Molecular beam density measurement methods and related equipment
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHERN UNIVERSITY OF SCIENCE AND TECHNOLOGY
- Filing Date
- 2026-01-09
- Publication Date
- 2026-05-26
Smart Images
Figure CN122084734A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of molecular beam technology, and in particular to a method for measuring molecular beam density and related equipment. Background Technology
[0002] Molecular beam physics is an important experimental technique in fields such as atomic and molecular physics, chemical reaction dynamics, and surface science, and is widely used to explore collisions, reactions, and energy transfer processes of microscopic particles. In these experimental studies, accurate knowledge of the molecular beam density is crucial for ensuring the accuracy of experimental results, calculating reaction cross-sections, and verifying the reproducibility of theoretical models.
[0003] Common measurement methods in related technologies include vacuum gauge reading, absorption spectroscopy, laser-induced fluorescence, and electron beam fluorescence. However, the core technical problem with these existing technologies is the difficulty in achieving precise absolute calibration of molecular beam density. Whether relying on roughly estimated vacuum gauge readings or on fluorescence or spectroscopy methods that depend on specific energy level transitions and require complex absorption models, it is difficult to establish a direct and highly accurate quantitative relationship between the detected signal and the actual molecular density. This often results in large systematic errors and complex models, making it impossible to accurately obtain the absolute density value of the molecular beam. Summary of the Invention
[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application provides a molecular beam density measurement method and related equipment, which can establish a quantitative calibration relationship by introducing a standard gas of known density, thereby achieving absolute measurement of molecular beam density and improving the accuracy of the measurement.
[0005] In a first aspect, embodiments of this application provide a molecular beam density measurement method applied to a molecular beam density measurement system. The molecular beam density measurement system includes a vacuum cavity, a precision leak valve and a vacuum ion gauge connected to the gas path of the vacuum cavity, a microchannel plate detector disposed within the vacuum cavity, and a laser ionization device for emitting laser light into an ionization region within the vacuum cavity. The method includes: The opening degree of the precision leak valve is controlled to introduce background gas into the vacuum chamber, and the standard density of the background gas is obtained through the vacuum ion gauge. The laser ionization device is controlled to photoionize the background gas, and the first ion signal generated by the background gas is collected by the microchannel plate detector. Establish a quantitative calibration relationship between the first ion signal and the standard density; The operating parameters of the laser ionization device are kept consistent with those used when constructing the quantitative calibration relationship. The laser ionization device is controlled to photoionize the target molecular beam, and the second ion signal generated by the target molecular beam is collected through the microchannel plate detector. Based on the second ion signal, the absolute density of the target molecular beam is calculated using the quantitative calibration relationship.
[0006] In some embodiments, obtaining the standard density of the background gas using the vacuum ion gauge includes: Read the equilibrium pressure value inside the vacuum chamber measured by the vacuum ion gauge; Obtain the ambient temperature inside the vacuum chamber; Based on the equilibrium pressure and the ambient temperature, the molecular number density of the background gas is calculated using the ideal gas law and used as the standard density.
[0007] In some embodiments, the method further includes: By adjusting the precision leak valve to multiple different opening degrees, multiple background gas environments with different density gradients are constructed within the vacuum chamber. For each of the background gas environments, the corresponding standard density and the first ion signal are obtained respectively; The step of constructing a quantitative calibration relationship between the first ion signal and the standard density includes: performing linear fitting on multiple standard densities and the corresponding first ion signals to obtain the linear response coefficient of the signal intensity relative to the gas density, which is used as the quantitative calibration relationship.
[0008] In some embodiments, the background gas is of the same type as the target molecular beam, and maintaining the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship includes: maintaining the laser wavelength, single pulse energy, and laser focusing position of the laser ionization device unchanged.
[0009] In some embodiments, acquiring the second ion signal generated by the target molecular beam through the microchannel plate detector includes: Adjust the timing delay between the laser pulse of the laser ionization device and the pulse of the target molecular beam; Scan the time-of-flight spectrum of the target molecular beam; The integrated intensity value of the second ion signal is obtained by integrating the ion peaks of the target component in the time-of-flight spectrum.
[0010] In some embodiments, the laser ionization device employs resonant enhanced multiphoton ionization technology or non-resonant multiphoton ionization technology; The microchannel plate detector includes a front accelerating electrode, a microchannel plate, and a rear collecting electrode, with an operating voltage range of 800V to 1500V.
[0011] In some embodiments, controlling the opening degree of the precision leak valve includes: controlling the background pressure within the vacuum chamber at... Torr to Variations within the Torr range.
