Isothermal heating method, phase transition measurement method, and pulsed laser isothermal heating system

Abstract

The present application provides an isothermal heating method, a phase transition measurement method, and a pulse laser isothermal heating system. The isothermal heating method comprises: acquiring a target sample; and within a preset target duration, using a target laser to irradiate a target area on the target sample, so that the temperature of the target area is maintained at a preset temperature within a preset temperature error range. By means of the isothermal heating method, the accuracy and consistency of experimental results are ensured, thereby accurately determining the correspondence between the phase transition temperature and the phase transition time.

Description

An isothermal heating method, a phase transition measurement method, and a pulsed laser isothermal heating system. Technical Field

[0001] This application relates to the field of thermal analysis technology, and in particular to a method for isothermal heating using laser pulses, a method for measuring phase transitions of materials, and a pulsed laser isothermal heating system. Background Technology

[0002] The phase transition boundary between amorphous and crystalline states is an important scientific topic. Although a large number of amorphous materials exist, the number of materials with known temperature-time transition (TTT) curves is very limited. Traditional thermal analysis techniques, such as differential scanning calorimetry (DSC) and differential thermal analysis (DTA), are limited by heating and cooling rates and cannot operate on sub-microsecond timescales. Furthermore, measurements of rapidly crystallizing materials typically involve phase transitions occurring in the femtosecond to microsecond range. Therefore, traditional thermal analysis techniques are insufficient to match the nucleation rates of rapidly crystallizing materials.

[0003] Therefore, faster measurement methods are needed to study the isothermal nucleation process of amorphous materials on ultrafast timescales. Summary of the Invention

[0004] This application provides an isothermal heating method, a phase transition measurement method, and a pulsed laser isothermal heating system. By setting the minimum target duration to the femtosecond level, the phase transition duration of rapidly crystallizing materials is adapted, providing favorable support for the study of isothermal nucleation processes of amorphous materials on ultrafast timescales.

[0005] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0006] In a first aspect, embodiments of this application provide a method for isothermal heating using laser pulses, comprising acquiring a target sample; irradiating a target region on the target sample with a target laser for a preset target duration, thereby maintaining the temperature of the target region at a preset temperature within a preset temperature error.

[0007] According to some embodiments of this application, the minimum value of the target duration is in the microsecond, nanosecond, picosecond, or femtosecond range, and the temperature error is 1°C.

[0008] According to some embodiments of this application, the intensity waveform of the target laser includes multiple steps, and the laser intensity corresponding to the multiple steps decreases sequentially over time within the target duration.

[0009] According to some embodiments of this application, the target laser comprises a plurality of laser pulses, the intensity of which decreases over time within the target duration.

[0010] According to some embodiments of this application, the laser intensity corresponding to each step is predetermined based on the preset temperature.

[0011] According to some embodiments of this application, the pre-setting of the intensity of each laser pulse among the plurality of laser pulses further includes: determining the laser intensity corresponding to each step of the target laser based at least on the heat transfer characteristics of the target sample, the energy absorption characteristics of the target laser, and the preset temperature.

[0012] According to some embodiments of this application, the pre-setting of the laser intensity corresponding to each step in the target laser includes using finite element simulation technology to pre-set the laser intensity corresponding to each step in the target laser.

[0013] According to some embodiments of this application, the target area is the area on the target sample that has been irradiated by a laser.

[0014] According to some embodiments of this application, the target duration is 30fs-200μs.

[0015] Secondly, embodiments of this application provide a method for measuring the phase transition of a material, including obtaining a target sample, wherein the target sample is a target material; heating the target sample to a preset temperature based on the isothermal heating method described in any one of the first aspects, so as to determine the minimum phase transition time required for the target material to undergo a phase transition at the preset temperature.

[0016] According to some embodiments of this application, the preset temperature is lower than the melting point of the target material.

[0017] According to some embodiments of this application, determining the minimum phase transition time required for the target material to undergo the phase transition at the preset temperature includes heating the target sample at the preset temperature for a first duration using the isothermal heating method, and determining that the target sample has not undergone the phase transition; heating the target sample at the preset temperature for a second duration using the isothermal heating method, and determining that the target sample has undergone the phase transition, wherein the time difference between the first duration and the second duration is an integer multiple of the minimum value of the target duration; and determining that the minimum phase transition time for the target material at the preset temperature from the start of heating to the start of the phase transition is between the first duration and the second duration.

[0018] According to some embodiments of this application, it is determined whether the target material has undergone the phase transition based on reflectivity.

[0019] Thirdly, embodiments of this application provide a pulsed laser isothermal heating system, including a sample stage configured to hold a target sample; a laser located on one side of the sample stage, which emits a target laser onto the target sample for a preset duration to irradiate a target area on the target sample; and a control circuit communicatively connected to the laser and configured to control the laser to generate the required target laser. The isothermal heating system performs the method described in either the first or second aspect.

[0020] According to some embodiments of this application, the laser further includes a master oscillator power amplifier, wherein the optical wavelength of the master oscillator power amplifier is 1064 nm.

[0021] According to some embodiments of this application, the laser includes an arbitrary waveform generator, and the arbitrary waveform generator module operates at a high frequency.

[0022] According to some embodiments of this application, the laser provides tunable laser pulses with a pulse width range of 30 fs to 200 μs.

[0023] According to some embodiments of this application, the laser further includes a beam shaper for converting a Gaussian beam into a flat-top beam, thereby optimizing the energy distribution of the beam cross-section.

[0024] In summary, this specification provides an isothermal heating method, a phase transition measurement method, and a pulsed laser isothermal heating system that heats a target sample to a preset temperature and maintains it at a substantially constant temperature within a femtosecond timeframe. For example, the method disclosed in this specification can maintain the target sample at approximately the target temperature for less than 100 fs, with a temperature error of 1°C. Therefore, the heating method described in this specification can reduce the error in the time it takes for a material to undergo a phase transition at a given temperature to the femtosecond to submicrosecond level. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this specification, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 shows a schematic diagram of a pulsed laser isothermal heating system provided according to an embodiment of this specification;

[0027] Figure 2 shows a flowchart of a method for measuring the phase change of a material according to an embodiment of this specification;

[0028] Figure 3 shows a flowchart of a method for isothermal heating by laser pulses according to an embodiment of this specification;

[0029] Figure 4A shows the Raman spectrum of the Ge2Sb2Te5 (GST225) thin film provided according to the embodiments of this specification;

[0030] Figure 4B shows the refractive index (n) and extinction coefficient (k) spectra of GST225 in amorphous and crystalline states according to embodiments of this specification;

[0031] Figure 4C shows the attenuation coefficient (α) spectra of GST225 in amorphous and crystalline states according to embodiments of this specification;

[0032] Figure 4D shows the reflectance (R) spectra of GST225 in amorphous and crystalline states according to embodiments provided in this specification;

[0033] Figure 5A shows the Tt curves extracted from finite element simulation results under various laser pulse powers and pulse widths, provided by embodiments according to this specification.

[0034] Figure 5B shows the Tt curves extracted from finite element simulation results under various laser pulse powers and critical pulse widths, provided by embodiments according to this specification.

[0035] Figure 6A illustrates a strategy for constructing a TTT graph according to an embodiment of this specification;

[0036] Figure 6B shows a simulation of a 200 ns stepped laser waveform on an 800K isothermal platform provided according to an embodiment of this specification;

[0037] Figure 7A shows the reflectivity versus pulse width curves of the GST225 under isothermal heating at 750 K according to an embodiment of this specification;

[0038] Figure 7B shows the TTT diagram of the GST225 provided according to an embodiment of this specification.

