Self-delayed double-target pair collision plasma generating device and generating method

Abstract

The application discloses a self-delayed double-target collision plasma generating device and a generating method, and belongs to the technical field of plasma, which comprises a laser system, a vacuum chamber and a target assembly arranged in the vacuum chamber, wherein the target assembly comprises a first composite target and a second plane target along the laser propagation direction; the first composite target comprises a film substrate and a first tin layer; the second plane target comprises a second tin layer; and a predetermined interval is arranged between the film substrate and the second tin layer. The laser system emits a single-beam pulsed laser focused on the first composite target, ablates the first tin layer to generate a first plasma, breaks through the film substrate, transmits the laser energy to ablate the second tin layer to generate a second plasma, and the first plasma and the second plasma collide with each other to form a stagnation layer. The application utilizes a single-beam laser and a special composite target structure to realize self-delayed plasma collision through a physical mechanism, simplifies the system structure and improves the confinement performance of the plasma stagnation layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plasma, in particular to a self-delayed double-target collision plasma generating device and a generating method. BACKGROUND

[0002] Laser-induced plasma, in English, is called Laser-Produced Plasma, denoted as LPP, is an important topic in high-energy density physics, atomic and molecular physics, and spectroscopy research. In particular, the plasma produced by laser bombardment of high atomic number materials such as tin contains complex ion energy level transition processes in its interior, which can radiate specific wavebands, such as the characteristic spectrum of extreme ultraviolet waveband near 13.5 nm, and has important research value in the fields of microphysical diagnosis and short-wavelength radiation physics.

[0003] In the research of laser interaction with tin target, how to obtain high-density, long-lifetime and stagnation-state plasma has always been a core physical problem faced by the field. The current single-pulse laser bombardment of single-target technology has the following main limitations in practical application and physical experiments. In the traditional single-target excitation mode, the tin plasma group generated by the laser pulse has extremely high initial pressure and will undergo violent adiabatic expansion. This rapid expansion leads to a sharp drop in the density and temperature of the plasma core region, so that the tin ions are maintained in a high ionization state, such as Sn 8+ ~Sn 14+ , and the time for specific transition radiation is extremely short, usually only nanoseconds. This rapid dissipation mechanism limits the energy conversion efficiency and spectral quality of the plasma radiation. Laser-induced plasma releases a large number of high-energy ions and particles during the expansion process, which are usually referred to as "fast ions". These uncontrolled high-energy particles are ejected in all directions, which can cause serious physical sputtering and surface damage to the plasma-facing components or observation windows in the vacuum chamber.

[0004] In order to overcome the problems of lifetime limitation caused by plasma hydrodynamic expansion and sputtering damage caused by excessive ion kinetic energy, the physics community has proposed a collision plasma scheme, that is, two oppositely moving plasma flows are used for inelastic collision to convert directed kinetic energy into internal energy, thereby forming a long-lifetime stagnation layer. However, the existing collision plasma generation scheme usually needs to rely on a complex double-pulse laser system or a precise optical path, and requires precise spatiotemporal synchronization of two lasers or two plasma flows on the nanosecond or even picosecond scale. This high dependence on external optical systems and timing control makes the plasma generating device have low integration, high debugging difficulty, and is difficult to be popularized as a general experimental platform.

[0005] In summary, the existing laser plasma generation technology has the problems of short stagnation layer lifetime caused by too fast plasma expansion, serious damage to vacuum chamber components caused by too high ion directed kinetic energy, and the need for a complex double-pulse laser system in traditional collision plasma technology, which is difficult to control in time and space and has high cost. SUMMARY

[0006] The present application provides a self-delayed double-target collision plasma generation device and a generation method, which effectively solves the technical problems of low integration and difficult debugging of the plasma generation device caused by the existing double-fluid collision control system, and provides a self-delayed double-target collision plasma generation device with simple structure and high efficiency plasma collision and constraint realized by physical self-synchronization mechanism. The self-delayed collision of double plasma flows is realized under single laser action, thereby effectively prolonging the existence time of the plasma stagnation layer and inhibiting the escape of high-energy ions.

