Miniaturized ultra-stable cavity system

Abstract

The invention discloses a miniaturized ultra-stable cavity system. An outer layer vacuum device comprises a copper pipe, a feed-through, a titanium vacuum cavity, a vacuum cavity base, a vacuum getter, a left vacuum flange observation window and a right vacuum flange observation window; a heat shielding aluminum cover is arranged in the titanium vacuum cavity, and a ceramic cylindrical fixing seat in the heat shielding aluminum cover and the cylindrical ULE ultra-stable cavity form a composite ultra-stable cavity structure; the ultra-stable cavity system provided by the invention can provide a miniaturized optical reference with better medium and short-term frequency stability for an integrated low-noise photo-generated microwave source, a transportable atomic optical clock, a satellite-borne laser and the like, and has very important engineering application value.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-stable lasers and relates to a miniaturized ultra-stable cavity system. Background Art

[0002] Ultrastable lasers have important applications in cutting-edge high-tech fields due to their extremely high frequency stability, ultra-narrow laser linewidth and ultra-low noise, especially in quantum precision measurement, atomic optical clocks, gravitational wave detection, optical frequency transmission, precision spectroscopy and quantum computing.

[0003] Most ultra-stable lasers are achieved by using the Pound Drever Hall (PDH) technology to lock the laser frequency to the resonant frequency of an ultra-stable cavity with ultra-high reflectivity. Based on this method, the length stability of the ultra-stable cavity is transferred to the laser frequency stability. In order to reduce the influence of ambient temperature and mechanical vibration on the length of the ultra-stable cavity, the ultra-stable cavity is usually placed in an ultra-high vacuum chamber with special shock absorption and temperature insulation design. At present, the stability of the laser frequency locked to the resonant frequency of the ultra-stable cavity placed in an ultra-high vacuum has reached the E-16 or even E-17 level. The performance of frequency stability is mainly limited by the influence of thermal noise of the cavity mirror film layer.

[0004] Ultra-stable cavity materials are mostly made of ultra-low expansion glass (ULE). A major characteristic of this material is that it has a zero expansion temperature point near room temperature. When the temperature of the ULE cavity is controlled near this point, its length change rate is minimal. Another low expansion coefficient material used for ultra-stable cavities is single crystal silicon, but the zero expansion temperature point of this material is on the order of K, and liquid helium is required for cooling. The refrigeration equipment is complex and the maintenance cost is expensive. At the same time, the demand for ultra-stable cavities that can adapt to applications in harsh and unpredictable environments has led to the emergence of solid-state medium ultra-stable cavities with strong rigidity. Solid-state medium ultra-stable cavities have the characteristics of small structure, but ultra-stable cavities of this material have high thermal refraction noise and temperature sensitivity, and their frequency stability is on the order of E-13 or above.

[0005] Therefore, it is necessary to develop a miniaturized ultra-stable cavity with simple structure, strong rigidity, high frequency stability and large-scale manufacturing capability. Summary of the invention

[0006] The purpose of the present invention is to design a miniaturized cylindrical ultra-stable cavity system to address the shortcomings of existing experimental-grade vacuum ultra-stable cavities, such as large size and high cost. The system has low vibration sensitivity and temperature sensitivity, small size, simple structure, and can meet the needs of large-scale production and portable use.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a miniaturized ultra-stable cavity system, including a vacuum cavity base and a titanium vacuum cavity fixedly connected to the vacuum cavity base by screws, a heat-shielding aluminum cover and a getter are respectively arranged in the titanium vacuum cavity, the heat-shielding aluminum cover is fixed to the vacuum cavity base by an aluminum plate base, the heat-shielding aluminum cover and the aluminum plate base constitute a heat-shielding aluminum cavity, a flange observation window for collimation and transmission of the laser light path, a copper tube for primary extraction of the vacuum degree in the titanium vacuum cavity, and a feedthrough for connecting an external current source to activate the getter are sequentially arranged on the top of the titanium vacuum cavity, an external light-through hole is arranged on the heat-shielding aluminum cover facing the flange observation window, and the heat-shielding aluminum cover has a through hole in the heat-shielding aluminum cover. A ULE ultra-stable cavity with a vent is fixed through a ceramic cylindrical fixing seat, the vent is located at the center of the side wall of the ULE ultra-stable cavity and is arranged along the radius direction of the cavity, the fixing seat is fixedly connected to the aluminum plate base by screws, the ceramic cylindrical fixing seat and the cylindrical ULE ultra-stable cavity constitute a composite ultra-stable cavity structure, the ULE ultra-stable cavity is respectively provided with a left FS cavity mirror and a right FS cavity mirror through a left O-ring and a right O-ring, a first indium steel fixing ring and a second indium steel fixing ring for limiting the left FS cavity mirror and the right FS cavity mirror are sequentially arranged outside the ULE ultra-stable cavity from top to bottom, and an inner light hole is arranged on the ULE ultra-stable cavity, which is located between the first indium steel fixing ring and the second indium steel fixing ring and is directly facing the outer light hole.

