Ultra-high frequency full-field digital holographic vibration measurement system and method

Abstract

The application provides an ultrahigh frequency full-field digital holographic vibration measurement system and method, which comprises a femtosecond pulse light source, a pulse front matching off-axis holographic light path, a photoelectric reference clock extraction, a phase shift and synchronous frequency multiplication excitation, a hologram synchronous acquisition, and a full-field complex vibration reconstruction and diagnosis processing subsystem. With femtosecond pulse repetition frequency as a time reference, a reference clock is extracted and a coherent locked radio frequency excitation is generated, and through controllable phase shift, frequency flash freezing sampling is realized; the pulse front matching off-axis holographic light path is adopted to maintain the full field of view interference fringe contrast under wide spectrum femtosecond light; after a two-dimensional detector acquires a hologram sequence, through off-axis complex field reconstruction, non-equal interval phase-locked demodulation based on a measured delay table and time-space joint noise suppression, the device full-field vibration amplitude, phase, modal topography and k-space spectrum are obtained. The application is suitable for non-contact full-field vibration diagnosis of MHz to several GHz band micro-nano devices.

Description

Technical Field

[0001] This invention relates to the fields of micro / nano electromechanical systems, optical interferometry, digital holographic microscopy, ultrafast optics, and radio frequency synchronous measurement technology. Specifically, it relates to an ultra-high frequency full-field digital holographic vibration measurement system and method. In particular, it relates to an ultra-high frequency full-field digital holographic vibration measurement system and method based on femtosecond optical frequency comb synchronization.

[0002] This invention is particularly applicable to the full-field vibration amplitude and phase characterization, modal diagnosis, stray mode identification, energy leakage path analysis, and process defect location of thin-film bulk acoustic resonators (FBAR), bulk acoustic resonators (BAW), laterally excited bulk acoustic devices (XBAR), surface acoustic wave devices (SAW), piezoelectric micromechanical ultrasonic transducers (PMUT), on-chip phononic crystals, nano-photoacoustic structures, and quantum acoustic devices in radio frequency front-end filters. Background Technology

[0003] With the development of technologies such as 5G / 6G wireless communication, RF front-end filtering, quantum acoustics, on-chip phonon manipulation, and high-frequency sensing, an increasing number of micro / nano electromechanical devices (MEMS) are operating in the frequency range of MHz to tens of GHz. These devices exhibit extremely high stiffness and energy density at high frequencies, with typical mechanical displacement amplitudes decreasing to the picometer or even femtometer scale, while vibration wavelengths can be shortened to the micrometer or submicrometer scale. Material inhomogeneity, boundary scattering, release process defects, local stress gradients, acoustic leakage channels, and parasitic modes can all significantly affect the device's quality factor, insertion loss, out-of-band clutter, power handling capability, and frequency stability. Therefore, a measurement technique is needed that can directly obtain the full-field vibration amplitude, phase, and modal distribution under actual operating conditions.

[0004] Traditional electrical measurement methods, such as impedance spectroscopy, S-parameter testing, equivalent circuit fitting, or resonance curve analysis, can obtain the overall electrical response of a device, but they struggle to directly reveal local acoustic modes, boundary leakage paths, weak stray modes, and local energy concentration regions within the device. While finite element simulation can provide modal predictions for ideal structures, it is difficult to fully model material gradients, boundary defects, local stresses, and parasitic couplings in real devices, making it challenging to achieve closed-loop optimization of device design relying solely on simulation.

[0005] Scanning laser Doppler vibration measurement and scanning zero-difference or heterodyne interferometry can achieve high point displacement sensitivity, but they inherently require point-by-point scanning. For devices with areas ranging from hundreds of micrometers to millimeters and containing multiple local modes or boundary leakage paths, obtaining a complete full-field modal profile often takes a long time. In frequency bands above several GHz, the noise and bandwidth of photodetectors, mixers, lock-in amplifiers, and high-frequency electronic links also limit system performance.

[0006] Methods such as Brillouin scattering, X-ray diffraction microscopy, microwave impedance microscopy, and scanning electron microscopy can obtain information on phonon frequency, wave vector, local potential, or lattice deformation under specific scenarios, but they usually have problems such as low scattering efficiency, expensive equipment, the need for synchrotron radiation, contact scanning, inability to directly obtain absolute displacement field, or inability to cover the full field structure under actual working conditions.

[0007] Ultrafast pump-probe methods utilize the time-resolved capability of femtosecond pulses to study high-frequency acoustic processes, theoretically covering an extremely wide frequency range. However, conventional pump-probe systems rely on mechanical delay lines or dual-laser asynchronous sampling, and in most cases, they are single-point or scanning measurements. Furthermore, when the device under test needs to operate at its actual electric drive operating point, optical pumping excitation may introduce problems such as thermoelastic response, nonlinear coupling, or inconsistencies with actual RF operating conditions.

[0008] Traditional stroboscopic holography can overcome camera frame rate limitations and acquire vibrational phase states in a lower frequency range. However, when the measurement frequency increases to GHz and higher, the pulse width, photoelectric synchronization jitter, optical path coherence, holographic fringe contrast, speckle noise, and delay nonlinearity of traditional nanosecond or subnanosecond pulse sources all become limiting factors. Especially in wide-field-of-view off-axis holography, if a broadband ultrashort pulse source is used, simply replacing the continuous light off-axis interference structure with a femtosecond source will lead to inconsistencies in the arrival time and spatial carrier frequency of pulses of different wavelength components, resulting in a decrease in interference fringe contrast or fragmentation of fringes across the entire field of view.

[0009] Therefore, a new ultra-high frequency full-field vibration measurement scheme is needed: on the one hand, the extremely short time gate width of femtosecond pulses is used to freeze GHz-level vibrations; on the other hand, the stable repetition frequency of the femtosecond optical frequency comb is used to generate radio frequency excitation coherently locked with the device under test; at the same time, a digital holographic optical path that can take into account both off-axis spatial carrier frequency and full-field pulse time coincidence is constructed under broadband femtosecond light conditions, and a full-field complex field reconstruction algorithm suitable for real delay nonlinearity and strong background noise is used.

[0010] Patent application CN111678611A discloses a real-time measurement system and method for full-field information based on high repetition frequency femtosecond pulses. The system includes a first optical splitter, an amplitude modulator, an arbitrary waveform generator, a second optical splitter, an ultra-wideband time-domain probe optical path, a dispersive Fourier transform optical path, and a data acquisition and processing component. The first optical splitter is used to split the signal under test into N time-domain demultiplexed signals. The amplitude modulator is connected one-to-one with each of the N time-domain demultiplexed signals, and in each time-domain demultiplexed signal channel, the amplitude modulator is used to perform time-domain modulation on the signal under test, achieving time-domain demultiplexing and frequency reduction separation. The second optical splitter is connected one-to-one with each of the N time-domain demultiplexed signals after frequency reduction. The data acquisition and processing component includes a high-speed photodetector, a high-speed sampler, and a processing terminal. However, this patent cannot completely solve the existing technical problems, nor can it meet the needs of this invention. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the purpose of this invention is to provide an ultra-high frequency full-field digital holographic vibration measurement system and method.

[0012] The ultra-high frequency full-field digital holographic vibration measurement system provided by the present invention includes: a femtosecond pulse source subsystem, a pulse leading edge matching off-axis holographic optical path subsystem, a photoelectric reference clock extraction subsystem, a phase shift and synchronous frequency doubling excitation subsystem, a hologram synchronous acquisition subsystem, and a full-field complex vibration reconstruction and diagnostic processing subsystem; The femtosecond pulse source subsystem generates periodic femtosecond or picosecond pulse trains, and the repetition frequency of the pulse trains serves as the optical time reference for the system. The femtosecond pulse source subsystem is connected to the pulse leading edge matching off-axis holographic optical path subsystem and the photoelectric reference clock extraction subsystem, respectively. Part of the pulse light generated by the femtosecond pulse source subsystem is input to the pulse leading edge matching off-axis holographic optical path subsystem as measurement light, and the other part is input to the photoelectric reference clock extraction subsystem. The photoelectric reference clock extraction subsystem extracts an electrical reference clock from a femtosecond pulse train, and the frequency of the electrical reference clock maintains a deterministic phase relationship with the repetition frequency of the femtosecond pulses; The output of the photoelectric reference clock extraction subsystem is connected to the input of the phase offset and synchronous frequency doubling excitation subsystem, and the electrical reference clock is input to the phase offset and synchronous frequency doubling excitation subsystem. The phase offset and synchronous frequency doubling excitation subsystem generates an electrical excitation signal for the device under test based on the electrical reference clock, and controlsably adjusts the phase of the electrical excitation signal relative to the femtosecond pulse train; The output of the phase shift and synchronous frequency doubling excitation subsystem is connected to the device under test (DUT) to apply the electrical excitation signal to the DUT. The pulse leading edge matching off-axis holographic optical path subsystem receives the measurement light from the femtosecond pulse source subsystem and divides the measurement light into object light and reference light. The object light illuminates the device under test and carries the phase modulation caused by the surface displacement of the device under test. The reference light and the object light coincide in the image plane of the two-dimensional detector or its conjugate plane to form off-axis holographic interference. The hologram synchronous acquisition subsystem includes a two-dimensional array detector and its synchronous control module. The two-dimensional array detector records the hologram or hologram sequence formed by the off-axis holographic interference. The output end of the hologram synchronous acquisition subsystem is connected to the input end of the full-field complex vibration reconstruction and diagnostic processing subsystem, and transmits the recorded hologram data to the full-field complex vibration reconstruction and diagnostic processing subsystem. The full-field complex vibration reconstruction and diagnostic processing subsystem receives the hologram data, processes the hologram or hologram sequence, and obtains the full-field vibration amplitude, phase, modal morphology, and frequency domain acoustic diagnostic results of the device under test.

[0013] Preferably, the pulse width of the pulse train generated by the femtosecond pulse source subsystem is less than one-tenth of the vibration period under test; the excitation frequency of the device under test... With femtosecond pulse repetition frequency Satisfying Relationship:

[0014] Where N is an integer, such that when each femtosecond pulse arrives at the device under test, the device under test is in the same vibration phase, thus forming a stroboscopic frozen hologram when the camera exposure time is much longer than the vibration period.