[0007] The first object of the present application is to provide a self-delayed double-target collision plasma generation device, comprising:

[0008] A vacuum chamber and a laser system for generating incident pulsed laser.

[0009] A target assembly arranged in the vacuum chamber; along the laser propagation direction, the target assembly comprises a first composite target and a second planar target arranged at intervals; the first composite target comprises a film substrate and a first tin layer deposited on the film substrate; the second planar target comprises a second tin layer arranged in parallel on one side of the film substrate; a collision region is defined between the film substrate and the second tin layer, and the distance of the collision region is 0.5mm-2mm.

[0010] The laser system emits a single beam of pulsed laser focused on the first composite target, ablates the first tin layer to generate a first plasma expanding in the laser direction, breaks through the film substrate, transmits the laser energy to ablate the second tin layer, generates a second plasma expanding in the opposite direction of the laser, and the first plasma and the second plasma collide in the opposite direction in the collision region to form a stagnation layer and emit enhanced characteristic spectral lines.

[0011] As a preferred embodiment, the film substrate is one or a combination of polyethylene (PE), polypropylene (PP), polyimide (PI), and polyethylene terephthalate (PET).

[0012] As a preferred embodiment, the thickness of the film substrate is 10μm-50μm. More preferably, the thickness of the film substrate is 25μm.

[0013] As a preferred embodiment, the distance of the collision region is 1mm.

[0014] As a preferred embodiment, the thickness of the first tin layer is 50nm-200nm.

[0015] As a preferred embodiment, the target assembly further comprises a target moving mechanism, which supports and drives the first composite target and the second planar target to move synchronously to ensure that each pulse laser acts on the unbroken area on the first composite target.

[0016] The second object of the present application is to provide a method for generating a double-target collision plasma, which uses the self-delayed double-target collision plasma generating device of any one of the above-mentioned embodiments to generate a double-target collision plasma, and the method comprises:

[0017] The incident pulse laser is emitted by the laser system, the front energy of the incident pulse laser is used to ablate the first tin layer on the first composite target in the vacuum chamber, and a first plasma expanding in the laser direction is generated, while the laser energy breaks the film substrate of the first composite target.

[0018] The second tin layer of the second planar target behind the film substrate is ablated by the transmitted laser energy after the film substrate is broken, and a second plasma expanding in the opposite direction of the laser is generated.

[0019] The first plasma and the second plasma collide in the collision area between the first composite target and the second planar target, form a plasma stagnation layer in a stagnation state, and emit enhanced characteristic spectrum lines under excitation.

[0020] As a preferred embodiment, the incident pulse laser is a Nd:YAG laser with a wavelength of 1064nm and a pulse width of nanosecond level.

[0021] As a preferred embodiment, the center wavelength of the characteristic spectrum line is 13.5nm. The collision area of the first plasma and the second plasma is excited to generate a characteristic spectrum line with a center wavelength of 13.5nm, and the collision makes the average kinetic energy of the generated tin ions lower than that of the tin ions generated by using a single target.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The application provides a self-delayed double-target collision plasma generating device, a first composite target and a second plane target are arranged in a vacuum chamber, and a collision area is arranged on the first composite target and the second plane target, a single-beam pulsed laser ablates a first tin layer of the first composite target to generate a first plasma, and breaks through a film base, transmitted laser energy ablates a second tin layer of the second plane target to generate a second plasma, the first plasma and the second plasma collide with each other in the collision area, a stagnation layer is formed, and enhanced characteristic spectral lines are emitted by excitation.

[0024] The application utilizes the 'burn-through' effect of the film base as a passive optical switch, and realizes the time sequence excitation of the double targets by using only a single laser, which avoids the dependence on double lasers, a light splitting path and a precise electronic delay control system in the traditional collision technology, greatly reduces the complexity and cost of the system, and improves the stability of the plasma generation experiment, that is, the application provides a collision plasma generating device which has a simple structure and does not need a double-pulse system. Through the collision of the first plasma and the second plasma, a high-density, high-temperature and slow-expanding stagnation layer is formed between the first composite target and the second plane target, the plasma is effectively constrained in the region, the duration of the specific energy level jump of the tin ions, such as 13.5 nm, is significantly prolonged, and the efficiency of the laser energy coupled to the plasma radiation energy is improved, that is, the long life and high-quality spectrum of the stagnation layer are realized. The collision process of the first plasma and the second plasma converts the directional kinetic energy of the plasma into internal energy, that is, heat energy, and significantly reduces the average kinetic energy of the tin ions ejected outward, which effectively reduces the sputtering damage of the high-speed ions to the plasma facing components and the observation window, and prolongs the service life of the key physical elements, that is, the kinetic energy of the plasma is thermalized by using the self-delayed double-target collision plasma generating device provided by the application, and the sputtering damage is reduced.