[0012] In some embodiments, the molecular beam density measurement system further includes a laser focusing lens, which is disposed at the optical path output end of the laser ionization device; controlling the laser ionization device to photoionize the background gas includes: The laser is focused onto the ionization region directly opposite the microchannel plate detector using the laser focusing lens, and the focal diameter does not exceed a preset diameter threshold.
[0013] Secondly, embodiments of this application provide a molecular beam density measurement device, comprising: The first control module is used to control the opening degree of the precision leak valve, introduce background gas into the vacuum chamber, and obtain the standard density of the background gas through a vacuum ion gauge. The second control module is used to control the laser ionization device to photoionize the background gas and to collect the first ion signal generated by the background gas through the microchannel plate detector. The construction module is used to construct a quantitative calibration relationship between the first ion signal and the standard density; The third control module is used to keep the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship, control the laser ionization device to photoionize the target molecular beam, and collect the second ion signal generated by the target molecular beam through the microchannel plate detector. The calculation module is used to calculate the absolute density of the target molecular beam based on the second ion signal and using the quantitative calibration relationship.
[0014] Thirdly, embodiments of this application provide an electronic device, including: a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the molecular beam density measurement method as described in any one of the embodiments of the first aspect of this application.
[0015] Fourthly, embodiments of this application provide a computer-readable storage medium storing a program that is executed by a processor to implement the molecular beam density measurement method as described in any one of the embodiments of the first aspect of this application.
[0016] The molecular beam density measurement method according to the embodiments of this application has at least the following beneficial effects: The molecular beam density measurement method according to embodiments of this application is applied to a molecular beam density measurement system. The molecular beam density measurement system includes a vacuum chamber, a precision leak valve and a vacuum ion gauge connected to the gas path of the vacuum chamber, a microchannel plate detector disposed within the vacuum chamber, and a laser ionization device for emitting laser light into the ionization region within the vacuum chamber. The method includes: controlling the opening degree of the precision leak valve to introduce background gas into the vacuum chamber and obtaining the standard density of the background gas through the vacuum ion gauge; controlling the laser ionization device to photoionize the background gas and acquiring a first ion signal generated by the background gas through the microchannel plate detector; constructing a quantitative calibration relationship between the first ion signal and the standard density; maintaining the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship, controlling the laser ionization device to photoionize the target molecular beam and acquiring a second ion signal generated by the target molecular beam through the microchannel plate detector; and calculating the absolute density of the target molecular beam based on the second ion signal using the quantitative calibration relationship.
[0017] This application first introduces background gas into the vacuum chamber by controlling a precision leak valve and obtains its standard density by combining the reading of a vacuum ion gauge. This establishes a standard reference with known and controllable density, providing a quantitative benchmark for the subsequent conversion of electrical signals into physical density. Then, by performing photoionization detection on the background gas and establishing a quantitative calibration relationship between the ion signal and the standard density, complex variables that are difficult to measure directly, such as the gain of the microchannel plate detector, the laser ionization cross section, and the effective working volume, can be integrated into a definite response coefficient, effectively eliminating the interference of systematic errors on the measurement results. Subsequently, by acquiring the ion signal of the target molecular beam while maintaining consistent laser operating parameters, the measurement and calibration processes are ensured to be under the same physical conditions, guaranteeing the applicability and effectiveness of the calibration coefficient in target measurement. Finally, by substituting the signal of the target molecular beam into the quantitative calibration relationship, the absolute density value of the target molecular beam can be directly derived, solving the problem of absolute calibration that is difficult to achieve using traditional methods. This application's embodiments can establish a quantitative calibration relationship by introducing a standard gas of known density, thereby achieving absolute measurement of molecular beam density and improving measurement accuracy.
[0018] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description
[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1A flowchart of an optional molecular beam density measurement method provided for an embodiment of this application; Figure 2 This is a schematic diagram of the molecular beam density measurement system provided in the embodiments of this application; Figure 3 A flowchart of another optional molecular beam density measurement method provided for embodiments of this application; Figure 4 This is a quantitative calibration curve of MCP signal intensity versus gas density measured in an embodiment of this application. Figure 5 The characteristic curve of MCP operating voltage versus signal strength variation under the same gas density is provided for the embodiments of this application; Figure 6 A schematic diagram of the molecular beam density measurement device provided in the embodiments of this application; Figure 7 This is a schematic diagram of the hardware structure of the electronic device provided in the embodiments of this application. Detailed Implementation
[0020] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.
[0021] In the description of this application, "several" means one or more, "more than" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, while "above," "below," "within," etc. are understood to include the stated number. Where "first" or "second" is mentioned, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.