[0015] Preferably, the pulse leading edge matching off-axis holographic optical path subsystem modulates the phase leading edge and pulse leading edge of the reference light through a reflective blazed grating; Within the image plane of the two-dimensional detector, the reference light phase satisfies a non-zero lateral phase gradient to form off-axis fringes; simultaneously, the arrival time difference between the pulse peaks of the reference light and the object light is less than the time gate width threshold determined by the measurement signal-to-noise ratio requirement within the effective field of view. Let the transverse wave vector of the reference ray in the transverse x-direction of the image plane be... Its derivative with respect to angular frequency is ,but Determine the off-axis fringe spatial carrier frequency. The gradient along the x-direction, which determines the arrival time of the pulse peak, is achieved through a combination of a grating and an imaging system. For non-zero Approaching zero, thus achieving pulse leading-edge matching while maintaining the off-axis carrier frequency, wherein, For the reference light wave vector component in the transverse x-direction of the image plane, ω is the angular frequency.

[0016] Preferably, the phase shift and synchronous frequency doubling excitation subsystem maintains and Under coherent locking conditions, a controllable delay is applied to the reference clock, excitation signal, or sampling trigger signal. The vibration phase corresponding to the m-th sampling state is Add initial phase, composed of multiple The corresponding hologram or complex field result recovers the full-field vibration amplitude and phase of the device under test, whereby... This represents the controllable delay amount corresponding to the m-th sampling state.

[0017] Preferably, the phase offset and synchronous frequency doubling excitation subsystem includes a programmable delay unit, a synchronous phase-locked loop, and a power amplifier; The clock reference signal output by the optoelectronic reference clock extraction subsystem is input to the programmable delay unit. The output of the programmable delay unit is connected to the reference input of the synchronous phase-locked loop (PLL). The output of the PLL is connected to the input of the power amplifier. The output of the power amplifier is connected to the device under test (DUT). The programmable delay unit performs a controllable delay on the input clock reference signal. The PLL performs reference-locked frequency multiplication on the delayed clock reference signal to generate an RF excitation source signal. The power amplifier amplifies the RF excitation source signal and applies it to the DUT.

[0018] Preferably, the delay amount of the programmable delay unit is calibrated to obtain a lookup table between the delay code and the actual delay, and the actual delay lookup table is used to construct the non-equal interval sampling phase-locked basis function in the full-field complex vibration reconstruction; During reconstruction, use a real time delay for each spatial pixel or each effective region. Constructing reference basis functions and holographic phase sequence or complex field difference sequence and The complex vibration quantity is obtained by weighted multiplication and summation. ,in Here, m represents the weighting coefficient, and m represents the sampling state number. It is an exponential function, where i is the imaginary unit. These are the spatial coordinates of the two-dimensional detector's image plane. The modulus corresponds to the vibration amplitude, and the argument corresponds to the vibration phase.

[0019] Preferably, the photoelectric reference clock extraction subsystem includes a photodetector, a bandpass filter, a low-noise amplifier, a limiting amplifier, and a high-speed comparator; The pulsed light from the femtosecond pulse source subsystem is input to the photodetector, which converts the femtosecond pulse train into an electrical signal containing the repetition frequency and its harmonics. The output of the photodetector is connected to the input of the bandpass filter, which extracts a narrowband component near the repetition frequency or its harmonics from the electrical signal. The output of the bandpass filter is connected to the input of the low-noise amplifier, which improves the signal-to-noise ratio of the extracted signal to obtain a low-phase-noise approximate sinusoidal reference signal. The output of the low-noise amplifier is connected to the input of the limiting amplifier, which limits the amplitude of the approximate sinusoidal reference signal within a predetermined range. The output of the limiting amplifier is connected to the input of the high-speed comparator, which converts the limited signal into a differential digital clock. The differential digital clock serves as the output signal of the photoelectric reference clock extraction subsystem.

[0020] Preferably, the hologram synchronous acquisition subsystem acquires an object light image, a reference light image, a vibration-free hologram, a vibrating hologram, or a combination thereof in each phase state; the two-dimensional array detector is a global shutter camera; the hologram synchronous acquisition subsystem includes a synchronization control module, which is connected to the femtosecond pulse source subsystem, the phase shift and synchronous frequency doubling excitation subsystem, and the two-dimensional array detector, and is used to control the acquisition timing.

[0021] Preferably, the full-field complex vibration reconstruction and diagnostic processing subsystem performs the following processing on the acquired hologram: intensity normalization, off-axis holographic frequency domain sideband extraction, complex field reconstruction, reference state phase subtraction, phase unwrapping or local phase correction, non-equal interval complex phase-locked demodulation based on measured delay table, spatial filtering, ring region masking, complex field averaging, amplitude and phase output, as well as modal diagnosis based on complex vibration field, k-space spectrum analysis and energy leakage path identification; Reconstructing the field and By calculating the equivalent phase difference or the equivalent phase difference obtained by differential analysis of adjacent frames. The optical path phase change caused by the vibration of the device under test is obtained; for reflective measurements, the out-of-plane displacement and phase change satisfy... ,in, The image plane complex field is obtained by off-axis holographic complex field reconstruction when the device under test is in an unexcited state. The image plane complex field reconstructed under the excitation-on state of the device under test; The effective wavelength after system calibration. To perform arguments operations on complex numbers, This is the conjugate operation for complex numbers. The complex field of the image plane reconstructed from the (k+1)th vibration state. The complex field of the image plane reconstructed from the k-th vibration state. This represents the out-of-plane displacement change on the surface of the device under test. This represents the change in optical path phase caused by vibration.

[0022] The ultra-high frequency full-field digital holographic vibration measurement method provided by the present invention, applied to the aforementioned ultra-high frequency full-field digital holographic vibration measurement system, includes the following steps: Step 1: Generate a periodic femtosecond or picosecond pulse train through the femtosecond pulse source subsystem, and use the repetition frequency of the pulse train as an optical time reference; Step 2: Extract an electrical reference clock from the femtosecond or picosecond pulse train, wherein the frequency of the electrical reference clock maintains a deterministic phase relationship with the repetition frequency of the pulse train; Step 3: Generate an electrical excitation signal for the device under test (DUT) based on the electrical reference clock, and controllably adjust the phase of the electrical excitation signal relative to the pulse train; the frequency of the electrical excitation signal and the repetition frequency of the pulse train satisfy an integer multiple relationship, so that when each pulse reaches the DUT, the DUT is in the same vibration phase, thereby forming a stroboscopic freeze state when the detector exposure time is much longer than the vibration period. Step 4: Divide the pulse train into object light and reference light, so that the object light illuminates the device under test and carries the phase modulation caused by the surface displacement of the device under test, so that the reference light has a non-zero transverse phase vector on the image plane of the detector to generate an off-axis spatial carrier frequency, and at the same time, limit the difference between the pulse peak arrival time of the reference light and the object light within the effective field of view to within a preset threshold, thereby realizing off-axis digital holographic interference with pulse leading edge matching; Step 5: While maintaining coherent locking between the electrical excitation signal and the pulse train, a controllable delay is applied to the reference clock, excitation signal, or sampling trigger signal to change the phase of the electrical excitation signal relative to the pulse train, thereby acquiring corresponding holograms or hologram sequences under different vibration phases; the holograms or hologram sequences are recorded by a two-dimensional array detector; Step 6: Perform off-axis holographic complex field reconstruction on the acquired holograms or hologram sequences to obtain the image plane complex field under each sampling state; Step 7: Based on the true delay value corresponding to each sampling state, construct the non-equal interval sampling phase-locked basis function, and perform complex phase-locked demodulation on the complex field sequence of each pixel or each effective region to extract the complex vibration quantity at the frequency to be measured, and obtain the full field vibration amplitude and phase of the device under test. Step 8: Based on the full-field vibration amplitude and phase, output the vibration mode morphology, k-space spectrum and energy leakage diagnosis results of the device under test.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention extracts a reference clock from a femtosecond optical frequency comb and generates a coherent locked radio frequency excitation, so that optical sampling and electrical excitation share the same time reference, thereby reducing phase drift and synchronization error; (2) This invention performs phase-locked loop and spatiotemporal joint noise suppression through dynamic delay table calibration, which can compensate for delay link nonlinearity and sampling phase error, and improve the amplitude and phase recovery accuracy of the GHz band; (3) By outputting full-field amplitude, phase, modal morphology, k-space spectrum and energy leakage path, this invention can not only be used as a measuring instrument, but also as a diagnostic tool for the design optimization and failure analysis of radio frequency acoustic devices. (4) Compared with the traditional scanning interferometric vibration measurement method, the present invention adopts two-dimensional array holographic acquisition, which records the vibration information in the entire field of view at the same time in each phase state. It does not require point-by-point scanning, which can significantly shorten the full-field modal measurement time and avoid phase inconsistency caused by environmental drift during the scanning process. (5) Compared to direct detection relying on high-speed photodetectors This invention utilizes femtosecond stroboscopic freezing and off-axis holographic reconstruction to perform point-based interferometry measurements of vibrations, eliminating the need for a 2D camera. The bandwidth can record the phase state of ultra-high frequency vibrations, thereby reducing the bandwidth requirements of the detection electronics; (6) Compared with the traditional nanosecond stroboscopic holographic method, the present invention uses femtosecond or picosecond pulses as time gates, which can achieve more accurate transient freezing in a higher frequency range, and is particularly suitable for weak vibration measurement at the level of 1 GHz and even 100 GHz. (7) Compared with the simple solution of using femtosecond light in the traditional off-axis holographic optical path, the present invention makes the broadband femtosecond reference light coincide with the object light pulse time in the effective field of view by pulse leading edge matching, while retaining the off-axis spatial carrier frequency, which can improve the contrast of holographic stripes and the signal-to-noise ratio of full-field reconstruction. Attached Figure Description

[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the overall architecture of the ultra-high frequency full-field digital holographic vibration measurement system based on femtosecond optical frequency comb synchronization of the present invention; Figure 2 This is a schematic diagram illustrating the femtosecond stroboscopic freezing and phase shift sampling principle of the present invention; Figure 3This is a schematic diagram of an embodiment of the off-axis digital holographic optical path for pulse leading edge matching according to the present invention; Figure 4 This is a schematic diagram illustrating the matching relationship between the forward tilt of the reference light phase and the leading edge of the pulse in this invention. Figure 5 This is a schematic diagram of the photoelectric reference clock extraction, programmable phase offset, and synchronous frequency doubling excitation link of the present invention; Figure 6 This is a schematic diagram of the non-equal interval sampling and complex phase-locked reconstruction process based on the measured delay lookup table of the present invention; Figure 7 This is a schematic diagram of the off-axis holographic complex field reconstruction and spatiotemporal joint noise suppression algorithm of the present invention; Figure 8a and Figure 8b This is a schematic diagram of the output results of the present invention for the diagnosis of full-field modes, k-space spectrum and energy leakage of radio frequency acoustic devices; Figure 9 This is a schematic diagram of the delay sequence for acquiring holograms or complex field results according to a predetermined delay sequence in this invention; Figure 10a Microscopic images of multi-polarized FBAR resonators. Figure 10b The results are from vibration measurements. Figure 11 This is a schematic diagram illustrating the application of the present invention to the extraction of complex vibration fields and analysis of acoustic parameters in surface acoustic wave (SAW) devices.

