JP5390941B2 - Visible light mirror, visible light oscillation gas laser, and ring laser gyro - Google Patents

Description

  The present invention relates to a technique for improving the ultraviolet resistance of a dielectric multilayer optical element such as a high reflectivity mirror.

  He-Ne lasers (oscillation wavelength 633 nm) used for ring laser gyros and the like and other high reflectivity mirrors that reflect other gas lasers are generally composed of a dielectric multilayer film. This dielectric multilayer film is formed from the plasma of the laser medium. It is known that absorption loss at the used wavelength (laser oscillation wavelength) increases and deteriorates as a reversible phenomenon when irradiated with radiated ultraviolet rays.

As a method for solving such a problem, it is conceivable that the mirror is constituted only by a UV-insensitive high refractive index / low refractive index dielectric ¼ wavelength layer pair, and this technique is disclosed in Patent Document 1. Yes. However, in the case of a generally known insensitive material, since the refractive index is low, it is necessary to increase the number of layer pairs in order to obtain sufficient reflectance. Therefore, in order to reduce the number of layer pairs, a mirror is applied to a substrate, which is an ultraviolet sensitive high refractive index / low refractive index dielectric quarter wavelength layer pair, and a plurality of ultraviolet insensitive high refractive materials deposited thereon. An ultraviolet-resistant high-reflectivity mirror constituted by a two-stage structure with a refractive index / low-refractive-index dielectric quarter-wave layer pair is also considered, and is disclosed in Patent Document 2. Specifically, as a UV-sensitive high refractive index / low refractive dielectric 1/4 wavelength layer pair, while using a TiO ₂ / SiO ₂ layer pair that has been generally used as a high reflectivity mirror, In order to reduce the influence due to the poor absorption loss characteristic of the TiO ₂ film, the ultraviolet insensitive high refractive index / low refractive index dielectric 1 on the ultraviolet sensitive high refractive index / low refractive index dielectric 1/4 wavelength layer pair. A / 4 wavelength layer pair, for example a HfO ₂ / SiO ₂ layer pair, is deposited. With such a two-stage configuration, while suppressing the number of layers of the whole by the application of _TiO 2 / SiO ₂ layer pairs of high reflectance (high refractive index ratio), a high _TiO 2 / SiO ₂ layers having UV sensitivity By retracting the pair behind the UV-insensitive HfO ₂ / SiO ₂ layer pair, the amount of UV light reaching the TiO ₂ / SiO ₂ layer pair portion is reduced, and an increase in loss in the TiO ₂ / SiO ₂ layer pair is caused by the mirror. The effect on reflectivity is reduced.

JP-A-7-72330 Japanese Patent Laid-Open No. 2-192189

  Although a visible light mirror having high UV resistance can be realized by a conventional method, it is desirable that the most effective realization method can be selected from a plurality of realization methods according to the use conditions, manufacturing conditions, and the like of the mirror.

  In view of such circumstances, there is a problem of realizing a visible light mirror having high ultraviolet resistance and high reflectivity by a method different from the conventional method.

  In order to solve the above-described problems, a visible light mirror according to the present invention includes a substrate and a layer of dielectric material formed on the substrate and induced to increase visible light absorption by irradiation with ultraviolet rays. A visible light mirror stack layer portion that is a multilayer mirror that reflects light, and an ultraviolet mirror that is formed on the visible light mirror stack layer portion and has a reflectance of 50% or more in a predetermined wavelength band in the ultraviolet region A stack layer portion.

  The present invention has an effect of realizing a visible light mirror having high ultraviolet resistance and high reflectivity by a method different from the conventional one.

The figure which illustrates the emission spectrum in the ultraviolet region of a He-Ne laser. The figure which illustrates that a difference arises in total loss (= absorption loss + scattering loss + transmission loss) by the presence or absence of an ultraviolet-ray in the mirror which consists of an ultraviolet sensitive material. The figure which illustrates the measuring system of the mirror total loss in an ultraviolet irradiation environment. The figure which illustrates the structure of the visible light mirror of this invention. The figure which shows the relationship between the reflectance performance data of the visible light mirror 10 which concerns on FIG. 4, and the spectrum of the ultraviolet-ray radiated | emitted from He and Ne each atom which are laser media. The enlarged view of a wavelength 400nm or less part of FIG. The figure which illustrates the difference of the total loss of the visible light mirror of a conventional structure, and the visible light mirror of this invention. The figure which shows the structural example of the visible light oscillation gas laser 30 and the ring laser gyroscope 40. FIG.

