Mechanical loss measuring device

Abstract

The application provides a mechanical loss measuring device, and relates to the technical field of material mechanics. The mechanical loss measuring device comprises a containing assembly, which forms a vacuum chamber; a clamping assembly, which is installed in the vacuum chamber and is used for clamping a first part of a test substrate, a second part of the test substrate extends from the clamping assembly, and the second part is formed with an optical film to be measured; and a driving assembly, which is suitable for driving the second part to vibrate. The natural frequency of the clamping assembly is greater than the natural frequency of the test substrate, so that resonance coupling between the clamping assembly and the test substrate is avoided. First incident laser passes through a light transmission part and is incident on the optical film to be measured. First reflected laser, which is obtained after the first incident laser is reflected by the optical film to be measured, carries vibration information of the optical film to be measured, and the first reflected laser is used for determining the mechanical loss of the optical film to be measured. The mechanical loss measuring device can stably excite the natural vibration of the test substrate at a low frequency of 100 Hz or below, and the measurement result of the mechanical loss has accuracy.

Description

Technical Field

[0001] This invention relates to the field of materials mechanics, and more specifically, to a device for measuring mechanical loss. Background Technology

[0002] For the measurement of mechanical loss of thin film materials, there are several high-precision and mature technical methods, such as the node support method, the disk suspension method, and the fused silica cantilever method. Although the substrate and sample support and fixation methods of the above methods are different, the measurement principle is the same: in a high vacuum environment, the intrinsic vibration mode of the sample is excited by a high-voltage electrostatic signal of a specific frequency, and then the free decay of the sample amplitude after the excitation is turned off is measured. After obtaining the decay curve, the mechanical loss data is obtained by exponential fitting, and the mechanical loss of the thin film is separated by combining the elastic energy ratio.

[0003] Currently, a few attempts have been made to optimize thin-film mechanical loss measurement technology, but existing optimization schemes still have significant limitations. Some measurement devices suffer from problems such as vibration interference due to unreasonable structural design, resulting in insufficient measurement stability; while other devices have attempted to optimize the support and vibration damping structure, they have not yet broken through the limitation of measurement frequency.

[0004] While the aforementioned attempts have improved the measurement theory and technology of thin film mechanical loss to some extent, they have not yet solved the key technical problems. Precision measurement systems that have critical requirements for low-mechanical-loss optical thin films, such as laser interferometric gravitational wave detection and ultra-stable lasers for optical atomic clocks, focus on measurement frequencies of 100Hz and below, which current measurement systems cannot meet. This technical bottleneck not only seriously hinders the research progress in the field of thin film mechanical loss but also restricts the development of downstream precision measurement devices towards lower thermal noise and higher measurement accuracy. Summary of the Invention

[0005] In view of this, the present invention provides a mechanical loss measuring device, comprising:

[0006] It contains components, forms a vacuum chamber inside, and has a light-transmitting part that communicates with the vacuum chamber;

[0007] A clamping assembly is installed in a vacuum chamber, and a first part is configured to clamp a test substrate, a second part of the test substrate extends out from the clamping assembly, and an optical thin film to be tested is formed on the second part;

[0008] The drive assembly, installed inside the vacuum chamber, is suitable for driving the vibration of the second part;

[0009] The intrinsic frequency of the clamping component is configured to be greater than that of the test substrate to avoid resonant coupling between the clamping component and the test substrate; the first incident laser passes through the light-transmitting part and is incident on the optical film under test. After being reflected by the optical film under test, a first reflected laser carrying the vibration information of the optical film under test is obtained. The first reflected laser is suitable for determining the mechanical loss of the optical film under test.

[0010] According to an embodiment of the present invention, the clamping assembly includes:

[0011] Two clamping parts are arranged opposite each other, each clamping part including:

[0012] Mounting plate;

[0013] The clamping plate protrudes from one end of the mounting plate closest to the other mounting plate in a direction perpendicular to the mounting plate;

[0014] Support ribs connect the mounting plate and the clamping plate;

[0015] A gap is formed between the two mounting plates to accommodate the first part. The two mounting plates are brought closer together by external fasteners and deformed to hold the first part within the gap.

[0016] According to an embodiment of the present invention, the wavelength of the first incident laser is configured to be outside the absorption band of the optical thin film under test and the test substrate.

[0017] According to an embodiment of the present invention, the transmission direction of the first incident laser is perpendicular to the plane in which the second part is located, and the area and shape of the cross section of the light-transmitting part along the direction orthogonal to the first incident laser are respectively matched with the area and shape of the light spot of the first incident laser.

[0018] According to an embodiment of the present invention, the mechanical loss measuring device further includes:

[0019] Laser emitting assembly, suitable for emitting the first initial laser beam;

[0020] A first polarization conversion component is adapted to convert a first initial laser into a first linearly polarized laser having a first polarization direction.

[0021] The second polarization conversion component is suitable for converting the first linearly polarized laser into a circularly polarized laser with a transmission direction perpendicular to the plane where the second part is located. The circularly polarized laser is used as the first incident laser and is incident on the optical thin film to be tested.

[0022] The second polarization conversion component is also suitable for converting the first reflected laser into a second linearly polarized laser with a second polarization direction; the first polarization conversion component is suitable for reflecting the second linearly polarized laser; the second linearly polarized laser reflected by the first polarization conversion component is used to obtain the mechanical loss of the optical thin film under test.

[0023] According to an embodiment of the present invention, the wavelength of the first initial laser is configured to be outside the absorption band of the optical thin film under test and the test substrate.

[0024] According to an embodiment of the present invention, the above-described mechanical loss measuring device further includes:

[0025] The reflective assembly is installed inside the vacuum chamber;

[0026] The vacuum chamber has a first mounting state in which a clamping assembly and a drive assembly are installed, and a second mounting state in which a reflective assembly is installed. The vacuum chamber is configured to switch between the first mounting state and the second mounting state.

[0027] When the vacuum chamber is in the second installation state, the second incident laser passes through the light-transmitting part and is incident on the reflective component. It is reflected by the reflective component to obtain the second reflected laser. The second reflected laser is used to determine the vibration noise in the vacuum chamber.

[0028] According to an embodiment of the present invention, the frequency at which the driving component drives the test substrate to vibrate is configured to be different from the frequency of the vibration noise.

[0029] According to an embodiment of the present invention, the mechanical loss measuring device further includes:

[0030] A light-generating component suitable for generating a second initial laser beam;

[0031] A beam splitting assembly is suitable for splitting a second initial laser beam into two sub-lasers, wherein the first sub-laser beam is incident on a reference plane, and the second laser beam is incident on a second polarization conversion assembly as the second incident laser.

