CN112268861A - Dual-wavelength femtosecond pumping detection heat reflection system - Google Patents
Dual-wavelength femtosecond pumping detection heat reflection system Download PDFInfo
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Abstract
The application discloses a dual-wavelength femtosecond pumping detection heat reflection system, wherein an electro-optical modulator in the system is used for modulating a first pumping laser beam to obtain a second pumping laser beam; the frequency multiplier is used for adjusting the wavelength of the first detection laser beam to obtain a second detection laser beam; the delay device is used for delaying the second detection laser beam; the detector is used for receiving the detection reflected laser beam, performing photoelectric conversion processing on the detection reflected laser beam and generating a voltage signal, wherein the detection reflected laser beam is a second detection laser beam reflected by the sample to be detected; the first optical filter is used for filtering the laser beam input to the detector; the control device is used for converting the voltage signal into a heat reflection signal; and adjusting the delay time of the delay device to obtain heat reflection signals at different times, and analyzing and processing the heat reflection signals to obtain thermophysical parameters of the sample to be detected. By means of the method, the signal to noise ratio can be improved, and the measurement accuracy is improved.
Description
Technical Field
The application relates to the technical field of optics, in particular to a dual-wavelength femtosecond pumping detection heat reflection system.
Background
At present, film materials are widely applied to the fields of microelectronics, photoelectronics and the like, and when the micro devices work, extremely high heat flow density is generated, and the heat accumulation directly influences the working efficiency and reliability of the micro devices. In order to solve the heat dissipation problem, the heat transport property of the thin film material forming the micro device needs to be accurately represented so as to reveal the heat transport mechanism; the measurement can be carried out by means of an ultrashort pulse laser pumping detection technology, but the pumping light elimination efficiency of the existing laser pumping detection technology is low, so that the signal-to-noise ratio is low, and the measurement accuracy is insufficient.
Disclosure of Invention
The application provides a dual wavelength femto second pumping surveys heat reflection system can improve the SNR, improves measurement accuracy.
In order to solve the technical problem, the technical scheme adopted by the application is as follows: there is provided a dual wavelength femtosecond pumping detection heat reflection system comprising: the device comprises a light-emitting component, a first light-splitting device, an electro-optical modulator, a frequency multiplier, a delay device, a first optical filter and a control device, wherein the light-emitting component is used for generating laser beams; the first light splitting device is arranged on an emergent light path of the light emitting component and is used for splitting the laser beam into a first pumping laser beam and a first detection laser beam; the electro-optical modulator is arranged on a light path of the first pumping laser beam and is used for modulating the first pumping laser beam to obtain a second pumping laser beam, wherein the second pumping laser beam is incident to the surface of the sample to be detected; the frequency multiplier is arranged on the light path of the first detection laser beam and is used for adjusting the wavelength of the first detection laser beam to obtain a second detection laser beam, wherein the second detection laser beam is incident to the surface of the sample to be detected; the delay device is arranged on an emergent light path of the frequency multiplier and used for delaying the second detection laser beam; the detector is arranged on a reflection light path of the sample to be detected and used for receiving the detection reflection laser beam, carrying out photoelectric conversion processing on the detection reflection laser beam and generating a voltage signal, wherein the detection reflection laser beam is a second detection laser beam reflected by the sample to be detected; the first optical filter is arranged on a reflection light path of the sample to be detected and used for filtering the laser beam input to the detector so as to enable the detection reflection laser beam to be incident to the detector; the control device is connected with the delay device and the detector and is used for receiving the voltage signal output by the detector and converting the voltage signal into a heat reflection signal; and adjusting the delay time of the delay device to obtain heat reflection signals at different times, and analyzing and processing the heat reflection signals to obtain thermophysical parameters of the sample to be detected.
In order to solve the technical problem, the technical scheme adopted by the application is as follows: there is provided a dual wavelength femtosecond pumping detection heat reflection system comprising: the device comprises a light source component, an electro-optical modulator, a frequency multiplier, a delay device, a detector, a light source component, a first optical filter and a control device, wherein the light source component is used for generating a first pumping laser beam and a first detection laser beam; the electro-optical modulator is arranged on a light path of the first pumping laser beam and is used for modulating the first pumping laser beam to obtain a second pumping laser beam, wherein the second pumping laser beam is incident to the surface of the sample to be detected; the frequency multiplier is arranged on a light path of the first detection laser beam and is used for adjusting the wavelength of the first detection laser beam to obtain a second detection laser beam, wherein the second detection laser beam is incident to the surface of the sample to be detected, and the wavelength of the second detection laser beam is different from that of the second pumping laser beam; the delay device is arranged on an emergent light path of the electro-optical modulator and used for delaying the second pumping laser beam; the detector is arranged on a reflection light path of the sample to be detected and used for receiving the detection reflection laser beam, carrying out photoelectric conversion processing on the detection reflection laser beam and generating a voltage signal, wherein the detection reflection laser beam is a second detection laser beam reflected by the sample to be detected; the first optical filter is arranged on a reflection light path of the sample to be detected and used for filtering the laser beam input to the detector so as to enable the detection reflection laser beam to be incident to the detector; the control device is connected with the delay device and the detector and is used for receiving the voltage signal output by the detector and converting the voltage signal into a heat reflection signal; and adjusting the delay time of the delay device to obtain heat reflection signals at different times, and analyzing and processing the heat reflection signals to obtain thermophysical parameters of the sample to be detected.