[0039] The following is an explanation of the symbols in the attached figures:

[0040] Pulsed laser isothermal heating system 001; sample stage 1000; laser 2000; control circuit 3000; main oscillator power amplifier 100; semiconductor seed diode 200; focusing lens 800; intensity modulator 300; arbitrary waveform generator 400; fiber amplifier 500; pump control module 600; beam shaper 700. Embodiments of the present invention

[0041] The following description provides specific application scenarios and requirements for this specification, intended to enable those skilled in the art to make and use the contents of this specification. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this specification. Therefore, this specification is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0042] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not restrictive. For example, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” used herein may also include the plural forms. When used in this specification, the terms “comprising,” “including,” and / or “containing” mean that the associated integers, steps, operations, elements, and / or components are present, but do not exclude the presence of one or more other features, integers, steps, operations, elements, components, and / or groups, or that other features, integers, steps, operations, elements, components, and / or groups may be added to the system / method.

[0043] In this application, "X includes at least one of A, B, or C" means that X includes at least A, or X includes at least B, or X includes at least C. That is, X can include any combination of A, B, and C, or any combination of A, B, and C, as well as other possible content / elements. The arbitrary combination of A, B, and C can be A, B, C, AB, AC, BC, or ABC.

[0044] In this application, unless explicitly stated otherwise, the relationships between structures can be direct or indirect. For example, when describing "A is connected to B," unless it is explicitly stated that A and B are directly connected, it should be understood that A can be directly connected to B or indirectly connected to B. Similarly, when describing "A is on top of B," unless it is explicitly stated that A is directly above B (AB is adjacent and A is above B), it should be understood that A can be directly above B or indirectly above B (AB is separated by other elements, and A is above B). And so on.

[0045] Considering the following description, these and other features of this specification, as well as the operation and function of related structural elements, and the economy of assembly and manufacture of components, can be significantly improved. This description also includes all figures and text in the accompanying drawings, all of which form part of this specification. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to limit the scope of this specification. It should also be understood that the drawings are not drawn to scale.

[0046] Before describing the specific embodiments in this specification, we will first introduce the application scenarios to which the technical solutions provided in this specification are applicable.

[0047] The technical solutions provided in this specification are applicable to measuring the time required for a material to undergo a phase transition, such as the time required for a material to transform from an amorphous state to a crystalline state. The material can be any material with an arbitrary crystallization rate, especially ultrafast crystallizing materials. Ultrafast crystallizing materials are characterized by crystallization occurring on timescales from femtoseconds to microseconds, such as metallic glasses, amorphous semiconductor materials, nanocrystalline materials, perovskite materials, and other amorphous alloys. Specifically, metallic glasses can be Zr-based alloys and Fe-based alloys; amorphous semiconductor materials can be Ge-Sb-Te (GST) alloys and amorphous silicon (a-Si); nanocrystalline materials can be nanocrystalline metals and nanocrystalline alloys; and other amorphous alloys can be Al-based and Ti-based amorphous alloys. It is understood that other crystallizing materials (fast crystallizing materials, moderately crystallizing materials, slow crystallizing materials, and ultraslow crystallizing materials) are also within the scope of this specification.

[0048] Typically, heating is used to transform a material from an amorphous state to a crystalline state. Differential scanning calorimetry (DSC) can be used to measure the time required for this transformation. DSC typically uses a DSC instrument for heating, and its heating rate range can be... arrive Correspondingly, it is suitable for detecting phase transitions within tens of hours to milliseconds. However, the duration of phase transitions in ultrafast crystallizing materials is on the order of femtoseconds to microseconds. Obviously, this is beyond the detection capability of DSC equipment. Therefore, differential scanning calorimetry (DSC) cannot measure the duration of phase transitions in ultrafast crystallizing materials.

[0049] Another method for heating materials is laser heating. Lasers have the advantages of high energy density and fast sample heating speed. However, during the process of heating a sample with a laser, the temperature of the irradiated area of ​​the sample continues to rise as the energy of the laser pulse is deposited, making it impossible to accurately determine the relationship between phase transition temperature and phase transition time.

[0050] To ensure the accuracy and consistency of experimental results, it is necessary to maintain a constant or approximately constant temperature in the irradiated area of ​​the target sample. Therefore, this specification provides an isothermal heating method, a phase transition measurement method, and a pulsed laser isothermal heating system. Here, isothermal heating refers to heating the target object to a target temperature and then maintaining that temperature for a certain period of time (with an error less than a preset value).

[0051] According to the isothermal heating method described in this specification, after acquiring the target sample, the target region on the target sample is continuously irradiated with a target laser, so that the temperature of the target region is maintained at a preset temperature for a target duration. This means that, using the heating method described in this specification, the phase transition time of materials whose phase transition rate is greater than the target duration at the preset temperature can be determined. The method disclosed in this specification can maintain a substantially constant temperature on the femtosecond scale after heating the target sample to the preset temperature. For example, the method disclosed in this specification can maintain the target sample at approximately the target temperature for a femtosecond scale (e.g., less than 100 fs), with a temperature error of 1°C. Therefore, using the heating method described in this specification, the error in measuring the phase transition time of a material at a certain temperature can be reduced to the femtosecond to microsecond scale. Furthermore, the method described in this specification can also be used to measure the phase transition time of materials with phase transition times on the femtosecond to microsecond scale.

[0052] Figure 1 shows a schematic diagram of a pulsed laser isothermal heating system according to an embodiment of this specification. As shown in Figure 1, the pulsed laser isothermal heating system 001 (PLIHS) can refer to a system that uses a pulsed laser to achieve isothermal heating of materials. The pulsed laser isothermal heating system 001 may include a sample stage 1000, a laser 2000, and a control circuit 3000.

[0053] The sample stage 1000 is the location where the pulsed laser isothermal heating system 001 holds the sample. The sample stage 1000 can fix the sample to be heated and precisely control its position. Specifically, the sample stage 1000 can have multi-dimensional movement capabilities; for example, it can move precisely in the X, Y, and Z directions. This allows the sample to be accurately positioned in three-dimensional space so that the laser pulses output from the laser 2000 can precisely heat the area on the sample to be heated.

[0054] The laser 2000, located on one side of the sample stage 1000, is the core component of the pulsed laser isothermal heating system 001. It provides precisely controllable laser pulses to heat the target sample. The laser pulses have high energy density, enabling rapid heating of the target sample within a short time when irradiated. Specifically, during operation, the laser 2000 emits a target laser beam towards the sample stage 1000 to irradiate a target area on the sample. The duration (pulse width) of the target laser is adjustable. For example, the duration can range from femtoseconds to microseconds. For instance, the laser 2000 can provide an adjustable pulse width from 30 fs to 200 μs. As an application example, the laser 2000 can accurately reproduce complex waveforms derived from finite element simulations with high temporal precision.

[0055] The laser 2000 features a programmable amplitude waveform. Specifically, the laser 2000 allows users to customize the amplitude waveform of laser pulses through programming. Furthermore, the laser 2000 can generate laser pulses with specific waveforms, such as lasers with monotonically decreasing intensity or a stepped waveform, thereby achieving precise control over the temporal distribution of laser energy.

[0056] Laser 2000 includes a master oscillator power amplifier 100 (Tailored pulse generating module, MOPA), a semiconductor seed diode 200, a focusing lens 800, and control circuitry (not shown). Additionally, laser 2000 may also include one or more of an intensity modulator 300, an arbitrary waveform generator 400 (AWG), a fiber amplifier 500, a pumping control module 600, or a beam shaper 700.

[0057] The master oscillator power amplifier 100 can emit laser light of a target wavelength. The wavelength of the laser can be any wavelength that satisfies the technical solutions described in this specification. In some embodiments, the wavelength of the light emitted by the master oscillator power amplifier 100 is 1064 nm, meaning that the master oscillator power amplifier 100 can generate laser pulses with a wavelength of 1064 nm. Furthermore, the shape of the laser pulses generated by the master oscillator power amplifier 100 can be any shape, such as rectangular, Gaussian, or other specific shapes.