[0025] The application flexibly regulates the relative delay time and collision position of the first plasma and the second plasma generated by adjusting the thickness of the polymer film, the distance between the two targets and the laser energy, so as to optimize the collision kinetic characteristics of the plasma. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The application provides a self-delayed double-target collision plasma generating device.

[0027] Figure 2 The application provides a self-delayed double-target collision plasma generating device.

[0028] Figure 3A first plasma schematic diagram generated by laser acting on a target assembly according to an embodiment of the present application expands in the reverse laser propagation direction and the forward laser propagation direction at the same time.

[0029] Figure 4 A second plasma schematic diagram generated by laser passing through a first composite target to act on a Sn bulk target according to an embodiment of the present application and a plasma stagnation layer formed by collision.

[0030] Figure 5 A comparison diagram of plasma characteristic spectrum generated by a double-target collision mode and a conventional single-target mode according to the present application, i.e., a time evolution waveform of 13.5 nm, shows the effect of prolonging the life of the stagnation layer.

[0031] Figure 6 A plasma ion emission spectrum diagram generated by a double-target collision mode according to an embodiment of the present application, shows the narrowband spectral characteristics of tin ions in a specific energy level transition.

[0032] Reference signs:

[0033] 1, vacuum chamber, 2, laser system; 3, first composite target, i.e., front target, 31, thin film substrate, 32, first tin layer, 4, second tin layer, i.e., rear Sn bulk target, 5, target moving mechanism, 6, plasma stagnation layer; 7, radiation signal monitoring assembly, L is incident pulsed laser, d is the distance of the collision region, P 1 is a first plasma, P 2 is a second plasma. DETAILED DESCRIPTION

[0034] In order for those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments, but the embodiments are not limiting of the present application. The following test methods and detection methods are conventional methods unless otherwise specified; the reagents and raw materials are commercially available unless otherwise specified.

[0035] For the above-mentioned existing laser plasma technology, first, the existing laser plasma generation technology has the problem of short stagnation layer life caused by too fast plasma expansion; second, the problem of serious damage to the vacuum chamber assembly caused by too high ion directed kinetic energy; third, the problem of complex double-pulse laser system, difficult time and space synchronization control and high cost of traditional collision plasma technology. In view of the above technical problems, the present application provides a self-delay double-target collision plasma generation device and method.

[0036] The technical solutions of the present application will be described in detail below.

[0037] The present application first provides a self-delay double-target collision plasma generation device, such as Figure 1As shown, it includes:

[0038] Vacuum chamber 1, which is connected to a vacuum pump assembly, is used to maintain the internal air pressure below 10 during operation. -4 A high vacuum environment of Pa is used to reduce the absorption of plasma characteristic spectral lines, such as 13.5 nm, by the background gas.

[0039] Laser system 2 is used to generate incident pulsed laser light. Laser system 2 includes a high-power pulsed Nd:YAG laser and its associated beam transmission and focusing optical elements. In this invention, the laser output wavelength is 1064 nm, the pulse width is approximately 10 ns, and the single-pulse energy is 100 mJ to 800 mJ. After being focused by a focusing lens, the laser beam is incident perpendicularly onto the surface of the target assembly, with the focal spot diameter controlled between 100 μm and 300 μm.