Through the scheme, the beneficial effects of the application are that: frequency doubling is carried out on the first detection laser beam by using a frequency doubler, so that the wavelength of the first detection laser beam is changed, and a second detection laser beam is obtained; modulating the first pumping laser beam by using an electro-optical modulator to generate a second pumping laser beam; the wavelength of the second detection laser beam is different from that of the second pumping laser beam, so that dual-wavelength laser pumping detection can be realized; a double-modulation processing mode is adopted, the first detection laser beam and the first pumping laser beam are modulated, the problem that the stability of the equipment changes along with the environmental conditions such as temperature or humidity can be greatly solved, and the robustness and the precision of the system are improved; and usable first light filter carries out the filtering to the laser beam of inputing to the detector, guarantees only to detect reflection laser beam and can input the detector, prevents that the second from pumping the laser beam and to detecting the interference of reflection laser beam, can promote the SNR for measuring the degree of accuracy improves.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts. Wherein:
FIG. 1 is a schematic structural diagram of a first embodiment of a dual wavelength femtosecond pumping detection heat reflection system provided by the present application;
FIG. 2 is a schematic structural diagram of a second embodiment of a dual wavelength femtosecond pumping detection heat reflection system provided by the present application;
FIG. 3 is a schematic structural diagram of a time delay device in the embodiment shown in FIG. 2;
FIG. 4 is a schematic diagram of the connection of the light emitting assembly, spectrometer and third light directing assembly of the embodiment shown in FIG. 2;
FIG. 5 is a schematic diagram of the connection of the first light emitting device, the second light emitting device, and the third light directing assembly in the embodiment shown in FIG. 2;
FIG. 6 is a schematic structural diagram of a third embodiment of a dual wavelength femtosecond pumping detection heat reflection system provided by the present application;
FIG. 7 is a schematic structural diagram of a fourth embodiment of a dual wavelength femtosecond pumping detection heat reflection system provided by the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a first embodiment of a dual-wavelength femtosecond pumping detection heat reflection system provided by the present application, the system including: a light source assembly 101, an electro-optical modulator 102, a delay device 103, a frequency multiplier 104, a detector 105, a first optical filter 106 and a control device 107.
The light source assembly 101 is configured to generate a first pumping laser beam and a first detection laser beam, a wavelength of the first pumping laser beam may be the same as a wavelength of the first detection laser beam, the light source assembly 101 may include one laser or a plurality of lasers, the laser may be a femtosecond laser, for example, a wavelength of the femtosecond laser is 1040nm, a pulse width of the generated laser beam is 100fs, a temporal resolution of the system may be improved by using the femtosecond laser, and a spatial resolution of the system may be further improved.
The electro-optical modulator 102 is disposed on an optical path of the first pumping laser beam, and is configured to modulate the first pumping laser beam to obtain a second pumping laser beam; specifically, the second pumping laser beam is incident on the surface of the sample 200 to be measured, the sample 200 to be measured is an article requiring detection of a thermophysical parameter, such as a nano material or a micro-nano material, and the sample 200 to be measured may have a single-layer structure or a multi-layer structure, where the thermophysical parameter includes thermal conductivity, specific heat capacity, interfacial thermal conductivity, or interfacial thermal resistance.
A delay device 103 is disposed on the output optical path of the electro-optical modulator 102, and is configured to delay the second pumping laser beam; specifically, the delay device 103 adjusts its position after receiving the signal sent by the control device 107, so that the transmission time of the second pumping laser beam is changed, thereby adjusting the time when the second pumping laser beam reaches the sample 200 to be measured.
The frequency multiplier 104 is disposed on the optical path of the first detection laser beam, and is configured to adjust the wavelength of the first detection laser beam to obtain a second detection laser beam; specifically, the second detection laser beam is incident on the surface of the sample 200 to be measured, the wavelength of the second detection laser beam is different from the wavelength of the second pumping laser beam, and the second harmonic (i.e., the second detection laser beam) is generated by performing frequency doubling on the first detection laser beam, and the wavelength of the second detection laser beam may be half of the wavelength of the first detection laser beam; for example, the wavelength of the first detection laser beam is 1040nm, and the wavelength of the second detection laser beam is 520 nm; it will be appreciated that the first detection laser beam may also be modulated using a chopper to generate the second detection laser beam.
The detector 105 is arranged on a reflection light path of the sample 200 to be detected and is used for receiving the detection reflection laser beam, performing photoelectric conversion processing on the detection reflection laser beam and generating a voltage signal; specifically, the detector 105 may be a photodetector, and the detection reflected laser beam is a second detection laser beam reflected by the sample 200 to be measured.
The control device 107 is connected with the delay device 103 and the detector 105, and is used for receiving the voltage signal output by the detector 105 and converting the voltage signal into a heat reflection signal; and adjusting the delay time of the delay device 103 to obtain heat reflection signals at different times, and analyzing and processing the heat reflection signals to obtain thermophysical parameters of the sample 200 to be measured.
Further, laser pumping detection is divided into two steps, a first step: heating the surface of the sample 200 to be measured by using the second pumping laser, so that the surface of the sample 200 to be measured instantaneously generates a temperature rise of about several degrees, which is called a pumping process, the surface heat of the sample 200 to be measured is gradually transferred to the inside of the sample 200 to be measured, and the change of the surface temperature of the sample 200 to be measured changes the laser reflectivity of the surface of the sample 200 to be measured; the second step is that: the second detection laser beam is used for monitoring the attenuation process of the surface temperature of the sample 200 to be detected along with time, and the process is called a detection process, because the reflectivity of the surface of the sample 200 to be detected to the second detection laser beam is approximately in a linear relation with the temperature in a smaller temperature range, the change of the surface temperature of the sample 200 to be detected along with time can be obtained by monitoring the change of the intensity of the detection reflection laser beam along with time. The time for the second pumping laser beam to reach the surface of the sample 200 to be measured is controlled by the delay device 103, and the delay device 103 can change the optical path length of the second pumping laser beam, so that an adjustable optical path difference is provided between the second pumping laser beam and the second detection laser beam, so as to monitor the laser reflectivity of the sample 200 to be measured at different time points after heating.