[0058] The master oscillator power amplifier 100 includes a low-power master oscillator and a high-power power amplifier. The master oscillator can be optically connected to the power amplifier. The optical connection method can be fiber optic coupling or free-space coupling, which is not limited here. The low-power master oscillator can be used to generate a low-power seed light A. Seed light A is transmitted to the input of the power amplifier via fiber optic coupling or free-space coupling. The power amplifier receives the transmitted seed light A and amplifies it to the required power level.

[0059] The semiconductor seed diode 200 is a type of semiconductor laser, typically made using diode materials such as GaAs and InGaAs. The semiconductor seed diode 200 can directly generate seed light B, which possesses high output power and a small size. The semiconductor seed diode 200 can be used in conjunction with a master oscillator. Specifically, seed light A and seed light B can be combined to leverage their respective advantages, resulting in a seed light C with high stability, good beam quality, high power, and a compact size. The beam combining of seed light A and seed light B can be achieved using a beam combiner, a polarization beam splitter, or optical elements.

[0060] The intensity modulator 300 is an optical device used to modulate the intensity of an optical signal. Located after the semiconductor seed diode 200, the intensity modulator 300 modulates the intensity of the seed light C. Specifically, the intensity modulator 300 includes an input terminal and an output terminal. The input terminal receives the seed light C after it has been combined. After modulating the seed light C, the intensity modulator 300 outputs the modulated seed light C from the output terminal. The intensity modulator 300 can be an electro-optic modulator (EOM), an acousto-optic modulator (AOM), or other types of modulators, and is not limited thereto.

[0061] The arbitrary waveform generator 400 is a signal source capable of generating arbitrary waveforms. The signal generated by the arbitrary waveform generator 400 is used to drive the intensity modulator 300. In other words, the intensity modulator 300 can modulate the intensity of the seed light C according to the signal generated by the arbitrary waveform generator 400, achieving precise control over the waveform of the seed light C. The arbitrary waveform generator 400 module operates at a high frequency. Specifically, the operating frequency of the arbitrary waveform generator 400 module is close to 8 GHz.

[0062] With the cooperation of the low-power master oscillator in the master oscillator power amplifier 100, the semiconductor seed diode 200, the power amplifier, the forced modulator, and the arbitrary waveform generator 400, the pulsed laser isothermal heating system 001 can output laser pulses that maintain good beam quality and pulse characteristics.

[0063] Fiber optic amplifier 500 is used to enhance the intensity of seed light C to overcome its attenuation during long-distance transmission. Fiber optic amplifier 500 can be connected in series with intensity modulator 300. Seed light C, modulated by intensity modulator 300, can then enter fiber optic amplifier 500 to enhance its intensity. Fiber optic amplifier 500 can be an erbium-doped fiber amplifier 500, a Raman fiber amplifier 500, a semiconductor optical amplifier, or other types of fiber optic amplifier 500; no limitation is made herein.

[0064] The fiber amplifier 500 may include pump light. The pump light can be an energy source used to excite the gain medium in the fiber amplifier 500, enabling particles in the medium to transition from the ground state to the excited state, thereby amplifying the passing seed light C.

[0065] The pump control module 600 is used to manage and control the pump light in the fiber amplifier 500. Specifically, the pump control module 600 can ensure that the fiber amplifier 500 receives appropriate energy input by controlling the power output of the pump light source, thereby maintaining a stable gain level. The pump control module 600 can also prevent excessive pump power from damaging the fiber amplifier 500 by monitoring the status of the pump light. Furthermore, the pump control module 600 can dynamically adjust the intensity of the pump light to adapt to control requirements under different conditions.

[0066] A beam shaper 700, located after the fiber amplifier 500, is an optical element used to modify the cross-sectional intensity distribution of the light beam. The beam shaper 700 can be used to improve the quality of the seed beam C, transforming it from a Gaussian beam to a top-hat beam. Specifically, the seed beam C enhanced by the fiber amplifier 500 has a Gaussian intensity distribution. This means that the seed beam C is brightest at the center, with the intensity gradually decreasing away from the center. This distribution leads to uneven energy distribution. A top-hat beam, on the other hand, means that the intensity distribution of the beam is relatively uniform within a certain area, i.e., the intensity difference between the central and peripheral regions is small. This distribution provides a more uniform energy distribution. Therefore, to optimize the energy distribution of the beam cross-section and make the energy distribution of the seed beam C more uniform, the beam shaper 700 is used to transform the seed beam C from a Gaussian distribution to a top-hat beam. The beam shaper 700 can be a diffractive optical element (DOE), a microlens array (MLAs), a specially designed lens, a free-space optical element, or other type of beam shaper 700, and is not limited thereto.

[0067] A focusing lens 800 is located after the beam shaper 700 and is used to focus the seed light C, which has been transformed by the beam shaper 700, onto a very small focal region, thereby outputting the seed light C as a high-energy-density laser pulse. The focusing lens 800 can be a spherical lens, aspherical lens, cylindrical lens, compound lens, or other type of focusing lens 800, and is not limited thereto. The focusing lens 800 is located in front of the sample stage 1000, so that the laser pulse output from the focusing lens 800 can act on the sample on the sample stage 1000.

[0068] The control circuit 3000 coordinates and controls various components of the pulsed laser isothermal heating system 001, such as the master oscillator power amplifier 100, semiconductor seed diode 200, intensity modulator 300, arbitrary waveform generator 400, fiber amplifier 500, pump control module 600, beam shaper 700, focusing lens 800, sample stage 1000, etc. Specifically, the control circuit 3000 can trigger the laser 2000 to generate the target laser and adjust the frequency (i.e., pulse width) and repetition rate (i.e., the number of pulses generated per unit time) of the target laser. The control circuit 3000 can also adjust the energy level of the target laser. Furthermore, the control circuit 3000 can synchronize the operation of various components. For example, when using the intensity modulator 300, beam shaper 700, or other optical elements, the control circuit 3000 needs to ensure that the operation of these components is coordinated with the generation of the seed light C. In addition, the control circuit 3000 can provide a user interface, allowing the operator to set parameters, monitor system status, and diagnose problems. This can be achieved through a touchscreen, buttons, or other forms of human-machine interface.

[0069] This specification does not limit the type of control circuit 3000. Specifically, control circuit 3000 can be at least one of the following: microcontroller, digital signal processor (DSP), programmable logic controller (PLC), field-programmable gate array (FPGA), microprocessor, or embedded system.

[0070] Figure 2 shows a flowchart of a material phase transition measurement method P200 provided according to an embodiment of this specification. The pulsed laser isothermal heating system 001 described above can perform the material phase transition measurement method P200. Specifically, the control circuit 3000 can coordinate with other components in the system 001 to perform the method P200.

[0071] As shown in Figure 2, the phase transition measurement method P200 for materials may include steps S210 and S220.

[0072] S210: Obtain the target sample, wherein the target sample is the target material.

[0073] The target material is the material to be measured for phase transition. Before the phase transition measurement, the target sample is amorphous. The target material can be a material whose phase transition time is in the range of femtoseconds to microseconds, or a material whose phase transition time is longer than the range of femtoseconds to microseconds. This application uses a material whose phase transition time at a certain temperature is in the range of femtoseconds to microseconds as an example for illustration.

[0074] Materials undergoing phase transitions in the femtosecond to microsecond range are primarily certain types of phase transition materials, especially those capable of completing the transition from an amorphous to a crystalline state in an extremely short time. These materials typically possess very high nucleation rates and rapid grain growth capabilities, enabling them to complete the phase transition process in an exceptionally short period. Typical examples include certain amorphous metal alloys (such as Zr-based alloys and Fe-based alloys) and phase transition memory materials (such as Ge-Sb-Te alloys).