[0022] In the description of this application, it should be understood that the orientation descriptions, such as up, down, left, right, front, and back, are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0023] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0024] In the description of this application, it should be noted that, unless otherwise explicitly defined, terms such as "setting," "installation," and "connection" should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of the above terms in this application based on the specific content of the technical solution. Furthermore, the identification of specific steps in the following text does not imply a limitation on the order of steps or execution logic. The execution order and logic between each step should be understood and inferred from the content described in the embodiments.
[0025] Molecular beam physics is an important experimental technique in fields such as atomic and molecular physics, chemical reaction dynamics, and surface science, and is widely used to explore collisions, reactions, and energy transfer processes of microscopic particles. In these experimental studies, accurate knowledge of the molecular beam density is crucial for ensuring the accuracy of experimental results, calculating reaction cross-sections, and verifying the reproducibility of theoretical models.
[0026] Common measurement methods in related technologies include vacuum gauge reading, absorption spectroscopy, laser-induced fluorescence, and electron beam fluorescence. However, the core technical problem with these existing technologies is the difficulty in achieving precise absolute calibration of molecular beam density. Whether relying on roughly estimated vacuum gauge readings or on fluorescence or spectroscopy methods that depend on specific energy level transitions and require complex absorption models, it is difficult to establish a direct and highly accurate quantitative relationship between the detected signal and the actual molecular density. This often results in large systematic errors and complex models, making it impossible to accurately obtain the absolute density value of the molecular beam.
[0027] Based on this, this application first introduces background gas into the vacuum chamber by controlling a precision leak valve and obtains its standard density by combining the reading of a vacuum ion gauge. This allows the construction of a standard reference with known and controllable density, providing a quantitative benchmark for the subsequent conversion of electrical signals into physical density. Then, by performing photoionization detection on the background gas and establishing a quantitative calibration relationship between the ion signal and the standard density, complex variables that are difficult to measure directly, such as the gain of the microchannel plate detector, the laser ionization cross section, and the effective working volume, can be integrated into a definite response coefficient, effectively eliminating the interference of system errors on the measurement results. Subsequently, by acquiring the ion signal of the target molecular beam while maintaining consistent laser operating parameters, it is ensured that the measurement and calibration processes are under the same physical conditions, guaranteeing the applicability and effectiveness of the calibration coefficient in target measurement. Finally, by substituting the signal of the target molecular beam into the quantitative calibration relationship for calculation, the absolute density value of the target molecular beam can be directly derived, solving the problem of the difficulty in performing absolute calibration using traditional methods. This application's embodiments can establish a quantitative calibration relationship by introducing a standard gas of known density, thereby achieving absolute measurement of molecular beam density and improving measurement accuracy.
[0028] Please see Figure 1 This invention provides a molecular beam density measurement method, applied to a molecular beam density measurement system. The molecular beam density measurement system includes a vacuum cavity, a precision leak valve and a vacuum ion gauge connected to the gas path of the vacuum cavity, a microchannel plate detector disposed within the vacuum cavity, and a laser ionization device for emitting laser light into the ionization region within the vacuum cavity. The method may include, but is not limited to, the following steps 101 to 105: Step 101: Control the opening degree of the precision leak valve to introduce background gas into the vacuum chamber, and obtain the standard density of the background gas through a vacuum ion gauge.
[0029] Step 102: Control the laser ionization device to photoionize the background gas, and collect the first ion signal generated by the background gas through the microchannel plate detector.
[0030] Step 103: Establish the quantitative calibration relationship between the first ion signal and the standard density.
[0031] Step 104: Keep the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship, control the laser ionization device to photoionize the target molecular beam, and collect the second ion signal generated by the target molecular beam through a microchannel plate detector.
[0032] Step 105: Based on the second ion signal, the absolute density of the target molecular beam is calculated using the quantitative calibration relationship.
