Pulse continuous composite type optical fiber laser sustained plasma light source

Abstract

The application discloses a pulse-continuous composite fiber laser sustained plasma light source, and solves the problem that the existing high-brightness pulse fiber laser sustained plasma light source is prone to extinguishing when the pulse interval is greater than or equal to the relaxation time of the plasma, and specifically comprises a pulse-continuous composite fiber laser, an arc lamp and a laser transmission conversion assembly; the pulse-continuous composite fiber laser is used for outputting composite laser containing pulse laser and continuous laser; the arc lamp is used for generating initial plasma; the input end of the laser transmission conversion assembly is connected with the output end of the pulse-continuous composite fiber laser through an optical fiber, the output end of the laser transmission conversion assembly corresponds to the arc lamp, the laser transmission conversion assembly is used for receiving the composite laser, coupling the pulse laser and the continuous laser in the composite laser, and focusing the pulse laser and the continuous laser to the central region of the plasma in the arc lamp; the optical system F number range of each component in the laser transmission conversion assembly is 0-9.

Description

TECHNICAL FIELD

[0001] The present application relates to a plasma light source, in particular to a pulsed continuous composite fiber laser sustained plasma light source. BACKGROUND

[0002] The laser-sustained plasma light source refers to a kind of plasma broadband light source realized by using the principle of continuous optical discharge of gas, and its working process is as follows: first, an initial plasma is generated by arc discharge, and then high-power laser is focused to the plasma, because the plasma will form strong absorption to the incident laser, so the plasma can still maintain its high-temperature light-emitting state by absorbing laser energy after the power is turned off.The laser-sustained plasma light source has the advantages of high brightness, wide spectrum and long service life, and is widely used in semiconductor wafer defect detection, hyperspectral imaging radiation calibration and optical product evaluation, and has become a high-end core component of semiconductor wafer defect detection equipment and spectral imaging radiation calibration system.

[0003] The laser used in the traditional high-brightness laser-sustained plasma light source is usually a high-power continuous fiber laser, so it can be called a high-brightness continuous fiber laser-sustained plasma light source. There is usually a minimum injection laser power for the normal operation of the laser-sustained plasma light source, i.e. the plasma maintenance threshold. The maintenance threshold of the high-brightness continuous fiber laser-sustained plasma light source is usually only tens of watts, such as 30-80 W. When the continuous laser power injected into the plasma increases, the central temperature of the plasma also increases, thereby increasing the luminous brightness of the plasma light source. Therefore, the brightness of the laser-sustained plasma light source can be generally improved by increasing the output power of the continuous fiber laser.

[0004] However, the high-brightness continuous fiber laser-sustained plasma light source scheme has obvious shortcomings in obtaining a higher-brightness laser-sustained plasma light source: as the injection continuous laser power increases, the plasma size will continuously grow in the opposite direction of the incident laser, and due to the refractive defocusing effect of the plasma (there is a refractive index gradient distribution in the plasma), the continuously growing plasma will in turn hinder the injection of incident laser into the center of the plasma, thereby forming a brightness saturation effect, i.e. the luminous brightness of the plasma light source cannot be further improved by increasing the injection continuous laser power.

[0005] For this purpose, some researchers proposed a technical solution of high-brightness laser plasma light source based on high average power pulse (or quasi-continuous) fiber laser, which can be called high-brightness pulse fiber laser plasma light source solution. This technical solution can effectively overcome the technical defects of brightness saturation effect of high-brightness continuous fiber laser plasma light source at present. This is because the interaction between high average power pulse laser and plasma is discontinuous. After the current pulse action is completed, the plasma size will shrink, the refractive defocusing effect of the plasma is weakened, and the next pulse can be effectively injected into the center of the plasma, so as to overcome the brightness saturation effect. Although the high-brightness pulse fiber laser plasma light source can effectively enhance the brightness compared with the high-brightness continuous fiber laser plasma light source, and the brightness can be enhanced by more than 10 times, this technical solution also has defects: because the relaxation time of the plasma is usually μs order, when the time interval between pulses is greater than or equal to the relaxation time, that is, the repetition frequency of the pulse fiber laser is below several hundred kHz, the plasma will be extinguished due to the lack of laser energy injection. SUMMARY

[0006] The purpose of the present application is to provide a pulse-continuous composite fiber laser plasma light source to solve the technical problems of the existing high-brightness pulse fiber laser plasma light source that the plasma is not easy to maintain and is easy to extinguish when the pulse interval is greater than or equal to the relaxation time of the plasma.

