JP2007012981A - Laser with high reflective coating on interior total reflection surface of optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the disadvantage that the polarizing condition of an incident light varies because the conventional optical prism utilizes the total reflection for the interior reflection. <P>SOLUTION: The laser uses an element formed by depositing a high-reflective dielectric multilayer film on the reflective surface of a prism (optical element) made of optical glass, optical crystal or solid state laser medium. The reflective surface utilizes the total reflection or interior high reflection. Thus, the interior reflection of the element is the reflection of the dielectric film, no phase difference appears between the P- and S-waves caused by the reflection and the polarizing condition of an incident light is conserved. The dielectric multilayer reflective film may be a narrow band high reflective film or a broad band high reflective film. A few light passing through the reflective film makes a usual total reflection at the interface of the light and air, but, if the reflectivity of the reflective film is high, the reflectivity of the reflective film remains in the total reflection and the phase difference is few between the P- and S-waves. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention uses a prism that is emitted without changing the polarization state of incident light and that is not easily damaged by laser light as a reflector of a laser resonator, and has a simple configuration of the optical system and output intensity and transverse mode components. The present invention relates to a laser device in which a highly reflective coating is provided on the internal total reflection surface of an optical element that can obtain output light with improved output.

  For example, optical elements such as right-angle prisms and zigzag slab type solid-state laser rods that are manufactured by polishing the surface of optical glass or optical crystal and using total reflection on one or more of these surfaces have extremely high reflection loss. Since it is small, the loss of the laser beam can be reduced by using it in the optical system of the laser device. However, the reflection at the total reflection surface causes a phase difference between the S wave component and the P wave component of the light. Here, the S (or P) wave component is light in which the electric field vector is linearly polarized perpendicular to (or parallel to) the incident surface (that is, the incident surface of the reflection law) that is a plane including the normal line of the reflection surface and the incident light beam. It is. For this reason, when linearly polarized light is incident on a right angle prism, it is generally emitted as elliptically polarized light.

  In order to prevent this, as shown in the case of the right-angle prism of FIG. 1, the reflections 2a and 2b on the total reflection surface must be made to reflect only the S wave component or only the P wave component. For this purpose, it is necessary to direct the polarization direction of the incident light so that the polarization direction 5 is perpendicular or parallel to the incident surface which is a surface including incident / exit light rays in total reflection. Alternatively, in the prism having a plurality of total reflection surfaces therein, it is necessary to devise the shape of the prism so that the number of times the incident linearly polarized light is reflected by the P wave and S is equal.

  In this way, the polarization direction of incident light is limited to a specific direction with respect to the prism shape. Alternatively, the prism has a complicated shape, and high shape accuracy is required, resulting in an increase in manufacturing cost.

  In order to prevent this phase difference from occurring in the prior art, a metal film having a high reflectivity has been deposited on the surface of the prism where total reflection is performed, and internal reflection has been replaced with metal reflection. However, the metal reflection has a reflection loss, and when a high intensity light such as a laser beam is incident, the metal film is damaged, so that it cannot be used for a strong laser beam.

  The present invention solves these drawbacks and changes the polarization state of light incident on an optical element including total internal reflection, such as a right-angle prism, a dove prism, a corner cube reflector, a zigzag slab solid laser rod, and the like. It is intended to realize a laser device having a simple configuration and improved output intensity and transverse mode by using the optical element that is emitted without any damage and is not easily damaged by high-intensity light. And

  FIG. 2 shows laser oscillators described in Patent Document 1 and Patent Document 2 using a knife-edge right-angle prism (Polo prism) as a first example. This laser oscillator basically comprises an optical resonator composed of a solid-state laser medium 7 optically pumped by a semiconductor laser 8 driven by a drive circuit 9, and the Porro prisms 6a and 6b and a polarizer 10. .