[0033] Please see Figure 2The molecular beam density measurement system provided in this embodiment of the invention includes a vacuum chamber that maintains a high vacuum environment. As shown in the figure, the vacuum chamber typically serves as the reaction center, with a precision leak valve and a vacuum ion gauge connected to the gas inlet on its side wall. The precision leak valve acts as a control valve for gas introduction, precisely regulating the flow rate of the background gas entering the vacuum chamber. The vacuum ion gauge, acting as a pressure monitoring component, directly probes or connects to the interior of the chamber to provide real-time feedback on the absolute pressure within the chamber. An ionization region (i.e., the intersection of the laser and the molecular beam in the figure) is defined in the central region of the vacuum chamber. A laser ionization device, used to emit high-energy laser light into this region, is typically located outside the vacuum chamber. The generated light path enters through an optical window on the vacuum chamber and is focused on the ionization region. The laser ionization device mainly includes a pulsed laser, an optical path transmission assembly, and a focusing lens. The pulsed laser, located outside the vacuum chamber, emits a high-energy laser beam with a specific wavelength and pulse width. The optical path transmission assembly (such as a mirror group) guides the laser beam to the optical entrance window of the vacuum chamber. A focusing lens is typically positioned at the front of the optical entrance window or integrated into the window assembly. Its function is to converge the originally parallel laser beam into a high-energy-density focal point. This laser beam enters the vacuum chamber through the optical entrance window, and its focal point is precisely adjusted to the ionization region at the center of the vacuum chamber. Furthermore, a microchannel plate detector is positioned downstream of the flight path of the ionization region (usually perpendicular to the direction of the molecular beam and the laser beam). This detector receives the ion signal generated in the ionization region and accelerated by the electric field. The spatial arrangement of these components constitutes a complete measurement optical and gas path structure, from gas introduction, pressure calibration, photoionization excitation to signal acquisition.
[0034] In step 101 of some embodiments, the precision leak valve connected to the side wall of the vacuum chamber is first adjusted. Please refer to... Figure 2 As shown, as the opening of the precision leak valve gradually increases, background gas from the external gas source is continuously injected into the vacuum chamber through the gas path. At this time, a vacuum ion gauge located on or near the other side of the chamber begins to operate, monitoring the pressure changes within the chamber in real time. When the pressure inside the chamber reaches a stable static equilibrium value, the vacuum ion gauge reads the absolute pressure value of the background gas and, combined with the ambient temperature inside the chamber, calculates the standard density of the background gas in the ionization region based on the ideal gas law. This step utilizes the high precision characteristics of the vacuum ion gauge in static measurement mode, establishing an absolute physical benchmark for subsequent relative measurements.
[0035] Furthermore, to ensure the accuracy of the calibration results, the background gas is preferably the same type of gas as the target molecular beam. Using the same gas for calibration ensures that the background gas and the target molecular beam have the same photoionization cross section and transition probability during photoionization, thus eliminating the need for complex correction factors. In another embodiment, if the same gas cannot be used due to experimental limitations, an inert gas with similar physicochemical properties and a known relative ionization cross section can be selected as a reference gas, and this cross section ratio can be incorporated into the subsequent quantitative relationship construction for correction.
[0036] In step 102 of some embodiments, triggering is performed while maintaining the stability of the background gas density. Figure 2 The laser ionization device shown is in operation. A laser beam passes through an optical window and is focused onto an ionization region at the center of the vacuum cavity, interacting with background gas molecules dispersed throughout the cavity (e.g., a multiphoton ionization process). The ionized background gas ions, under the influence of the cavity's electric field, drift along a path perpendicular to the laser direction, ultimately colliding with a microchannel plate detector located at the top or bottom. The microchannel plate detector converts the received ion flow into an electrical pulse signal, i.e., a first ion signal. The signal intensity of the first ion signal reflects the degree to which the background gas of a known density is ionized at the current laser power density.
[0037] In step 103 of some embodiments, the data acquisition system ( Figure 2 (The diagram shows the process using a computer and oscilloscope) The system receives the first ion signal and compares its intensity value with the standard density value obtained in step 101. Since the ion signal intensity is linearly proportional to the molecular density in the unsaturated ionization region, a quantitative calibration relationship can be constructed using this set of "known density - known signal intensity" data pairs. This relationship essentially calibrates the comprehensive response factor of the entire measurement system, including laser ionization efficiency, ion transport efficiency, and microchannel plate detection efficiency.
[0038] In some embodiments, the method provided in this application may further include, but is not limited to, the following steps: Adjust the precision leak valve to multiple different opening degrees to create multiple background gas environments with different density gradients within the vacuum chamber; For each background gas environment, the corresponding standard density and first ion signal are obtained respectively; Correspondingly, step 103, which involves establishing a quantitative calibration relationship between the first ion signal and the standard density, may also include, but is not limited to, the following steps: Linear fitting was performed on multiple standard densities and their corresponding first ion signals to obtain the linear response coefficient of signal intensity relative to gas density, which was used as a quantitative calibration relationship.