[0032] The second polarization conversion component is adapted to reflect the second incident laser to the reflection component. The second beam of laser is reflected by the reflection component to obtain the second reflected laser. The second polarization conversion component is also adapted to reflect the second reflected laser to the beam splitting component. The beam splitting component is also adapted to make the second reflected laser and the reference reflected laser obtained by reflection from the reference surface interfere to obtain the interference laser. The interference laser is used to determine the frequency of vibration noise in the vacuum chamber.

[0033] According to an embodiment of the present invention, the above-described mechanical loss measuring device further includes:

[0034] A temperature control component, connected to the vacuum chamber, is used to maintain the vacuum chamber at a predetermined temperature.

[0035] An electrical signal generating component is suitable for generating voltage signals, which are used to drive the test substrate to vibrate using a driving component.

[0036] Coaxial cable, suitable for transmitting voltage signals to drive components.

[0037] Based on the above technical solution, the mechanical loss measurement device provided by the present invention has at least the following beneficial effects: The vacuum chamber formed by the accommodating components provides an air-damped testing environment for the mechanical loss measurement of optical thin films, avoiding the attenuation interference of the air medium on the vibration of the test substrate. When there is no resonant coupling between the clamping components and the test substrate, the energy of the vibration of the test substrate will not be transferred to the clamping components and consumed through the connection anchor point between the two, ensuring that the free decay vibration of the test substrate and the optical thin film under test is dominated only by its own mechanical loss, avoiding additional energy loss interference, and providing accurate raw data for subsequent exponential fitting calculation of mechanical loss. At the same time, resonant coupling will cause the test substrate to generate non-intrinsic vibration modes, causing the measured vibration frequency, decay time and other key parameters to deviate from the true value. The mechanical loss measurement device of the present invention enables the test substrate to be stably excited with intrinsic vibration in the low frequency range of 100Hz and below, reflecting the actual mechanical characteristics of the optical thin film under test, and making the measurement results of mechanical loss accurate and reliable. Attached Figure Description

[0038] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0039] Figure 1 A schematic diagram of a mechanical loss measuring device provided according to an embodiment of the present invention is shown.

[0040] Figure 2 A perspective view of a housing assembly provided according to an embodiment of the present invention is shown.

[0041] Figure 3 A schematic diagram of a test substrate provided according to an embodiment of the present invention is shown.

[0042] Figure 4 A partial structural schematic diagram of a clamping assembly provided according to an embodiment of the present invention is shown.

[0043] Figure 5 A schematic diagram of another part of the structure of the clamping assembly provided according to an embodiment of the present invention is shown.

[0044] Figure 6 A schematic diagram of mechanical loss measurement according to an embodiment of the present invention is shown.

[0045] Figure 7 A spectrum diagram of vibration noise provided according to an embodiment of the present invention is shown.

[0046] Figure 8 The mechanical loss measurement results are for the test substrate without optical thin film in this embodiment of the invention.

[0047] Figure 9 The mechanical loss measurement results of the test substrate coated with an optical thin film according to an embodiment of the present invention are shown.

[0048] Explanation of reference numerals in the attached figures

[0049] 10: Receiving component; 11: Light-transmitting part; 12: Main body; 121: First vacuum interface; 123: Third vacuum interface; 13: Cold plate; 15: Adsorbent pump; 16: Temperature controller; 17: High voltage power supply; 18: Vacuum gauge; 20: Clamping component; 21: Clamping part; 211: Mounting plate; 211a: Second mounting hole; 212: Clamping plate; 212a: First mounting hole; 22: Support rib; 30: Drive component; 31: Support member; 32: Electrostatic drive board; 40: Test substrate; 41: First part; 42: Second part; 50: Laser emission assembly; 60: First polarization conversion assembly; 61: First polarizer; 62: First half-wave plate; 63: First polarization beam splitter; 64: First optical fiber; 65: First optical fiber collimator; 66: First mirror; 67: First optical isolator; 70: Second polarization conversion assembly; 71: Quarter-wave plate; 72: Reversible mirror; 73: Second mirror; 74: Optical block; 80: Detection assembly; 81: Third mirror; 82: First lens group; 83: First photodetector; 84: Attenuator; 85: Lock-in amplifier; 86: First data acquisition card; 87: Processing mechanism; 88: Second signal generator; 90: Light generation assembly; 91: Helium-neon laser; 92: Second optical isolator; 93: Second lens group; 94: Second optical fiber collimator; 95: Second optical fiber; 97: Third optical fiber collimator; 9 8: Fourth reflecting mirror; 99a: Second polarizer; 99b: Second half-wave plate; 100: Beam splitter assembly; 110: Fifth reflecting mirror; 120: Piezoelectric ceramic; 130: Second high-voltage amplifier; 140: Third signal generator; 150: Sixth reflecting mirror; 160: Focusing assembly; 170: Second photodetector; 180: Second data acquisition card; 190: Electrical signal generation assembly; 191: First signal generator; 192: First high-voltage amplifier. Detailed Implementation

[0050] In the process of realizing this invention, it was discovered that the related technologies could neither measure the mechanical loss of optical thin films at frequencies of 100Hz and below, nor characterize the mechanical loss of optical thin films at an extremely low temperature of 4K.

[0051] Ultra-high reflectivity optical thin films are optical films capable of achieving ultra-high reflectivity of over 99.999% in specific wavelength bands. They are generally fabricated on optical substrates based on distributed Bragg mirror structures and are core components of precision measurement systems such as optical atomic clocks, gravitational wave detection, atomic and molecular trace analysis, and laser gyroscopes. To reduce thermal noise and improve system stability, some advanced precision measurement devices need to operate in low-temperature environments: for example, ultra-stable laser systems using single-crystal silicon optical cavities need to operate at extremely low temperatures of 4K and below to suppress thermal noise between the optical substrate and the optical thin film; next-generation laser interferometry gravitational wave detection systems are also planned to operate in a similar low-temperature range.

[0052] According to fluctuation dissipation theory, material thermal noise and mechanical loss are positively correlated. The thermal noise level of a corresponding system can be assessed by measuring the mechanical loss of an optical thin film. Currently, there is an urgent need for precision measurement systems for low-mechanical-loss optical thin films, with the key noise frequency band concentrated at 100Hz and below. However, the measurement of mechanical loss in this frequency band is significantly affected by the testing environment, especially measurements under 4K low-temperature conditions and 100Hz low-frequency conditions, where current technology remains inadequate.