[0075] The methods for obtaining the target material include, but are not limited to, chemical co-precipitation, physical vapor deposition (PVD), chemical vapor deposition (CVD), melt spinning, powder metallurgy, and sol-gel methods. Those skilled in the art should understand that other methods for obtaining the target material are also within the scope of this specification.

[0076] S220: The target sample is heated to the preset temperature by isothermal heating with laser pulses to determine the minimum phase transition time required for the target material to undergo a phase transition at the preset temperature.

[0077] Laser pulse heating using the pulsed laser isothermal heating system 001 can achieve heating rates in the femtosecond to microsecond range. Specifically, the pulsed laser isothermal heating system 001 can briefly irradiate the target sample with high-energy-density laser pulses, instantly raising the temperature of the target sample. Rapid heating of the target sample by the pulsed laser isothermal heating system 001 can transform the target sample from an amorphous state to a crystalline state after a period of time. Specifically, as mentioned above, the target sample is in an amorphous state. Through rapid heating, the target sample can absorb a large amount of energy in a very short time, causing the atoms or molecules inside the target sample to rearrange, thereby transforming it into a crystalline state.

[0078] During laser pulse heating of a sample using the pulsed laser isothermal heating system 001, the temperature of the irradiated area continuously increases with the energy deposition of the laser pulse, making it impossible to accurately determine the correlation between phase transition temperature and phase transition time. Therefore, to ensure the accuracy and consistency of experimental results, it is necessary to maintain a constant or approximately constant temperature in the irradiated area of ​​the target sample. To achieve this, this specification provides the following method for isothermal heating using laser pulses.

[0079] Figure 3 shows a flowchart of a method P300 for isothermal heating by laser pulses according to an embodiment of this specification. A pulsed laser isothermal heating system 001 (or "system 001") can execute the method P300 for isothermal heating by laser pulses. Specifically, a control circuit 3000 can coordinate other components in the system 001 to execute the method P300.

[0080] As shown in Figure 3, the isothermal heating method P300 using laser pulses may include steps S310 and S320.

[0081] S310: Obtain the target sample.

[0082] In this step, the operator of system 001 or the control circuit of system 001 controls the transfer mechanism to place the target sample on the sample stage 1000.

[0083] The target sample in step S310 is the same as the target sample in step S210. Furthermore, the methods for obtaining the target sample in step S310 and step S210 are also the same, and will not be repeated here.

[0084] S320: Within a preset target duration, the target region on the target sample is continuously irradiated with a target laser, so that the temperature of the target region is maintained at a preset temperature within a preset temperature error. In some embodiments, the target duration is in the microsecond, nanosecond, femtosecond, or picosecond range. For example, if the minimum target duration is less than 100 fs, the temperature error is 1°C.

[0085] A target laser refers to a laser of a specific intensity set within a target duration to achieve a preset temperature. The target laser can be a single laser pulse or multiple laser pulses emitted continuously. When the target laser is a single laser pulse, it acts on the target area of ​​the target sample with a predetermined waveform intensity within the target duration. When the target laser is multiple laser pulses emitted continuously, multiple laser pulses are emitted continuously within the target duration and act sequentially on the target area of ​​the target sample.

[0086] The pulsed laser isothermal heating system 001 isothermally heats the target area within the target duration, thus completing the heating process. When the target laser is a single laser pulse, the target duration is the pulse width of the target laser. When the target laser consists of multiple continuously emitted laser pulses, the target duration is the sum of the pulse widths of the multiple laser pulses. Specifically, when multiple laser pulses continuously irradiate the target area without interval, the target duration is the sum of the irradiation times of the multiple laser pulses, that is, the target duration is the sum of the pulse widths of the multiple laser pulses. For ease of description, the following explanation uses a single laser pulse as an example.

[0087] The pulse width range of the pulsed laser isothermal heating system 001 determines the target duration. As mentioned above, the pulsed laser isothermal heating system 001 provides an adjustable pulse width from 30 fs to 200 μs, and the accuracy achievable for duration adjustment is in the femtosecond to microsecond range. That is, the pulse width range of the pulsed laser isothermal heating system 001 is 30 fs to 200 μs, and the pulse width can be adjusted in femtosecond to microsecond steps. Therefore, the minimum target duration can be 30 fs, meaning the minimum target duration is less than 100 fs. It is understood that the target duration can be manually set according to actual needs and is not limited here.

[0088] In some embodiments, the minimum target duration may be less than 50 fs. In some embodiments, the minimum target duration may be less than 150 fs. In some embodiments, the minimum target duration may be less than 200 fs. In some embodiments, the minimum target duration may be less than 250 fs. And so on, in some embodiments, the minimum target duration may be less than 0.5 ns.

[0089] In some embodiments, the target duration ranges from 30 fs to 200 μs. In some embodiments, the target duration ranges from 50 fs to 200 μs. In some embodiments, the target duration ranges from 100 fs to 200 μs. In some embodiments, the target duration ranges from 150 fs to 200 μs. In some embodiments, the target duration ranges from 200 fs to 200 μs. In some embodiments, the target duration ranges from 250 fs to 200 μs. And so on, in some embodiments, the target duration ranges from 0.5 ns to 200 μs.

[0090] When the duration of laser irradiation on a target is in the femtosecond to microsecond range, this technique can be used to detect ultrafast crystallization materials with phase transition times in the femtosecond to microsecond range, providing strong support for scientific research and technological progress in related fields.

[0091] When a target laser irradiates a target sample, the area on the sample irradiated by the target laser can be called the target region. The area of ​​the target region can be on the order of square millimeters to square centimeters, for example, 0.5 mm. 2 1mm 2 1.5 mm 2 2 mm 2 0.5 cm 2 1cm 2 1.5 cm 2 2 cm 2 ,etc.

[0092] Within the preset target duration, the temperature of the target region remains at the preset temperature. This preset temperature can be set according to experimental requirements; for example, it refers to a specific temperature that the target sample is expected to reach and maintain in order to measure the time required for a phase transition. For instance, this preset temperature could be 888K, 800 K, 750 K, 700 K, 650 K, and 600 K, etc. It is understood that the preset temperature in the P300 step of the isothermal heating method using laser pulses can be set according to the specific application scenario and is not limited here.

[0093] It should be noted that, in reality, an absolutely constant temperature is impossible. Therefore, the preset temperature in this application refers to the temperature range [T-ε, T+ε] within a specified temperature T plus or minus a certain error ε. Maintaining a constant temperature / keeping at the preset temperature means maintaining the temperature within the temperature range [T-ε, T+ε]. That is, the temperature in the target area can be maintained near the preset temperature, and the difference between the actual temperature of the target area and the preset temperature remains within the preset temperature error. For example, in some embodiments, maintaining a constant temperature / keeping at the preset temperature means that the temperature error ε is 1°C, that is, the maximum allowable difference between the actual temperature of the target area and the preset temperature is ±1°C. For example, if the preset temperature is 750 K (476.85°C), then maintaining the actual temperature between 475.85°C and 477.85°C is considered maintaining a constant temperature / keeping at the preset temperature. In some embodiments, the temperature error ε is 0.9°C. In some embodiments, the temperature error ε is 0.7°C. In some embodiments, the temperature error ε is 0.5°C. In some embodiments, the temperature error ε is 0.3°C. In some embodiments, the temperature error ε is 0.1°C.

[0094] After determining the preset temperature, system 001 then determines the intensity of the target laser based on that preset temperature. That is, in order to achieve constant temperature heating at the preset temperature, system 001 next needs to determine the intensity of the target laser so that the target laser is sufficient to maintain the thermal balance in the target area at that time, thereby maintaining the temperature of the target area at the preset temperature.