[Discussion]
First, FIG. 1 shows an emission spectrum in the ultraviolet region of a He—Ne laser. As can be seen from FIG. 1, the ultraviolet rays radiated from the plasma of the laser medium separately from the laser oscillation light are distributed over a wide wavelength range in the ultraviolet region. When a mirror made of an ultraviolet sensitive material is used in an environment where ultraviolet rays are radiated in this way, there arises a problem that the laser output is lowered due to a decrease in the reflectivity of the mirror. It has not been clarified in the past whether the spectrum of all ultraviolet rays or only a part of the wavelength components is involved in this problem.

Accordingly, the inventors of the Ta ₂ O ₅ / SiO ₂ mirror, which is an example of a high refractive index / low refractive index dielectric quarter-wave layer pair mirror made of an ultraviolet sensitive material, are irradiated when ultraviolet rays are not irradiated. An experiment was conducted to examine the change in the loss of the mirror at the used wavelength of 633 nm (laser oscillation light) when irradiated and indirectly irradiated through four types of ultraviolet cut filters. The results are shown in FIG. The mirror is composed of 37 layers by alternately stacking 19 layers of Ta ₂ O ₅ films and 18 layers of SiO ₂ films. As shown in FIG. 3, the measurement system according to the experiment includes the above-described mirror as a sample in the optical path of the optical resonator including the reference mirror 1 and the reference mirror 2, and the He-Ne laser. A cavity ring-down type apparatus was used in which the loss of the mirror was evaluated by observing the attenuation of light intensity in the resonator when the injected light was resonated and the injected light was cut off. A mercury xenon lamp is used as the light source of the ultraviolet irradiation device, and the transmittance of each ultraviolet cut filter is 20% or less at each edge wavelength shown in FIG.

As shown in FIG. 2, when the mirror is irradiated with ultraviolet rays, the total loss of the mirror is increased, and when irradiated through the ultraviolet cut filter, the total loss is reduced. However, depending on how the band of the UV cut filter is selected, even if it blocks only a part of wavelength components in the UV region, the loss is the same as when a filter that blocks the entire UV region is inserted. It was found that a reduction effect can be obtained. That is, it is a part of the wavelength component of the irradiated ultraviolet ray that induces an increase in the loss of the ultraviolet sensitive material of the mirror. In the example of FIG. 2, more specifically, in the case of the mirror composed of the Ta ₂ O ₅ / SiO ₂ layer pair, if a cut filter of 320 nm or less is inserted in the ultraviolet light irradiated to the mirror, the blocking region covers the entire ultraviolet region. The change characteristic of the total loss is almost the same as when the cut filter of 460 nm or less is inserted. However, when the UV cut filter is replaced with a filter of 300 nm or less, it is clear compared with the previous two cut filters. Total loss increased. In other words, the wavelength component boundary to be cut is between 320 nm and 300 nm in order to obtain the same loss reduction effect as when a filter for blocking the entire ultraviolet region is inserted. Therefore, it can be seen that if the wavelength component of at least 320 nm or less of the ultraviolet light incident on the mirror is sufficiently blocked, the purpose of suppressing the increase in loss due to the ultraviolet light can be achieved.

  Considering the application of an ultraviolet cut filter composed of a dielectric multilayer film as an overcoat for a specific multilayer mirror, it has a blocking range that covers the entire ultraviolet range and is suitable for actually covering a laser mirror. It is generally not easy to construct a layer structure. On the other hand, it is relatively easy to clarify the ultraviolet band that induces the loss increase according to the multilayer mirror, and to suitably form an overcoat layer on the multilayer mirror that sufficiently blocks the band. is there.

  Hereinafter, embodiments of the present invention will be described in detail.

The visible light mirror 10 according to the first embodiment will be described with reference to FIG.
<Visible light mirror 10>
FIG. 4 shows a configuration example of the visible light mirror 10 of the first embodiment. The visible light mirror 10 includes a substrate 11, a visible light mirror stack layer portion 12, an ultraviolet mirror stack layer portion 13, and a protective layer 14.