[0040] like Figure 2 As shown, a target assembly is disposed within the vacuum chamber 1. Along the laser propagation direction, the target assembly includes a first composite target 3 spaced apart as a front target and a second planar target as a rear target. The first composite target 3 includes a thin film substrate 31 and a first tin layer 32 deposited on the thin film substrate 31. The second planar target includes a second tin layer 4, which is disposed parallel to one side of the thin film substrate 31. A collision region is provided between the thin film substrate 31 and the second tin layer 4, and the distance between the collision regions is 0.5 mm to 2 mm.

[0041] The first composite target 3, serving as a front target, consists of a thin film substrate 31 that is transparent to lasers or easily ablated, and a first tin layer 32 attached to the thin film substrate 31. The second planar target, serving as a rear target, includes a second tin layer 4 and is a bulk Sn target. A collision region is provided between the first composite target and the second planar target, with a distance d between them. The laser system 2 is configured to emit a single high-intensity laser pulse focused onto the first composite target 3. Ablation of the first composite target 3 generates a first tin plasma, i.e., the first plasma. P Simultaneously, it can penetrate the thin film substrate 31 of the first composite target, allowing the transmitted laser energy to continue acting on the second planar target behind it to generate a second tin plasma, i.e., the second plasma. P 2. Due to the blocking and delaying effect of the thin film substrate 31, the first plasma... P 1 and the second plasma P 2. Violent collisions occur in the gap region between the two targets, forming a high-density, high-temperature plasma stagnation layer 6.

[0042] The first composite target 3, i.e. the front target, is composed of a thin film substrate 31 and a first tin layer 32 deposited thereon. In the present embodiment, the thin film substrate 31 preferably adopts a polyethylene film with a thickness of 10 μm to 50 μm. The material is selected as the substrate mainly based on the following three key physical properties: first, having a low atomic number, Low-Z property. Polyethylene is mainly composed of carbon and hydrogen elements, and the plasma generated by the low atomic number elements has a very small absorption cross section for the 13.5 nm wavelength band, which means that even if a small amount of substrate plasma is mixed in the collision process, it will not significantly absorb the characteristic spectrum of the tin plasma, thereby ensuring high energy coupling efficiency of the device. Second, having high spectral purity, the line spectrum radiation generated by carbon and hydrogen elements is mainly concentrated in the long wavelength band, and there is no strong radiation peak near 13.5 nm, which makes the spectral background of the device output lower, which is beneficial to subsequent spectral analysis and diagnosis. Third, having a suitable ablation and breakdown threshold, the polyethylene film can be rapidly gasified and burned through under the action of nanosecond laser pulses, forming a clear light transmission channel, thereby ensuring that the subsequent laser energy can be efficiently transmitted and act on the rear second planar target.

[0043] The first tin layer 32 is prepared by pulsed laser deposition technology, i.e. PLD, and the specific preparation steps are as follows: first, select a polyethylene film with a thickness of 25 μm, and use anhydrous ethanol and deionized water for ultrasonic cleaning and drying in turn; second, place the cleaned substrate in a deposition chamber with a vacuum degree better than 10 -4 Pa; third, use the plume generated by laser bombardment of a high-purity tin target to deposit a dense and uniform tin film on the side of the polyethylene film facing the laser incidence; and finally, control the deposition time by real-time monitoring by a quartz crystal microbalance until the film thickness reaches 50 nm to 200 nm, to obtain a nanoscale Sn film, i.e. the first tin layer 32. As an alternative, the tin layer can also be prepared by direct current magnetron sputtering or electron beam evaporation technology.

[0044] Regarding the configuration of the second planar target, i.e. the rear target, the second planar target is selected from high-purity tin bulk materials, and the surface thereof is polished to obtain the second tin layer 4. The first composite target 3 and the second tin layer 4 are placed in a non-contact parallel manner, and the distance between the collision region set between the two is 0.5 mm to 2.0 mm. This distance is a key parameter that determines the timing and position of the collision of the two plasma.