The first optical filter 106 is disposed on the reflection optical path of the sample 200 to be detected, and is configured to filter the laser beam input to the detector 105, so that the detection reflection laser beam is incident to the detector 105; specifically, the first optical filter 106 may be a high-selectivity light-transmitting filter, and the first pumping laser beam, the second pumping laser beam, the first detection laser beam, and the second detection laser beam can be thoroughly filtered by using the first optical filter 106, so that only the detection reflection laser beam enters the detector 105, the problem of low signal-to-noise ratio in a conventional single-wavelength system is solved, and the measurement accuracy can be greatly improved.
The embodiment provides a dual-wavelength femtosecond pumping detection heat reflection system, which is characterized in that a frequency multiplier 104 is used for carrying out frequency multiplication on a first detection laser beam emitted by a light source assembly 101, so that the wavelength of the first detection laser beam is changed, and a second detection laser beam is generated; because the wavelength of the second detection laser beam is different from that of the second pumping laser beam, dual-wavelength laser pumping detection can be realized, and the laser beam input into the detector 105 can be filtered by using the first optical filter 106, so that only the detection reflection laser beam is input into the detector 105, the interference of pumping light on the detection light is prevented, the signal-to-noise ratio is favorably improved, nearly three orders of magnitude can be improved, and the measurement accuracy is improved; in addition, a double-modulation processing mode is adopted, the first detection laser beam and the first pumping laser beam are modulated, the problem that the stability of the equipment changes along with the environmental conditions such as temperature or humidity can be greatly solved, and the robustness and the precision of the system are improved; the ultrafast laser beam can interact with a sample 200 to be measured, and thermophysical property measurement of materials such as nano fluid, a solid-liquid interface, a porous medium, powder and the like is realized.
Referring to fig. 2, fig. 2 is a schematic structural diagram of a second embodiment of a dual-wavelength femtosecond pumping detection heat reflection system provided in the present application, in which the dual-wavelength femtosecond pumping detection heat reflection system in this embodiment includes, in addition to the devices in the first embodiment, further: a second optical filter 108, a first reflection assembly 109, a second light guide assembly 110, a third optical filter 111, a second light splitting device 112, a polarization direction adjusting device 113, a light combining assembly 114, and a focusing lens 115.
The light source assembly 101 includes: light emitting component 1011, third light directing component 1012, optical isolator 1013, flare straightening component 1014, first light directing component 1015 and first light splitting device 1016.
The light emitting element 1011 is used for generating a laser beam, and the laser beam emitted from the light emitting element 1011 can enter 1/2 wave plate (not shown in the figure), and the polarization direction is adjusted by 1/2 wave plate.
The third light guiding assembly 1012 is disposed on an exit light path of the light emitting assembly 1011, and is configured to reflect and/or transmit a laser beam, and the laser beam transmitted by the third light guiding assembly 1012 is incident on the first light splitting device 1016; specifically, the laser beam transmitted by the third light guiding component 1012 is incident to the optical isolator 1013.
The optical isolator 1013 is disposed on an exit light path of the light emitting element 1011 and controls the unidirectional propagation of the laser beam.
The flare correcting component 1014 is arranged on an emergent light path of the optical isolator 1013 and is used for correcting the laser beam output by the optical isolator 1013; specifically, since the spot of the laser beam emitted by the laser may be elliptical, the spot correction assembly 1014 is used to change the shape of the spot back to a perfect circle; further, the speckle correcting element 1014 includes a first cylindrical lens and a second cylindrical lens (not shown), the first cylindrical lens may be a concave mirror, and the second cylindrical lens may be a convex mirror.
The first light guiding assembly 1015 is disposed on an exit optical path of the flare correcting assembly 1014, and is used for guiding the laser beam output by the flare correcting assembly 1014 to the first light splitting device 1016.
A first light splitting device 1016 is disposed on an exit light path of the light emitting assembly 1011, for splitting the laser beam into a first pumping laser beam and a first detection laser beam; specifically, the first light splitting device 1016 is disposed on an exit light path of the first light guiding assembly 1015, and can split the laser beam exiting from the first light guiding assembly 1015; for example, the laser beam may be divided into a horizontally polarized laser beam and a vertically polarized laser beam, the vertically polarized laser beam may pass through the first optical splitting device 1016, and the horizontally polarized laser beam is reflected by the first optical splitting device 1016, the vertically polarized laser beam may be used as the first pump laser beam, and the horizontally polarized laser beam may be used as the first detection laser beam, the polarization directions of the two laser beams are perpendicular to each other, so that the first pump laser beam and the first detection laser beam are distinguished.
In a specific embodiment, a polarizer (not shown) may be further disposed on the outgoing light path of the first light guiding assembly 1015, and the polarizer is mounted on a rotatably adjustable adjusting frame (not shown), so that the ratio of the components of the laser beam in the horizontal direction and the vertical direction can be changed by rotating the polarizer, thereby changing the ratio of the intensities of the two laser beams to realize the distribution of different ratios.
The second filter 108 is disposed on the optical path of the first pumping laser beam, and is configured to filter the laser beam output by the first optical splitter 1016, so that the first pumping laser beam is incident on the electro-optical modulator 102; specifically, the second filter 108 is disposed on the reflected light path of the first light splitting device 1016.
The first reflection assembly 109 is disposed on an exit light path of the second optical filter 108, and is configured to reflect the first pumping laser beam output by the second optical filter 108 to the electro-optical modulator 102; after the first pump laser beam passes through the electro-optic modulator 102, the laser intensity will be loaded with a signal of a particular waveform and frequency to generate a second pump laser beam.
The control device 107 comprises a signal generator 1071, the signal generator 1071 is connected with the electro-optical modulator 102, the electro-optical modulator 102 is used for receiving the carrier signal generated by the signal generator 1071, and modulating the first pumping laser beam by using the carrier signal to obtain a second pumping laser beam; the penetration depth of the heat energy in the sample 200 to be measured is in positive correlation with the modulation frequency, and the heat penetration depth caused by the second pumping laser beam can be adjusted by changing the modulation frequency so as to measure the thermophysical property of the sample 200 to be measured; a smaller thermal penetration depth can be achieved using the electro-optic modulator 102 to enable measurement of interface thermal transport properties.