[0025] Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0027] This invention aims to address the problem that existing high-frequency micro / nano vibration measurement technologies cannot simultaneously meet the following requirements: non-contact, full-field, quantitative, picometer-level or higher sensitivity vibration measurement of micro / nano devices in actual working conditions within the frequency range of MHz to tens of GHz; phase freezing of ultra-high frequency vibrations under low camera frame rate conditions; maintaining stable off-axis holographic fringes across the entire field of view under femtosecond broadband light source conditions; obtaining accurate vibration amplitude and phase even under conditions of phase noise, delay nonlinearity, and synchronization state switching in electronic frequency doubling and delay links; and recovering full-field complex vibrations against the background of strong speckle noise, environmental disturbances, uneven light intensity, and device thermal drift.

[0028] The present invention also aims to provide a diagnostic method that can further obtain modes, phases, k-space spectra, energy leakage paths, boundary scattering, and weak stray modes from a full-field complex vibrational object field, so as to support the design optimization of radio frequency acoustic devices and micro / nano phononic devices.

[0029] To address the aforementioned technical problems, this invention provides an ultra-high frequency full-field digital holographic vibration measurement system based on femtosecond optical frequency comb synchronization, comprising: a femtosecond pulse source subsystem, a pulse leading edge matching off-axis holographic optical path subsystem, a photoelectric reference clock extraction subsystem, a phase shift and synchronous frequency doubling excitation subsystem, a hologram synchronous acquisition subsystem, and a full-field complex vibration reconstruction and diagnostic processing subsystem.

[0030] The femtosecond pulse source subsystem is used to generate periodic femtosecond or picosecond pulse trains. Preferably, the pulse width of the pulse train is less than one-tenth of the measured vibration period, more preferably less than one-hundredth of the measured vibration period; the repetition frequency of the pulse train serves as the optical time reference of the system. The femtosecond pulse source can be a mode-locked solid-state laser, a mode-locked fiber laser, a femtosecond oscillator, a frequency-doubled femtosecond laser, a pulse-compressed picosecond laser, or an equivalent pulse source capable of providing a stable repetition frequency and a sufficiently short time gate width.

[0031] The pulse-lead-matched off-axis holographic optical path subsystem is used to split the femtosecond pulse into an object beam and a reference beam. The object beam illuminates the device under test (DUT) and carries phase modulation caused by the surface displacement of the DUT. The reference beam and the object beam coincide in the image plane of the two-dimensional detector or its conjugate plane to form off-axis holographic interference. The reference beam has a non-zero transverse phase vector in the image plane to generate a separable off-axis spatial carrier frequency. At the same time, the difference in the pulse peak arrival time of the object beam and the reference beam within the effective field of view is limited to a preset threshold, thereby maintaining full-field high-contrast interference under broadband femtosecond light conditions.

[0032] The photoelectric reference clock extraction subsystem is used to extract an electrical reference clock from a femtosecond pulse train. Preferably, it includes one or more of the following: a photodetector, a bandpass filter, a low-noise amplifier, a limiting amplifier, a high-speed comparator, a differential clock shaper, and a clock distributor. The frequency of the electrical reference clock is equal to the femtosecond pulse repetition frequency or its division / harmonic frequency, and maintains a deterministic phase relationship with the femtosecond pulse train.

[0033] The phase offset and synchronous frequency doubling excitation subsystem is used to generate an electrical excitation signal for the device under test based on the electrical reference clock, and to controllably adjust the phase of the electrical excitation signal relative to the femtosecond pulse train. Preferably, the subsystem includes one or more of the following: a programmable delay unit, an analog delay unit, a digital phase-locked loop, a frequency synthesizer, a direct digital synthesizer, an integer or fractional frequency doubling phase-locked loop, a phase reset circuit, and a power amplifier phase and position monitoring circuit.

[0034] The excitation frequency of the device under test With femtosecond pulse repetition frequency satisfy , where N is an integer, such that when each femtosecond pulse arrives at the device under test, the device under test is in the same vibration phase, thus forming a stroboscopic frozen hologram when the camera exposure time is much longer than the vibration period.

[0035] The phase shift and synchronous frequency doubling excitation subsystem maintains and Under coherent locking conditions, a controllable delay is applied to the reference clock, excitation signal, or sampling trigger signal. The vibration phase corresponding to the m-th sampling state is Add initial phase. (Multiple) The full-field vibration amplitude and phase of the device under test can be recovered from the corresponding hologram or complex field result.

[0036] The hologram synchronous acquisition subsystem includes a two-dimensional array detector and its synchronous control module. The two-dimensional array detector can be a CCD, CMOS, sCMOS, back-illuminated camera, global shutter camera, area array photodetector, or other detector capable of recording two-dimensional holographic interferograms. Preferably, the acquisition subsystem acquires an object light image, a reference light image, a vibration-free hologram, a vibrating hologram, or a combination thereof in each phase state for normalization, background subtraction, and phase difference.

[0037] The full-field complex vibration reconstruction and diagnostic processing subsystem is used to process the acquired holograms or hologram sequences. Preferably, it performs the following steps: intensity normalization, off-axis holographic frequency domain sideband extraction, complex field reconstruction, reference state phase subtraction, phase unwrapping or local phase correction, non-equal interval complex phase-locked demodulation based on measured delay tables, spatial filtering, ring mask processing, complex field averaging, amplitude and phase output, as well as modal diagnosis based on the complex vibration field, k-space spectrum analysis, and energy leakage path identification.

[0038] Preferably, the pulse leading edge matching off-axis holographic optical path subsystem modulates the phase front and pulse leading edge of the reference light through a transmission grating, a reflective blazed grating, a prism, a diffractive optical element, a spatial light modulator, a fiber dispersion compensator, an imaging relay system, or a combination thereof.

[0039] Preferably, the pulse leading edge matching off-axis holographic optical path satisfies the following conditions: within the image plane of the two-dimensional detector, the reference light phase satisfies a non-zero lateral phase gradient to form off-axis fringes; at the same time, the arrival time difference between the pulse peaks of the reference light and the object light is less than several times the width of the femtosecond pulse within the effective field of view, or less than the time gate width threshold determined by the measurement signal-to-noise ratio requirement.

[0040] Preferably, the pulse leading edge matching off-axis holographic optical path can adopt a Mach-Zehnder structure, a Thyman-Green structure, a Michelson structure, a common optical path structure, a polarization multiplexing structure, or a multi-reference arm structure.

[0041] Preferably, the delay amount of the programmable delay unit is calibrated to obtain a lookup table between the delay code and the actual delay, and the actual delay lookup table is used to construct the non-equal interval sampling phase-locked basis function in the full-field complex vibration reconstruction.

[0042] Preferably, the synchronous frequency multiplication excitation subsystem has a deterministic phase reset function, which enables the phase of the output radio frequency signal to quickly restore the locked relationship with the femtosecond reference clock after switching frequencies, switching delay codes, or relocking.

[0043] Preferably, the full-field complex vibration reconstruction employs complex phase-locked demodulation. For each pixel or each effective region, at the actual sampling time... Lower structure Or its equivalent basis function, multiplied and summed with the holographic phase sequence or complex field sequence, to obtain the complex vibration amplitude at the corresponding frequency, where It is an exponential function. It is the imaginary unit.

[0044] Preferably, the diagnostic processing subsystem transforms the complex vibration field to k-space, analyzes the acoustic wave vector distribution, principal mode energy, stray mode energy, boundary leakage energy, or local scattering characteristics, and uses the results to optimize device layout, boundary structure, release region, electrode shape, material layer thickness, or acoustic reflection structure.

[0045] The term "femtosecond pulse" as used in this specification does not limit the pulse width to strictly within the range of 1 fs to 999 fs; picosecond pulses, compressed pulses, or equivalent ultrashort pulses can all be used as the pulse light source of this invention, provided that a sufficiently short time gate width relative to the vibration period to be measured can be provided and a stable repetition frequency is available.

[0046] The term "full field" as used in this specification refers to the simultaneous acquisition of vibration information by multiple spatial sampling points within the effective field of view of the two-dimensional detector, and does not require coverage of the entire physical area of ​​the device under test. Expanding the field of view by scanning the sample stage, stitching together multiple fields of view, or using different objective lens magnifications are also optional embodiments of this invention.

[0047] The term "GHz" as used in this specification does not preclude the use of this invention in the frequency range of MHz or hundreds of MHz; when the frequency of the device under test is low, this invention can still obtain high-precision full-field vibration results through femtosecond stroboscopic and holographic complex field reconstruction.

[0048] Example 1: System overall structure.