[0007] In order to achieve the above purpose, the present application adopts the following technical solution:

[0008] A pulse-continuous composite fiber laser plasma light source, characterized in that it comprises a pulse-continuous composite fiber laser, an arc lamp and a laser transmission conversion assembly.

[0009] The pulse-continuous composite fiber laser is used to output composite laser containing pulse laser and continuous laser; the continuous laser is used to maintain the constant brightness of the plasma, and its power range is 30-80 W; the pulse laser is used to improve the brightness of the plasma, and its power is greater than 100 W, its repetition frequency range is 1 kHz-1 MHz, and its pulse width is 100 ns-500 μs.

[0010] The arc lamp is used to generate initial plasma.

[0011] The input end of the laser transmission conversion assembly is connected with the output end fiber of the pulse-continuous composite fiber laser, the output end of the laser transmission conversion assembly corresponds to the arc lamp, the laser transmission conversion assembly is used for receiving the composite laser, coupling the pulse laser and the continuous laser in the composite laser, and focusing to the plasma center area in the arc lamp; the optical system F number range formed by each component in the laser transmission conversion assembly is 0-9.

[0012] Further, the pulse-continuous composite fiber laser comprises a driving circuit, a laser seed source and a fiber amplifier.

[0013] The driving circuit is electrically connected with the laser seed source, and is used for providing a composite current signal comprising a pulse current and a direct current to the laser seed source.

[0014] The laser seed source is connected with the input end fiber of the fiber amplifier, and is used for converting the composite current signal into a composite laser and delivering the composite laser to the fiber amplifier.

[0015] The output end of the fiber amplifier is connected with the input end fiber of the laser transmission conversion assembly, and is used for amplifying the power of the composite laser and delivering the composite laser to the laser transmission conversion assembly through the fiber output head.

[0016] Further, the pulse-continuous composite fiber laser comprises a continuous laser, an optical modulator and a fiber amplifier.

[0017] The output end of the continuous laser is connected with the input end fiber of the optical modulator, and is used for outputting continuous laser.

[0018] The output end of the optical modulator is connected with the input end fiber of the fiber amplifier, and the optical modulator is used for receiving the continuous laser output by the continuous laser and modulating the continuous laser into the composite laser, and then delivering the composite laser to the fiber amplifier.

[0019] The output end of the fiber amplifier is connected with the input end fiber of the laser transmission conversion assembly, and is used for amplifying the power of the composite laser and delivering the composite laser to the laser transmission conversion assembly through the fiber output head.

[0020] Further, the optical modulator is an acousto-optic modulator, an electro-optic modulator or a magneto-optic modulator.

[0021] Further, the fiber amplifier is a one-stage or multi-stage fiber amplifier.

[0022] Further, the laser transmission conversion assembly comprises a collimating and expanding system and a focusing lens.

[0023] The collimation and beam expansion system is arranged on the light path of the composite laser output by the fiber connected with the pulse continuous composite fiber laser, and is used for collimating and beam expanding the composite laser.

[0024] The focusing lens is arranged on the light path between the collimation and beam expansion system and the arc lamp, and is used for focusing the collimated and beam expanded composite laser to the plasma center region in the arc lamp.

[0025] Further, the F number of the optical system composed of the collimation and beam expansion system and the focusing lens is 3.

[0026] Further, the laser transmission conversion assembly comprises a laser reflecting mirror and an ellipsoidal mirror.

[0027] The laser reflecting mirror is arranged on the light path of the composite laser output by the fiber connected with the pulse continuous composite fiber laser, and is used for reflecting the composite laser to the ellipsoidal mirror.

[0028] The ellipsoidal mirror is arranged on the light path after the reflection of the laser reflecting mirror, and the concave surface of the ellipsoidal mirror faces the laser reflecting mirror.