The delay device 103 includes an electronic control displacement platform 1031 and a second reflection component 1032 arranged on the electronic control displacement platform 1031, the electronic control displacement platform 1031 is connected to the control device 107, and is configured to receive the delay signal output by the control device 107, and adjust a position of the second reflection component 1032 on the electronic control displacement platform 1031 based on the delay signal, so as to adjust a time interval at which the second detection laser beam and the second pumping laser beam reach the sample 200 to be measured; specifically, as shown in fig. 3, the electrically controlled displacement platform 1031 includes a base 31 and a movable platform 32 disposed on the base 31, and the movable platform 32 can move on the base 31 along a horizontal direction and/or a vertical direction to move a second reflective component 1032 disposed on the movable platform 32, so as to adjust the optical path of the second pumping laser beam.
Further, as shown in fig. 2, the control device 107 further includes a motion controller 1072, the motion controller 1072 is connected to the movable platform 32 and is configured to send a delay signal to the movable platform 32 to make the movable platform 32 move along with the second reflective component 1032.
The second light guiding assembly 110 is disposed on the optical path of the first detection laser beam, and is configured to guide the first detection laser beam to the frequency multiplier 104; specifically, the second light guiding assembly 110 is disposed on a transmission light path of the first light splitting device 1016, and guides the first detection laser beam emitted from the first light splitting device 1016 to the frequency multiplier 104.
The third optical filter 111 is disposed on the output optical path of the frequency multiplier 104, and is configured to filter the laser beam output by the frequency multiplier 104, so that the second detection laser beam is incident on the second optical splitter 112, and the first detection laser beam can be filtered, thereby ensuring that only the second detection laser beam enters the second optical splitter 112.
The second optical splitter 112 is disposed on an exit optical path of the frequency multiplier 104, and is configured to reflect the second detection laser beam output by the frequency multiplier 104 to the light combining component 114, specifically, the second optical splitter 112 is disposed on an exit optical path of the third optical filter 111; the polarization direction adjusting device 113 is disposed on the optical path of the second beam splitter 112, and is configured to adjust the polarization direction of the second detection laser beam and the polarization direction of the detection reflected laser beam, and the detection reflected laser beam is transmitted to the second beam splitter 112 through the polarization direction adjusting device 113, and then transmitted to the detector 105 by the second beam splitter 112.
The light combining component 114 is disposed on the exit light path of the delay device 103 and the exit light path of the electro-optical modulator 102, and is configured to combine the second pumping laser beam and the second detection laser beam to obtain a combined laser beam, and inject the combined laser beam into the sample 200 to be measured, where the light combining component 114 may be a cold mirror. The focusing lens 115 is disposed on the light emitting path of the light combining component 114, and is configured to focus the combined laser beam onto the surface of the sample 200 to be measured, and the focusing lens 115 may be an objective lens.
In a specific embodiment, the polarization direction adjusting device 113 may be an 1/4 wave plate, assuming that the polarization direction of the second detection laser beam is a horizontal direction and the polarization direction of the second pumping laser beam is a vertical direction, the second detection laser beam emitted from the third optical filter 111 is reflected by the second optical splitter 112 to the 1/4 wave plate, the polarization direction is changed by 45 degrees, the second detection laser beam emitted from the 1/4 wave plate is incident to the light combiner 114, is emitted to the surface of the sample 200 to be detected through the light combiner 114 and the focusing lens 115, is reflected by the surface of the sample 200 to be detected to form a detection reflected laser beam, the detection reflected laser beam enters the 1/4 wave plate through the focusing lens 115 and the light combiner 114, the polarization direction is changed by 45 degrees, at this time, the polarization direction is changed by 90 degrees with respect to the second detection laser beam emitted from the third optical filter 111, that is, the polarization direction of the detection reflected laser beam exiting from the 1/4 wave plate is vertical, and at this time, the detection reflected laser beam is transmitted to the first optical filter 106 by the second optical splitter 112 after entering the second optical splitter 112, so as to distinguish the detection reflected laser beam from the second detection laser beam.
With continued reference to fig. 2, the control device 107 further includes an acquisition processing circuit 1073, and the acquisition processing circuit 1073 is connected to the detector 105, and is configured to adjust the heat reflection signal to obtain a real curve of the surface temperature of the sample 200 to be measured changing with time, and obtain the thermophysical property parameter by using the real curve.
Further, the acquisition processing circuit 1073 may be a lock-in amplifier, and may extract and amplify a useful signal through the lock-in amplifier, so as to obtain a decay curve (i.e., a real curve) of the surface temperature of the sample 200 to be measured changing with time, and then fit the decay curve (i.e., an ideal curve) of the surface temperature of the sample 200 to be measured changing with time, which is calculated by using the heat transfer model, so as to finally obtain an unknown thermophysical property parameter. Specifically, the actual value of the thermophysical parameter can be determined by continuously adjusting the value of the thermophysical parameter to minimize the error between the theoretical calculation result and the experimental measurement result of the temperature decay curve.
In a specific embodiment, the control device 107 further includes an electro-optical modulation driver (not shown), which may be an analog signal driver, and the electro-optical modulation driver may modulate the first pumping laser beam into a high-quality sine wave output by using the analog signal driver, and compared with the digital signal driver, the higher harmonic noise in the signal collected by the detector 105 is greatly reduced, so that the lock-in amplifier may operate at a low noise level in practical use, which is helpful to improve the signal-to-noise ratio.