[0049] like Figure 1 As shown, this embodiment relates to an ultra-high frequency full-field holographic vibration measurement system and method based on femtosecond optical comb synchronization. Its overall workflow includes steps S1 to S5. First, in step S1, a femtosecond laser generates a femtosecond pulse laser train with an adjustable repetition frequency. This femtosecond pulse laser train serves as both an ultrashort pulse illumination source for holographic interferometry and a time reference and frequency reference source for the system. Subsequently, in step S2, the femtosecond pulse laser train is split into two beams by a beam splitter. One beam enters the off-axis holographic interferometry optical path and further forms the object beam and reference beam, while the other beam enters the photoelectric detection link and is converted into a synchronization electrical signal. Next, in step S3, the synchronization electrical signal, after undergoing shaping, controllable delay, and phase-locked frequency doubling, generates a synchronization frequency doubling excitation signal that is coherently locked to the femtosecond pulse optical train and has a controllable phase. This synchronization frequency doubling excitation signal is then applied to the device under test (DUT), ensuring that the DUT is in a defined vibration phase at the arrival of each femtosecond pulse. Simultaneously, the object beam and reference beam form spatial carrier frequency interference in the off-axis holographic optical path, modulating the transient vibration information of the device into the wavefront phase relationship. Further, in step S4, by adjusting the phase relationship or delay relationship between the synchronization electrical signal and the phase-locked frequency doubling signal, synchronization frequency doubling excitation signals locked at different time phases are generated. This causes the femtosecond pulses to stroboscopically freeze the DUT at different vibration phases, and the corresponding off-axis holographic interference image sequence is acquired by an area array detector. The holographic interference image sequence can be modulated into a sequence with single-frequency characteristics or known sequence time-domain characteristics. Finally, in step S5, the off-axis holographic interferometric image sequence is processed by holographic decomposition, complex phase-locked extraction in sequence order, non-equidistant sampling compensation, spatial filtering, and amplitude-phase reconstruction to obtain the full-field vibration amplitude, phase, modal shape, and related dynamic characteristics of the device under test at the target excitation frequency. Therefore, this embodiment achieves unified timing locking between the femtosecond light source, GHz-level synchronous excitation, off-axis holographic imaging, and full-field complex vibration field reconstruction by using a femtosecond laser pulse train simultaneously as the optical sampling source and synchronization frequency reference. This enables high-precision, non-scanning, full-field quantitative measurement of ultra-high frequency weak vibrations under long-exposure camera conditions. Figure 2 As shown, the system includes a femtosecond pulse source subsystem A, a pulse leading edge matching off-axis holographic optical path subsystem B, an optoelectronic reference clock extraction subsystem C, a phase shift and synchronous frequency doubling excitation subsystem D, a hologram synchronous acquisition subsystem E, a full-field complex vibration reconstruction and diagnostic processing subsystem F, and a sample stage, radio frequency probe, vacuum chamber or environmental control module for carrying the device under test (DUT).

[0050] like Figure 3 As shown, the femtosecond pulse source subsystem A generates a repetition frequency of... A pulse train. A portion of the pulse train enters the pulse leading edge matching off-axis holographic optical path subsystem B as measurement light; the other portion or its built-in photoelectric detection signal enters the photoelectric reference clock extraction subsystem C to generate an electrical reference clock.

[0051] The phase shift and synchronous frequency doubling excitation subsystem D takes an optoelectronic reference clock as input and generates a frequency of The radio frequency excitation signal is applied to the device under test (DUT) through an radio frequency power amplifier, GSG probe, or package port. The radio frequency excitation signal maintains an integer multiple of the femtosecond pulse train and a coherent lock-in relationship.

[0052] While the device under test (DUT) vibrates, the object light generated by the femtosecond pulse source illuminates the DUT. The out-of-plane displacement of the DUT surface changes the phase of the returning object light. The reference light and the object light interfere at the two-dimensional detector, forming a hologram with an off-axis spatial carrier frequency. Since the arrival time of the femtosecond pulse is coherently fixed with the vibration phase of the DUT, the two-dimensional detector accumulates an equivalent static full-field hologram at a certain vibration phase over a long exposure time.

[0053] like Figure 4 As shown, by changing the delay, phase word, PLL initial phase, DDS phase accumulation word, or equivalent sampling phase in the phase offset and synchronous frequency doubling excitation subsystem D, hologram sequences can be acquired under multiple vibration phases. The full-field complex vibration reconstruction and diagnostic processing subsystem F processes the hologram sequences to obtain the full-field amplitude distribution of the DUT. and phase distribution ,in These represent the horizontal and vertical position coordinates, respectively.

[0054] Example 2: Femtosecond pulse light source and pulse leading edge matching off-axis holographic optical path.

[0055] In a preferred embodiment, the femtosecond pulse source is a mode-locked fiber femtosecond laser with a center wavelength located at [insert wavelength here]. to Within the range, the repetition frequency is located to Within the range, the pulse width is located to Within the range. More preferably, a center wavelength of approximately The pulse width is approximately tens of femtoseconds, and the repetition frequency is approximately... The femtosecond pulses are used for microscopic reflective holographic measurements. The above parameters are merely examples and should not be construed as limiting the scope of protection of this invention.

[0056] like Figure 5As shown, after the femtosecond pulse enters the optical path, it is split into object light and reference light by a polarization device, beam splitter, or fiber beam splitter. The object light is expanded, collimated, and illuminated onto the surface of the device under test (DUT) by a microscope objective, and then reflected by the DUT and returned to the two-dimensional detector via the imaging system. The reference light, after delay adjustment, wavefront adjustment, pulse leading edge adjustment, and imaging relay, coincides with the object light at the two-dimensional detector.

[0057] like Figure 6 As shown, under femtosecond broadband light conditions, off-axis holographic optical paths require not only that the reference light have a phase wavefront tilt angle relative to the object light, but also that the pulse envelopes of the reference light and the object light coincide in time within the effective field of view. Let the central transverse wave vector of the reference light in the transverse x-direction of the image plane be... Its derivative with respect to angular frequency is ,but The off-axis fringe spatial carrier frequency is determined, and The gradient along the x-direction determines the arrival time of the pulse peak, where For the reference light wave vector component in the transverse (x-direction) direction of the image plane, The angular frequency is [value missing]. This invention utilizes a combination of a grating, a diffraction element, and an imaging system to [achieve / determine / enhance / etc.]. For non-zero Approaching zero, thus achieving pulse leading-edge matching while maintaining the off-axis carrier frequency.

[0058] In one embodiment, a transmission grating is disposed in the reference arm. The transmission grating generates first-order diffracted light as the reference light, while the zeroth and other diffracted orders are blocked. After mapping by a 4f coherent imaging system, the transverse phase vector provided by the grating is scaled to a spatial carrier frequency range suitable for sampling by a two-dimensional detector, while its first-order group delay transverse gradient is controlled within an allowable range, thereby forming stable off-axis femtosecond holographic fringes.

[0059] In another embodiment, a reflective blazed grating is provided in the reference arm. By selecting the center wavelength, grating period, incident angle, and diffraction angle, the first derivative of the transverse wave vector of the reference light with respect to the wavelength is made close to zero near the center wavelength; further, the reference light is mapped onto a two-dimensional detector through a relay imaging system, so that the reference light has an off-axis phase wavefront on the image plane and the pulse leading edge coincides with the object light pulse leading edge.

[0060] In another implementation, a Thyman-Green structure with a reflective blazed grating is employed. The grating operates close to Littrow or other predetermined geometric relationships, and the relay imaging system and mirrors rearrange the group delay gradient of the reference light so that the reference light pulse energy surface aligns with the object light energy surface at the two-dimensional detector, while simultaneously providing an off-axis spatial carrier frequency through the reference light geometric tilt angle.

[0061] To improve interference stability, the object beam and reference beam can employ a polarization multiplexing structure, in which polarization beam splitters, quarter-wave plates, half-wave plates, and polarizers are used to control the separation, return, and beam combining of the two arms; alternatively, non-polarization beam splitters, fiber couplers, free-space collimators, or other equivalent optical structures can be used.

[0062] Preferably, when adjusting the optical path, the excitation of the device under test is first turned off, and a femtosecond off-axis hologram is acquired on a two-dimensional detector; the pulse leading edge matching state is evaluated by normalized fringe visibility, frequency domain sideband intensity, carrier signal-to-noise ratio, and full field-of-view local contrast; when the fringe contrast in the effective field of view exceeds a preset threshold and the frequency domain sideband is fully separated from the zero-frequency term, the optical path is considered to meet the requirements for subsequent ultra-high frequency vibration measurement.

[0063] Example 3: Photoelectric reference clock extraction and synchronous frequency doubling excitation.

[0064] like Figure 7 As shown, in a preferred embodiment, a high-speed photodetector is disposed inside or outside the femtosecond laser to convert the femtosecond pulse train into a pulse train containing... The electrical signal and its harmonics. This electrical signal is extracted by a bandpass filter. or The nearby narrowband components are then amplified by a low-noise amplifier to improve the signal-to-noise ratio, resulting in a low-phase-noise approximate sinusoidal reference signal.

[0065] The approximate sinusoidal reference signal is converted into a differential digital clock via AC coupling, impedance matching, and a high-speed comparator. The differential digital clock can be LVDS, CML, LVPECL, PECL, HCSL, or other high-speed differential level formats.

[0066] To achieve vibration phase scanning, the differential digital clock enters a programmable delay unit. The programmable delay unit can employ a digital delay chip, an analog delay circuit, a delay phase-locked loop, a phase interpolator, a DDS phase controller, or a combination thereof. Preferably, the programmable delay unit has a picosecond or sub-picosecond relative delay resolution.

[0067] The delayed reference clock enters the synchronization frequency multiplier unit. The synchronization frequency multiplier unit can employ a wideband phase-locked frequency synthesizer, an integer N phase-locked loop, a fractional N phase-locked loop, a direct digital synthesizer, a harmonic generator, a frequency multiplier, a mixer, or a combination thereof. The RF excitation frequency output by the synchronization frequency multiplier unit... It satisfies a predetermined frequency multiplication, division, mixing, or coherent locking relationship with the reference clock frequency.

[0068] In one specific implementation, the reference clock is shaped into a differential clock by a high-speed comparator, then fed into a programmable delay chip to generate a picosecond-level phase shift. This shift is subsequently converted to a differential level suitable for the frequency synthesizer input and input to the phase-locked loop frequency synthesizer. Internally, the frequency synthesizer forms a closed loop through a phase detector, loop filter, voltage-controlled oscillator, and frequency divider to ensure the output frequency meets the requirements. Or other pre-arranged relationships.

[0069] Preferably, the synchronous frequency multiplication unit has a deterministic synchronization or phase reset function. After switching the delay code, updating the frequency parameters, or relocking, this function ensures that the initial phase of the output RF signal does not produce random ambiguity relative to the reference clock, thereby guaranteeing that the phase relationship between different sampling states is calculable and repeatable.

[0070] Preferably, the system also includes an I / Q mixing synchronization monitoring link. This link orthogonally mixes one RF signal output from the synchronization frequency multiplier unit with a reference path or another coherent signal to obtain an I / Q low-frequency voltage, which is used to monitor phase offset linearity, frequency multiplication output stability, and delay code switching status. The monitoring results can be used for alarms, discarding abnormal frames, or feedback correction of the delay lookup table.