[0053] Existing measurement devices mostly employ cooling structures to achieve low-temperature environments, but they generally suffer from limited cooling efficiency, high thermal load, and significant vibration interference at low temperatures, making it difficult to simultaneously meet the requirements for extremely low temperatures and low frequencies. While some devices can reach certain low-temperature levels, their minimum test frequencies are still far above 100Hz due to limitations in cooling capacity, thermal management design, and environmental vibration, failing to cover the critical frequency bands required for practical applications. Other devices, although approaching the target low temperature, cannot conduct effective measurements at that temperature due to intensified vibration.

[0054] In summary, existing measurement systems not only fail to meet the requirements for measuring the mechanical loss of optical thin films at low frequencies of 100 Hz and below, but also cannot simultaneously meet the requirements for measuring the mechanical loss of optical thin films at both 4K ultra-low temperatures and 100 Hz and below. This restricts research progress in the field of optical thin film mechanical loss characterization.

[0055] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0056] Figure 1 A schematic diagram of a mechanical loss measuring device provided according to an embodiment of the present invention is shown.

[0057] Figure 2 A perspective view of a housing assembly provided according to an embodiment of the present invention is shown.

[0058] Figure 3 A schematic diagram of a test substrate provided according to an embodiment of the present invention is shown.

[0059] like Figures 1-3 As shown, the mechanical loss measuring device includes: a receiving component 10, a clamping component 20, and a driving component 30. The receiving component 10 forms a vacuum chamber and has a light-transmitting portion 11 communicating with the vacuum chamber. The clamping component 20 is installed within the vacuum chamber and includes a first portion 41 configured to clamp a test substrate 40. A second portion 42 of the test substrate 40 (e.g., a thinned silicon cantilever) extends from the clamping component, and a test optical film is formed on the second portion 42. The driving component 30 is installed within the vacuum chamber and is adapted to drive the test substrate to vibrate. The eigenfrequency of the clamping component 20 is configured to be greater than the eigenfrequency of the test substrate to avoid resonant coupling between the clamping component and the test substrate. When the second portion is vibrating, a first incident laser passes through the light-transmitting portion 11 and is incident on the test optical film. After being reflected by the test optical film, a first reflected laser carrying the vibration information of the test optical film is obtained. The first reflected laser is used to determine the mechanical loss of the test optical film.

[0060] According to an embodiment of the present invention, the vacuum chamber formed by the housing component 10 provides an air-damped testing environment for the measurement of mechanical loss of the optical thin film, avoiding the attenuation interference of the air medium on the vibration of the test substrate. When there is no resonant coupling between the clamping component 20 and the test substrate 40, the energy of the vibration of the test substrate will not be transferred to the clamping component and consumed through the connection anchor point between the two, ensuring that the free decay vibration of the test substrate 40 and the optical thin film under test is dominated only by its own mechanical loss, avoiding additional energy loss interference, and providing accurate raw data for subsequent exponential fitting calculation of mechanical loss. At the same time, resonant coupling will cause the test substrate to generate non-intrinsic vibration modes, causing the measured vibration frequency, decay time and other key parameters to deviate from the true value. The mechanical loss measurement device of the present invention enables the test substrate 40 to be stably excited with intrinsic vibration in the low frequency range of 100Hz and below, reflecting the actual mechanical properties of the optical thin film under test, and making the measurement results of mechanical loss accurate and reliable.

[0061] Figure 4 A partial structural schematic diagram of a clamping assembly provided according to an embodiment of the present invention is shown.

[0062] Figure 5 A schematic diagram of another part of the structure of the clamping assembly provided according to an embodiment of the present invention is shown.

[0063] like Figures 4-5As shown, the clamping assembly 20 includes two clamping portions 21 disposed opposite to each other and a support rib 22. Each clamping portion 21 includes a mounting plate 211 and a clamping plate 212. The clamping plate 212 protrudes from one end of the mounting plate 211 near the other mounting plate 211 in a direction orthogonal to the mounting plate 211. The support rib 22 connects the mounting plate 211 and the clamping plate 212. A gap is formed between the two mounting plates to accommodate the first portion. The two mounting plates 211 are brought closer together and deformed under the action of external fasteners to hold the first portion within the gap.

[0064] According to an embodiment of the present invention, the support rib 22 connects the mounting plate 211 and the clamping plate 212, which can enhance the connection strength and structural rigidity of the mounting plate and the clamping plate. On the other hand, it can increase the overall eigenfrequency of the clamping assembly 20, making it much higher than the eigenfrequency of the test substrate, avoiding resonant coupling between the clamping assembly 20 and the test substrate, and ensuring the accuracy of mechanical loss measurement data.

[0065] According to an embodiment of the present invention, the material of the clamping component 20 can be gold-plated oxygen-free copper.

[0066] According to an embodiment of the present invention, the number of support ribs 22 is at least one, and the orthographic projection of the support rib 22 in a direction parallel to the plane of the mounting plate and the plane of the clamping plate can be, for example, an equilateral triangle. The thickness of each support rib 22 along the projection direction can be the same or different. Multiple pairs of first mounting holes 212a are formed on both clamping plates 212. Two of the first mounting holes in each pair of first mounting holes 212a are respectively formed on the two clamping plates 212 and are directly opposite each other in a direction perpendicular to the clamping plates. Each pair of first mounting holes is used to pass through bolts, the ends of which are threaded into nuts to achieve a detachable connection between the two clamping plates. Multiple second mounting holes 211a are formed on each mounting plate 211 for mounting the mounting plate into the vacuum chamber.

[0067] According to an embodiment of the present invention, the driving assembly 30 includes a support member 31 and an electrostatic driving plate 32. The electrostatic driving plate 32 is mounted on the support member 31. An external voltage signal is applied to the comb-shaped electrodes of the electrostatic driving plate 32, and the electrostatic driving plate 32 is adapted to drive the second part of the test substrate to vibrate under the action of the external voltage signal. The comb-shaped electrodes are made of alumina ceramic to reduce heat leakage.

[0068] According to an embodiment of the present invention, the housing assembly 10 can be configured as a thermostat, for example. The housing assembly includes a main body 12, on which a light-transmitting portion 11 is formed. A cold plate 13 is disposed within the housing assembly 10, dividing the vacuum chamber into a first sub-chamber and a second sub-chamber distributed vertically. A plurality of through holes are formed on the cold plate 13 for communication between the first and second sub-chambers. The first sub-chamber is located above the second sub-chamber. The clamping assembly 20 and the driving assembly 30 are both located on the cold plate 13 and within the first sub-chamber. The thermostat is suitable for maintaining the temperature of the test substrate 40 at a predetermined temperature.