With continued reference to fig. 2, the control device 107 further includes a processor 1074, which is connected to the signal generator 1071, the mobile controller 1072, and the acquisition processing circuit 1073, and is configured to control the signal generator 1071, the mobile controller 1072, and the acquisition processing circuit 1073, or receive signals sent by the signal generator 1071, the mobile controller 1072, or the acquisition processing circuit 1073; for example, the step length and time of movement of the electronic control displacement platform 1031 can be controlled, the frequency and voltage of the carrier signal output by the signal generator 1071 are controlled, and the integration time and data acquisition of the phase-locked amplifier are controlled, wherein the integration time indicates how long the phase-locked amplifier extracts signals such as average amplitude or phase and the like from the signals in a long time period, the longer the integration time is, the more beneficial the noise brought by the filtering environment is, but the longer the integration time is, the longer the time for acquiring data is, however, various devices have their own stable time, so that the increased data acquisition time may increase a lot of uncertainty, which is not beneficial to correctly obtaining the measurement result, and therefore, a proper integration time needs to be set; in addition, the collected data may be processed to obtain thermophysical parameters of the sample 200.
In a specific embodiment, as shown in fig. 4, the dual wavelength femtosecond pumping probe heat reflection system further includes: and a spectrometer 41, wherein the spectrometer 41 is disposed on the reflection light path of the third light guiding assembly 1012, and is used for collecting the spectrum of the laser beam reflected by the third light guiding assembly 1012 to detect the wavelength of the laser beam.
It is understood that the spectrum of the second pumping laser beam and the spectrum of the wavelength of the second detection laser beam may be collected, and by detecting the spectra, it may be determined whether the wavelength of the corresponding laser beam meets the requirements; in addition, the waveform of the laser beam can be detected by an oscilloscope to determine the stability of the laser beam.
In another embodiment, as shown in FIG. 5, the light emitting assembly 1011 can include a first light emitting device 51 and a second light emitting device 52, the first light emitting device 51 being for generating a first pumping laser beam; the second light emitting device 52 is for generating a first detection laser beam; the third light guiding assembly 1012 is disposed on the light emitting paths of the first light emitting device 51 and the second light emitting device 52, and is configured to transmit the first pumping laser beam to the first light splitting device 1016 and reflect the first detection laser beam to the first light splitting device 1016.
In this embodiment, the pumping light is filtered by the first optical filter 106, so that the influence of the pumping light on the measurement signal can be minimized; the second pumping laser beam and the second detection laser beam can be combined into a beam of collinear light through the light combination component 114, the collinear design enables debugging to be simpler, and the shape of a focused light spot is closer to a perfect circle; in addition, the frequency of the carrier signal can be adjusted to make the second pumping laser beam output by the electro-optical modulator 102 different, so that multi-frequency detection can be realized, and thermophysical parameters such as film thermal conductivity, specific heat capacity, interface thermal resistance and the like can be obtained at the same time.
Referring to fig. 6, fig. 6 is a schematic structural diagram of a third embodiment of a dual-wavelength femtosecond pumping detection heat reflection system provided by the present application, the system including: a light emitting component 601, a first light splitting device 602, an electro-optical modulator 603, a frequency multiplier 604, a delay device 605, a detector 606, a first optical filter 607 and a control device 608.
A first light splitting device 602 is disposed on an exit light path of the light emitting assembly 601, and is configured to split the laser beam into a first pumping laser beam and a first detection laser beam; specifically, the first light splitting device 602 may be a polarization light splitting prism, the vertically polarized laser beam may be reflected to the electro-optical modulator 603, and the horizontally polarized laser beam may be transmitted to the frequency doubler 604, so as to split the laser beam.
The electro-optical modulator 603 is disposed on a reflection light path of the first optical splitter 602, that is, the first optical splitter 602 is disposed on a light path of the first pumping laser beam, and is configured to modulate the first pumping laser beam to obtain a second pumping laser beam, and the second pumping laser beam is incident on the surface of the sample 200 to be measured.
The frequency multiplier 604 is disposed on the transmission light path of the first light splitting device 602, that is, the frequency multiplier 604 is disposed on the light path of the first detection laser beam, and is configured to adjust the wavelength of the first detection laser beam to obtain a second detection laser beam, and the second detection laser beam is incident on the surface of the sample 200 to be detected.
The delay device 605 is disposed on the outgoing light path of the frequency multiplier 604 and configured to delay the second detection laser beam; relative to the second pumping laser beam, the time of the second detection laser beam reaching the surface of the sample 200 to be measured can be controlled by the delay device 605, the moving precision of the delay device 605 can reach the micrometer level, and the precision of the corresponding delay time is in the femtosecond level, so that the heat transfer behavior in the nanosecond time range can be measured.
The detector 606 is disposed on a reflection light path of the sample 200 to be detected, and is configured to receive the detection reflection laser beam, perform photoelectric conversion processing on the detection reflection laser beam, and generate a voltage signal, where the detection reflection laser beam is a second detection laser beam reflected by the sample 200 to be detected.
The first optical filter 607 is disposed on the reflective optical path of the sample 200 to be detected, and is used for filtering the laser beam input to the detector 606, so that the detection reflective laser beam is incident to the detector 606; specifically, the first filter 607 may be a narrowband filter, and the pumping light (including the first pumping laser beam and the second pumping laser beam) and the detection light (including the first detection laser beam and the second detection laser beam) can be thoroughly filtered by using the first filter 607, so that only the detection reflection laser beam enters the detector 606, the problem of low signal-to-noise ratio in the conventional single-wavelength system is solved, the measurement accuracy can be greatly improved, and the efficiency of filtering the pumping light by the narrowband filter can reach 10-3To 10-4。
The control device 608 is connected to the delay device 605 and the detector 606, and is configured to receive the voltage signal output by the detector 606 and convert the voltage signal into a heat reflection signal; the delay time of the delay device 605 is adjusted to obtain the thermal reflection signals at different times, and the thermal reflection signals are analyzed to obtain the thermophysical parameters of the sample 200 to be measured.
In this embodiment, the wavelength of the second detection laser beam is different from the wavelength of the second pumping laser beam, so that dual-wavelength laser pumping detection can be realized; before the two beams of laser light reach the detector 606 after being reflected by the sample 200 to be measured, the second pumping laser beam can be filtered by using a narrow band filter, so that the problem of too low signal-to-noise ratio in a conventional single-wavelength system can be solved, the measurement precision can be greatly improved, and the accurate measurement of the surface reflectivity change of the sample 200 to be measured is realized.