  The ridgeline of the right-angle prism 6a is rotated around the incident optical axis so as not to be parallel or perpendicular to the plane (optical path plane) including the optical path of the L-shaped resonator. The ridge line of the right-angle prism 6b is perpendicular or parallel to the optical path surface. There is a half-wave phase plate 11a in front of the incident surface of the right-angle prism 6a. In the adjustment of the half-wave phase plate, first, the polarization direction of the light passing through the right-angle prism is adjusted so as to be perpendicular or parallel to the ridgeline. Next, this half-wave plate is further rotated around the optical axis so that the optimum laser output can be obtained from the polarizer 10.

  Each time the laser beam travels back and forth through the resonator, the transverse mode pattern rotates in one direction at an angle twice the angle formed by the two ridge lines viewed along the optical axis, while maintaining the polarization direction. Is done. For this reason, this resonator can be said to be an image rotation type resonator. By adjusting the rotation angle of this transverse mode pattern, all higher-order transverse modes are suppressed, and it is possible to obtain a good fundamental transverse mode or a transverse mode with a uniform and flat intensity distribution. It is a feature. Even if the laser medium 7 is excited from one side surface, this effect does not change. Such an optical element using the total reflections 2a and 2b inside the prism has an advantage that the reflection film is not required to be deposited, the element is completed only by optical polishing, and the reflection loss is extremely small.

  However, as is well known, in total reflection, the phase delay amounts δp and δs of these light waves at the time of reflection differ depending on whether the incident light is P-polarized light or S-polarized light. For example, let us consider total reflection when light travels from the glass toward the air at the interface between the optical glass BK7 having a refractive index of about 1.5 and air. FIG. 3 shows the incident angle with respect to the interface on the horizontal axis and the phase delay amounts δp and δs on the vertical axis. The phase delays of both P-polarized light and S-polarized light coincide with each other when the critical angle is 41.5 degrees and the incident angle is 90 degrees, but there is a difference in the incident angle between them. For this reason, when the incident light with respect to the reflecting surface is linearly polarized light that is a combination of the P wave and the S wave on the total reflecting surface, the phases of the reflected waves are shifted. As a result, the reflected wave becomes elliptically polarized light.

  Therefore, in the right-angle prism shown in FIG. 1, when the polarization direction 5 is parallel or perpendicular to the ridge line 1 that is the intersection line of the two total reflection surfaces, and the incident light 3 is incident on the ridge line 1 at a right angle. The incident light 3 becomes the outgoing light 4 without changing its polarization. However, in other cases, the incident linearly polarized light is output as elliptically polarized light. The phase difference due to two total reflections is 0.42π and 0.27π for BK7 glass and fused silica, respectively, when the wavelength of light is 1064 nm. For this reason, each of these prisms can function as a quarter-wave plate and a quarter-wave plate.

  A polarization preserving prism shown in FIG. 4 is known as a prism that turns the optical path 180 degrees without generating a phase difference between the P wave and the S wave and without changing the polarization state of the emitted light. This is a structure in which a 180-degree folded right-angle prism having a ridge line 1 and a 90-degree folded right-angle prism are combined, and incident light 3 is emitted four times by total reflections 2a to 2d having an incident angle of 45 degrees. Since all reflections are total reflection, it can withstand strong laser light. The light is divided into a P wave component and an S wave component on the surface where the incident light is first totally reflected.

  The light of the P (or S) wave component is totally reflected as S (or P) wave, S (or P) wave, and P (or S) wave after the next reflecting surface to become outgoing light. Since any light component of the incident light is subjected to total reflection as the same number of S waves and P waves, there is no phase difference as a whole. Therefore, the incident light 3 linearly polarized in an arbitrary direction becomes the outgoing light 4 while being linearly polarized, although the polarization direction is rotated.

  The right-angle prism has three optically polished surfaces, and the performance is determined by the angular accuracy at which the two total reflection surfaces intersect. On the other hand, this polarization-maintaining prism has four optical polished surfaces, and the performance is determined by the angular accuracy at which three total reflection surfaces intersect each other. For this reason, high precision is required for manufacturing the prism, and it is also expensive.