[0069] According to an embodiment of the present invention, the main body 12 is provided with five vacuum interfaces communicating with the second sub-chamber. The first vacuum interface 121 is connected to a molecular pump assembly. The second vacuum interface is connected to an adsorbent pump 15. The third vacuum interface 123 is connected to a temperature controller 16, a heater, and a thermometer. The fourth vacuum interface is connected to a high-voltage power supply 17. The fifth vacuum interface is connected to a vacuum gauge 18. The molecular pump assembly is used to obtain an initial vacuum level within the vacuum chamber. The adsorbent pump 15 is used to maintain a low-vibration vacuum within the vacuum chamber. The temperature controller 16 and the heater are used to regulate the temperature of the vacuum chamber. The thermometer is used to measure the temperature of the vacuum chamber. The high-voltage power supply 17 is connected to an electrostatic drive board and is used to transmit external voltage signals to the electrostatic drive board. The vacuum gauge 18 (e.g., a wide-range vacuum gauge) is used to monitor the vacuum level within the vacuum chamber.

[0070] According to an embodiment of the present invention, the above-described mechanical loss measuring device further includes: an electrical signal generating component 190 and a coaxial cable. The electrical signal generating component 190 is adapted to generate a voltage signal, which is adapted to cause the driving component 30 to drive the test substrate to vibrate. The coaxial cable is adapted to transmit the voltage signal to the driving component 30 to reduce thermal leakage. The electrical signal generating component 190 includes a first signal generator 191 and a first high-voltage amplifier 192. The first signal generator 191 is used to generate a voltage signal. The first high-voltage amplifier 192 is used to amplify the voltage signal. The first high-voltage amplifier 192 is connected to a high-voltage feedthrough 17 to transmit the amplified voltage signal to the electrostatic drive board through the high-voltage feedthrough 17.

[0071] According to an embodiment of the present invention, by designing the clamping component 20, a stable and vibration-free fixed structure for the test substrate is constructed, which avoids the interference of background vibration on the intrinsic vibration of the test substrate at the structural level, ensuring that the test substrate can achieve stable intrinsic vibration excitation and detection in the low-frequency band of 100Hz and below, and realizing precise control of the measurement frequency and effective guarantee of low-frequency measurement.

[0072] The mechanical loss measuring device of this invention can also simultaneously perform low-frequency mechanical loss measurement in an extreme low-temperature environment of 4K. The following is a detailed description.

[0073] According to an embodiment of the present invention, the wavelength of the first incident laser is configured to be outside the absorption band of the test substrate and the optical thin film under test. Since the wavelength of the first incident laser avoids the absorption band of the test substrate and the optical thin film under test, the light absorption coefficient of the test substrate and the optical thin film under test to the first incident laser approaches zero, thereby avoiding heat generation from absorption and ensuring that low-frequency mechanical loss measurements can be carried out in an extreme low-temperature environment of 4K.

[0074] According to an embodiment of the present invention, the second part is configured to have a strip-shaped structure, the transmission direction of the first incident laser is perpendicular to the plane in which the second part is located, and the area and shape of the cross section of the light-transmitting part 11 along the direction orthogonal to the first incident laser are respectively matched with the area and shape of the light spot of the first incident laser.

[0075] According to an embodiment of the present invention, the first incident laser enters and exits perpendicular to the plane containing the second part, so that the beam passes through the light-transmitting part with an incident / reflection angle of nearly 0 degrees. Compared with the oblique incident method, there is no need to reserve additional light-transmitting space to accommodate the oblique propagation of the beam. Combined with the matching design of the cross-sectional area of ​​the light-transmitting part 11 and the incident laser spot, the area of ​​the light-transmitting part 11 (e.g., an optical window) can be reduced as much as possible while ensuring that the beam of the first incident laser passes through completely. The reduction in the area of ​​the optical window can effectively reduce the external heat radiation entering the cryostat through the window, reduce the system heat load, and provide key protection for the cryostat to maintain the 4K extreme low temperature.

[0076] According to an embodiment of the present invention, the above-described mechanical loss measuring device further includes: a laser emitting component 50, a first polarization conversion component 60, and a second polarization conversion component 70. The laser emitting component 50 is adapted to emit a first initial laser, the wavelength of which is configured to be outside the absorption band of the test substrate and the optical thin film under test. The laser emitting component 50 may, for example, be a 1550 nm semiconductor laser emitting component.

[0077] The first polarization conversion component 60 is suitable for converting a first initial laser into a first linearly polarized laser with a first polarization direction. The first polarization conversion component 60 includes: a first polarizer 61, a first half-wave plate 62, and a first polarization beam splitter 63. The first polarizer 61 is suitable for converting the first initial laser into a linearly polarized laser. The first half-wave plate 62 is used to adjust the polarization direction of the first initial laser output from the first polarizer 61, and the first polarization beam splitter 63 is used to transmit the first initial laser output from the first half-wave plate 62. By rotating, the first half-wave plate 62 adjusts the polarization direction of the linearly polarized laser converted by the first polarizer, making the polarization direction match the transmission axis of the first polarization beam splitter 63, allowing the first initial laser to pass through the polarization beam splitter, maximizing the energy utilization of the first initial laser, ensuring stable light intensity incident on the test substrate 40, and adapting to the light intensity requirements of low-frequency weak vibration detection.

[0078] According to an embodiment of the present invention, the first polarization conversion component 60 further includes: a first optical fiber 64, a first optical fiber collimator 65, and a plurality of first reflectors 66. Figure 1 Two first optical isolators 67 are shown in the diagram. A first optical fiber 64 is used to transmit a first initial laser beam. A first optical fiber collimator 65 is located at the laser emission end of the first optical fiber 64 to collimate the first initial laser beam transmitted through the first optical fiber 64, ensuring the directionality of laser propagation and the regularity of the laser spot shape, laying the foundation for precise control and transmission of the subsequent optical path. The first optical isolator 67 is located on the laser emission side of the first optical fiber collimator 65 to achieve unidirectional transmission of the first initial laser beam, blocking the backlight reflected from subsequent optical elements in the optical path from entering the first optical fiber 64 and the laser emission assembly, preventing backlight interference with the stable output of the laser emission assembly and damage to the laser emission assembly. Multiple first reflectors 66 are disposed between the first optical isolator 67 and the first polarizer 61 to change the optical path of the first initial laser beam.

[0079] According to an embodiment of the present invention, the second polarization conversion component 70 is adapted to convert a first linearly polarized laser into a circularly polarized laser having a circular polarization state and a transmission direction perpendicular to the plane containing the second part, wherein the circularly polarized laser is incident on the optical thin film to be tested as the first incident laser.

[0080] According to an embodiment of the present invention, the second polarization conversion component 70 is further adapted to convert the first reflected laser into a second linearly polarized laser having a second polarization direction. The first polarization conversion component is adapted to reflect the second linearly polarized laser. The above-described mechanical loss measuring device further includes: a detection component 80, adapted to detect the second linearly polarized laser from the first polarization conversion component to obtain the mechanical loss of the optical thin film under test.