<Substrate 11>
The substrate 11 is desirably made of a material having a low coefficient of thermal expansion, such as a glass ceramic material. This is because it is desired that the change in the dimensions to be received with respect to the temperature change within the operating temperature range of the He-Ne ring laser gyroscope is small. However, the present invention is not limited to this, and other materials may be used.

<Visible Light Mirror Stack Layer 12>
The visible light mirror stack layer portion 12 is a multilayer mirror that reflects visible light and includes a layer of a dielectric material that is formed on the substrate 11 and in which an increase in visible light absorption is induced by ultraviolet irradiation.

For example, the visible light mirror stack layer portion 12 includes a plurality of high refractive index / low refractive index dielectric quarter-wave layer pairs. The visible light mirror stack layer portion 12 reaches light having a reduced amount of ultraviolet rays that has passed through an ultraviolet mirror stack layer portion 13 to be described later. Therefore, the high refractive index dielectric material applied here has a high ultraviolet sensitivity. It is possible to make a selection with an emphasis on high reflectance without worrying about the thickness. An example of a high refractive index dielectric material suitable for such a configuration is Ta ₂ O ₅ , and an example of a low refractive index dielectric material is SiO ₂ . For example, the visible light mirror stack layer 12 has 37 layers by alternately laminating 19 Ta ₂ O ₅ films and 18 SiO ₂ films each having an optical film thickness of ¼ wavelength of the used wavelength of 633 nm (laser oscillation light). Consists of. As shown in FIG. 2, with such a configuration, the total loss with respect to visible light of a specific wavelength when there is no ultraviolet irradiation is about 30 ppm. The visible light mirror stack layer portion 12 is considered to have high reflectivity if the total loss with respect to visible light of a specific wavelength when there is no ultraviolet irradiation is 50 ppm or less. In the case where the ultraviolet mirror stack layer portion 13 is not interposed, as can be seen from FIG. 2, this layer has a total loss of about 180 ppm when irradiated with ultraviolet rays, and a total loss of about 30 ppm when there is no irradiation. It is a layer of dielectric material in which an increase in visible light absorption of 180 ppm-30 ppm = about 150 ppm is induced upon irradiation.

  Note that this embodiment does not limit the content of the invention. For example, even if the total loss for visible light of a specific wavelength when the visible light mirror stack layer portion 12 is not irradiated with ultraviolet rays is greater than 50 ppm, a visible light mirror with a high total reflection rate can be configured when irradiated with ultraviolet rays. Good. In addition, for example, other materials may be used for the high refractive index / low refractive index dielectric, and the number of alternating layers may be appropriately selected as necessary.

<Ultraviolet mirror stack layer 13>
The ultraviolet mirror stack layer portion 13 is formed on the visible light mirror stack layer portion 12 and is composed of a multilayer mirror having a reflectance of 50% or more in a predetermined wavelength band in the ultraviolet region.

  For example, the ultraviolet mirror stack layer portion 13 is composed of a plurality of high-refractive index / low-refractive index dielectric quarter-wave layer pairs so that the reflectance in a predetermined wavelength band in the ultraviolet region is 50% or more. .

Examples of the high refractive index dielectric material suitable for such a configuration include HfO _{2 and} ZrO ₂ , and examples of the low refractive index dielectric material include SiO ₂ . For example, the ultraviolet mirror stack layer 13 is a multilayer mirror having a reflectivity of about 90% in a short wavelength region of 320 nm or less, and an HfO ₂ layer having an optical film thickness of ¼ wavelength of 270 nm and SiO _{2 It} consists of 16 layers by ₂ 8 layers, or alternate lamination of ZrO ₂ 8 layers and SiO ₂ 8 layers.