[0071] The radio frequency excitation signal can be applied to the device under test (DUT) via a power amplifier, adjustable attenuator, DC blocking capacitor, radio frequency probe, probe stage, package pins, or test fixture. For measurements requiring a vacuum or controlled atmosphere, the DUT can be placed in a vacuum chamber, atmosphere chamber, or temperature control stage, while simultaneously performing microscopic holographic imaging through an optical window.

[0072] Example 4: Phase offset sampling, delay calibration and non-equal interval phase lock.

[0073] like Figure 8a and Figure 8b As shown, in an ideal phase scan, the delay step between adjacent sampling states is constant, and the vibration phase changes at equal intervals. However, in practice, programmable delay units, PLLs, comparators, and wiring can all introduce nonlinear delay errors. If phase-locked demodulation is performed directly according to the nominally equal-interval phases, significant amplitude and phase deviations will occur in the GHz band. Therefore, this embodiment uses delay calibration and a non-equal-interval complex phase-locked method. In the figure, Frequency is the frequency, Recovered amplitude is the recovered amplitude, and Recovered phase is the recovered phase.

[0074] During calibration, the input reference signal and output delay signal of the programmable delay unit are simultaneously input to a high-bandwidth oscilloscope, sampling oscilloscope, vector network analyzer, phase noise analyzer, time interval analyzer, or IQ phase measurement circuit to obtain the true relative delay corresponding to different delay codes. .

[0075] Preferably, for a binary weighted delay chip, the actual delay of each weight bit is measured separately, and the delay lookup table of all codewords is obtained by superimposing the measurements; alternatively, the codeword-delay lookup table can be obtained by directly traversing all codewords. This lookup table can be stored in a host computer, microcontroller, FPGA, memory, or measurement software.

[0076] like Figure 9 As shown, during the measurement process, the system acquires holograms or complex field results according to a predetermined delay sequence. The delay sequence can be a monotonically increasing sequence, an equivalent uniform phase sequence, a randomly shuffled sequence, a complementary sequence, a sequence covering multiple periods, or a modulation sequence used to suppress 1 / f noise.

[0077] During complex phase-locked reconstruction, a real delay is used for each spatial pixel or each effective region. Constructing reference basis functions and holographic phase sequence or complex field difference sequence and The complex vibration quantity is obtained by weighted multiplication and summation. ,in is the weighting coefficient, and m is the sampling state number. The modulus corresponds to the vibration amplitude, and the argument corresponds to the vibration phase.

[0078] When the sampling point distribution does not satisfy the orthogonality condition or there are missing frames, complex phase-locked reconstruction can be expressed as a least-squares problem. By using... and Using the basis function, weighted least squares fitting is performed on the time series of each pixel to recover the in-phase and quadrature components at the frequency to be measured.

[0079] To further reduce low-frequency drift and strong background noise, the delay sequence can be designed so that the effective vibration signal corresponds to a modulation frequency that avoids 1 / f noise in the frame sequence dimension. The reconstruction algorithm first extracts this single-frequency component in the time dimension, and then performs low-pass, band-pass, ring stripping, or complex field averaging in the spatial dimension, thereby improving the identifiability of picometer-level weak vibrations.

[0080] Example 5: High-axis holographic complex field reconstruction and image sequence processing.

[0081] In a preferred embodiment, at least one or more of four types of images are acquired for each measurement state: object light image when only object light is illuminating and reference light is off. Reference light diagram when only reference light is applied and object light is off. Vibrationless hologram of the device under test when it is unexcited or the excitation is turned off. Vibrational hologram of the device under test when the excitation is turned on. .

[0082] To eliminate the effects of uneven illumination, variations in sample reflectivity, and the envelope of reference light intensity, the following methods can be used: and right and Normalization is performed. The normalized hologram mainly contains cosine fringe terms related to the phase difference between the object beam and the reference beam, which is beneficial for subsequent Fourier sideband extraction.

[0083] After performing a two-dimensional Fourier transform on the normalized hologram, the zero-frequency term is located at the center of the spectrum, while the positive and negative first-order sidebands are respectively off from the center of the spectrum. Select one of the sidebands and apply a rectangular window, circular window, Gaussian window, Hamming window, Tukey window, super-Gaussian window, or adaptive window function for filtering. Then, shift it to the center of the spectrum and perform an inverse Fourier transform to obtain the complex field of the image plane.

[0084] Reconstruct the complex field for both the vibration-free state and the vibration-existing state. and By calculating the equivalent phase difference or the equivalent phase difference obtained by differential analysis of adjacent frames. The optical path phase change caused by the vibration of the device under test is obtained. For reflective measurements, the out-of-plane displacement and phase change satisfy... ,in, The image plane complex field obtained by off-axis holographic complex field reconstruction in the unexcited (excitation off) state of the device under test is used as a reference state; The image plane complex field reconstructed under the excitation-on state of the device under test indicates the presence of vibration. The effective wavelength after system calibration. To perform operations on the argument (phase angle) of a complex number, This is the conjugate operation for complex numbers. The image plane complex field reconstructed from the (k+1)th vibration state. The complex field of the image plane reconstructed from the k-th vibration state. This represents the out-of-plane displacement change on the surface of the device under test. This represents the change in optical path phase caused by vibration.

[0085] To improve robustness, multi-frame complex averaging can be performed on the complex field instead of directly averaging the phase map; ring masks can be constructed for low signal-to-noise ratio regions, saturated regions, edge regions, dust regions, and obvious outlier regions; effective pixel masks can also be constructed based on object light intensity, reference light intensity, stripe contrast, frequency domain sideband energy, and local phase residuals.

[0086] When the phase result exists When encountering phase jumps or local anomalies, phase unwrapping based on spatial continuity, Poisson unwrapping based on reliable gradients, local correction based on region connectivity, phase correction based on center-outward propagation, or smoothing constraints based on complex field continuity can be employed. Furthermore, directly phase-locking the complex field result and using the Bessel method for inverse solving can avoid the influence of phase ambiguity.

[0087] For multiple subgroup holographic sequences, the first frame or reference frame of each subgroup can be used as the reference complex field of that subgroup to obtain the complex vibration field of each subgroup. Then, the complex vibration field of each subgroup is averaged to suppress slow drift, speckle variation and environmental disturbance.

[0088] During the measurement result output stage, the following can be output: vibration amplitude diagram, phase diagram, real part diagram, imaginary part diagram, animation sequence, local profile, frequency response curve, spatial average amplitude, regional integrated energy, principal mode projection coefficient, stray mode projection coefficient, and k-space spectrum.

[0089] Example 6: Measurement and diagnosis of GHz FBAR / BAW / XBAR devices.

[0090] like Figure 10a As shown, in one application embodiment, the device under test is a thin-film bulk acoustic resonator (FBAR). This device is connected to an RF excitation port via a GSG probe, with the RF excitation frequency at 14.87 GHz. The system performs femtosecond stroboscopic holographic measurements to obtain the following results: Figure 10b The full-field vibration measurement results.

[0091] For the complex vibration field at each frequency, the active region mask is first determined based on the device micrograph, electrode region, or amplitude threshold. Then, the average amplitude, peak amplitude, phase coherence, total regional energy, and boundary energy flow are calculated within the active region for comparison with the electrical S-parameters, impedance spectrum, or equivalent circuit fitting results.

[0092] The k-space spectrum can be obtained by performing a two-dimensional Fourier transform on the complex vibration field. By comparing the k-space energy distribution at different frequencies, the thickness principal mode, transverse standing waves, boundary scattering, long-wavelength parasitic modes, higher-order stray modes, and energy leakage channels can be identified.

[0093] Near the resonant and anti-resonant frequencies, the full-field amplitude and phase distribution of the device may differ significantly. Using the full-field measurement results of this invention, the changes in the acoustic field distribution at the series resonant point, the parallel anti-resonant point, and nearby frequencies can be directly observed, thereby explaining Q-value degradation, insertion loss, and out-of-band ripple in the electrical response.

[0094] like Figure 11As shown, in another application embodiment, the device under test is a SAW (Sound Wave Acoustic) device. The complex vibration field obtained by this invention can be used to extract the sound wave propagation direction, local scattering center, acoustic band gap, boundary reflection, and group velocity direction.

[0095] The diagnostic results can be fed back into the device design process to adjust electrode shape, piezoelectric layer thickness, release boundary, acoustic reflector, support structure, damping structure, material stacking, and process parameters, thereby improving device Q value, reducing spurious response, improving in-band flatness, or increasing power handling capability.

[0096] Example 7: Alternative implementation methods.

[0097] The femtosecond pulse light source in this invention can employ free-space output, fiber optic output, frequency doubling output, adjustable repetition frequency output, or multi-wavelength output. For devices under test with different materials and surface reflectivities, the operating wavelength can be selected in the range of 400nm to 2000nm, and optimized according to the objective lens numerical aperture and camera response.

[0098] The two-dimensional detector in this invention can be selected from different models with high pixel count, high full-well capacity, high quantum efficiency, low readout noise, high dynamic range or high frame rate according to measurement requirements; when the light intensity is low, multi-frame accumulation, pixel merging, electron multiplication or cooling camera can be used.

[0099] The phase offset in this invention can be applied to the reference clock path, RF excitation path, sampling trigger path, or algorithm equivalent phase path. As long as a known or calibrable vibration phase change can be formed, it falls under the phase offset sampling method of this invention.

[0100] The synchronous excitation in this invention can be a sine wave, pulse wave, amplitude modulation signal, phase modulation signal, frequency sweep signal, multi-tone signal, or broadband excitation signal. For linear steady-state measurements, single-frequency sine excitation is preferred; for transient or nonlinear response measurements, pulse train, multi-frequency synthesis, or frequency sweep excitation can be used.

[0101] The holographic interference optical path in this invention can operate in air, vacuum, inert gas, liquid, or temperature-controlled environments. For devices requiring reduced air disturbance or acoustic damping, measurement is preferably performed within a vacuum cavity; for devices in liquid or biological environments, transparent windows and immersion objectives can be used.

[0102] The algorithm in this invention can be executed by a general-purpose computer, graphics processing unit (GPU), digital signal processor (DSP), field-programmable gate array (FPGA), embedded processor, or cloud computing platform. To improve real-time performance, the Fourier reconstruction, complex phase-locked loop (CLL), and filtering steps can be executed in parallel on a GPU or FPGA.

[0103] The above embodiments illustrate the system structure, optical path design, synchronous electronics, sampling method, holographic reconstruction algorithm, and application scenarios of the present invention. It should be understood that the scope of protection of the present invention is not limited by the specific device models, wavelengths, frequencies, amplification factors, delay chips, frequency synthesizers, camera models, and algorithm parameters described in the above embodiments.