[0081] According to an embodiment of the present invention, the second polarization conversion component 70 includes: a quarter-wave plate 71, a flip-flop mirror 72, and a plurality of second mirrors 73. The quarter-wave plate 71 is used to convert a first linearly polarized laser into a circularly polarized laser. The flip-flop mirror 72 has a first operating mode and a second operating mode. In the first operating mode, the flip-flop mirror 72 is in an optical path avoidance position and does not receive any light beam. In the second operating mode, the flip-flop mirror 72 is in an optical path reflection position and is used to reflect the received light beam. During the optical path transmission and incident on the test substrate of the circularly polarized laser, the flip-flop mirror 72 is always in the first operating mode, and the circularly polarized laser can be incident unobstructed from the quarter-wave plate 71 onto the plurality of second mirrors 73, and after being reflected by the plurality of second mirrors 73, it is incident on the optical film under test in the cryostat. The second polarization conversion component 70 also includes a light block 74 for collecting stray light.

[0082] According to an embodiment of the present invention, the second polarization conversion component 70 is further adapted to convert the first reflected laser into a second linearly polarized laser having a second polarization direction. The first polarization conversion component 60 is adapted to reflect the second linearly polarized laser. The above-described mechanical loss measuring device further includes: a detection component 80, adapted to detect the second linearly polarized laser from the first polarization conversion component 60 to obtain the mechanical loss of the optical thin film under test.

[0083] According to an embodiment of the present invention, the first reflected laser light passes sequentially through a plurality of second reflecting mirrors 73 and is then incident on a quarter-wave plate 71, where it is converted into a second linearly polarized laser light with a second polarization direction. The second linearly polarized laser light is reflected by the first polarization beam splitter 63 of the first polarization conversion assembly 60 and enters the detection assembly 80.

[0084] According to an embodiment of the present invention, the detection component 80 includes a plurality of third reflecting mirrors 81, a first lens group 82, and a first photodetector 83. A second linearly polarized laser is sequentially reflected by the plurality of third reflecting mirrors 81 and then incident on the first lens group 82. After collimation and focusing by the first lens group 82, it is incident on the detection center of the first photodetector 83. The first photodetector 83 receives the focused second linearly polarized laser and converts the optical signal into an electrical signal, realizing the conversion from the vibration signal of the test substrate to an optical signal and then to an electrical signal. This vibration-electrical signal is used to determine the mechanical loss of the optical thin film under test.

[0085] According to an embodiment of the present invention, the detection component 80 further includes: an attenuator 84, a lock-in amplifier 85, a first data acquisition card 86, a processing mechanism 87, and a second signal generator 88. The attenuator 84 is used to adjust the amplitude of the first electrical signal; the lock-in amplifier 85 is used to convert the vibration electrical signal into an amplitude signal while suppressing noise; the first data acquisition card 86 is used to acquire the amplitude signal; and the processing mechanism 87 is used to obtain the mechanical loss of the optical thin film under test based on the acquisition results of the first data acquisition card 86. The second signal generator 88 is used to provide a reference AC signal for the lock-in amplifier.

[0086] The following combination Figure 6 The principle of mechanical loss measurement is explained in detail.

[0087] Figure 6 A schematic diagram of mechanical loss measurement according to an embodiment of the present invention is shown.

[0088] like Figure 1 and Figure 6As shown, the first polarizer 61 converts the unpolarized initial laser light into a linearly polarized laser light in a single direction. The first half-wave plate 62 calibrates the polarization direction of this linearly polarized laser light by rotation adjustment. After polarization adjustment, the initial laser light is incident on the first polarization beam splitter 63, and then on the quarter-wave plate 71, which converts the linearly polarized laser light into circularly polarized light. This circularly polarized light is incident perpendicularly on the surface of the test substrate at the end of the optical path. When the sample vibrates, it causes a slight deflection in the propagation direction of the first reflected laser light. The reflected circularly polarized laser light is reflected back along the original optical path, and after passing through the quarter-wave plate 71 again, it is converted into a linearly polarized laser light orthogonal to the direction of the first linearly polarized laser light. This orthogonal linearly polarized laser light cannot be transmitted after reaching the polarization beam splitter and is reflected to the first photodetector, such as an indium gallium arsenide four-quadrant photodetector. The indium gallium arsenide four-quadrant photodetector is divided into four quadrant regions, and the initial incident position of the light spot is marked by gray dots in the figure. The attached figure also provides the calculation formula for the vibration signal: by calculating the ratio of the difference in the received light intensity in the four quadrants to the sum, the displacement signals in the X and Y directions are obtained respectively, i.e., Equations (1) and (2) realize the quantification of the two-dimensional micro-vibration of the cantilever beam sample.

[0089] (1);

[0090] (2).

[0091] in, This represents the displacement signal in the X direction. The displacement signal in the Y direction is represented by Q1, Q2, Q3, and Q4. Q1 represents the light intensity / photocurrent in the upper left quadrant of the detector, Q2 represents the light intensity / photocurrent in the upper right quadrant, Q3 represents the light intensity / photocurrent in the lower left quadrant, and Q4 represents the light intensity / photocurrent in the lower right quadrant. Based on the displacement signals in the X and Y directions, the two-dimensional offset of the first incident laser spot when the optical film under test vibrates can be calculated, thus yielding the mechanical loss of the optical film under test.

[0092] According to an embodiment of the present invention, in order to further avoid the influence of thermostat vibration on the experiment at low temperatures, the present invention employs a laser Michelson interferometer structure to measure the background vibration of the thermostat. As an auxiliary measurement structure in this embodiment, the purpose of this structure is to solve a technical problem: general helium cycle refrigeration systems exhibit significant vibration noise, which is even more pronounced at extreme low temperatures such as 4K. However, since this vibration generally originates from the mechanical movement of the cold head and other components, it possesses characteristic vibrational spectra. Therefore, if the background vibration spectrum of the test system is determined, thinned silicon cantilever arms of varying thicknesses can be fabricated to ensure that the fundamental mode eigenfrequency avoids the noise peak, thus obtaining an ideal test environment. Furthermore, the purpose of measuring vibration noise is also to ensure that the frequency at which the driving component drives the test substrate to vibrate is configured to be different from the vibration noise frequency within the vacuum chamber, avoiding resonance interference. The laser Michelson interferometer structure is described in detail below.