[0045] In order to realize continuous experiments, the application is also equipped with a target moving mechanism 5. Since a single laser pulse can break through the polyethylene film to form a hole, the target moving mechanism 5 is configured to drive the first composite target 3 and the second planar target to move synchronously during each laser pulse interval, ensuring that each new laser pulse can act on the fresh target surface. The target moving mechanism 5 is composed of a multi-axis moving insulating target seat and a four-channel electrically controlled translation stage control box. The first composite target 3 and the second planar target are clamped and fixed on the multi-axis moving insulating target seat, and the four-channel electrically controlled translation stage control box is an MC600 series controller purchased from Beijing Zhuoli Han Guang Instrument Co., Ltd., which mainly performs a "step-stagnant" planar scanning mode to drive the multi-axis moving insulating target seat to move accurately along a predetermined trajectory with a fixed step length. With its superior multi-dimensional adjustment capability and micron-level resolution, this mechanism not only ensures that the first composite target 3 and the second planar target are accurately sent into the focal region each time, but also fine-tunes the focal length during operation, thereby realizing long-time and high-stability optimal output of the light source.

[0046] The laser system 2 emits a single pulse laser beam focused on the first composite target 3, ablates the first tin layer 32 to generate a first plasma expanding in the laser direction P 1, and breaks through the film substrate 31, and the transmitted laser energy ablates the second tin layer 4 to generate a second plasma expanding in the opposite direction of the laser P 2. P 1 and the second plasma P 2 collide with each other in the collision area to form a plasma stagnation layer 6 and emit enhanced characteristic spectral lines.

[0047] The application realizes the generation of collision plasma by using the self-delay collision plasma generation device constructed as described above. The device utilizes the energy evolution of a single laser pulse in time and space to realize self-triggering plasma collision. The specific physical generation process is illustrated in the following examples.

[0048] Example 1

[0049] A method for generating a double-target collision plasma, using the self-delay collision plasma generation device described above, includes the following steps:

[0050] The first stage is pre-target ablation and first plasma generation: when the front of the incident pulse laser with an energy of 450 mJ reaches the surface of the first composite target 3, it first interacts with the first tin layer 32. Since the thickness of the first tin layer 32 is only 100 nm, the laser energy rapidly ionizes it to generate a first plasma expanding at a high speed in the laser direction P 1.

[0051] The second stage is the thin film substrate breakdown and energy transmission: with the continuous injection of pulsed laser energy, the thin film substrate 31 with a thickness of 25 μm is ablated and finally broken down within a nanosecond time scale, the first plasma P 1will expand towards the back side of the thin film substrate 31 along the laser incidence direction, as shown in Fig. 1. At this time, the remaining energy of the laser pulse, mainly the peak part or the trailing part of the pulse, transmits through the hole on the thin film substrate 31, propagates 1 mm in the vacuum, i.e. the interval of the collision region between the thin film substrate 31 and the second tin layer 4 is 1 mm, and then hits the second tin layer 4 of the second planar target behind. Figure 3

[0052] The third stage is the rear target ablation and the second plasma generation: the transmitted laser energy acts on the second tin layer 4 of the second planar target, generating the second plasma P 2.

[0053] The fourth stage is the plasma collision and the formation of the stagnation layer: due to the backward recoil velocity component of the first plasma P 1or due to the stagnation of the expansion tail, the second plasma P 2expands at a high speed forward, and the two plasma flows collide violently in the gap region between the first composite target 3 and the second planar target, i.e. the region with a predetermined interval. The collision converts the directional kinetic energy of the plasma into heat energy, causing the density of the local region to rise sharply and the expansion speed to approach zero, forming a plasma stagnation layer 6 that can be maintained for a long time, as shown in Fig. 6. Figure 4

[0054] Example 2

[0055] A method for generating a double-target collision plasma, which is performed by using the self-delayed collision plasma generating device described above, comprising the following steps:

[0056] The first stage is the front target ablation and the first plasma generation: when the front edge of the incident pulsed laser with an energy of 150 mJ reaches the surface of the first composite target 3, it first interacts with the first tin layer 32. Since the thickness of the first tin layer 32 is only 50 nm, the laser energy ionizes it rapidly, generating the first plasma P 1that expands at a high speed along the laser direction.

[0057] The second stage is the thin film substrate breakdown and energy transmission: with the continuous injection of pulsed laser energy, the thin film substrate 31 with a thickness of 10 μm is ablated and finally broken down within a nanosecond time scale, the first plasma P ​​1The laser pulse will expand along the laser incidence direction towards the back side of the thin film substrate 31. At this time, the residual energy of the laser pulse, mainly the peak part or the trailing part of the pulse, will pass through the hole on the thin film substrate 31, propagate in the vacuum for 0.5 mm, and then hit the second tin layer 4 of the second planar target behind.