[0095] When a high-energy target laser pulse irradiates a target area of ​​a sample, even if the sample material is opaque, the laser will still penetrate a certain thickness of the sample, and its energy will be absorbed by the target area. The target area's temperature rises due to the absorption of the target laser's energy. In the initial heating phase, the target laser rapidly heats the target area to the target temperature. As the temperature rises, heat conduction occurs between the target area and its surroundings. To maintain thermal equilibrium in the target area, continuous heating with the target laser is necessary. Initially, the temperature difference between the target area and its surroundings is large, resulting in rapid heat conduction and heat loss from the target area. To maintain thermal equilibrium in the target area, the subsequent target laser intensity remains at a high level; however, as time progresses, the temperature of the surrounding areas gradually increases, the heat conduction rate between the target area and its surroundings slows down, and heat loss from the target area decreases. At this point, the energy input from the target laser to maintain thermal equilibrium in the target area also decreases. Therefore, the intensity of the target laser decreases over time within the target duration. For example, if the intensity of the target laser is a stepped waveform, the intensity of the laser corresponding to each step in the target laser decreases sequentially within the target duration; if the target laser includes multiple laser pulses, the intensity of the multiple laser pulses decreases over time within the target duration.

[0096] Next, this application will be described by taking the intensity of the target laser as a stepped waveform as an example.

[0097] After the target laser heats the target area to the target temperature, the laser intensity of the target laser needs to decay with time within the target duration to maintain a constant temperature in the target area. Specifically, the target laser first irradiates the target sample at a laser intensity of W1 for a duration of t1 in the first stage (i.e., when the laser intensity is at the first step). The temperature of the target area will continue to rise until it reaches the preset temperature and remains at the preset temperature within the duration of t1, that is, within the temperature range [T - ε, T + ε]. Before the temperature of the target area exceeds the preset temperature, the first stage ends. At this time, it comes to the second stage (i.e., when the laser intensity is at the second step), and the target laser irradiates the target sample at a laser intensity of W2 for a duration of t2, where W2 < W1. At the beginning of this stage, because the energy input in the second stage is less than that in the first stage, the temperature of the target area will first decrease within the temperature range [T - ε, T + ε]. However, as the temperature of the surrounding area rises, the heat dissipation rate of the target area gradually decreases, and due to the cumulative effect of laser pulses, the final heat dissipation rate is lower than the heating rate of the target laser. Therefore, the temperature of the target area will instead rise. In the second stage, the temperature of the target area will remain within the temperature range [T - ε, T + ε]. The critical duration is defined as the maximum pulse duration that enables the target sample to maintain thermal equilibrium at the preset temperature [T - ε, T + ε]. Exceeding the critical duration, the temperature of the target sample will rise above the temperature range [T - ε, T + ε]. Therefore, in order to keep the target sample at the preset temperature, the duration of the second stage, t2, is set to be equal to or less than this critical duration. And so on, after the second stage, it continues to enter the third stage (i.e., when the laser intensity is at the third step). In the third stage, the target laser irradiates the target sample at a laser intensity of W3 for a duration of t3, and in the fourth stage, the target laser irradiates the target sample at a laser intensity of W4 for a duration of t4... And so on, until the laser intensity of the target laser is reduced to W n . It can be understood that W1 > W2 > W3 >... > W n .

[0098] The laser intensity corresponding to each step in the target laser can be determined by a combination of factors. Specifically, pre-setting the laser intensity corresponding to each step in the target laser includes: determining the laser intensity corresponding to each step in the target laser based at least on the thermal transfer characteristics of the target sample, the energy absorption characteristics of the target laser, and the preset temperature. The thermal transfer characteristics of the target sample can include physical parameters such as thermal conductivity, specific heat capacity, and thermal diffusivity. The thermal transfer characteristics of the target sample determine the temperature change and heat distribution after absorbing energy. Specifically, a high specific heat capacity will cause the temperature of the target sample to rise more slowly when absorbing the same amount of energy. High thermal conductivity will result in a more uniform temperature distribution inside the target sample. High thermal conductivity leads to rapid heat conduction, resulting in a more uniform heat distribution within the sample. High thermal diffusivity means that heat diffuses quickly within the sample, resulting in a more uniform temperature distribution.

[0099] The energy absorption characteristics of a target laser refer to the absorption efficiency of the target sample for the energy corresponding to each step of the target laser beam. This depends on the material properties of the target sample, such as extinction coefficient, reflectivity, attenuation coefficient, and scattering coefficient. The material properties of the target sample determine how much energy from the target laser is absorbed, thus affecting the temperature change. Specifically, the higher the extinction coefficient, the more energy the sample absorbs, and the faster the temperature rises. The higher the reflectivity, the less energy the sample absorbs, and the slower the temperature rises. The higher the attenuation coefficient, the less energy the sample absorbs, and the slower the temperature rises. The higher the scattering coefficient, the less energy the sample absorbs, and the slower the temperature rises.

[0100] Any feasible method can be used to determine the intensity of the aforementioned multiple target laser pulses. For example, the embodiments of this specification utilize finite element simulation technology to pre-set the laser intensity corresponding to each step in the target laser. Specifically, the laser intensity corresponding to each step in the target laser can be set by the pulse power and pulse width. Further, the heat transfer characteristics of the target sample, the energy absorption characteristics of the target laser, and the preset temperature are input into the finite element model, and the pulse width and laser intensity of the target laser are preset, that is, the duration and intensity of the laser corresponding to each step in the target laser are preset. Given the pulse width and laser intensity of the target laser, the duration for which the target sample reaches and maintains the preset temperature is determined.

[0101] Using the above settings, while maintaining a constant preset temperature, system 001 (control circuit 3000) determines the duration and intensity of the laser corresponding to each step in the target laser, and constructs multiple curves of the preset temperature T versus heating time t for the target sample. The horizontal axis of these curves represents the heating time t, and the vertical axis represents the preset temperature. Multiple curves represent the preset temperature T versus heating time t of the target sample measured under target lasers with different pulse widths and laser intensities. It is assumed that all materials exhibit thermal isotropy, all surfaces are cooled by air, and there is no forced convection. The ambient temperature is assumed to be consistently 293 K. The preset temperature T is extracted from the center of the target region. The duration t of each curve is the pulse width of the target laser corresponding to that curve.

[0102] Based on the aforementioned curve of preset temperature T versus heating time t, a finite element method (FEM) simulation model is used to simulate the heating process of the target sample irradiated by the target laser. Furthermore, based on the same curve, a target laser with a specific pulse width and intensity is set in the FEM simulation model to simulate the target region reaching the preset temperature under laser irradiation. As mentioned above, to maintain the temperature of the target region at the preset temperature within a duration exceeding the critical time, the laser intensity needs to be reduced when the laser reaches the critical time, allowing the target laser to be simulated with a different square wave, and so on. Thus, the FEM simulation model obtains the stepped waveform of the target laser corresponding to the preset temperature while maintaining the target sample at the preset temperature.

[0103] Based on the stepped waveform of the laser pulse obtained from the finite element simulation model, the pulsed laser isothermal heating system 001 can set the stepped waveform of the target laser when isothermally heating the target sample, thereby completing the isothermal heating of the target sample.

[0104] To verify the accuracy of the stepped waveform of the target laser obtained from the finite element simulation model, this application validated the results obtained from the finite element simulation model using a thermodynamic model. Specifically, a thermodynamic model of the target sample was established based on the heat transfer characteristics of the target sample, the energy absorption characteristics of the target laser, and the preset temperature.

[0105] The heat transfer process of the target laser irradiating the target sample can be described by the heat transfer equation of formula (1):

[0106]

[0107] Where λ is thermal conductivity, T is temperature, Q is the heat absorbed by system 001, t is time, ρ is density, and C is... p It is specific heat capacity. It is the velocity vector in Euler coordinates.