Note that the second deposition section of the patent document 2 is configured similarly to the present embodiment by HfO ₂ and SiO ₂ is, its optical thickness, a quarter wavelength of the operating wavelength 633 nm (laser oscillation light) is there. On the other hand, the ultraviolet mirror stack layer portion 13 of this embodiment has an optical film thickness of a quarter wavelength of 270 nm in order to reflect ultraviolet rays, and is different in technical idea from Patent Document 2. Also, the number of layers is different. Furthermore, since the ultraviolet mirror stack layer portion 13 of this embodiment reflects ultraviolet rays, the ultraviolet rays irradiated to the visible light mirror stack layer portion 12 are reduced. Therefore, in the visible light mirror stack layer portion 12, physical changes and chemical changes due to ultraviolet rays can be suppressed, and the visible light mirror 10 has an effect that durability is higher than that of the conventional one.

  FIG. 5 shows the relationship between the reflectance performance data (calculated values) of the visible light mirror 10 according to FIG. 4 and the spectrum of ultraviolet rays radiated from He and Ne atoms as the laser medium. FIG. 6 is an enlarged view of a portion having a wavelength of 400 nm or less in FIG. 5 and 6, it can be seen that the visible light mirror 10 has a reflectance of 90% or more in the region of 320 nm or less in the ultraviolet region. Moreover, it has a reflectance of 99% or more in the upper and lower 40 to 50 nm centering on 633 nm in the visible light region. In particular, at a wavelength of 633 nm at the oscillation frequency, the reflectivity is 99.9930%. Hereinafter, the simulation result will be described.

  As can be seen from FIG. 2, by protecting the visible light mirror stack layer portion 12 with an ultraviolet cut filter, it is possible to suppress an increase in total loss due to irradiation with ultraviolet rays. Therefore, an ultraviolet reflective multilayer mirror that plays the role of this filter is applied to the ultraviolet mirror stack layer portion 13.

The wavelength band in which the ultraviolet mirror stack layer portion 13 should reflect ultraviolet rays, in other words, the wavelength band in which the effect of suppressing the increase in total loss in the visible light mirror stack layer portion 12 can be obtained efficiently by UV protection is the visible light mirror. It depends on the material of the high refractive index / low refractive index dielectric 1/4 wavelength layer pair applied to the stack layer portion 12. For example, in the case of Ta ₂ O ₅ / SiO ₂ , as can be seen from FIG. 2, there is no significant difference in the effect between the cut filter of 320 nm or less, the cut filter of 380 nm or less, and the cut filter of 460 nm or less. The loss is relatively large. Therefore, in the case of Ta ₂ O ₅ / SiO ₂ , a visible light mirror stack layer portion is obtained by applying a multilayer mirror that exhibits a reflectance of 50% or more in a short wavelength region of 320 nm or less to the ultraviolet mirror stack layer portion 13. It can be said that the arrival of ultraviolet rays that induces an increase in visible light absorption at 12 can be effectively suppressed.

  In addition, when the wavelength band which the visible light mirror stack layer part 12 and the ultraviolet-ray mirror stack layer part 13 reflect is near, mutual reflected light becomes easy to interfere. Therefore, it is desirable that the wavelength bands reflected by the visible light mirror stack layer portion 12 and the ultraviolet mirror stack layer portion 13 are separated. Therefore, when the wavelength used is 633 nm (laser oscillation light), the UV mirror stack layer 13 has a shorter wavelength of 320 nm or less than a multilayer mirror showing a reflectance of 50% or higher in a short wavelength region of 460 nm or less. The use of a multilayer mirror that exhibits a reflectance of 50% or more in the wavelength region provides higher performance.

Incidentally, the simulation results for ZrO ₂ is not described, the size of the band gap of ZrO _2, the band gap of (HfO ₂ and ZrO ₂ bulk material since it is equivalent to HfO ₂ is HfO ₂ 5 .63 eV (220 nm in terms of light wavelength), ZrO ₂ is 5.4 eV (230 nm in terms of light wavelength), and is considered to have equivalent durability against ultraviolet rays. This is because, if a material is irradiated with light corresponding to the size of the band gap, light energy is absorbed, and damage such as structural defects occurs in the process of losing the absorbed energy due to heat or lattice relaxation. In other words, the larger the band gap of the substance, the more difficult it is to absorb light energy and no damage occurs, so that the durability against ultraviolet rays is excellent.