Referring to fig. 7, fig. 7 is a schematic structural diagram of a fourth embodiment of a dual-wavelength femtosecond pumping detection heat reflection system provided in the present application, in which the dual-wavelength femtosecond pumping detection heat reflection system in this embodiment includes, in addition to the devices in the third embodiment, further: the optical isolator 609, the spot correction component 610, the first light guide component 611, the second optical filter 612, the first reflection component 613, the second light guide component 614, the third optical filter 615, the second beam splitter 616, the polarization direction adjusting component 617, the light combining component 618, and the focusing lens 619.
The optical isolator 609 is arranged on an emergent light path of the light-emitting component 601 and is used for controlling the unidirectional transmission of laser beams; specifically, the optical isolator 609 can ensure that the laser beam with a certain polarization direction can only pass through one side, and effectively prevent the reflected laser beam from entering the light-emitting component 601, thereby avoiding the situation that the light-emitting component 601 is unstable or even damaged due to overheating.
The flare correcting component 610 is disposed on an exit optical path of the optical isolator 609, and is used for correcting the laser beam output by the optical isolator 609.
The first light guiding assembly 611 is disposed on an exit light path of the flare correcting assembly 610, and is configured to guide the laser beam output by the flare correcting assembly 610 to the first light splitting device 602.
The first light splitting device 602 is disposed on the exit light path of the first light guiding assembly 611, and is configured to split the laser beam into a first pumping laser beam and a first detection laser beam; specifically, the first beam splitter 602 may split the laser beam into two beams, a first pumping laser beam and a first detection laser beam, at a certain energy ratio.
The second filter 612 is disposed on the optical path of the first pumping laser beam, and is configured to filter the laser beam output by the first optical splitter 602, so that the first pumping laser beam is incident to the electro-optical modulator 603; specifically, the first pumping laser beam exiting from the second filter 612 is incident on the first reflective element 613.
The first reflection element 613 is disposed on an exit light path of the second filter 612, and is configured to reflect the first pumping laser beam output by the second filter 612 to the electro-optical modulator 603.
The control means 608 comprises a signal generator 6081, the signal generator 6081 being connected to the electro-optical modulator 603, the electro-optical modulator 603 being configured to receive a carrier signal generated by the signal generator 6081, and to modulate the first pumping laser beam with the carrier signal to obtain the second pumping laser beam.
In a specific embodiment, a first beam expander (not shown) may be further disposed on the light exiting path of the electro-optical modulator 603, for expanding the beam diameter of the second pumping laser beam; specifically, since the larger the beam diameter, the smaller the divergence angle after propagating the same distance, the beam diameter of the second pump laser beam may be increased, for example, 2 times after passing through the first beam expander, in order to reduce the divergence of the second pump laser beam due to the longer path traveled.
A second light directing assembly 614 is disposed in the optical path of the first detection laser beam for directing the first detection laser beam to the frequency multiplier 604; the first detection laser beam can generate second harmonic wave through frequency doubling, the wavelength of the second harmonic wave is shortened to half of the original wavelength, and a second detection laser beam is obtained, and the second detection laser beam has the same frequency as the first detection laser beam and the pulse width close to the first detection laser beam, so that the dual-wavelength optical path design is realized.
The third filter 615 is disposed on an outgoing light path of the frequency multiplier 604 and is configured to filter the laser beam output by the frequency multiplier 604, so that the second detection laser beam is incident on the delay device 605, and the first detection laser beam can be prevented from entering the delay device 605.
The delay device 605 includes an electrically controlled displacement platform 6051 and a second reflection assembly 6052 disposed on the electrically controlled displacement platform 6051, the electrically controlled displacement platform 6051 is connected to the control device 608, and is configured to receive a delay signal output by the control device 608, and adjust a position of the second reflection assembly 6052 on the electrically controlled displacement platform 6051 based on the delay signal, so as to adjust a time interval between the second detection laser beam and the second pumping laser beam reaching the sample 200 to be measured.
Further, as shown in fig. 7, the control device 608 further includes a movement controller 6082, where the movement controller 6082 is connected to the electrically controlled displacement platform 6051, and is configured to send a delay signal to the electrically controlled displacement platform 6051, so that the electrically controlled displacement platform 6051 drives the second reflection assembly 6052 to move; specifically, the second detection laser beam emitted from the third filter 615 is incident on the second reflection assembly 6052 and then reflected by the second reflection assembly 6052 to the second beam splitter 616.
The delay time of the second detection laser beam can be controlled by a mobile controller 6082, and a 60cm ultra-long displacement platform can be used as the electric control displacement platform 6051; the second reflecting assembly 6052 includes two reflecting mirrors (not shown in the figure), and adopts a double-reflection optical path design, so that the time length of the measurable signal reaches 8ns seconds, the observable time range is widened, and meanwhile, the accuracy of measuring the thermophysical property of the sample 200 to be measured can be greatly improved.
Further, with the movement of the electric control displacement platform 6051, the optical path length of the second detection laser beam is gradually changed, and since the laser is gradually diffused in the propagation process, the light spot size of the second detection laser beam incident to the sample 200 to be measured is changed, and in order to reduce the influence of the change of the light spot size on the measurement, the second detection laser beam may be expanded by a second beam expander (not shown in the figure) before passing through the delay device 605, that is, the second beam expander is disposed on the exit optical path of the third optical filter 615, and the beam diameter of the second detection laser beam may be expanded, for example, 2 times or 3.3 times; the divergence angle of the second detection laser beam is reduced as much as possible by the beam expansion, thereby minimizing the effect of the retardation device 605 on the size of the optical spot.
