the laser medium 3 and the excitation light source 4 and efficiently makes the light from the excitation light source 4 incident on the laser medium 3. The polarizer 7 has a function of an output reflecting mirror. The first roof prism 1, the second roof prism 2, the laser medium 3, the polarizer 7, and the Pockels cell 14 are all located concentrically and the polarizer 7 is arranged at a Brewster angle with respect to the optical axis. ing. The first roof prism 1 is translated in the x-axis direction by the first roof prism translation means 10, and the second roof prism 2 is translated in the y-axis direction by the second roof prism translation means 11. Is possible.

Next, a method for extending the resonator length from R to 2R will be described. 10 is a cross-sectional view with respect to the yz plane including the first optical path 5a of FIG. 1, in which (a) is before the second roof prism 2 is translated, and (b) is the second roof prism 2. It is a figure after translation. When the resonator length is extended from R to 2R, the light confined in the first and second roof prisms 1 and 2 from the second roof prism 2 parallel moving means 11 in FIG. The light is not incident on the second ridge line 2a of the prism 2, but is translated so that all the light is reflected by the third or fourth reflecting surfaces 2b and 2c.

Next, a method for extending the resonator length from 2R to 4R will be described. 11 is a cross-sectional view with respect to the xz plane including the first optical path 5a of FIG. 1, in which (a) is before translation of the first roof prism 1, and (b) is parallel to the first roof prism 1. FIG. It is a figure after a movement. When the resonator length is extended from 2R to 4R, the light confined in the first and second roof prisms 1 and 2 from the first roof prism 1 parallel moving means 10 in (a) is The light is not incident on the first ridge line 1a of the prism 1, but is translated so that all the light is reflected by the first or second reflecting surface.

Next, the operation will be described. The operation is the same as in the first embodiment.

In the pulse width variable laser resonator according to the second embodiment, as in the first embodiment, the size of the entire resonator is not changed, the mechanical stability is high, the laser output is significantly changed, and the optical energy due to the increase of the internal energy of the resonator is obtained. It is resistant to vibrations because it can prevent damage to the parts and compensate for the tilt. In addition, since the polarizer can be fixed, it is possible to make the emission position constant, and for each roof prism, since the tilt-invariant direction is only one direction, parallel movement is easy.

In the first and second embodiments, the case where the roof prism is used has been described. Needless to say, the roof prism can also be used in a reflection device in which the reflection surface is replaced with a reflection mirror.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows Embodiment 1 of this invention. 1 is an external view showing a first roof prism 1 of the present invention. It is explanatory drawing which shows the operation | movement at the time of the resonator length R of Embodiment 1 of this invention. It is the schematic which shows the parallel displacement of ASSY when extending the resonator length of Embodiment 1 of this invention from R to 2R. It is explanatory drawing which shows the operation | movement at the time of the resonator length 2R of Embodiment 1 of this invention. It is the schematic which shows the parallel displacement of ASSY when extending the resonator length of Embodiment 1 of this invention from 2R to 4R. It is explanatory drawing which shows the operation | movement at the time of the resonator length 4R of Embodiment 1 of this invention. It is explanatory drawing which shows the reflection state of the laser beam which injected into the roof prism when the roof prism of FIG. 1 inclines. It is a schematic block diagram which shows Embodiment 2 of this invention. It is explanatory drawing which shows the parallel displacement of the 2nd roof prism 2 when extending the resonator length of Embodiment 2 of this invention from R to 2R. It is explanatory drawing which shows the parallel displacement of the 1st roof prism 1 when extending the resonator length of Embodiment 2 of this invention from 2R to 4R.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 1st roof prism, 1a 1st ridgeline, 1b 1st reflective surface, 1c 2nd reflective surface, 1d 1st entrance plane, 1e 5th reflective surface, 2nd 2nd roof prism, 2a 1st 2 ridge lines, 2b third reflective surface, 2c fourth reflective surface, 2d first incident surface, 2e fifth reflective surface, 3 laser medium, 4 excitation light source, 5a first optical path, 5b second Optical path, 5c third optical path, 5d fourth optical path, 5e fifth optical path, 5f sixth optical path, 5g seventh optical path, 5h eighth optical path, 6 reflector, 7 polarizer, 8 ASSY, 9 ASSY Parallel moving means, 10 First roof prism parallel moving means, 11 Second roof prism parallel moving means, 12 Roof prism, 12a Ridge line, 12b Reflecting surface, 12c Reflecting surface, 12d Incident surface, 13a Incident light path, 13b Reflecting light path , 3c optical path 14 Pockels cell, 15 optical axis.

Claims (2)

Laser resonance comprising a first roof prism having first and second reflecting surfaces arranged at right angles to each other and a second roof prism having third and fourth reflecting surfaces arranged at right angles to each other And
A laser medium installed on the optical axis of the laser resonator;
An excitation light source for exciting the laser medium;
A reflector for holding the laser medium and the excitation light source and confining the excitation light generated from the excitation light source;
Translation means for translating the reflector in the direction perpendicular to the optical axis of the laser resonator,
The pulse width variable laser resonator according to claim 1, wherein the parallel movement means moves the reflector in the direction perpendicular to the optical axis of the laser resonator, whereby the resonator length of the laser resonator varies. Laser resonance comprising a first roof prism having first and second reflecting surfaces arranged at right angles to each other and a second roof prism having third and fourth reflecting surfaces arranged at right angles to each other And
A laser medium installed on the optical axis of the laser resonator;
An excitation light source for exciting the laser medium;
A reflector for holding the laser medium and the excitation light source and confining the excitation light generated from the excitation light source;
First roof prism translation means for translating the first roof prism in a direction perpendicular to the optical axis of the laser resonator;
A second roof prism translation means for translating the second roof prism in a direction perpendicular to the optical axis of the laser resonator;
The first and second roof prism translation means translates at least one of the first and second roof prisms in a direction perpendicular to the optical axis of the laser resonator. A variable pulse width laser resonator, wherein the resonator length varies.

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