<Combination Method of Visible Light Mirror Stack Layer 12 and Ultraviolet Mirror Stack Layer 13>
Note that the reflectance (for example, 50%) in the short wavelength region of 320 nm or less in the ultraviolet mirror stack layer is preferably as high as possible from the viewpoint of blocking ultraviolet rays, but as a side effect, the reflectance in the visible light region is reduced. . Therefore, the reflectance of 320 nm or less to be provided in the ultraviolet mirror stack layer portion is determined on a case-by-case basis by a trade-off with the ultraviolet sensitivity of the visible light mirror stack layer portion. For example, as a high refractive index dielectric applied to the visible light mirror stack layer 12, a material having a high ultraviolet sensitivity and a high reflectivity (for example, a loss with respect to visible light of a specific wavelength when there is no ultraviolet irradiation is 50 ppm or less). For example, when Ta ₂ O ₅ ) having a loss of about 30 ppm is selected, alternating lamination of HfO ₂ and SiO ₂ having a high ultraviolet reflectance on the ultraviolet mirror stack layer portion 13 even if the reflectance is slightly reduced. Alternatively, by applying a multilayer film mirror composed of alternately laminated layers of ZrO ₂ and SiO ₂ , a visible light mirror with high reflectivity can be expected. On the other hand, when a material having a relatively low ultraviolet sensitivity is used for the visible light mirror stack layer portion 12, even if a multilayer mirror having an ultraviolet reflectivity of about 50% is applied to the ultraviolet mirror stack layer portion 13, for example, As a result, it is expected to realize a visible light mirror having a somewhat high reflectance. That is, if the ultraviolet mirror stack layer portion 13 has a reflectance appropriately selected from a range of 50% or more according to the ultraviolet sensitivity of the visible light mirror stack layer portion 12 in a predetermined wavelength band of ultraviolet rays. Good. Further, if the visible light mirror stack layer portion 12 has a sufficiently small loss at the used wavelength in the non-irradiated state, the ultraviolet mirror stack layer portion 13 itself is allowed to have a certain amount of loss at the used wavelength. The predetermined wavelength band of the ultraviolet rays irradiates the multilayer mirror with broadband ultraviolet rays, and replaces and inserts a plurality of appropriately selected ultraviolet cut filters having different blocking ranges into the ultraviolet rays to reduce the total loss of the multilayer mirror. Can be determined by the method of measuring.

<Protective layer 14>
The protective layer 14 is formed, for example, on the uppermost layer (for example, HfO ₂ layer) of the ultraviolet mirror stack layer portion 13. The protective layer 14 is, for example, a SiO ₂ layer having a half-wavelength optical layer thickness, and is a physical protective layer having no particular optical function.

<Effect>
As described above, the present invention reflects the ultraviolet ray that induces an increase in total loss with a high reflectivity, and has a new means of overcoating the ultraviolet mirror stack layer on the visible light mirror stack layer. This realizes a visible light mirror having a high reflectivity and a high reflectivity.

<Simulation results>
In FIG. 7, the visible light mirror stack layer portion 12 (Ta ₂ O ₅ / SiO ₂ layer pair) that does not overcoat the ultraviolet mirror stack layer portion 13 and the visible light mirror only of the protective layer 14 are widely used in the ultraviolet region. Similar to the experimental data of the total loss value for 633 nm light when irradiated with light having a spectrum distribution, the experimental data of the conventional configuration disclosed in Patent Document 2, and the visible light mirror 10 having the configuration of FIG. The comparison with the calculated value in the case of irradiating the light is shown. The measurement system related to the experiment has a configuration in which the ultraviolet cut filter is removed from the configuration of FIG. 3, and in this configuration, the measurement was performed by turning on / off the ultraviolet irradiation device. In FIG. 7, circles indicate total loss values for 633 nm wavelength light when ultraviolet rays are not irradiated, and diamonds indicate total loss values for 633 nm wavelength light when ultraviolet rays are irradiated. The calculated value of the visible light mirror 10 of Example 1 was obtained as follows. In the actual measurement value of only the visible light mirror stack layer portion 12 that does not overcoat the UV mirror stack layer portion 13, the loss increase upon 100% UV irradiation is 150 ppm. Estimated to be 1.5 ppm. From FIG. 5, the reflectance of the ultraviolet mirror stack layer portion 13 in the wavelength range that induces an increase in the loss of the visible light mirror 10 is about 90%, and the loss increase calculation of the visible light mirror 10 of Example 1 during the ultraviolet irradiation is performed. The value was estimated as (100% -90% reflection) × 1.5 ppm = 15 ppm. In FIG. 7, the total loss value (about 70 ppm) when the visible light mirror 10 has no ultraviolet rays is a value obtained from the reflectivity 99.9930% obtained in the case of 633 nm in FIG. 5. As can be seen from FIG. 7, when there is no ultraviolet irradiation, the total loss of the mirror that does not overcoat the ultraviolet mirror stack layer 13 is the smallest, and the total loss of the mirror according to the prior art is the second lowest, but the ultraviolet irradiation is performed. In this case, although the conventional mirror can suppress the increase in total loss as compared with the mirror that does not overcoat the UV mirror stack layer 13, the suppression effect of the increase in total loss of the configuration of FIG. Is even more pronounced, and the total loss value under UV irradiation is below that of prior art mirrors. This experimental result also shows that the structure of the present invention has excellent ultraviolet resistance.