[0008] The miniaturized ultra-stable cavity system, wherein the flange observation window comprises a left vacuum flange observation window and a right vacuum flange observation window respectively arranged on both sides of the titanium vacuum cavity, the outer light through hole comprises an outer left light through hole and an outer right light through hole, and the inner light through hole comprises an inner left light through hole and an inner right light through hole. The left vacuum flange observation window / the right vacuum flange observation window is axially concentric with the outer left light through hole / the outer right light through hole and the inner left light through hole / the inner right light through hole.

[0009] In the miniaturized ultra-stable cavity system, the inner light hole, the outer light hole and the air hole are of the same size, and the inner light hole and the outer light hole penetrate the ULE ultra-stable cavity and intersect the air hole perpendicularly at the center of the central axis.

[0010] The miniaturized ultra-stable cavity system has a left FS cavity mirror which is a plane mirror coated with an anti-reflection film on one side and a high-reflection film on the other side, and a right FS cavity mirror which is a plano-concave mirror with an anti-reflection film on one flat surface and a high-reflection film on the other concave surface, and the curvature radius of the concave surface is 1000 mm.

[0011] In the miniaturized ultra-stable cavity system, the transmittance of the anti-reflection film coated on the left FS cavity mirror and the right FS cavity mirror is 99.9%, so that most of the laser power can pass through the film layer; the reflectivity of the high-reflection film coated on the left FS cavity mirror and the right FS cavity mirror is greater than 99.999%, so that the laser power can form a standing wave between the left FS cavity mirror and the right FS cavity mirror for amplification, thereby improving the intensity of the collected signal of the ultra-stable cavity system.

[0012] The miniaturized ultra-stable cavity system has high-reflection film sides of the left FS cavity mirror and the right FS cavity mirror glued to the two sides of the ULE ultra-stable cavity by optical glue, and is concentrically arranged with the ULE ultra-stable cavity; the diameter of the anti-reflection film and high-reflection film area plated on the left FS cavity mirror and the right FS cavity mirror is consistent with the diameter of the light-through hole, and the diameter of the left FS cavity mirror and the right FS cavity mirror is smaller than the diameter of the ULE ultra-stable cavity.

[0013] The beneficial effect of the present invention is that the ultrastable cavity system of the present invention can provide a miniaturized optical reference with good medium- and short-term frequency stability for integrated low-noise photogenerated microwave sources, portable atomic optical clocks, satellite-borne lasers, etc., and has very important engineering application value. The promotion of the application of the present invention can replace the traditional frequency stabilization technology based on atomic gas chambers, further improve the performance indicators of related quantum precision measurement instruments, and promote the technological development of related scientific fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0015] Figure 2 1 is the composition structure of the vacuum interior in the embodiment of the present invention.

[0016] Figure 3 Schematic diagram of the composition structure of the ultra-stable cavity in the embodiment of the present invention.

