Patent Application
20190324175
Multilayer interference mirrors utilized as laser mirrors in Ring Laser Gyroscopes (RLGs) are continually exposed to high energy plasma operating environments that degrade the mirrors by reducing oxide in the refraction materials and thereby inducing photochromic losses. These mirrors are typically formed as stacks of alternating (e.g., ¼λ, thickness) layers of relatively high and relatively low index of refraction materials.
In order to reduce the degrading effects of the high energy plasma operating environments, the high index of refraction materials are typically formed with metal oxides having a relatively high bonding energy to oxygen (e.g., Zirconium Oxide or ZrO2). For example, ZrO2 is often utilized as the top layer of the stacks in interference mirrors, because ZrO2 exhibited a relatively high resistance to degradation in high energy plasma environments. Additionally, ZrO2 is compatible with the relatively high temperatures to which the mirrors are exposed during the manufacturing processes of the RLGs involved. However, a problem with utilizing ZrO2 as the top layer of the stack in an interference mirror is that ZrO2 tends to form a micro-crystalline structure when deposited. These micro-crystalline structures may create scattering sites that can increase the photochromic losses in the interference mirrors involved and also reduce their operational lives.
Aluminum Oxide (AiO3) is another material that is often utilized as the top layer of the stack in interference mirrors, because AiO3 also has a relatively large heat of formation and exhibits a relatively high resistance to degradation in plasma environments. Also, the AiO3 materials utilized exhibit superior ultra-violet (UV) energy blocking characteristics that function to protect the integrity of the underlying layers in the stacks of the interference mirrors involved. However, a significant manufacturing problem with utilizing AiO3 as the outer/top layer in an interference mirror is that the AiO3 material is etched relatively easily by the chemical cleaning and storage solutions commonly utilized during the manufacturing process, which degrades the outer surface of the interference mirror involved. Therefore, the need exists for a technique that can be utilized to protect the AiO3 outer/top layer of the interference mirror during the manufacturing process, and thereby eliminate the surface degradation of the outer/top layer caused by the chemical cleaning and storage solutions utilized.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for methods for enhancing the manufacture of multilayer interference mirrors utilized, for example, in RLG devices.
Embodiments disclosed herein present techniques for enhancing the durability and manufacturability of multilayer interference mirrors utilized as laser mirrors in RLG devices.
Embodiments of the present disclosure can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:
In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize features relevant to the present disclosure. Reference characters denote like elements throughout the figures and text.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of specific illustrative embodiments in which the embodiments may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.
For this example embodiment, the enhanced multilayer mirror 100 also includes an outermost layer (e.g., durability layer) 106 deposited on the ZrO2 layer 102a. In this example embodiment, the outermost layer 106 is a metal oxide material having a relatively high heat of formation (e.g., Aluminum Oxide or AiO2/Al2O3). As such, for this embodiment, the AiO2/Al2O3 material is selected for the outermost layer 106 primarily because the AiO2/Al2O3 material has superior UV energy blocking characteristics and can thereby protect the underlying ZrO2 and SiO2 layers in that regard. However, on the other hand, the AiO2/Al2O3 material has manufacturing challenges because it can be etched and its surface degraded (e.g., referred to as etching degradation) by the cleaning and storage solutions utilized during the fabrication finishing process. Consequently, in order to mitigate these manufacturing process problems, an overcoat 108 of a process-friendly (e.g., SiO2) material, which is impervious to the etching degradation caused by the cleaning and storage finishing solutions, is applied to the outer surface of the outermost layer 106. For example, a thin coating of (e.g., 10 angstroms in thickness) of a SiO2 material can be applied (e.g., utilizing a suitable deposition process) as an overcoat to the outermost (e.g., durability) layer 106. In this embodiment, the multilayer mirror 100 including the stack of substantially quarter-wavelength layers and the process-friendly overcoat 108 is formed (e.g., by a suitable deposition process) on a substrate 110.
