Ultra-compact high extinction ratio laser pulse cleaning device and method

Abstract

The present invention provides an ultra-compact high extinction ratio laser pulse cleaning device and method. The device comprises: a laser oscillator, a pulse stretcher, a pulse amplifier, a first broadband high-reflection mirror, a first broadband polarizer, an electro-optical switch, a second broadband polarizer, a second broadband high-reflection mirror and a third broadband high-reflection mirror; wherein the first broadband polarizer and the second broadband polarizer are placed orthogonally to each other; the laser oscillator generates a seed laser, which is sequentially pulse stretched by the pulse stretcher and pulse amplified by the pulse amplifier; the amplified laser pulse sequentially passes through the first broadband high-reflection mirror, the first broadband polarizer, the electro-optical switch, and the second broadband polarizer to form an incident light path; the laser pulse emitted after passing through the second broadband polarizer sequentially passes through the second broadband high-reflection mirror, the second broadband polarizer, the electro-optical switch, the first broadband polarizer and the third broadband high-reflection mirror to form a reflected light path.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to an ultra-compact high extinction ratio laser pulse cleaning device and method. Background Art

[0002] The advent of chirped pulse amplification (CPA) technology has greatly developed ultrashort and ultra-intense lasers. Ultrashort and ultra-intense laser pulses can interact with materials to produce light sources of various wavelengths (such as extreme ultraviolet, X-rays, etc.), and can also be used as a driver for high-energy electron beams.

[0003] At present, ultrashort and ultraintense laser pulses can reach peak powers of tens of petawatts. As the peak power of the laser pulse increases, the power of the pre-pulse before the main pulse (a few nanoseconds to tens of nanoseconds) will also increase. These pre-pulses are usually generated due to the limitation of the extinction ratio of the polarization element and the secondary reflection of the optical reflective element. The ratio of the main pulse to the pre-pulse is generally defined as the temporal contrast of the pulse. At present, in physical experiments on the interaction between ultrashort and ultraintense lasers and matter, the peak power density of the focused laser pulses generally used is higher than 10 17 W / cm2, and the peak power density of its pre-pulse is also higher than 10 11 W / cm2, such intensity is enough to cause the problem of pre-plasma before the main pulse interacts with the material to generate plasma. The appearance of pre-plasma will affect the characteristics of the main pulse or the material itself, and then affect the accelerated particles or the generated radiation source. Figure 1 As shown in Figure 1, the temporal contrast of the pulses must be large enough to ensure that the intensity of the pre-pulse does not exceed the ionization threshold of the material. Therefore, it is extremely important to improve the nanosecond signal-to-noise ratio of the laser pulse.

[0004] In the prior art, the technology for improving the nanosecond contrast of laser pulses (such as Wang Zhaohua, Wei Zhiyi, Zhang Jie. A new method for improving the contrast of femtosecond ultra-intense laser pulses [J]. Physics, 2007, 36(6):483-488.) is to use a single-pass electro-optical switch to pass the femtosecond laser pulse whose contrast is to be improved through a pulse cleaning device once. With this prior art, due to the limitation of the extinction ratio of components, a single pass through the pulse cleaning device can only improve the pulse contrast by a certain amount. If a higher pulse contrast is desired, one has to add another set of existing pulse cleaning devices. This will undoubtedly increase the space of the laser system and the cost of using components, and the steps for setting up the optical components are also relatively cumbersome. Summary of the invention

[0005] In view of the problems of complicated structure and installation steps in existing laser pulse cleaning devices or methods, the present invention provides an ultra-compact high extinction ratio laser pulse cleaning device and method.

[0006] The present invention provides an ultra-compact high extinction ratio laser pulse cleaning device, comprising: a laser oscillator, a pulse stretcher, a pulse amplifier, a first broadband high-reflection mirror, a first broadband polarizer, an electro-optical switch, a second broadband polarizer, a second broadband high-reflection mirror and a third broadband high-reflection mirror; wherein the first broadband polarizer and the second broadband polarizer are placed orthogonally to each other;

[0007] The laser oscillator generates a seed laser, and the seed laser is sequentially pulse stretched by the pulse stretcher and pulse amplified by the pulse amplifier;

[0008] The amplified laser pulse passes through the first broadband high-reflection mirror, the first broadband polarizer, the electro-optical switch, and the second broadband polarizer in sequence to form an incident light path;

[0009] The laser pulse emitted after passing through the second broadband polarizer passes through the second broadband high-reflection mirror, the second broadband polarizer, the electro-optical switch, the first broadband polarizer and the third broadband high-reflection mirror in sequence to form a reflection light path.