  For example, in Patent Document 2, the total loss during UV irradiation is 140 ppm, and the total loss of the visible light mirror 10 without UV irradiation is 70 ppm. Therefore, if the ultraviolet mirror stack layer portion has a reflectivity of 100− (140−70) /1.5=53.3% or more, it is estimated that the total loss is smaller than that in the prior art during the ultraviolet irradiation. be able to. Furthermore, as described above, since the ultraviolet mirror stack layer portion 13 reflects the ultraviolet rays, the visible light mirror stack layer portion 12 has an effect that the physical change and the chemical change due to the ultraviolet rays can be suppressed as compared with the prior art. Play.

  Therefore, if the reflectivity of the UV mirror stack layer portion 13 in a predetermined wavelength band in the UV region is about 50%, a total loss equivalent to that of the conventional technology is realized, and a visible light mirror having higher durability is achieved. Can be realized. Further, if the reflectance is 60% or more, the total loss can be reduced as compared with the prior art, and a visible light mirror with higher durability can be realized.

  By forming an optical resonator for laser oscillation using the visible light mirror described in the first embodiment, a low-loss visible light oscillation gas laser 30 can be configured.

  FIG. 8 shows a configuration example of the visible light oscillation gas laser 30 used in the ring laser gyro 40. For example, the visible light mirror 10 can be applied to the visible light oscillation gas laser 30 used in a ring laser gyro described in JP 2007-93551 A (hereinafter referred to as “reference document 1”).

  An outline of the visible light oscillation gas laser 30 will be described. For example, the visible light oscillation gas laser 30 includes a laser light oscillation cavity 41, three visible light mirrors 10a, 10b, and 10c that form an optical path of the laser light, and a voltage application unit (not shown).

  For example, a mixture of helium and neon (not shown) is placed in the cavity 41. The visible light oscillation gas laser 30 shown in FIG. 8 is applied with a voltage by a voltage applying means (not shown). By applying this voltage, a counterclockwise laser beam 45 enters a closed optical path 44 including a cavity 41 for laser beam oscillation, one laser beam reflecting mirror 10a, and two laser beam reflecting movable mirrors 10b and 10c. And the clockwise laser beam 46 oscillates. The mirror surface portions of the laser beam reflecting mirror 10a and the two laser beam reflecting movable mirrors 10b and 10c are constituted by the visible light mirror 10 described in the first embodiment. Further, the laser light reflecting mirror 10a is appropriately designed so that the laser light can pass therethrough.

  The oscillated counterclockwise laser beam 45 and the clockwise laser beam 46 are emitted from the laser beam reflecting mirror 10a. With such a configuration, a low-loss visible light oscillation gas laser 30 can be configured.

  By forming a ring laser resonator for angular velocity detection using the visible light mirror described in the first embodiment, a ring laser gyro with improved angular velocity detection accuracy can be configured. FIG. 8 shows a configuration example of the ring laser gyro 40. For example, the visible light mirror described in Example 1 can be applied to the ring laser gyro described in Reference 1.

  An outline of the ring laser gyro 40 will be described. For example, the ring laser gyro 40 includes a rotation vibration generating unit 50, a periodic signal generating unit 53, a right-angle prism 47, a photo sensor 48, a signal processing unit 51, and a bias signal removing unit 52 in addition to the visible light oscillation gas laser 30. Also good.