In a specific embodiment, a beam reducer (not shown) may be further disposed on the outgoing light path of the delay device 605, for reducing the beam diameter of the second probing laser beam outputted from the delay device 605, such as to 1/4.
The second beam splitter 616 is disposed on the light emitting path of the delay device 605, and is configured to reflect the second detection laser beam delayed by the delay device 605 to the light combining component 618; a polarization direction adjusting device 617, disposed on the optical path of the second beam splitting device 616, for adjusting the polarization direction of the second detection laser beam and the polarization direction of the detection reflected laser beam; specifically, the detection reflected laser beam is transmitted to the second beam splitting device 616 through the polarization direction adjustment device 617, and then transmitted to the detector 606 by the second beam splitting device 616, and the polarization direction adjustment device 617 may be an 1/4 wave plate.
The light combining component 618 is disposed on the exit light path of the delay device 605 and the exit light path of the electro-optical modulator 603, and is configured to combine the second pumping laser beam and the second detection laser beam to obtain a combined laser beam, and inject the combined laser beam into the sample 200 to be measured.
The focusing lens 619 is disposed on an exit optical path of the light combining component 618, and is used for focusing the combined laser beam onto the surface of the sample 200 to be measured.
The second beam splitter 616 and the 1/4 wave plate in the detection optical path can separate the detection reflected laser beam reflected by the surface of the sample 200 to be detected from the optical path; specifically, the polarization direction of the second detection laser beam after passing through the retardation device 605 is the horizontal direction, and can completely pass through the second light splitting device 616; the second detection laser beam passes through the 1/4 wave plate twice before and after reaching the sample 200 to be measured, and the polarization direction of the second detection laser beam is changed from the horizontal direction to the vertical direction, and is completely reflected when returning to the second beam splitter 616. Since the signal carried by the second detection laser beam may be weak, even a small amount of the second pumping laser beam reaches the detector 606, the measurement signal is seriously affected, in order to reduce interference, the first optical filter 607 is disposed in front of the detector 606, the filtering efficiency of the first optical filter 607 for the second pumping laser beam is far higher than that depending on the polarization direction, and the first optical filter 607 may be a high selective transmittance optical filter.
The control device 608 further includes an acquisition processing circuit 6083, and the acquisition processing circuit 6083 is connected to the detector 606, and is configured to adjust the heat reflection signal to obtain a real curve of the surface temperature of the sample 200 to be measured changing with time, and obtain the thermophysical property parameter by using the real curve.
Further, the collecting and processing circuit 6083 may be a lock-in amplifier, and after the synthesized laser beam enters the detector 606, the corresponding light intensity signal is converted into a voltage signal and transmitted to the lock-in amplifier, and the lock-in amplifier may extract a useful signal; by varying the delay time, a time-varying curve of the heat reflection signal can be obtained.
In a specific embodiment, the carrier signal provided by the signal generator 6081 is a square wave signal, and the filtering principle of the lock-in amplifier is also realized by multiplying the signal to be measured and the reference square wave signal, so that the odd high frequency component carried by the square wave cannot be filtered by the lock-in amplifier, which affects the accuracy of the signal, and at this time, a filtering and amplifying circuit can be added between the detector 606 and the lock-in amplifier to filter the voltage signal output by the detector 606.
It is understood that the number of the delay devices 605 is not limited to one, and delay devices, which are referred to as a first delay device and a second delay device (not shown), may be disposed on both the detection optical path and the pumping optical path, and the moving ranges of the first delay device and the second delay device may be different, and may be set according to the specific application requirements, and are not limited herein; for example, the first delay device is a delay device on the detection optical path, and the displacement length of the first delay device is 60cm, and the second delay device is a delay device on the pumping optical path, and the displacement length of the second delay device is 5 cm; when solving the non-equilibrium heat transport problem a second delay means of 5cm may be used, whereas when solving the heat transport problem in the time range of hundreds of ps to ns a first delay means of 60cm may be used.
The control device 608 further includes a processor 6084, which is connected to the signal generator 6081, the motion controller 6082 and the acquisition processing circuit 6083, and is configured to control the signal generator 6081, the motion controller 6082 and the acquisition processing circuit 6083, or receive signals sent by the signal generator 6081, the motion controller 6082 and the acquisition processing circuit 6083; for example, the step length and time of the movement of the electrically controlled displacement platform 6051 can be controlled, the frequency and voltage of the carrier signal output by the signal generator 6081 can be controlled, and the integration time and data acquisition of the phase-locked amplifier can be controlled; in addition, the collected data may be processed to obtain thermophysical parameters of the sample 200.
In a specific embodiment, a removable aluminum mirror may be further added before the detector 606 to reflect the detection reflected laser beam to a CCD (Charge-coupled Device) camera connected to a computer, and the quality of the surface of the sample 200 to be detected and the degree of coincidence between the second pumping laser beam and the second detection laser beam may be observed by the CCD camera. In addition, if the facula coincidence degree is not satisfactory, the accessible controlling means 608 controls and closes optical subassembly 618 and take place the angle deflection, in order to change the facula of second pumping laser beam or the facula position of second detection laser beam, make the facula of second pumping laser beam and the accurate coincidence of the facula of second detection laser beam, can eliminate because ambient temperature changes, the problem that the facula coincidence degree that optical element vibration arouses reduces, realize automatic control facula coincidence degree, control accuracy is higher, and can observe the microstructure on the sample 200's surface that awaits measuring in real time, realize the accurate control of measuring position and the accurate measurement of microstructure thermal conductivity.
In this embodiment, the light combining component 618 and the second light splitting device 616 are used to design the light path returned from the original path, and the light path returned from the original path has the characteristics of simple and effective light path; meanwhile, before the second detection laser beam enters the detector 606, the second pumping laser beam is thoroughly filtered by using a high selective permeability filter, so that the signal to noise ratio can be improved, the measurement precision is greatly improved, the accurate measurement of the surface reflectivity change of the sample 200 to be measured is realized, the time length of the measurable signal is longer, the observable time range is widened, and the measurement accuracy is greatly improved.