[0010] Furthermore, a broadband half-wave plate is arranged between the first broadband polarizer and the second broadband polarizer.

[0011] Furthermore, the incident angles of the first broadband high-reflection mirror and the third broadband high-reflection mirror are both 45°, and the incident angle of the second broadband high-reflection mirror ranges from 0° to 5°.

[0012] Furthermore, the working bandwidths of the first broadband polarizer and the second broadband polarizer are both greater than 100 nm, and the extinction ratio is >10000:1.

[0013] The present invention provides an ultra-compact high extinction ratio laser pulse cleaning method, comprising:

[0014] Step 1: The laser oscillator generates a seed laser;

[0015] Step 2: allowing the seed laser to enter a pulse stretcher to stretch its pulse width to a preset value;

[0016] Step 3: inputting the laser pulse whose pulse width reaches a preset value into a pulse amplifier for pulse amplification to obtain an amplified laser pulse;

[0017] Step 4: allowing the amplified laser pulse to pass through a first broadband high-reflection mirror and a first broadband polarizer in sequence;

[0018] Step 5: at any time in the time interval between the main pulse and the pre-pulse in the laser pulse, turn on the electro-optical switch, so that the main pulse passes through the electro-optical switch and then passes through the second broadband polarizer;

[0019] Step 6: directing the laser pulse toward a second broadband high-reflection mirror;

[0020] Step 7: The laser pulse reflected by the second broadband high-reflection mirror passes through the second broadband polarizer, the electro-optical switch and the first broadband polarizer in sequence, and then is emitted to the third broadband high-reflection mirror.

[0021] Beneficial effects of the present invention:

[0022] The present invention provides an ultra-compact high extinction ratio laser pulse cleaning device, which greatly saves space compared with the prior art in which each component is placed independently by compactly integrating a first broadband polarizer, an electro-optical switch, a second broadband polarizer and a second broadband high-reflection mirror.

[0023] The ultra-compact high extinction ratio laser pulse cleaning method provided by the present invention can essentially increase the laser pulse nanosecond time contrast by 4-6 orders of magnitude by only using one set of pulse cleaning devices to reduce the number and space of optical components, thereby achieving a cleaning effect that can only be achieved by using two sets of pulse cleaning devices in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of a main pulse and a pre-pulse provided in the prior art;

[0025] Figure 2 A schematic structural diagram of an ultra-compact high extinction ratio laser pulse cleaning device provided by an embodiment of the present invention;

[0026] Figure numerals: 1 is a laser oscillator, 2 is a pulse stretcher, 3 is a pulse amplifier, 4 is a first broadband high-reflection mirror, 5 is a first broadband polarizer, 7 is an electro-optical switch, 8 is a second broadband polarizer, 9 is a second broadband high-reflection mirror, and 10 is a third broadband high-reflection mirror. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 2As shown, an embodiment of the present invention provides an ultra-compact high extinction ratio laser pulse cleaning device, comprising: a laser oscillator 1, a pulse stretcher 2, a pulse amplifier 3, a first broadband high-reflection mirror 4, a first broadband polarizer 5, an electro-optical switch 7, a second broadband polarizer 8, a second broadband high-reflection mirror 9 and a third broadband high-reflection mirror 10; the laser oscillator 1 generates a seed laser, and the seed laser is sequentially pulse stretched by the pulse stretcher 2 and pulse amplified by the pulse amplifier 3; the amplified laser pulse sequentially passes through the first broadband high-reflection mirror 4, the first broadband polarizer 5, the electro-optical switch 7, and the second broadband polarizer 8 to form an incident light path; the laser pulse emitted after passing through the second broadband polarizer 8 sequentially passes through the second broadband high-reflection mirror 9, the second broadband polarizer 8, the electro-optical switch 7, the first broadband polarizer 5 and the third broadband high-reflection mirror 10 to form a reflected light path. Among them, the electro-optical switch 7 is composed of a high-voltage generating module, an electro-optical crystal, and a power control module. Its function is that when the laser pulse passes through the electro-optical crystal, the power control module controls the high-voltage generating module to provide half-wave high voltage to the electro-optical crystal, so that the polarization state of the laser pulse passing through the electro-optical switch 7 changes by 90°.