  However, if the right angle prism 6a of the laser oscillator in FIG. 2 is replaced with such a polarization maintaining prism, the half-wave phase plate 11a can be omitted. As a result, the structure of this laser is simplified, and the adjustment of its oscillation is only the rotation of the right-angle prism. The adjustment is easy, and the angle of the right-angle prism is rotated so as to obtain an optimum output, and the transverse mode may be finely adjusted in the vicinity of the angle so that the transverse mode becomes a fundamental mode or a flat intensity distribution.

  Further, in the Dove prism used for rotating the optical image shown in FIG. 5, the entrance surface and the exit surface are refracting surfaces having a Brewster incident angle, and there is one total reflection 2a inside. If the incident light 3 is linearly polarized light that is polarized in the direction of the normal line of the total reflection surface, it passes through the prism without loss and becomes outgoing light 4 that remains linearly polarized. However, light polarized in other directions is subject to reflection loss at the entrance and exit surfaces. Further, light whose polarization direction is not perpendicular or parallel to the total reflection surface is emitted as elliptically polarized light.

  Therefore, in order to use these prisms in a laser device that generates linearly polarized light, it is necessary to combine them with one or two half-wave phase plates, which has the disadvantage that the configuration and adjustment of the device are complicated. Further, in the laser oscillator shown in FIG. 2, when the right-angle prism 6a is rotated, it is necessary to redo the adjustment of the half-wave phase plate 11 to obtain the optimum output.

  For example, a corner cube prism shown in FIG. 6 is used as an optical element that reverses the light incident direction and turns the optical path back. For this reason, if two reflectors are opposed to each other, a resonator is formed. Even if the orientation of these reflectors is deviated, the optical axis is maintained, so that the resonator is extremely stable against such an optical axis deviation. The image and polarization of the emitted light are rotated 180 degrees from those of the incident light. This has one incident surface and three total reflection surfaces, which are in contact with each other at a right angle. The linearly polarized incident light 3 is subjected to three total reflections 2a to 2c by these total reflection surfaces to become outgoing light 4. However, even if a linearly polarized light beam is incident on the first total reflection surface as an S-wave or P-wave, it is incident on the next reflection surface as a light beam that is obliquely polarized with respect to the incident surface of the reflection law. For this reason, when linearly polarized light enters the prism, it is always emitted as elliptically polarized light. For this reason, it has not been possible to use this reflector in a laser resonator that needs to maintain polarization.

  In order to preserve polarization while using this prism as a retroreflector, a highly reflective metal film may be deposited on the reflection surfaces of the total reflections 2a to 2c, and the total reflection may be replaced with metal reflection. However, metal reflection has light absorption, and has a drawback that the reflectance as a prism is lowered. Further, when a strong laser beam is incident on the metal film, the metal film is damaged due to the absorption of the laser beam. For this reason, a strong laser beam cannot be incident on the prism or used in the laser device.

FIG. 7 shows a zigzag slab solid-state laser rod. The laser beam is totally reflected on the side surface of the laser rod. Excitation light is absorbed inside the rod, and the inside of the rod generates heat due to stimulated emission of the excited active element. This heat is dissipated from the rod surface. Accordingly, heat generation and heat dissipation of the rod are not spatially balanced, and a stress field due to thermal expansion is generated inside the rod. This distorts the refractive index profile of the rod and further generates birefringence. Even if the laser medium is uniform, such a non-uniform refractive index distribution is generated. Therefore, as the linearly polarized laser beam enters and travels through the rod, the polarization plane rotates and the elliptically polarized laser beam is converted. Is done. When such light is totally reflected on the side surface of the rod, a phase difference is generated between the P wave component and the S wave component, so that the ellipticity of the polarization is further increased. As a result, the polarization state of the laser beam is greatly disturbed, which is a major cause of deterioration of the transverse mode in the laser oscillator.
Japanese Patent Laid-Open No. 2003-198815 US Pat. No. 6,816,533 B2

  Since the metal reflection film has a characteristic light absorption spectrum derived from the conduction electronic state of each metal, if a laser beam, such as a prism on which the metal reflection film is deposited, is irradiated with strong laser light, the energy is absorbed and damaged. Is done. For this reason, it has been impossible to make a powerful pulse laser beam incident on these optical elements or use them in a laser resonator.

