Phase resolved brillouin optical spectrum system

Abstract

The present disclosure provides a phase resolved Brillouin optical spectrum system, comprising: a microwave pulse signal generating device configured to generate a first microwave pulse signal and a second microwave pulse signal; a quasi-particle excitation device configured to carry a sample and absorb the first microwave pulse signal to locally excite quasi-particles in the sample; a laser light source configured to generate laser light to focus on a target position of the sample to cause Brillouin scattering of the quasi-particles to generate Brillouin scattered light; wherein the target position is adjustable; an electro-optic modulator configured to modulate the phase of the laser light under the driving of the second microwave pulse signal to generate frequency-shifted reference light, the frequency-shifted reference light interfering with the Brillouin scattered light; wherein by adjusting the target position, a phase resolved Brillouin optical spectrum measurement is performed.

Description

Technical Field

[0001] This disclosure relates to the field of Brillouin spectroscopy testing technology, and in particular to a phase-resolved Brillouin spectroscopy system. Background Technology

[0002] With the rapid development of technology, Brillouin spectroscopy has been widely used to measure the properties of acoustic waves in materials and spin waves in magnetic materials, including confined acoustic phonons, magnon-phonon coupling, Bose-Einstein condensation of magnons, formation of spin wave envelope solitons, and Dzyaloshinskii-Moriya interactions. In addition to traditional frequency analysis, Brillouin spectrometers can also achieve wave vector, time- and spatial resolution, as well as temperature, magnetic field, and pressure-dependent Brillouin spectral measurements, making them suitable for studying various materials from bulk to nanoscale. Combined with wave vector resolution techniques, Brillouin spectrometers can measure the dispersion of phonons and magnons, which is crucial for understanding the electronic, phonon, and magnon characteristics of materials. Time-resolved techniques can analyze the propagation and relaxation characteristics of spin waves, while spatial resolution techniques can further determine the spatial distribution of spin waves during propagation.

[0003] However, time-resolved and spatially resolved techniques are based on simple counting of inelastically scattered photons and are only sensitive to the intensity of spin waves. Therefore, they can only study the shape of spin wave pulses and cannot obtain phase information about magnetic excitations. Although all nonlinear effects can be clearly observed through changes in shape and intensity, the lack of phase information also leads to an incomplete description of the underlying physical processes. Therefore, there is a need to develop phase-resolved Brillouin spectroscopy systems. Summary of the Invention

[0004] In view of this, the present disclosure provides a phase-resolved Brillouin spectroscopy system for at least partially solving the above-mentioned technical problems.

[0005] Embodiments of this disclosure provide a phase-resolved Brillouin spectroscopy system, comprising: a microwave pulse signal generating device configured to generate a first microwave pulse signal and a second microwave pulse signal; a quasi-particle excitation device configured to carry a sample and absorb the first microwave pulse signal to locally excite quasi-particles in the sample; a laser source configured to generate a laser beam such that the laser beam is focused at a target position on the sample to induce Brillouin scattering with the quasi-particles, thereby generating Brillouin scattered light; wherein the target position is adjustable; and an electro-optic modulator configured to modulate the phase of the laser beam under the drive of the second microwave pulse signal to generate a frequency-shifted reference beam, the frequency-shifted reference beam interfering with the Brillouin scattered light; wherein, by adjusting the target position, phase-resolved Brillouin spectroscopy measurements are performed.

[0006] According to an embodiment of the present disclosure, a microwave pulse signal generating apparatus includes: a pulse generator configured to generate a pulse signal; a microwave source configured to generate a continuous microwave signal and convert the continuous microwave signal into an initial microwave pulse signal under the action of the received pulse signal; and a power beam splitter configured to split the initial microwave pulse signal into two paths to obtain a first microwave pulse signal and a second microwave pulse signal.

[0007] According to embodiments of the present disclosure, the microwave pulse signal generating apparatus further includes an attenuator configured to adjust the intensity of the second microwave pulse signal.

[0008] According to embodiments of the present disclosure, the microwave pulse signal generating apparatus further includes a phase shifter configured to adjust the phase of the second microwave pulse signal.