[0030] As an implementable embodiment, the incident angles of the first broadband high-reflection mirror 4 and the third broadband high-reflection mirror 10 are both 45°, the incident angle of the second broadband high-reflection mirror 9 ranges from 0 to 5°, the working bandwidths of the first broadband polarizer 5 and the second broadband polarizer 8 are both greater than 100 nm, and the extinction ratio is >10000:1.

[0031] On the basis of the above embodiment, in the embodiment of the present invention, a broadband half-wave plate is further provided between the first broadband polarizer 5 and the second broadband polarizer 8. Specifically, the broadband half-wave plate is used to correct the position of the electro-optical switch 7. After the correction, when the device operates normally to clean the laser pulse, the broadband half-wave plate needs to be removed from the incident light path.

[0032] Example 2

[0033] Corresponding to the device provided in Example 1, the embodiment of the present invention further provides an ultra-compact high extinction ratio laser pulse cleaning method, comprising:

[0034] S201: Laser oscillator 1 generates seed laser;

[0035] S202: allowing the seed laser to enter the pulse stretcher 2 to stretch its pulse width to a preset value;

[0036] S203: inputting the laser pulse whose pulse width reaches the preset value into the pulse amplifier 3 for pulse amplification to obtain an amplified laser pulse;

[0037] S204: allowing the amplified laser pulse to pass through the first broadband high-reflection mirror 4 and the first broadband polarizer 5 in sequence;

[0038] S205: at any time in the time interval between the main pulse and the pre-pulse in the laser pulse, turning on the electro-optical switch 7, so that the main pulse passes through the electro-optical switch 7, and then passes through the second broadband polarizer 8;

[0039] S206: directing the laser pulse toward the second broadband high-reflection mirror 9;

[0040] S207 : The laser pulse reflected by the second broadband high-reflection mirror 9 passes through the second broadband polarizer 8 , the electro-optical switch 7 and the first broadband polarizer 5 in sequence, and then is emitted to the third broadband high-reflection mirror 10 .

[0041] Specifically, the main pulse in the amplified laser pulse obtained in step S203 and the pre-pulse before the main pulse have the same polarization state at this time, the time interval between the main pulse and the pre-pulse is generally between several to tens of nanoseconds, and the duration of the high-voltage pulse after the electro-optical switch 7 is turned on is about 10ns.

[0042] First, after the pre-pulse and the main pulse in the amplified laser pulse pass through the first broadband polarizer 5 (which acts as an analyzer), the polarization states of the main pulse and the pre-pulse in the laser pulse are still the same (for example, both are in a horizontal polarization state at this time);

[0043] Then, the pre-pulse in the laser pulse reaches the electro-optical switch 7 first, and at this time the electro-optical switch 7 is not turned on and is still in the closed state, so the polarization state of the pre-pulse after passing through the electro-optical switch 7 remains unchanged (i.e., it is still in the horizontal polarization state), and when the main pulse reaches the electro-optical switch 7, the electro-optical switch 7 is turned on, and the polarization state of the main pulse after passing through the electro-optical switch 7 changes by 90° (i.e., from the previous horizontal polarization state to the vertical polarization state). Therefore, after passing through the electro-optical switch 7, the polarization states of the main pulse and the pre-pulse in the laser pulse are orthogonal to each other: the main pulse is in the vertical polarization state, and the pre-pulse is in the horizontal polarization state.