  Further, in the optical glass or fused silica prism, in order to clean the total reflection surfaces, frictional static electricity is generated when these surfaces are rubbed with cleaning paper or cloth, and the surface is easily charged to 1000 V or more. For this reason, on the contrary, dust may be easily adsorbed.

  Since the conventional optical prism uses total reflection for internal reflection, there is a drawback that the polarization state of incident light changes. To preserve the polarization state, for example, in order to convert linearly polarized incident light directly into linearly polarized outgoing light, use a specially shaped prism or deposit a metal reflection film to replace total reflection with metal reflection. There was a need.

  In the present invention, by making this reflective film a highly reflective dielectric multilayer film, it is possible to obtain an optical element that is much less susceptible to laser light than conventional ones.

  In addition, since the dielectric reflecting film used in the present invention generally generates less frictional static electricity than optical glass, it has the effect of preventing the generation of this static electricity and facilitating cleaning of the reflecting surface.

  In addition, the present invention changes the polarization state of incident light while maintaining the optical function of the conventional prism by depositing a highly reflective dielectric multilayer film on the total reflection surface without changing the shape of the conventional prism. It is possible to add a function of emitting light without making it.

  It can be easily understood from the reflection of the optical arrangement shown in FIG. 8 that even if the surface causes total reflection with respect to incident light, normal reflection is obtained by depositing a dielectric reflection film thereon. It is assumed that there is a highly reflective dielectric multilayer film 13a in an optical medium 12 such as optical glass spread uniformly in space. The light incident on this film is naturally reflected by the reflecting film and does not reach the back surface of the film. Therefore, even if there is an optical medium on the back side of the film, the reflection by this film is not affected. In a normal design of a high reflectivity dielectric multilayer film, the reflection phase difference between the P wave and the S wave becomes zero at the maximum reflectivity wavelength. Accordingly, the reflection film changes light having an incident angle to the critical angle of 90 degrees from the critical angle of the optical medium from total reflection to normal reflection. As a result, light is normally reflected at all incident angles from 0 to 90 degrees, and no phase difference between the P wave and the S wave occurs in all incident angle ranges. Or even if it occurs, a large phase difference as in the case of total reflection does not occur.

  The present invention relates to a laser using an element in which a highly reflective dielectric multilayer film is deposited on a reflecting surface using total reflection or internal high reflection in a prism (optical element) made of optical glass, an optical crystal, or a solid laser medium. Device. As a result, the internal reflection of the element becomes a reflection of the dielectric film, and no phase difference is applied between the P wave and S in the reflection. Accordingly, linearly polarized incident light is emitted as linearly polarized light, regardless of the direction of polarization with respect to the total reflection surface. Also, elliptically polarized incident light is emitted without changing the ellipticity. Thus, the polarization state of incident light is preserved. The dielectric multilayer reflection film may be a narrow band high reflection film such as a laser light reflection film or a broadband high reflection film that reflects light in a wide wavelength region of the visible light region. The slight amount of light that has passed through the reflective film is totally reflected at the interface with air as usual. A phase difference is generated between the P wave and the S wave of the light component, and is superimposed on the reflection component of the reflection film. Therefore, if the reflectance of the reflective film is high, the reflectance of the prism remains completely reflected, and the phase difference between the P wave and the S wave hardly occurs.

  For this reason, the laser device of the present invention is a laser device including a laser resonator, a laser medium, and an excitation light source for exciting the laser medium, and uses the reflection from at least one total reflection surface of the laser resonator. The total reflection surface of the laser device in which the optical path is formed is provided with a dielectric multilayer reflection film on the total reflection surface, and the ratio of light reflected by the dielectric multilayer reflection film on the total reflection surface is reflected by total reflection. It is assumed that it has an optical path equivalent to the optical path that is larger than the ratio and replaced with the total reflection surface that suppresses the change in the polarization state of reflection on the total reflection surface.