[0058] The third stage is the post-target ablation and the second plasma generation: the transmitted laser energy acts on the second tin layer 4 of the second planar target to generate a second plasma that expands at a high speed in the opposite direction of the laser propagation P

[0059] The fourth stage is the plasma collision and the formation of the stagnation layer: due to the first plasma P 1with a backward recoil velocity component, or due to the stagnation of the expanding tail, the second plasma P 2expands at a high speed forward, and the two plasma flows collide violently in the gap region between the first composite target 3 and the second planar target, i.e., the region with a predetermined distance. The collision converts the directed kinetic energy of the plasma into thermal energy, causing the density of the local region to increase sharply and the expansion speed to approach zero, forming a plasma stagnation layer 6 that can be maintained for a long time.

[0060] In the above embodiment 2, the laser parameters are adjusted. Considering that the thin film substrate 31 and the first tin layer 32 are relatively thin and the laser burn-through speed is relatively fast, in order to match the shorter gap distance to achieve the best collision opportunity, the energy of the incident laser pulse is appropriately reduced to 150 mJ.

[0061] Experimental results and analysis: under the parameter conditions of embodiment 2, the front of the laser pulse rapidly burns through the relatively thin first composite target 3. Due to the gap distance of the collision region being only 0.5 mm, the flight time of the front and rear two plasmas is relatively short, and the collision occurs relatively early and the collision region is more concentrated. The monitoring results show that although the plasma stagnation layer 6 generated is slightly smaller in volume than that of embodiment 1, its density is extremely high. The full width at half maximum (FWHM) of the EUV radiation waveform is measured to be 20 ns. Although the radiation duration is shorter than that of embodiment 1, i.e., 40 ns, it is still significantly improved compared to the existing single-target mode, i.e., 10 ns, which is about 2 times, proving that the collision enhancement mechanism of the present application is still effective under the parameters of embodiment 2.

[0062] Embodiment 3

[0063] A method for generating a double-target collision plasma, which is carried out by using the above-mentioned self-delayed collision plasma generation device, comprising the following steps:

[0064] ​The first stage is pre-target ablation and first plasma generation: when the front of the incident laser pulse with energy of 750 mJ reaches the surface of the first composite target 3, it first interacts with the first tin layer 32. Since the thickness of the first tin layer 32 is only 200 nm, the laser energy quickly ionizes it, generating the first plasma that expands at a high speed along the laser direction P 1.

[0065] The second stage is thin film substrate breakdown and energy transmission: with the continuous injection of pulse laser energy, the thin film substrate 31 with a thickness of 50 μm is ablated and finally broken down by the laser within a nanosecond time scale. The first plasma P 1will also expand along the laser incident direction towards the back side of the thin film substrate 31. At this time, the remaining energy of the laser pulse, mainly the peak or trailing part of the pulse, transmits through the hole on the thin film substrate 31, propagates 2 mm in vacuum, i.e. the distance between the thin film substrate 31 and the second tin layer 4 of the second planar target is 2 mm, and then hits the second tin layer 4 of the second planar target behind.

[0066] The third stage is post-target ablation and second plasma generation: the transmitted laser energy acts on the second tin layer 4 of the second planar target, generating the second plasma that expands at a high speed in the opposite direction of the laser propagation P 2.

[0067] The fourth stage is plasma collision and stagnation layer formation: since the first plasma P 1has a backward recoil velocity component, or due to the stagnation of the expanding tail, and the second plasma P 2expands at a high speed forward, the two plasma flows collide violently in the gap region between the first composite target 3 and the second planar target, i.e. in the region with a predetermined distance. The collision converts the directional kinetic energy of the plasma into thermal energy, causing the density of the local region to rise sharply and the expansion speed to approach zero, forming a plasma stagnation layer 6 that can be maintained for a long time.