[0104] Any system or method that uses the stable repetition frequency of a femtosecond or equivalent ultrashort pulse light source as a time reference to generate a high-frequency electrical excitation coherently locked to it, and records the stroboscopic freezing full-field vibration state of the device under test through a full-field digital holographic method with pulse leading edge matching, thereby reconstructing the full-field complex vibration information, should fall within the scope of this invention.

[0105] Example 8 This invention addresses the problems in existing femtosecond off-axis holographic interference optical paths, such as short coherence length of femtosecond pulses, significant broadband spectral dispersion, transverse group delay drift caused by simple reference light tilt angle, and difficulty in maintaining the contrast of interference fringes across the entire field of view. It proposes a femtosecond off-axis holographic interference optical path with pulse leading edge matching and its adjustment method.

[0106] The key problem to be solved by this invention is not simply generating off-axis fringes, but rather satisfying the following two constraints simultaneously under femtosecond broadband pulse conditions: First, the reference light and the object light have a non-zero transverse phase wave vector difference at the two-dimensional detector to form an off-axis holographic spatial carrier frequency; Second, the relative group delay gradient of the reference light and the object light within the effective field of view of the two-dimensional detector is compensated to a preset range so that stable interference can be generated at each transverse position.

[0107] To achieve the above objectives, the present invention relates to a femtosecond off-axis holographic interference optical path with pulse leading edge matching, comprising: a femtosecond pulse source, a beam splitting and polarization control module, a measurement arm, a reference arm, a pulse leading edge matching module, a beam combining imaging module, and a two-dimensional detector.

[0108] The femtosecond pulse source is used to generate broadband pulsed light with a preset center wavelength, preset pulse width, and preset repetition frequency. Preferably, the pulse width of the femtosecond pulse source is 10 fs to 10 ps, ​​more preferably 30 fs to 500 fs; the center wavelength can be visible light, near infrared, or communication band, and can be obtained as a suitable detection wavelength for microscopic interferometry through frequency doubling, sum-frequency conversion, spectral compression, or spectral shaping.

[0109] The beam splitting and polarization control module is used to split the femtosecond pulse light into a measurement beam and a reference beam, and to ensure that the two beams have a controllable power ratio, polarization state, and optical path difference before beam combining. Preferably, the beam splitting and polarization control module includes one or more of the following: a polarizing beam splitter, a half-wave plate, a quarter-wave plate, a non-polarizing beam splitter, an optical fiber collimator, a piezoelectric displacement stage, and a precision stepper motor.

[0110] The measuring arm is used to illuminate the surface of the sample under test with measuring light and to image the object light after reflection, scattering, or transmission by the sample onto a two-dimensional detector. Preferably, the measuring arm includes a beam expander and collimator module, a microscope objective, a tube mirror, a 4f imaging system, a polarization backlight separation structure, and a sample stage, so that the surface under test and the two-dimensional detector or its intermediate image plane are in a conjugate relationship.

[0111] The reference arm is used to form a reference beam coherently superimposed with the object beam. The reference arm includes a pulse leading-edge matching module, which is configured to ensure that the reference beam has a non-zero transverse phase vector relative to the object beam at the two-dimensional detector, while simultaneously ensuring that the relative pulse peak arrival time difference between the reference beam and the object beam within the effective field of view of the two-dimensional detector is less than a preset threshold.

[0112] To describe the pulse leading-edge matching condition, the frequency domain phase of the reference light or object light near the detector surface is written as: ,in, Angular frequency, In three-dimensional space coordinates, Using time as the coordinate. With the center frequency as the coordinate. The first-order approximation of the vicinity is: , ,in, The transverse wave vector in the x-direction of the reference or object light. express As angular frequency changes, The transverse wave vector in the y-direction of the reference light or object light; , The transverse wave vectors in the x and y directions at the center frequency correspond to the off-axis holographic space carrier frequency; This represents the gradient of the pulse peak arrival time on the horizontal axis, corresponding to the tilt of the pulse leading edge.

[0113] The pulse leading edge matching module ensures that the reference beam and the object beam satisfy the following at the detection surface: the transverse phase wave vector difference between the reference beam and the object beam. It is not zero, and its magnitude is such that the positive and negative first-order interference spectra and the zero-order spectrum can be separated in the two-dimensional Fourier domain. These are the transverse phase wave vector differences in the x and y directions, respectively; and the transverse group delay gradient between the reference beam and the object beam. The modulus is less than a preset threshold, or the arrival time difference of the maximum relative pulse peak generated within the effective field of view of the two-dimensional detector. Less than the preset threshold denoted as the transverse group delay gradients in the x and y directions, respectively.

[0114] Preferably, the preset threshold is set to be less than 10 times the full width at half maximum (FWHM) of the femtosecond pulse intensity, and more preferably less than 1 times the FWHM of the femtosecond pulse intensity. For typical tens to hundreds of femtosecond pulses, the It can be limited to the range of several femtoseconds to hundreds of femtoseconds.

[0115] Preferably, the pulse leading edge matching module includes a transverse wavefront generating element and a relay imaging element. The transverse wavefront generating element is used to generate an off-axis transverse phase wavefront of the reference light; the relay imaging element is used to map the plane containing the transverse wavefront generating element, its Fourier surface, or its conjugate surface to the vicinity of the two-dimensional detector, thereby simultaneously controlling the phase wavefront and the pulse leading edge. The transverse wavefront generating element may be a transmissive grating, a reflective grating, a blazed grating, a volume holographic grating, a diffractive optical element, a prism group, an optical wedge, a spatial light modulator, a metasurface device, or a combination thereof.

[0116] In a preferred implementation, the transverse wave vector generating element is a transmissive grating. The transmissive grating is configured to allow the reference light to select its first-order diffracted beam as the reference wave, and the grating plane or its conjugate plane is mapped onto the detector surface via a relay imaging system. In this case, the transverse wave vector of the first-order diffracted beam is primarily determined by the grating period. Under ideal or near-normal incidence conditions, the first derivative of its transverse wave vector with respect to the optical frequency is close to zero, thereby giving the detector surface a non-zero spatial carrier frequency and a substantially flat pulse leading edge.

[0117] In another preferred implementation, the transverse wave vector generating element is a reflective blazed grating. The reflective blazed grating, by selecting the incident angle and the first-order diffraction angle, makes the first derivative of the transverse wave vector of the reference light at the center wavelength approach zero. Preferably, for the center wavelength... and grating period Adjusting the incident angle under the constraints of the reflection grating equation and first-order diffraction angle To satisfy the condition near the center wavelength or The pulse leading-edge compensation condition is used to generate a high-efficiency off-axis reference light while reducing the dispersion of the transmission substrate. λ is the wavelength of light.

[0118] In another preferred implementation, the transverse wave vector generating element is a reflective blazed grating, and it is placed under Littrow geometry or near-Littrow geometry conditions. The reference arm further includes a symmetrical relay imaging structure and a reflection structure, so that the initial pulse leading edge tilt caused by grating dispersion is reshaped or canceled during relay propagation, while a stable phase wavefront tilt is introduced by the beam combiner path, the polarization beam splitter reflection path, or the reference arm geometry path, thereby achieving separate control of the phase wavefront tilt and pulse leading edge matching. Near-Littrow geometry refers to an optical system configuration that is close to but does not precisely satisfy the above-mentioned Littrow conditions.

[0119] Littrow geometry (also known as Littrow configuration) is a special operating state of a reflective diffraction grating. In this configuration, the grating is adjusted so that light of a particular diffraction order (usually first-order diffraction) returns along the original direction of the incident beam.

[0120] The beam combining imaging module is used to superimpose the object beam with a reference beam matched by the pulse leading edge, and form an off-axis holographic interferogram on a two-dimensional detector. Preferably, the beam combining imaging module includes one or more of the following: a polarization beam combiner, a non-polarization beam splitter, a tube lens, a microscope objective, a polarizer, and an aperture. The two-dimensional detector can be a CCD, CMOS, sCMOS, InGaAs array detector, or other area array detector.

[0121] This invention also provides a method for adjusting the femtosecond off-axis holographic interferometric optical path with pulse leading edge matching, comprising the following steps: S1, constructing a measurement arm and a reference arm so that the object beam and the reference beam coincide at the two-dimensional detector; S2, adjusting the transverse wave vector generating element of the reference arm so that the spatial frequency of the interference fringes is within the allowable range of sampling and Fourier reconstruction by the two-dimensional detector; S3, adjusting the optical path length, dispersion compensation, relay imaging position, grating incident angle, or reflection geometry of the reference arm so that the contrast of the full-field interference fringes reaches a preset value; S4, calculating the normalized interference term based on the separately acquired object beam intensity map, reference beam intensity map, and holographic interferogram, and evaluating the full-field fringe visibility, local visibility distribution, and carrier frequency domain signal-to-noise ratio; S5, iteratively adjusting the reference arm based on the evaluation results so that the full-field fringe contrast, spatial carrier frequency separation, and pulse leading edge matching degree meet the measurement requirements.

[0122] In step S4, the normalized interference term From hologram intensity Light intensity and reference light intensity Calculated. Through... By performing local sliding window interference contrast statistics, the local visibility distribution of the full-field fringes can be obtained; by analyzing... By performing a two-dimensional Fourier transform, the off-axis carrier peak position, the degree of separation between the positive and negative first-order spectra, and the signal-to-noise ratio of the carrier energy relative to the background energy can be obtained.

[0123] This invention also provides a femtosecond stroboscopic full-field vibration measurement system including a femtosecond off-axis holographic interference optical path with pulse leading edge matching. The system further includes a photoelectric synchronous excitation module, a radio frequency drive module, a time delay or phase shift module, an image acquisition and control module, and a holographic reconstruction module. By coherently locking the periodic vibration of the device under test with the femtosecond pulse train, the system can repeatedly sample the same vibration phase within the camera exposure time and reconstruct the full-field vibration amplitude and phase from the off-axis hologram.

[0124] Example 9 This invention addresses the problems in existing femtosecond stroboscopic measurement systems, such as the difficulty in maintaining low-jitter coherent locking between GHz excitation and femtosecond optical combs, unequal sampling intervals in high-frequency stroboscopic sampling due to programmable delay nonlinearity, and amplitude and phase errors in traditional equal-step phase-locked reconstruction at frequencies above GHz. It proposes a low-jitter GHz excitation synchronization and calibration delay stroboscopic phase-locked reconstruction method and system based on femtosecond optical combs.