  The total reflection surfaces are equal two surfaces A and B sandwiching the right angle of the isosceles right-angle prism having surfaces A, B, and C, and the dielectric multilayer reflection film on the surfaces A and B. , An antireflection film is provided on the surface C, and light enters and exits on the surface C.

  The total reflection surface is a surface C excluding two equal surfaces sandwiching the right angle of the isosceles right-angle prism having surfaces A, B, and C, and A and B. A multi-layer reflective film is attached, an antireflection film is provided on surfaces A and B, and light is incident or emitted on surface A or surface B.

  The total reflection surface is a total reflection surface in an optical element that rotates an optical image.

  The total reflection surface is a total reflection surface provided on the solid laser medium.

  The total reflection surface is a total reflection surface provided on the nonlinear optical medium.

  Or said total reflection surface is a total reflection surface provided in the optical element which folds an optical path.

  Alternatively, the total reflection surface is provided with an optical element that bends the optical path.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, the description will be given focusing on the reflector of the laser device. Further, in the following description, the same reference numerals are used for devices having the same function or similar functions unless there is a special reason.

  FIG. 9 shows a polarization-preserving 180-degree folded right-angle prism used for the reflector of the laser resonator. High reflection dielectric multilayer films 13a and 13b are vapor-deposited on the optically polished surface which is the two total reflection surfaces. Regardless of the angle of the polarization direction of the linearly polarized incident light with respect to the ridgeline of the prism, the outgoing light remains linearly polarized. A dielectric multilayer film having a high reflectivity may be deposited in accordance with the wavelength band of light using this prism.

  If the prism 6a of the laser oscillator shown in FIG. 2 is replaced with this prism, the optimum output and the optimum mode pattern can be easily obtained only by adjusting the rotation angle of this prism. For this purpose, the angle of the right-angle prism is rotated to obtain an optimum output, and fine adjustment is performed so that the transverse mode becomes a fundamental mode or a flat intensity distribution near the angle.

  FIG. 10 shows a polarization-maintaining right-angle prism that can also be used in a laser resonator and bends the optical path by 90 degrees. The highly reflective dielectric multilayer film 13a is applied to the total reflection surface, and the output light 4 is linearly polarized regardless of the direction of polarization of the linearly polarized incident light 3 with respect to the incident surface of the reflection law. Remains.

  FIG. 11 shows a polarization-maintaining doublet prism in the laser resonator for rotating the optical path. A highly reflective dielectric multilayer film 13a is vapor-deposited on the optically polished surface, which is a total reflection surface, and the incident angle at the entrance / exit surface of the prism is smaller than the Brewster angle, and a dielectric non-reflective film is vapor-deposited on these surfaces. It may be. Regardless of the angle of polarization of the linearly polarized incident light with respect to the normal of the reflecting surface of the prism, the emitted light remains linearly polarized. The optical image is rotated by the rotation of the prism, and the polarization direction is also rotated accordingly. A dielectric multilayer film having a high reflectivity may be deposited in accordance with the wavelength band of light using this prism.

  FIG. 12 shows a ring type laser oscillator using a normal dove prism. The laser oscillator is configured by the laser medium 7 excited by the excitation device 16 and the ring optical resonator formed by the polarizer 10 and the reflecting mirrors 14a and 14b. The resonator has an optical path formed by reflection several times. The reflecting mirror 14c is for returning the counterclockwise laser beam as a clockwise laser beam into the resonator and obtaining a clockwise oscillation from the laser. On the optical path of the resonator, there are a dove prism 15 and half-wave phase plates 11a and 11b. The transverse mode pattern of the laser light that circulates around the resonator by the Dove prism rotates in a certain direction. When the rotation angle of the mode pattern per one round of the resonator is optimally adjusted, the laser oscillation of the fundamental transverse mode or the transverse mode pattern having a uniform and flat intensity distribution can be obtained similarly to the laser oscillator shown in FIG. . The half-wave phase plate 11 a is used to make the polarization direction of the laser light perpendicular to the reflecting surface of the Dove prism, and the half-wave phase plate 11 b is adjusted so as to obtain an optimum output from the polarizer 10.