[0039] In some embodiments, the background gas environment construction and data acquisition steps do not simply involve setting a single gas inlet volume. Instead, the precision leak valve is adjusted to multiple different opening positions, thereby constructing multiple background gas environments with different density gradients within the vacuum chamber. Here, density gradient refers to the discrete stable states in which the gas molecule number density within the vacuum chamber increases or decreases in a step-like manner according to a preset step size. For each stable state (i.e., each background gas environment), a data acquisition process is simultaneously triggered: on one hand, the current absolute pressure is read using a vacuum ion gauge and converted into a standard density; on the other hand, the laser ionization device is controlled to emit a laser, and the corresponding first ion signal is recorded by a microchannel plate detector. Through this process, the system obtains a calibration dataset containing multiple data point pairs (density values, signal strength values), covering the expected measurement dynamic range.
[0040] In step 103 (constructing a quantitative calibration relationship) of some embodiments, the data acquisition system no longer relies solely on the ratio calculation of a single data point, but instead performs statistical analysis on the multiple standard densities and corresponding first ion signals obtained above. Specifically, a linear fitting algorithm is used, with the standard density as the abscissa and the integrated intensity of the first ion signal as the ordinate, to plot a calibration curve. Through fitting operations, the slope of the straight line is calculated, and this slope is the linear response coefficient. The linear response coefficient is a comprehensive physical quantity that intuitively characterizes the photoelectric conversion efficiency and signal amplification capability of the measurement system for a unit density of molecules under the current laser power, focusing conditions, and detector gain. To gain a deeper understanding of the calibration principle of this application, the intensity of the first ion signal... Physically, this can be represented as:
[0041] in, For the gain of the microchannel plate detector, For ion collection efficiency, For multiphoton ionization cross section, For laser intensity, For gas density, This refers to the effective interaction volume between the laser and the gas. In the calibration and measurement process of this application, since the laser and detector parameters are kept constant, and for the same gas, all parameters in the above formula except for density n are combined into a single constant term (i.e., the linear response coefficient K). Therefore, this application does not require separate measurement of the laser interaction volume V or ionization cross-section, which are difficult to obtain accurately. This can be obtained directly through experimental fitting. The linear relationship with n enables the calibration of complex physical processes.
[0042] By employing the steps of adjusting the precision leak valve to construct the gradient and linear fitting described above, this embodiment of the application uses a multi-point calibration method instead of a single-point calibration method, thereby improving the robustness and accuracy of the calibration results. On the one hand, multi-point fitting can effectively identify and eliminate individual abnormal data points caused by laser energy jitter or reading deviation, reducing the impact of random errors on the calibration coefficients. On the other hand, this process can verify whether the measurement system maintains good linearity within its operating range, preventing nonlinear distortion caused by detector saturation or space charge effects due to excessively high background gas density, thus ensuring that the final obtained linear response coefficients can truly and objectively reflect the system's detection sensitivity to the target molecular beam.
[0043] In step 104 of some embodiments, the precision leak valve is first closed and the background gas in the vacuum chamber is evacuated, restoring the vacuum chamber to a vacuum state. Then, the target molecular beam to be measured is controlled to be pulsed into the vacuum chamber and passes through the ionization region. Crucially, all optical parameters of the laser ionization device (such as wavelength, energy, and focus position) must be kept identical to those in step 102. When the laser beam strikes the target molecular beam again, the particles in the molecular beam are ionized, and the resulting ions are also captured by the microchannel plate detector, thereby acquiring the second ion signal generated by the target molecular beam.
[0044] Please see Figure 3 In some embodiments, the step of acquiring the second ion signal generated by the target molecular beam through a microchannel plate detector in step 104 may also include, but is not limited to, steps 301 to 303.
[0045] Step 301: Adjust the timing delay between the laser pulse of the laser ionization device and the pulse of the target molecular beam.
[0046] Step 302: Scan the time-of-flight spectrum of the target molecular beam.
[0047] Step 303: Integrate the ion peaks of the corresponding target components in the time-of-flight spectrum to obtain the integrated intensity value of the second ion signal.
[0048] In step 301 of some embodiments, since the target molecular beam typically enters the vacuum cavity in the form of short pulses, and the laser pulse has an extremely short duration, the encounter time between the two must be precisely controlled. First, the timing delay between the laser pulse from the laser ionization device and the pulse of the target molecular beam is adjusted. Specifically, a digital delay generator triggers the pulse valve and the laser switch respectively, scanning the time difference between them. The timing delay refers to the time interval from the moment the pulse valve opens to release the molecular beam to the moment the laser emits light and reaches the ionization region. By adjusting this parameter, it can be ensured that the laser pulse precisely hits the moment when the target molecular beam pulse density is at its maximum (i.e., at the pulse peak).