[0068] In the above embodiment 3, the laser parameters are adjusted. Considering that the thin film substrate 31 and the first tin layer 32 are relatively thin and the laser burn-through speed is relatively fast, in order to match the shorter gap distance to achieve the best collision opportunity, the energy of the incident laser pulse is appropriately reduced to 750 mJ.

[0069] Experimental results and analysis: under the parameter conditions of the above embodiment 3, the thicker target material introduces a longer burn-through delay time, and the larger spacing of the collision region, i.e. 2.0 mm, makes the plasma collision occur at a later time after the laser pulse acts, and the collision region is more extended in space. The monitoring results show that the formed plasma stagnation layer 6 maintains a very long time. The full width at half maximum, i.e. FWHM, of the EUV radiation waveform is measured to be 50 ns. Although the peak intensity may be slightly lower than that of embodiment 1, the extremely long pulse duration significantly improves the total EUV energy of a single pulse. The results prove that under the parameters defined in embodiment 3, the present application can still stably achieve efficient plasma collision and radiation enhancement.

[0070] Experimental results and physical effect verification

[0071] In order to verify the effect of the self-delayed collision plasma generation device provided by the present application, comparative experiments are also carried out, and the experimental conditions are kept consistent with the laser parameters. The traditional single-target mode and the double-target structure mode of the self-delayed collision plasma generation device of the present application are tested respectively.

[0072] In the existing technical solutions in the field, the most basic form is the traditional single-target mode laser plasma.

[0073] The typical device structure includes: a vacuum chamber configured with a high vacuum environment, a solid planar target material installed in the chamber, and a high-power pulsed laser, i.e. a Nd:YAG laser, located outside the chamber. The pulsed laser emitted by the laser is focused by a focusing lens and directly incident on the surface of the solid planar target.

[0074] The plasma generation and radiation process is as follows: when the high-power density nanosecond laser pulse acts on the target surface, the target surface instantaneously absorbs the laser energy, undergoes melting, vaporization and rapid ionization, forming a high-temperature and high-density plasma. After the formation of the plasma, due to the extremely high pressure gradient inside the plasma, it will immediately expand in a nearly hemispherical free adiabatic manner towards the vacuum environment at a speed close to the sound speed.

[0075] The limitation is that: in this free expansion process, the electron density and temperature of the plasma will drop sharply. Since radiation mainly occurs in high-valence ions within a certain density and temperature window, the rapid expansion of the plasma results in a very short time for the plasma to be in the optimal radiation window. Therefore, the radiation pulse duration generated by the traditional single-target mode is usually short, for example, for a 10 ns driving laser, the EUV radiation pulse width is usually only about 10 ns or less, which limits the EUV energy conversion efficiency of a single pulse. In addition, high-energy ions are directly ejected from the target surface, which can easily cause serious damage to the collection optical elements.

[0076] Compared with the above-mentioned traditional single-target mode, the double-target structure mode of the self-delayed collision plasma generation device has the following advantages: first, the extension of the plasma radiation lifetime, as shown in Figure 5 The waveform of the 13.5 nm characteristic spectral line is monitored using a fast photodiode detector. In the traditional single-target mode, the radiation waveform presents a narrow peak with a half-height width, and the duration is usually about 10 ns, which is caused by the rapid density drop due to the free expansion of the plasma. In the double-target collision mode of the present application, the plasma is effectively constrained in the collision region due to the formation of the plasma stagnation layer 6, and the temperature and density suitable for exciting specific energy level transitions are maintained. The experimental measurement shows that the half-height width of the radiation waveform is significantly broadened to 40 ns. The extension of the radiation duration directly proves that the plasma expansion process is effectively controlled.

[0077] Second, the spectral characteristics, as shown in Figure 6 The emission spectrum of the stagnation layer region is measured using a flat-field grating spectrometer. The results show that a high-intensity narrow-band radiation peak is presented near 13.5 nm, which is the unresolved transition array radiation of tin ions. Due to the low absorption characteristics of the polyethylene substrate, the entire spectral background is low, and the in-band integrated energy is significantly better than that in the single-target case.