  Replacing the Dove prism of FIG. 12 with the prism of FIG. 11 with a highly reflective dielectric multilayer film eliminates the need for two half-wave phase plates. In this case, optical adjustment for obtaining a predetermined transverse mode is easy. For this purpose, the Dove prism is rotated so as to obtain an optimum output, and the rotation angle may be further finely adjusted so as to obtain an optimum mode pattern in the vicinity thereof.

  FIG. 13 shows a polarization maintaining corner cube prism that can be used as a reflector of a laser resonator. High reflection dielectric multilayer films 13a to 13c are deposited on the optically polished surface which is the three total reflection surfaces. Regardless of the angle of polarization of the linearly polarized incident light 3 with respect to the ridgeline of the reflector, the outgoing light 4 remains linearly polarized in the same direction as the incident light. A dielectric multilayer film having a high reflectivity may be deposited in accordance with the wavelength band of light using this prism.

  FIG. 14 shows a ring type laser oscillator using two polarization maintaining corner cube prisms facing each other. Two corner cube prisms 17a and 17b face each other to form a ring resonator. On the optical path, there is a laser medium 7 that is excited by the excitation device 16. Further, there are a half-wave phase plate 11a and a polarizer 10 for extracting output light on the optical path. As for the laser output light, the laser light that circulates counterclockwise around the resonator has its polarization direction changed by the half-wave phase plate, and its component is reflected by the polarizer and extracted. The reflecting mirror 14c is used to obtain oscillation in a single direction by suppressing the oscillation of the clockwise laser beam as in the laser of FIG.

  In the ring type laser oscillator shown in FIG. 15, in order to use the above-described resonator as an image rotation type resonator, one polarization maintaining corner cube prism 17a is replaced with a polarization maintaining right angle prism 6a, and an optical image rotating element is used. A certain polarization preserving dove prism 15 is inserted on the optical path.

  FIG. 16 shows a polarization-maintaining rhomboid prism used for translating the optical path. This has a shape in which two 90 degree right angle prisms are combined. By depositing highly reflective dielectric multilayer films 13a and 13b on the upper and lower end surfaces, linearly polarized light is emitted as linearly polarized light regardless of the polarization direction. A dielectric multilayer film having a high reflectivity may be deposited in accordance with the wavelength band of light using this prism.

  FIG. 17 shows a polarization maintaining pentaprism that bends the optical path in the laser resonator by 90 degrees. This prism uses two internal reflections, but these are not total reflections but reflections by a highly reflective film. For this reason, in this prism, linearly polarized light does not originally become elliptically polarized light. Conventionally, a metal film is deposited on the reflective surface. However, by replacing this with the highly reflective dielectric multilayer films 13a and 13b, a prism that can be used for powerful laser light can be obtained.

  FIG. 18 shows a laser oscillator using a polarization maintaining zigzag slab laser rod for amplifying laser light. A zigzag slab laser rod 18 that is pumped by the pumping light source 16 is included in the optical resonator constituted by the reflecting mirror 14 a and the output mirror 19. In order to perform Q-switch oscillation, a Pockels cell 21, a quarter-wave plate 20 and a polarizer 10 driven by the drive circuit 22 are arranged on the optical path. In the conventional laser rod, the laser beam is totally reflected on the side surface of the rod. By depositing the highly reflective dielectric multilayer films 13a and 13b on the side surfaces, total reflection is replaced with normal reflection. Even if the laser light traveling inside the laser rod is elliptically polarized due to the non-uniform refractive index inside the rod, the elliptically polarized light is not further increased by side reflection, and deterioration of the transverse mode of the laser light can be suppressed.