[0049] In step 302 of some embodiments, after determining and setting the delay parameters, laser ionization is triggered and the time-of-flight spectrum of the target molecular beam is scanned. The time-of-flight spectrum is a graph with ion flight time as the x-axis and signal intensity as the y-axis. Since ions of different mass numbers require different times to travel the same distance under the same electric field acceleration, the microchannel plate detector records all ion signals generated by ionization in the order of arrival time. In this step, the oscilloscope or acquisition card records not just a voltage value, but a complete waveform curve containing time information. This curve can clearly distinguish the ion signal of the target component from the ion signal of any impurity gases that may remain in the cavity on the time axis, achieving mass spectrometry separation.
[0050] In step 303 of some embodiments, the theoretical arrival time window of the target molecule on the spectrum is first determined based on its charge-to-mass ratio. Then, the ion peaks of the corresponding target component in the time-of-flight spectrum are integrated. The integrated intensity value refers to the sum of the areas enclosed by the signal waveform and the baseline within the selected time window. Compared to simply reading the peak height, this accurately reflects the total number of ions generated by the laser pulse. Finally, the calculated integrated area is used as the integrated intensity value of the second ion signal, which is then substituted into the quantitative calibration relationship for density calculation.
[0051] In step 105 of some embodiments, the newly acquired second ion signal is inverted. Specifically, since the operating state of the measurement system (including laser parameters and detector gain) remains unchanged, the detection sensitivity coefficient of the system can be considered unchanged. Assuming the linear response coefficient obtained through linear fitting in step 103 is K, and the integrated intensity value S of the second ion signal obtained in step 104 is , the absolute density n of the target molecular beam can be obtained through the formula... The calculation yields the absolute density value of the target molecular beam by directly substituting the intensity of the second ion signal into the calibration formula.
[0052] To further verify the effectiveness and accuracy of the molecular beam density measurement method provided in the embodiments of this application, the calibration and measurement process using hydrogen as the target molecule is described in detail below with specific experimental parameters and data.
[0053] In this embodiment, the background pressure of the vacuum system is maintained at Between (i.e.) to Pa). The laser ionization device uses an Nd:YAG pulsed laser to pump a pulsed dye laser, and outputs pulsed laser light with a wavelength of approximately 201 nm through a frequency doubling module (BBO crystal). The laser pulse width is approximately 10 ns, and the repetition frequency is 10 Hz. The microchannel plate detector adopts a double-layer MCP structure; please refer to [link / reference]. Figure 4 , Figure 4 The graph shows the corresponding curves of MCP gain voltage versus signal value under the same gas density. As can be seen from the graph, the signal gain increases exponentially with the increase of the voltage across the MCP. To ensure detection sensitivity while avoiding excessive noise or entering the nonlinear saturation region, the operating voltage in this embodiment is set between 1000V and 1400V, with a gain of approximately [missing value]. The molecular beam source uses a pulse valve to generate an ultrasonic hydrogen molecular beam. The back pressure of the pulse valve is set to 3 MPa, and the beam velocity is approximately 2670 m / s.
[0054] First, corresponding to step 101, standard hydrogen gas is slowly introduced into the vacuum chamber using a precision adjustable leak valve. By adjusting the opening of the leak valve, diffused hydrogen environments of different densities are created within the vacuum chamber. The pressure change P within the vacuum chamber is read using a vacuum ion gauge, and combined with the ambient temperature T (set to room temperature, approximately 300K) and Boltzmann's constant k, the ideal gas law is applied. The hydrogen molecule number density *n* under different leak valve opening degrees was calculated. For example, the vacuum level of the detection chamber was... Adjustments can be made within a specified range.
[0055] Then, corresponding to steps 102-103, adjust the laser wavelength to the resonant wavelength of hydrogen (approximately 201 nm) while maintaining a constant laser energy. For each density of diffused hydrogen environment constructed in step 2, use a microchannel plate detector to measure the intensity S (mV) of the ion signal generated by photoionization and record multiple sets of data points (density n, signal S). Please refer to [link to relevant documentation]. Figure 5 , Figure 5 The calibration curves of MCP signal intensity versus gas density measured in this embodiment are shown. As shown in the figure, within the selected density range, the ion signal intensity detected by MCP exhibits a significant linear increasing trend with increasing gas density, verifying that the two satisfy a linear proportional relationship in the unsaturated region. Linear fitting was performed on the measurement data to establish a quantitative relationship between MCP signal intensity and gas density. In this embodiment, the quantitative relationship obtained by fitting is:
[0056] Wherein, linear response coefficient .