[0108] Q is the heat absorbed by system 001. That is, Q can include all heat sources that cause temperature increases, including external energy input and heat generated by internal chemical reactions, friction, etc. Furthermore, Q includes the energy Q of the target laser absorbed by the target region of the target sample. s Q s Q refers to the energy absorbed by the surface or interior of a target sample when it is irradiated by a laser. This energy is converted into heat, causing the temperature of the target sample to rise. In other words, Q... s This is the main heat source causing the temperature rise of the target sample. Given the complexity of the heat absorption process during the phase transition of the target sample, Q is calculated. s The time interval t can be calculated from the start of laser irradiation of the target to the start of the phase transition. sen .

[0109] Regarding Q s There are two heat transfer models. These two heat transfer models are described below.

[0110] Heat transfer model 1: Q s From sensible heat (Q) sen ), latent heat (Q) lat ) and heat conducted to the surrounding environment (Q) dis It consists of three parts. Among them, sensible heat (Q) sen Sensible heat (Q) characterizes the heat absorbed by the target sample during heating, but without accompanying phase change. In other words, sensible heat (Q) sen This causes a change in the temperature of the target sample, but the phase state of the target sample remains unchanged. Latent heat (Q) lat The heat absorbed by the target sample during a phase transition, while the sample temperature remains constant throughout the process, is represented by Q. The heat conducted to the surrounding environment (Q) is also represented by Q. dis Sensible heat (Q) characterizes the heat exchanged between the target sample and its surrounding environment through conduction, convection, or radiation. This heat exchange reduces the temperature difference between the target sample and its environment. sen ), latent heat (Q) lat ) and heat conducted to the surrounding environment (Q) dis The interaction between the laser and the target sample during the heating process jointly determines the temperature change and energy conversion of the target sample. The calculation formulas are shown in (2) and (3):

[0111]

[0112]

[0113] Where P is the instantaneous laser power of the target laser, R is the reflectivity, α is the attenuation coefficient, z is the thickness of the target sample, and C...p ρ is the specific heat capacity, ρ is the density, r is the equivalent radius of the target sample, and I is the density. hf (t) is the heat flux of the target area irradiated by the target laser, which includes the losses conducted to the bottom and the losses conducted to the non-laser-irradiated areas, S hf This represents the corresponding heat dissipation interface area.

[0114] Heat transfer model 2: Neglecting Q dis This model neglects surface radiation and convective heat transfer from the target sample. In this model, the laser irradiation time is on the order of femtoseconds to microseconds, which is extremely short. Therefore, it can be assumed that the radiation and convective heat transfer effects between the target sample and its surrounding environment are very weak and can be ignored within this extremely short time. In this case, latent heat, i.e., Q, is neglected. s From sensible heat (Q) sen ) and heat conducted to the surrounding environment (Q) dis It consists of two parts. The calculation formulas are shown in (4) and (5):

[0115]

[0116]

[0117] In this process, after the target laser penetrates to a certain depth into the target sample, the intensity of the target laser will decrease to a proportion of its initial intensity. As shown in equations (6) and (7), the Beer-Lambert law can be used to simulate this process. It is understood that the Beer-Lambert law does not consider refraction, scattering, or other phenomena.

[0118]

[0119]

[0120] According to the above formulas (6) and (7), Q s It can be obtained from the following formula (8):

[0121]

[0122] Where I is the energy density of the target laser, I0 is the initial incident laser energy density, R is the reflectivity, α is the attenuation coefficient, and z is the distance and depth along the incident laser pulse path from the surface of the target sample. I can be the heat source in the heat transfer equation.

[0123] Calculations confirmed that the data obtained from the finite element simulation model conformed to the thermodynamic model, i.e. or This indicates that the stepped waveform of the target laser obtained through the finite element simulation model is reliable. Furthermore, the pulsed laser isothermal heating system 001 sets the stepped waveform of the target laser in the actual experiment based on the stepped waveform obtained from the finite element simulation model, and this method is reliable. In other words, the pulsed laser isothermal heating system 001 heats the target sample using this method, and the temperature of the target area on the target sample reaches and is maintained at the preset temperature; this conclusion is correct.

[0124] It's important to note that the P300 isothermal heating method using laser pulses has multiple applications. For example, in heat treatment processes, isothermal heating is commonly used in metal processing, such as normalizing and annealing, to improve the plasticity and toughness of materials. In chemical reaction kinetics research, maintaining a constant temperature allows for more accurate measurement of reaction rates and study of the effects of catalysts. In polymer crystallization processes, controlling the heating temperature allows for the study of crystallization rate, crystallinity, and crystal morphology. In glass forming, isothermal heating helps control the fluidity and viscosity of glass, resulting in better forming effects. In biomedical applications, isothermal heating can simulate temperature conditions in the body to study the behavior of biomolecules at constant temperatures, such as protein folding and DNA replication. Isothermal heating can also be used for accelerated aging tests, simulating the performance changes of materials exposed to constant temperatures over long periods. Finally, in catalytic activity testing, isothermal heating can be used to evaluate the catalytic efficiency and stability of catalysts at fixed temperatures. In addition, as mentioned above, the isothermal heating method P300 using laser pulses can be applied to the study of material phase transitions. That is, when studying the phase transition characteristics of a target material, isothermal heating can be used to observe the time required for the target material to undergo a phase transition at a certain preset temperature.

[0125] To measure the phase transition time required for the target material to undergo a phase transition, the target sample can be heated to a preset temperature using the aforementioned isothermal heating method P300 via laser pulses. Specifically, based on the aforementioned isothermal heating method P300 via laser pulses, system 001 heats the target sample and maintains it at the preset temperature for a certain duration, then determines whether the target material has undergone a phase transition within that duration. If no phase transition occurs, a longer heating time is set, maintaining the preset temperature, and the target sample is isothermally heated again using the same isothermal heating method P300 to determine whether the target material has undergone a phase transition. This process is repeated, gradually increasing the heating time until the target material undergoes a phase transition.

[0126] For example, if a target sample is heated isothermally at a preset temperature for a first duration without a phase transition, and then heated again at the same temperature for a second duration using the same method (P300), it is determined that a phase transition has occurred. Therefore, the duration of the phase transition at the preset temperature can be determined to be between the first and second durations. For instance, if a target sample is heated at a preset temperature of 750K for 1000 nanoseconds without a phase transition, but then undergoes a phase transition at 750K for 1010 nanoseconds, then the duration of the phase transition from an amorphous to a crystalline state can be considered to be between 1000 and 1010 nanoseconds.

[0127] In other words, if the above-mentioned isothermal heating method P300 can perform isothermal heating for at least Δt seconds, then the heating time can be increased to an accuracy of Δt seconds each time. That is, through method P300, system 001 can capture the phase change rate at a minimum of Δt seconds.

[0128] Because the minimum isothermal heating duration achievable by the target laser in method P300 is Δt seconds, the time difference between the first and second durations must be an integer multiple of the minimum target duration Δt seconds. It is understandable that the ratio between the time difference between the first and second durations and the minimum target duration Δt seconds can be any multiple, such as equal, one, two, three, ten, twenty, fifty, one hundred, N times, etc. No restrictions are imposed here.

[0129] In some embodiments, reflectivity can be used to determine whether a target material has undergone a phase transition (e.g., a transition from an amorphous to a crystalline state). Specifically, changes in reflectivity can serve as an indirect indicator that the target material has undergone a phase transition. During a phase transition, the surface properties of the target material change, resulting in a change in its reflectivity. For example, when a target material transitions from an amorphous to a crystalline state, changes in its surface roughness and structure lead to changes in reflectivity. When a significant change in reflectivity occurs, it indicates that the surface properties of the target material have changed, i.e., a phase transition has taken place.

[0130] As a practical application of the P200 phase transition measurement method for materials, it can measure the minimum phase transition time required for a target material to undergo a phase transition at multiple different preset temperatures, thus obtaining multiple data pairs of preset temperatures and minimum phase transition times. Plotting these data pairs together yields the TTT (Time-Temperature Transformation) curve for the target material. The TTT curve can be used to describe the kinetic behavior of the target material from an amorphous to a crystalline state. The TTT curve presents a "C"-shaped curve. Different parts of the curve represent the phase transition tendency of the target material under different preset temperatures and minimum phase transition times. The nose point is the lowest temperature point on the curve, corresponding to the fastest cooling rate. At the nose point, the target material undergoes a phase transition. The nose point is also known as the critical transition temperature, which is the temperature at which the target material is most likely to undergo a phase transition.