[0017] The figures are marked as follows: 1—copper tube, 2—feedthrough, 3—titanium vacuum chamber, 4—vacuum chamber base, 5—left vacuum flange observation window, 6—right vacuum flange observation window, 7—heat shielding aluminum cover, 8—aluminum plate base, 9—fixing seat, 10—first indium steel fixing ring, 11—second indium steel fixing ring, 12—left O-ring, 13—right O-ring, 14 / 15—M4 screw, 16—M3 screw, 17—getter, 18—outer right light hole, 19—outer left light hole, 20—ULE ultra-stable cavity, 21—left FS cavity mirror, 22—right FS cavity mirror, 23—inner left light hole, 24—inner right light hole, 25—vent. DETAILED DESCRIPTION

[0018] To facilitate understanding of the present application, the present application will be described more comprehensively below with reference to relevant drawings and embodiments.

[0019] like Figure 1 , Figure 2 and Figure 3 As shown, this example provides a miniaturized ultra-stable cavity system, and the outer vacuum device structure is composed of a copper tube 1, a feedthrough 2, a titanium vacuum cavity 3, a vacuum cavity base 4, a vacuum getter 17, a left vacuum flange observation window 5 and a right vacuum flange observation window 6.

[0020] The titanium vacuum chamber 3 and the vacuum chamber base 4 are fixed together by M4 screws 14 for vacuum packaging. The volume of the titanium vacuum chamber 3 is about 8 cm 2 Two CF16 vacuum flange observation windows are installed at the center of a pair of side surfaces of the titanium vacuum chamber 3. The left vacuum flange observation window 5 and the right vacuum flange observation window 6 are coated with an anti-reflection film with a transmittance greater than 99.9%@1550nm. A copper tube 1 is arranged above the titanium vacuum chamber 3 to connect the titanium vacuum chamber 3 and the external molecular pump to perform low vacuum primary extraction on the vacuum system. When the vacuum value in the titanium vacuum chamber 3 reaches E-4Pa, the molecular pump vacuum extraction operation is stopped and the copper tube 1 is clamped off.

[0021] The feedthrough 2 is a bridge for connecting an external current source and a vacuum getter 17 placed inside the vacuum chamber. -4 When the vacuum getter 17 is at 0.0400 Pa, current is passed to activate the vacuum getter 17, so that the vacuum getter 17 can continue to absorb the gas in the vacuum chamber and maintain the low vacuum degree inside the titanium vacuum chamber 3. The low vacuum degree titanium vacuum chamber 3 can effectively reduce the influence of external air pressure fluctuations, temperature fluctuations, etc. on the length stability of the ULE ultra-stable chamber 20.

[0022] The inner aluminum shielding layer structure of the ultra-stable cavity system of the present invention is composed of a shielding aluminum cover 7, an aluminum plate base 8 and M4 screws 15. The aluminum shielding layer can be polished to reduce the influence of external temperature changes on the length stability of the ultra-stable cavity 20. The shielding aluminum cover 7 and the aluminum plate base 8 are fixedly connected by M4 screws 15. Two light holes 25 are opened on the side wall of the shielding aluminum cover 7. When the system is vacuum-extracted, the outer right light hole 18 and the outer left light hole 19 can also be used for ventilation.

[0023] The composite ultra-stable cavity structure in the inner aluminum shielding layer is composed of a ceramic cylindrical fixing seat 9, a cylindrical ULE ultra-stable cavity 20, a first indium steel fixing ring 10, a second indium steel fixing ring 11, a left O-ring 12, a right O-ring 13, and an M3 screw 16. The fixing seat 9 is used to install the ULE ultra-stable cavity 20, and its internal hole center diameter is consistent with the diameter of the ULE ultra-stable cavity 20. The left O-ring 12 is placed on one side of the ultra-stable cavity 20, and the right O-ring 13 is placed on the other side of the ultra-stable cavity 20.