[0044] Next, the laser pulse passes through the second broadband polarizer 8. Since the second broadband polarizer 8 and the first broadband polarizer 5 are placed orthogonally, only the main pulse in the laser pulse can pass through the second broadband polarizer 8, while the pre-pulse in the laser pulse is reflected out of the optical path by the second broadband polarizer 8, thereby realizing the first cleaning of the laser pulse. Due to the limitation of the extinction ratio of the electro-optical crystal, the single cleaning of the pre-pulse can only reach a certain extent. Therefore, there may be residual pre-pulses in the laser pulse after the first cleaning.

[0045] Finally, the laser pulse emitted from the second broadband polarizer 8 is directed toward the second broadband high-reflection mirror 9 and reflected by the second broadband high-reflection mirror 9. The reflected laser pulse (i.e., the main pulse and a small amount of remaining pre-pulses) then passes through the second broadband polarizer 8, the electro-optical switch 7, and the first broadband polarizer 5 in sequence. Since the duration of the high-voltage pulse after the electro-optical switch 7 is turned on is about 10ns, and the time from the first time the laser pulse passes through the electro-optical switch 7 to the second time it passes through the electro-optical switch 7 is <1ns, the laser pulse is still in a horizontal polarization state when it passes through the first broadband polarizer 5 for the second time. After passing through the first broadband polarizer 5, it is directed toward the third broadband high-reflection mirror 10, thereby achieving the second cleaning of the laser pulse.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultra-compact high extinction ratio laser pulse cleaning device, characterized in that: include: A laser oscillator, a pulse stretcher, a pulse amplifier, a first broadband high-reflection mirror, a first broadband polarizer, an electro-optical switch, a second broadband polarizer, a second broadband high-reflection mirror and a third broadband high-reflection mirror; wherein the first broadband polarizer and the second broadband polarizer are placed orthogonally to each other; The laser oscillator generates a seed laser, and the seed laser is sequentially pulse stretched by the pulse stretcher and pulse amplified by the pulse amplifier; The amplified laser pulse passes through the first broadband high-reflection mirror, the first broadband polarizer, the electro-optical switch, and the second broadband polarizer in sequence to form an incident light path; wherein, at any time in the time interval between the main pulse and the pre-pulse in the laser pulse, the electro-optical switch is turned on, so that the main pulse passes through the electro-optical switch and then passes through the second broadband polarizer; The laser pulse emitted after passing through the second broadband polarizer passes through the second broadband high-reflection mirror, the second broadband polarizer, the electro-optical switch, the first broadband polarizer and the third broadband high-reflection mirror in sequence to form a reflection light path.

2. The device according to claim 1, characterized in that A broadband half-wave plate is also arranged between the first broadband polarizer and the second broadband polarizer; the broadband half-wave plate is used to correct the position of the electro-optical switch (7); after the correction, when the device operates normally to clean the laser pulse, the broadband half-wave plate is removed from the incident light path.

3. The device according to claim 1, characterized in that The incident angles of the first broadband high-reflection mirror and the third broadband high-reflection mirror are both 45°, and the incident angle of the second broadband high-reflection mirror ranges from 0° to 5°.

4. The device according to claim 1, characterized in that The working bandwidths of the first broadband polarizer and the second broadband polarizer are both greater than 100 nm, and the extinction ratio is >10000:

1.

5. An ultra-compact high extinction ratio laser pulse cleaning method, characterized in that: include: Step 1: The laser oscillator generates a seed laser; Step 2: allowing the seed laser to enter a pulse stretcher to stretch its pulse width to a preset value; Step 3: inputting the laser pulse whose pulse width reaches a preset value into a pulse amplifier for pulse amplification to obtain an amplified laser pulse; Step 4: allowing the amplified laser pulse to pass through a first broadband high-reflection mirror and a first broadband polarizer in sequence; Step 5: at any time in the time interval between the main pulse and the pre-pulse in the laser pulse, turn on the electro-optical switch, so that the main pulse passes through the electro-optical switch and then passes through the second broadband polarizer; Step 6: directing the laser pulse toward a second broadband high-reflection mirror; Step 7: The laser pulse reflected by the second broadband high-reflection mirror passes through the second broadband polarizer, the electro-optical switch and the first broadband polarizer in sequence, and then is emitted to the third broadband high-reflection mirror.

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