[0131] Using the TTT curves and quantitative models (9)-(13) obtained above, multiple kinetic parameters of this target material during the phase transition process can be obtained, such as the critical interface energy σ(T). * Critical nucleation viscosity η (T) * (e.g., ...). This quantitative model establishes a quantitative relationship between the critical nucleation time (t*) and the critical nucleation temperature (T*). Furthermore, the critical nucleation time (t*) characterizes the time at the nose point, and the critical nucleation temperature (T*) characterizes the temperature at the nose point.

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] The following are specific measurement embodiments related to the above content of this disclosure. It should be clarified that the following embodiments are merely for illustrating the isothermal heating method, phase transition measurement method, and pulsed laser isothermal heating system disclosed above. The specific implementation methods and objectives used are only one or more methods conforming to the methods and target materials described above. Those skilled in the art can use other materials to perform isothermal heating on materials or measure the phase transition time of materials according to the methods described above, without departing from the core spirit of the application. For example, the following embodiments use Ge2Sb2Te5 (GST225) as the experimental material. Those skilled in the art will fully understand that the above-described isothermal heating method, phase transition measurement method, and pulsed laser isothermal heating system can also be applied to other materials, as long as they conform to the core spirit of the disclosure in this specification. Due to space limitations, this disclosure does not specifically describe embodiments using other materials here.

[0138] The target sample is an 18nm GST225 thin film. The specific placement method of the GST225 thin film is as follows: a 2nm thick silicon dioxide layer is coated on a 40nm thick silicon substrate, and then an 18nm thick GST225 thin film is placed on top of this silicon dioxide layer.

[0139] Figure 4A shows the Raman spectrum of the GST225 thin film provided according to the embodiments of this specification; Figure 4B shows the refractive index (n) spectrum and extinction coefficient (k) spectrum of the amorphous and crystalline states of GST225 provided according to the embodiments of this specification; Figure 4C shows the attenuation coefficient (α) spectrum of the amorphous and crystalline states of GST225 provided according to the embodiments of this specification; Figure 4D shows the reflectance (R) spectrum of the amorphous and crystalline states of GST225 provided according to the embodiments of this specification.

[0140] Figure 4A shows a microscopic image of a square shadow formed on the surface of an 18 nm thick GST225 film after laser irradiation. Figure 4A characterizes the GST225 phase state inside and outside the shadow using Raman spectroscopy. The Raman spectrum of “A” shows a unique peak at 105 cm⁻¹, attributed to the A₁ mode of GeTe₄ corner-shared tetrahedra, indicating that GST225 is in a crystalline state. In contrast, the Raman spectra of “B” and “C” both show specific peaks at approximately 74 cm⁻¹, 125 cm⁻¹, and 150 cm⁻¹, respectively. The peak at 74 cm⁻¹ corresponds to the E mode of the GeTe₄ tetrahedron, the peak at 125 cm⁻¹ corresponds to the A₁ mode of the GeTe₄₋ₙGₑₙ (n = 0, 1, 2) tetrahedron, and the peak at 150 cm⁻¹ corresponds to the Sb-Te bond vibration in the SbmTe₃ (m = 1, 2) unit. These specific peaks indicate that GST225 is in an amorphous state.

[0141] Therefore, after irradiation by the pulsed laser isothermal heating system 001, the square shaded area in Figure 4A shows a uniform amorphization effect. Subsequently, large-area scanning laser irradiation was performed on the GST225 film, and ellipsometric measurement was achieved using the sample stage 1000. The refractive index (n) spectrum and extinction coefficient (k) spectrum of the GST225 film were then obtained (as shown in Figure 4B), and the attenuation coefficient (α) spectrum (as shown in Figure 4C) and reflectance (R) spectrum (as shown in Figure 4D) were calculated. Observation of the Raman spectrum of GST225 shows a significant difference between the amorphous and crystalline states.

[0142] The heat transfer process in a GST225 thin film during laser pulse irradiation, in which the GST225 film is in an amorphous state, was analyzed using a finite element method (FEM) simulation model. Based on the output wavelength and waveform of the pulsed laser isothermal heating system 001, the pulsed laser source in the FEM simulation model was set as a square flat-top profile beam with a wavelength of 1064 nm. Table 1 lists the physical parameter values ​​of the GST225 thin film used in the simulation.

[0143] Table 1. Physical parameter values ​​of GST225 thin film

[0144] Physical parameters (units, values) Thermal conductivity (λ) W / m·K 0.5 Density (ρ) g / cm³ 6.0 Specific heat capacity (Cp) J / g·K 0.3

[0145] Figure 5A shows the Tt curves extracted from finite element simulation results under various laser pulse powers and pulse widths, provided according to embodiments of this specification; Figure 5B shows the Tt curves extracted from finite element simulation results under various laser pulse powers and critical pulse widths, provided according to embodiments of this specification. A series of finite element simulations were performed with various square pulse powers and pulse widths to explore the melting point (Tt) of GST225. m The thermal equilibrium condition at 888 K is shown in Figures 5A and 5B. An insufficiently powerful 5.2 W laser pulse requires a 6 ns extended duration to reach T0 on the GST225 surface. m Conversely, a laser pulse with sufficient power of 6.1W can rapidly reach T on the GST225 surface. m If the duration exceeds 2.8 ns, the surface temperature will rise above the melting point, potentially causing material ablation.

[0146] To verify the accuracy of the finite element simulation results, the heat of melting from the start of laser pulse irradiation to the beginning of melting of the GST225 thin film was calculated using energy conservation. As mentioned above, latent heat was neglected to simplify the calculation. The model was used for calculation. As shown in Table 2, the target sample under different pulse power and different pulse width were calculated. , and The calculation results of the three sets of laser parameters show that the sum of the last two energies is within an acceptable range. and The sum of their energies and The difference can be attributed to the use of heat transfer model 2 in the calculation process, and the calculation results are shown in Table 2. Surface radiation and convective heat transfer effects lead to higher laser pulse power (7.9 W) at higher pulse power. and The sum of their energies and There are more significant differences between them. Given the considerable dependence of these calculations on the simulated sample surface temperature and the input melting temperature, the small differences in energy conservation indicate that the simulated temperature values ​​are reliable, i.e. and The sum of their energies and The differences are within an acceptable range. Since energy is conserved in the finite element simulation results, the finite element simulation results can be concluded to be reliable, and therefore the Tt curve derived from the finite element simulation results is also reliable.

[0147] Table 2. Various energy terms during laser pulse irradiation.

[0148]

[0149] Figure 6A illustrates the strategy for constructing a TTT curve according to an embodiment of this specification; Figure 6B illustrates a 200 ns stepped laser waveform simulation of an 800K isothermal platform according to an embodiment of this specification. As shown in Figure 6B, the preset temperature of the isothermal platform is 800K. This isothermal platform is simulated using the calibrated finite element model described above. The laser pulse waveform is formed by a stepped waveform with a pulse width of 200 ns. To reach and maintain the preset temperature of 800K, the amplitude of the laser pulse power needs to be adjusted. Once it is found that the temperature of the target material in the target region cannot be maintained at the preset temperature of 800K, the laser pulse power must be immediately reduced so that the amplitude of the laser pulse is reduced sufficiently to maintain a balanced stepped waveform. Using this method, laser pulse waveforms for isothermal platforms at any temperature can be obtained, such as 750 K, 700 K, 650 K, and 600 K, etc. As shown in 6A, after obtaining multiple isothermal platforms at preset temperatures, a TTT curve can be established based on the preset temperature and the target time to reach the preset temperature.