[0024] The left FS cavity mirror 21 and the right FS cavity mirror 22 are installed on the ULE ultra-stable cavity 20 through the left O-ring 12 and the right O-ring 13 respectively. The first indium steel fixing ring 10 and the second indium steel fixing ring 11 are arranged from top to bottom outside the ULE ultra-stable cavity 20 to limit the left FS cavity mirror 21 and the right FS cavity mirror 22. The left O-ring 12 and the right O-ring 13 are used for fixing and buffering between the first indium steel fixing ring 10 and the second indium steel fixing ring 11 and the ULE ultra-stable cavity 20, and also prevent the indium steel ring from damaging the ultra-stable cavity glass when fixing. The diameter of the first indium steel fixing ring 10 and the second indium steel fixing ring 11 is consistent with the diameter of the ULE ultra-stable cavity 20, and the thickness is 4mm. The axial center hole passes through the indium steel ring, and the diameter of the hole center is consistent with the size of the light hole of the ultra-stable cavity 20, which does not block the laser from passing. The fixing seat 9 and the aluminum plate base 8 are fixedly connected by M3 screws 16. The ceramic cylindrical fixing seat 9 is a microcrystalline glass ceramic with a low temperature expansion coefficient, which has the characteristics of both glass and ceramic, and can effectively further reduce the influence of the change of the external temperature on the change of the cavity length of the ULE ultra-stable cavity 20.

[0025] The ULE ultra-stable cavity 20 is cylindrical, with a cavity diameter of 35mm and a length of 6mm. The inner left light hole 23 and the inner right light hole 24 have a diameter of 3mm, and the vent hole 25 also has a diameter of 3mm. The inner light hole and the outer light hole pass through the ULE ultra-stable cavity 20 and the vent hole 25 are perpendicular to each other and cross the central axis. The thermal expansion coefficient of the ULE ultra-stable cavity 20 material is in the order of E8K, and the cylindrical cavity is easy to process, has good symmetry, and is less sensitive to vibration. The left FS cavity mirror 21 and the right FS cavity mirror 22 are made of fused quartz, and their thermal expansion coefficient is in the order of E7K. The diameter of the two FS cavity mirrors is 12.7mm and the thickness is 6mm. The contact surfaces of the left FS cavity mirror 21 and the right FS cavity mirror 22 with the ULE ultra-stable cavity 20 are coated with an ultra-high reflective film layer with a reflectivity greater than 99.999%@1550nm. The FS cavity mirror has a higher mechanical quality factor than the ULE and lower thermal noise than the ULE.

[0026] The left FS cavity mirror 21 is a plane mirror with an anti-reflection film on one side and a high-reflection film on the other side, and the right FS cavity mirror 22 is a plane concave mirror with an anti-reflection film on one side and a high-reflection film on the other side, and the radius of curvature of the concave surface is 1000mm. The transmittance of the anti-reflection film coated on the left FS cavity mirror 21 and the right FS cavity mirror 22 is 99.9%, so that most of the laser power can pass through the film layer; the reflectivity of the high-reflection film coated on the left FS cavity mirror 21 and the right FS cavity mirror 22 is greater than 99.999%, so that the laser power can form a standing wave between the left FS cavity mirror 21 and the right FS cavity mirror 22 to amplify, thereby improving the intensity of the collected signal of the ultra-stable cavity system. The high-reflection film sides of the left FS cavity mirror 21 and the right FS cavity mirror 22 are glued to the two sides of the ULE ultra-stable cavity 20 by optical glue, and are arranged concentrically with the ULE ultra-stable cavity 20; the diameters of the anti-reflection film and high-reflection film areas coated on the left FS cavity mirror 21 and the right FS cavity mirror 22 are consistent with the diameter of the ULE light hole, and the diameters of the left FS cavity mirror 21 and the right FS cavity mirror 22 are smaller than the diameter of the ULE ultra-stable cavity 20.

[0027] After the ultra-stable cavity system of the present invention is assembled, the vacuum in the titanium vacuum cavity 3 is extracted by connecting the copper tube 1 to an external pump. After the vacuum extraction is completed, the copper tube 1 is cut off, and the getter 17 is used to maintain the low vacuum environment in the titanium vacuum cavity 3. The whole system has a simple structure, is easy to operate, and is both miniaturized and portable.