  The laser light emitted from the visible light oscillation gas laser 30 described in the second embodiment is interfered by the action of the right-angle prism 47 of the ring laser gyro 40 and forms interference fringes on the photosensor 48 of the ring laser gyro 40.

  Interference fringe information (movement direction, speed, etc.) detected by the photosensor 48 of the ring laser gyro 40 is input to the signal processing unit 51 of the ring laser gyro 40 and converted into angular velocity information. The angular velocity information output by the signal processing unit 51 is input to the bias signal removing unit 52 of the ring laser gyro 40. The periodic signal generator 53 of the ring laser gyro 40 generates and outputs an appropriate periodic signal. The periodic signal output by the periodic signal generator 53 is input to the rotational vibration generator 50 of the ring laser gyro 40. The rotational vibration generator 50 of the ring laser gyro 40 operates in accordance with the periodic signal output by the periodic signal generator 53 and applies rotational vibration to the entire ring laser gyro 40. For this reason, rotational vibration is applied in the circumferential direction of the optical path 44, and as a result, rotational vibration is applied in the circumferential direction of the laser light. The rotational vibration generating unit 50 includes a monitor unit (not shown). The monitor unit detects the rotational vibration state (position, rotational speed, etc.) of the entire cavity 41, and outputs the detected rotational vibration state as a monitor signal. The angular velocity information output by the signal processing unit 51, the periodic signal output by the periodic signal generating unit 53, and the monitor signal output by the monitoring unit of the rotational vibration generating unit 50 are sent to the bias signal removing unit 52 of the ring laser gyro 40. Entered. The bias signal removal unit 52 removes the vibration angular velocity signal corresponding to the applied rotational vibration in the circumferential direction from the angular velocity information using the periodic signal and / or the monitor signal, and outputs the result as the angular velocity signal. . This angular velocity signal represents the angular velocity in motion of the ring laser gyro 40 or a device including the ring laser gyro 40.

  With such a configuration, it is possible to generate a laser with low loss, and thereby it is possible to configure a ring laser gyro with improved angular velocity detection accuracy.

  In each of the visible light mirrors 10a, 10b, and 10c, ultraviolet light is reflected together with visible light. However, since the resonance condition in the optical resonator 20 is set so that visible light is strengthened, the ultraviolet light is resonant. It is attenuated when it does not meet the conditions or is absorbed by the inner wall of the cavity.

  It should be noted that the structures and methods disclosed in Examples 1 to 3 explain the principle of the present invention. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects as illustrative and illustrative rather than restrictive. Therefore, it is not the above description of the preferred embodiment, but the scope of the invention that defines the scope of the invention. All modifications to the embodiments described herein that fall within the meaning and scope equivalent to the claims are embraced within the scope of the invention.

  The present invention is particularly useful when it is desired to configure a dielectric multilayer optical element to which light containing ultraviolet rays is incident with low loss.

DESCRIPTION OF SYMBOLS 10 Visible light mirror 11 Substrate 12 Visible light mirror stack layer part 13 Ultraviolet mirror stack layer part 14 Protective layer 30 Visible light oscillation gas laser 40 Ring laser gyro

Claims (3)

A substrate,
A visible light mirror stack layer portion which is a multilayer film mirror formed on the substrate and made of alternating layers of Ta ₂ O ₅ and SiO ₂ and reflecting visible light;
It is formed on the visible light mirror stack layer part, and is composed of an alternating stack of optical film thicknesses of 1/4 wavelength of ultraviolet light of either HfO ₂ and SiO ₂ or ZrO ₂ and SiO _{2 and has} a thickness of 250 nm or more and 320 nm or less. An ultraviolet mirror stack layer portion that is a multilayer mirror having a reflectance in a wavelength band of 50% or more , and
The visible light mirror stack layer portion is characterized by having a loss of 50 ppm or less with respect to visible light of a specific wavelength when there is no ultraviolet irradiation,
Visible light mirror. A visible light oscillation gas laser comprising an optical resonator for laser oscillation using the visible light mirror according to claim 1 . A ring laser gyro comprising a ring laser resonator for angular velocity detection using the visible light mirror according to claim 1 .

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