[0093] According to an embodiment of the present invention, the mechanical loss measuring device further includes a reflective component mounted within a vacuum chamber. The vacuum chamber has a first mounting state with the clamping component 20 and the driving component 30 mounted, and a second mounting state with the reflective component mounted; the vacuum chamber is configured to switch between the first and second mounting states. When the vacuum chamber is in the second mounting state, a second incident laser light passes through the light-transmitting portion 11 and is incident on the reflective component, where it is reflected to obtain a second reflected laser light. This second reflected laser light is used to determine the vibration noise within the vacuum chamber.

[0094] According to an embodiment of the present invention, both the device for generating the second incident laser and the device for detecting vibration noise using the second reflected laser are laser-Michelson interferometers. The laser-Michelson interferometer comprises a light-generating component 90 and a beam-splitting component 100. The light-generating component 90 is adapted to generate a second initial laser. The beam-splitting component 100 is adapted to split the second initial laser into two sub-lasers. The first sub-laser is incident on a reference plane, and the second laser is incident as the second incident laser onto a second polarization conversion component. The second polarization conversion component is adapted to reflect the second incident laser to a reflection component, and the second laser is reflected by the reflection component to obtain a second reflected laser. The second polarization conversion component is also adapted to reflect the second reflected laser to the beam-splitting component 100. The beam-splitting component 100 is also adapted to cause interference between the second reflected laser obtained by the reflection component and the reference reflected laser obtained by the reference plane, resulting in an interference laser. The interference laser is used to determine the frequency of vibration noise within the vacuum chamber.

[0095] The light generating assembly 90 includes: a helium-neon laser 91 (633nm low-noise laser), a second optical isolator 92, a second lens group 93, a polarization device, a second fiber collimator 94, a second fiber 95, a third fiber collimator 97, and multiple fourth reflectors 98. The helium-neon laser 91 generates a second initial laser, and the second optical isolator 92 prevents reflected laser light from damaging the helium-neon laser 91. The second lens group 93 is used for beam expansion / contraction of the second initial laser to improve coupling efficiency. The polarization device includes a second polarizer 99a and a second half-wave plate 99b. The second polarizer 99a converts the second initial laser into a linearly polarized laser, and the second half-wave plate 99b adjusts the polarization direction of the linearly polarized second initial laser. The second fiber collimator 94 is used to collimate the second initial laser output from the collimating polarization device. The second fiber 95 transmits the second initial laser collimated by the second lens group 93, and the third fiber collimator 97 collimates the second initial laser output from the second fiber 95. Multiple ( Figure 1 (Two are shown) The fourth reflector 98 is used to reflect the second initial laser after it has been collimated by the third fiber collimator 97, so as to change the optical path of the second initial laser. The beam splitter assembly 100 can be, for example, a beam splitter.

[0096] According to an embodiment of the present invention, the laser Michelson interferometer structure further includes a fifth reflecting mirror 110, a piezoelectric ceramic 120, a second high-voltage amplifier 130, and a third signal generator 140. The fifth reflecting mirror 110 reflects the first sub-laser beam output from the beam splitter. The third signal generator 140 provides an excitation signal. The second high-voltage amplifier 130 amplifies the excitation signal generated by the third signal generator to an order of magnitude sufficient to drive the piezoelectric ceramic 120. The piezoelectric ceramic 120 drives the fifth reflecting mirror 110 to move under the action of the excitation signal. The reflecting surface of the fifth reflecting mirror 110 is the reference surface. The first sub-laser beam is reflected by the reference surface to obtain a reference reflected laser. The optical path of the reference reflected laser can be changed during the movement of the fifth reflecting mirror 110.

[0097] According to an embodiment of the present invention, during the background noise detection phase, the flip-flop mirror 72 of the second polarization conversion component 70 is in a second operating mode. The flip-flop mirror 72 and a plurality of second mirrors 73 sequentially reflect the second beam of laser light, causing the second beam of laser light to be incident on the reflection component located in the vacuum chamber, thus obtaining the second reflected laser light. After passing through the plurality of second mirrors 73 and the flip-flop mirror 72, the second reflected laser light is incident on the beam splitting component 100. The second reflected laser light and the reference reflected laser light interfere at the beam splitting component 100, resulting in interference laser light.

[0098] According to an embodiment of the present invention, the laser Michelson interferometer structure further includes a sixth reflecting mirror 150, a focusing component 160, a second photodetector 170 (e.g., a silicon-based amplified photodetector), a second data acquisition card 180, and a processing component. The sixth reflecting mirror 150 reflects the interfering laser, the focusing component 160 focuses the interfering laser, the second photodetector 170 detects the interfering laser to obtain a detected electrical signal, and the processing component analyzes the electrical signal to obtain its frequency. The processing component and the processing mechanism 87 can be the same device or different devices.

[0099] The following are specific embodiments and in conjunction with Figure 1 The measurement process of the mechanical loss measuring device is described in detail.

[0100] First, the vibration and noise inside the vacuum chamber are detected.

[0101] Step 1: Adjust the distance between the two convex lenses in the second lens group 93 to collimate the beam of the second initial laser (helium-neon laser) generated by the helium-neon laser 91 and make its beam spot as small as possible. Rotate the second polarizer 99a to maximize the transmitted light power. The second half-wave plate 99b is used to adjust the polarization direction of the second initial laser to align with the polarization-maintaining axis of the second fiber 95. Adjust the position and elevation angle of the second fiber collimator 94 and the third fiber collimator 97 to maximize the coupling efficiency. This part completes the construction of the polarization-adjustable light generation component 90.

[0102] Step 2: Remove the test substrate 40, clamping assembly 20, and driving assembly 30 from the thermostat, and install the reflective assembly on the cold plate 13. Adjust the optical path alignment of the Michelson interference structure so that the second initial laser, after being split, is incident on the fifth reflector 110 driven by the piezoelectric ceramic 120 and the reflective assembly within the cavity. The reflected light from the fifth reflector 110 and the reflective assembly reconverges, forming equal-inclination interference fringes, which are then focused by the focusing assembly 160 (e.g., a convex lens) onto the second photodetector 170 (e.g., a silicon-based amplified photodetector). Use the third signal generator 140 to generate a DC signal, which is amplified to approximately 200V by the second high-voltage amplifier 130 to drive the piezoelectric ceramic 120 to displace the fifth reflector 110. Adjust the magnitude of the DC signal from the third signal generator 140 and the amplification factor of the second high-voltage amplifier 130. The signal on the second photodetector 170 will change periodically. Adjust its value to half the sum of the maximum and minimum values. At this point, the optical path for measuring vibration noise reaches its most sensitive state.