[0150] Isothermal heating at 800K, 750K, 700K, 650K, and 600K can be performed using the following method: 10 different pulse widths, ranging from 200 ns to 20 ns, with intervals of 20 ns. For isothermal heating at 650K and 600K, 20 different pulse widths, ranging from 2000 ns to 100 ns, with intervals of 100 ns.

[0151] As described above, a significant change in reflectivity can serve as evidence of critical nucleation, allowing for accurate determination of the critical nucleation time. Figure 7A shows the reflectivity versus pulse width curves of GST225 isothermally heated to 750 K according to an embodiment of this specification. As shown in Figure 7A, the reflectivity exhibits a significant increase with an 80 ns pulse width. Therefore, 80 ns is designated as the critical nucleation time at 750 K. Similarly, the critical nucleation times of GST225 at preset temperatures of 800 K, 750 K, 700 K, 650 K, and 600 K are obtained. As shown in Figure 7A, once the phase transition occurs, a bright crystalline region appears against a darker amorphous background, in stark contrast to Figure 4A.

[0152] Based on the above results, the TTT (Total Time) diagram of GST225 was plotted. Figure 7B shows the TTT diagram of GST225 provided according to the embodiment of this specification. As shown in Figure 7B, the critical nucleation times at 800K, 750K, 700K, and 650K were determined to be 80ns, 80ns, 100ns, and 900ns, respectively. It should be noted that the critical nucleation time at 600K exceeds the limit of the pulsed laser isothermal heating system 001.

[0153] The model was used to fit the data in the TTT diagram, and the crystallization kinetic parameters of GST225 at the nose point were obtained based on the model and formulas (9)-(13), as shown in Table 3.

[0154] Table 3. Quantitative analysis of several derived parameters of GST225 determined by TTT plot analysis. All temperature and time-related physical parameters were obtained at the nose point.

[0155]

[0156] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0157] In summary, after reading this detailed disclosure, those skilled in the art will understand that the foregoing detailed disclosure may be presented by way of example only and may not be restrictive. Although not explicitly stated herein, those skilled in the art will understand that this specification requires various reasonable changes, improvements, and modifications to the embodiments. These changes, improvements, and modifications are intended to be made by this specification and are within the spirit and scope of the exemplary embodiments described herein.

[0158] Furthermore, certain terms in this specification have been used to describe embodiments of this specification. For example, "an embodiment," "an embodiment," and / or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with that embodiment may be included in at least one embodiment of this specification. Therefore, it is to be emphasized and understood that two or more references to "an embodiment" or "an embodiment" or "alternative embodiment" in various parts of this specification do not necessarily refer to the same embodiment. Moreover, specific features, structures, or characteristics may be suitably combined in one or more embodiments of this specification.

[0159] It should be understood that in the foregoing description of the embodiments in this specification, various features are combined in a single embodiment, drawing, or description for the purpose of simplifying the description and to aid in understanding a feature. However, this does not mean that the combination of these features is necessary, and those skilled in the art may extract some features as individual embodiments when reading this specification. That is, the embodiments in this specification can also be understood as an integration of multiple sub-embodiments. It is also valid when each sub-embodiment contains fewer than all the features of a single foregoing disclosed embodiment.

[0160] Every patent, patent application, publication of a patent application, and other material, such as articles, books, specifications, publications, documents, and literature (excluding any related historical examination documents), cited in this disclosure is incorporated herein for all purposes related to this disclosure, for example, in the specification and claims of this disclosure. However, in the event of any inconsistency or conflict between the descriptions, definitions, and / or terms of the foregoing materials and the descriptions, definitions, and / or terms used in this disclosure, the descriptions, definitions, and / or terms used in this disclosure shall prevail. Finally, it should be understood that the embodiments of the applications disclosed herein are illustrative of the principles of the embodiments of this specification. Other modified embodiments are also within the scope of this specification. Therefore, the embodiments disclosed in this specification are merely examples and not limitations. Those skilled in the art can implement the applications in this specification using alternative configurations based on the embodiments in this specification. Therefore, the embodiments in this specification are not limited to the embodiments precisely described in the applications.

Claims

1. A method for isothermal heating using laser pulses, characterized in that, include: Obtain the target sample; Within a preset target duration, the target area on the target sample is irradiated with a target laser, so that the temperature of the target area is maintained at a preset temperature within a preset temperature error.

2. The method according to claim 1, characterized in that, The minimum target duration is in the microsecond, nanosecond, picosecond, or femtosecond range, and the temperature error is 1°C.

3. The method according to any one of claims 1-2, characterized in that, The intensity of the target laser decreases over time within the target duration.

4. The method according to claim 3, characterized in that, The intensity waveform of the target laser includes multiple steps, and the laser intensity corresponding to the multiple steps decreases sequentially over time within the target duration.

5. The method according to claim 3, characterized in that, The target laser comprises multiple laser pulses, the intensity of which decreases over time within the target duration.

6. The method according to any one of claims 3-4, characterized in that, Based on the preset temperature, the laser intensity corresponding to each step is predetermined.

7. The method according to claim 4, characterized in that, The pre-setting of the laser intensity corresponding to each step in the target laser also includes: determining the laser intensity corresponding to each step in the target laser based at least on the heat transfer characteristics of the target sample, the energy absorption characteristics of the target laser, and the preset temperature.

8. The method according to claim 6, characterized in that, The step of pre-determining the laser intensity corresponding to each step includes: The laser intensity corresponding to each step in the target laser is pre-set using finite element simulation technology.

9. The method according to any one of claims 1-2, characterized in that, The target area is the region on the target sample that has been irradiated by the laser.

10. The method according to any one of claims 1-2, characterized in that, The target duration is 30 fs-200 μs.

11. A method for measuring the phase transition of a material, characterized in that, include: Obtain a target sample, wherein the target sample is a target material; The target sample is heated to the preset temperature using the isothermal heating method described in any of claims 1-10, so as to determine the minimum phase transition time required for the target material to undergo a phase transition at the preset temperature.

12. The measurement method according to claim 11, characterized in that, The preset temperature is lower than the melting point of the target material.

13. The measurement method according to claim 11, characterized in that, Determining the minimum phase transition time required for the target material to undergo the phase transition at the preset temperature includes: The target sample is heated at a preset temperature for a first duration using the isothermal heating method, and it is determined that the target sample has not undergone the phase transition. The target sample is heated at a preset temperature for a second duration using the isothermal heating method, and it is determined that the target sample has undergone the phase transition. The time difference between the first duration and the second duration is an integer multiple of the minimum value of the target duration. The minimum phase transition time of the target material from the start of heating to the start of the phase transition at the preset temperature is determined to be between the first time and the second time.

14. The measurement method according to claim 13, characterized in that, Also includes: Whether the target material has undergone the phase transition is determined based on reflectivity.

15. A pulsed laser isothermal heating system, characterized in that, include: The sample stage is configured to hold the target sample. A laser, located on one side of the sample stage, emits a target laser toward the target sample within a preset time period to irradiate the target area on the target sample. as well as A control circuit, communicatively connected to the laser, is configured to control the pulsed laser to generate the desired target laser. The isothermal heating system performs the method as described in any one of claims 1-14.

16. The system according to claim 15, characterized in that, The laser also includes a master oscillator power amplifier, the optical wavelength of which is 1064 nm.

17. The system according to claim 15, characterized in that, The laser includes an arbitrary waveform generator, and the arbitrary waveform generator module operates at a high frequency.

18. The system according to claim 15, characterized in that, The laser provides tunable laser pulses with a pulse width ranging from 30 fs to 200 μs.

19. The system according to claim 15, characterized in that, The laser also includes a beam shaper for converting a Gaussian beam into a flat-top beam, thereby optimizing the energy distribution across the beam cross-section.

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