[0009] According to embodiments of this disclosure, the system further includes: a beam splitter configured to reflect the laser and the frequency-shifted reference light, and transmit the frequency-shifted reference light and the Brillouin scattering light.

[0010] According to embodiments of this disclosure, the system further includes a polarizer configured to adjust the relative intensities of the frequency-shifted reference light and the Brillouin scattered light to optimize the interference between the frequency-shifted reference light and the Brillouin scattered light.

[0011] According to embodiments of this disclosure, the system further includes a Fabry-Perot interferometer configured to analyze the interference results of the frequency-shifted reference light and the Brillouin scattered light, and output an interference signal of a preset frequency.

[0012] According to embodiments of this disclosure, the frequency-shifted reference light and the Brillouin scattered light have the same frequency.

[0013] According to embodiments of this disclosure, quasiparticles include acoustic phonons or magnets; when the quasiparticles are magnets, the sample is a magnetic material and the quasiparticle excitation device is a resonant cavity.

[0014] According to embodiments of this disclosure, when the quasiparticle is a magnon, the system further includes a magnetic field generating device configured to apply a magnetic field to a magnetic material on the surface of the resonant cavity.

[0015] According to the phase-resolved Brillouin spectroscopy system of this disclosure, a laser source generates a laser beam that is focused onto a target position on the sample and undergoes Brillouin scattering with quasiparticles to obtain Brillouin scattered light. A microwave pulse signal, after passing through an electro-optic modulator, detunes a small portion of the laser beam, generating sidebands that serve as frequency-shifted reference light. The Brillouin scattered light and the reflected frequency-shifted reference light interfere with each other, and both are analyzed using a Fabry-Perot interferometer to obtain the intensity-frequency relationship. By moving the target position, the intensity, frequency, spatial, and phase relationships can be obtained. Attached Figure Description

[0016] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic diagram illustrating the connection structure of a phase-resolved Brillouin spectroscopy system according to an embodiment of the present disclosure is shown.

[0018] Figure 2 A schematic diagram of a phase-resolved Brillouin spectroscopy system according to another embodiment of the present disclosure is shown.

[0019] Explanation of reference numerals in the attached figures:

[0020] 10-Microwave signal generating device, 11-Pulse generator, 12-Microwave source, 13-Power beam splitter, 14-Attenuator, 15-Phase shifter, 16-Switch, 20-Quasiparticle excitation device, 30-Laser source, 40-Electro-optic modulator, 50-Beam splitter, 60-Polarizer, 70-Fabry-Perot interferometer. Detailed Implementation

[0021] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0023] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0024] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0025] The embodiments disclosed herein provide an easy-to-build, low-cost phase-resolved Brillouin spectroscopy system capable of studying the formation and dynamics of coherent states in magnon gases, as well as two-dimensional spin wave phase profiles. Specific embodiments are described below.

[0026] Figure 1 A schematic diagram of the connection structure of a phase-resolved Brillouin spectroscopy system according to an embodiment of the present disclosure is shown.

[0027] like Figure 1 As shown, a phase-resolved Brillouin spectroscopy system may include: a microwave pulse signal generating device 10, a quasi-particle excitation device 20, a laser source 30, and an electro-optic modulator 40.

[0028] The microwave pulse signal generating device 10 is configured to generate a first microwave pulse signal and a second microwave pulse signal.

[0029] The quasi-particle excitation device 20 is configured to carry the sample and absorb a first microwave pulse signal to locally excite quasi-particles in the sample. Specifically, the frequency of the first microwave pulse signal received by the quasi-particle excitation device 20 is equal to the resonant frequency of the quasi-particle excitation device 20, so that the quasi-particle excitation device 20 can absorb the microwave pulse signal to the maximum extent to locally excite quasi-particles in the sample. The wave corresponding to the quasi-particles propagates to the laser spot position, and the quasi-particles undergo Brillouin scattering with the photons of the incident laser, producing Brillouin scattered light.