The above description is only an example of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings, or which are directly or indirectly applied to other related technical fields, are intended to be included within the scope of the present application.
Claims (10)
1. A dual wavelength femtosecond pumping detection heat reflection system, comprising:
a light emitting assembly for generating a laser beam;
the first light splitting device is arranged on an emergent light path of the light emitting component and is used for splitting the laser beam into a first pumping laser beam and a first detection laser beam;
the electro-optical modulator is arranged on a light path of the first pumping laser beam and is used for modulating the first pumping laser beam to obtain a second pumping laser beam, wherein the second pumping laser beam is incident to the surface of a sample to be measured;
the frequency multiplier is arranged on the light path of the first detection laser beam and is used for adjusting the wavelength of the first detection laser beam to obtain a second detection laser beam, wherein the second detection laser beam is incident to the surface of the sample to be detected;
the delay device is arranged on an emergent light path of the frequency multiplier and is used for delaying the second detection laser beam;
the detector is arranged on a reflection light path of the sample to be detected and used for receiving the detection reflection laser beam, carrying out photoelectric conversion processing on the detection reflection laser beam and generating a voltage signal, wherein the detection reflection laser beam is a second detection laser beam reflected by the sample to be detected;
the first optical filter is arranged on a reflection light path of the sample to be detected and used for filtering the laser beam input to the detector so as to enable the detection reflection laser beam to be incident to the detector;
the control device is connected with the delay device and the detector and used for receiving the voltage signal output by the detector and converting the voltage signal into a heat reflection signal; and adjusting the delay time of the delay device to obtain heat reflection signals at different times, and analyzing and processing the heat reflection signals to obtain thermophysical parameters of the sample to be detected.
2. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 1,
the dual-wavelength femtosecond pumping detection heat reflection system further comprises an optical combination component, wherein the optical combination component is arranged on an emergent light path of the delay device and an emergent light path of the electro-optical modulator and used for combining the second pumping laser beam with the second detection laser beam to obtain a combined laser beam, and the combined laser beam is injected into the sample to be detected.
3. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 2,
the dual-wavelength femtosecond pumping detection heat reflection system also comprises a second light splitting device and a polarization direction adjusting device, wherein the second light splitting device is arranged on an emergent light path of the delay device and is used for reflecting a second detection laser beam delayed by the delay device to the light combination component; the polarization direction adjusting device is arranged on the light path of the second light splitting device and is used for adjusting the polarization direction of the second detection laser beam and the polarization direction of the detection reflection laser beam; wherein the detection reflected laser beam is transmitted to the second light splitting device through the polarization direction adjusting device, and is transmitted to the detector by the second light splitting device.
4. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 1,
the dual-wavelength femtosecond pumping detection heat reflection system further comprises a focusing lens, wherein the focusing lens is arranged on an emergent light path of the light combination component and used for gathering the combined laser beam to the surface of the sample to be detected.
5. The dual wavelength femtosecond pumping probe heat reflection system according to claim 1, further comprising:
the optical isolator is arranged on an emergent light path of the light-emitting component and used for controlling the unidirectional transmission of the laser beam;
and the light spot correction component is arranged on the emergent light path of the optical isolator and used for correcting the laser beam output by the optical isolator.
6. The dual wavelength femtosecond pumping probe heat reflection system according to claim 5, further comprising:
the first light guide component is arranged on an emergent light path of the facula correction component and used for guiding the laser beam output by the facula correction component to the first light splitter;
the second optical filter is arranged on a light path of the first pumping laser beam and is used for filtering the laser beam output by the first optical splitter so as to enable the first pumping laser beam to be incident to the electro-optical modulator;
and the first reflection assembly is arranged on an emergent light path of the second optical filter and used for reflecting the first pumping laser beam output by the second optical filter to the electro-optical modulator.
7. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 1,
the delay device comprises an electric control displacement platform and a second reflection assembly arranged on the electric control displacement platform, the electric control displacement platform is connected with the control device and used for receiving the delay signal output by the control device, and the position of the second reflection assembly on the electric control displacement platform is adjusted based on the delay signal so as to adjust the time interval between the second detection laser beam and the second pumping laser beam reaching the sample to be detected.
8. The dual wavelength femtosecond pumping probe heat reflection system according to claim 7, further comprising:
a second light guide member disposed on an optical path of the first detection laser beam for guiding the first detection laser beam to the frequency multiplier;
and the third optical filter is arranged on an emergent light path of the frequency multiplier and is used for filtering the laser beam output by the frequency multiplier so as to enable the second detection laser beam to be incident to the second reflection assembly.
9. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 1,
the control device comprises a collection processing circuit, the collection processing circuit is connected with the detector and is used for adjusting the heat reflection signal to obtain a real curve of the surface temperature of the sample to be detected changing along with time, and the thermophysical property parameter is obtained by utilizing the real curve.
10. The dual wavelength femtosecond pumping probe thermoreflectance system of claim 1,
the control device comprises a signal generator, the electro-optical modulator is connected with the signal generator and used for receiving a carrier signal generated by the signal generator, and the carrier signal is used for modulating the first pumping laser beam to obtain the second pumping laser beam.
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| CN106769881A (en) * | 2016-12-16 | 2017-05-31 | 中国科学院工程热物理研究所 | A kind of thermal conductivity scanning system that heat reflection technology is detected based on pumping |
| CN108107008A (en) * | 2017-12-11 | 2018-06-01 | 南京大学 | A kind of time domain heat reflection spectral measurement system |
| CN109085197A (en) * | 2018-06-29 | 2018-12-25 | 中国科学院电工研究所 | Heat reflection measuring system |
| CN109164136A (en) * | 2018-08-16 | 2019-01-08 | 中国科学院电工研究所 | Thermoelectricity transports parameter high pass system for measuring quantity and method |
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Application publication date: 20210126 |