Returning to the method 300, a layer 106 of a durable optical material (e.g., AiO2 in this embodiment) is deposited (e.g., utilizing an electron beam or ion beam deposition process) on the exposed surface of the outermost layer 102a of the high index of refraction optical material ZrO2 (306). This “durability layer” 106 has enhanced UV energy blocking characteristics and also provides physical protection for the underlying layers of ZrO2 and SiO2. An over-coating 108 of an additional protective material (e.g., SiO2) is then deposited (e.g., utilizing an electron beam or ion beam deposition process) on the exposed surface of the durability layer 106 (308). As such, this protective over-coating 108 protects the underlying layer 106 because the material utilized (e.g., SiO2) is impervious to the etching degradation that can occur to the durability layer 106 due to the cleaning and storage solutions utilized during the final fabrication process.
It should be understood that elements of the above described embodiments and illustrative figures may be used in various combinations with each other to produce still further embodiments which are explicitly intended as within the scope of the present disclosure.
Example 1 includes a multilayer mirror, comprising: a plurality of alternating layers of a high index of refraction optical material and a low index of refraction optical material; a durability layer of an optical material disposed on the plurality of alternating layers; and an overcoat of a protective material on an outermost surface of the durability layer.
Example 2 includes the multilayer mirror of Example 1, wherein the high index of refraction material comprises a Zirconium Oxide (ZrO2) layer of material.
Example 3 includes the multilayer mirror of any of Examples 1-2, wherein the low index of refraction material comprises a Silicon Oxide (SiO2) layer of material.
Example 4 includes the multilayer mirror of any of Examples 1-3, wherein the durability layer comprises an Aluminum Oxide (AiO2) layer of material.
Example 5 includes the multilayer mirror of any of Examples 1-4, wherein the overcoat of the protective material comprises a coating of a SiO2 material.
Example 6 includes the multilayer mirror of any of Examples 1-5, wherein the plurality of alternating layers comprise a plurality of substantially quarter wavelength structures.
Example 7 includes the multilayer mirror of any of Examples 1-6, further comprising a substrate material under the plurality of alternating layers.
Example 8 includes the multilayer mirror of any of Examples 5-7, wherein the coating of the SiO2 material is substantially thinner than the thickness of each layer of the plurality of layers.
Example 9 includes the multilayer mirror of any of Examples 1-8, wherein the multilayer mirror comprises a reflective mirror for a laser cavity in a ring laser gyroscope (RLG).
Example 10 includes the multilayer mirror of any of Examples 1-9, wherein the overcoat is impervious to etching degradation.
Example 11 includes a ring laser gyroscope, comprising: a laser block assembly; a cavity in the laser block assembly; and a plurality of multilayer mirrors in the cavity, wherein at least one multilayer mirror of the plurality of multilayer mirrors comprises: a plurality of alternating layers of a high index of refraction optical material and a low index of refraction optical material; a durability layer of an optical material disposed on the plurality of alternating layers; and an overcoat of a protective material on an outermost surface of the durability layer.
Example 12 includes the ring laser gyroscope of Example 11, wherein the durability layer comprises an Aluminum Oxide layer of material.
Example 13 includes the ring laser gyroscope of any of Examples 11-12, wherein the overcoat of the protective material comprises a coating of a SiO2 material.
Example 14 includes the ring laser gyroscope of any of Examples 11-13, wherein the plurality of multilayer mirrors comprises three or more multilayer reflective mirrors.
Example 15 includes the ring laser gyroscope of any of Examples 11-14, wherein the high index of refraction optical material comprises Zirconium Oxide and the low index of refraction optical material comprises Silicon Oxide.
Example 16 includes a method, comprising: forming a plurality of layers of a first index of refraction optical material on a substrate; forming a plurality of layers of a second index of refraction optical material between the layers of the first index of refraction optical material; forming a layer of a durable optical material on an outermost layer of the plurality of layers of the first index of refraction optical material; and forming an over-coating of a protective material on a surface of the layer of the durable optical material.
Example 17 includes the method of Example 16, wherein the forming the plurality of layers of the first index of refraction optical material comprises forming layers of Zirconium Oxide.
Example 18 includes the method of any of Examples 16-17, wherein the forming the plurality of layers of the second index of refraction optical material comprises forming layers of Silicon Oxide.
Example 19 includes the method of any of Examples 16-18, wherein the forming the layer of the durable optical material comprises forming a layer of Aluminum Oxide.
Example 20 includes the method of any of Examples 16-19, wherein the forming the over-coating comprises forming a coating of Silicon Oxide.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the presented embodiments. Therefore, it is manifestly intended that embodiments be limited only by the claims and the equivalents thereof.