[0057] Next, following steps 104-105, close the precision leak valve and evacuate the background gas. Open the pulse valve to generate a stable hydrogen molecular beam. Focus the laser onto the molecular beam path, ensuring the laser is perpendicular to the molecular beam and that the laser wavelength, energy, and focusing position are completely consistent with the calibration process. By adjusting the time-of-flight spectrum of the molecular beam and integrating the hydrogen ion peaks, the ionization integrated signal intensity along the molecular beam's flight direction is measured. The value is 6000mV. Substituting the measured signal intensity into the above quantitative calibration formula, the absolute density of the molecular beam is calculated. :
[0058] Using the above method, the absolute calibration of hydrogen molecular beam density was successfully achieved with a relative error of less than 5%. Compared with traditional methods, this method has higher measurement accuracy and better repeatability.
[0059] Please see Figure 6 This application also provides a molecular beam density measurement device, which can realize the above-mentioned molecular beam density measurement method, including: The first control module is used to control the opening degree of the precision leak valve, introduce background gas into the vacuum chamber, and obtain the standard density of the background gas through a vacuum ion gauge. The second control module is used to control the laser ionization device to photoionize the background gas and to collect the first ion signal generated by the background gas through the microchannel plate detector. The module is used to construct a quantitative calibration relationship between the first ion signal and the standard density; The third control module is used to keep the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship, control the laser ionization device to photoionize the target molecular beam, and collect the second ion signal generated by the target molecular beam through the microchannel plate detector. The calculation module is used to calculate the absolute density of the target molecular beam based on the second ion signal and using a quantitative calibration relationship.
[0060] The molecular beam density measurement method according to embodiments of this application is applied to a molecular beam density measurement system. The molecular beam density measurement system includes a vacuum chamber, a precision leak valve and a vacuum ion gauge connected to the gas path of the vacuum chamber, a microchannel plate detector disposed within the vacuum chamber, and a laser ionization device for emitting laser light into the ionization region within the vacuum chamber. The method includes: controlling the opening degree of the precision leak valve to introduce background gas into the vacuum chamber and obtaining the standard density of the background gas through the vacuum ion gauge; controlling the laser ionization device to photoionize the background gas and acquiring a first ion signal generated by the background gas through the microchannel plate detector; constructing a quantitative calibration relationship between the first ion signal and the standard density; maintaining the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship, controlling the laser ionization device to photoionize the target molecular beam and acquiring a second ion signal generated by the target molecular beam through the microchannel plate detector; and calculating the absolute density of the target molecular beam based on the second ion signal using the quantitative calibration relationship.
[0061] This application first introduces background gas into the vacuum chamber by controlling a precision leak valve and obtains its standard density by combining the reading of a vacuum ion gauge. This establishes a standard reference with known and controllable density, providing a quantitative benchmark for the subsequent conversion of electrical signals into physical density. Then, by performing photoionization detection on the background gas and establishing a quantitative calibration relationship between the ion signal and the standard density, complex variables that are difficult to measure directly, such as the gain of the microchannel plate detector, the laser ionization cross section, and the effective working volume, can be integrated into a definite response coefficient, effectively eliminating the interference of systematic errors on the measurement results. Subsequently, by acquiring the ion signal of the target molecular beam while maintaining consistent laser operating parameters, the measurement and calibration processes are ensured to be under the same physical conditions, guaranteeing the applicability and effectiveness of the calibration coefficient in target measurement. Finally, by substituting the signal of the target molecular beam into the quantitative calibration relationship, the absolute density value of the target molecular beam can be directly derived, solving the problem of absolute calibration that is difficult to achieve using traditional methods. This application's embodiments can establish a quantitative calibration relationship by introducing a standard gas of known density, thereby achieving absolute measurement of molecular beam density and improving measurement accuracy.
[0062] Reference Figure 7 , Figure 7 The hardware structure of an electronic device according to another embodiment is illustrated. The electronic device includes: The processor 701 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application. The memory 702 can be implemented as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 702 can store the operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 702 and is called and executed by the processor 701 to execute the molecular beam density measurement method of the embodiments of this application. The input / output interface 703 is used to implement information input and output; The communication interface 704 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, Ethernet cable, etc.) or wireless means (such as mobile network, Wi-Fi, Bluetooth, etc.). Bus 705 transmits information between various components of the device (e.g., processor 701, memory 702, input / output interface 703, and communication interface 704); The processor 701, memory 702, input / output interface 703, and communication interface 704 are connected to each other within the device via bus 705.
[0063] This application also provides a computer program product, which includes a computer program. A processor of a computer device reads and executes the computer program, causing the computer device to perform the molecular beam density measurement method described above.
[0064] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in this disclosure and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “including,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatuses.
[0065] It should be understood that in this disclosure, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.