[0028] The miniaturized ultrastable cavity system proposed in this embodiment provides a new laser frequency stabilization solution for realizing low-size, weight and power (low-SWaP) transportable atomic optical clocks, portable ultrastable femtosecond optical combs, satellite-borne frequency-stabilized lasers and other fields. Such an ultrastable cavity system provides frequency instability of the order of E-14 for laser frequency stabilization, which will be helpful for low-SWaP atomic optical clock applications. The miniaturized ultrastable cavity device introduced here is a general platform for quantum precision measurement. Future work using this system can explore applications including inertial sensing using atomic interferometry, electric field measurement using Rydberg spectroscopy, and higher performance compact photogenerated microwave solutions using optical transitions.

[0029] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A miniaturized ultrastable cavity system, characterized in that: The invention comprises a vacuum chamber base (4) and a titanium vacuum chamber (3) connected to the vacuum chamber base (4); a heat shielding aluminum cover (7) and a getter (17) are respectively arranged in the titanium vacuum chamber (3); a flange observation window for laser light path alignment and transmission, a copper tube (1) for extracting the vacuum degree in the chamber, and a feedthrough (2) for activating the getter (17) are arranged in sequence on the titanium vacuum chamber (3); an external light hole facing the flange observation window is arranged on the heat shielding aluminum cover (7); and the heat shielding aluminum cover (7) is fixed by a fixing seat (9) inside the heat shielding aluminum cover (7). A ULE ultra-stable cavity (20) with a vent hole (25) is provided, a left FS cavity mirror (21) and a right FS cavity mirror (22) are mounted on the ULE ultra-stable cavity (20) via a left O-ring (12) and a right O-ring (13), a first indium steel fixing ring (10) and a second indium steel fixing ring (11) are arranged outside the ULE ultra-stable cavity (20), and an inner light hole is arranged on the ULE ultra-stable cavity (20) and is located between the first indium steel fixing ring (10) and the second indium steel fixing ring (11) and is directly facing the outer light hole.

2. A miniaturized ultrastable cavity system according to claim 1, characterized in that: The flange observation window comprises a left vacuum flange observation window (5) and a right vacuum flange observation window (6) respectively arranged on two sides of the titanium vacuum chamber (3); the external light through hole comprises an external left light through hole (19) and an external right light through hole (18); and the internal light through hole comprises an internal left light through hole (23) and an internal right light through hole (24).

3. A miniaturized ultrastable cavity system according to claim 2, characterized in that: The inner light through hole, the outer light through hole and the vent hole (25) are of the same size, and the inner light through hole and the outer light through hole penetrate the ULE ultra-stable cavity (20) and the vent hole (25) and intersect each other perpendicularly at the central axis.

4. A miniaturized ultrastable cavity system according to claim 1, 2 or 3, characterized in that: The left FS cavity mirror (21) is a plane mirror with an anti-reflection film on one side and a high-reflection film on the other side, and the right FS cavity mirror (22) is a plano-concave mirror with an anti-reflection film on one flat surface and a high-reflection film on the other concave surface, and the curvature radius of the concave surface is 1000 mm.

5. A miniaturized ultrastable cavity system according to claim 4, characterized in that: The transmittance of the antireflection film coated on the left FS cavity mirror (21) and the right FS cavity mirror (22) is 99.9%, and the reflectivity of the high reflection film coated on the left FS cavity mirror (21) and the right FS cavity mirror (22) is greater than 99.999%.

6. A miniaturized ultrastable cavity system according to claim 5, characterized in that: The high-reflection film sides of the left FS cavity mirror (21) and the right FS cavity mirror (22) are adhered to the two sides of the ULE ultra-stable cavity (20) by optical glue, and are concentric with the ULE ultra-stable cavity (20); the diameters of the anti-reflection film and high-reflection film regions coated on the left FS cavity mirror (21) and the right FS cavity mirror (22) are consistent with the diameter of the light-through hole, and the diameters of the left FS cavity mirror (21) and the right FS cavity mirror (22) are smaller than the ULE ultra-stable cavity (20).

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