[0030] The laser source 30 is configured to generate a laser with a certain energy (frequency). The laser is focused at the target position on the sample and undergoes Brillouin scattering with quasiparticles to produce Brillouin scattered light. The target position is adjustable.

[0031] The electro-optic modulator 40 is configured to modulate the phase of the laser under the drive of the second microwave pulse signal to generate a frequency-shifted reference light, which interferes with the Brillouin scattered light.

[0032] According to embodiments of this disclosure, by adjusting the target position, Brillouin scattered light corresponding to different positions can be generated. The Brillouin scattered light corresponding to each target position interferes with the frequency-shifted reference light to achieve phase-resolved Brillouin spectrum measurement.

[0033] Figure 2 A schematic diagram of a phase-resolved Brillouin spectroscopy system according to another embodiment of the present disclosure is shown.

[0034] like Figure 2 As shown, based on the above embodiments, the microwave pulse signal generating device 10 may include: a pulse generator 11, a microwave source 12, and a power beam splitter 13.

[0035] Pulse generator 11 is configured to generate pulse signals and input the pulse signals to microwave source 12. For example, pulse generator 11 can generate pulse signals with a pulse period of T and a pulse width of Δt.

[0036] The microwave source 12 is configured to generate a continuous microwave signal and, under the action of a received pulse signal, convert the continuous microwave signal into an initial microwave pulse signal.

[0037] The power beam splitter 13 is configured to split the initial microwave pulse signal into two paths to obtain a first microwave pulse signal and a second microwave pulse signal.

[0038] Furthermore, the microwave pulse signal generating device 10 may also include a switch 16, which includes a first switch 161 and a second switch 162. The first switch 161 can be used to control the opening and closing of the channel corresponding to the first microwave pulse signal, and the second switch 162 can be used to control the opening and closing of the channel corresponding to the second microwave pulse signal.

[0039] Continue reading Figure 2 Based on the above embodiments, the microwave pulse signal generating device 10 may further include an attenuator 14 configured to adjust the intensity of the second microwave pulse signal.

[0040] Continue reading Figure 2 Based on the above embodiments, the microwave pulse signal generating device 10 may further include a phase shifter 15 configured to adjust the phase of the second microwave pulse signal.

[0041] According to embodiments of this disclosure, the second microwave pulse signal, after passing through attenuator 14, phase shifter 15 and electro-optic modulator 40, can detune a small portion of the laser, generating a sideband as a frequency-shifted reference light, the intensity and phase of which are adjusted by the attenuator and phase shifter, respectively.

[0042] Continue reading Figure 2 Based on the above embodiments, the phase-resolved Brillouin spectroscopy system further includes:

[0043] Beam splitter 50 is configured to reflect the laser beam and a frequency-shifted reference beam, and transmit the frequency-shifted reference beam and Brillouin scattering beam. The laser beam is focused onto the target position on the sample by reflecting the laser beam.

[0044] Continue reading Figure 2 Based on the above embodiments, the phase-resolved Brillouin spectroscopy system further includes:

[0045] Polarizer 60 is configured to adjust the relative intensity of the frequency-shifted reference light and the Brillouin scattered light to optimize their interference. In other words, polarizer 60 enables better interference between the frequency-shifted reference light and the Brillouin scattered light.

[0046] Continue reading Figure 2 Based on the above embodiments, the phase-resolved Brillouin spectroscopy system further includes:

[0047] The Fabry-Perot interferometer 70 is configured to analyze the interference results of frequency-shifted reference light and Brillouin scattered light and output an interference signal at a preset frequency.

[0048] Based on the above embodiments, the frequency-shifted reference light and the Brillouin scattered light have the same frequency to ensure temporal coherence.

[0049] Based on the above embodiments, the quasi-particles include acoustic phonons or magnetic resonators; when the quasi-particles are magnetic resonators, the sample is a magnetic material and the quasi-particle excitation device 20 is a resonant cavity.

[0050] Furthermore, when the quasiparticle is a magnon, the phase-resolved Brillouin spectroscopy system also includes:

[0051] A magnetic field generating device is configured to apply a magnetic field to the magnetic material on the surface of a resonant cavity in order to study the phase correlation properties of magnetic excitation.