  FIG. 19 shows a four-path laser amplifier using a polarization-maintaining solid-state laser rod 7 for amplifying laser light. One end face of the laser rod is processed into a knife-edge right-angle prism shape so that the laser beam is folded back 180 degrees. High reflection dielectric multilayer films 13a and 13b are vapor-deposited on this end face, and the laser beam is reflected by normal reflection instead of total reflection. The prism end face ridge line is actually rotated around the optical axis of the rod so as to form an angle of 45 degrees from the paper surface.

  The incident laser beam 3 linearly polarized in a plane parallel to the paper surface passes through the polarizer 10, travels while being amplified inside the laser rod 7, and is folded back 180 degrees at the prism-shaped end surface. At this time, the laser light becomes linearly polarized light polarized in a direction perpendicular to the paper surface. The laser beam emitted from the laser rod is reflected by the polarizer 10 and the reflecting mirror 14c, and is incident on the laser rod again. This light is reflected by the end face of the laser rod, and the polarization direction is changed again parallel to the paper surface. This light passes through the laser rod and the polarizer to become outgoing light 4. The laser light incident on the amplifier passes through the laser rod four times before being emitted, and is greatly amplified.

  The feature of this rod is that each time the laser beam is reflected by the reflection end of the laser rod, the component perpendicular to the plane of the polarization component and the component parallel to the paper surface are switched. Even if there is birefringence in the laser rod, since the birefringence felt by the light component linearly polarized in the parallel direction and the perpendicular direction on the paper surface is equal, the birefringence is compensated. Another advantage is that this makes it possible to make laser amplifiers that are less affected by birefringence.

  Even in a highly reflective dielectric multilayer film, very little light may pass through the reflective film. The slight amount of light that has passed through the reflection film causes total reflection at the boundary between the external environment such as air or vacuum and the multilayer film, or part of the light is transmitted into the air and the rest is reflected. In the case of the former total reflection, there is a phase difference between the P wave and the S wave of the reflection component. In the case of the latter reflection, it is well known that the phase of the P wave of the reflection component increases by π at the incident angle of the Brewster angle. However, it is very easy to make the reflectivity of the highly reflective dielectric multilayer film 99.5% or higher. Therefore, the linearly polarized light incident on the internal reflection surface of the optical element is almost directly reflected by the linearly polarized light, and the proportion of light that changes to elliptically polarized light or changes its polarization direction is extremely below 0.5%. Can be small.

  In addition, when the objective is to slightly improve the output of the laser device, it is not necessary to have a high reflectivity as described above. For example, the reflectivity of the dielectric multilayer reflective film is set to 80% or more, and the rest is used. The above object can also be achieved by making total reflection.

The reflector of the laser device can be made of various materials. For example, quartz glass, optical crystal, laser crystal, optical transparent plastic, and the like can be used. For example, when a reflector created using a nonlinear optical medium such as LiNbO ₃ is used, a high-intensity laser beam is applied to the nonlinear optical medium in the same manner as when the nonlinear optical medium is disposed in the optical resonator of a conventional laser device. The non-linear optical effect can be easily generated. Further, the number of components of the apparatus can be reduced as compared with the case where the reflector and the nonlinear optical medium are provided separately. Further, as is apparent from the optical path shown in FIG. 1, FIG. 4, or FIG. 6, in the present invention, not only one specific crystal axis but also other crystal axes are used. Thus, the present invention is particularly suitable when a plurality of crystal axes are also desired. Further, since the dielectric multilayer reflective film is used, the degree of freedom in design is great in determining the optical path, and the design can be made according to the nonlinear optical medium.

As the dielectric multilayer reflective film, an organic material such as a fluororesin, an acrylic resin or a silicon resin is used in addition to an inorganic material such as Ta ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , MgF ₂ or SiO _2. be able to.