[0103] Step 3: Start the molecular pump assembly to bring the temperature inside the thermostat to a level better than... A vacuum environment of Pa was created, then the adsorbent pump 15 was started, and the molecular pump group was turned off to obtain the lowest possible vibration environment. Helium cycling cooling was initiated in the thermostat to bring it to the extreme low temperature of 4K. Due to thermal expansion and contraction, the optical path may slightly shift; in this case, the previous step needs to be repeated to readjust the optical path to the most sensitive measurement state.

[0104] Step 4, the interference of two coherent beams of the same amplitude (the second reflected laser obtained by reflection by the reflector and the reference reflected laser obtained by reflection by the reference surface) in the case of perfect parallelism, the signal formula on the second photodetector 170 is expressed as Equation (3).

[0105] (3).

[0106] in The light intensity on the second photodetector; Let be the light intensity of one of the coherent beams; The intensity of another coherent beam; is the refractive index, which is generally taken as 1 in the atmosphere and in a vacuum; It is the wavelength of the second incident laser. Let be the arm length of one of the coherent beams; The arm length of the other coherent beam.

[0107] When the vibration inside the thermostat causes a slight change in the optical path difference between the two coherent beams, the intensity fluctuation of the light output from the second photodetector 170... It can be expressed as equation (4).

[0108] (4).

[0109] According to equation (4), the change in the optical path difference between the two coherent beams caused by vibration inside the thermostat can be obtained. The change is expressed as equation (5).

[0110] (5).

[0111] By measurement The shaking is and the individual power of the two laser beams and Then you can calculate The vibration noise inside the thermostat cavity was then calculated.

[0112] Step 5: After measuring and acquiring the vibration noise in the time domain, use Fourier transform algorithms such as DFT (Discrete Fourier Transform) or FFT (Fast Fourier Transform) to calculate the spectrum of the vibration signal and analyze the frequency range that is not disturbed during mechanical loss measurement.

[0113] In this embodiment, background vibration measurements were performed at the cold finger limit low temperature of 2.2K, and the time-domain and frequency-domain data were obtained as follows: Figure 7 As shown.

[0114] Figure 7 A spectrum diagram of vibration noise provided according to an embodiment of the present invention is shown.

[0115] like Figure 7 The figure shows the spectral measurement results of vibration noise generated by background vibration, calculated using the FFT method. The horizontal axis represents frequency, and the vertical axis represents amplitude. The measurement results show that the vibration is relatively small near 100Hz and at 500Hz and above. Based on this, the dimensional design of the thinned silicon cantilever was found to be... The two lowest frequency eigenmodes of the silicon cantilever under the given conditions are located in the frequency region with relatively small vibrations. Therefore, a thinned silicon cantilever was prepared accordingly for subsequent experiments.

[0116] Secondly, the mechanical loss of the test substrate was measured.

[0117] Step 1, the test substrate used in this embodiment is The thinned silicon cantilever, it should be noted, comprises a first part and a second part. The first part is first cleaned with IPA and deionized water, then clamped between the two clamping portions 21 of the clamping assembly 20. The clamping assembly 20 is then quickly placed into the thermostat, and the clamping assembly is mounted on the cold plate 13. The distance between the silicon cantilever and the drive assembly 30 (e.g., an electrostatic drive plate) is adjusted to approximately 1 mm. The molecular pump group is then activated to bring the temperature inside the thermostat to a level better than... In a vacuum environment of Pa, the adsorbent pump 15 is then started, and the molecular pump group is turned off to obtain the lowest possible vibration environment.

[0118] Step 2: Adjust the position of the first lens group to collimate the output beam of the laser emitting component (e.g., a 1550nm semiconductor laser) and minimize the beam spot size. Adjust the multiple first reflecting mirrors 66 to ensure the beam is incident directly onto all polarizing optical elements. Rotate the first polarizer 61 to maximize the output laser power, ensuring the output power matches the output of the laser emitting component 50. Rotate the first half-wave plate 62 so that all the laser output from the first half-wave plate 62 is transmitted through the first polarizing beam splitter 63 (PBS), matching the polarization direction with the PBS. Rotate the quarter-wave plate 71 so that its polarization direction differs from the laser obtained after transmission through the PBS by 45 degrees, resulting in circularly polarized laser. After being reflected by the second mirror 73, the circularly polarized light is incident on the thinned silicon cantilever. The resulting first reflected laser is a circularly polarized laser with the polarization direction opposite to that of the first incident laser. After passing through a quarter-wave plate again, it becomes a linearly polarized laser orthogonal to the original polarization direction. When it passes through the PBS again, it is reflected and split. After being focused by the third mirror 81 and the first lens group 82, it illuminates the center of the first photodetector (for example, an indium gallium arsenide four-quadrant photodetector).

[0119] Step 3: Start the thermostat to cool down to the extreme low temperature of 4K. Based on the dimensions of the test substrate, use finite element simulation software to calculate and estimate its eigenfrequency. Use a second signal generator 88 to generate a biased AC signal and scan around these calculated frequencies to obtain the accurate eigenfrequency. Use the specific eigenfrequency to excite specific mode vibrations of the thinned silicon cantilever, and its equation of motion is expressed as Equation (6).

[0120] (6).

[0121] in It is the vibration position that evolves over time. It is the initial amplitude. It is the vibration frequency. It is mechanical wear and tear. It is time. It is the phase angle.

[0122] Equation (7) is obtained by filtering out phase information that is unrelated to mechanical loss through lock-in amplification.

[0123] (7).

[0124] The AC signal is turned off, allowing it to decay freely. The amplitude signal is then collected as a function of exponential decay. By fitting the data, the ring-down time can be obtained. Furthermore, the vibration frequency can be determined according to equation (8). Decline Time Calculated mechanical losses .

[0125] (8).

[0126] In practical experiments, since it is not possible to obtain a standalone optical thin film, it is often necessary to conduct tests in conjunction with a substrate. Therefore, it is necessary to first measure the mechanical loss of the uncoated substrate. Then, the thin film is prepared on the substrate, and a second test is performed to obtain the mechanical loss of the substrate with the thin film. Then, the mechanical loss of the thin film is calculated according to equation (9). .

[0127] (9).

[0128] in It tests the Young's modulus of the substrate. It is the Young's modulus of the thin film. It measures the thickness of the substrate. It refers to the thickness of the optical thin film.

[0129] Step 4: In this embodiment, mechanical loss measurements were performed on the substrate before and after depositing the amorphous silicon optical thin film at a temperature of 4K and a fundamental mode frequency of 85Hz. The results are as follows: Figure 8 and Figure 9 As shown.

[0130] Figure 8 The mechanical loss measurement results are for the test substrate without optical thin film in this embodiment of the invention.

[0131] Figure 9 The mechanical loss measurement results of the test substrate coated with an optical thin film according to an embodiment of the present invention are shown.