[0052] To more clearly illustrate the phase-resolved Brillouin spectroscopy system provided by the embodiments of this disclosure, a specific example is given below.

[0053] In this example, the wavelength of the spin wave generated by external excitation in yttrium iron garnet (YIG) is obtained using the phase-resolved Brillouin spectroscopy system provided in the embodiments of this disclosure. By interfering a reference light with inelastic scattered light using a reference light with a fixed phase, the interference signal contains the amplitude and phase information of the propagating spin wave. A pulse generator 11 generates a pulse signal with a pulse width of 1 μs and a pulse period of 10 μs, and inputs this pulse signal into a microwave source 12, converting the continuous microwave signal into a microwave pulse signal. The microwave pulse signal is split into two paths by a power beam splitter 13, one of which is used to excite a spin wave on the sample surface. The YIG is connected to the power beam splitter 13 via a quasi-particle excitation device 20 (such as an antenna or a coplanar waveguide resonant cavity). The frequency of the microwave pulse signal is equal to the resonant frequency of the quasi-particle excitation device 20 to ensure that the microwave signal is absorbed by the resonant cavity to the maximum extent, thereby locally exciting a spin wave in the YIG. When the locally excited spin wave in the YIG propagates to the laser spot and undergoes Brillouin scattering with the incident photon, Brillouin scattered light is generated. Another microwave pulse signal passes through attenuator 14, phase shifter 15, and electro-optic modulator 40 to detune a small portion of the laser, generating sidebands that serve as a frequency-shifted reference light. The Brillouin scattered light and the reflected frequency-shifted reference light interfere with each other, and after passing through beam splitter 50 and polarizer 60, they enter the Fabry-Perot interferometer 70.

[0054] To observe the interference signal, three conditions must be met between the frequency-shifted reference light and the Brillouin scattered light: First, the frequency-shifted reference light must have the same frequency as the Brillouin scattered light to ensure temporal coherence. Since the electro-optic modulator 40 and the resonant cavity such as the antenna or coplanar waveguide used to excite the spin wave are all driven by the same microwave source 12, this ensures the coherence of the frequency-shifted reference light and the Brillouin scattered light. Depending on the applied pump frequency, a small portion of the laser undergoes a red (blue) shift, producing sidebands. For frequency-shifted reference light generated by modulating the phase of the incident laser using the electro-optic modulator 40, since the selected modulation amplitude is very small, the intensity of the frequency-shifted reference light is on the same order of magnitude as the intensity of the Brillouin scattered light scattered by the spin wave. However, the intensity of the frequency-shifted reference light and the Brillouin scattered light is many orders of magnitude lower than the total laser intensity, so second-order effects such as the Brillouin scattering of the frequency-shifted reference light by the spin wave can be ignored. Second, the intensity of the frequency-shifted reference light must be comparable to the intensity of the Brillouin scattered light to obtain the maximum interference contrast. The intensity of the frequency-shifted reference light can be adjusted using a phase-stable, tunable attenuator 14 to match the intensity of the Brillouin scattered light. The phase of the frequency-shifted reference light can be adjusted using an adjustable phase shifter 15. Third, for the two beams to interfere, they must have the same polarization direction. The light inelastically scattered from the spin wave (Brillouin scattered light) has its polarization rotated by 90° relative to the incident light, while the frequency-shifted reference light is simply reflected from the sample surface, thus maintaining the polarization of the incident light. A polarizer 60 with a polarization plane orientation between 0° and 90° is placed in front of the Fabry-Perot interferometer 70. Changing the orientation of the polarizer 60 can adjust the relative intensity of the two beams to optimize their interference. When only switch 162 is closed, the frequency-shifted reference light signal is detected at Fabry-Perot interferometer 70; when only switch 161 is closed, the Brillouin scattered light signal is detected at Fabry-Perot interferometer 120; when both switches 161 and 162 are closed, the interference signal of the frequency-shifted reference light and the Brillouin scattered light is detected at Fabry-Perot interferometer 70.