It is a figure which shows the total reflection in a right angle prism. It is a figure which shows the laser oscillator of a prior art example. It is a figure which shows the phase delay with respect to the incident angle of the reflection which occurs in the interface of quartz glass and air. It is a figure which shows the reflection by a polarization preserving prism. It is a figure which shows the reflection by a dove prism. It is a figure which shows the reflection in a corner cube prism. It is a figure which shows the reflection in a zigzag slab solid-state laser rod. It is a figure for demonstrating the reflection by a dielectric reflecting film. It is a figure which shows the reflection in a polarization preservation | save 180 degree | times folding right angle prism. It is a figure which shows the reflection in a polarization-maintaining right angle prism. It is a figure which shows the reflection in a polarization preserving dove prism. It is a figure which shows the ring-type laser oscillator using a normal dove prism. It is a figure which shows the reflection in a polarization preservation corner cube prism. It is a figure which shows the ring-type laser oscillator which used two polarization preservation corner cube prisms facing each other. It is a figure which shows the ring type laser oscillator which used the resonator of FIG. 14 as the image rotation type resonator. It is a figure which shows the reflection in a polarization-maintaining rhomboid prism. It is a figure which shows the reflection in a polarization preserving pentaprism. It is a figure which shows the laser oscillator using a polarization preservation zigzag slab laser rod. It is a figure which shows the laser amplifier of a quadruple optical path using the polarization-maintaining solid state laser rod.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Right-angle prism 2a, 2b, 2c, 2d Reflection in a total reflection surface 3 Incident light 4 Outgoing light 5 Polarization direction 6a, 6b Polarization-maintaining right-angle prism 7 Laser medium 8 Semiconductor laser 9 Drive circuit 10 Polarizer 11a, 11b Half wavelength Phase plate 12 Optical medium 13a, 13b High reflective dielectric multilayer film 14a, 14b, 14c Reflector 15 Dove prism 16 Excitation device 17a, 17b, 17c Polarization preserving corner cube prism 18 Zigzag slab laser rod 19 Output mirror 20 1/4 Wave plate

Claims (8)

A laser device including a laser resonator, a laser medium, and an excitation light source for exciting the laser medium,
The total reflection surface of the laser device in which the optical path of the laser resonator is formed using reflection by at least one total reflection surface,
A dielectric multilayer reflective film is provided on the total reflection surface, and the ratio of the reflected light by the dielectric multilayer reflection film on the total reflection surface is made larger than the ratio of the reflected light by total reflection. A laser device having a highly reflective coating on an internal total reflection surface of an optical element, having an optical path equivalent to an optical path replaced with a total reflection surface in which a change in polarization state is suppressed.   The total reflection surfaces are the same two surfaces A and B sandwiching the right angle of the isosceles right angle prism having two side surfaces A, B and C, and a dielectric multilayer reflection film is attached to the surfaces A and B. 2. The laser device according to claim 1, wherein an antireflection film is provided on the surface C, and light is incident / exited on the surface C, wherein the internal reflection surface of the optical element is provided with a high reflection coating.   The total reflection surface is a surface C excluding two equal surfaces sandwiching the right angle of the isosceles right-angle prism having surfaces A, B, and C, and A and B, and a dielectric multilayer on the surface C. 2. A reflection film is provided, an antireflection film is provided on surfaces A and B, and light is incident on or emitted from surface A or surface B, so that the internal reflection surface of the optical element according to claim 1 is highly reflective. Laser device with coating.   2. The laser device according to claim 1, wherein the total reflection surface is a total reflection surface on an optical element that rotates an optical image.   2. The laser apparatus according to claim 1, wherein the total reflection surface is a total reflection surface provided on a solid-state laser medium.   2. The laser device according to claim 1, wherein the total reflection surface is a total reflection surface provided on a nonlinear optical medium.   2. The laser device according to claim 1, wherein the total reflection surface is a total reflection surface provided on an optical element that turns back an optical path.   2. The laser device according to claim 1, wherein an optical element that bends an optical path is provided on the total reflection surface.

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