[0132] like Figure 8 and Figure 9 As shown, the horizontal axis represents time, and the vertical axis represents the amplitude of the vibration signal. Exponential decay fitting was performed on the data, yielding a decay characteristic time of 39680 s for the uncoated state and 11147 s for the coated state. The values ​​were calculated according to equation (8). , The mechanical loss of the aSi:H optical thin film was calculated. It is represented by equation (10).

[0133] (10).

[0134] This invention separates the thermostat and the low-vibration helium cycle refrigeration system and applies them to the field of mechanical loss measurement, achieving for the first time the measurement of mechanical loss of optical substrates and optical thin films with frequencies as low as 100Hz and temperatures as low as 4K.

[0135] This invention employs a clamping assembly with excellent thermal conductivity that does not vibrately couple with the sample, uses a lower-vibration adsorbent pump 15 instead of a molecular pump assembly to maintain the vacuum, and uses a low-thermal-drift support material within the cryostat. These measures ensure the measurement of sample vibration modes down to 100 Hz.

[0136] This invention utilizes a 1550nm laser to detect sample vibration, eliminating heat generation from laser absorption by the test substrate (silicon); it separates incident and reflected light through linear-circular-linear polarization conversion, making the incident / reflection angle nearly 0 degrees, thus minimizing the area of ​​the optical window; and it employs a thermally conductive alumina ceramic electrostatic drive board and a single-channel coaxial high-voltage cable to minimize heat leakage from the vibration excitation module. These measures ensure an extreme low temperature of 4K.

[0137] To further avoid the impact of cryostat vibration on the experiment, this embodiment of the invention uses a laser Michelson interferometer to measure the background vibration of the cryostat. After data acquisition and Fourier transform, the characteristic frequency peak of the background vibration can be obtained. Based on this, the size of the thinned silicon cantilever sample is optimized so that its intrinsic frequency avoids the characteristic peak of the cryostat background vibration, thus minimizing the impact of cryostat vibration on the experiment.

[0138] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A mechanical loss measuring device, characterized in that, include: It contains components, forms a vacuum chamber inside, and has a light-transmitting portion communicating with the vacuum chamber; A clamping assembly is installed in the vacuum chamber, and a first portion is configured to clamp a test substrate, a second portion of the test substrate extending from the clamping assembly, on which an optical thin film to be tested is formed; A drive assembly, installed within the vacuum chamber, is suitable for driving the vibration of the second part; The intrinsic frequency of the clamping component is configured to be greater than the intrinsic frequency of the test substrate to avoid resonant coupling between the clamping component and the test substrate; the first incident laser passes through the light-transmitting part and is incident on the optical film under test, and after being reflected by the optical film under test, a first reflected laser carrying the vibration information of the optical film under test is obtained. The first reflected laser is suitable for determining the mechanical loss of the optical film under test.

2. The mechanical loss measuring device according to claim 1, characterized in that, The clamping assembly includes: Two clamping parts are arranged opposite each other, each clamping part including: Mounting plate; A clamping plate protrudes from one end of the mounting plate near the other mounting plate in a direction orthogonal to the mounting plate; Support ribs connect the mounting plate and the clamping plate; A gap is formed between the two mounting plates to accommodate the first portion. The two mounting plates are brought closer together by external fasteners and deformed to hold the first portion within the gap.

3. The mechanical loss measuring device according to claim 1, characterized in that, The wavelength of the first incident laser is configured to be outside the absorption band of the optical thin film under test and the test substrate.

4. The mechanical loss measuring device according to claim 1, characterized in that, The transmission direction of the first incident laser is perpendicular to the plane containing the second part, and the area and shape of the cross section of the light-transmitting part along the direction orthogonal to the first incident laser are respectively matched with the area and shape of the light spot of the first incident laser.

5. The mechanical loss measuring device according to claim 4, characterized in that, The mechanical loss measuring device also includes: Laser emitting assembly, suitable for emitting the first initial laser beam; A first polarization conversion component is adapted to convert the first initial laser into a first linearly polarized laser having a first polarization direction. The second polarization conversion component is adapted to convert the first linearly polarized laser into a circularly polarized laser with a transmission direction perpendicular to the plane containing the second part, wherein the circularly polarized laser is used as the first incident laser and incident on the optical thin film to be tested. The second polarization conversion component is further adapted to convert the first reflected laser into a second linearly polarized laser with a second polarization direction; the first polarization conversion component is adapted to reflect the second linearly polarized laser; the second linearly polarized laser reflected by the first polarization conversion component is used to obtain the mechanical loss of the optical thin film under test.

6. The mechanical loss measuring device according to claim 5, characterized in that, The wavelength of the first initial laser is configured to be outside the absorption band of the optical thin film under test and the test substrate.

7. The mechanical loss measuring device according to claim 5, characterized in that, Also includes: A reflective assembly is installed inside the vacuum chamber; The vacuum chamber has a first mounting state in which the clamping assembly and the driving assembly are installed, and a second mounting state in which the reflective assembly is installed, and the vacuum chamber is configured to switch between the first mounting state and the second mounting state. When the vacuum chamber is in the second installation state, the second incident laser passes through the light-transmitting part and is incident on the reflective component, and is reflected by the reflective component to obtain the second reflected laser. The second reflected laser is used to determine the vibration noise in the vacuum chamber.

8. The mechanical loss measuring device according to claim 7, characterized in that, The frequency at which the driving component drives the test substrate to vibrate is configured to be different from the frequency of the vibration noise.

9. The mechanical loss measuring device according to claim 7, characterized in that, The mechanical loss measuring device also includes: A light-generating component suitable for generating a second initial laser beam; The beam splitting assembly is suitable for splitting the second initial laser beam into two sub-lasers, wherein the first sub-laser beam is incident on a reference plane, and the second laser beam is incident on the second polarization conversion assembly as the second incident laser. The second polarization conversion component is adapted to reflect the second incident laser to the reflection component, and the second beam laser is reflected by the reflection component to obtain the second reflected laser. The second polarization conversion component is also adapted to reflect the second reflected laser to the beam splitting component, and the beam splitting component is also adapted to cause the second reflected laser and the reference reflected laser obtained by reflection from the reference surface to interfere to obtain the interference laser. The interference laser is used to determine the frequency of vibration noise in the vacuum chamber.

10. The mechanical loss measuring device according to claim 1, characterized in that, Also includes: A temperature control component, connected to the vacuum chamber, is adapted to maintain the vacuum chamber at a predetermined temperature; An electrical signal generating component is suitable for generating a voltage signal, the voltage signal being suitable for causing the driving component to drive the test substrate to vibrate. A coaxial cable is used to transmit the voltage signal to the drive assembly.

Images