[0029] The arc lamp is located in the concave surface of the ellipsoidal mirror, so that the ellipsoidal mirror can focus the reflected composite laser signal to the plasma center region in the arc lamp.

[0030] Further, the F number of the optical system composed of the laser reflecting mirror and the ellipsoidal mirror is 0.4.

[0031] Further, the rare gas in the arc lamp comprises xenon, krypton, argon, neon, helium and / or trace mercury elements.

[0032] The beneficial effects of the present application are as follows:

[0033] The pulse continuous composite fiber laser maintained plasma light source provided by the present application adopts a pulse continuous composite fiber laser as a driving light source, and can output a composite laser containing pulse laser and continuous laser. The continuous laser ensures that the plasma in the arc lamp is always injected with laser energy during the interval of the pulse laser, so that the plasma is not extinguished, and the problem that the plasma in the high-brightness pulse fiber laser maintained plasma light source is difficult to maintain and easily extinguished is effectively solved. The pulse laser can make the plasma in the arc lamp generate a high-brightness laser maintained plasma light source, and the technical advantages of the existing high-brightness pulse fiber laser maintained plasma light source are maintained. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a structural schematic diagram of a pulse continuous composite fiber laser maintained plasma light source embodiment one of the present application;

[0035] Figure 2 1 is a schematic structural diagram of a pulsed continuous composite fiber laser in Example 1 of the present invention;

[0036] Figure 3 This is a curve diagram of the laser signal output by the pulse continuous composite fiber laser in Example 1 of the present invention;

[0037] Figure 4 This is a schematic structural diagram of a second embodiment of a pulsed continuous composite fiber laser-maintained plasma light source according to the present invention;

[0038] Figure 5 It is a schematic structural diagram of the pulse continuous composite fiber laser in the second embodiment of the present invention.

[0039] 10-pulse continuous composite fiber laser, 11-fiber output head, 20-collimation and beam expansion system, 21-focusing lens, 22-laser reflector, 23-ellipsoidal mirror, 30-arc lamp, 31-electrode, 101-driving circuit, 102-laser seed source, 103-fiber amplifier, 104-acousto-optic modulator, 105-continuous laser. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a pulse continuous composite fiber laser maintained plasma light source, such as Figure 1 As shown, the laser system comprises a pulsed continuous-wave hybrid fiber laser 10, an arc lamp 30, and a laser transmission conversion assembly. In this embodiment, the arc lamp 30 is preferably a short-arc xenon lamp. The laser transmission conversion assembly includes a collimating beam expansion system 20 and a focusing lens 21, which are sequentially arranged along the laser transmission direction. The optical system formed by the laser transmission conversion assembly has an F-number of 3.

[0043] The structure of the pulse continuous composite fiber laser 10 is as follows: Figure 2As shown, it comprises driving circuit 101, laser seed source 102, fiber amplifier 103 and fiber output head 11 arranged in sequence, and the fiber amplifier 103 adopts multi-stage fiber amplifier. The laser seed source 102 in this embodiment adopts internal modulation method to generate "pulse + continuous" composite laser signal, and the basic process is as follows: first, the driving circuit 101 generates a composite current signal containing pulse current and direct current, that is, the output current signal contains pulse current component and a small amount of continuous (or direct current) component; then the composite current signal is loaded to the laser seed source 102 to generate a composite laser signal. After the composite laser is amplified by the fiber amplifier 103, the final output power of the high-power "pulse + continuous" composite laser is 1000W, and the output signal characteristics are as follows Figure 3 As shown, it comprises driving circuit 101, laser seed source 102, fiber amplifier 103 and fiber output head 11 arranged in sequence, and the fiber amplifier 103 adopts multi-stage fiber amplifier. The laser seed source 102 in this embodiment adopts internal modulation method to generate "pulse + continuous" composite laser signal, and the basic process is as follows: first, the driving circuit 101 generates a composite current signal containing pulse current and direct current, that is, the output current signal contains pulse current component and a small amount of continuous (or direct current) component; then the composite current signal is loaded to the laser seed source 102 to generate a composite laser signal. After the composite laser is amplified by the fiber amplifier 103, the final output power of the high-power "pulse + continuous" composite laser is 1000W, and the output signal characteristics are as follows