[0066] It should be understood that in the description of the embodiments of this application, "multiple" means two or more, "greater than", "less than", "exceeding" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself.
[0067] In the several embodiments provided in this disclosure, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.
[0068] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0069] Furthermore, the functional units in the various embodiments of this disclosure can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.
[0070] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this disclosure, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this disclosure. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.
[0071] It should also be understood that the various implementation methods provided in this application can be combined arbitrarily to achieve different technical effects.
[0072] The above is a detailed description of the embodiments of this disclosure. However, this disclosure is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of this disclosure. All such equivalent modifications or substitutions are included within the scope defined by the claims of this disclosure.
Claims
1. A method for measuring molecular beam density, characterized in that, An application is made in a molecular beam density measurement system, the system comprising a vacuum chamber, a precision leak valve and a vacuum ion gauge connected to the gas path of the vacuum chamber, a microchannel plate detector disposed within the vacuum chamber, and a laser ionization device for emitting laser light into an ionization region within the vacuum chamber, the method comprising: The opening degree of the precision leak valve is controlled to introduce background gas into the vacuum chamber, and the standard density of the background gas is obtained through the vacuum ion gauge. The laser ionization device is controlled to photoionize the background gas, and the first ion signal generated by the background gas is collected by the microchannel plate detector. Establish a quantitative calibration relationship between the first ion signal and the standard density; The operating parameters of the laser ionization device are kept consistent with those used when constructing the quantitative calibration relationship. The laser ionization device is controlled to photoionize the target molecular beam, and the second ion signal generated by the target molecular beam is collected through the microchannel plate detector. Based on the second ion signal, the absolute density of the target molecular beam is calculated using the quantitative calibration relationship.
2. The molecular beam density measurement method according to claim 1, characterized in that, The process of obtaining the standard density of the background gas using the vacuum ion gauge includes: Read the equilibrium pressure value inside the vacuum chamber measured by the vacuum ion gauge; Obtain the ambient temperature inside the vacuum chamber; Based on the equilibrium pressure and the ambient temperature, the molecular number density of the background gas is calculated using the ideal gas law and used as the standard density.
3. The molecular beam density measurement method according to claim 1, characterized in that, The method further includes: By adjusting the precision leak valve to multiple different opening degrees, multiple background gas environments with different density gradients are constructed within the vacuum chamber. For each of the background gas environments, the corresponding standard density and the first ion signal are obtained respectively; The step of constructing a quantitative calibration relationship between the first ion signal and the standard density includes: performing linear fitting on multiple standard densities and the corresponding first ion signals to obtain the linear response coefficient of the signal intensity relative to the gas density, which is used as the quantitative calibration relationship.
4. The molecular beam density measurement method according to claim 1, characterized in that, The background gas is of the same type as the target molecular beam. Maintaining the operating parameters of the laser ionization device consistent with those used when constructing the quantitative calibration relationship includes keeping the laser wavelength, single pulse energy, and laser focusing position of the laser ionization device unchanged.
5. The molecular beam density measurement method according to claim 1, characterized in that, The acquisition of the second ion signal generated by the target molecular beam through the microchannel plate detector includes: Adjust the timing delay between the laser pulse of the laser ionization device and the pulse of the target molecular beam; Scan the time-of-flight spectrum of the target molecular beam; The integrated intensity value of the second ion signal is obtained by integrating the ion peaks of the target component in the time-of-flight spectrum.
6. The molecular beam density measurement method according to claim 1, characterized in that, The laser ionization device employs either resonant enhanced multiphoton ionization technology or non-resonant multiphoton ionization technology. The microchannel plate detector includes a front accelerating electrode, a microchannel plate, and a rear collecting electrode, with an operating voltage range of 800V to 1500V.
7. The molecular beam density measurement method according to claim 1, characterized in that, The control of the opening degree of the precision leak valve includes: controlling the background pressure inside the vacuum chamber at... Torr to Variations within the Torr range.
8. The molecular beam density measurement method according to claim 1, characterized in that, The molecular beam density measurement system further includes a laser focusing lens, which is disposed at the optical path output end of the laser ionization device; controlling the laser ionization device to photoionize the background gas includes: The laser is focused onto the ionization region directly opposite the microchannel plate detector using the laser focusing lens, and the focal diameter does not exceed a preset diameter threshold.
9. An electronic device, characterized in that, include: The device includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the molecular beam density measurement method as described in any one of claims 1 to 8.
10. A computer-readable storage medium, characterized in that, The storage medium stores a program that is executed by a processor to implement the molecular beam density measurement method as described in any one of claims 1 to 8.