[0125] The objectives of this invention include: first, converting the repetition frequency of a femtosecond pulse train or its harmonics into a low-noise electrical reference clock with high fidelity; second, applying a programmable and calibrable picosecond-level time offset to the reference clock; third, coherently synthesizing an excitation signal from the offset reference clock or applying a corresponding phase shift to the excitation signal while maintaining its phase controllability; fourth, establishing a lookup table between the delay control code and the actual sampling time; and fifth, constructing a non-equal-interval complex-locked phase nucleus using the actual sampling time to achieve accurate reconstruction of the full-field vibration amplitude and phase.

[0126] To achieve the above objectives, the present invention relates to a low-jitter GHz bandwidth excitation synchronization system based on a femtosecond optical comb, comprising a femtosecond optoelectronic reference clock extraction module, a low-noise clock shaping module, a programmable delay / phase offset module, a delay calibration and lookup table module, a coherent GHz excitation synthesis module, a phase synchronization and status monitoring module, an acquisition and control interface module, and a calculation and processing module.

[0127] The femtosecond photoelectric reference clock extraction module is used to obtain the laser repetition frequency from the femtosecond laser pulse train. A coherent electrical reference signal. Preferably, the module includes a high-speed photodetector inside or outside the femtosecond laser, an RF bandpass filter, a low-noise amplifier, a power divider, and an impedance matching network. The photodetector converts the femtosecond pulse train into a signal containing... The electrical signal and its harmonics; the radio frequency bandpass filter selects the fundamental frequency, harmonics or preset harmonic components from the electrical signal; the low noise amplifier improves the signal-to-noise ratio of the reference signal and provides sufficient zero-crossing slope for subsequent comparison shaping.

[0128] Preferably, the repetition frequency of the femtosecond optical pulse train is 1MHz to 1GHz, more preferably 10MHz to 250MHz; preferably, the femtosecond laser that generates the femtosecond optical pulse sequence has an adjustable repetition frequency function; the reference signal output by the femtosecond optoelectronic reference clock extraction module can be one or more of the following: sine wave, limited sine wave, square wave, differential clock, LVDS, CML, LVPECL, PECL or CMOS clock.

[0129] The low-noise clock shaping module is used to shape the reference signal into a digital clock with steep edges, low jitter, and low common-mode noise. Preferably, the module includes an AC coupling network, a bias network, an impedance termination, a high-speed comparator, a limiting amplifier, a clock buffer, or a level shifter. By performing a zero-crossing comparison on the bandpass-filtered reference sine signal at a stable threshold, the timing information of the femtosecond optical pulse train can be mapped to low-jitter electrical edges.

[0130] The programmable delay / phase shift module is used to apply a controllable relative delay to the digital clock to achieve scanning of the vibration phase of the device under test relative to the sampling time of the femtosecond optical pulse. Preferably, the module includes a digital delay chip, an analog delay circuit, a delay-locked loop, a digital phase interpolator, an RF phase shifter, a vector modulator, an adjustable transmission line, a DDS phase accumulator, or a combination thereof. The programmable delay / phase shift module outputs delay or phase shift control codes from the controller. And switch the delay value in each sampling step or each group of sampling steps.

[0131] The delay calibration and lookup table module is used to measure and store the delay control code D and the actual delay. The module establishes the correspondence between these parameters. Calibration data can be obtained through high-speed oscilloscope edge statistics, lock-in amplifiers, vector network analyzer phase slope measurement, IQ mixer phase measurement, time interval analyzer, sampling oscilloscope, dual-channel comparison, cross-correlation algorithm, or phase noise analyzer. Calibration results are stored as delay lookup tables, piecewise polynomials, spline functions, temperature compensation models, or multidimensional calibration matrices.

[0132] The coherent GHz excitation synthesis module is used to coherently multiply the delayed or phase-shifted reference clock to the target excitation frequency. Preferably, the module includes an integer N phase-locked loop, a fractional N phase-locked loop, a broadband frequency synthesizer, a DDS, a direct digital synthesis-mixer chain, a comb harmonic selector, an active frequency multiplier, a passive frequency multiplier, an injection-locked oscillator, an opto-mixer, or a combination thereof. The target excitation frequency can satisfy... Or other frequency relationships coherent with the femtosecond optical comb, where N is an integer or rational number. This is the frequency offset used for equivalent slow scans or heterodyne measurements. This is the electrical reference clock frequency obtained after photoelectric detection and clock shaping.

[0133] Preferably, when the coherent GHz excitation synthesis module uses a PLL-type scheme, the phase-locked loop (PLL) has a phase synchronization or phase reset function, enabling it to realign the phase of the output GHz excitation to the input reference clock after the delay control code switch. The phase synchronization or phase reset function can be implemented through the PLL's synchronization port, frequency divider reset, triggered vector modulation, gated restart, or phase detection feedback.

[0134] Preferably, when the coherent GHz excitation synthesis module uses a DDS-type scheme, the numerically controlled oscillator or phase accumulator in the DDS should have a phase synchronization function or an initial phase zeroing calibration function relative to the input clock to achieve initial phase alignment with the input reference clock. More preferably, the DDS used has an output phase adjustment function, thereby partially replacing the function of the programming delay / phase offset module.

[0135] The phase synchronization and status monitoring module is used to monitor the phase relationship between the femtosecond reference clock, the delayed reference clock, the GHz excitation signal, and the image acquisition trigger. Preferably, this module includes an I / Q mixer, a power divider, a directional coupler, a phase detector, a lock-in amplifier, a spectrum analysis unit, a low-speed ADC, an FPGA, an MCU, or a computer acquisition card. The system can determine whether the current stroboscopic state meets the acquisition requirements based on the monitored I / Q output, phase residual, amplitude residual, or unlock flag, and can perform phase compensation, resynchronization, or removal of abnormal frames.

[0136] The acquisition and control interface module is used to establish a timing relationship between delay control code switching, GHz excitation phase synchronization, sample stabilization, and image exposure. Preferably, this module sends synchronization control signals to the camera, image acquisition card, excitation source, PLL, delay chip, aperture, shutter, or host computer, so that each delayed sampling step corresponds to one or more holograms, interferometric images, or photoelectric sampling data.

[0137] The computational processing module is used to perform calibration delay stroboscopic coding and non-equal interval complex-locked phase reconstruction based on the delay lookup table and the acquired data. For the k-th sampling step, the system uses the delay control code... The actual sampling time is obtained by looking up the table. Or obtain the equivalent phase within the vibration period. The aforementioned and It can be determined by the system's initial phase, the fixed delay of the transmission link, a reference frame, or calibration measurements. Among these, This represents the actual sampling time of the k-th sampling step. To delay, This refers to the initial time offset caused by the system's initial phase or a fixed delay. This represents the equivalent sampling phase of the k-th sampling step within the vibration period. The target vibration angular frequency, This is the initial phase or fixed phase offset of the system.

[0138] When the object of measurement is a two-dimensional holographic complex field sequence, let Let be the pixel complex field value of the k-th frame after single-frame holographic reconstruction, reference correction, background subtraction, or normalization, and let the target vibration angular frequency be . The computational processing module then constructs a non-equal-interval complex locked phase core. And calculate the matched filtering result: ,in These are the weighting coefficients. The normalization coefficient is... For the non-equal interval complex-locked phase core corresponding to the k-th frame, The imaginary unit, It is a natural exponential function. The amplitude of the full-field complex vibration obtained from the reconstruction. The modulus corresponds to the vibration amplitude distribution, and the argument corresponds to the vibration phase distribution.

[0139] When the sampling phase distribution is uneven, or there are missing frames, abnormal frames, or multiple frequency components, the non-equal-interval complex phase-locked reconstruction can adopt a least-squares form. An observation model is established for each pixel. Alternatively, a matrix model can be established that includes the target frequency, DC term, drift term, harmonic term, and noise term. The complex vibration coefficients are solved using weighted least squares, regularized least squares, robust regression, non-uniform DFT, NUFFT, Kalman filtering, or Bayesian estimation. For the observation value of the kth sampling point, The complex amplitude coefficient of the positive frequency component. The complex amplitude coefficient of the negative frequency component. This is either a DC term or a constant bias term. For the noise term at the k-th sampling point, The vector formed by the observations of all sampling points. For the observation matrix, Let be the vector of model parameters to be solved. This is the noise vector.

[0140] Preferably, the calculation processing module can introduce multi-dimensional compensation for the delay lookup table based on temperature, power supply, level, frequency, codeword transition history, or board-level channels. The lookup table can be represented as... Where T is temperature, V is power supply or input amplitude, f is reference frequency or excitation frequency, and ch is channel number. The system can insert calibration steps before, after, or during measurement to update the lookup table or perform post-correction on the measurement results.

[0141] This invention also provides a method for calibrating delayed stroboscopic coding and non-equal interval complex phase-locked reconstruction, comprising the following steps: S1, extracting a reference clock coherent with the repetition frequency from a femtosecond pulse train; S2, performing low-noise filtering, amplification, and comparison shaping on the reference clock; S3, applying a programmable delay or phase shift to the shaped clock; S4, generating an excitation signal of a given frequency through phase-locked frequency multiplication or equivalent coherent frequency synthesis; S5, generating a delay lookup table used in a single acquisition based on the calibration results of each delay control code; S6, driving the device under test according to a preset delay code sequence and acquiring a stroboscopic image sequence; S7, converting the delay lookup table into the actual sampling time or sampling phase of each frame; S8, constructing a non-equal interval complex phase-locked kernel based on the actual sampling time; S9, performing complex phase-locked reconstruction on each pixel or each measurement point to obtain the amplitude and phase of the target vibration.