[0078] Finally, the ion kinetic energy suppression effect. Experimental observation shows that due to the collision between the forwardly ejected second plasma and the backwardly ejected first plasma, the directional velocity of the ions is randomized, which is equivalent to setting a buffer layer for high-speed ions, significantly reducing the average kinetic energy of the tin ions ejected from the plasma source, which plays a crucial role in protecting the radiation signal monitoring components 7 or observation windows located in front of the device, slowing down the physical sputtering corrosion of the surface, and prolonging the service life of the key physical diagnostic elements.

[0079] In summary, by adopting the double-target structure arranged in front and back, and reasonably configuring the parameters of the first composite target 3, the thin film substrate 31 with a thickness of 10 μm to 50 μm, the first tin layer 32 with a thickness of 50 nm to 200 nm, and the distance between the two targets in the collision region of 0.5 mm to 2.0 mm, the present application can cleverly utilize the physical time delay generated by laser burning through the thin film substrate to achieve efficient plasma collision under single-pulse driving in a wide parameter window. Experiments show that within the parameter range of each component defined in the present application, the self-delayed double-target collision plasma generation device can form a stable plasma stagnation layer, successfully solving the problems of short plasma radiation lifetime, low energy coupling efficiency, and serious ion sputtering damage in the prior art.

[0080] Obviously, many modifications and variations of the present application are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A self-delayed dual-target collision plasma generator, comprising a vacuum chamber (1) and a laser system (2), characterized in that, Also includes: The target assembly is disposed within the vacuum chamber (1); Along the laser propagation direction, the target assembly includes a first composite target (3) and a second planar target spaced apart; the first composite target (3) includes a thin film substrate (31) and a first tin layer (32) deposited on the thin film substrate (31); the second planar target includes a second tin layer (4), which is arranged parallel to one side of the thin film substrate (31); a collision region is provided between the thin film substrate (31) and the second tin layer (4), and the spacing between the collision regions is 0.5 mm to 2 mm; the thickness of the thin film substrate (31) is 10 μm to 50 μm; the thickness of the first tin layer (32) is 50 nm to 200 nm; The laser system (2) emits a single pulsed laser beam that is focused on the first composite target (3), ablates the first tin layer (32) to generate a first plasma that expands in the direction of the laser beam and penetrates the thin film substrate (31). The transmitted laser energy ablates the second tin layer (4) to generate a second plasma that expands in the opposite direction of the laser beam. The first plasma and the second plasma collide in the collision region to form a stagnant layer and are excited to emit enhanced characteristic spectral lines.

2. The self-delayed dual-target collision plasma generator according to claim 1, characterized in that, The film substrate (31) is one or more of polyethylene, polypropylene, polyimide and polyethylene terephthalate.

3. The self-delayed dual-target collision plasma generator according to claim 1, characterized in that, The distance between the collision zones is 1 mm.

4. The self-delayed dual-target collision plasma generator according to claim 1, characterized in that, The target assembly also includes a target moving mechanism (5), which supports and drives the first composite target (3) and the second planar target to move synchronously.

5. A method for generating dual-target collision plasma, characterized in that, The self-delayed dual-target collision plasma generator according to any one of claims 1 to 4 is used to generate dual-target collision plasma, the generation method comprising: The laser system (2) emits an incident pulse laser, and the leading edge energy of the incident pulse laser is used to ablate the first tin layer (32) on the first composite target (3) in the vacuum chamber (1) and generate the first plasma that expands in the direction of the laser. At the same time, the laser energy breaks through the thin film substrate (31) of the first composite target. The second tin layer (4) of the second planar target behind it is ablated by the transmitted laser energy after the thin film substrate (31) is broken down, generating a second plasma that expands in the opposite direction of the laser. The first plasma and the second plasma collide in the collision region between the first composite target and the second planar target, forming a stagnant plasma stagnation layer and being excited to emit enhanced characteristic spectral lines.

6. The method for generating dual-target collision plasma according to claim 5, characterized in that, The incident pulsed laser is an Nd:YAG laser with a wavelength of 1064 nm and a pulse width on the order of nanoseconds.

7. The method for generating dual-target collision plasma according to claim 5, characterized in that, The center wavelength of the characteristic spectral line is 13.5 nm.

Images