[0055] By fixing the phase of the frequency-shifted reference light and moving the target position, the interference signal can be measured at different locations in space, revealing periodic oscillations in its intensity. The points of maximum intensity correspond to constructive interference, while the points of minimum intensity correspond to destructive interference. The distance between two adjacent points of maximum intensity corresponds to the wavelength of the excited spin wave.

[0056] The phase-resolved Brillouin spectroscopy system provided in this disclosure is simple and convenient to implement and operate, and the cost of building this phase-resolved Brillouin spectroscopy system is low. In addition to providing frequency information of spin waves in the frequency domain, this phase-resolved Brillouin spectroscopy system can also measure phase information while preserving spatial resolution. It can be used to study the formation of coherent states in magnon gases, the evolution of nonlinear spin wave eigenmodes, the phase variation of linear and nonlinear spin waves with their propagation distance (i.e., phase accumulation), the uniqueness of the spin wave excitation process, and the two-dimensional phase structure of spin beams in magnetically anisotropic media, etc., making it suitable for widespread use in laboratories. The phase-resolved Brillouin spectroscopy system provided by this invention has broad applicability and can be applied to the study of other quasiparticles (such as acoustic phonons).

[0057] Those skilled in the art will understand that the features described in the various embodiments of this disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments of this disclosure can be combined and / or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0058] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A phase-resolved Brillouin spectroscopy system, characterized in that, include: The microwave pulse signal generating device (10) includes a pulse generator (11), a microwave source (12), and a power beam splitter (13), wherein the pulse generator (11) is configured to generate a pulse signal; The microwave source (12) is configured to generate a continuous microwave signal and, under the action of the received pulse signal, convert the continuous microwave signal into an initial microwave pulse signal. The power beam splitter (13) is configured to split the initial microwave pulse signal into two paths to obtain a first microwave pulse signal and a second microwave pulse signal. The quasi-particle excitation device (20) is configured to carry the sample and absorb the first microwave pulse signal to locally excite quasi-particles in the sample; A laser source (30) is configured to generate a laser so that the laser is focused on a target position of the sample and undergoes Brillouin scattering with the quasiparticles to generate Brillouin scattered light; wherein the target position is adjustable; An electro-optic modulator (40) is configured to modulate the phase of the laser under the drive of the second microwave pulse signal to generate a frequency-shifted reference light, the frequency-shifted reference light interfering with the Brillouin scattered light, the frequency-shifted reference light and the Brillouin scattered light having the same frequency; Specifically, phase-resolved Brillouin spectroscopy is measured by adjusting the target position; The Fabry-Perot interferometer (70) is configured to analyze the interference result of the frequency-shifted reference light and the Brillouin scattered light and output an interference signal of a preset frequency.

2. The system according to claim 1, characterized in that, The microwave pulse signal generating device (10) further includes: The attenuator (14) is configured to adjust the intensity of the second microwave pulse signal.

3. The system according to claim 1 or 2, characterized in that, The microwave pulse signal generating device (10) further includes: A phase shifter (15) is configured to adjust the phase of the second microwave pulse signal.

4. The system according to claim 1, characterized in that, The system also includes: The beam splitter (50) is configured to reflect the laser and the frequency-shifted reference light, and transmit the Brillouin scattered light and the frequency-shifted reference light reflected back by the sample.

5. The system according to claim 1, characterized in that, The system also includes: A polarizer (60) is configured to adjust the relative intensity of the frequency-shifted reference light and the Brillouin scattered light to optimize the interference between the frequency-shifted reference light and the Brillouin scattered light.

6. The system according to claim 1, characterized in that, The quasi-particles include acoustic phonons or magnetorons; In the case where the quasiparticle is a magnetic oscillator, the sample is a magnetic material, and the quasiparticle excitation device (20) is a resonant cavity.

7. The system according to claim 6, characterized in that, When the quasi-particle is a magnon, the system further includes: A magnetic field generating device is configured to apply a magnetic field to the magnetic material on the surface of the resonant cavity.

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