[0142] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0143] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A high-frequency full-field digital holographic vibration measurement system, characterized in that, include: The system includes a femtosecond pulse source subsystem, a pulse leading edge matching off-axis holographic optical path subsystem, a photoelectric reference clock extraction subsystem, a phase shift and synchronous frequency doubling excitation subsystem, a hologram synchronous acquisition subsystem, and a full-field complex vibration reconstruction and diagnostic processing subsystem. The femtosecond pulse source subsystem generates periodic femtosecond or picosecond pulse trains, and the repetition frequency of the pulse trains serves as the optical time reference for the system. The femtosecond pulse source subsystem is connected to the pulse leading edge matching off-axis holographic optical path subsystem and the photoelectric reference clock extraction subsystem, respectively. Part of the pulse light generated by the femtosecond pulse source subsystem is input to the pulse leading edge matching off-axis holographic optical path subsystem as measurement light, and the other part is input to the photoelectric reference clock extraction subsystem. The photoelectric reference clock extraction subsystem extracts an electrical reference clock from a femtosecond pulse train, and the frequency of the electrical reference clock maintains a deterministic phase relationship with the repetition frequency of the femtosecond pulses; The output of the photoelectric reference clock extraction subsystem is connected to the input of the phase offset and synchronous frequency doubling excitation subsystem, and the electrical reference clock is input to the phase offset and synchronous frequency doubling excitation subsystem. The phase offset and synchronous frequency doubling excitation subsystem generates an electrical excitation signal for the device under test based on the electrical reference clock, and controlsably adjusts the phase of the electrical excitation signal relative to the femtosecond pulse train; The output of the phase shift and synchronous frequency doubling excitation subsystem is connected to the device under test (DUT) to apply the electrical excitation signal to the DUT. The pulse leading edge matching off-axis holographic optical path subsystem receives the measurement light from the femtosecond pulse source subsystem and divides the measurement light into object light and reference light. The object light illuminates the device under test and carries the phase modulation caused by the surface displacement of the device under test. The reference light and the object light coincide in the image plane of the two-dimensional detector or its conjugate plane to form off-axis holographic interference. The hologram synchronous acquisition subsystem includes a two-dimensional array detector and its synchronous control module. The two-dimensional array detector records the hologram or hologram sequence formed by the off-axis holographic interference. The output end of the hologram synchronous acquisition subsystem is connected to the input end of the full-field complex vibration reconstruction and diagnostic processing subsystem, and transmits the recorded hologram data to the full-field complex vibration reconstruction and diagnostic processing subsystem. The full-field complex vibration reconstruction and diagnostic processing subsystem receives the hologram data, processes the hologram or hologram sequence, and obtains the full-field vibration amplitude, phase, modal morphology, and frequency domain acoustic diagnostic results of the device under test.

2. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 1, characterized in that, The pulse width of the pulse train generated by the femtosecond pulse source subsystem is less than one-tenth of the vibration period under test; the excitation frequency of the device under test... With femtosecond pulse repetition frequency Satisfying Relationship: Where N is an integer, such that when each femtosecond pulse arrives at the device under test, the device under test is in the same vibration phase, thus forming a stroboscopic frozen hologram when the camera exposure time is much longer than the vibration period.

3. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 2, characterized in that, The pulse leading edge matching off-axis holographic optical path subsystem modulates the phase leading edge and pulse leading edge of the reference light through a reflective blazed grating; Within the image plane of the two-dimensional detector, the reference light phase satisfies a non-zero lateral phase gradient to form off-axis fringes; simultaneously, the arrival time difference between the pulse peaks of the reference light and the object light is less than the time gate width threshold determined by the measurement signal-to-noise ratio requirement within the effective field of view. Let the transverse wave vector of the reference ray in the transverse x-direction of the image plane be... Its derivative with respect to angular frequency is , Determine the off-axis fringe spatial carrier frequency. The gradient along the x-direction, which determines the arrival time of the pulse peak, is achieved through a combination of a grating and an imaging system. For non-zero Approaching zero, thus achieving pulse leading-edge matching while maintaining the off-axis carrier frequency, wherein, For the reference light wave vector component in the transverse x-direction of the image plane, ω is the angular frequency.

4. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 3, characterized in that, The phase shift and synchronous frequency doubling excitation subsystem maintains and Under coherent locking conditions, a controllable delay is applied to the reference clock, excitation signal, or sampling trigger signal. The vibration phase corresponding to the m-th sampling state is Add initial phase, composed of multiple The corresponding hologram or complex field result recovers the full-field vibration amplitude and phase of the device under test, whereby... This represents the controllable delay amount corresponding to the m-th sampling state.

5. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 4, characterized in that, The phase shift and synchronous frequency doubling excitation subsystem includes a programmable delay unit, a synchronous phase-locked loop, and a power amplifier; The clock reference signal output by the optoelectronic reference clock extraction subsystem is input to the programmable delay unit. The output of the programmable delay unit is connected to the reference input of the synchronous phase-locked loop (PLL). The output of the PLL is connected to the input of the power amplifier. The output of the power amplifier is connected to the device under test (DUT). The programmable delay unit performs a controllable delay on the input clock reference signal. The PLL performs reference-locked frequency multiplication on the delayed clock reference signal to generate an RF excitation source signal. The power amplifier amplifies the RF excitation source signal and applies it to the DUT.

6. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 5, characterized in that, The delay amount of the programmable delay unit is calibrated to obtain a lookup table between the delay code and the actual delay, and the actual delay lookup table is used to construct the non-equal interval sampling phase-locked basis function in the full-field complex vibration reconstruction. During reconstruction, use a real time delay for each spatial pixel or each effective region. Constructing reference basis functions and holographic phase sequence or complex field difference sequence and The complex vibration quantity is obtained by weighted multiplication and summation. ,in Here, m represents the weighting coefficient, and m represents the sampling state number. It is an exponential function, where i is the imaginary unit. These are the spatial coordinates of the two-dimensional detector's image plane. The modulus corresponds to the vibration amplitude, and the argument corresponds to the vibration phase.

7. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 1, characterized in that, The photoelectric reference clock extraction subsystem includes a photodetector, a bandpass filter, a low-noise amplifier, a limiting amplifier, and a high-speed comparator; The pulsed light from the femtosecond pulse source subsystem is input to the photodetector, which converts the femtosecond pulse train into an electrical signal containing the repetition frequency and its harmonics. The output of the photodetector is connected to the input of the bandpass filter, which extracts a narrowband component near the repetition frequency or its harmonics from the electrical signal. The output of the bandpass filter is connected to the input of the low-noise amplifier, which improves the signal-to-noise ratio of the extracted signal to obtain a low-phase-noise approximate sinusoidal reference signal. The output of the low-noise amplifier is connected to the input of the limiting amplifier, which limits the amplitude of the approximate sinusoidal reference signal within a predetermined range. The output of the limiting amplifier is connected to the input of the high-speed comparator, which converts the limited signal into a differential digital clock. The differential digital clock serves as the output signal of the photoelectric reference clock extraction subsystem.

8. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 1, characterized in that, The hologram synchronous acquisition subsystem acquires object light image, reference light image, vibration-free hologram, vibration hologram, or a combination thereof in each phase state; the two-dimensional array detector is a global shutter camera; the hologram synchronous acquisition subsystem includes a synchronization control module, which is connected to the femtosecond pulse source subsystem, the phase shift and synchronous frequency doubling excitation subsystem, and the two-dimensional array detector, and is used to control the acquisition timing.

9. The ultra-high frequency full-field digital holographic vibration measurement system according to claim 1, characterized in that, The full-field complex vibration reconstruction and diagnostic processing subsystem performs the following processing on the acquired holograms: intensity normalization, off-axis holographic frequency domain sideband extraction, complex field reconstruction, reference state phase subtraction, phase unwrapping or local phase correction, non-equal interval complex phase-locked demodulation based on measured delay tables, spatial filtering, ring mask processing, complex field averaging, amplitude and phase output, as well as modal diagnosis based on complex vibration fields, k-space spectrum analysis and energy leakage path identification; Reconstructing the field and By calculating the equivalent phase difference or the equivalent phase difference obtained by differential analysis of adjacent frames. The optical path phase change caused by the vibration of the device under test is obtained; for reflective measurements, the out-of-plane displacement and phase change satisfy... ,in, The image plane complex field is obtained by off-axis holographic complex field reconstruction when the device under test is in an unexcited state. The image plane complex field reconstructed under the excitation-on state of the device under test; The effective wavelength after system calibration. To perform arguments operations on complex numbers, This is the conjugate operation for complex numbers. The complex field of the image plane reconstructed from the (k+1)th vibration state. The complex field of the image plane reconstructed from the k-th vibration state. This represents the out-of-plane displacement change on the surface of the device under test. This represents the change in optical path phase caused by vibration.

10. A method for measuring ultra-high frequency full-field digital holographic vibration, characterized in that, The method applied to the ultra-high frequency full-field digital holographic vibration measurement system according to claims 1 to 9 includes the following steps: Step 1: Generate a periodic femtosecond or picosecond pulse train through the femtosecond pulse source subsystem, and use the repetition frequency of the pulse train as an optical time reference; Step 2: Extract an electrical reference clock from the femtosecond or picosecond pulse train, wherein the frequency of the electrical reference clock maintains a deterministic phase relationship with the repetition frequency of the pulse train; Step 3: Generate an electrical excitation signal for the device under test (DUT) based on the electrical reference clock, and controllably adjust the phase of the electrical excitation signal relative to the pulse train; the frequency of the electrical excitation signal and the repetition frequency of the pulse train satisfy an integer multiple relationship, so that when each pulse reaches the DUT, the DUT is in the same vibration phase, thereby forming a stroboscopic freeze state when the detector exposure time is much longer than the vibration period. Step 4: Divide the pulse train into object light and reference light, so that the object light illuminates the device under test and carries the phase modulation caused by the surface displacement of the device under test, so that the reference light has a non-zero transverse phase vector on the image plane of the detector to generate an off-axis spatial carrier frequency, and at the same time, limit the difference between the pulse peak arrival time of the reference light and the object light within the effective field of view to within a preset threshold, thereby realizing off-axis digital holographic interference with pulse leading edge matching; Step 5: While maintaining coherent locking between the electrical excitation signal and the pulse train, a controllable delay is applied to the reference clock, excitation signal, or sampling trigger signal to change the phase of the electrical excitation signal relative to the pulse train, thereby acquiring corresponding holograms or hologram sequences under different vibration phases; the holograms or hologram sequences are recorded by a two-dimensional array detector; Step 6: Perform off-axis holographic complex field reconstruction on the acquired holograms or hologram sequences to obtain the image plane complex field under each sampling state; Step 7: Based on the true delay value corresponding to each sampling state, construct the non-equal interval sampling phase-locked basis function, and perform complex phase-locked demodulation on the complex field sequence of each pixel or each effective region to extract the complex vibration quantity at the frequency to be measured, and obtain the full field vibration amplitude and phase of the device under test. Step 8: Based on the full-field vibration amplitude and phase, output the vibration mode morphology, k-space spectrum and energy leakage diagnosis results of the device under test.

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