[0044] The basic working process of the pulse-continuous composite fiber laser maintained plasma light source proposed in this embodiment is as follows: first, load high-voltage power supply on the electrode 31 of the short-arc xenon lamp to ignite xenon plasma, then start the pulse-continuous composite fiber laser 10, delay for several seconds, then turn off the high-voltage power supply, and finally use the composite laser to maintain the xenon plasma in the short-arc xenon lamp in a high-temperature light-emitting state. Since the repetition frequency of the pulse laser in the composite laser is 10kHz and the pulse width is 10μs, the time interval between the completion of the action of the previous pulse and the arrival of the next pulse is 90μs. Within this time interval, the small amount of continuous laser (power of 50W) in the composite laser is mainly used to continue to maintain the plasma light-emitting, so as to ensure that the plasma does not extinguish within this time interval, thereby effectively solving the problem that the plasma in the plasma light source maintained by the current high-brightness pulse fiber laser is difficult to maintain.

[0045] Embodiment two

[0046] As shown in Figure 4 The pulse-continuous composite fiber laser maintained plasma light source proposed in this embodiment comprises a pulse-continuous composite fiber laser 10, a laser transmission conversion assembly and an arc lamp 30, and the arc lamp 30 in this embodiment is also selected as a short-arc xenon lamp. The laser transmission conversion assembly comprises a laser reflector 22 and an ellipsoidal mirror 23 arranged in sequence along the laser transmission direction. The F number of the optical system formed by the laser transmission conversion assembly is 0.4. The short-arc xenon lamp is located in the concave surface of the ellipsoidal mirror 23.

[0047] AsFigure 5 As shown, the pulse-continuous composite fiber laser 10 comprises a continuous laser 105, an acousto-optic modulator 104, a fiber amplifier 103 and a fiber output head 11 arranged in sequence, and the fiber amplifier 103 is a multi-stage fiber amplifier. The pulse-continuous composite fiber laser 10 in this embodiment generates a "pulse + continuous" composite laser by using an external modulation method, and the basic process is as follows: first, a continuous laser is generated by using the continuous laser 105, and then a modulation signal is loaded by using the acousto-optic modulator 104, so as to generate a composite laser. The proportion of the continuous laser in the composite laser can be adjusted by the static working point of the acousto-optic modulator 104. After the composite laser is amplified by the fiber amplifier 103, a high-power "pulse + continuous" composite laser with an output power of 1000W is finally output, and the output signal characteristics are as follows: Figure 3 As shown, the output signal contains a pulse laser component and a small amount of continuous laser component, the repetition frequency of the pulse laser component is 100 kHz, and the pulse width is 1 μs. By adjusting the static working point of the acousto-optic modulator 104, the power of the continuous laser in the output laser of the pulse-continuous composite fiber laser 10 exceeds the threshold power required for maintaining the plasma, which is about 50W.

[0048] The basic working process of the pulse-continuous composite fiber laser for maintaining the plasma light source proposed in this embodiment is similar to that of embodiment one. Since the repetition frequency of the pulse laser in the pulse-continuous composite fiber laser 10 is 100 kHz, and the pulse width is 1 μs, the time interval from the completion of the action of the previous pulse to the arrival of the next pulse is 9 μs. In this time interval, the small amount of continuous laser component (with a power of 50W) in the composite laser is mainly used to continue to maintain the plasma light emission, so as to ensure that the plasma does not extinguish in this time interval, thereby effectively solving the problem that the plasma of the high-brightness pulse fiber laser maintained plasma light source is difficult to maintain.

[0049] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any change or replacement within the technical scope disclosed in the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A pulse continuous wave composite fiber laser sustained plasma light source, characterized by: The pulse-continuous composite fiber laser (10), the arc lamp (30) and the laser transmission transformation assembly are included; The pulse-continuous composite fiber laser (10) is used for outputting the composite laser containing the pulse laser and the continuous laser; the continuous laser is used for maintaining the plasma constant, and the power range is 30-80 W; the pulse laser is used for improving the plasma brightness, and the power is greater than 100 W, the repetition frequency range is 1 kHz-1 MHz, and the pulse width is 100 ns-500 μs; The arc lamp (30) is used for generating the initial plasma; The input end of the laser transmission transformation assembly is connected with the output end fiber of the pulse-continuous composite fiber laser (10), the output end of the laser transmission transformation assembly corresponds to the arc lamp (30), the laser transmission transformation assembly is used for receiving the composite laser, coupling the pulse laser and the continuous laser in the composite laser, and focusing to the plasma center region in the arc lamp (30); the optical system F number range formed by each component in the laser transmission transformation assembly is 0-9.

2. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 1, characterized in that: The pulse-continuous composite fiber laser (10) includes the driving circuit (101), the laser seed source (102) and the fiber amplifier (103); The driving circuit (101) is electrically connected with the laser seed source (102), and is used for providing the composite current signal containing the pulse current and the direct current to the laser seed source (102); The laser seed source (102) is connected with the input end fiber of the fiber amplifier (103), and is used for converting the composite current signal into the composite laser and delivering to the fiber amplifier (103); The output end of the fiber amplifier (103) is connected with the input end fiber of the laser transmission transformation assembly, and is used for amplifying the power of the composite laser and delivering to the laser transmission transformation assembly through the fiber output head (11).

3. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 1, characterized in that: The pulse-continuous composite fiber laser (10) includes the continuous laser (105), the optical modulator and the fiber amplifier (103); The output end of the continuous laser (105) is connected with the input end fiber of the optical modulator, and is used for outputting the continuous laser; The output end of the optical modulator is connected with the input end fiber of the fiber amplifier (103), and the optical modulator is used for receiving the continuous laser output by the continuous laser (105) and modulating the continuous laser into the composite laser, and then delivering to the fiber amplifier (103); The output end of the fiber amplifier (103) is connected with the input end fiber of the laser transmission transformation assembly, and is used for amplifying the power of the composite laser and delivering to the laser transmission transformation assembly through the fiber output head (11).

4. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 3, characterized in that: The optical modulator is an acousto-optic modulator, an electro-optic modulator or a magneto-optic modulator.

5. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 2 or 3 or 4, characterized in that: The fiber amplifier (103) is a one-stage or multi-stage fiber amplifier.

6. The pulse continuous wave compound fiber laser sustained plasma light source according to any one of claims 1-4, characterized in that: The laser transmission transformation assembly includes the collimation beam expansion system (20) and the focusing lens (21); The collimation beam expansion system (20) is arranged on the light path of the composite laser output by the fiber connected with the pulse-continuous composite fiber laser (10), and is used for collimating and expanding the beam of the composite laser; The focusing lens (21) is arranged on the light path between the collimating beam expander system (20) and the arc lamp (30), and is used for focusing the collimated and expanded composite laser to the plasma center region in the arc lamp (30).

7. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 6, characterized in that: The F number of the optical system composed of the collimating beam expander system (20) and the focusing lens (21) is 3.

8. The pulse continuous wave compound fiber laser sustained plasma light source according to any one of claims 1-4, characterized in that: The laser transmission conversion assembly comprises a laser reflecting mirror (22) and an ellipsoidal mirror (23). The laser reflecting mirror (22) is arranged on the light path of the composite laser output from the fiber connected with the pulse-continuous composite fiber laser (10), and is used for reflecting the composite laser to the ellipsoidal mirror (23). The ellipsoidal mirror (23) is arranged on the light path after the reflection of the laser reflecting mirror (22), and the concave surface of the ellipsoidal mirror (23) faces the laser reflecting mirror (22). The arc lamp (30) is located in the concave surface of the ellipsoidal mirror (23), so that the ellipsoidal mirror (23) can focus the reflected composite laser signal to the plasma center region in the arc lamp (30).

9. The pulse continuous wave compound fiber laser sustained plasma light source according to claim 8, characterized in that: The F number of the optical system composed of the laser reflecting mirror (22) and the ellipsoidal mirror (23) is 0.

4.

10. A pulse-continuous composite fiber laser-maintained plasma light source according to any one of claims 1 to 4, characterized in that: The rare gas in the arc lamp (30) comprises xenon, krypton, argon, neon, helium and / or trace mercury elements.

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